AND

T HE A STROPHYSICAL J OURNAL ,479:642è658,1997April 20

1997.The American Astronomical Society.All rights reserved.Printed in U.S.A.

(HUBBL E SPACE T EL ESCOPE IMAGES OF A SAMPLE OF 20NEARBY

LUMINOUS QUASARS 1

J OHN N.S OFIA AND D AVID H.B AHCALL ,K IRHAKOS ,S AXE

Institute for Advanced Study,School of Natural Sciences,Princeton,NJ 08540

AND

D ONALD P.S CHNEIDER

Department of Astronomy and Astrophysics,The Pennsylvania State University,University Park,PA 16802

Received 1996August 21;accepted 1996November 8

ABSTRACT

Observations with the Wide-Field Camera of the Hubble Space Telescope (HST )are presented for a representative sample of 20intrinsically luminous quasars with redshifts smaller than 0.30.These obser-vations show that luminous quasars occur in diverse environments that include ellipticals as bright as the brightest cluster galaxies (two),apparently normal ellipticals (10),apparently normal spirals with H II regions (three),complex systems of gravitationally interacting components (three),and faint surrounding nebulosity (two).The quasar host galaxies are centered on the quasar to the accuracy of our measure-ments,400pc.There are more radio-quiet quasars in galaxies that appear to be ellipticals (seven)than in spiral hosts (three),contrary to expectations.However,three,and possibly Dve,of the six radio-loud quasars have detectable elliptical hosts,in agreement with expectations.The luminous quasars studied in this paper occur preferentially in luminous galaxies.The average absolute magnitude of the hosts is 2.2mag brighter than expected for a Deld galaxy luminosity function.

The superb optical characteristics of the repaired HST make possible the detection of close galactic companions;we detect eight companion galaxies within projected distances of 10kpc from quasar nuclei.The presence of very close companions,the images of current gravitational interactions,and the higher density of galaxies around the quasars suggest that gravitational interactions play an important role in triggering the quasar phenomenon.

Subject headings:galaxies:clusters:general ègalaxies:interactions ègalaxies:structure è

quasars:general

1.

INTRODUCTION

Figures and (Plates 25è28)tell the main story of this 12paper.We urge the reader to look at these beautiful HST images before continuing with the text and the quantitative details.

We summarize in this paper the results of our analysis of HST -WFPC2observations of a representative sample of 20of the most luminous nearby (z \0.30)

(M V

\[22.9)quasars.The goal of these observations was to help under-stand the quasar phenomenon by determining the environ-ment in which quasars occur.The main result of this paper is that there is not one type of environment but instead a wide range of environments in which the most luminous quasars appear to be embedded.The HST images also contain a number of extraordinary phenomena and some surprises,including very close companions,host ellipticals for radio-quiet quasars,spiral hosts with well-developed arms and prominent H II regions,galaxies caught in the act of merging,apparently faint galactic hosts,and very extended emission.

Some partial results of this study have been reported previously:Bahcall,Kirhakos,&Schneider hereafter (1994,hereafter hereafter Paper Paper I;1995a,Paper II;1995b,III;Bahcall et al.hereafter and 1995c),(1995d,Paper IV),Kirhakos,&Schneider For those aspects of Bahcall,(1996).the work that depend upon the subtraction of a stellar

1Based on observations with the NASA/ESA Hubble Space Telescope ,obtained at the Space Telescope Science Institute,which is operated by the Association of Universities for Research in Astronomy,Inc.,under NASA contract NAS 5-26555.

point-spread function (PSF),there are small,quantitative di?erences between the results described in this paper and previous results we have reported.In the previous work,we used a stellar PSF determined from a red standard star,F141.In the present work,we have used stellar PSFs that were obtained for four separate blue stars (see the dis-cussion in of the PSFs constructed by &Burrows °4Krist The visual appearance of the hosts in the subtracted 1996).images is,in a few cases,signiDcantly improved by using the PSFs of the blue stars.

Other HST studies of quasar imaging (although many of the objects do not satisfy our luminosity criterion)include &Morris et al.and Hutchings (1995),Hutchings (1994),et al.Disney (1995).

The subject of quasar environments has a long and dis-tinguished history.Some representative papers that report on ground-based observations are Kristian (1973),Wycko?et al.Wehinger,&Gehren (1980),Wycko?,(1981),Tyson,Baum,&Kreidl et al.et al.(1982),Hutchings (1982),Gehren et al.(1984),Heckman (1984),Malkan (1984),Malkan,Margon,&Chanan Persson,&Oke (1984),Boroson,et al.&(1985),Smith (1986),Hutchings (1987),Stockton MacKenty Janson,&Ne?(1987),Yee (1987),Hutchings,&Hintzen &(1989),Romanishin (1989),Ve ron-Cetty Woltjer &Ne?et al.(1990),Hutchings (1992),Dunlop and McLeod &Rieke (1993),(1994a,1994b).

The analyses described in these pioneering ground-based studies are made difficult because of atmospheric seeing;the light from the bright central (nuclear)sources may be a few magnitudes brighter than the total emission from the host galaxies.Nevertheless,there is agreement (within typically 1642

HST IMAGES OF NEARBY LUMINOUS QUASARS

643

mag or better)between our HST observations and previous ground-based estimates of the total apparent magnitudes of the host emission,although HST reveals details not pre-viously accessible and corrects some important conjectures that are not supported by the higher resolution observ-ations.

The paper is organized as follows.In we describe the °2,sample selection and observations;in we present the °3,unprocessed data;in we describe the method of remo-°4,ving the light due to the quasar (PSF subtraction)and present the data after a stellar PSF is subtracted;in we °5,describe the methods of analysis of the data;in we °6,report on the measurements of the host galaxies;in °7,we discuss the presence of companion galaxies;in we °8,compare our measurements with results from some ground-based observations;in we comment on the environment °9,and host galaxy of each quasar;and in we summarize °10,and discuss our results.We assume in this paper that H 0

\

100km s ~1Mpc ~1and )0

\1.0.

2.

SAMPLE SELECTION AND OBSERVATIONS

We describe in this section how the sample was selected and how the observations were performed (°2.1)(°2.2).2.1.Sample Selection

A sample of 14quasars was selected solely on the basis of luminosity redshift (z 10.20),and galactic

(M V \[22.9),latitude (o b o [35?).All the quasars in the &Ve

ron-Cetty Ve ron catalog that satisDed the redshift,luminosity,(1991)and galactic latitude criteria were included in this sample;no distinction was made on the basis of radio or other secondary properties.One may choose to call this set of quasars a ““complete sample ??within the context of the &Ve ron Ve ron-Cetty (1991)catalog.2

The 14quasars with z 10.20have an average (median)absolute magnitude (23.2)and an average

S M V T \[23.4redshift S z T \0.17.Only

three radio-loud quasars are

present in the original sample of 14objects.In the Ve ron-&Ve ron catalog,there are an additional four Cetty (1996)quasars with z 10.20that satisfy our luminosity and galac-tic latitude requirements;all are radio quiet.

By combining the time available from GTO and GO programs,an additional six quasars with redshifts in the range 0.20\z \0.30were added to the original sample of 14objects;these additional objects satisDed the same lumi-nosity and galactic latitude constraints as the original sample.The additional objects contain three radio-loud quasars;the total sample of 20contains six quasars that are classiDed as radio loud,i.e.,with W Hz ~1

L 5GHz

Z 1026et al.The additional six objects are (Kellermann 1994).slightly brighter in the optical on the average (median),([24.1),and have slightly larger redshifts,S M V T \[24.0S z T \0.26.The range of absolute magnitudes in the six added objects,is included within

[24.61M V \[22.9,the range of absolute magnitudes spanned by the original

sample of 14objects,i.e.,[25.61M V

\[22.9.

2The concept of a ““complete ??sample of quasars requires clariDcation since a variety of techniques,including radio emission,optical colors,variability,and X-ray emission,are used to discover quasars.It is conceiv-able,indeed likely,that there is at least one object satisfying our deDning sample criteria that has not yet (in 1996)been recognized observationally.For lack of a better term,we use here the designation ““complete sample ??in a limited sense to mean all the objects within a speciDed catalog having stated characteristics.

In what follows,we shall refer to the total sample of 20quasars as a ““representative sample ??with M V

\[22.9

and z \0.30.The average (median)absolute magnitude for the full sample is [23.6([23.2);the average redshift S z T \0.19.Nearly all (18)of the quasars have 15.1\V \16.7,but two are much brighter in the optical band:3C 273(V \12.8)and HE 1029[140(V \13.9).2.2.Observations

A journal of the observations is given in which Table 1,lists the following quantities for each object:the date observed,the longest exposure time of a single image,the detected number of electrons pixel ~1s ~1in the sky,the quasar redshift,the distance in kiloparsecs that corresponds to an angular separation of 1A as seen from Earth,the apparent V magnitude (from &Ve ron Ve ron-Cetty 1996),the absolute V magnitude (without k -correction),the radio properties (an X identiDes the radio-loud quasars),and in the last column the existence of HST spectroscopy (a ““K ??indicates that the HST /FOS observations were taken as part of the HST Quasar Absorption Line Key Project,and some of the results are reported by et al.and Bahcall 1993et al.an ““O ??indicates that other FOS Jannuzi 1997);observations exist).

The quasars were observed with the Wide Field/Planetary Camera-2(WFPC2)through the F606W Dlter,which is similar to the V bandpass but is slightly redder;the mean wavelength and FWHM of the F606W system response are 5935and 1500respectively.The F606W A ,Dlter was chosen because of its high throughput.In all of the quasars discussed here,redshifted H b and [O III ]are included in the bandpass.At a given angular radius,the scattered light in the Wide Field Camera-2(WF)is about 5times less than the scattered light in the Planetary Camera (see &Burrows We chose to use the WF Krist 1994).instead of the PC in the original formulation of this program because of the likelihood that the host galaxies would have low surface brightnesses that extended over areas large compared to the WF resolution or about (0A .10.2kpc).The results reported here support the original choices,since the observed galaxy extensions are indeed large compared to the WF resolution.

The center of light of all quasars was placed within 4A ^1A from the center of the Wide-Field Camera CCD 3(WF3).Three exposures were taken of each quasar.The integration times for 14objects were 1400,500,and 200s;the exposures for the remaining six objects were 1100,600,and 100s.

The size of WF3is 800]800pixels (exposed area D 770]750pixels),and its image scale is pixel ~1.0A .0996We report measured F606W magnitudes on the HST photometric scale established by et al.Holtzman (1995b).The adopted photometric zero point for 1electron s ~1is 24.94mag for the F606W Dlter.For further information about the WFPC2,see et al.Burrows (1994),Trauger (1994),and Holtzman et al.Additional details of the (1995a,1995b).observational procedures are given in and Paper I Paper II.The innermost regions of the quasar images are saturated in all of the longest exposures out to a radius except B 0A .3,for the two optically brightest quasars in our sample,HE 1029[140and 3C 273,in which cases the images were saturated out to and respectively.The number of B 0A .50A .7,saturated pixels in the central region of the quasar images were typically 30pixels for the longest exposures.In addi-

644BAHCALL ET AL.

