The Stellar Mass - Halo Mass Relation for Low Mass X-ray Groups at 0.5

0.51 MB·English

by  Shannon G. Patel

Accepted to ApJL
PreprinttypesetusingLATEXstyleemulateapjv.5/2/11
THE STELLAR MASS – HALO MASS RELATION FOR LOW MASS X-RAY GROUPS AT 0.5<z <1 IN THE
CDFS WITH CSI*
Shannon G. Patel1, Daniel D. Kelson, Rik J. Williams, John S. Mulchaey, Alan Dressler, Patrick J.
McCarthy, Stephen A. Shectman
CarnegieObservatories,813SantaBarbaraStreet, Pasadena,CA91101,USA
Accepted to ApJL
5 ABSTRACT
1 Since z ∼1, the stellar mass density locked in low mass groups and clusters has grown by a factor
0
of ∼ 8. Here we make the first statistical measurements of the stellar mass content of low mass
2
X-ray groups at 0.5 < z < 1, enabling the calibration of stellar-to-halo mass scales for wide-field

n optical and infrared surveys. Groups are selected from combined Chandra and XMM −Newton
a X-ray observations in the Chandra Deep Field South (CDFS). These ultra-deep observations allow
J us to identify bona fide low mass groups at high redshift and enable measurements of their total

8 halo masses. We compute aggregate stellar masses for these halos using galaxies from the Carnegie-
Spitzer-IMACS (CSI) spectroscopic redshift survey. Stars comprise ∼ 3−4% of the total mass of

A] grouphalos with masses 1012.8 <M200/M⊙ <1013.5 (about the mass of Fornax and 1/50ththe mass
of Virgo). Complementing our sample with higher mass halos at these redshifts, we find that the
G stellar-to-halomassratiodecreasestowardhigherhalomasses,consistentwithotherworkinthelocal
. and high redshift universe. The observedscatter about the stellar-halomass relationis σ ∼0.25 dex,
h whichisrelativelysmallandsuggeststhattotalgroupstellarmasscanserveasaroughproxyforhalo
p
mass. We find no evidence for any significant evolution in the stellar-halo mass relation since z . 1.
-
o Quantifying the stellar content in groups since this epoch is critical given that hierarchical assembly
r leads to such halos growing in number density and hosting increasing shares of quiescent galaxies.
t
s
a
[ 1. INTRODUCTION direct methods for inferring halo membership and halo
mass scales.
The buildup of stellar mass in dark matter halos has
1 The two relevant measurements for directly probing
been measured in the local universe with a variety of
v groupmass scales are the halo mass and the total group
methods,indirectlywithabundancematchingtechniques
6
stellar mass. At high redshift, reliable detection of
6 (Behroozi et al. 2013; Moster et al. 2013) and more di-
galaxy groups as well as halo mass estimates require
9 rectly with measurements of stellar and total masses of
deep X-ray imaging. We therefore utilize the ultra deep
1 individual halos (Kravtsov et al. 2014). These stellar
Chandra+XMM Newton group catalog in the CDFS
0 mass– halo massrelationsprovide strongconstraintson
of Finoguenov et al. (2014). To find galaxies within
. models of galaxy formation (e.g., Genel et al. 2014).
1 these groups, we require a survey with sufficient red-
While much of the attention has been focussed on the
0 ⋆ shift precision, which is uniform, and which has well-
stellar content of L halos, recent work has highlighted
5 characterized completeness corrections to relatively low
the relevance of the higher mass scales represented by
1 stellar masses. The Carnegie-Spitzer-IMACS (CSI) sur-
groups and clusters, where various feedback processes
v: are predicted to operate. Kravtsov et al. (2014) for in- vey (Kelson et al. 2014) meets these criteria and is used
i stance show discrepancies between stellar-to-halo mass in this work.
X We assume a cosmologywith H =70km s−1 Mpc−1,
ratios computed for clusters from abundance matching 0
r and from direct observations. Meanwhile, at z . 1, ΩM =0.30, and ΩΛ =0.70. Stellar masses are based on
a a Kroupa (2001) IMF.
