We study the ultraviolet to far-infrared (hereafter UV-to-IR) SEDs of a sample of intermediate-redshift (0.2 less than or equal to z < 0.7) UV-selected galaxies from the ELAIS N1 and ELAIS N2 fields ...by fitting a multi-wavelength data set to a library of GRASIL templates. Star formation related properties of the galaxies are derived from the library of models by using Bayesian statistics. We find a decreasing presence of galaxies with low attenuation and low total luminosity as redshift decreases, which does not hold for high total luminosity galaxies. In addition, the dust attenuation of low-mass galaxies increases as redshift decreases, and this trend seems to disappear for galaxies with unk greater than or equal to 10 super(11) M unk. This result is consistent with a mass-dependent evolution of the dust-to-gas ratio, which could be driven by a mass-dependent efficiency of star formation in star-forming galaxies. The specific star formation rates (SSFR) decrease with increasing stellar mass at all redshifts, and for a given stellar mass the SSFR decreases with decreasing redshift. The differences in the slope of the M*-SSFR relation found between this work and others at similar redshift could be explained by the adopted selection criteria of the samples, which for a UV-selected sample, favors blue, star-forming galaxies.
The shell game: a panoramic view of Fornax Bate, N. F; McMonigal, B; Lewis, G. F ...
Monthly notices of the Royal Astronomical Society,
10/2015, Letnik:
453, Številka:
1
Journal Article
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We present a panoramic study of the Fornax dwarf spheroidal galaxy, using data obtained as part of the VLT Survey Telescope (VST) ATLAS Survey. The data presented here – a subset of the full survey – ...uniformly cover a region of 25 deg2 centred on the galaxy, in g, r and i bands. This large area coverage reveals two key differences to previous studies of Fornax. First, data extending beyond the nominal tidal radius of the dwarf highlight the presence of a second distinct red giant branch population. This bluer red giant branch appears to be co-eval with the horizontal branch population. Secondly, a shell structure located approximately 1
$_{.}^{\circ}$
4 from the centre of Fornax is shown to be a mis-identified background overdensity of galaxies. This last result casts further doubt on the hypothesis that Fornax underwent a gas-rich merger in its relatively recent past.
The new multi-epoch near-infrared VISTA Variables in the Via Lactea (VVV) survey is sampling 562 deg super(2) of the Galactic bulge and adjacent regions of the disk. Accurate astrometry established ...for the region surveyed allows the VVV data to be merged with overlapping surveys (e.g., GLIMPSE, WISE, 2MASS, etc.), thereby enabling the construction of longer baseline spectral energy distributions for astronomical targets. However, in order to maximize use of the VVV data, a set of transformation equations are required to place the VVV JHK sub(S) photometry onto the 2MASS system. The impetus for this work is to develop those transformations via a comparison of 2MASS targets in 152 WV fields sampling the Galactic disk. The transformation coefficients derived exhibit a reliance on variables such as extinction. The transformed data were subsequently employed to establish a mean reddening law of E sub(J-H)/E sub(H-Ks) = 2.13 + or - 0.04, which is the most precise determination to date and merely emphasizes the pertinence of the VVV data for determining such important parameters.
We construct rest-frame luminosity functions (LFs) at 3.6, 4.5, 5.8, 8 and 24 μm over the redshift range 0 < z < 2 for galaxies and 0 < z < 4 for optical quasi-stellar objects (QSOs), using optical ...and infrared (IR) data from the Spitzer Wide-area Infrared Extragalactic (SWIRE) Survey. The 3.6- and 4.5-μm galaxy LFs show evidence for moderate positive luminosity evolution up to z∼ 1.5, consistent with the passive ageing of evolved stellar populations. Their comoving luminosity density was found to evolve passively, gradually increasing out to z∼ 0.5-1 but flattening, or even declining, at higher redshift. Conversely, the 24-μm galaxy LF, which is more sensitive to obscured star formation and/or active galactic nuclei (AGN) activity, undergoes strong positive evolution, with the derived IR energy density and star formation rate (SFR) density ∝ (1 +z)γ with γ= 4.5+0.7
−0.6 and the majority of this evolution occurring since z∼ 1. Optical QSOs, however, show positive luminosity evolution in all bands, out to the highest redshifts (3 < z < 4). Modelling as L*∝ (1 +z)γ gave γ= 1.3+0.1
−0.1 at 3.6 μm, γ= 1.0+0.1
−0.1 at 4.5 μm and stronger evolution at the longer wavelengths (5.8, 8 and 24 μm), of γ∼ 3. Comparison of the galaxy LFs to predictions from a semi-analytic model based on cold dark matter (CDM) indicates that an initial mass function (IMF) skewed towards higher mass star formation in bursts compared to locally be preferred. As a result, the currently inferred massive SFRs in distant submm sources may require substantial downwards revision.
