A large sample of spectroscopic redshifts in the ACS-GOODS region of the HDF-N

A large sample of spectroscopic redshifts in the ACS-GOODS region of the HDF-N
A large sample of spectroscopic redshifts in the ACS-GOODS region of the HDF-N

a r X i v :a s t r o -p h /0401354v 1 18 J a n 2004

Draft version February 2,2008

Preprint typeset using L A T E X style emulateapj v.04/03/99

A LARGE SAMPLE OF SPECTROSCOPIC REDSHIFTS IN THE ACS-GOODS REGION

OF THE HDF-N

L.L.Cowie,1,2A.J.Barger,1,3,4,2E.M.Hu,1,2P.Capak 1,2A.Songaila 1,2

Submitted to the Astronomical Journal

ABSTRACT

We report the results of an extensive spectroscopic survey of galaxies in the roughly 160arcmin 2ACS-GOODS region surrounding the HDF-N.We have identi?ed 787galaxies or stars with z ′<24,R <24.5,or B <25lying in the region.The spectra were obtained with either the DEIMOS or LRIS spectrographs on the Keck 10m telescopes.The results are compared with photometric redshift estimates and with redshifts from the literature,as well as with the redshifts of a parallel e?ort led by a group at Keck.Our sample,when combined with the literature data,provides identi?cations for 1180sources.

We use our results to determine the redshift distributions with magnitude,to analyze the rest-frame color distributions with redshift and spectral type,and to investigate the dependence of the X-ray galaxy properties on the local galaxy density in the redshift interval z =0?1.5.We ?nd the rather surprising result that the galaxy X-ray properties are not strongly dependent on the local galaxy density for galaxies in the same luminosity range.

Subject headings:cosmology:observations —early universe —galaxies:distances and

redshifts —galaxies:evolution —galaxies:formation

1.INTRODUCTION

The Hubble Deep Field-North (HDF-N;Williams et al.1996;Ferguson,Dickinson,&Williams 2000)remains the single most intensively studied region on the sky.In addition to the de?ning HST WFPC2ob-servations of the central 5.3arcmin 2area (the HDF-N proper),the ?eld was also the target of the deepest X-ray exposure to date,the 2Ms Chandra Deep Field-North (CDF-N)observation (Alexander et al.2003;Barger et al.2003),which covers about 460arcmin 2.Even wider areas have been covered with ultradeep ground-based optical and near-infrared imaging (Ca-pak et al.2003and references therein)and with very deep 20cm radio observations with the VLA (Richards 2000).

Most recently,a roughly 160arcmin 2region,cov-ering the HDF-N proper and lying mostly within the CDF-N,was observed with the ACS camera on HST in four passbands (F435W,F606W,F775W,F850LP)as part of the GOODS HST Treasury program (here-after,ACS-GOODS;Giavalisco et al.2003).This re-gion will also be the target of the deepest SIRTF observations,as part of the GOODS SIRTF Legacy

program (M.Dickinson,PI).While not quite as deep as the HDF-N proper,the ACS-GOODS survey pro-vides a very deep,high spatial resolution image of a moderately large area of sky.

While photometric redshift surveys can cover large areas—avoiding the problems of cosmic variance,which can be signi?cant in areas the size of the ACS-GOODS region—and are useful for determin-ing the evolution of the luminosity function and the universal star formation history (see Capak et al.2004for a photometric redshift analysis of the 600arcmin 2Suprime-Cam ?eld around the HDF-N),spectroscopic redshift surveys are needed to deter-mine the evolution of clustering and the environmen-tal dependences of galaxy properties,such as their X-ray,submillimeter,and radio emission.Spectroscopic redshifts are also required for determining the distri-bution of spectral types,which may be combined with galaxy morphologies from the ACS-GOODS observa-tions,and for determining line luminosities,which provide an alternative way of approaching the star formation history.Finally,spectroscopic redshifts may be used to re?ne photometric redshift estimates and to test what fraction of photometric redshifts are

1

Visiting Astronomer,W.M.Keck Observatory,which is jointly operated by the California Institute of Technology,the University of California,and the National Aeronautics and Space Administration.2

Institute for Astronomy,University of Hawaii,2680Woodlawn Drive,Honolulu,HI 96822;cowie@https://www.360docs.net/doc/8e12494035.html,;barger@https://www.360docs.net/doc/8e12494035.html,;hu@https://www.360docs.net/doc/8e12494035.html,;capak@https://www.360docs.net/doc/8e12494035.html, 3

Department of Astronomy,University of Wisconsin-Madison,475North Charter Street,Madison,WI 53706.4

Department of Physics and Astronomy,University of Hawaii,2505Correa Road,Honolulu,HI 96822.