Williams et al.(2012)measureadramaticincreaseinthe
numberdensityofgalaxygroupsoveranepochwhenstar 2. DATAANDANALYSIS
formationactivity is greatly diminished, both in relative
2.1. Chandra and XMM-Newton X-ray Imaging
intensity (i.e., SSFR, Fumagalli et al. 2012) and in the
number of galaxies that display active levels of star for- We utilize combined Chandra and XMM-Newton X-
mationatafixedmass. Giventhatthesemassivehalosat ray observations in the CDFS (Finoguenov et al. 2014)
highredshiftrepresentsiteswheregalaxiesarequenched toselectgroupsathighredshift. Theseobservationsrep-
atlevels abovethatin the field(Patel et al. 2009, 2011), resent the deepest X-ray data to date. For the analy-
ananalysisofenvironmentaltrendsprovidesinsightinto sis presented here, we cull the list of 46 X-ray groups
themechanismsthatcontributetowardthegrowthofthe from Finoguenov et al. (2014) to those with redshifts in
redsequence. Directlymeasuringthemassscalesofthese the range 0.5 < z < 1 and flags of 1 or 2, indicat-
halos in which galaxies undergo quenching will provide ing well defined centroids and redshift determinations
strongerconstraintsontherelevantmechanismsthanin- fromfollowupspectroscopy. Inaddition,weincludeonly
those groups with CSI coverage in the ECDFS, out of
[email protected] 4.8 sq degs in the SWIRE CDFS field. Only 23 groups
*ThisLetterincludesdatagatheredwiththe6.5mMagellan remain in the catalog. Total masses, M200, given in
Telescopes locatedatLasCampanas Observatory,Chile. Finoguenov et al.(2014)areestimatedfromtheLX−M
2 Patel et al.
Figure 1. ExampleX-raydetected groupsintheCDFS.Thecolorimagesareconstructed fromHST/WFC3J125 andH160 bands. The
centersofthegroupsaremarkedwithagreenplussignandthevirialradii,R200,areindicatedbythelargedashedgreencircles. Galaxies
thatarecharacterizedasmembersofthegrouparecircledinblue,whilenearbyfieldgalaxiesarecircledinredandorangebasedontheir
redshiftoffsetfromthegroup. Clearoverdensitiesexistinthevicinityoftheidentifiedgroupcenters.
relationinLeauthaud et al.(2010),whichwascalibrated is ∼ 50−60% over 17 < i < 25.5 AB mag and a broad
withweaklensingbasedmassestimatesintheCOSMOS range of color. To accurately account for galaxies that
field. Thoughthelowesthalomasseswerederivedbyex- were not observed with the UDP or which did not have
trapolating the latter relation, Finoguenov et al. (2014) well constrained redshifts, galaxies are assigned weights
confirmedthe reliability ofthe halomass estimates from according to their inverse completeness in bins of ob-
stacked weak lensing and clustering analyses. R val- served magnitude ([3.6]), observed color (i−[3.6]), and
200
ues follow from these mass estimates. local source density (see, e.g., Kelson et al. 2014).
EventhoughtheCDFShasbeenextensivelystudiedby
2.2. CSI Spectroscopy and Completeness other surveys, with numerous high-resolution redshifts
We utilize a redshift catalog in the CDFS constructed available in the literature (e.g., Cooper et al. 2012), we
from new CSI observations. The handling of the data refrain from combining the multiple available datasets.
is similar to that in the XMM-LSS field (Kelson et al. The different selection functions in other work would
2014),thoughourdeepDECamphotometryprovidesfor makeitdifficultto produce ahomogeneousdatasetfrom
more uniform completeness as a function of magnitude. the aggregateof all the available surveys,despite poten-
Briefly, CSI targets were selected in the Spitzer IRAC tially boosting the levelof completeness. The depth and
3.6 µm band with magnitudes brighter than 21 AB mag homogeneity of the CSI data simplify the analysis, and
andobservedwiththe UniformDispersionPrism(UDP) the relatively uniform ∼ 50−60% completeness is high
on IMACS (Dressler et al. 2011) at Magellan. Redshifts enough to robustly characterize the stellar mass content
were measured by fitting the available spectrophotome- of these X-ray groups. Lastly, while other works have
try (spectrum+ ugrizJHK)withSEDs generatedfrom usedphotometriccatalogstoassembleorcalibrategalaxy
stellarpopulationsynthesismodels. Incomparisonswith samplesingroupsintheCDFS(e.g.,Giodini et al.2009;
high-resolution redshifts from Cooper et al. (2012) we Erfanianfar et al. 2014), our sample is exclusively spec-
find a biweight scatter of σz/(1+z) ∼ 0.008 for both troscopic.
