A Wide Area Survey for High-Redshift Massive GalaxiesNumber Counts and Clustering

of BzKs and EROs

X.Kong, M.Onodera, C.Ikuta (NAOJ), K.Ohta (Kyoto),N.Tamura (Durham), A.Renzini, E.Daddi, L. Da Costa (ESO),

A.Cimatti (Arcetri), T.Broadhurst (Tel’Aviv), L.F.Olsen (Cote d’Azur)

N. ARIMOTO (NAOJ)

Kong et al. (2006), Astro-ph/0510299, ApJ in press

Formation of Giant Ellipticals

Massive ellipticals are the products of recent hierarchical merging of disk galaxies taking place largely at z<1.5 with moderate SFRs (Cole et al. 2000), fully assembled massive galaxies with M*>1011Mo at z>2 are extremely rare.

Massive Galaxies in the Redshift Desert (z>1.3)

Glazebrook et al. (2004) Cimatti et al. (2004)

Previous Spectroscopic Surveys

1) K20 (Cimatti et al. 2002) 52 arcmin2

2) HDFN (Ferguson et al. 2000) 5.3 arcmin2

3) GOODS (Giavalisco et al. 2004) 　 160 arcmin2

4) HST/ACS UDF (Yan et al 2004) 12 arcmin2

5) GDDS (McCarthy et al 2004) 121 arcmin2

6) LBGs@z ～ 2 (Steidel et al 2004) 100 arcmin2

Massive galaxies are quite rare and likely highly clusteredat all redshifts, hence small areas such as those explored

so far are subject to large cosmic variance.

EIS Deep 3a Survey

We have undertaken a fairly deep, wide-field imaging with the Subaru/Suprime-Cam of two fields of 900 arcmin2 each for part of which near-IR data are available from ES

O NTT observations.

7. EIS3a-F (Subaru/NTT, Ks=20.8) 320 arcmin2

8. Daddi-F (Subaru/NTT, Ks=19.0) 600 arcmin2

The prime aim of this survey is to understandhow and when the present-day massive

galaxies formed. To this end, the imaging observations have been optimized for the use of optical/near-infrared multi-colour selection

criteria to identify both star forming and passive galaxies (BzK selection).

Kong et al . (2006) astro-ph/0510299

Subaru/Sup-Cam Observation

Daddi FieldRA=14:49:29, DEC=09:00:00 (J2000.0)

Subaru/Suprime-Cam BIz’: 2003/03/02-04WHT R : 1998/03/19-21NTT/SOFI K : 1999/03/27-30 BRIz’ (940 arcmin2) 3σ in 2”(AB) B(AB)=26.59 R(AB)=25.64 I(AB)=25.62 z’(AB)=25.31

K (600 arcmin2) 3σ in 2”(AB) Ks(AB)=20.91

940arcmin2

600arcmin2

Subaru/Sup-Cam Observation

ESO Imaging Survey (EIS Deep 3a) FieldRA=11:24:50, DEC=-21:42:00 (J2000.0)

Subaru/Suprime-Cam BRIz’: 2003/03/02-04NTT/SOFI JK : 2002/03/28-31 BRIz’ (940 arcmin2) 3σ in 2”(AB) B(AB)=27.46 R(AB)=26.87 I(AB)=26.56 z’(AB)=26.07

JK (320 arcmin2) 3σ in 2”(AB) J(AB)=23.40, Ks(AB)=22.70

940arcmin2

320arcmin2

K-band Galaxy Number CountsDifferential K-band Galaxy Counts

BzK-Selected Galaxies (K20)

BzK=(z-K)-(B-z)>-0.2(Daddi et al 2004, ApJ 617, 746)

(z-K)>2.5

Why BzK-selection if efficient for cullingstar-forming and passive galaxies at 1.4<z<2.5?

star-forming BzK galaxy at z=1.6

B z K

K20 Daddi et al (2004)