Vol.479

TABLE 1Q UASAR S AMPLE

Time Sky Level kpc Object

Date (s)(e ~pixel ~1s ~1)

z arcsec ~1V M V

(QSO)a Radio-loud

FOS b

PG 0052]251.......1994Dec 514000.1140.155 1.7515.4[23.0PHL 909.............1994Oct 1714000.1360.171 1.8815.7[22.9NAB 0205]02......1994Oct 2614000.1390.155 1.7515.4[23.00316[346............1994Nov 2014000.0750.265 2.5515.1[24.5PG 0923]201.......1995Mar 2314000.1360.190 2.0415.8[23.1PG 0953]414.......1994Feb 311000.1100.239 2.3815.3[24.1K

PKS 1004]130......1995Feb 2614000.1500.240 2.3915.2[24.2X

PG 1012]008.......1995Feb 2514000.1290.185 2.0015.6[23.2HE 1029[140.......1995Feb 614000.1000.086 1.2213.9[23.2PG 1116]215.......1994Feb 811000.1280.177 1.9314.7[24.0K,O PG 1202]281.......1994Feb 811000.1160.165 1.8315.6[23.0K 3C 273................1994Jun 511000.1510.158 1.7812.9[25.6X K,O PKS 1302[102......1994Jun 911000.1360.286 2.6715.2[24.6X

K PG 1307]085.......1994Apr 514000.1290.155 1.7515.1[23.3PG 1309]355.......1995Mar 2614000.0880.184 1.9915.6[23.2O PG 1402]261.......1995Mar 714000.0890.164 2.1315.5[23.0PG 1444]407.......1994Jun 2711000.0710.267 2.5615.7[23.9K,O

3C 323.1..............1994Jun 911000.0820.266 2.5516.7[22.9X PKS 2135[147......1994Aug 1514000.1740.200 2.1115.5[23.5X O

PKS 2349[014......

1994

Sep 18

1400

0.161

0.173

1.90

15.3

[23.4

X

a Computed for and km s ~1Mpc ~1.In this cosmology,brightest cluster galaxies have &Schneider

)0\1.0H 0\100M V B [22.0(Hoessel &Lauer and the characteristic (Schechter-)magnitude for Deld galaxies is et al.1985;Postman 1995)M V *\[20.5(Schechter 1976;Kirshner 1983;

Ellis,&Peterson Efstathiou,1988).

b K \HST Quasar Absorption Line Key Project;O \Other FOS observations.

tion,D 15saturated pixels were present due to the ““vertical bleeding.??For HE 1029[140and 3C 273,the number of saturated pixels was approximately 105and 190,respec-tively,plus 90and 390from the vertical bleeding (see Fig.1).The initial data processing (bias frame removal and ?at-Deld calibration)was performed at the Space Telescope Science Institute with their standard software package.The individual images of each quasar were aligned to better than 0.3pixel;this made it easy to identify and eliminate cosmic-ray events.Cosmic rays were identiDed by a pixel-by-pixel comparison of pairs of images;the intensity of a pixel con-taining a cosmic ray was replaced by the scaled value of the intensity of the pixel in the other image.The ?at-Deld cor-rections were based upon pre?ight calibrations;these cali-brations remove the small-scale (few pixel)sensitivity variations.The typical signal and rms of the noise of the sky in the long exposures (in detected photons per pixel)are 157and 14,respectively.

The sky level corresponds to an average surface bright-ness of approximately 22.2mag arcsec ~2.The limiting surface brightness at which objects can be detected is typically between 25and 26mag arcsec ~2(F606W);see Table 2.

3.

THE UNPROCESSED IMAGES

We present in this section the images as received from STScI,without further processing except for the removal of cosmic rays.

shows a 23A ]23A WF image of each of the 20Figure 1quasars,plus the image of a blue star (upper left -hand panel ).The images displayed are the longest individual exposures we have.Many,but not all,of the quasars are noticeably nonstellar,and host galaxies are visible on the unprocessed HST images.The exposure time of the star image shown in the top panel of is 20s,which yields a total number Figure 1of counts similar to that obtained in the quasar images.The star is MMJ 6490in the M67cluster.Its apparent V magni-

tude is 10.99,and its B [V \0.11Mars-(Montgomery,chall,&Janes 1993).

Some features of host galaxies are obvious in Figure 1.Normal spiral galaxies,with prominent H II regions envelop PG 0052]251and PG 1402]261.Host elliptical galaxies are clearly seen in the images of PHL 909,HE 1029[140,PG 1116]215,and 3C 273.There are three obvious cases of current gravitational interaction:0316[346,PG 1012]008,and PKS 2349[014.

Some of the host galaxies are seen even in our shortest exposures (200s;see et al.for short-exposure Bahcall 1996images of PG 0052]251and PHL 909).In some cases,such as NAB 0205]02,PG 0953]414,and PG 1307]085,it is difficult to distinguish the quasar image from the star even in our longest exposures.

4.

IMAGES AFTER SUBTRACTION OF A STELLAR PSF

The major challenge in the analysis of these HST data is the removal of the light produced by the quasar,which is presumed to be a point source.We have adopted an empiri-cal approach.We have used images of stars observed at the same location on the detector as the quasars to determine the PSF of the stellar quasar.

For about half of the quasars considered here,the prin-cipal observational results concerning the host environment can be obtained without the PSF subtraction.Examples of exceptions are the hosts of NAB 0205]02,PG 0953]414,PG 1444]407,and 3C 323.1,which are more apparent in than in Close companions for PKS Figure 2Figure 1.1302[102,PKS 2135[147,and PKS 2349[014are also more clearly visible after the subtraction of a stellar PSF.The stellar PSF was measured in Cycle 5(HST program 5849)by obtaining a set of 13images for each of four blue stars in the M67cluster.The calibration stars (and their B [V colors)are MMJ 6481([0.073),MMJ 6490(0.11),MMJ 6504(0.22),and MMJ 6511(0.34).The apparent mag-nitudes range from V \10.03to V \10.99.For each star,a

No.2,1997HST IMAGES OF NEARBY LUMINOUS QUASARS645

series of four images were used by&Burrows

Krist(1996) to produce a PSF that samples the full dynamic range of the star image and covers the saturation range found in the quasar images.In these calibration images,the radius of the saturated region varies from to the exposure times

0A.00A.6;

range from0.1to100s.

The PSF data are publicly available at

There is a detailed documenta-https://www.wendangku.net/doc/179320936.html,/jnb.

tion regarding the PSF data and their use at this site(go to HST Images)by J.Krist and C.Burrows describing how the PSFs were constructed.

Whenever PSF subtractions were required,we used all four PSFs determined by Krist and Burrows.For each case, we selected the result that gave the cleanest subtraction(i.e., the fewest artifacts produced).

WeDtted a stellar PSF to each quasar image and sub-tracted a multiple of the normalized PSF to search for underlying di?use light from hosts.The bestDt was deter-mined by minimizing the di?erences between the quasar and the PSF using a s2-routine calculated in two distinct areas:azimuthal averages and narrow regions centered on the di?raction spikes.The two methods gave essentially same results(see di?ering in inferred host galaxy

Paper II),

magnitude by^0.1mag.The quasar images with the PSF subtracted presented in this paper were obtained by mini-mizing the s2in unsaturated annular region(typical inner and outer radii of1A and3A),centered on the quasar. Adjustments of the amount of PSF subtraction were often made after visual inspection of the““best-Dt??PSF-subtracted images.

We have estimated some of the likely systematic uncer-tainties in the subtraction process by subtracting a best-Dt PSF of the standard star,MMJ6504,from the image of another standard star,MMJ6490.We have Cycle5obser-vations of MMJ6490observed at the same position in WF3 as the sample quasars.(upper left-hand panel)

Figure2

shows the image of the bestDt of MMJ6504subtracted from MMJ6490.The PSF subtraction,star from star,is very good,although some faint di?use residuals are still present.If we scale the intensity of MMJ6490so that the central brightness corresponds to the apparent magnitude of one of our typical quasars,i.e.,V\15.6,then the residual““nebulosity??left over when the MMJ6504PSF is subtracted is about21.0mag.

shows the images for all the quasars in our Figure2

sample after a best-Dt stellar PSF was subtracted from the original images shown in Figure1.

lists the major diameter of the host galaxies in Table2

arcseconds and in kiloparsecs,the surface brightness of the isophote for which the size was measured,and a tentative morphological classiDcation.For each quasar,the magni-tude of the host galaxy was calculated using three di?erent methods,aperture photometry(see and one-

° 5.1), dimensional and two-dimensional galaxy modeling(see and

°°5.2 5.3).

We determined the size of the quasar hosts by examining the PSF-subtracted images and measuring the faintest iso-photes of the host galaxy.The morphological classiDcation was done by visual inspection of the images and following as closely as possible the classiDcation given in The Hubble Atlas of Galaxies by In a number of cases

Sandage(1961).

indicated by(?)in we have denoted as““En??

Table2,

featureless,smooth hosts that do not show any obvious discontinuities or morphological features.

5.METHODS OF ANALYSIS

In this section,we describe the di?erent methods of analysis that we have used to determine the properties of the quasar hosts.The measured quantities are presented in Tables and discussed in°°We describe in°°2è66è7. 5.1 di?erent methods for estimating the magnitude of the è5.3

host galaxies.We discuss in our results for aperture

°5.1

photometry,in the radial proDleDts,and in the

°5.2°5.3 two-dimensionalDts.

Some of the host environments are complex,including merging or tidally interacting galaxies and close compan-ions.The smooth de Vaucouleurs or exponential disk models used in°°and are obviously not realistic

5.2 5.3

descriptions of the light distribution for complex environ-ments.In order to provide a common basis of comparison

TABLE2

S IZE AND M ORPHOLOGY OF H OST G ALAXIES

M AJOR D IAMETER

I SOPHOTE(F606W)

O BJECT arcsec kpc(mag arcsec~2)M ORPHOLOGY

PG0052]251.......203525.1Sb

PHL909.............193624.7E4

NAB0205]02......91625.0S0?

0316[346............174325.6Complex,interaction

PG0923]201.......132724.8E1

PG0953]414.......112625.8Faint,tail?

PKS1004]130......153625.0E2

PG1012]008.......183625.0Interacting galaxies

HE1029[140.......404926.0E1

PG1116]215.......142725.1E2

PG1202]281.......101824.7E1,bright companion

3C273................295225.4E4

PKS1302[102......154025.2E4(?)two close companions PG1307]085.......91624.6Faint E1(?)

PG1309]355.......183625.7Sab

PG1402]261.......143025.6SBb

PG1444]407.......102625.2E1(?)

3C323.1..............112825.1E3(?)(bright companion) PKS2135[147......153224.8E1(companions)

PKS2349[014......214024.5Complex,interacting

646BAHCALL ET AL.Vol.479

with ground-based observations,we provide the results of Dts with smooth models for all of the host environments, complex or not.

5.1.Aperture Photometry

We performed aperture photometry in circular annuli centered on the quasars,after a best-Dt PSF was subtracted. An inner radius of was used for all quasars,except

r\1A.0

for HE1029[140and3C273.In most observations,the region r\1A is heavily contaminated by artifacts left by the PSF subtraction.The saturated areas in the images of HE 1029[140and3C273are larger;for those two cases,the inner radii used were and respectively.The outer

1A.52A.0,

radii chosen in general represent how far we could see the host galaxy(see The aperture magnitudes calcu-

Table3).

lated using an inner radius are typically D0.6mag

r\1A.0

fainter than the total magnitude for the galaxy that was estimated byDtting a model(see°°to the measured

5.2è5.3)

surface brightness.A di?erence between aperture and model magnitudes is expected because the aperture magnitudes do not include the area within1A of the quasar;all of the models we considered have surface brightnesses that increase monotonically toward the center.

5.2.One-dimensional Radial ProDles

The one-dimensional azimuthally averaged surface brightness proDles of the host galaxies were constructed from the HST data after subtraction of a best-Dt stellar PSF.Regions a?ected by saturation,di?raction spikes,or residual artifacts from the PSF subtraction were not included in the azimuthally averaged proDles.For each galaxy,we obtained a best-Dtting exponential disk (hereafter Disk)and a Vaucouleurs hereafter

de(1948,GdV) proDle thatDts the observed data in the region ro1A.The total magnitudes obtained this way are systematically brighter than the ones obtained by aperture photometry which excludes the innermost,saturated regions of (°5.1),

the proDles.

5.3.T wo-dimensional Fit

The HST imaging provides greater detail than has been available previously in ground-based images of luminous quasars.Traditionally,the properties of host galaxies have been determined in ground-based studies by making model Dts to azimuthally averaged radial proDles(see°5.2).