red and blue galaxies. At z = 1, the stellar mass com-
pleteness limit is M ∼1010.3 M⊙. 2.3. Group MeCmablceurslahtiiponanadndAgUgnrecgearttaeinSttyellar Mass
We note thatgroupnumbers79and68do notcontain
CSIgalaxiesabovethemasscutofM >1010.3M⊙(some ForeachX-raygroup,weassignCSIgalaxiesabovethe
galaxies may have been missed due to slit collisions and mass limit within the projected virial radii, R200, and
other sources of incompleteness), though both contain within |∆z|/(1+z) < 0.02. This large redshift window
galaxiesbelowthislimit. Theseareboththelowestmass encompassesbothmembersandcontaminants(seebelow
groups in the sample with halo mass estimates of Mh ∼ forcorrection). Wesumthestellarmassesofthegalaxies
1012.8 M⊙. Also, number 63 had a large uncertainty on down to Mstars(> 1010.3 M⊙), multiplying by the com-
the stellar mass estimate (see below). We exclude these pleteness weights. Onspatialscales comparableto those
groups from our analysis leaving a total sample of 20 of the groups at 0.5 < z < 1 (e.g., D ∼ 1′), the com-
X-ray groups in the CDFS. pletenesscorrectionaccuratelyreproducesgalaxycounts
The spectroscopic completeness for CSI in the CDFS towithin∼20%,anuncertaintythatisfactoredintothe
Stellar Mass – Halo Mass Relation for Groups at 0.5<z <1 3
Figure 2. SelectionpropertiesoftheX-raygroupsample. (a)Rest-frameX-rayluminosity(0.1-2.4keV)versusredshiftforgroupsfrom
ourprimarysampleinthedeepCDFSfield(black)andthecomparisonsampleintheshallowerCOSMOSfield(gray). Filledcirclesindicate
flag=1 while open symbols indicate flag=2 (see text in Section 3.1). (b) M200 versus redshift for the same sample. The CDFS sample
reacheslowerhalomassesatz>0.5,probingbelowM <1013.3 M⊙.
totalerrorbudgetontheaggregatestellarmassmeasure- 0.2 dex.
ments. Figure 1 shows two example low-mass groups in the
To account for galaxies below our stellar mass com- CDFS. Color images were constructed using HST CAN-
pleteness limit, we correctthese groupstellar masses as- DELSWFC3J andH imaging(Grogin et al.2011;
125 160
suming a Schechter function with α=−1 and logM∗ = Koekemoer et al. 2011). Within the virial radii (dashed
10.9. Integrating down to M = 109 M⊙ we find a cor- greencircles),Figure1showsclearoverdensitiesofgroup
rection factor of 1.27. Changing α and M∗ within rea- members (blue circles) relative to field galaxies within
sonable ranges yields an uncertainty of ∼ 30% in this the same redshift slice (red and orange circles), indicat-
correction, which is added to the error budget. ingthatweareabletoreliablyplacegalaxiesintogroups
We derive a contamination correction for every group withourdataandcomputerobustaggregatestellarmass
bysubtractingoffthestellarmasscontributionfromfore- totals.
groundand backgroundgalaxies. We measured the stel-
lar mass within circular apertures of radius R at spa- 2.4. COSMOS Comparison Sample
200
tiallocationsthatdidnotoverlapwithothergroupsnear
We compare our results for low-mass groups at 0.5 <
z . We compute the aggregate stellar mass of galax-
group z < 1 to low-mass groups at 0.1 < z < 0.5 and to high-
ies at |∆z|/(1+z ) < 0.02 in these apertures and
group massgroupsat0.5<z <1,bothderivedfromthe wider
take the mean and standard deviation to represent the
field, butshallowerX-raydatafromCOSMOS(fora de-
backgroundand its uncertainty (typically ∼18%).