Photometric vs Spectroscopic Redshifts

BzKs

High-z galaxies Deep 3a fieldStar-forming

galaxies at z>1.4 ( sBzKs) Old galaxies at

z>1.4: (pBzKs)

stars

BzKs

BzK(ERO) BzK BzK BzK

ERO ERO ERO ERO

387 sBzK 121 pBzK

108 sBzK 48 pBzK

513 ERO

337 EROs

Star/Galaxy Separation

(z-K)AB-0.3(B-z)AB<-0.5

Sky densities of sBzKs, pBzKs, EROs

arcmin-2

Number Counts of sBzKs, pBzKs, and EROs

EROs

galaxies

sBzKs

pBzKs

Number Counts of sBzKs, pBzKs, and EROs

• For EROs, the slope of the number counts is variable, being steeper at bright magnitudes and flattening out towards faint magnitude.

• The pBzKs number counts have a similar shape, but the break in the count slope is shifted to 1-1.5 magnitude fainter.

• Both EROs and pBzKs have fairly narrow redshift distribution: peaked at z ～ 1 (EROs) and at z ～ 1.7 (pBzKs).

• The number counts are direct probes of their respective luminosity functions. The shift in the counts is consistent with the different typical redshift of the two populations.

• The counts of sBzKs have roughly the same slope at all K-band magnitude, which reflects the much wider redshift distribution of this class of galaxies.

Photo-z Distribution

Two Point Correlation Functions w(Θ)

Daddi-F Deep 3a-F

Landy & Szalay (1993)

Angular Clustering Amplitude

EROs, sBzKs, and pBzKs distribute in a very inhomogeneous way in the sky.

EROs and sBzKs appear to be strongly clustered, but pBzKs clustered most strongly inboth fields.

The clustering strengths of allthe three populations increase with K-band luminosity.

Physical Properties of sBzKs and pBzKs

• Supposing <z> ～ 2 for sBzKs, we have derived their physical properties, such as the reddening, star formation rate, and the stellar mass.

(While errors by a factor of 2 or more may affect individual estimates, the average quantities should be relatively robust.)

• Reddening : E(B-V)=0.25(B-z+0.1)AB ←UV Continuum slope (Calzetti law)

• SFR : SFR(Mo/yr)=L1500[erg/s/Hz]/8.85x1027

• Stellar Mass : log(M*/1011Mo)=-0.4(Ktot-20.14Vega)

The field area is the histogram for sBzKs which associated with X-ray sources (25%).

The dashed lines are for the stellar mass histograms of pBzKs. Above 1011Mo the numbers of sBzKs and pBzKs are similar.

Correlation between Colour Excess E(B-V), SFR and stellar mass for sBzKs

• There is evidence for an intrinsic correlation between SFR and reddening at z ～ 2 star-forming galaxies, with galaxies with higher star formation having more dust obscuration (>5σ level).

• The correlation between E(B-V) and stellar mass Is likely to be intrinsic, with more massive galaxies being also more absorbed (>7σ level).

• Given the previous two correlations, not surprisingly we also find a correlation between SFR and stellar masses (>4σ level).

• The upper edge in the SFR vs M* appear to be intrinsic, showing a limit on the maximum SFR that can be present in a galaxy of a given mass.

Brinchmann et al (2004)

SFRs/mass @ z ～ 2 were ～ 10 times larger than today.

Downsizing Effects?

• At z=0 the vast majority of massive galaxies (M*>1011Mo) are passively evolving “red” galaxies, while at z ～ 2 actively star forming (sBzKs) and passive (pBzKs) galaxies exist in similar numbers, and most massive galaxies tend to be the most actively star forming galaxies.

• This can be seen as yet another manifestation of the downsizing effect, with massive galaxies completing their star formation at an earlier epoch compared to less massive galaxies, which instead have more prolonged star formation.