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in error in a given?eld.Some classes of sources,such as broad-line AGNs or sources that have very strong emission lines,frequently have bad photometric red-shifts(e.g.,see Barger et al.2003),and spectroscopic measurements can be used to determine how common such sources are.The present paper,and a parallel paper by Wirth et al.(2004),describe two e?orts to spectroscopically identify large,well-de?ned samples in the ACS-GOODS region.

The region around the HDF-N was intensively ob-served spectroscopically by a number of groups us-ing the Low-Resolution Imaging Spectrograph(LRIS; Oke et al.1995)on the Keck10m telescopes.This was a labor-intensive e?ort,since typically only20?30sources could be observed in each mask,and~1hr observations were required.However,spectra were obtained for671sources(see the compilation of Co-hen et al.2000for full referencing).Analyses of vari-ous aspects of this sample are given in Cohen(2001) and Cohen(2002).

The recent implementation of the Deep Extragalac-tic Imaging Multi-Object Spectrograph(DEIMOS; Faber et al.2003)on the Keck II10m telescope has greatly increased the speed with which such obser-vations may be carried out.DEIMOS can observe around100or more sources per mask,and its higher resolution and quantum e?ciency make identi?ca-tions more straightforward.The long axis of the?eld-of-view of the instrument is well matched to the18 arcminute long axis of the ACS-GOODS?eld,and most of the ACS-GOODS?eld can be covered in two DEIMOS pointings.With DEIMOS it should be pos-sible to identify nearly all of the sources with optical AB magnitudes brighter than24in the red through the entire ACS-GOODS area.

Recognizing this,two parallel e?orts were begun in Spring2003to map spectroscopically the galaxies in the ACS-GOODS area with DEIMOS.A team led by Keck astronomers(hereafter,the Keck Team Redshift Survey or KTRS)focused purely on an R magnitude selected sample in the ACS-GOODS region,using ob-serving and reduction techniques developed for the DEEP-2project(Davis et al.2003).This sample is described in the paper by Wirth et al.(2004).Our own sample was embedded within observations tar-geted at high-redshift galaxies and X-ray and radio selected galaxies in the wider regions,as described in Hu et al.(2004),Barger et al.(2003),and Cowie et al.(2004).Free regions of the masks that lay within the ACS-GOODS area were?lled with magnitude se-lected samples chosen to have z′<23.5,R<24,or B<24.5.Some fainter sources were also included where no suitable brighter targets could be obtained. Combining our DEIMOS data with our LRIS data from earlier runs,we now have spectroscopic iden-ti?cations for787sources in the?eld with z′<24, R<24.5,or B

In the present paper we describe our spectroscopic sample and compare it with other spectroscopic and photometric redshift samples,focusing on our sam-ple’s completeness.We then analyze our z′<23.5 selected sample in detail to look at how the colors and the star formation and AGN signatures of the galaxies depend on their density environment over the z=0?1.5redshift range.We take H0= 65h65km s?1Mpc?1and use an?M=1

3 cosmology.

2.OBSERVATIONS

Since the ACS-GOODS observations were in progress at the time of our mask designs,the astro-metric and photometric properties of the sample were taken from the ground-based catalog of Capak et al. (2003).In the present paper we use the astrometric positions from the ACS-GOODS catalog,which were kindly provided by Mauro Giavalisco,but we con-tinue to use the photometric magnitudes from Capak et al.We chose the DEIMOS sample from galaxies in the area with z′<23.5,supplemented by galaxies with R<24or with B<24.5.Where no primary target could be?tted into a slit mask,we included sources up to half a magnitude fainter.As noted above,many of the sources already had redshifts in the literature or from our own previous LRIS spec-troscopy.In planning our DEIMOS observations,we prioritized unobserved sources over those with exist-ing redshifts.However,where no unobserved target was available,we included sources with known red-shifts,since one of our primary goals was to obtain as uniform a set of spectra for the sources as possible. The new spectroscopic observations were obtained with DEIMOS on Keck II the nights of UT2003Jan-uary29–30,March27,April25–27,and May27. The observations were made with the600lines per mm grating,giving a resolution of3.5?A and a wave-length coverage of5300?A.The spectra were centered at an average wavelength of7200?A,though the exact wavelength range for each spectrum depends on the slit position.Each~1hr exposure was broken into three subsets,with the sources stepped along the slit by1.5′′in each direction.The spectra were reduced in the same way as previous LRIS spectra(see Cowie et al.1996)by forming a primary sky subtraction from the median of the dithered images,registering and combining the images with a cosmic ray rejec-tion?lter,removing geometric distortion,and then

