184 research outputs found
The Evolution of the Visible and Hidden Star Formation in the Universe: Implication from the Luminosity Functions at FUV and FIR
Based on GALEX and IRAS/Spitzer datasets, we have found that both FUV and FIR
luminosity functions (LFs) show a strong evolution from z=0 to z=1, but the FIR
LF evolves much stronger than the FUV one. Consequently, the FIR/FUV luminosity
density ratio increases from 4 (z=0) to 15 (z=1). It means that more than 80%
of the star-forming activity in the Universe is hidden by dust at z=1. To
explore this issue further, we have performed a combined analysis of the galaxy
sample in FUV and FIR. For the Local Universe we used GALEX-IRAS sample,
whereas at z=1 we used the Lyman-break galaxy sample selected by GALEX bands
constructed by Burgarella et al. (2005), which is known to be representative of
visible (i.e., non-obscured) star-forming galaxies at z=1. From these datasets,
we constructed the LFs of the FUV-selected galaxies by the survival analysis
to, take into account the upper-limit data properly. We discovered that the FIR
LF of the Lyman-break galaxies show a significant evolution comparing with the
local FIR LF, but it is a factor of 2-3 lower than the global FIR LF (Le Floc'h
et al. 2005). This indicates that the evolution of visible galaxies is not
strong enough to explain the drastic evolution of the FIR LF. Namely, a
FIR-luminous, rapidly diminishing population of galaxies is required.Comment: 4 pages, 4 figures, conference proceedings of "At the Edge of the
Universe", Sintra 9-13 October 200
The Formation of Galaxies, the Formation of Old Globular Clusters and the Link with High-Redshift Objects
In this paper, we are exploring the properties of old, metal-poor globular
clusters in galaxies. We investigate whether their properties are related to
the properties of their host galaxies, and whether we can constrain their
formation. The main result is that the mean metallicities of old GC systems are
found to lie in a narrow range -1.7 < [Fe/H] < -1.1 (80 % of the population).
Moreover, no correlations are found between the mean metallicities and other
galaxy properties which implies a GC formation independent of the host
galaxies. Further, we try to identify the sites of old, metal-poor GC
formation, with any currently known high redshift objects. We find that the
metalicities of damped Ly systems in the redshift range 1.6 < z < 4 are
consistent with our GC metalicities, which suggests that these high-density
neutral gas objects may be the progenitors of the old, metal-poor globular
clusters.Comment: 7 pages, 6 figures, to appear in A.S.P. Conf. Series "Massive Stellar
Clusters" held in Strasbourg, Nov. 8-10, 1999, eds. A. Lancon et C. Boily.
The files for Figs.2 were wron
Deep 15um AKARI observations in the CDFS: estimating dust luminosities for a MIR-selected sample and for Lyman Break Galaxies and the evolution of L(dust)/L(UV) with the redshift
Deep observations of the CDFS have been secured at 15um with AKARI/IRC
infrared space telescope (ESA open time). From these observations, we define a
sample of MIR-selected galaxies at 15um and we also obtain 15um flux densities
for a sample of LBGs at z=1 already observed at 24um with Spitzer/MIPS. Number
counts for the MIR-selected sample show a bump around a 15um flux density of
0.2mJy that can be attributed to galaxies at z>0.4 and at z>0.8 for the fainter
part of the bump. This bump seems to be shifted as compared to other works and
a possible origin can be the Cosmic variance. Thanks to this dataset, we have
tested, on the two above samples at z=1, the validity of the conversions from
monochromatic luminosities nu.f(nu) at a rest-frame wavelength of 8um by a
comparison with total dust luminosities estimated from Spitzer rest-frame 12um
data that we use as a reference. We find that the 8um dust luminosities are not
all consistent and that some of them are better when compared to L(dust)
evaluated from longer wavelength luminosities. We also find that the rest-frame
8um luminosities provide globally good estimates of L(dust). By comparing our
data for the two samples to several libraries of SEDs, we find that models can
explain the diversity of the observed f(24)/f(15) ratio quite reasonably for
the MIR-selected sample and better for the LBG sample which are less dispersed
than the MIR selection. However, when we analyse the luminosity dependence of
this ratio, we find important discrepancies. Finally, we revisit the evolution
of L(dust)/L(UV) ratio with the redshift z by re-calibrating previous L(dust)
at z=2 based on our results and added new data points at higher redshifts. The
decreasing trend is amplified as compared to the previous estimate.Comment: Paper accepted for publication in PAS
Effects of dust scattering albedo and 2175 A bump on ultraviolet colours of normal disc galaxies
We discuss dust properties in the interstellar medium (ISM) of nearby normal
galaxies, by comparing observations in the ultraviolet (UV) with simulations by
a radiative transfer model. The observed UV colours of nearby galaxies show a
reddening relative to their expected intrinsic colours. Some authors argued
that the Milky Way dust cannot reproduce the reddening because of the prominent
2175 \AA absorption bump. Other authors proposed a reduction mechanism of the
bump strength in an {\it attenuation law} derived from the ratio of the
observed intensity to the intrinsic one through an age-selective attenuation
(i.e., young stars are more attenuated selectively). We newly find that the
wavelength dependence of the scattering albedo also has a strong effect on the
UV colour; an albedo decreasing toward shorter wavelengths (except for the
absorption bump range) produces a significant UV reddening. After comparing the
observed UV colours of nearby normal galaxies with those expected from
radiative transfer simulations assumed several dust models, we find two sorts
of dust suitable for these galaxies: (1) dust with a bump and a smaller albedo
for a shorter wavelength (except for the bump range), and (2) dust without any
bump but with an almost constant albedo. If very small carbonaceous grains
responsible for the common unidentified infrared emission band are also the
bump carrier, the former dust is favorable. Finally, we derive mean attenuation
laws of various dust models as a function of the UV attenuation, and derive
some relations between the UV attenuation and observable/theoretical
quantities.Comment: MNRAS in pres
CIGALEMC: Galaxy Parameter Estimation using a Markov Chain Monte Carlo Approach with Cigale
We introduce a fast Markov Chain Monte Carlo (MCMC) exploration of the
astrophysical parameter space using a modified version of the publicly
available code CIGALE (Code Investigating GALaxy emission). The original CIGALE
builds a grid of theoretical Spectral Energy Distribution (SED) models and fits
to photometric fluxes from Ultraviolet (UV) to Infrared (IR) to put contraints
on parameters related to both formation and evolution of galaxies. Such a
grid-based method can lead to a long and challenging parameter extraction since
the computation time increases exponentially with the number of parameters
considered and results can be dependent on the density of sampling points,
which must be chosen in advance for each parameter. Markov Chain Monte Carlo
methods, on the other hand, scale approximately linearly with the number of
parameters, allowing a faster and more accurate exploration of the parameter
space by using a smaller number of efficiently chosen samples. We test our MCMC
version of the code CIGALE (called CIGALEMC) with simulated data. After
checking the ability of the code to retrieve the input parameters used to build
the mock sample, we fit theoretical SEDs to real data from the well known and
studied SINGS sample. We discuss constraints on the parameters and show the
advantages of our MCMC sampling method in terms of accuracy of the results and
optimization of CPU time.Comment: 12 pages, 8 figures, 4 tables, updated to match the version accepted
for publication in ApJ; code available at http://www.oamp.fr/cigale
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