Contribution of sBzKs to SFRD

25% AGN Contamination

SFRD=0.06 Mo/yr/Mpc3

for sBzKs in Deep3a-F(KVega<20)

SFRD=0.013 Mo/yr/Mpc3

for sBzKs in Daddi-F(KVega<19.2)

SFRD=0.044±0.08 Mo/yr/Mpc3

for sBzKs in GOODS-S(KVega<20; Daddi et al 2004)

for the volume in the redshiftrange 1.4<z>2.5

cosmic variance?Substantial contribution to the total SFRDis likely come from KVega>20 sBzKs.

Contribution of sBzKs and pBzKs to Stellar Mass Density

25% AGN contamination

ρ*(sBzKs)=2.45x107 Mo/Mpc3

ρ*(pBzKs)=1.79x107 Mo/Mpc3

for Deep3a-F(KVega<20)

for the volume in the redshiftrange 1.4<z>2.5

logρ*(total)=7.7 Mo/Mpc3

logρ*(total)=7.86 Mo/Mpc3

(1.5<z<2.0, Fontana et al 04)logρ*(total)=7.65 Mo/Mpc3

(2.0<z<2.5, Fontana et al 04)logρ*(total) ～ 7.5 Mo/Mpc3

(@z ～ 2, Dickinson et al 03)

Images of BzKs at z ～ 2

K>20 HST/ACS F435W, F850LP & K-band (VLT+ISAAC)

A sample of 9 galaxies at 1.7<z<2.23 with bright K-band magnitudes 18.7<K<20 has recently been discovered (Daddi et al. 2003, astro-ph/0308456).

Summary and Conclusions (I)

BzK selection is a quite powerful way to separatehigh-z galaxies such as sBzKs, pBzKs and EROs

at 1.4<z<2.5.

1) Down to the K-band limit of the survey the log of the number counts of sBzKs increases linearly with the

K-magnitude, while that of both EROs and pBzKs flattens out by Kvega ～ 19.

EROs are in a modest redshift shell (z ～ 1), while pBzKs are also in a relatively narrow

redshift shell but at higher redshift (z ～ 1.7).sBzKs are drawn from a large range of redshifts,

and their relative numbers increase sharply with redshift.

Summary and Conclusions (II) 2) The clustering properties of EROs and sBzKs are

very similar, clustering amplitudes ～ 10 timeshigher than generic galaxies in the same magnitude range.

This suggests an evolutionary link between sBzKsat z ～ 2 and EROs at z ～ 1, with star formationon sBzKs quenching by z ～ 1 thus producing

passively evolving EROs.

The clustering amplitude of pBzKs is even higherthan that of sBzKs and EROs, suggesting that quenching epoch of star formation in massive galaxies depends on environmental density.

Summary and Conclusions (III)

3) sBzK galaxies (KVega<20) have median reddeningE(B-V) ～ 0.40, average SFR ～ 190 Mo/yr,

typical stellar mass ～ 1011 Mo, and ～ solar metallicity.

The high SFRs, large masses and high metallicitiesof sBzKs suggest that these z ～ 2

star forming galaxies are the precursors of z=1 passive EROs and z=0 early-type galaxies.

Summary and Conclusions (IV) 4) The number density of massive pBzKs

(KVega<20, M*>1011 Mo) is about 1/2 of similarly massive early-type galaxies at z=0.

The quenching of star formation in massivestar-forming galaxies must result in a

doubling since <z> ～ 1.7 in the number of massive,passive galaxies.

It is indeed quite reassuring that the number of M*>1011 Mo sBzKs is very close to that of pBzKs.

We argue that most of this star-formation quenching is likely to take place between z ～ 2 and z ～ 1.

Massive Early-type GalaxiesEvolutionary Tracks (M*>1011Mo)

z ～ 0 　　　　　 z ～ 1 　　　 　　 z ～ 2 z>2

Early-type Galaxies

Passive

EROs sBzKs

pBzKs ?

sRjLsnumber density 1/2

number density 1/2

number density 1

E(B-V) ～ 0.4SFR ～ 190Mo/yr

Z ～ Zo

strong clusteringstrong clustering

strong clustering very very strong clustering

SMGs

40-200Myr

0.5-1Gyr