1,147 research outputs found
The GREATS H+[OIII] Luminosity Function and Galaxy Properties at : Walking the Way of JWST
The James Webb Space Telescope will allow to spectroscopically study an
unprecedented number of galaxies deep into the reionization era, notably by
detecting [OIII] and H nebular emission lines. To efficiently prepare
such observations, we photometrically select a large sample of galaxies at
and study their rest-frame optical emission lines. Combining data from
the GOODS Re-ionization Era wide-Area Treasury from Spitzer (GREATS) survey and
from HST, we perform spectral energy distribution (SED) fitting, using
synthetic SEDs from a large grid of photoionization models. The deep
Spitzer/IRAC data combined with our models exploring a large parameter space
enables to constrain the [OIII]+H fluxes and equivalent widths for our
sample, as well as the average physical properties of galaxies, such
as the ionizing photon production efficiency with
. We
find a relatively tight correlation between the [OIII]+H and UV
luminosity, which we use to derive for the first time the [OIII]+H
luminosity function (LF) at . The [OIII]+H LF is higher
at all luminosities compared to lower redshift, as opposed to the UV LF, due to
an increase of the [OIII]+H luminosity at a given UV luminosity from
to . Finally, using the [OIII]+H LF, we make
predictions for JWST/NIRSpec number counts of galaxies. We find that
the current wide-area extragalactic legacy fields are too shallow to use JWST
at maximal efficiency for spectroscopy even at 1hr depth and JWST
pre-imaging to mag will be required.Comment: 13 pages, 9 figures, accepted for publication in MNRA
Structure and star formation in galaxies out to z=3: evidence for surface density dependent evolution and upsizing
We present an analysis of galaxies in the CDF-South. We find a tight relation
to z=3 between color and size at a given mass, with red galaxies being small,
and blue galaxies being large. We show that the relation is driven by stellar
surface density or inferred velocity dispersion: galaxies with high surface
density are red and have low specific star formation rates, and galaxies with
low surface density are blue and have high specific star formation rates.
Surface density and inferred velocity dispersion are better correlated with
specific star formation rate and color than stellar mass. Hence stellar mass by
itself is not a good predictor of the star formation history of galaxies. In
general, galaxies at a given surface density have higher specific star
formation rates at higher redshift. Specifically, galaxies with a surface
density of 1-3 10^9 Msun/kpc^2 are "red and dead" at low redshift,
approximately 50% are forming stars at z=1, and almost all are forming stars by
z=2. This provides direct additional evidence for the late evolution of
galaxies onto the red sequence. The sizes of galaxies at a given mass evolve
like 1/(1+z)^(0.59 +- 0.10). Hence galaxies undergo significant upsizing in
their history. The size evolution is fastest for the highest mass galaxies, and
quiescent galaxies. The persistence of the structural relations from z=0 to
z=2.5, and the upsizing of galaxies imply that a relation analogous to the
Hubble sequence exists out to z=2.5, and possibly beyond. The star forming
galaxies at z >= 1.5 are quite different from star forming galaxies at z=0, as
they have likely very high gas fractions, and star formation time scales
comparable to the orbital time.Comment: 20 pages, accepted for publication in ApJ, 2008, 68
Finite size scaling in the 2D XY-model and generalized universality
In recent works (BHP), a generalized universality has been proposed, linking
phenomena as dissimilar as 2D magnetism and turbulence. To test these ideas, we
performed a MC study of the 2D XY-model. We found that the shape of the
probability distribution function for the magnetization M is non Gaussian and
independent of the system size --in the range of the lattice sizes studied--
below the Kosterlitz-Thoules temperature. However, the shape of these
distributions does depend on the temperature, contrarily to the BHP's claim.