Cowie et al.3

applying a pro?le weighted extraction to obtain the spectrum.The wavelength calibration was made us-ing a polynomial?t to the night sky spectrum. Each spectrum was individually inspected,and a redshift was measured only where a robust identi-?cation was possible.The high resolution of the DEIMOS observations greatly simpli?es the identi-?cation of sources dominated by single strong emis-sion lines since it resolves the doublet structure of the[OII]3727?A line.As discussed below,most of the magnitude-limited sample sources could be iden-ti?ed.The incompleteness is largest at the faint end, but in a small number of cases(about5?10%,de-pending on the mask)the spectra were problematic in some way(e.g.,the sources were at the edge of a CCD chip or in the heavily distorted and vignetted regions at the edge of the mask);these are present at all mag-nitudes.Sources that were observed but could not be identi?ed(independent of the cause)are retained in our main table(Table1).

In Table1we list the905sources that we observed with either DEIMOS or LRIS and have spectra for, from any part of the ACS-GOODS area,and satisfy-ing the magnitude constraints z′<24,R<24.5,or B<25.Table1is ordered by R magnitude and gives the right ascension and declination in decimal degrees (from the ACS-GOODS catalog),the z′,R,and B magnitudes(from the ground-based data of Capak et al.2003),and the measured redshift.The magni-tudes are3′′diameter aperture magnitudes corrected to total magnitudes.Where a source is saturated or otherwise problematic,the magnitudes are omitted. In the redshift column,sources which were observed but not identi?ed are shown as“obs”.Of the sources in the table,787are identi?ed,comprising704galax-ies and83stars.We refer to the sample in Table1 as the“Hawaii”sample.

In Table2we combined the identi?ed sources in the “Hawaii”sample with redshifts from the literature to form a more complete table.Including the data from C00,D01,and S03,we have redshifts or stellar iden-ti?cations for1180sources.Table2gives the right ascension and declination in decimal degrees from the ACS-GOODS catalog,the HK′,z′,I,R,V,B,and U magnitudes from Capak et al.(2003),the redshift and its source(H=Hawaii,C00,D01,or S03),the photometric redshift from Capak et al.(2004),and the odds assigned to it(see§3.2).Sources in the sam-ple that are compact in the ACS-GOODS images and are classi?ed as stars from the empirical star-galaxy separation criterion(V?I)?2.0(I?HK′)=?1.1 given in Barger et al.(1999)are assigned as stars in the photometric redshift list.We refer to the sample in Table2as the“total”sample.

There are a very small number of discrepant sources,where di?erent groups have assigned di?er-ent redshifts.In only one instance does a Hawaii DEIMOS redshift di?er from a Hawaii LRIS redshift. In this case,the DEIMOS redshift also turns out to be inconsistent with other groups’measurements (see Table3),so we adopt the LRIS redshift in our “Hawaii”sample.

3.TESTS

https://www.360docs.net/doc/8e12494035.html,parison with other catalogs

In order to compare the“Hawaii”sample with the KTRS sample of Wirth et al.(2003)and the litera-ture samples(C00,D01,and S03),we?rst combined the KTRS and literature samples to form the“other”sample.In the small number of cases where there were discrepancies,we somewhat arbitrarily resolved these in favor of KTRS,then C00,then D01,and then S03.There are552overlapping identi?cations be-tween the“Hawaii”sample and the“other”sample. Of these,512are galaxies and40are stars.All of the star identi?cations are consistent in the two samples. In Figure1we compare the“Hawaii”galaxy redshifts with the“other”galaxy redshifts and?nd that nearly all of these are also consistent.Considering a redshift to be discrepant if it deviates by more than0.01,we ?nd that only seven of the overlap galaxies are dis-crepant,in addition to the one internally inconsistent galaxy discussed in§2;the latter source is not shown in Fig.1because we adopted our LRIS redshift in-stead of our DEIMOS redshift.These eight galaxies give an upper bound of1.4%of sources where the identi?cations might be problematic in the“Hawaii”sample;they are summarized and brie?y described in Table3.

