15 research outputs found
IR and UV Galaxies at z=0.6 -- Evolution of Dust Attenuation and Stellar Mass as Revealed by SWIRE and GALEX
We study dust attenuation and stellar mass of star-forming
galaxies using new SWIRE observations in IR and GALEX observations in UV. Two
samples are selected from the SWIRE and GALEX source catalogs in the
SWIRE/GALEX field ELAIS-N1-00 ( deg). The UV selected sample
has 600 galaxies with photometric redshift (hereafter photo-z) and NUV (corresponding to \rm L_{FUV} \geq 10^{9.6} L_\sun).
The IR selected sample contains 430 galaxies with mJy
(\rm L_{dust} \geq 10^{10.8} L_\sun) in the same photo-z range. It is found
that the mean ratios of the z=0.6 UV galaxies are
consistent with that of their z=0 counterparts of the same . For
IR galaxies, the mean ratios of the z=0.6 LIRGs (\rm
L_{dust} \sim 10^{11} L_\sun) are about a factor of 2 lower than local LIRGs,
whereas z=0.6 ULIRGs (\rm L_{dust} \sim 10^{12} L_\sun) have the same mean
ratios as their local counterparts. This is consistent
with the hypothesis that the dominant component of LIRG population has changed
from large, gas rich spirals at z to major-mergers at z=0. The stellar
mass of z=0.6 UV galaxies of \rm L_{FUV} \leq 10^{10.2} L_\sun is about a
factor 2 less than their local counterparts of the same luminosity, indicating
growth of these galaxies. The mass of z=0.6 UV lunmous galaxies (UVLGs: \rm
L_{FUV} > 10^{10.2} L_\sun) and IR selected galaxies, which are nearly
exclusively LIRGs and ULIRGs, is the same as their local counterparts.Comment: 27 pages, 8 figures, to be published in the Astrophysical Journal
Supplement series dedicated to GALEX result
The European Large Area ISO Survey IX: the 90 micron luminosity function from the Final Analysis sample
We present the 90 micron luminosity function of the Final Analysis of the
European Large Area ISO Survey (ELAIS), extending the sample size of our
previous analysis (paper IV) by about a factor of 4. Our sample extends to
z=1.1, around 50 times the comoving volume of paper IV, and 10^{7.7} <
h^{-2}L/Lsun < 10^{12.5}. From our optical spectroscopy campaigns of the
northern ELAIS 90 mircon survey (7.4 deg^2 in total, to S(90um)>70mJy), we
obtained redshifts for 61% of the sample (151 redshifts) to B<21 identified at
7 microns, 15 microns, 20cm or with bright (B<18.5) optical identifications.
The selection function is well-defined, permitting the construction of the 90
micron luminosity function of the Final Analysis catalogue in the ELAIS
northern fields, which is in excellent agreement with our Preliminary Analysis
luminosity function in the ELAIS S1 field from paper IV. The luminosity
function is also in good agreement with the IRAS-based prediction of Serjeant &
Harrison (2004), which if correct requires luminosity evolution of (1+z)^{3.4
+/- 1.0} for consistency with the source counts. This implies an evolution in
comoving volume averaged star formation rate at z<~1 consistent with that
derived from rest-frame optical and ultraviolet surveys.Comment: MNRAS accepted. 7 pages, 5 figures. Uses BoxedEPS (included
Extending PLE models into the mid-IR, far-IR & sub-mm
Simple pure luminosity evolution (PLE) models, in which galaxies brighten at
high redshift due to increased star-formation rates (SFRs), are known to
provide a good fit to the colours and number counts of galaxies throughout the
optical and near-infrared. We show that optically defined PLE models, where
dust reradiates absorbed optical light into infrared spectra composed of local
galaxy templates, fit galaxy counts and colours out to 8um and to at least
z=2.5. At 24-70um, the model is able to reproduce the observed source counts
with reasonable success if 16% of spiral galaxies show an excess in mid-IR flux
due to a warmer dust component and a higher SFR, in line with observations of
local starburst galaxies. There remains an under-prediction of the number of
faint-flux, high-z sources at 24um, so we explore how the evolution may be
altered to correct this. At 160um and longer wavelengths, the model fails, with
our model of normal galaxies accounting for only a few percent of sources in
these bands. However, we show that a PLE model of obscured AGN, which we have
previously shown to give a good fit to observations at 850um, also provides a
reasonable fit to the Herschel/BLAST number counts and redshift distributions
at 250-500um. In the context of a LCDM cosmology, an AGN contribution at
250-870um would remove the need to invoke a top-heavy IMF for high-redshift
starburst galaxies, although the excellent fit of the galaxy PLE model at
shorter wavelengths would still need to be explained.Comment: 14 pages, 11 figures; submitted to MNRA
Galaxy Counts at 24 Microns in the SWIRE Fields
This paper presents galaxy source counts at 24 microns in the six Spitzer
Wide-field InfraRed Extragalactic (SWIRE) fields. The source counts are
compared to counts in other fields, and to model predictions that have been
updated since the launch of Spitzer. This analysis confirms a very steep rise
in the Euclidean-normalized differential number counts between 2 mJy and 0.3
mJy. Variations in the counts between fields show the effects of sample
variance in the flux range 0.5-10 mJy, up to 100% larger than Poisson errors.
Nonetheless, a "shoulder" in the normalized counts persists at around 3 mJy.
The peak of the normalized counts at 0.3 mJy is higher and narrower than most
models predict. In the ELAIS N1 field, the 24 micron data are combined with
Spitzer-IRAC data and five-band optical imaging, and these bandmerged data are
fit with photometric redshift templates. Above 1 mJy the counts are dominated
by galaxies at z less than 0.3. By 300 microJy, about 25% are between z ~
0.3-0.8, and a significant fraction are at z ~ 1.3-2. At low redshifts the
counts are dominated by spirals, and starbursts rise in number density to
outnumber the spirals' contribution to the counts below 1 mJy.Comment: 10 pages, 8 figures, accepted 3 November 2007 for publication in The
Astronomical Journal, formatted with emulateapj styl
Photometric redshifts and luminosity functions from the SWITZER SWIRE survey
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