To take advantage of the HST resolution,we have devel-oped software toDt a two-dimensional model to the PSF-subtracted quasar images.For each quasar,weDtted an analytic galaxy model(exponential disk or de Vaucouleurs proDle)to the data and calculated the s2.The area used for theDt was approximately an annular region,centered on the quasar,that excluded the central area and the

(r\1A.0), remnants of the di?raction spikes or other artifacts clearly due to improper PSF subtraction.WeDtted four param-eters:the(x,y)pixel position of the center,the total number of counts,and the radius(e?ective radius or scale length)in the galaxy model.

We begin the iteration by giving the software the position of the quasar nucleus and calculate only the total number of counts.The number of counts found in this step is entered as the initial guess for the galaxy brightness,and the program thenDts the counts and radius,keeping the posi-tionDxed.Finally,we supply the software with the pre-viously calculated counts and radius and ask the software toDt all four parameters.

We tested the software for the two-dimensionalDts in di?erent ways.Initially,we created two model galaxies:a disk and an elliptical galaxy.We checked how well the two-dimensional software reproduced the position of the center of the model galaxies,the scale length or e?ective radius,and the total number of counts.We made extensive checks by varying the input parameters and the order in which the parameters wereDtted.The best results were achieved when we followed the three-step iterative process in the order described above.WeDtted each model galaxy with an exponential disk and a de Vaucouleurs modelèthe smallest s2residuals were obtained when the disk galaxy wasDtted by an exponential disk model and the elliptical wasDtted by a de Vaucouleurs model.For the model gal-axies,the discrepancy in position and size were\1pixel. The discrepancy in the total number of counts was D1%. The accuracy achieved in the simulations is greater than can be achieved with the real data because of the imperfect subtraction of the PSF for the HST images.

The host galaxies of PG0052]251and PHL909were also used to test the two-dimensional software.We com-pared the software output position with our measured posi-tion for the center of the galaxy(agreement better than0A.2), compared the total number of counts with the value we estimated from aperture photometry(agreement turned out to be0.1mag for PG0052]251,and0.5mag for PHL909), and veriDed that the output scale length or e?ective radius were plausible.

6.MAGNITUDES AND POSITIONS OF HOST GALAXIES

In this section,we report on the measurements of the magnitude and position of the host galaxies.

In we list the magnitudes for the host galaxies Table3,

measured using aperture photometry;the inner and outer radii used in performing aperture photometry are listed as well.The outer radius indicates how far from the quasar the host galaxy was clearly visible.We transformed the mea-sured F606W aperture magnitudes to V applying k-corrections calculated by Shimasaku,&Ichikawa

Fukugita,

Given the redshift of the quasar and the morphologi-(1995).

cal type of the host,we used Table6and Figure14b of Fukugita et al.to obtain the(F606W[V)color.For the cases in which we are uncertain about the morphological type of the host,we assumed an average of the (F606W[V)color for ellipticals and Sab galaxies.

lists the results for the one-dimensional and two-Table4

dimensional galaxy modelDtting.The two-dimensional models are somewhat fainter than the corresponding one-dimensionalDts.Specially,weDnd

S m

606W,2v D

[m

606W,1v D

T\

G0.4^0.2,

0.3^0.1,

GdV

Disk

.(1)

The magnitudes obtained by modelDts are brighter than those obtained by aperture photometry since the models include estimated contributions from the inner(saturated) regions of the images.On average,

S m

606W,1v D

[m

606W,aperture

T\

G[1.1^0.2,

[0.4^0.2,

GdV

Disk

.(2)

As shows,the magnitudes of the host galaxies equation(3)

estimated byDtting a model to the azimuthal averaged

GdV

No.2,1997HST IMAGES OF NEARBY LUMINOUS QUASARS647

TABLE3

A PERTURE M AGNITUDES FOR H OST G ALAXIES

I NNER O UTER A PERTURE P HOTOMETRY A PERTURE

R ADIUS R ADIUS P HOTOMETRY

O BJECT(arcsec)(arcsec)m

F606M

F606

(F606[V)a M

V

PG0052]251....... 1.010.017.1[21.3[0.31[21.0

PHL909............. 1.010.017.5[21.1[0.41[20.7

NAB0205]02...... 1.0 4.519.5[18.9[0.31[18.6

0316[346............ 1.011.518.2[21.4[0.47[20.9

PG0923]201....... 1.0 6.518.3[20.6[0.42[20.2

PG0953]414....... 1.0 5.519.1[20.3[0.38[19.9

PKS1004]130...... 1.07.517.7[21.7[0.48[21.2

PG1012]008....... 1.0 4.517.8[21.0[0.39[20.6

HE1029[140....... 1.520.016.5[20.6[0.35[20.2

PG1116]215....... 1.08.017.7[21.0[0.41[20.6

PG1202]281....... 1.0 5.018.6[20.0[0.40[19.6

3C273................ 2.015.016.6[21.9[0.40[21.5

PKS1302[102...... 1.07.518.4[21.4[0.50[20.9

PG1307]085....... 1.0 4.518.7[19.7[0.37[19.3

PG1309]355....... 1.09.017.4[21.4[0.35[21.0

PG1402]261....... 1.07.518.1[20.4[0.30[20.1

PG1444]407....... 1.0 5.018.8[20.8[0.47[20.3

3C323.1.............. 1.0 5.518.9[20.7[0.47[20.2

PKS2135[147...... 1.07.518.1[20.9[0.45[20.4

PKS2349[014...... 1.012.016.7[22.0[0.41[21.6

et al.

a Fukugita1995.

radial proDle of the residual light are on average1.0mag

brighter than the magnitudes obtained from aperture pho-

tometry;Dtting an exponential disk model gives magnitudes

that are on average0.5brighter than the results from aper-

ture photometry.For the two-dimensional modelDts,we

have on average

S o m

606W,2v D [m

606W,aperture

o T\

G[0.7^0.2,

[0.2^0.1,

GdV

Disk

.

(3)

lists our best estimate absolute V magnitudes.In Table5

computing the entries in we used the k-correction

Table5,values of et al.that are listed in the next-to-Fukugita(1995)

last column of In computing the absolute magni-

Table3.

tudes,we selected the best-Dt model based on the morphol-ogy of the host galaxy,unless the morphology is uncertain, and for those cases,we list the model that gives the smallest s2residuals.

The results from the two-dimensionalDts indicate that the host galaxies are,on average,centered on the quasar with

S*r T\0.4^0.4kpc.(4) The host galaxies are typically centered within400pc of the location of the quasar point source.If we eliminate from the

TABLE4

M ODEL F ITS TO S TELLAR Q UASAR PLUS H OST G ALAXY

O NE-DIMENSIONAL T WO-DIMENSIONAL

GdV Exponential Disk GdV Exponential Disk

O BJECT m

F606r(arcsec)a m

F606

r(arcsec)b m

F606

r(arcsec)a m

F606

r(arcsec)b

PG0052]251.......16.1 4.716.8 1.416.7 1.817.2 1.3 PHL909.............16.7 2.517.4 1.017.2 2.317.6 1.5 NAB0205]02......18.00.618.70.618.40.719.00.7 0316[346............17.2 3.418.0 1.117.8 2.118.3 1.2 PG0923]201.......17.3 2.518.0 1.017.5 2.918.2 1.3 PG0953]414.......17.9 2.318.5 1.118.2 1.818.8 1.1 PKS1004]130......16.7 1.617.30.916.9 1.217.5 1.0 PG1012]008.......16.3 6.217.3 1.417.0 3.417.7 1.6 HE1029[140.......15.9 2.816.4 1.516.2 3.216.7 1.9 PG1116]215.......16.6 1.917.3 1.016.9 1.417.5 1.2 PG1202]281.......17.4 1.518.10.917.7 1.418.3 1.0 3C273................15.6 2.316.2 1.316.0 3.716.7 1.6 PKS1302[102......17.1 2.617.8 1.117.7 1.418.2 1.1 PG1307]085.......17.4 1.818.10.917.8 1.318.4 1.0 PG1309]355.......16.4 2.817.1 1.116.8 2.017.3 1.2 PG1402]261.......16.9 2.217.6 1.017.6 1.518.3 1.6 PG1444]407.......17.6 1.318.2 1.017.8 1.318.4 1.0 3C323.1..............17.8 1.418.40.918.1 1.618.7 1.0 PKS2135[147......17.2 2.017.8 1.117.4 2.618.0 1.3 PKS2349[014......15.9 5.616.6 1.616.2 4.816.8 2.5

a E?ective radius.

b Exponential scale length.

648

BAHCALL ET AL.

Vol.479

TABLE 5

A BSOLUTE V ISUAL M AGNITUDES FOR Q UASAR H OST G ALAXIES

O NE -DIMENSIONAL

T WO -DIMENSIONAL O BJECT

M V (1-D)Best Model M V (2-D)Best Model PG 0052]251.......[21.3Disk [20.9Disk PHL 909.............[21.5GdV [21.0GdV NAB 0205]02......[19.4Disk [19.1Disk 0316[346............[21.1Disk [20.8Disk PG 0923]201.......[21.2GdV [21.0GdV PG 0953]414.......[20.5Disk [20.2Disk PKS 1004]130......[22.5GdV [22.0GdV PG 1012]008.......[22.1GdV [20.7Disk HE 1029[140.......[20.8GdV [20.5GdV PG 1116]215.......[21.7GdV [21.4GdV PG 1202]281.......[20.8GdV [20.5GdV 3C 273................[22.5GdV [22.1GdV PKS 1302[102......[21.5Disk [21.1Disk PG 1307]085.......[20.6GdV [20.2Disk PG 1309]355.......[21.3Disk [21.1Disk PG 1402]261.......[20.6Disk [19.9Disk PG 1444]407.......[20.9Disk [20.5Disk 3C 323.1..............[21.3GdV [21.0GdV PKS 2135[147......[21.3GdV [21.1GdV PKS 2349[014......

[22.4

GdV

[22.1

GdV

comparison the most extreme examples of especially complex environments (0316[346,PG 1012]008,and PKS 2349[014)the results are

S*r T \0.2^0.2kpc .

(5)

The two-dimensional (one-dimensional)model GdV gives magnitudes for the host that are on average 0.6mag (0.7mag)brighter than the exponential disk estimates.

7.

COMPANION GALAXIES

Inspection of the HST images of the quasar Delds reveals a number of companion galaxies projected close to the

quasars.The relatively long exposures (1100or 1400s),combined with the excellent angular resolution,allowed galaxies to be identiDed down to limiting magnitude and as close as 1A or 2A from the central m (F606W)[25.0quasar.We performed aperture photometry on the galaxies in the quasar Delds using circular apertures with radii of as appropriate.

0A .3è10A ,We counted the number of companion galaxies brighter than a speciDed limiting absolute magnitude that were found to have a metric separation from one of the quasars of less than or equal to some predetermined distance.We choose a priori a limiting absolute magnitude of M V \

[16.5(4mag fainter than L *)and a maximum separation of

25kpc (see Paper II).

lists all galaxies found around the quasars that Table 6satisfy these speciDcations.This table gives for each quasar the number of companion galaxies that are at least as bright as (if they have the same redshift as the

M V \[16.5quasar)

and that are projected within 25kpc of the center of light of the quasar.The separations both in arcseconds and in kpc are also given in along with the brightnesses Table 6,of the companion galaxies,tabulated in both apparent and absolute magnitude.

The density of companion galaxies brighter than M V

\

[16.5,within 25kpc of the quasars,may be higher around quasars with elliptical hosts.There are two companions for four spiral hosts and 13companions for 12elliptical hosts.et al.examined the clustering of galaxies Fisher (1996)around all the quasars in this sample and found a signiD-cant enhancement of galaxies within a projected separation of h ~1kpc of the quasars.Modeling the quasar/[100galaxy correlation function as a power law with a slope given by the galaxy/galaxy correlation function,et al.Fisher Dnd that the ratio of the quasar/galaxy to galaxy/(1996)galaxy correlation functions is 3.8^0.8.The galaxy counts within r \15h ~1kpc of the quasars are too high for the density proDle to have an appreciable core radius (Z 100

TABLE 6

G ALAXY C OMPANIONS B RIGHTER THAN WITHIN

M (F606W)\[16.525kpc OF THE Q UASAR

D ISTANCES

M AGNITUDES N UMBER OF Q UASAR C OMPANIONS

arcseconds kpc m

F606M F606PG 0052]251.......