tailed study, see Giodini et al. 2009). We standardize
After measuring the stellar mass within R , we cor-
200 the group stellar masses in COSMOS with ours in the
rect the value to that expected within r assuming a
200 CDFS by measuring them in the same manner as de-
sphericallysymmetricNFWprofile(Navarro et al.1996)
scribed in the previous section and using the photomet-
seen in projection (e.g., Giodini et al. 2009, see their
ricredshiftsandstellarmassesfromGeorge et al.(2011).
Equation7). WeassumeanNFWprofilewithconcentra-
Whilethisapproachdiffersfromsummingredshiftlikeli-
tion of c=4 resulting in a multiplicative correction fac-
hoodfunctionswithintheredshiftwindowsofthegroups,
tor of ∼0.78. The range of typical concentration values
as carriedout in George et al.(2011), there is very good
associated with high mass halos (c ∼ 3−5, Duffy et al.
agreementbetweenthetwomethodswithascatterinthe
2008) impacts the correction factor by only ∼ 3% and
aggregate stellar masses of only ∼ 0.06 dex and a neg-
therefore does not significantly affect our results or con-
ligible offset. We convert the COSMOS stellar masses
clusions.
from Chabrier to Kroupa IMF by adding 0.05 dex. In
Lastly, there is an additional source of uncertainty
total,the COSMOSsample consists of125groups,69at
due to the statistical uncertainties in the individual
0.5 < z < 1 and 56 at 0.1 < z < 0.5 with halo masses
mbaassesdmonearseupreeamteUnDtsP. Tobhseertvyaptiicoanlssatnatdisstpiceacltruonpcheorttoaminetyt-, spanning 1012.8 < M200/M⊙ < 1014.3 and with X-ray
flag=1 or flag=2 and no other flags.
ric SED fitting, is ∼ 0.1 dex per galaxy. This does not
include contributions due to systematic effects such as 3. RESULTS
different stellar population synthesis models and IMF
3.1. Galaxy Group Sample Properties
variations.
The total uncertainty in the aggregate stellar mass Figure 2a shows the X-ray luminosity of X-ray groups
measurement for a typical group in our sample is ∼ as a function of redshift. Redshifts were determined
4 Patel et al.
Figure 3. The stellar mass-halo mass relation (Mstars versus M200) for high mass halos at 0.5 < z < 1. Stellar mass measurements
represent the aggregate mass instars of all galaxies inthe halo. (a) Individual X-raydetected groups inthe CDFSand COSMOSare in
black and gray, respectively. Clusters from GCLASS are in green (vanderBurgetal. 2014). Measurements and uncertainties from the
threedatasetshavebeenstandardizedwhenpossible. Dottedlinesacrossthefigureindicateratiosofstellar-to-halomassof0.01and0.1for
reference. AbiweightfittotheCDFS+COSMOSdata(blueline)indicatesaslopeof0.84±0.10andanobservedscatterofσ=0.25dex.
Fittingallofthedata,includingGCLASS(greenline),theslopebecomes0.72±0.07andtheobservedscatterσ=0.25dex. Theless-than-
unityslopeindicates that fewerstars areformed/assembledinhighermasshalos. Therelativelysmallobservedscatter impliesthat total
stellar mass serves as a good proxy for the total halomass inthis regime. (b) Median stellar to halo mass ratio fordifferent bins inhalo
mass. Vertical error bars represent bootstrapped uncertainties. Black horizontal error bars indicate the bin range while the thicker gray
errorbarsrepresentthe25-75thpercentilevaluesforthehalomassesineachsubsample. Atlowgroupmassesof1012.8 <M/M⊙<1013.5
probedmostlybythedataintheCDFS,starsmakeup3−4%ofthetotalmassofthehalos. Theorangecurveindicatesthez∼0relation
fromabundancematching.