HAWAII REDSHIFT

O

T

H

E

R

R

E

D

S

H

I

F

T

Fig. 1.—“Hawaii”spectroscopic redshift versus“other”spectroscopic redshift(from the KTRS and literature sam-ples).There are512overlapping galaxy identi?cations be-tween the“Hawaii”sample and the“other”sample,only seven of which have discrepant redshifts.

3.2.Photometric redshift comparison

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We next compared the “total”sample of redshifts (from the Hawaii observations and the literature)with the photometric redshift catalog of Capak et al.(2004).The photometric redshift estimates are based on ultradeep imaging in seven colors from U to HK ′(Capak et al.2003)and were computed using the Bayesian code of Ben′?tez (2000).This code as-signs odds that the redshift lies close to the estimated value.We only use those cases where the odds lie above 90%.The imaging data also saturate at bright magnitudes,so we restrict the comparison to sources with R >20.This gives a sample of 1078sources with both spectroscopic and photometric redshifts,which we compare in Figure 2.Fourteen of the sources are broad-line AGNs,where the photometric estimates may be poorer since the templates do not properly model such sources.We have distinguished these sources in Figure 2with larger solid squares.97%of the photometric redshifts agree to within a multi-plicative factor of 1.3with the spectrosopic redshifts.This is consistent with the expectation from the odds assigned to the photometric redshifts.The agreement is independent of magnitude over the R =20?24range.

SPECTROSCOPIC REDSHIFT

P H O T O M E T R I C

Fig.2.—Photometric redshift versus spectroscopic redshift for the 1078sources from the “total”sample with 20

We may also use the photometric redshifts to test whether there are redshift intervals where the spec-troscopic identi?cations are substantially incomplete.In Figure 3we compare for three magnitude bins the histogram (dotted line )of the spectroscopic redshifts (from the “total”sample)with the histogram (dashed line )of the photometric redshifts.In the R =20?22and R =22?23bins,the shapes of the two his-tograms are similar,and an appropriate renormal-ization (solid line )produces close agreement between the two distributions.However,in the R =23?24

interval,a higher fraction of sources are expected to lie at z >1.5on the basis of the photometric redshifts than are spectroscopically observed at such redshifts.This is the well-known spectroscopic “desert”,where the [OII]3727?A line has moved out of the optical window,while the ultraviolet signatures have not yet entered.

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23

REDSHIFT

110

100

1000

N U M B E R

20-22

1

2

3

REDSHIFT

110

100

1000

N U M B E R

22-23

1

23

REDSHIFT

110

100

1000

N U M B E R

23-24

Fig. 3.—Observed spectroscopic (from the “total”sam-ple;dotted )and photometric (dashed )redshift distributions for three magnitude bins:(a)R =20?22,(b)R =22?23,and (c)R =23?24.Solid line shows the spectroscopic dis-tribution renormalized to match the total number of sources.Only region of signi?cant incompleteness is the spectroscopic desert at z =1.5?2in the faintest magnitude (R =23?24)interval.

Cowie et al.

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R MAGNITUDE

I D E N T I F I E D F R A C T I O

N

Z MAGNITUDE

I D E N T I F I E D F R A C T I O N

Fig. 4.—Fractional completeness in 0.5mag intervals of the “Hawaii”DEIMOS spectroscopic identi?cations using (a)the R selected sample and (b)the z ′selected sample.

https://www.360docs.net/doc/8e12494035.html,pleteness

We next tested the fractional completeness of the “Hawaii”DEIMOS spectroscopic identi?cations ver-sus magnitude.The results,which should be typical of what can be achieved with 1hour exposures on this instrument,are given in Figure 4.Below R =23,nearly all of the observed sources are identi?ed,ex-cept in a very small fraction of cases where there were problems with the spectra.The completeness

begins to drop o?beyond R =23,and by R =24,it has fallen to about 60%.Some part of this may be a consequence of there being a higher fraction of z >1.5sources at these fainter magnitudes,since such sources in the spectroscopic desert are hard to identify.The photometric redshift estimates shown in Figure 3predict that 13%of the sources in the R =23.75?24.25interval should lie between z =1.5and z =2,while only 5sources are spectroscopically identi?ed in this redshift interval.This suggests that about a third of the incompleteness is caused by red-shift evolution moving the sources into di?cult red-shift ranges and that the remaining incompleteness is primarily caused by the lower S/N in the spectra of

the fainter

sources.