114.124.618.8[19.6PHL 909.............112.523.521.4[17.2NAB 0205]02......18.314.520.0[18.4PG 0923]201.......210.922.219.5[19.411.022.518.0[20.9PG 0953]414.......18.219.622.7[16.7PG 1012]00........2 3.3 6.717.6[21.26.813.719.0[19.8PG 1116]215.......112.323.819.3[19.4PG 1202]281.......3 5.29.518.9[19.78.415.321.5[17.19.617.521.3[17.3PKS 1302[102......2 1.1 2.920.3[19.52.3 6.221.5[18.3HE 1029]140a ......1 4.1 5.020.7[16.43C 323.1..............1 2.7 6.920.6[19.0PKS 2135[147......2 1.9 3.919.5[19.55.511.719.7[19.3PKS 2349[014......

2

1.9 3.520.8[17.911.6

22.0

21.4

[17.3

a Absolute magnitude of the close companion is 0.1mag fainter than the assumed limiting magnitude.

No.2,1997HST IMAGES OF NEARBY LUMINOUS QUASARS 649

h ~1kpc).These results provide further support for the idea that low-redshift quasars are located preferentially in groups of 10è20galaxies rather than in rich clusters.Fisher et al.do not detect a signiDcant di?erence in the clustering amplitudes derived from radio loud and radio quiet sub-samples.

8.

COMPARISON WITH GROUND -BASED OBSERVATIONS

In this section we compare the results of HST -based images of luminous quasars with previously published rep-resentative analyses of ground-based observations.In °8.1,we compare our HST measurements with the Ve ron-Cetty &Woltjer i -band results,in with the Dunlop et (1990)°8.2,al.near-infrared images,and in with the &°8.3,McLeod Rieke H -band observations.

(1994b)&Woltjer:Annular Regions 8.1.Ve ron -Cetty &Woltjer suggested that the appar-Ve ron-Cetty (1990)ent magnitudes of host galaxies should be measured in a Dxed metric annulus that is well removed from the quasar nucleus.They proposed an annular region of 12.5è25.0kpc for and km s ~1Mpc ~1.The Ve ron-Cetty

)0\0.0H 0

\50&Woltjer proposal compares directly measurements of the same quantity made by separate groups using di?erent techniques.In this way,measurement uncertainties can be separated from di?erences caused by the variety of choices in the models used to Dt to the observations.We have three objects in common with Ve ron-Cetty &Woltjer:PKS 1302[102,PKS 2135[147,and PKS 2349[014.The speciDed annular regions are and 2A .174A .35,and and and for the three quasars,2A .825A .63,3A .156A .30respectively.All three quasars have close companion gal-axies in the regions speciDed by Ve ron-Cetty &Woltjer (see The close companions of PKS 1302[102and Table 6).PKS 2349[014were not noticed on the ground-based images.

summarizes the aperture photometry that was Table 7performed in the same annular regions as Ve ron-Cetty &Woltjer.We list the i -band annular magnitudes obtained by Ve ron-Cetty &Woltjer and their estimated absolute V -magnitude,converted to the cosmological parameters used in this paper,the absolute magnitude we measured in the HST images (excluding the light of the companions)with the F606W,and our estimated absolute V -magnitude.We also include in the table the total absolute V -magnitude Ve ron-Cetty &Woltjer obtained for the host galaxies (Dtting a spheroidal model)and our estimated two-dimensional V -band host galaxy magnitude.

The agreement between our results and the ground-based observations of Ve ron-Cetty &Woltjer for the aperture photometry between 12.5and 25kpc is satisfactory but not

as precise as we would have hoped.The average di?erence between our estimated and that of Ve ron-Cetty &

M V

Woltjer is

S M V (i )[M V (F606)T (12.5h 25kpc)VCW

\[0.4^0.1mag .

(6)This discrepancy cannot be attributed to the contribution of companion galaxies.In the case of PKS 1302[102,the companion at 2A lies inside the annular region studied (12è25kpc);if we include its light,our estimated brightness for the host increases 0.2mag.Part of the companion galaxy from PKS 2135[147lies in the annular region 5A .5considered,but &Woltjer also sub-Ve ron-Cetty (1990)tracted its contribution from their measurements.The compact companion at 2A of PKS 2349[014lies outside the annular region considered.The Ve ron-Cetty &Woltjer magnitudes for the host that were estimated by Dtting a spheroidal model are typically about 1mag brighter than our two-dimensional model magnitudes,i.e.,

S M V (i )(model)VCW [M V (F606)

(2-D)T \[0.8^0.4mag .

(7)lists the annulus measurements of the whole Table 8sample.For the range of redshifts in our sample,the desig-nated Ve ron-Cetty &Woltjer annular region 12.5è25kpc km s ~1Mpc ~1,corresponds approx-(H 0\50)0\0.0)imately to 6è12kpc with our chosen cosmological param-eters.In we list for each quasar the inner and outer Table 8radii in arcseconds,the apparent and absolute F606aper-ture magnitude,and the absolute V magnitude in the annulus (see adopted values for F606[V values in Table As stressed by &Woltjer these 3).Ve ron-Cetty (1990),annular measurements can be compared to future measure-ments obtained by other techniques.

8.2.Dunlop et al .

et al.obtained deep ground-based near-Dunlop (1993)infrared images in the K band for a sample of nearby (z \0.4)radio-loud and radio-quiet quasars.They built a library of infrared PSFs by observing many bright stars.The nuclear component was removed by selecting from the library the PSF that produced the best match to the quasar PSF.The stellar PSF was scaled to the same height as the central peak of the quasar.Dunlop et al.suggest that their procedure will cause the luminosities of the hosts to be overestimated,but in practice the sign of the error could depend on whether there was a positive or a negative ?uc-tuation in the measured light in the central peak.An aper-ture diameter of 12A was used by Dunlop et al.to measure

TABLE 7

C OMPARISON WITH R ESULTS OF &W OLTJER V E RON -C ETTY (1990)

12.5kpc è25kpc

O BJECT m i a M

V (i )a M F606b M V (F606)b M V

(model)a M V (F606)(2-D)b PKS 1302[102......

19.5[20.3[20.4[20.0[22.0[21.1PKS 2135[147......18.9[19.9[19.9[19.4[22.2[21.1PKS 2349[014......

17.6

[20.7[20.8

[20.4

[22.5

[22.1

&Woltjer a Ve ron-Cetty 1990.b HST results,this paper.

650

BAHCALL ET AL.Vol.479

TABLE 8A NNULAR M AGNITUDES

r 1r 2Object

(arcsec)a (arcsec)b m

F606M

F606M V PG 0052]251....... 3.43 6.8618.3[20.1[19.8PHL 909............. 3.19 6.3818.8[19.8[19.4NAB 0205]02...... 3.43 6.8620.7[17.7[17.40316[346............ 2.80 4.7119.8[19.8[19.3PG 0923]201....... 2.96 5.9119.3[19.6[19.2PG 0953]414....... 2.52 5.0420.1[19.3[18.9PKS 1004]130...... 2.51 5.0218.9[20.5[20.0PG 1012]008....... 3.00 6.0018.1[20.7[20.3HE 1029[140....... 5.5611.1118.0[19.1[18.7PG 1116]215....... 3.11 6.2219.0[19.7[19.3PG 1202]281....... 3.28 6.5619.9[18.8[18.43C 273................ 3.37 6.7417.8[20.7[20.3PKS 1302[102...... 2.25 4.4919.4[20.4[19.9PG 1307]085....... 3.43 6.8619.9[18.5[18.1PG 1309]355....... 3.02 6.0318.7[20.1[19.7PG 1402]261....... 3.28 6.5619.5[19.0[18.7PG 1444]407....... 2.34 4.6919.7[19.9[19.43C 323.1.............. 2.35 4.7119.9[19.7[19.2PKS 2135[147...... 2.84 5.6919.1[19.9[19.4PKS 2349[014......

3.16

6.32

17.9[20.8

[20.4

N OTE .èF606magnitudes of host galaxies measured in an annulus between radii of 6kpc and 12kpc for km s ~1Mpc ~1,H 0\100)0\1.0.

(These radii corresponds approximately to 12.5kpc and 25kpc for

H 0\50km s ~1Mpc ~1,)0\0.0)

a Inner radius \6kpc.

b Outer radius \12kpc.

the magnitudes of the hosts.We have eight quasars in common.

compares the HST and the Dunlop et al.results.Table 9We list the K magnitude they obtained for the host galaxies using an aperture of diameter 12A ,the K absolute magni-tude for the host,using our comoslogical parameters,the color (V [K )for an elliptical galaxy obtained from Bruzual &Charlot the corresponding V absolute magnitude (1993),expected,the two-dimensional model V absolute magnitude estimated from the HST -F606W images (see next-to-last column of and the di?erence between the V abso-Table 5),lute magnitude derived from both bands,The average

*M V

.discrepancy is

S o *M V o T \S o M V (K )[M V (F606)

o T \1.0^0.6mag .

(8)For seven of the eight cases,our estimated magnitudes are brighter than obtained by et al.Dunlop (1993).

8.3.McL eod &Rieke

McLeod &Rieke obtained ground-based (1994a,1994b)images of luminous quasars in the H band.For most cases,they determined a one-dimensional proDle for the quasar,subtracted a stellar PSF,and then Dtted the resulting proDle with an analytic galaxy model.We have 14quasars in common.To compare the results,we transform both the

TABLE 9

C OMPARISON BETWEEN A BSOLUTE V M AGNITUDES FOR Q UASAR H OST G ALAXIES E XPECTE

D FROM

K -B AND AND FROM HST [F606W M EASUREMENTS

Object

K gal a M K (V [K )b M

V (K )M

V (F606)(2-D)c *M

V PG 0052]251.......15.14[23.3 3.90[19.4[20.9 1.5PHL 909.............14.40[24.2 3.95[20.3[21.00.7PG 0923]201.......14.95[23.9 4.00[19.9[21.0 1.1PG 0953]414.......15.28[24.1 4.20[19.9[20.20.3PKS 1004]13.......15.12[24.3 4.20[20.1[22.0 1.9PG 1012]00........13.94[24.9 4.00[20.9[20.7[0.2PKS 2135[147......14.75[24.2 4.10[20.1[21.1 1.0PKS 2349[014......

13.98

[24.7

3.95

[20.8[22.1

1.3et al.a Dunlop 1993.

b (V [K )for elliptical galaxy from &Charlot Bruzual 1993.

c This work (derive

d from two-dimensional galaxy model Dtting).

TABLE 10

C OMPARISON BETWEEN A BSOLUTE V M AGNITUDES FOR Q UASAR H OST G ALAXIES E XPECTED

FROM H -B AND AND FROM HST F606W M EASUREMENTS

Object H gal a (V [H )normal

b

M V (H )M V (F606)(2-D)c *M V (1)

(2)(3)(4)(5)

(6)PG 0052]251.......14.46 3.16[20.8[20.90.1PG 0923]201.......14.86 3.22[20.8[21.00.2PG 0953]414.......15.38 3.32[20.7[20.2[0.5PKS 1004]130......14.86 3.32[21.2[22.00.8PG 1012]008.......14.02 3.21[21.6[20.7[0.9PG 1116]215.......13.97 3.20[21.6[21.4[0.2PG 1202]281.......15.07 3.18[20.3[20.50.23C 273................13.01 3.17[22.3[22.1[0.2PKS 1302[102......14.79 3.47[21.5[21.1[0.4PG 1307]085.......15.24 3.16[20.0[20.20.2PG 1309]355.......14.55 3.21[21.0[21.10.1PG 1402]261.......14.95 3.18[20.4[19.9[0.5PG 1444]407.......15.19 3.42[21.0[20.5[0.53C 323.1..............

