85 research outputs found
The Physical Properties of LBGs at z>5: Outflows and the "pre-enrichment problem"
We discuss the properties of Lyman Break galaxies (LBGs) at z>5 as determined
from disparate fields covering approximately 500 sq. arcmin. While the broad
characteristics of the LBG population has been discussed extensively in the
literature, such as luminosity functions and clustering amplitude, we focus on
the detailed physical properties of the sources in this large survey (>100 with
spectroscopic redshifts). Specifically, we discuss ensemble mass estimates,
stellar mass surface densities, core phase space densities, star-formation
intensities, characteristics of their stellar populations, etc as obtained from
multi-wavelength data (rest-frame UV through optical) for a subsample of these
galaxies. In particular, we focus on evidence that these galaxies drive
vigorous outflows and speculate that this population may solve the so-called
``pre-enrichment problem''. The general picture that emerges from these studies
is that these galaxies, observed about 1 Gyr after the Big Bang, have
properties consistent with being the progenitors of the densest stellar systems
in the local Universe -- the centers of old bulges and early type galaxies.Comment: 4 pages, to appear in "Pathways Through an Eclectic Universe", J. H.
Knappen, T. J. Mahoney, and A. Vazedekis (Eds.), ASP Conf. Ser., 200
Deep VLT V-band Imaging of the Field of a z=10 Candidate Galaxy: Below the Lyman Limit?
We present a deep 16.8 ks V-band image of the field of a candidate z=10
galaxy magnified by the foreground (z=0.25) cluster A1835. The image was
obtained with FORS1 on VLT-Kueyen to test whether the V-band lies below the
Lyman limit for this very high redshift candidate. A detection would
unambiguously rule out that the source is at z=10. The 3sigma detection limit
of the image in the area of the z=10 candidate is V_AB=28.0 mag in a 2 arcsec
diameter aperture (about 3 times the seeing FWHM of 0.7 arcsec). No source at
the position of the candidate galaxy is detected down to this limit. Formally,
this is consistent with the V-band probing below the Lyman limit in the
rest-frame of a z=10 source. However, given the recent non-detection of the
object in a deep H-band exposure with NIRI on Gemini North down to H_AB=26.0
mag (3sigma in a 1.4 arcsec aperture) and concerns about the detection of the
reported associated emission line, it may be possible that this source is
spurious. We discuss several astrophysical possibilities to explain the
puzzling nature of this source and find none of them compelling.Comment: accepted for publication in Ap
The size-star formation relation of massive galaxies at 1.5<z<2.5
We study the relation between size and star formation activity in a complete
sample of 225 massive (M > 5 x 10^10 Msun) galaxies at 1.5<z<2.5, selected from
the FIREWORKS UV-IR catalog of the CDFS. Based on stellar population synthesis
model fits to the observed restframe UV-NIR SEDs, and independent MIPS 24
micron observations, 65% of galaxies are actively forming stars, while 35% are
quiescent. Using sizes derived from 2D surface brightness profile fits to high
resolution (FWHM_{PSF}~0.45 arcsec) groundbased ISAAC data, we confirm and
improve the significance of the relation between star formation activity and
compactness found in previous studies, using a large, complete mass-limited
sample. At z~2, massive quiescent galaxies are significantly smaller than
massive star forming galaxies, and a median factor of 0.34+/-0.02 smaller than
galaxies of similar mass in the local universe. 13% of the quiescent galaxies
are unresolved in the ISAAC data, corresponding to sizes <1 kpc, more than 5
times smaller than galaxies of similar mass locally. The quiescent galaxies
span a Kormendy relation which, compared to the relation for local early types,
is shifted to smaller sizes and brighter surface brightnesses and is
incompatible with passive evolution. The progenitors of the quiescent galaxies,
were likely dominated by highly concentrated, intense nuclear star bursts at
z~3-4, in contrast to star forming galaxies at z~2 which are extended and
dominated by distributed star formation.Comment: 6 pages, 4 figures, accepted for publication in Ap
SINFONI Integral Field Spectroscopy of z~2 UV-selected Galaxies: Rotation Curves and Dynamical Evolution
We present 0.5" resolution near-IR integral field spectroscopy of the Ha line
emission of 14 z~2 UV-selected BM/BX galaxies obtained with SINFONI at ESO/VLT.
