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Star Forming Proto-Elliptical
Galaxies @ z>2 ?
Subaru/Sup-Cam
C.Ikuta (NAOJ)
X.Kong (NAOJ)
M.Onodera (Tokyo)
K.Ohta (Kyoto)
N.Tamura (Durham)
VLT/VMOS
A.Renzini (ESO)
E.Daddi (ESO)
A.Cimatti (Arcetri)
T.Broadhurst (Hebrew)
N.Arimoto (NAOJ)
Why universe @ z～2?
1) A large fraction of the stars in the presentday universe formed !
2) Bright QSO activity reached its peak !
3) Rapidly star forming galaxies of compact
and disordered morphologies became the
normal Hubble sequence galaxies of the
z<1 universe !
© Toho Co., Ltd.
Formation of Massive Galaxies
Massive galaxies are the product of rather
recent hierarchical merging of pre-existing
disk galaxies taking place largely at z<1.5
with moderate SFRs (eg, cole et al. 2000).
Fully assembled massive Mass
galaxies
with Evolution
Function
(Baugh rare.
et al. 2002)
Ms>1E11Mo at z>2 are extremely
Formation of Massive Galaxies
Alternatively, massive galaxies formed at
much higher redshifts (z>2-3), through a
short and intense epoch of star formation,
followed by passive evolution.
Ages of Virgo Ellipticals
Y.Yamada et al. (2004)
Observational Test
Search for high-z Massive Systems
Deep Spectroscopic Surveys of Field
Galaxies selected in the K-band
(Broadhurst et al. 1992)
K20 Project (Daddi, Renzini, Cimatti et al.)
A New Population of near-IR
bright, z～2 Galaxies
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).
Why New Population?
Because
1) they lie in the redshift-desert
at z～1.5-2 where no strong
spectral features,
2) they are not LBGs, because UV
continuum slope is too red,
3) they are not EROs, because
R-K colours are often too blue.
The existence of NIR Bright z～2 Galaxies clearly
outlines a major failure of semianalytical CDM
modeling of high-z massive galaxies.
Nature of NIR Bright Galaxies
1) actively star forming galaxies (>100-500Mo/yr)
2) irregular light distribution, clumpy SF regions,
high detected asymmetries, ongoing mergers?
3) low light concentration similar to local starbursts
and ULIRGs
4) old underlyings, half light radii～6kpc (large)
Proto-Ellipticals @ z～2?
If high SFRs > 100 Mo/yr are really
present, it is clear that in a few 100 Myr
a full M* galaxy will be assembled.
However, high SFRs prevent a fair mass
estimate from the photometry.
The galaxies appear significantly clustered,
similar to EROs and local massive ellipticals.
Are these galaxies massive early-type
galaxies in the act of their formation?
Subaru/Sup-Cam Observation
K20
52 arcmin^2
FIRES
20 arcmin^2
GOOD-South 160 arcmin^2
Subaru/Suprime-Cam Observations
March 2-4, 2003, 0.”5-0.”7 seeing
1) BRIz’+JK 900 arcmin^2
Ks(AB)=22.6(5σ) 400 arcmin^2
z’(AB)=26.1, B(AB)=27.7(5σ)
2) BRIz’+ K 900 arcmin^2 (Daddi-F)
Ks(AB)=21.3(5σ) 500 arcmin^2
z’(AB)=25.4, B(AB)=27.0(5σ)
VLT/VMOS Observations
New populations are easily identified photometrically.
Targets: NewPops EROs PEs(z>1.5) FIRES(J-K>2.3)
Field 1
Daddi-F
464
146
1200:
400
82
46
253
?
We aim at determining redshifts, space densities, and
clustering properties of a statistically significant
populations of massive starburst galaxies at z～2,
such as NewPops, EROs, PEs, & FIRES, in total ～1000.
VLT/VMOS 4 nights in January 2004
Clustering of z～2 Galaxies
New Pops & FIRES (Field-1)
New Pops & EROs (Daddi-F)
Pilot Exploratory Programs
in view of Subaru/FMOS
A new population of galaxies appear to have high
star formation rate (>100Mo/yr), irregular and
possibly merging-like morphologies, large
masses, and strong redshift clustering,
suggesting that they are massive early-type
galaxies in the act of major assembly episodes.
1) VLT/ISAAC NIR Spectroscopy 2.5n
2) Subaru/CISCO/OHS NIR Spectroscopy 4n
Crucial Questions
1) How massive are they?
2) How severe is the apparent conflict
with the ΛCDM hierarchical model
predictions?
3) Are they early-type galaxies in formation?
4) What is their SFR?
5) Are they assembling by merging?
Subaru/FMOS Observation
Targeted Lines: [O II]λ3727, [O III]λ4959, 5007,
Hα(λ6563Å), [N II]λλ6548, 6584
[S II]λ6717, and possibly Hβ(λ4861Å), in the
near-IR domain for New Pops and other
Galaxies (EROs, FIRES, LBGs) with 1.5<z<2.5.
Key Words: Mass, SFR, Metallicity, Merging, AGN
SFRs and Reddening
1) Estimate reddening and SFRs from the
observed emission line luminosities. The
comparison of UV-band and Hα, [O II],
[O III], and possibly Hβ based SFRs will allow
an independent and more reliable estimate of
the reddenning, thus corrected SFRs for our
galaxies.
If high SFRs (>100Mo/yr) will be confirmed,
it is clear that in a few 100 Myr a full M*
galaxy will be assembled.
Metallicity
2) Estimate metallicity of z～2 starburst galaxies
from R23 by using [O II], [O III] vs Hβ (or Hα
by assuming intrinsic ratio of Hβ/Hα
constant) as metallicity indicator.
If these z～2 starbursts are progenitors of
z～1 EROs and local ellipticals, their metallicity
should be high, at least near-solar or more.
Metallicity is a good indicator of stellar mass.
Dynamical Masses
3) Derive stringent limits on the dynamical masses
of our galaxies, by measuring the intrinsic width
of the Hα emission line, deriving in this way
the velocity dispersion.
Expected masses of our targets are order of one
magnitude larger than the observed
z～２ LBGs (Erb et al. 2003). We will obtain
Mdyn/L(K) to compare the Mdyn with stellar
mass derived from UV-Submm SEDs.
Formation Scenario
5) Compare the masses with the predictions of
different models of massive galaxy formation.
Baugh et al (2000) predicted ～６ massive
galaxies of Mstar=1E11Mo for 1.7<z<2.3 for our
total field of 900 arcmin^2.
Even a detection of single galaxy with mass
larger than 1E11Mo would allow us to set
stringent observational constraints on
theoretical models of galaxy formation.
Stellar Populations
4) Derive stellar ages and metallicities by
measuring line indices such as Hβ, Mgb, CN,
G-band, Fe4383, Fe5270, Fe5335, Fe5406,
Ca4227, from stacked spectra.
In a current cosmology Ho=70km/s/Mpc, Ωm=0.3,
Ωλ=0.7, the universe at z=2.3
is 2.8 Gyr old.
Merging?
6) Investigate the presence of merging systems
with a help of HST/ACS images. Quite often a
few distinct blobs are detected in UV.
The secure detection of large velocity separations
would give the first direct demonstration of
assembling systems at z=2.
AGNs
7) Use [S II]λ6717/Hα and [N II]λ6548,
6584/Hα to check for the presence of AGNs.
[N II]/Hα line ratio for abundance and
ionization degree.
We have XMM images of the fields. Our
preliminary analysis shows that there are lots of
New Pops detected in X-rays!