14.80

3.42

[21.4

[21.0

[0.4

&Rieke a McLeod 1994b.&Rieke b McLeod 1995.

c This work (derive

d from two-dimensional galaxy model Dtting.)

No.2,1997HST IMAGES OF NEARBY LUMINOUS QUASARS 651

H -band and the F606W magnitudes to the V band.We used the k -corrections and the relative sensitivities of the di?erent bands calculated by et al.to Fukugita (1995)convert our F606W measurements to V (see °6).

To transform the H -band magnitudes to V ,we assumed (V [H )D 3.0for normal galaxies plus a k -correction given by &Rieke For objects not in their table,McLeod (1995).we interpolated in redshift to obtain the expected (V [H )for a normal galaxy.

lists the following information:column (1):Table 10quasar;column (2):McLeod-Rieke H -band magnitude for the host galaxy;column (3):color (V [H )for normal gal-axies including k -correction;column (4):absolute V magni-tude based on the H -band measurements and calculated assuming km s ~1Mpc ~1,and column (5):

H 0\100)0

;absolute two-dimensional model V magnitude estimated from F606W images;and column (6):di?erence between absolute V magnitude estimated from H -band and F606W images.The average discrepancy is

S o M V (H )[M V (F606)

o T \0.4^0.2mag .(9)

For eight of the 14cases,the McLeod &Rieke lumi-nosities are brighter than the HST luminosities.In some cases,the di?erence is clearly due to the McLeod &Rieke magnitudes also including the companion galaxies (see PG 1012]008in Figs.and and the discussion in 12°9).

9.

COMMENTS ON INDIVIDUAL CASES

In this section we will discuss the images of each of the quasars.summarizes the morphological informa-Table 2tion obtained from the HST images,and Tables give 3è5the inferred luminosities of the host galaxies.For compari-sons,the absolute magnitudes reported by other authors have been converted to our cosmological https://www.wendangku.net/doc/179320936.html,r-mation about close galaxy companions is summarized in Table 6.

Measurements of the surface brightness along the major axes of the relatively bright elliptical host galaxies of PHL 909,PG 0923]201,PKS 1004]130,HE 1029[140,PG 1116]215,3C 273,and PKS 2135[147do not show evi-dence of discontinuity in the light distribution.Thus,all the apparently elliptical hosts discussed below for which we could make detailed photometry satisfy the criterion of having smooth light distributions.The HST images reveal spiral host galaxies with H II regions for three quasars,PG 0052]251,PG 1309]355,and PG 1402]261.It should be feasible to obtain spectra of the brightest H II regions.The spectra may reveal the composition of the material that makes up the quasar hosts and perhaps provide further clues to the quasar phenomenon.

PG 0052]251.èThe host is a beautiful spiral galaxy (see et al.for a detailed discussion).The spiral host Bahcall 1996is evident even in our 200s exposure.The southern spiral arm extends the farthest from the quasar (in the direction of the companion).There is good agreement between the absolute V magnitude estimated from the &Rieke McLeod H -band image measurements and our two-(1994b)dimensional model estimate based on the HST https://www.wendangku.net/doc/179320936.html,ler (1996,private communication)has recently obtained spectra for some of the bright H II regions identiDed et al.in the HST images.The H II regions (Bahcall 1996)observed have the same redshift as the quasar.The second and third quasar nuclei suggested by Hutchings et al.(1989;the second nucleus was conDrmed by et al.Dunlop 1993),

are seen on the HST images to be,respectively,a bright H II region in the spiral arm of the host galaxy and a foreground star in the Galaxy.

PHL 909(0054]144).èThe quasar host is a normal elliptical E4galaxy (see et al.for a more exten-Bahcall 1996sive discussion and a variety of images).This radio-quiet quasar does not occur in a spiral galaxy,as the convention-al view had suggested before the HST observations.We did not detect extended emission toward the western compan-ion galaxy,as suggested by et al.The ellip-Dunlop (1993).tical host is apparent in our 200s image.

NAB 0205]02.èThe appearance of this quasar in the HST images (see resembles,on visual inspection,Fig.1)that of a bright star.Indeed,it is hard to distinguish the quasar from a star by just looking at the images (see Fig.1).After PSF subtraction,we detect a small disklike host galaxy (see with size and inclination similar to the Fig.2),companion position angle PA \332?.The scale 8A .3A ,length of the host is only D 1.2kpc,and the absolute visual magnitude is [19.1.

(Plate 29)compares the host image after sub-Figure 3traction of a blue standard star,MMJ 6481(see Fig.3a ),and after the subtraction of a red standard star,F141(see The image of the host galaxy obtained after the Fig.3b ).subtraction of the PSF for the blue standard star is signiD-cantly clearer than the image obtained using the red star PSF.However,there is very little di?erence quantitatively,\0.1mag,between the host galaxy magnitudes we deter-mined from the two subtracted images.

Ridgway,&Kellogg recently obtained Stockton,(1997)ground-based images in two line-free continuum bands that show a deDnite host galaxy elongated roughly northwest-southeast as well as some extended low surface brightness material to the west.In agreement with our results,they report that the host galaxy has about the same luminosity and orientation as the companion in the shorter wavelength image,but the host has somewhat redder colors than the companion.NAB 0205]02was not resolved in the deep images taken by et al.Smith (1986).

(Plate 30)shows a fascinating object,Drst Figure 4noticed by &MacKenty The object,which Stockton (1987).is 12A to the east of the quasar,is visible in their [O III ]image but is absent from their continuum image.It appears as a point source with a bright jetlike structure to the south and a much fainter and curved extension to the north.The width of the jet and of the curved extension is less than 0.3kpc.The total apparent F606W magnitude of the object is 22.6,and the extension of the jetlike structure and curved tail are (1.2kpc)and (1.9kpc),respectively.The 0A .71A .1o?set of this object from the quasar position is *a \1A .1and *d \1A .7.

0316[346.èThe morphology of the host environment is complex,probably the result of gravitational interactions with a neighboring galaxy.Figures and show clearly 12what appear to be tidal tails that extend about 20kpc west of the quasar.There are also bright di?use clumps within D 5kpc of the quasar,which may contain H II regions.We do not see unambiguous signs of a compact remnant close to the center of light of the quasar.The radial proDle is reasonably described by an exponential disk from radius D 1A to 6A .There is a relatively bright peculiar spiral galaxy mag)projected of the quasar,PA \67?.(m 606

\20.726A .7PG 0923]201.èThe host of this radio-quiet quasar is an E2elliptical,a member of a small group of galaxies.The two

652BAHCALL ET AL.Vol.479

galaxies at PA \151?,and PA \162?,have red-11A .0,15A .1,shifts similar to the quasar et al.the com-(Heckman 1984);panion at 15A southeast is not shown in Figures and 1 2.The V magnitude estimated from &Rieke McLeod (1994b)H -band images is in good agreement (0.1mag)with the magnitude determined from our two-dimensional model.PG 0953]414.èLow surface brightness fuzz was detected in the early HST images (Bahcall et al.1994,and conDrmed to be real by longer (Cycle 5)expo-1995a)sures.We are unable to establish the morphology of the fuzz,which is faint and extended.et al.Hutchings (1989)suggested,on the basis of ground-based images,that the host of the quasar has spiral structure and is possibly inter-acting.The HST images do not provide convincing evi-dence for or against this conjecture.Spectroscopy of the fuzz around the quasar obtained by et al.Boroson (1985)shows that the o?-nuclear spectrum is dominated by a red continuum with H a and possibly [S II ]emission;Mg I b absorption might also be present.The absolute V magni-tude derived from &Rieke H -band McLeod (1994b)observations is 0.5mag brighter than our two-dimensional model estimate.

PKS 1004]130.èThe host is a bright elliptical,about as bright as the brightest cluster galaxies.There seems to be some structure in the inner region of the host The (r \2A .5).absolute V magnitude derived from &Rieke McLeod H -band observations is 0.8mag fainter than our (1994b)two-dimensional model estimate.&MacKenty Stockton presented narrow-band [O III ]images of this quasar (1987)but did not Dnd any signiDcant extended luminosity in the region between D 7to 28kpc (for and q 0\0.5H 0

\100

km s ~1Mpc ~1).obtained spectroscopic Stockton (1978)observations of the galaxies around the quasar and found that two of them have redshifts similar to the quasar red-shift.One of the galaxies is separated by (79.8kpc,33A .4PA \233?;not shown in Figs.and from the quasar and 12)has mag;the other is not in our HST image

m 606\20.0Deld of view.

PG 1012]008.èThis quasar is ““caught in the act ??of merging.The host of this quasar is seen in Figures and 12to be merging with a bright galaxy.The distance between the two galactic nuclei is 6.7kpc There is another (3A .3).compact galaxy (12.4kpc)north of the quasar,probably 6A .8taking part in the interaction as well.Both interacting com-panions are also visible in our 200s exposure.

(Plate 31)shows an expanded view of the PG Figure 51012]008image.et al.obtained spectra Heckman (1984)for both galaxies and found the expected absorption lines (H b ,Mg I ,Fe II ,and Na I )at the same redshift as the quasar.The absolute V magnitude based on the H -band measure-ment by &Rieke is 0.9mag brighter than McLeod (1994b)our two-dimensional model estimated value;we believe that part of this discrepancy is caused by the light of the merging galaxy being included in their model Dt.

HE 1029[140.èThis radio-quiet quasar has a bright elliptical host galaxy.Some faint structures resembling shells are seen at D 11A and 19A from the quasar.There is a compact galaxy north from the quasar;spectroscopy is 4A .1required to determine if it is associated with the quasar.et al.obtained R -band images and,based Wisotzki (1991)on spheroidal model Dts,reported the host to be a giant elliptical with R \15.2mag and mag.

M R \[22.0Assuming (V [R )D 0.8for elliptical galaxies at z D 0.1

et al.their absolute V magnitude for the (Fukugita 1995),host is [21.2mag.We obtained by Dtting a

M V

\[20.8model to the azimuthally averaged proDle of the host.GdV measured redshifts of galaxies in the Deld Wisotzki (1994)of HE 1029[140and found that four galaxies have red-shifts similar to the quasar.Wisotzki did not detect the close compact object at 4A projected separation.

The closest galaxy with a redshift known to be similar to the quasar lies at 134kpc PA \26?and was (\109A .4)detected in WF2(not shown in Figs.and The HST 12).images show that this Wisotzki companion galaxy has and is highly disturbed,prob-M V D [19.1(m 606\17.7)ably

an advanced stage of merger between two disk gal-axies.Two possibly galactic nuclei,separated by are 1A .4,visible,as well as H II regions.

There is a mag galaxy projected at m 606

\17.922A .9,

PA \23?,of the quasar,which Wisotzki showed to be a background galaxy with z \0.162.Wisotzki classiDed this galaxy as an elliptical,but the HST images show that it is a spiral galaxy (type D Sab).

PG 1116]215.èThe host of this radio-quiet quasar is probably an elliptical galaxy.The bright central region is surrounded by a faint smooth fuzz.Some arclike structures are seen in the center but are almost certainly PSF artifacts.The one-dimensional proDle is reasonably described by a de Vaucouleurs model.The V magnitude estimated from &Rieke H -band images is in good agree-McLeod (1994b)ment with the magnitude determined from our two-dimensional model.

&Rieke applied the techniques they McLeod (1995)developed to study their H -band ground-based images to reanalyze the HST Archive images of PG 1116]215.They subtracted just enough of the PSF of the red standard star,F141(B [V \1.11),from the azimuthally averaged quasar one-dimensional proDle to make the residual proDle almost turn over in the center.Because the HST images were satu-rated in the center,McLeod &Rieke normalized the light proDle just outside the saturation region.We note,however,that the region inside r D 2A is heavily contaminated by PSF artifacts when the PSF of the red star F141is used for the subtraction.If F141is used for the PSF subtraction,there are artiDcial radial spikesèwhich are not visible in their published HST image of this quasar.McLeod &Rieke state that the host of PG 1116]215““looks nearly identical ??to a Deld galaxy detected in WF4.An HST image of this Deld galaxy was published in Bahcall et al.(1995a,Fig.5c ).The Deld galaxy is rich in morphological details:it is a barred spiral with internal and external rings (RSBb).If it is at the same distance as the quasar,its absolute V mag-nitude is [20.9.Although the host and the Deld galaxy have apparently similar luminosities,they are morphologically quite di?erent.

