981 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
HerMES: Lyman Break Galaxies Individually Detected at 0.7 †z †2.0 in GOODS-N with Herschel/SPIRE
As part of the Herschel Multi-tiered Extragalactic Survey we have investigated the rest-frame far-infrared (FIR) properties of a sample of more than 4800 Lyman break galaxies (LBGs) in the Great Observatories Origins Deep Survey North field. Most LBGs are not detected individually, but we do detect a sub-sample of 12 objects at 0.7 2.5. The UV-to-FIR spectral energy distributions of the objects detected in the rest-frame FIR are investigated using the code CIGALE to estimate physical parameters. We find that LBGs detected by SPIRE are high-mass, luminous infrared galaxies. It appears that LBGs are located in a triangle-shaped region in the A_(FUV) versus log L_(FUV) = 0 diagram limited by A_(FUV) = 0 at the bottom and by a diagonal following the temporal evolution of the most massive galaxies from the bottom right to the top left of the diagram. This upper envelop can be used as upper limits for the UV dust attenuation as a function of L_(FUV). The limits of this region are well explained using a closed-box model, where the chemical evolution of galaxies produces metals, which in turn lead to higher dust attenuation when the galaxies age
Star Formation and Dust Extinction Properties of Local Galaxies as seen from AKARI and GALEX
An accurate estimation of the star formation-related properties of galaxies
is crucial for understanding the evolution of galaxies. In galaxies,
ultraviolet (UV) light emitted by recently formed massive stars is attenuated
by dust, which is also produced by star formation (SF) activity, and is
reemitted at mid- and far- infrared (IR) wavelengths. In this study, we
investigate the star formation rate (SFR) and dust extinction using UV and IR
data. We selected local galaxies which are detected at AKARI FIS 90 um and
matched the IRAS IIFSCz 60 um select catalog. We measured FUV and NUV flux
densities from GALEX images. We examined the SF and extinction of Local
galaxies using four bands of AKARI. Then, we calculated FUV and total IR
luminosities, and obtained the SF luminosity, L_{SF}, the total luminosity
related to star formation activity, and the SFR. We find that in most galaxies,
L_{SF} is dominated by L_{dust}. We also find that galaxies with higher SF
activity have a higher fraction of their SF hidden by dust. In fact, the SF of
galaxies with SFRs >20 M_{sun}/yr is almost completely hidden by dust. Our
results boast a significantly higher precision with respect to previously
published works, due to the use of much larger object samples from the AKARI
and GALEX all sky surveys.Comment: 9 pages, 12 figures, accepted for publication in Earth, Planets, and
Space, A few minor corrections, and a reference adde
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