Fig. 5.—Magnitude selected sources in the ACS-GOODS region.To simplify the complex geometry and eliminate sources that are poorly covered in the ACS tiling,we restrict to sources lying within the rectangular area shown.Rectangle is centered at 189.227018and 62.238091,with a long axis of 15.63arcmin and a short axis of 9.28arcmin.The long axis is oriented at 45degrees to the N-S direction and runs from NE to SW.

3.4.Fraction Observed

The ACS-GOODS region has a complex morphol-ogy due to the tiling process (see Fig.5).To eliminate the more poorly covered regions,from now on we re-strict our analysis to the rectangular 145arcmin 2area shown in Figure 5;hereafter we refer to this as the “restricted”?eld.The coordinates and size of this area are given in the Figure 5caption.The area con-tains 3460sources that satisfy the primary magnitude selection criteria (z ′<23.5,R <24,or B <24.5).Figure 6shows the fractional identi?cations versus R and z ′magnitude for the “total”sample in the restricted ?eld.Figure 7shows the same versus posi-tion along the long axis of the rectangle.More than a third of the sources have been identi?ed to R =24and z ′=23.5,with the fractions being higher at the brighter magnitudes.The “total”sample is rather strongly concentrated around the HDF-N proper (see Fig.7).

In order to show the current completeness of all spectrscopic data on the ?eld we have combined the present data with the KTRS sample of Wirth et al.(2003).In the restricted ?eld this raises the number of identi?ed sources to slightly more than 1800,or more than half the sources to R =24(see Fig.6).The inclusion of the KTRS data also substantially smooths the spatial distribution (see Fig.7).

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R MAGNITUDE

O B S E R V E D F R A C T I O N

Fig. 6.—Fractional completeness (open squares )of the R <24“total”sample in the restricted ?eld (as compared to all of the sources in the restricted ?eld,whether observed or not)vs.R magnitude.Total number of sources in each magnitude bin is shown along the top.Solid squares show the fractional completeness when combined with the KTRS sample in the restricted ?eld.

POSITION (ARCMINUTES)

O B S E R V E D F R A C T I O N

Fig.7.—Fractional completeness (open squares )of the R <24“total”sample in the restricted ?eld (as compared to all of the sources in the restricted ?eld,whether observed or not)vs.position along the long axis of the ACS-GOODS ?eld.Total number of sources at each position is shown along the top.Solid squares show the fractional completeness when combined with the KTRS sample in the restricted ?eld.

4.DISCUSSION

4.1.Redshift distribution

Figure 8shows the redshift-magnitude diagrams for the R <24and z ′<23.5selected sources in the “to-tal”sample in the restricted ?eld.At magnitudes R <23or z ′<22.5,nearly all of the sources at red-shifts higher than z =1.5are broad-line AGNs.At fainter magnitudes,the more normal galaxy popula-tion stretches beyond z =1.5into the redshift desert (see §3.3),and the truncation of the redshift distri-bution at z =1.5is clearly seen.A small number of galaxies have measured redshifts above z =2.A substantial fraction of the z >2sources have X-ray counterparts (large open squares )and may have sub-

stantial AGN contributions to their light,but many do not (see Barger et al.2003).

R MAGNITUDE

R E D S H I F T

Z MAGNITUDE

R E D S H I F T

Fig.8.—Spectroscopic redshift versus magnitude for the (a)R <24and (b)z ′<23.5selected sources in the “total”sam-ple in the restricted ?eld.Broad-line sources are denoted by large solid squares,and X-ray sources by large open squares.Stars are denoted by asterisks.

Cowie et al.

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REDSHIFT

D I S T A N C

E (M P c )

REDSHIFT

D I S T A N C

E (M P c )

Fig.9.—Pie diagrams for the spectroscopically identi?ed sources in the “total”sample in the restricted ?eld.(a)Slice parallel to the long axis of the ACS-GOODS region.(b)Slice parallel to the short axis.Angular distances are plotted versus redshift.Broad-line sources are denoted by large solid squares,and X-ray sources by large open squares.All of the broad-line AGNs are also X-ray sources.