PG 1202]281.èThe host of this radio-quiet quasar,also known as GQ Com,is a small elliptical E1galaxy.Stockton &MacKenty showed that the compact galaxy D 5A (1987)from the quasar,PA \71?,is at the same redshift as the quasar.et al.reported that the o?-nuclear Boroson (1985)spectra are dominated by a red continuum,with [O III ]lines and possibly H a in emission,and a possible Mg I b absorption feature.The V magnitude estimated from the &Rieke H -band images is in good agree-McLeod (1994b)ment with the magnitude determined by our two-dimensional model.

3C 273(PG 1226]023).èThe host galaxy is an elliptical.The V magnitude estimated from the &Rieke

McLeod

No.2,1997HST IMAGES OF NEARBY LUMINOUS QUASARS

653

H -band images is in good agreement with the mag-(1994b)nitude determined by our two-dimensional https://www.wendangku.net/doc/179320936.html,ing deep ground-based CCD images,et al.Tyson (1982)obtained for the host,which is in good agree-M V D [22.5ment with our

best two-dimensional model magnitude of The host is somewhat brighter than the M V

\[22.1.brightest galaxy in a rich cluster.measured Stockton (1980)redshifts for galaxies in the 3C 273Deld and found that four of them have redshifts similar to the quasar,in agreement with the suggestion of &Bahcall One of Bahcall (1970).those galaxies was detected (a spiral galaxy)in WF4:it lies at 75A east of the quasar (D 133kpc),and its redshift is z \0.1577.et al.obtained R \16.3for the Wycko?(1981)host,which is equivalent to mag.The inner

M V D [21.3part of the jet is barely visible in

the PSF-subtracted image in HST and Merlin observations of the 3C 273jet Figure 2.are reported in et al.Bahcall (1995d).

PKS 1302[102.èThe HST images show there are two small compact galaxies at 1A and 2A from the quasar,which are expected to spiral into the quasar in a time short com-pared to the Hubble time et al.The pres-(Bahcall 1995a).ence of these very close companions can be seen most clearly in the expanded image,Figure 8,of et al.Bahcall &Ne?performed optical imaging (1995a).Hutchings (1992)with resolution and reported structures at the positions 0A .5of those galaxies;they suggest the host is a mildly disturbed elliptical galaxy.The PSF-subtracted residual image (see appears to the eye to be similar to an elliptical Fig.2)galaxy,but an exponential disk Dts the data slightly better.The absolute V magnitude estimated for the host galaxy is 0.4mag fainter than the value determined from the McLeod &Rieke H -band observations and is 0.9mag fainter (1994b)than the value estimated from i -band images (Ve ron-Cetty &Woltjer et al.obtained R \19.01990).Wycko?(1981)for the host;using the et al.transform-Fukugita (1995)ations of galaxy colors,this corresponds to M V D [20.0.PG 1307]085.èThe host appears to be a small early-type galaxy.The absolute V magnitude estimated from our two-dimensional model of the HST image is 0.2mag fainter than the value derived from the McLeod &Rieke H -band images.

PG (Plate 32)shows an expanded 1309]355.èFigure 6view of the image for PG 1309]355with lower contrast than shown in Figures and The details near the center 1 2.of PG 1309]355are shown more clearly in after a Figure 6,best-Dt stellar PSF has been subtracted.This quasar has a bright early-type host galaxy,probably an Sab.Tightly wrapped spiral arms are clearly seen in the inner region surrounding the center of the quasar.Overall,the GdV model describes the radial proDle better than the exponen-tial disk model.The absolute V magnitude estimated from our two-dimensional model of the HST image is 0.1mag brighter than the value derived from the &Rieke McLeod H -band images.

(1994b)PG (Plate 33)shows an expanded 1402]261.èFigure 7view of the image of this quasar at two di?erent contrast levels.The HST images show that the host is a beautiful spiral.After the PSF subtraction,a bar and a possible inner ring are visible.The morphological type is approximately SBb(r?).H II regions are also visible along one of the spiral arms;they are less prominent than the H II regions seen in the spiral host of PG 0052]251.The relative positions and magnitudes of the brightest H II regions are marked for identiDcation in the upper panel in lists

Figure 7.Table 11TABLE 11

H II R EGIONS IN THE H OST G ALAXY OF PG 1402]261d *a *d Region m

F606W (arcsec)(arcsec)(arcsec)a ......23.7 2.8[0.3 2.8b ......24.3 2.9[1.5 2.5c.......25.3 2.9[2.1 2.0d ......25.6 3.5[3.3 1.3e.......25.5 4.6[4.5[0.9f .......26.2 4.8[4.5[1.8g ......26.2 5.0[4.2[2.8h ......25.9 5.3[3.8[3.7i .......25.6 4.1[1.1 4.0j .......

25.2

4.0

[2.7

3.0

for each H II region the aperture magnitude,the distance to the quasar nucleus,and the o?set in right ascension and declination between the H II region and the quasar nucleus.The magnitudes were measured using apertures of 0A .3.

PG 1402]261is a relatively isolated quasar.&Stockton MacKenty did not Dnd any signiDcant extended (1987)[O III ]emission around the quasar.&Rieke McLeod obtained H -band images;the absolute V magnitude (1994b)based on their measurement is 0.5mag brighter than the value estimated with our two-dimensional model of the HST images.

PG 1444]407.èThe host galaxy of this quasar is smooth and is elongated in the north-south direction.After the PSF subtraction,the nuclear region is seen as an extended structure running northeast-soutwest,as shown in A bar may be present.The exponential disk model Figure 2.describes the radial light distribution a little better than does the model.The overall appearance is most GdV similar to an E2galaxy.&Ne?originally Hutchings (1992)suggested the possibility of a bar in this host,which they proposed might be in an advanced stage of the merger of galaxies of very di?erent masses.The absolute V magnitude estimated from our two-dimensional model of the HST image is 0.5mag fainter than the value derived from the McLeod &Rieke H -band images.

3C 323.1(PG 1545]210).èA low surface brightness elliptical host galaxy appears in the HST images,as well a neighboring companion at a projected distance of D 7kpc,PA \292?)(see Figs.and The V magnitude of the (2A .7,12).host galaxy determined from the H -band images by &Rieke is 0.4mag brighter than the value McLeod (1994b)derived from our two-dimensional model of the HST images.More recently,Matthews,&Armus Neugebauer,obtained H -and K -band images of 3C 323.1;their (1995)estimated model Dt H -band magnitude for the host agrees with the results of &Rieke The measure-McLeod (1994b).ments of Neugebauer et al.suggest that if the host galaxy is a normal elliptical,its expected apparent V magnitude is D 17.5,and if it is a spiral galaxy,V D 16.9.These values are brighter than the V -band apparent magnitudes expected using a color transformation without reddening of our HST images (see but are consistent with the host galaxy Table 4)being a reddened elliptical,as pointed out by et Neugebauer al.The one-dimensional model Dts better the (1995).GdV surface brightness radial proDle of the quasar host in our HST image than does the exponential disk model.

took spectra of the companion galaxy at Stockton (1982)from the quasar and apparently detected [O III ]at the 2A .7same redshift as the https://www.wendangku.net/doc/179320936.html,plex,asymmetric extended

654BAHCALL ET AL.Vol.479

[O III ]emission is seen surrounding the quasar in [O III ]images obtained later by &MacKenty Stockton (1987).However,there is no excess of emission at the companion galaxy position in the [O III ]images.Stockton &Mac-Kenty conclude that the previously reported detection of [O III ]emission in the spectrum of the companion galaxy was fortuitous,since the emission is due to the general dis-tribution of ionized gas surrounding the quasar.Neuge-bauer et al.found that the H and K model Dt magnitudes obtained for the companion galaxy,when combined with the HST measurements by et al.give a Bahcall (1995a),color V [H consistent with the companion galaxy being a faint elliptical at the redshift of the quasar.

PKS 2135[147.èThe quasar host is an elliptical galaxy;the envelope is not featureless like PHL 909but rather contains some faint clumps.The image suggests the pres-ence of a jet at PA D 26?,with visual extension of and D 2A .4width The surface brightness of the jetlike feature is D 0A .5.23.4mag arcsec ~2(F606W),at from the quasar center 1A .7of light.Many galaxies are seen in the Deld;the closest companions to the quasar are at PA \128?,and 1A .9,5A .5,PA \119?,seen in Figures and Stockton 1 2.(1978,1982)obtained spectra of the Deld galaxies and found that four are at the same distance as the quasar,including the closest companions at projected separations of and Some-1A .95A .5.what later,&MacKenty obtained [O III ]Stockton (1987)images.They noted that the companion 2A southeast did not appear enhanced in the [O III ]images,indicating that the emission lines seen in the combined spectrum are due to extended emission around the quasar that is not conDned to the companion.&Hutchings reported Mg b Hickson (1987)in the spectrum of the secondary nucleus (the galaxy at 2A southeast)corresponding to a galaxy at the redshift of the quasar.

PKS 2135[147has been included in many imaging programs.For example,et al.measured Dunlop (1993)which gives Our two-M K (host)\[24.2,M V D [21.0.dimensional model analysis of HST

images gives M V D [21.1.&Woltjer obtained i -band

Ve ron-Cetty (1990)images and measured aperture photometry in an annulus with radii 12.5and 25kpc.They estimated M V

\[19.9.

We measured the absolute magnitude of the host in our HST images within the same annulus and obtained M V D

[19.4.et al.measured the absolute blue mag-Smith (1986)nitude to be which converts to M B D [21.5,M V D [19.9[if (B [V )D 1.6for an elliptical galaxy at z \0.2].

Wycko?

et al.obtained R \17.8,which corresponds to (1981)M V

D [19.3.PKS 2349[014.èThe quasar host galaxy is undergoing gravitational interaction,which is evidenced by apparently tidal arms and possibly also by a huge (D 50kpc)di?use o?-center nebulosity.A compact companion galaxy at 2A east is detected in the HST images.Bahcall et al.(1995b,provide an extensive discussion of this object and 1995c)include a number of di?erent images (the tidal wisps and extended nebulosity are seen most clearly in their Figs.1and 2;the close companion galaxy is featured in their Fig.3).et al.suggest that the quasar is interacting Dunlop (1993)with the three closest galaxies southeast of the quasar.The HST images do not show evidence for this interaction;the three galaxies do not seem to be morphologically disturbed,and no obvious link between them and the quasar is seen.Dunlop et al.measured which gives

M K

(host)\[24.7,Our two-dimensional model Dts to the HST M V

D [21.5.image of the host give similar to the light

M V

D [22.0,from a brightest cluster galaxy.

The radial proDle of the interacting system PKS 2349[014is well described by a de Vaucouleurs model.As pointed out by and et al.Toomre (1995)Bahcall (1995b),there are some morphological resemblances between PKS 2349[014and NGC 3921.has carefully Schweizer (1996)and extensively studied NGC 3921,suggesting that it is the result of a merger between two disk galaxies and is now a protoelliptical.In this case also,the mean light distribution of the system is well described by a r 1@4law.

10.

SUMMARY AND DISCUSSION

The images shown in Figures and establish the two 12main conclusions of this paper:(1)The most luminous nearby quasars exist in a variety of environments;(2)HST observations provide unique information about the circum-stances of the quasar phenomenon.Many of the most important results obtained in this paper are visible on the unprocessed images shown in which can be com-Figure 1,pared with the images with a stellar PSF subtracted shown in The subtraction of a stellar PSF is important in Figure 2.about half of the cases.

