a wide area survey for high redshift massive galaxies number counts and clustering of bzks and eros
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A Wide Area Survey for High-Redshift Massive Galaxies Number Counts and Clustering of BzKs and EROs. Kong et al. (2006), Astro-ph/0510299, ApJ in press. N. ARIMOTO (NAOJ). X.Kong, M.Onodera, C.Ikuta (NAOJ), K.Ohta (Kyoto), N.Tamura (Durham), A.Renzini, E.Daddi, L. Da Costa (ESO),

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a wide area survey for high redshift massive galaxies number counts and clustering of bzks and eros
A Wide Area Survey for High-Redshift Massive GalaxiesNumber Counts and Clusteringof BzKs and EROs

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


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)

formation of giant ellipticals
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
Massive Galaxies in the Redshift Desert (z>1.3)

Glazebrook et al. (2004)

Cimatti et al. (2004)

previous spectroscopic surveys
Previous Spectroscopic Surveys
  • K20 (Cimatti et al. 2002) 52 arcmin2
  • HDFN (Ferguson et al. 2000) 5.3 arcmin2
  • GOODS (Giavalisco et al. 2004) 160 arcmin2
  • HST/ACS UDF (Yan et al 2004) 12 arcmin2
  • GDDS (McCarthy et al 2004) 121 arcmin2
  • [email protected]~2 (Steidel et al 2004) 100 arcmin2

Massive galaxies are quite rare and likely highly clustered

at 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 ESO NTT observations.EIS Deep 3a Survey

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

The prime aim of this survey is to understand

how 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).

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

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

subaru sup cam observation
Subaru/Sup-Cam Observation

Daddi Field

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

Subaru/Suprime-Cam BIz’: 2003/03/02-04

WHT R : 1998/03/19-21

NTT/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)





subaru sup cam observation1
Subaru/Sup-Cam Observation

ESO Imaging Survey (EIS Deep 3a) Field

RA=11:24:50, DEC=-21:42:00 (J2000.0)

Subaru/Suprime-Cam BRIz’: 2003/03/02-04

NTT/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




differential k band galaxy counts
Differential K-band Galaxy Counts

K-band Galaxy Number Counts

bzk selected galaxies k20
BzK-Selected Galaxies (K20)



(Daddi et al 2004, ApJ 617, 746)


Why BzK-selection if efficient for culling

star-forming and passive galaxies at 1.4<z<2.5?




star-forming BzK galaxy at z=1.6

photometric vs spectroscopic redshifts
Photometric vs Spectroscopic Redshifts


K20 Daddi et al (2004)

high z galaxies deep 3a field
High-z galaxies Deep 3a field

Star-forming galaxies at z>1.4 (sBzKs)

Old galaxies at

z>1.4: (pBzKs)







387 sBzK

121 pBzK

513 ERO

108 sBzK

48 pBzK

337 EROs

star galaxy separation
Star/Galaxy Separation


number counts of sbzks pbzks and eros1
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.
two point correlation functions w
Two Point Correlation Functions w(Θ)

Landy & Szalay (1993)


Deep 3a-F


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 in

both fields.

The clustering strengths of all

the three populations

increase with K-band luminosity.

physical properties of sbzks and pbzks
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
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.
downsizing effects
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
Contribution of sBzKs to SFRD

SFRD=0.06 Mo/yr/Mpc3

for sBzKs in Deep3a-F


SFRD=0.013 Mo/yr/Mpc3

for sBzKs in Daddi-F


SFRD=0.044±0.08 Mo/yr/Mpc3

for sBzKs in GOODS-S

(KVega<20; Daddi et al 2004)

for the volume in the redshift

range 1.4<z>2.5

Substantial contribution to the total SFRD

is likely come from KVega>20 sBzKs.

cosmic variance?

25% AGN Contamination

contribution of sbzks and pbzks to stellar mass density
Contribution of sBzKs and pBzKs to Stellar Mass Density

ρ*(sBzKs)=2.45x107 Mo/Mpc3

ρ*(pBzKs)=1.79x107 Mo/Mpc3

for Deep3a-F(KVega<20)

for the volume in the redshift

range 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)

25% AGN contamination

images of bzks at z 2
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
Summary and Conclusions (I)
  • BzK selection is a quite powerful way to separate
  • high-z galaxies such as sBzKs, pBzKs and EROs
  • at 1.4<z<2.5.
  • 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
Summary and Conclusions (II)

2) The clustering properties of EROs and sBzKs are

very similar, clustering amplitudes ~10 times

higher than generic galaxies in the same magnitude range.

This suggests an evolutionary link between sBzKs

at z~2 and EROs at z~1, with star formation

on sBzKs quenching by z~1 thus producing

passively evolving EROs.

The clustering amplitude of pBzKs is even higher

than that of sBzKs and EROs, suggesting that

quenching epoch of star formation in massive

galaxies depends on environmental density.

summary and conclusions iii
Summary and Conclusions (III)

3) sBzK galaxies (KVega<20) have median reddening

E(B-V)~0.40, average SFR ~ 190 Mo/yr,

typical stellar mass ~1011 Mo,

and ~solarmetallicity.

The high SFRs, large masses and high metallicities

of 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
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 massive

star-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 galaxies evolutionary tracks m 10 11 mo
Massive Early-type GalaxiesEvolutionary Tracks (M*>1011Mo)

z~0 z~1 z~2 z>2






Early-type Galaxies



number density 1/2


strong clustering


strong clustering



number density 1/2


numberdensity 1

very very strong clustering

strong clustering