The well-known “velocity sheets”(C00)that are a consequence of the large scale clustering can be seen in the redshift-magnitude diagrams.These are more clearly visible in the pie diagrams of Figure 9,which show the distributions (a)parallel and (b)perpendic-ular to the long axis of the ACS-GOODS rectangle.The most prominent of the sheets lie at z =0.85and z =1.01.The sheets extend most of the way along the long axis (the drop-o?at the ends is a consequence of the higher incompleteness of the ob-servations at these positions—see Figure 7),but the z =1.01sheet is primarily found on the eastern side of the rectangle.The X-ray source positions (large open squares )and broad-line AGN positions (large solid squares )are shown on the pie diagrams.As has been previously noted,these also show velocity sheet structures (Barger et al.2002,2003;Gilli et al.2003).We shall return to the question of whether they are more concentrated into velocity sheets than the nor-mal galaxies in §4.3.

4.2.Galaxy colors versus redshift

Figure 10shows R ?z ′color versus redshift for the z ′<23.5“total”sample in the restricted ?eld.The upper bound of the distribution matches extremely well to the expected color of an elliptical galaxy.Ap-parently,very few galaxies are su?ciently reddened to lie above this envelope.There are only six such sources,three of which are galaxy pairs and radio sources (

solid squares ),suggesting they may be dusty mergers.It is unclear why the other three sources lie at these colors.

REDSHIFT

R -z ’

Fig.10.—R ?z ′color versus redshift for the z ′=23.5“total”sample in the restricted ?eld.Only sources with spec-troscopic redshifts are shown.Upper curve shows the color of the Coleman,Wu,&Weedman (1980)elliptical galaxy versus redshift,which almost perfectly maps the upper envelope of the distribution over the z =0?1redshift range.Only 6sources lie above the envelope,three of which are galaxy pairs and radio sources (solid squares ).

Because of the extensive color information avail-able (Table 2),we may analyze the galaxy colors in a more model-independent fashion by interpolating to form the rest-frame colors at each redshift.In Fig-ure 11we show the rest-frame 2800?8000?A color versus redshift.The upper bound matches the color of an elliptical galaxy and is nearly invariant from z =0?1.Beyond this redshift,the z ′selection be-comes biased against elliptical galaxies as the 4000?A

break enters the z ′band.The bottom of the dis-tribution corresponds to irregulars,star formers,and

broad-line AGNs (the latter are denoted by large solid squares).

The type selection versus absolute magnitude is il-lustrated in Figure 12,where we show the rest-frame absolute (a)8000?A and (b)2800?A magnitudes ver-sus redshift.For Figure 12a we use z ′<23.5,but we implicitly have a second selection since we need to interpolate between the HK ′magnitudes and the z ′magnitudes to determine the 8000?A magnitudes at high redshifts.To formalize this,we also limit the sample to HK ′<22.5.This HK ′selection is illustrated with a dashed curve computed for a ?at-spectrum source.Above this curve,all sources should

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be included,if we assume that all sources are redder than ?at f ν.However,the z ′selection means that we will omit redder sources at the higher redshifts and fainter magnitudes.We illustrate this for the case of an elliptical galaxy (solid curve )and a spi-ral galaxy (dashed curve ).At z =1.2we will omit ellipticals fainter than about ?22in the rest-frame 8000?A band.For Figure 12b we use R <24.Since this is a red-selected sample,we again illustrate the selection threshold for a ?at f νspectrum.All sources above this line should be included.

REDSHIFT

R E S T 2800-8000

Fig.11.—Rest-frame 2800?8000?A

color versus redshift for the z ′

<23.5sample.Only sources with spectroscopic red-shifts are https://www.360docs.net/doc/8e12494035.html,rge solid squares denote broad-line AGNs,and large open squares denote Chandra sources.

In Figures 12a and 12b,we also show the po-sitions of the sources with broad emission lines in their spectra (large solid squares )and the positions of the sources with high X-ray luminosities (L X >1042ergs s ?1;large open squares ).Most of the high ultraviolet luminosity sources fall in these categories and may have substantial AGN contributions.Pre-vious analyses have not been able to distinguish be-tween these sources and galaxies where the ultravi-olet light is dominated by star formation.Further discussion of the evolution of the light density and luminosity functions with redshift may be found in Capak et al.(2004).