Our results are based upon a representative sample of 20of the most luminous known and nearby

(M V

\[22.9)(z \0.30)quasars.The characteristics of the sample are summarized in and Table 1°2.1.

In separate subsections,we summarize and discuss below our results on host morphologies,host luminosities,com-parisons with our earliest analyses,close companions,ground-based studies,and future work.

10.1.Host Morphologies

Figures and show three hosts that apparently are 12normal spirals with H II regions (PG 0052]251,PG 1309]355,and PG 1402]261),seven ellipticals (PHL 909,PG 0923]201,PKS 1004]130,HE 1029[140,PG 1116]215,3C 273,and PKS 2135[147),as well as three obvious cases of current gravitational interaction (0316[346,PG 1012]008,and PKS 2349[014).There are also Dve other hosts that appear to be elliptical galaxies and are listed as En(?)in The hosts for two of the Table 2.quasars (NAB 0205]02and PG 0953]414)are faint and difficult to classify.

The host galaxies are centered on the quasars to the accu-racy of our measurements,^0.4kpc (see and °6eq.[6]).Seven of the 14radio-quiet quasars in our sample occur in hosts that are classiDed as elliptical galaxies in Table 2.Two particularly beautiful examples of elliptical hosts for radio-quiet quasars are shown in Figures and for PHL 12909and HE 1029[140.We have presented a more exten-sive discussion of the host of PHL 909in et al.Bahcall Five of the six radio-loud quasars in our sample (1996).appear to lie in elliptical galaxies.The sixth radio-loud quasar,PKS 2349[014,is in a complex interacting system containing a close companion,apparent tidal tails,and a large o?-center nebulosity.

The fact that about half of the radio-quiet quasars in our sample have elliptical hosts contradicts the conventional wisdom that radio-quiet quasars occur in spiral galaxies.However,we conDrm the expectation that most radio-loud quasars are in elliptical galaxies.

Three of the quasars in our sample,0316[346,PG 1012]008,and PKS 2349[014,have been ““caught in the

No.2,1997HST IMAGES OF NEARBY LUMINOUS QUASARS 655

act,??i.e.,the HST images of these quasars show dramatic evidence of currently intense gravitational interactions.Two of the three quasars caught in the act are radio quiet.In all three cases,the unprocessed images (see are Fig.1)sufficient to reveal extended curved features that look like the tidal arms generated in numerical simulations of inter-acting galaxies.For 0316[346and PKS 2349[014,there is no clear evidence for a normal host galaxy centered on the quasar.PG 1012]008appears to be an example of a merger currently going on between two comparable gal-axies.For a more extensive analysis of PKS 2349[014,the reader is referred to Bahcall et al.in which (1995b,1995c),the close companion,the tidal arms,the very extended o?-center nebulosity,and the possible host galaxy are all dis-cussed in some detail.

The HST images provide the best database to search for optical jets in nearby,luminous https://www.wendangku.net/doc/179320936.html,rmation on the existence or nonexistence of small-scale optical jets can constrain theories of the origin of radio and optical jets.We examined the images of all 20of the quasars for the existence of optical jets.With the exception of the well-known jet in 3C 273,the only other quasar for which we have found evidence for linear features is PKS 2135[147.Sensitive radio searches should be undertaken to test whether PKS 2135[147has a radio jet.For the other quasars,we can rule out the existence of a narrow optical feature with a surface brightness in excess of 24.5mag s ~2extending more than 3kpc beyond an inner region begin-ning at about 6kpc.

10.2.Host L uminosities

We list in our best estimates for the magnitudes Table 12of the host galaxies in our sample;these magnitudes were obtained (see by Dtting a two-dimensional analytic °5.3)galaxy model to the data.We also list the e?ective radius or exponential scale length and give the morphology of the host based on visual inspection of the images (see Table 2and The di?erent measurements of the brightnesses of

°3).the host environments are summarized and compared in Tables and and in The average best-Dt two-34° 6.dimensional model magnitudes for the hosts of the 14radio-quiet quasars is

S M V T model,radio v quiet

\[20.6^0.6mag .(10)

The hosts of the six radio-loud quasars are slightly brighter,S M V T model,radio v loud

\[21.6^0.6mag .(11)

The fact that in our sample the radio-loud quasars are,on the average,about a magnitude brighter than the radio-quiet quasars cannot be explained by a selection e?ect resulting from the fact that the radio-loud quasars have a slightly larger average redshift.In fact,the three radio-loud quasars with z 10.20have mag,and the

S M V T \[21.8three radio-loud quasars with 0.20\z \0.30have

mag.

S M V T \[21.4shows the two-dimensional model absolute Figure 8visual magnitudes (from of the host galaxies (and Table 12)other nebular material)versus the absolute visual magni-tudes of the quasars.In order to be detectable,the host must have a luminosity that is not too small when com-pared with the luminosity of the quasar.The minimum detectable host brightness depends strongly upon the assumed morphology of the host galaxy.We have shown by a series of numerical experiments,described in Table 3of that host galaxies are,on the average,visible on Paper II,our images down to about 4.2mag fainter than the quasar luminosity.

Galaxies that are smooth ellipticals are the most difficult to detect (see rows 5d and 5e of Table 3of For the Paper II).eight quasars discussed in smooth elliptical hosts Paper II,are,on average,visible on our images down to 3.5^0.5mag fainter than the quasar.The limiting brightnesses were determined by visually inspecting simulated galaxies placed in the actual HST quasar observations and are therefore somewhat subjective.

The diagonal line in represents the detection Figure 8limit for smooth ellipticals in an idealized sample in which

TABLE 12

S UMMARY OF M AGNITUDES AND M ORPHOLOGY FOR Q UASAR H OST G ALAXIES

T WO -DIMENSIONAL

r O BJECT z m 606(2-D)M V (2-D)(arcsec)a M ORPHOLOGY

PG 0052]251.......0.15517.2[20.9 1.3Sb PHL 909.............0.17117.2[21.0 2.3E4NAB 0205]02......0.15519.0[19.10.7S0?0316[346............0.26518.3[20.8 1.2Inter.PG 0923]201.......0.19017.5[21.0 2.9E1PG 0953]414.......0.23918.8[20.2 1.1?PKS 1004]130......0.24016.9[22.0 1.2E2PG 1012]008.......0.18517.7[20.7 1.6Inter.HE 1029[140.......0.08616.2[20.5 3.2E1PG 1116]215.......0.17716.9[21.4 1.4E2PG 1202]281.......0.16517.7[20.5 1.4E13C 273................0.15816.0[22.1 3.7E4PKS 1302[102......0.28618.2[21.1 1.1E4?PG 1307]085.......0.15517.8[20.2 1.3E1?PG 1309]355.......0.18417.3[21.1 1.2Sab PG 1402]261.......0.16418.3[19.9 1.6SBb PG 1444]407.......0.26718.4[20.5 1.0E1?3C 323.1..............0.26618.1[21.0 1.6E3?PKS 2135[147......0.20017.4[21.1 2.6E1PKS 2349[014......

0.173

16.2

[22.1

4.8

Inter.

a E?ective radius or exponential scale length.

656BAHCALL ET AL.Vol.479

F IG.8.èAbsolute visual magnitude of the host galaxies vs.the absolute

visual magnitude of the quasars.The magnitudes and morphologies of the

host galaxies are determined using two-dimensionalDts(see the summary

in the absolute magnitudes of the quasars are taken from

Table12);Table

The diagonal line represents the average detection limit of smooth ellip-

1.

ticals in an idealized sample;see the discussion in°10.2.

the limiting host magnitude is determined entirely by the

quasar luminosity.In calculating the limiting absolute

visual magnitudes for the hosts,we have included an

average k-correction(see et al.for ellipticals

Fukugita1995)

at z\0.2,as well as the average magnitude di?erence,3.1

mag,between the quasar and the faintest detectable host.

Thus

M limiting host \M

QSO

]*.(12)

The form of re?ects the fact that the limiting equation(12)

host luminosity must increase linearly with the luminosity of the quasar,since by assumption the noise introduced by the quasar signal determines how faint a host can be detected.Smooth ellipticals fainter than^0.5mag of the diagonal line in would not have been expected to

Figure8

be detected if this idealization of the problem is correct.For the three intrinsically faintest quasars in our sample,the noise introduced by the quasar,the host galaxy,and the background light are all similar.In practice,for our sample one might expect some?attening of the detection limit at the lowest quasar luminosities if photon noise is more important than systematic uncertainties in the subtraction of the quasar light.

&Rieke have suggested that there is a McLeod(1995)

linear relation between the quasar absolute magnitude and the minimum host galaxy absolute magnitude.They inter-pret this linear relation,shown in their Figure2,as indicat-ing that a more luminous host galaxy is required to fuel a more luminous quasar.The linear relation that theyDnd between M(host)and M(QSO)is essentially identical to our minimum detection limit for smooth ellipticals that is shown in(for V[H\3.0).As pointed out by Figure8

the relation described by McLeod&Rieke McLeod(1996),

cannot be an artifact produced by detection limits if all of their detections are real detections;an artiDcial correlation would be introduced only if true nondetections were inter-preted as marginal detections.

There is not convincing evidence in for a signiD-

Figure8

cant dependence of host luminosity upon the luminosity of the quasar.The apparent correlation that is suggested to the eye is due in large part to the fact that the single most luminous quasar in our sample,3C273,has the most lumi-nous host.

There is a hint in that the average luminosity of

Figure8

elliptical hosts is somewhat higher than for spiral hosts. Most of this di?erence,however,is due to the fact that,even for the same objects(see the de VaucouleursDtting

Table4),

formula yields estimated luminosities that are0.6mag brighter than the diskDtting function.The de Vaucouleurs formula introduces a luminosity peak in the unmeasured region that is not present in the disk formula.

Our results are inconsistent with the hosts having a Schechter luminosity function.The average absolute magni-tude for aDeld galaxy is about 1.8mag fainter than

[for an assumed minimum luminosity of M

V

(L*)\[20.5

see,e.g.,Ellis,&Peterson

M

V

(L*)\[17;Efstathiou,1988 for a discussion of theDeld galaxy luminosity function].In our sample(see and the average host is

Table12Fig.8),

Moreover,about half by number of the M

V

(L*)\[20.9.

Deld galaxies would be expected,in a volume-limited sample,to lie within a magnitude of the lower limit cuto?of the Schechter luminosity function[which may be fainter than Thus,if the host galaxies were dis-M

V

(L*)\[17].

tributed with a Schechter luminosity function,we would have expected that about half of the hosts in our sample would be fainter than and therefore unde-

M

V

(L*)\[18

tectable on the HST images.This is clearly not the case.

By comparing the two-dimensional model magnitudes of and with the results expected from a Table12Figure8

Schechter luminosity function,we conclude that,on average,the host galaxies of the luminous quasars in our sample are about2.2mag more luminous than typicalDeld galaxies.

10.3.Previous Analyses

The conclusions presented in this summary paper are di?erent in emphasis from the conclusions in ourDrst two studies(see Papers I and II).In our earlier work,we dis-cussed images of eight quasars(all are included in the sample in the current work)and reported the deDnitive detection of three host galaxies.We also presented limits on the brightnesses of the hosts for the otherDve quasars.The images presented in this paper show that more than half of the entire sample of20quasars has obvious hosts and that there is solid evidence that most,if not all,of the remaining quasars also have host galaxies.

The initial caution that we expressed regarding the detec-tion of host galaxies was due to a combination of the unlucky observing sequence and our conservatism about interpreting the complex HST images.The unprocessed HST data(see are sufficient to show,even to the

Fig.1)

untrained eye,that at least nine of the20quasars in our sample have obvious hosts or di?use environments.These obvious examples include the three spiral hosts(PG 0052]251,1309]355,and PG1402]261),the three quasars““caught in the act??(0316[346,PG1012]008, and PKS2349[014),and three prominent ellipticals(PHL 909,HE1029[140,and3C273).None of these quasars were among theDrst four objects(PG0953]414,PG 1116]215,PG1202]281,and PG1307]085)observed and only one(3C273,whose host we described in (Paper I),

No.2,1997HST IMAGES OF NEARBY LUMINOUS QUASARS657

together with the original observations)belonged Paper II

to the sample of eight quasars With a probability

(Paper II).

of9/20per observation of observing an obvious host,it was simply bad luck(about a5%chance)that only one of the initial eight quasars studied in and had an

Paper I Paper II obvious host.