The mean Ha half-light radius r_1/2 is about 4kpc and line emission is detected
over > ~20kpc in several sources. In 9 sources, we detect spatially-resolved
velocity gradients, from 40 to 410 km/s over ~10kpc. The observed kinematics of
the larger systems are consistent with orbital motions. Four galaxies are well
described by rotating disks with clumpy morphologies and we extract rotation
curves out to radii > ~10kpc. One or two galaxies exhibit signatures more
consistent with mergers. Analyzing all 14 galaxies in the framework of rotating
disks, we infer mean inclination- and beam-corrected maximum circular
velocities v_c of 180+-90 km/s and dynamical masses of (0.5-25)x10^10 Msun
within r_1/2. On average, the dynamical masses are consistent with photometric
stellar masses assuming a Chabrier/Kroupa IMF but too small for a 0.1-100 Msun
Salpeter IMF. The specific angular momenta of our BM/BX galaxies are similar to
those of local late-type galaxies. The specific angular momenta of their
baryons are comparable to those of their dark matter halos. Extrapolating from
the average v_c at 10kpc, the virial mass of the typical halo of a galaxy in
our sample is 10^(11.7+-0.5) Msun. Kinematic modeling of the 3 best cases
implies a ratio of v_c to local velocity dispersion of order 2-4 and
accordingly a large geometric thickness. We argue that this suggests a mass
accretion (alternatively, gas exhaustion) timescale of ~500Myr. We also argue
that if our BM/BX galaxies were initially gas rich, their clumpy disks will
subsequently lose their angular momentum and form compact bulges on a timescale
of ~1 Gyr. [ABRIDGED]Comment: Accepted for publication in the Astrophysical Journal. 17 pages, 5
color figure
The Far-Infrared, UV and Molecular Gas Relation in Galaxies up to z=2.5
We use the infrared excess (IRX) FIR/UV luminosity ratio to study the
relation between the effective UV attenuation (A_IRX) and the UV spectral slope
(beta) in a sample of 450 1<z<2.5 galaxies. The FIR data is from very deep
Herschel observations in the GOODS fields that allow us to detect galaxies with
SFRs typical of galaxies with log(M)>9.3. Thus, we are able to study galaxies
on and even below the main SFR-stellar mass relation (main sequence). We find
that main sequence galaxies form a tight sequence in the IRX--beta plane, which
has a flatter slope than commonly used relations. This slope favors a SMC-like
UV extinction curve, though the interpretation is model dependent. The scatter
in the IRX-beta plane, correlates with the position of the galaxies in the
SFR-M plane. Using a smaller sample of galaxies with CO gas masses, we study
the relation between the UV attenuation and the molecular gas content. We find
a very tight relation between the scatter in the IRX-beta plane and the
specific attenuation (S_A), a quantity that represents the attenuation
contributed by the molecular gas mass per young star. S_A is sensitive to both
the geometrical arrangement of stars and dust, and to the compactness of the
star forming regions. We use this empirical relation to derive a method for
estimating molecular gas masses using only widely available integrated
rest-frame UV and FIR photometry. The method produces gas masses with an
accuracy between 0.12-0.16 dex in samples of normal galaxies between z~0 and
z~1.5. Major mergers and sub-millimeter galaxies follow a different S_A
relation.Comment: 11 pages, 6 pages appendix, 11 figures, accepted to Ap
Dynamical Properties of z~2 Star Forming Galaxies and a Universal Star Formation Relation
We present the first comparison of the dynamical properties of different
samples of z~1.4-3.4 star forming galaxies from spatially resolved imaging
spectroscopy from SINFONI/VLT integral field spectroscopy and IRAM CO
millimeter interferometry. Our samples include 16 rest-frame UV-selected, 16
rest-frame optically-selected and 13 submillimeter galaxies (SMGs). We find
that restframe UV- and optically bright (K<20) z~2 star forming galaxies are
dynamically similar, and follow the same velocity-size relation as disk
galaxies at z~0. In the theoretical framework of rotating disks forming from
dissipative collapse in dark matter halos, the two samples require a spin
parameter ranging from 0.06 to 0.2. In contrast bright SMGs have larger
velocity widths and are much more compact. Hence, SMGs have lower angular
momenta and higher matter densities than either of the UV- or optically
selected populations. This indicates that dissipative major mergers may
dominate the SMGs population, resulting in early spheroids, and that the
majority of UV/optically bright galaxies have evolved less violently [...].