REDSHIFT

R E S T 8000A A B S M A G

REDSHIFT

R E S T 2800A A B S M A G

Fig.12.—Absolute rest-frame magnitude versus red-shift at (a)8000?A and (b)2800?A .In each case,sources with spectroscopic redshifts are denoted by small solid sym-bols,and sources with photometric redshifts are denoted by plus signs.Sources with broad emission lines are denoted by large solid squares,and sources with X-ray luminosities L X >1042ergs s ?1by large open squares.Dotted curve in (a)shows the HK ′<22.5selection for sources with a ?at f νspectrum,while solid and dashed curves show the z ′<23.5selection for an elliptical galaxy and a spiral galaxy,respec-tively.Solid curve in (b)shows the R <24selection for a ?at f νspectrum galaxy.The horizontal dashed lines show a reference absolute magnitude of -23for 8000?A and -21.5for

2800?A which roughly corresponds to the maximum observed values at high redshift for objects without AGN signatures.

4.3.X-ray properties versus environment

A large fraction of the most luminous galaxies har-bor AGNs.For all galaxies with M 8000?A

in the z =0?1range,based on either spectro-scopic or photometric redshifts,the fraction with L X >1042ergs s ?1is 6%,while for M 8000?A

1042ergs s ?1,82%lie in galaxies with M 8000?A

redshift range,where lower optical luminosity sources would still be seen.Neither result shows any strong redshift dependence.

Barger et al.(2002,2003)and Gilli et al.(2003)noted that the X-ray sources are concentrated into velocity sheets.This has been taken to imply that the X-ray activity is found preferentially in higher density regions.However,it is not clear that the X-ray sources are more concentrated into these regions than the luminous ?eld galaxies that contain them.

0.000

0.0050.0100.015

0.020

NUMBER MPC -3

0.00.20.40.60.8

1.0F R A C T I O N

Fig.13.—Density environment of X-ray sources with

M 8000?A

1042ergs s ?1

in the redshift interval z =0?1.2(dashed line )compared with that for ?eld sources with M 8000?A

There is no signi?cant di?erence at the 95%con?dence level.

In order to test this,we estimated a simple neigh-borhood density for each galaxy by measuring the number density of M 8000?A

to spectroscopic sources in the magnitude interval at that redshift.This density estimate is somewhwat crude since it assumes the sheets are uniform struc-tures over the rectangle at all redshifts and also uses a redshift dependent window to select the density,but it should be adequate for the present purposes.We then used a Kolmogorov-Smirnov test to com-pare the density environment of X-ray sources with

M 8000?A

1042ergs s ?1with ?eld sources with M 8000?A

are shown in Figure 13.The distribution of the X-ray sources is is not signi?cantly di?erent from that of the ?eld sources at the 95%con?dence level,and the two distributions could be consistent.It appears that there is no preference for the luminous X-ray sources to lie in higher density environments.Support was provided by NASA through grants HST-GO-09425.03-A (L.L. C.)and HST-GO-09425.30-A (A.J.B.)from the Space Telescope Sci-ence Institute,which is operated by the Associa-tion of Universities for Research in Astronomy,In-corporated,under NASA contract NAS5-26555.We also gratefully acknowledge support from NSF grants AST-0084816(L.L.C.),AST-0084847(A.J.B.),and AST-0071208(E.M.H.),NSF CAREER award AST-0239425(A.J.B.),NASA grants DF1-2001X (L.L.C.)and GO2-3187B (L.L.C.),the Univer-sity of Wisconsin Research Committee with funds granted by the Wisconsin Alumni Research Foun-dation (A.J.B.),the Alfred P.Sloan Foundation (A.J.B.),and the David and Lucile Packard Foun-dation (A.J.B.)

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Table1

Hawaii redshifts in the ACS-GOODS region R.A.(J2000.0)Decl.(J2000.0)z′R B z spec

R.A.(J2000.0)Decl.(J2000.0)z′R B z spec

R.A.(J2000.0)Decl.(J2000.0)z′R B z spec

R.A.(J2000.0)Decl.(J2000.0)z′R B z spec

R.A.(J2000.0)Decl.(J2000.0)z′R B z spec

R.A.(J2000.0)Decl.(J2000.0)z′R B z spec

R.A.(J2000.0)Decl.(J2000.0)z′R B z spec

R.A.(J2000.0)Decl.(J2000.0)z′R B z spec

R.A.(J2000.0)Decl.(J2000.0)z′R B z spec

R.A.(J2000.0)Decl.(J2000.0)z′R B z spec

R.A.(J2000.0)Decl.(J2000.0)z′R B z spec

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