from followup spectroscopy of red sequence candi- The slope is consistent with the value of α = 0.81 ±
date galaxies as described in George et al. (2011) and 0.11 found in Giodini et al. (2009) for their higher mass
Finoguenov et al. (2014, submitted). The filled symbols COSMOS group sample spanning 0.1 < z < 1. The
represent X-ray groups with centroids determined from implied stellar fraction for the COSMOS groups (∼ 2%
the X-rayimage(flag=1),while the opensymbolsrepre- at M200 ∼1013.5 M⊙) is also consistent with the results
sent centroids determined from the positions of the red of Leauthaud et al. (2012). The green data points in
sequence galaxies (flag=2). The median redshift for the Figure 3 represent measurements for clusters from the
CDFS sample is zmed ∼ 0.7. Figure 2b shows the COS- GCLASS survey (van der Burg et al. 2014). The green
MOS and CDFS group masses, M200, as a function of lineisafittoallthreedatasetsandresultsinα=0.72±
redshift. The error bars represent the statistical uncer- 0.07 and β = 2.20±0.97. The inclusion of the cluster
tainty and do not include the contribution due to the data results in a shallow slope which is consistent with
scatter in the LX −M relation (∼ 0.2 dex). As a re- the general trend found at high halo masses.
sult of the lower flux limits, CDFS reaches significantly The observed biweight scatter about the relation in
lower group masses at high redshift compared to COS- Equation 1 is σ = 0.25 dex, and is comparable for both
MOS. In particular, halos at z > 0.5 with mass below the CDFS andCOSMOSsamples. The similarscatteris
M200 <1013.3 M⊙ arealmostexclusivelydetectedinthe reassuringandimpliesthatourcompletenesscorrections
CDFS. arerobustandunbiased. Furthermore,thisobservational
scatter is remarkably small. When factoring in the un-
3.2. The Stellar Mass – Halo Mass Relation at certainties on the aggregate stellar mass measurements,
0.5<z <1 the intrinsic scatter must be quite low. Determination
ofthe intrinsic scatter requiresaccurateestimates of the
The aggregate stellar mass within X-ray groups at
observational errors. Because they total ∼ 0.2 dex, we
0.5 < z < 1 is compared to their total mass in Fig-
areunabletomakeaprecisedeterminationoftheintrin-
ure 3. In Figure 3a, the CDFS groups are shown us-
sic scatter. In any case, an upper limit for the intrinsic
ing the black points. The COSMOS groups are shown
scatter in the group stellar mass versus halo mass rela-
in light gray. Owing to its depth, the CDFS sample
tion of ∼ 0.25 dex reflects a relatively tight correlation
provides the only leverage on M /M for low mass
stars 200
suggesting that the former serves as a rough proxy for
groups (M200 <2×1013 M⊙). the latter. This has also been noted by other authors
The blue line is a biweight fit to the CDFS and COS-
(e.g., van der Burg et al. 2014).
MOS data of the form
Figure3bshowsthemedianstellartohalomassfordif-
ferentbinsinhalomass. ThebulkofthelowmassCDFS
logM =β+αlogM (1) group sample lies in the two lowest mass bins spanning
stars 200 1012.8 < M200/M⊙ < 1013.5. In these halos, which are
where α=0.84±0.10andβ =0.47±1.33(see Table 1).
Stellar Mass – Halo Mass Relation for Groups at 0.5<z <1 5
indicate the results at z ∼ 0 from abundance matching
(Kravtsov et al. 2014) and the associated error bars the
range of median values spanned by halos with masses in
the25-75thpercentileofthetwosub-samples. Again,we
donotfindanysignificantevolutioninthestellar-to-halo
mass ratio in the group regime at z .1.