This behavior is successfully explained by using an extended finite-size
scaling analysis and the existence of bounds for M.Comment: 7 pages, 5 figures. Submitted to Phys. Rev. Lett. Details of changes:
1. We emphasized in the abstract the range of validity of our results. 2. In
the last paragraph the temperature dependence of the PDF was slightly
re-formulate
UV Luminosity Functions from 132 z~7 and z~8 Lyman-Break Galaxies in the ultra-deep HUDF09 and wide-area ERS WFC3/IR Observations
We identify 73 z~7 and 59 z~8 candidate galaxies in the reionization epoch,
and use this large 26-29.4 AB mag sample of galaxies to derive very deep
luminosity functions to <-18 AB mag and the star formation rate density at z~7
and z~8. The galaxy sample is derived using a sophisticated Lyman-Break
technique on the full two-year WFC3/IR and ACS data available over the HUDF09
(~29.4 AB mag, 5 sigma), two nearby HUDF09 fields (~29 AB mag, 14 arcmin) and
the wider area ERS (~27.5 AB mag) ~40 arcmin**2). The application of strict
optical non-detection criteria ensures the contamination fraction is kept low
(just ~7% in the HUDF). This very low value includes a full assessment of the
contamination from lower redshift sources, photometric scatter, AGN, spurious
sources, low mass stars, and transients (e.g., SNe). From careful modelling of
the selection volumes for each of our search fields we derive luminosity
functions for galaxies at z~7 and z~8 to <-18 AB mag. The faint-end slopes
alpha at z~7 and z~8 are uncertain but very steep at alpha = -2.01+/-0.21 and
alpha=-1.91+/-0.32, respectively. Such steep slopes contrast to the local
alpha<~-1.4 and may even be steeper than that at z~4 where alpha=-1.73+/-0.05.
With such steep slopes (alpha<~-1.7) lower luminosity galaxies dominate the
galaxy luminosity density during the epoch of reionization. The star formation
rate densities derived from these new z~7 and z~8 luminosity functions are
consistent with the trends found at later times (lower redshifts). We find
reasonable consistency, with the SFR densities implied from reported stellar
mass densities, being only ~40% higher at z<7. This suggests that (1) the
stellar mass densities inferred from the Spitzer IRAC photometry are reasonably
accurate and (2) that the IMF at very high redshift may not be very different
from that at later times.Comment: 38 pages, 21 figures, 20 tables, ApJ, accepted for publicatio
ZFIRE: The Evolution of the Stellar Mass Tully-Fisher Relation to Redshift 2.0 < Z < 2.5 with MOSFIRE
Using observations made with MOSFIRE on Keck I as part of the ZFIRE survey,
we present the stellar mass Tully-Fisher relation at 2.0 < z < 2.5. The sample
was drawn from a stellar mass limited, Ks-band selected catalog from ZFOURGE
over the CANDELS area in the COSMOS field. We model the shear of the Halpha
emission line to derive rotational velocities at 2.2X the scale radius of an
exponential disk (V2.2). We correct for the blurring effect of a
two-dimensional PSF and the fact that the MOSFIRE PSF is better approximated by
a Moffat than a Gaussian, which is more typically assumed for natural seeing.
We find for the Tully-Fisher relation at 2.0 < z < 2.5 that logV2.2 =(2.18 +/-
0.051)+(0.193 +/- 0.108)(logM/Msun - 10) and infer an evolution of the
zeropoint of Delta M/Msun = -0.25 +/- 0.16 dex or Delta M/Msun = -0.39 +/- 0.21
dex compared to z = 0 when adopting a fixed slope of 0.29 or 1/4.5,
respectively. We also derive the alternative kinematic estimator S0.5, with a
best-fit relation logS0.5 =(2.06 +/- 0.032)+(0.211 +/- 0.086)(logM/Msun - 10),
and infer an evolution of Delta M/Msun= -0.45 +/- 0.13 dex compared to z < 1.2
if we adopt a fixed slope. We investigate and review various systematics,
ranging from PSF effects, projection effects, systematics related to stellar
mass derivation, selection biases and slope. We find that discrepancies between
the various literature values are reduced when taking these into account. Our
observations correspond well with the gradual evolution predicted by
semi-analytic models.Comment: 21 pages, 14 figures, 1 appendix. Accepted for publication by Apj,
February 28, 201
Dynamics and thermodynamics of axisymmetric flows: I. Theory
We develop new variational principles to study stability and equilibrium of
axisymmetric flows. We show that there is an infinite number of steady state
solutions. We show that these steady states maximize a (non-universal)
-function. We derive relaxation equations which can be used as numerical
algorithm to construct stable stationary solutions of axisymmetric flows. In a
second part, we develop a thermodynamical approach to the equilibrium states at
some fixed coarse-grained scale. We show that the resulting distribution can be
divided in a universal part coming from the conservation of robust invariants
and one non-universal determined by the initial conditions through the fragile
invariants (for freely evolving systems) or by a prior distribution encoding
non-ideal effects such as viscosity, small-scale forcing and dissipation (for
forced systems). Finally, we derive a parameterization of inviscid mixing to
describe the dynamics of the system at the coarse-grained scale
- âŠ