ABSTRACT
We report the discovery of a bright (
f
(250 μm)>400 mJy),
multiply lensed submillimeter galaxy HERMES J105751.1+573027 in
Herschel
/SPIRE Science Demonstration Phase data from the
HerMES ...project. Interferometric 880 μm Submillimeter Array observations resolve
at least four images with a large separation of ∼9″. A high-resolution adaptive
optics
K
p
image with Keck/NIRC2 clearly shows strong
lensing arcs. Follow-up spectroscopy gives a redshift of
z
=
2.9575, and the lensing model gives a total magnification of μ ∼ 11 ± 1. The
large image separation allows us to study the multi-wavelength spectral energy
distribution (SED) of the lensed source unobscured by the central lensing mass.
The far-IR/millimeter-wave SED is well described by a modified blackbody fit
with an unusually warm dust temperature, 88 ± 3 K. We derive a lensing-corrected
total IR luminosity of (1.43 ± 0.09) ×
10
13
L
☉
, implying a star formation
rate of ∼2500
M
☉
yr
−1
. However, models
primarily developed from brighter galaxies selected at longer wavelengths are a
poor fit to the full optical-to-millimeter SED. A number of other strongly
lensed systems have already been discovered in early
Herschel
data, and many more are expected as additional data are collected.
We present a mid-infrared (MIR) analysis of 35 quasars with spectroscopic redshifts selected from the Spitzer Wide-Area Infrared Extragalactic Survey (SWIRE). We discuss their optical and MIR colors ...and show that these quasars occupy well-defined regions in MIR color-color space. We examine the issue of type 1 active galactic nuclei candidate selection in detail and propose new selection methods based on MIR colors. The available multiband data allow us to construct two new, well-sampled quasar templates, covering wavelengths from the ultraviolet to the MIR.
We have carried out two extremely deep surveys with SPIRE, one of the two cameras on Herschel, at 250 μm, close to the peak of the far-infrared background. We have used the results to investigate the ...evolution of the rest-frame 250-μm luminosity function out to z = 2. We find evidence for strong evolution out to z $\simeq$ 1 but evidence for at most weak evolution beyond this redshift. Our results suggest that a significant part of the stars and metals in the universe today were formed at z $\preceq$ 1.4 in spiral galaxies.
We present the initial results from our search for high-redshift, z≳ 6, quasars using near-infrared (near-IR) data from the UKIRT Infrared Deep Sky Survey Large Area Survey. Our analysis of 106 deg2 ...of sky from Data Release 1 has resulted in the discovery of ULAS J020332.38+001229.2, a luminous (JAB= 20.0, JVega= 19.1, M1450=−26.2) quasar at z= 5.86. Following candidate selection from the combined IR and optical catalogue data and stacking of multiple epoch Sloan Digital Sky Survey (SDSS) data, we have obtained optical spectroscopy for the only two z≳ 6 quasar candidates. The Very Large Telescope FORS2 spectrum of ULAS J020332.38+001229.2 shows broad Lyα+ N v 1240 emission at ∼8350 Å and an abrupt continuum break due to absorption by the Lyα forest. The quasar is not present in the SDSS DR5 catalogue and the continuum spectral index of α=−1.4 (Fν∝να) is redder than a composite of SDSS quasars at similar redshifts (α=−0.5). The discovery of one z∼ 6 quasar in ∼100 deg2 in a complete sample within our selection criteria down to a median depth of YAB= 20.4 (7σ) is consistent with existing SDSS results. We describe our survey methodology, including the use of optical data from the SDSS and the highly effective procedures developed to isolate the very small surface density of high-probability quasar candidates.
We examine the rest-frame far-infrared emission from powerful radio sources with 1.4-GHz luminosity densities of 25 ≤ log(L
1.4/W Hz−1) ≤ 26.5 in the extragalactic Spitzer First Look Survey field. We ...combine Herschel/SPIRE flux densities with Spitzer/Infrared Array Camera and Multiband Imaging Photometer for Spitzer infrared data to obtain total (
m) infrared luminosities for these radio sources. We separate our sources into a moderate, 0.4 < z < 0.9, and a high, 1.2 < z < 3.0, redshift sub-sample and we use Spitzer observations of a z < 0.1 3CRR sample as a local comparison. By comparison to numbers from the Square Kilometre Array (SKA) Simulated Skies, we find that our moderate-redshift sample is complete and our high-redshift sample is 14 per cent complete. We constrain the ranges of mean star formation rates (SFRs) to be 3.4-4.2, 18-41 and 80-581 M⊙ yr−1 for the local, moderate- and high-redshift samples, respectively. Hence, we observe an increase in the mean SFR with increasing redshift which we can parametrize as ∼(1 + z)
Q
, where Q = 4.2 ± 0.8. However, we observe no trends of mean SFR with radio luminosity within the moderate- or high-redshift bins. We estimate that radio-loud active galactic nuclei (AGN) in the high-redshift sample contribute 0.1-0.5 per cent to the total SFR density at that epoch. Hence, if all luminous starbursts host radio-loud AGN we infer a radio-loud phase duty cycle of 0.001-0.005.
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