Given the repaired,but still complex and temporally vari-able,PSF of the HST,we presented our results(see Table3 of for the nondetections as a morphology-Paper II)

dependent limit on the brightness of the host galaxy.Spiral galaxies,with their azimuthal variation in brightness and regions of high surface brightness,could be seen to con-siderably fainter total brightnesses(more than a magnitude) than large,extended ellipticals with their smooth,regular proDles.As we have gained experience with the data,we have become more conDdent of our ability to judge the reality of low surface brightness features.Most importantly, during HST Observation Cycle5,we obtained additional images of PG0953]414,a quasar analyzed in that

Paper I showed very faint,extended nebulosity that was not cen-tered on the quasar.The Cycle5observations were obtained at a di?erent roll angle than those described in the new observations conDrmed the reality of the Paper I;

di?use features(the nebulosity remainedDxed in the sky when the telescope was rotated).The observations of PG 0953]414suggested that some of the faint features that we had initially worried could be PSF features were real.

In retrospect,it appears that the vast majority of our initial observations consisted of quasars whose hosts had smooth,regular https://www.wendangku.net/doc/179320936.html,paring our adopted bright-nesses of the hosts with the brightness limits set

(Table12)

in our earlier work by simulations(Table3in we

Paper II),

Dnd that the appropriate brightnesses limits(those for smooth ellipticals like5d and5e of Fig.5of were

Paper II) reasonably accurate.The detected brightnesses reported in of this paper range from considerably fainter than Table12

the limit(e.g.,PG0953]414)to slightly brighter Paper II

than the limit(e.g.,3C323.1).Since the morphology of the hosts of the initial quasars was biased toward one type of galaxy(the least favorable type as far as detectability),it was not accurate,as we did,to quote a detection limit that was the average of all the galaxy types.

10.4.Close Companions

The HST images frequently reveal companion galaxies that are projected very close to the quasar,in some cases as close as1A or2A.shows20galaxy companions that

Table6

are projected closer than25kpc to the center of light of a quasar and brighter than M(F606W)\[16.4.Altogether, 13of the20quasars in our sample have close companions that satisfy the requirements for inclusion in The

Table6. amplitude for the quasar-galaxy correlation function deter-mined from our data is3.8^0.8times larger than the galaxy-galaxy correlation function et al.

(Fisher1996).

10.5.Ground-based Studies

Our results for individual objects are compared in°8 with the results from previous ground-based observations. In general,the agreement with ground-based observations is satisfactory but not as precise as we would have hoped. The most straightforward comparison is with the results of &Woltjer in annular regions well Ve ron-Cetty(1990)

separated from the quasar.Even in this case,our HST mag-nitudes are,on average,0.4mag fainter than the Ve ron-Cetty&Woltjer values.Our two-dimensional model estimates for the total luminosities are,on average,0.8mag fainter than their one-dimensional modelDts.The average discrepancy between our results and those of et al.

Dunlop is1.0^0.6mag(our results are generally brighter (1993)

than those of Dunlop et al.),and the average discrepancy between our results and those of McLeod&Rieke is 0.4^0.2mag.

10.6.Future W ork

Some pre-HST theoretical analyses(e.g.,by Perry,

Falle,

&Dyson et al.and 1981,Weymann1982,Begelman1985,

Schiano,&Wolfe have suggested that lumi-Chang,1987)

nous quasars may have dramatic e?ects on their environ-ments via the radiation or hot winds that the quasar emits. The continuum images shown in this paper do not provide obvious evidence for the e?ects of the quasar on the host environment.In fact,the three spiral host galaxies and several of the host ellipticals appear remarkably normal. Broadband colors and spectroscopic observations are required in order to determine more sensitively whether the host galaxy is really oblivious to the presence of the lumi-nous quasar in its center.The theoretical modeling can now be made more speciDc and compared with the results of the HST observations for individual host galaxies.These studies will be important in constraining the timescale of the quasar phenomenon and the isotropy of the quasar emissions.If a quasar shines brightly for only a short period of time or if the emission is highly anisotropic,then the lack of a dramatic e?ect of the bright AGN on the surrounding medium may be more easily understood.

One of the key results that is apparent in Figures and

12 is the detailed evidence for gravitational interactions among the systems““caught in the act??(0316[346,PG1012]008, and PKS2349[014).Dynamical modeling of these systems could provide insights into the processes involved in the formation and fueling of quasars.

HST images provide detailed quantitative information about the environments in which the quasar phenomenon occurs.We hope to increase our sample in the future and to obtain color information about the objects discussed here. It should be feasible to obtain spectra of the brightest H II regions in the spiral hosts of PG0052]251,PG1309]355, and PG1402]261.Detailed comparisons between the HST and ground-based images will be very informative. We are grateful to P.Crane,M.Fall,O.Gnedin,K. Kellermann,K.McLeod,https://www.wendangku.net/doc/179320936.html,ler,G.Neugebauer,M. Rees,G.Rieke,and M.Strauss for valuable discussions, comments,and suggestions.J.Krist and C.Burrows con-structed the four stellar PSFs used in this work;we are grateful to them for their skill and generosity in providing these data.We would like to thank Digital Equipment Cor-poration for providing the DEC4000AXP Model610 system used for the computationally intensive parts of this project.This work was supported in part by NASA contract NAG5-1618,NAG5-3259,NASA grant NAGW-4452and grant GO-5343from the Space Telescope Science Institute, which is operated by the Association of Universities for Research in Astronomy,Incorporated,under NASA con-tract NAS5-26555.We have used the NASA/IPAC Extra-galactic Database(NED),operated by the Jet Propulsion Laboratory,Caltech,under contract with NASA,and NASA?s Astrophysics Data System Abstract Service(ADS).

658BAHCALL ET AL.

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汇编语言实现十进制加减计算器

课程设计 题目十进制数加减计算器学院计算机科学与技术 专业计算机科学与技术 班级计算机0808班 姓名何爽 指导教师袁小玲 2010 年12 月31 日

课程设计任务书 学生姓名：何爽专业班级：计算机0808班 指导教师：袁小玲工作单位：计算机科学与技术学院 题目: 十进制数加减计算器的设计 初始条件： 理论：学完“汇编语言程序设计”、“课程计算机概论”、“高级语言程序设计”和“数字逻辑”。 实践：计算机学院科学系实验中心提供计算机和软件平台。如果自己有计算机可以在其上进行设计。 要求完成的主要任务:（包括课程设计工作量及其技术要求，以及说明书撰写等具体要求） （1）十进制数加减计算器的设计。 （2）程序应有操作提示、输入和输出，界面追求友好，最好是菜单式的界面。 （3）设计若干用例（测试数据），上机测试程序并分析（评价）所设计的程序。 （4）设计报告格式按附件要求书写。课程设计报告书正文的内容应包括： 在正文第一行写课程设计题目； 1.需求说明（要求、功能简述）或问题描述； 2.设计说明（简要的分析与概要设计）； 3.详细的算法描述； 4.源程序与执行结果（含测试方法和测试结果）； 5.使用说明； 6.总结，包括设计心得（设计的特点、不足、收获与体会）和展望（该 程序进一步改进扩展的设想）。 时间安排： 设计时间一周：周1：查阅相关资料。 周2：系统分析,设计。 周3~4：编程并上机调试。 周5：撰写课程设计报告。 设计验收安排：20周星期五8:00起到计算机学院科学系实验中心进行上机验收。 设计报告书收取时间：20周的星期五下午5:00之前。 指导教师签名： 2010年12月31日 系主任（或责任教师）签名： 2010年12月31日

and_的用法【超全】

一、并列连词and所连接的分句在语义上的含义 1.表示在动作或事物的前后，一般译为“然后、随即”。 She came in and sat down. 她走了进来，随后就坐了下来。 I pulled the trigger and the gun went off. 我扣动扳机，枪随即响了。 2.表示递进关系，一般可译为“甚至、何况、还”等。 Friction is not always undesirable and can be very useful. 摩擦并不总是不好的，它甚至可能是有用的。 It was not easy to carry such a heavy load,and during the dog day. 提那样的重物已经是够困难的了，何况是在三伏天。 3.表示意义上的转折或让步，可译为“虽然、尽管、但、却”等。 He tried hard and (yet) he failed to get the job. 他努力尝试，却（仍然）没能得到那个工作。 You are not lazy,and still you are an idler. 你并不懒，但多少有点游手好闲。 4.表示对照、对比关系，可译为“而、却”。 She bought me cakes,and I helped her do her homework. 她买蛋糕给我吃，而我帮她做作业。 It can be difficult when you don’t think something is important and someone else does. 如果你并不认为某事重要而某人却认为重要，这时情况就可能不大好办。 5.表示对前面所述事项的结论或看法，and后可加分句或名词组，and一般不译出。 You gave him a piece of your mind,and a very good thing too. 你率直地批评他，这是件好事。 They disliked Joe——and that’s not surprising. 他们不喜欢乔，这并不让人惊讶。 6.表示因果关系，当前面的部分表示原因时，and=so that，译为“因此、从而、所以”；也有将表示原因的部分放在and后的，这时and=because，直接译为“因为”。 Sound is carried by air,and without air there can be no sound. 声音靠空气传播，因此没有空气也就没有声音。 Aluminum is used as the engineering material for planes and spaceships and it is both light and tough. 铝用作制造飞机和宇宙飞船的工程材料，因为铝质轻且韧性好。 7.引起一个插入句，用于中断语气，以便表示意见、看法。这时，and引起的句子中的主语多为第一人称，and引起的句子与句子其余部分用逗号隔开。

日本早期电影

xx电影之xx电影 一、xx电影的诞生 1.现存最早的xx电影： 歌舞伎片《赏红叶》 （1899） 2.新派剧： 起源于19世纪80年代的歌舞伎改革运动，最早与电影联手。 3.xx最早的故事片： 《闪电大盗》 （1899）用新派剧演员拍摄。 4.直到20年代中期，日本电影业中所有女性由男性扮演，称为“女形”。 5.1910年代日本电影生产基地开始建立： 1912年日本活动写真株式会社（日活）组建，在东京（现代题材的新派剧）和京都（历史题材的旧剧）—— 以两大城市为电影制作中心形成分庭抗礼的局面，为日本电影制造两副面孔。日本电影沿着对传统价值观的怀旧式肯定和对现代的西方价值观的追随这两条完全分离的线索发展而来。 二、xx电影中的“活弁” 1.活弁： 活动弁士（辨士），为电影做解说表演的。 2.电影和弁士的组合与日本口传文艺的渊源有关，如文乐中的净琉璃，歌舞伎中的义大夫等。

3.在真正意义上，日本从来不存在无声电影。 4.活弁的三种职能： ①作为叙述者与声优； ②作为评论阐释者； ③作为观众代表的表演。 5.弁士在30年代后期几乎销声匿迹，但影响有： ①电影的开头和结尾，通常会有不出场的旁白者冗长的画外音； ②惯用全景镜头和长镜头。 6.弁士的存在使日本电影独自探索出日本独有的电影叙事方式。 三、日本电影的黄金时代（19世纪20-30年代） 1.纯映画剧运动： ①1918年，由归山教正主持的电影艺术协会发起； ②电影不应是对下等戏剧的简单模仿，而必须以某种纯粹的状态呈现出电影独有的本质。 主张不要舞台剧本而要电影剧本，不要男旦而要女演员，不要弁士而要字幕。指出真正的电影离不开速度、写实和幻想。 ③试验性作品： xx的《生之xx》、《xx的少女》 （19）。2.两大创作群体： xx和日活 松竹：1920年在日本东京莆田创立制片厂，《路上的灵魂》

and的用法及含义

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and用法

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