These early disks may later evolve into spheroids via disk instabilities or
mergers. Because of their small sizes and large densities, SMGs lie at the high
surface density end of a universal (out to z=2.5) "Schmidt-Kennicutt" relation
between gas surface density and star formation rate surface density with a
slope of ~1.7.Comment: 14 pages, 3 figures, accepted for publication in ApJ, minor typos
correcte
A Substantial Population of Red Galaxies at z > 2: Modeling of the Spectral Energy Distributions of an Extended Sample
We investigate the nature of the substantial population of high-z galaxies
with Js-Ks>2.3 discovered as part of our FIRES survey. This colour cut
efficiently isolates z>2 galaxies with red rest-frame optical colors ("Distant
Red Galaxies" or DRGs). We select objects in the 2.5'x2.5' HDF-South (HDF-S)
and 5'x5' field around the MS1054-03 cluster; the surface densities at Ks<21
are 1.6+-0.6 and 1.0+-0.2 arcmin^-2. We discuss the 34 DRGs at 2<z<3.5: 11 at
Ks<22.5 in HDF-S and 23 at Ks<21.7 in the MS1054-03 field. We analyze the SEDs
constructed from our deep near-infrared (NIR) and optical imaging from the ESO
VLT and HST. We develop diagnostics involving I-Js, Js-H, and H-Ks to argue
that the red NIR colors of DRGs cannot be attributed solely to extinction and
require for many an evolved stellar population with prominent Balmer/4000A
break. In the rest-frame, the optical colours of DRGs fall within the envelope
of normal nearby galaxies and the UV colours suggest a wide range in star
formation activity and/or extinction. This contrasts with the much bluer and
more uniform SEDs of Lyman break galaxies (LBGs). From evolutionary synthesis
models with constant star formation, solar metallicity, Salpeter IMF, and
Calzetti et al. extinction law, we derive for the HDF-S (MS1054-03 field) DRGs
median ages of 1.7(2.0) Gyr, A_V = 2.7(2.4) mag, stellar masses 0.8(1.6)x10^11
Msun, M/L_V = 1.2(2.3) Msun/LVsun, and SFR = 120(170) Msun/yr. Models assuming
declining SFRs with e-folding timescales of 10Myr-1Gyr generally imply younger
ages, lower A_V's and SFRs, but similar stellar masses within a factor of two.
Compared to LBGs at similar redshifts and rest-frame L_V's, DRGs are older,
more massive, and more obscured for any given star formation history.
[ABRIDGED]Comment: Accepted for publication in the Astrophysical Journal. 27 pages, 14
b/w figure
HST and Spitzer imaging of red and blue galaxies at z~2.5: A correlation between size and star formation activity from compact quiescent galaxies to extended star forming galaxies
We present HST NICMOS+ACS and Spitzer IRAC+MIPS observations of 41 galaxies
at 2<z<3.5 in the FIRES MS1054 field with red and blue rest-frame optical
colors. About half of the galaxies are very compact (effective radii r_e < 1
kpc) at rest-frame optical wavelengths, the others are extended (1< r_e < 10
kpc). For reference, 1 kpc corresponds to 0.12 arcsec at z=2.5 in the adopted
cosmology. We separate actively star forming galaxies from quiescent galaxies
by modeling their rest-frame UV-NIR SEDs. The star forming galaxies span the
full range of sizes, while the quiescent galaxies all have r_e<2kpc. In the
redshift range where MIPS 24 micron imaging is a sensitive probe of re-radiated
dust emission (z<2.5), the 24 micron fluxes confirm that the light of the small
quiescent galaxies is dominated by old stars, rather than dust-enshrouded star
formation or AGN activity. The inferred surface mass densities and velocity
dispersions for the quiescent galaxies are very high compared to those in local
galaxies. The galaxies follow a Kormendy relation (between surface brightness
and size) with approximately the same slope as locally, but shifted to brighter
surface brightnesses, consistent with a mean stellar formation redshift of
z_f~5. This paper demonstrates a direct relation between star formation
activity and size at z~2.5, and the existence of a significant population of
massive, extremely dense, old stellar systems without readily identifiable
counterparts in the local universe.Comment: Accepted for publication in Ap
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