141 research outputs found
Evolution of the Dependence of Rest-frame Color and Morphology Distribution on Stellar Mass for Galaxies in the Hubble Deep Field North
Using the Subaru very deep K'-band imaging and HST WFPC2/NICMOS archival data
of the Hubble Deep Field North, we investigate the evolution of the stellar
mass, color, morphology of galaxies to z ~ 3. We mainly examine the rest-frame
U-V color distribution of galaxies as a function of stellar mass. At 0.3<z<2,
galaxies seem to be divided into the two populations at around the stellar mass
of ~5x10^9 M_solar. The low-mass galaxies have relatively bluer rest U-V color
and their color does not show clear correlation with stellar mass over the
range of 10^8-5x10^9 M_solar. On the other hand, at higher mass, the more
massive galaxies tend to have the redder U-V color. The average U-V color of
the low-mass galaxies becomes bluer gradually with redshift, from U-V ~ 0.2 at
z ~ 0.5 to U-V ~ -0.2 at z ~ 2. On the contrary, the correlation between the
stellar mass and rest U-V color of the high-mass population does not seem to
change significantly between z ~ 0.3 and z ~ 2. At z>2, it is seen that more
massive galaxies tend to have redder U-V color over the range of 10^9-10^10
M_solar. These results suggests that the star formation history of galaxies
depends on their stellar mass very much. The low-mass population is likely to
have relatively long star formation timescale. At the stellar mass larger than
~5x10^9 M_solar, there must be some mechanisms which suppress the star
formation in galaxies at 0<z<2.Comment: 45 pages, 31 figures, accepted for publication in Ap
MOIRCS Deep Survey. VIII. Evolution of Star Formation Activity as a Function of Stellar Mass in Galaxies since z~3
We study the evolution of star formation activity of galaxies at 0.5<z<3.5 as
a function of stellar mass, using very deep NIR data taken with Multi-Object
Infrared Camera and Spectrograph (MOIRCS) on the Subaru telescope in the
GOODS-North region. The NIR imaging data reach K ~ 23-24 Vega magnitude and
they allow us to construct a nearly stellar mass-limited sample down to ~
10^{9.5-10} Msun even at z~3. We estimated star formation rates (SFRs) of the
sample with two indicators, namely, the Spitzer/MIPS 24um flux and the
rest-frame 2800A luminosity. The SFR distribution at a fixed Mstar shifts to
higher values with increasing redshift at 0.5<z<3.5. More massive galaxies show
stronger evolution of SFR at z>~1. We found galaxies at 2.5<z<3.5 show a
bimodality in their SSFR distribution, which can be divided into two
populations by a constant SSFR of ~2 Gyr^{-1}. Galaxies in the low-SSFR group
have SSFRs of ~ 0.5-1.0 Gyr^{-1}, while the high-SSFR population shows ~10
Gyr^{-1}. The cosmic SFRD is dominated by galaxies with Mstar = 10^{10-11} Msun
at 0.5<z<3.5, while the contribution of massive galaxies with Mstar =
10^{11-11.5} Msun shows a strong evolution at z>1 and becomes significant at
z~3, especially in the case with the SFR based on MIPS 24um. In galaxies with
Mstar = 10^{10-11.5} Msun, those with a relatively narrow range of SSFR (<~1
dex) dominates the cosmic SFRD at 0.5<z<3.5. The SSFR of galaxies which
dominate the SFRD systematically increases with redshift. At 2.5<z<3.5, the
high-SSFR population, which is relatively small in number, dominates the SFRD.