4. DISCUSSION
Wehavemeasuredthestellarmass–halomassrelation
for low mass groups at 0.5 < z < 1, complementing
other work at these redshifts (e.g., Giodini et al. 2009;
van der Burg et al. 2014). For the low mass groups in
our CDFS sample, we find that about ∼ 3−4% of the
⋆
total mass is contained in stars, less than that of L
haloesbutmorethanthatofclusters,asisalsothetrend
in the local universe. The lack of (or slow) evolution in
thestellarfractionofsuchhalosisrelevantgiventhatthe
number density of these groups is observed to increase
Figure 4. Ratioofgroupstellarmasstohalomassversusredshift dramatically at z < 1 (Williams et al. 2012) indicating
f1o0r13t.w3)oabriensshoofwhnailnobmluaessa.ndLhowighmmaasssshianlorsed(1(100121.38.3<<MM//MM⊙⊙<< the growing significance of such environments.
1014). Resultsfromabundancematchingatz∼0(Kravtsovetal. Late-time formationof massive halos is expected from
2014) are shown as open squares. We do not find any significant hierarchical growth. Massive halos in the mass range
evolutionintheratioofstellartohalomassforgroupsatz.1. M200 > 1013 M⊙ are predicted to comprise ∼ 32% of
the total mass of all halos above M200 >1011.6 M⊙ (ap-
proximately the halo mass scale that would host central
Table 1 galaxiesatourstellarmasslimit)atz ∼1(basedonHM-
Bestfitparameterstostellar-halomassrelation Fcalc,Murray et al.2013;Tinker et al.2008). Byz ∼0,
this percentage rises substantially to ∼52%. For groups
SampleFitted α β (σdoebxs) N in the mass range 1013 <M200/M⊙ <1014, the percent-
age increases from ∼ 29% at z ∼ 1 to ∼ 36% at z ∼ 0.
CCDDFFSS,,CCOOSSMMOOSS,GCLASS 00..7824±±00..0170 20..2407±±01..9373 00..2255 9839 Clusters at M200 > 1014 M⊙ clearly contribute toward
the mass growth at z < 1 but even these structures are
Note. —ThefitcoefficientsαandβareindicatedinEquation1: built, in part, from groups (Berrier et al. 2009).
logMstars=β+αlogM200. Theobservedbiweightscatter about The increase in number densities of galaxy groups,
thisrelationisσobsandthenumberofhalosincludedinthefit,N. and the associated increase in the stellar mass density
Fitsapplyonlytothemassrangeprobedbythedatapresentedin
thiswork. within such halos, has implications for the buildup of
quiescent galaxies (QGs) since z ∼ 1. From z ∼ 1
10-20timesmoremassivethantheMilkyWay’shalo,the
to z ∼ 0 the quiescent fraction (QF) increases from
stellarmassconstitutes 3−4%ofthe totalmassbudget. ∼ 44% to ∼ 59% for galaxies with M > 1010.3 M⊙
3.3. No Significant Evolution in the Group Stellar to (Kelson et al. 2014; Muzzin et al. 2013). Down to this
mass limit, QFs are higher in rich environments com-
Halo Mass Ratio since z ∼1
paredtothefield(Dressler1980)withQFsof∼80%and
Here we examine the redshift evolution, if any, of the ∼35%ingroups/clustersandthefield,respectively(e.g.,
stellar mass – halo mass relation for groups. The or- Patel et al. 2011). As a consequence, the rise of groups
angecurveinFigure3bindicatesthestellar-to-halomass over the past ∼ 8 Gyr contributes substantially to the
ratio from abundance matching, empirically derived by evolving QF over that time. By assessing the star for-
Kravtsov et al.(2014,Figure12)atz ∼0. Giventhe er- mationactivityandquiescenceofgalaxiesingroupsover
rorbarsandanyadditionaluncertaintyduetosystematic the full 15 degs2 survey field of CSI, we will accurately
differencesbetweenthetwomeasurementmethods,there constrain the impact of large scale structure growth on
does not appear to be any significant evolution at z .1 thebuildupofQGsandthedeclineinglobalSFRDsince
in the stellar-to-halomass relation for M200 &1013 M⊙. z ∼1.
We can further examine and confirm the lack of evo-
lution by using additional measurements at lower red-
shifts (0 < z < 0.5) that were made in the same man- We thank Alexis Finoguenov for making his CDFS X-
ner as our own. Figure 4 shows the redshift evolu- ray catalog available.
tion for the median stellar-to-halo mass ratio for two
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