Major star formation in the universe at higher redshift seems to be associated
with a more rapid growth of stellar mass of galaxies.Comment: 16 pages, 13 figures, accepted for publication in Ap
The Number Density of Old Passively-Evolving Galaxies at z=1 in the Subaru/XMM-Newton Deep Survey Field
We obtained the number counts and the rest-frame B-band luminosity function
of the color-selected old passively-evolving galaxies (OPEGs) at z=1 with very
high statistical accuracy using a large and homogeneous sample of about 4000
such objects with z' <25 detected in the area of 1.03 deg^2 in the
Subaru/XMM-Newton Deep Survey (SXDS) field. Our selection criteria are defined
on the i'-z' and R-z' color-magnitude plane so that OPEGs at z=0.9-1.1 with
formation redshift z_f=2-10 are properly sampled. The limiting magnitude
corresponds to the luminosity of galaxies with M_*+3 at z=0. We made a pilot
redshift observations for 99 OPEG candidates with 19 < z' < 22 and found that
at least 78% (73/93) of the entire sample, or 95% (73/77) of these whose
redshifts were obtained are indeed lie between z=0.87 and 1.12 and the most of
their spectra show the continuum break and strong Ca H and K lines, indicating
that these objects are indeed dominated by the old stellar populations. We then
compare our results with the luminosity functions of the color- or the
morphologically-selected early type galaxies at z=0 taking the evolutionary
factor into account and found that the number density of old passive galaxies
with sim M_* magnitude at z~1 averaged over the SXDS area is 40-60% of the
equivalently red galaxies and 60-85% of the morphologically-selected E/S0
galaxies at z=0 depending on their luminosity evolution. It is revealed that
more than half, but not all, of the present-day early-type galaxies had already
been formed into quiescent passive galaxies at z=1.Comment: 28 pages, accepted for publication in Astrophysical Journal. The full
version of the paper including Fig.3 and Fig.4 (large size) in full
resolution is put at
http://optik2.mtk.nao.ac.jp/~yamada/astronomy/sxdsred.htm
MOIRCS Deep Survey IV: Evolution of Galaxy Stellar Mass Function Back to z ~ 3
We use very deep near-infrared (NIR) imaging data obtained in MOIRCS Deep
Survey (MODS) to investigate the evolution of the galaxy stellar mass function
back to z~3. The MODS data reach J=24.2, H=23.1, K=23.1 (5sigma, Vega
magnitude) over 103 arcmin^2 (wide) and J=25.1, H=23.7, K=24.1 over 28 arcmin^2
(deep) in the GOODS-North region. The wide and very deep NIR data allow us to
measure the number density of galaxies down to low stellar mass (10^9-10^10
Msun) even at high redshift with high statistical accuracy. The normalization
of the mass function decreases with redshift and the integrated stellar mass
density becomes ~ 8-18% of the local value at z~2 and ~ 4-9% at z~3, which are
consistent with results of previous studies in general fields. Furthermore, we
found that the low-mass slope becomes steeper with redshift from alpha ~- 1.3
at z~1 to alpha ~- 1.6 at z~3, and that the evolution of the number density of
low-mass (10^9-10^10 Msun) galaxies is weaker than that of M* (~10^11 Msun)
galaxies. This indicates that the contribution of low-mass galaxies to the
total stellar mass density has been significant at high redshift. The
steepening of the low-mass slope with redshift is opposite trend expected from
the stellar mass dependence of the specific star formation rate reported in
previous studies. The present result suggests that the hierarchical merging
process overwhelmed the effect of the stellar mass growth by star formation and
was very important for the stellar mass assembly of these galaxies at 1<~z<~3.Comment: 21 pages, 18 figures, accepted for publication in Ap
Evolution of the Fraction of Clumpy Galaxies at 0.2<z<1.0 in the COSMOS field
Using the Hubble Space Telescope/Advanced Camera for Surveys data in the
COSMOS field, we systematically searched clumpy galaxies at 0.2<z<1.0 and
investigated the fraction of clumpy galaxies and its evolution as a function of
stellar mass, star formation rate (SFR), and specific SFR (SSFR). The fraction
of clumpy galaxies in star-forming galaxies with Mstar > 10^9.5 Msun decreases
with time from ~0.35 at 0.8<z<1.0 to ~0.05 at 0.2<z<0.4 irrespective of the
stellar mass, although the fraction tends to be slightly lower for massive
galaxies with Mstar > 10^10.5 Msun at each redshift. On the other hand, the
fraction of clumpy galaxies increases with increasing both SFR and SSFR in all
the redshift ranges we investigated. In particular, we found that the SSFR
dependences of the fractions are similar among galaxies with different stellar
masses, and the fraction at a given SSFR does not depend on the stellar mass in
each redshift bin. The evolution of the fraction of clumpy galaxies from z~0.9
to z~0.3 seems to be explained by such SSFR dependence of the fraction and the
evolution of SSFRs of star-forming galaxies. The fraction at a given SSFR also
appears to decrease with time, but this can be due to the effect of the
morphological K-correction. We suggest that these results are understood by the
gravitational fragmentation model for the formation of giant clumps in disk
galaxies, where the gas mass fraction is a crucial parameter.Comment: 14 Pages, 13 Figures, 1 Table, Accepted for publication in Ap
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