1,428 research outputs found
FIREWORKS U38-to-24 micron photometry of the GOODS-CDFS: multi-wavelength catalog and total IR properties of distant Ks-selected galaxies
We present a Ks-selected catalog, dubbed FIREWORKS, for the Chandra Deep
Field South (CDFS) containing photometry in U_38, B_435, B, V, V_606, R, i_775,
I, z_850, J, H, Ks, [3.6 um], [4.5 um], [5.8 um], [8.0 um], and the MIPS [24
um] band. The imaging has a typical Ks limit of 24.3 mag (5 sigma, AB) and
coverage over 113 arcmin^2 in all bands and 138 arcmin^2 in all bands but H. We
cross-correlate our catalog with the 1 Ms X-ray catalog by Giacconi et al.
(2002) and with all available spectroscopic redshifts to date. We find and
explain systematic differences in a comparison with the 'z_850 + Ks'-selected
GOODS-MUSIC catalog that covers ~90% of the field. We exploit the U38-to-24
micron photometry to determine which Ks-selected galaxies at 1.5<z<2.5 have the
brightest total IR luminosities and which galaxies contribute most to the
integrated total IR emission. The answer to both questions is that red galaxies
are dominating in the IR. This is true no matter whether color is defined in
the rest-frame UV, optical, or optical-to-NIR. We do find however that among
the reddest galaxies in the rest-frame optical, there is a population of
sources with only little mid-IR emission, suggesting a quiescent nature.Comment: Accepted for publication in the Astrophysical Journal, 20 pages, 10
figures, reference to website correcte
Rest-Frame Optical Emission Lines in z~3.5 Lyman Break selected Galaxies: The Ubiquity of Unusually High [OIII]/Hbeta Ratios at 2 Gyr
We present K-band spectra of rest-frame optical emission lines for 24
star-forming galaxies at z~3.2-3.7 using MOSFIRE on the Keck 1 telescope.
Strong rest-frame optical [O III] and Hbeta emission lines were detected in 18
LBGs. The median flux ratio of [O III]5007 to Hbeta is 5.1+/-0.5, a factor of
5-10x higher than in local galaxies with similar stellar masses. The observed
Hbeta luminosities are in good agreement with expectations from the estimated
star-formation rates, and none of our sources are detected in deep X-ray
stacks, ruling out significant contamination by active galactic nuclei.
Combining our sample with a variety of LBGs from the literature, including 49
galaxies selected in a very similar manner, we find a high median ratio of
[OIII]/Hbeta = 4.8+0.8-1.7. This high ratio seems to be an ubiquitous feature
of z~3-4 LBGs, very different from typical local star-forming galaxies at
similar stellar masses. The only comparable systems at z~0 are those with
similarly high specific star-formation rates, though ~5x lower stellar masses.
High specific star-formation rates either result in a much higher ionization
parameter or other unusual conditions for the interstellar medium, which result
in a much higher [OIII]/Hbeta line ratio. This implies a strong relation
between a global property of a galaxy, the specific star-formation rate, and
the local conditions of ISM in star-forming regions.Comment: 14 pages, 8 figures, 5 color, published in ApJ, updated to reflect
published versio
A Rest-frame Optical View on z~4 Galaxies I: Color and Age Distributions from Deep IRAC Photometry of the IUDF10 and GOODS Surveys
We present a study of rest-frame UV-to-optical color distributions for z~4
galaxies based on the combination of deep HST/ACS+WFC3/IR data with
Spitzer/IRAC imaging. In particular, we use new, ultra-deep data from the IRAC
Ultradeep Field program (IUDF10). Our sample contains a total of ~2600 galaxies
selected as B-dropout Lyman Break Galaxies (LBGs) in the HUDF and one of its
deep parallel fields, the HUDF09-2, as well as GOODS-North and South. This
sample is used to investigate the UV continuum slopes beta and Balmer break
colors (J_125-[4.5]) as a function of rest-frame optical luminosity. The [4.5]
filter is chosen to avoid potential contamination by strong rest-frame optical
emission lines. We find that galaxies at M_z<-21.5 (roughly corresponding to
L*[z~4]) are significantly redder than their lower luminosity counterparts. The
UV continuum slopes and the J_125-[4.5] colors are well correlated. The most
simple explanation for this correlation is that the dust reddening at these
redshifts is better described by an SMC-like extinction curve, rather than the
typically assumed Calzetti reddening. After correcting for dust, we find that
the galaxy population shows mean stellar population ages in the range 10^8.5 to
10^9 yr, with a dispersion of ~0.5 dex, and only weak trends as a function of
luminosity. In contrast to some results from the literature, we find that only
a small fraction of galaxies shows Balmer break colors which are consistent
with extremely young ages, younger than 100 Myr. Under the assumption of smooth
star-formation histories, this fraction is only 12-19% for galaxies at
M_z<-19.75. Our results are consistent with a gradual build-up of stars and
dust in galaxies at z>4, with only a small fraction of stars being formed in
short, intense bursts of star-formation.Comment: 11 pages, 10 figures; submitted to Ap
ZFIRE: Using H equivalent widths to investigate the in situ initial mass function at z~2
We use the ZFIRE survey (http://zfire.swinburne.edu.au) to investigate the
high mass slope of the initial mass function (IMF) for a mass-complete
(log10(M/M)~9.3) sample of 102 star-forming galaxies at z~2 using
their H equivalent widths (H-EW) and rest-frame optical
colours. We compare dust-corrected H-EW distributions with predictions
of star-formation histories (SFH) from PEGASE.2 and Starburst99 synthetic
stellar population models. We find an excess of high H-EW galaxies that
are up to 0.3--0.5 dex above the model-predicted Salpeter IMF locus and the
H-EW distribution is much broader (10--500 \AA) than can easily be
explained by a simple monotonic SFH with a standard Salpeter-slope IMF. Though
this discrepancy is somewhat alleviated when it is assumed that there is no
relative attenuation difference between stars and nebular lines, the result is
robust against observational biases, and no single IMF (i.e. non-Salpeter
slope) can reproduce the data. We show using both spectral stacking and Monte
Carlo simulations that starbursts cannot explain the EW distribution. We
investigate other physical mechanisms including models with variations in
stellar rotation, binary star evolution, metallicity, and the IMF upper-mass
cutoff. IMF variations and/or highly rotating extreme metal poor stars
(Z~0.1Z) with binary interactions are the most plausible explanations
for our data. If the IMF varies, then the highest H-EWs would require
very shallow slopes (>-1.0) with no one slope able to reproduce the
data. Thus, the IMF would have to vary stochastically. We conclude that the
stellar populations at z~2 show distinct differences from local populations and
there is no simple physical model to explain the large variation in
H-EWs at z~2.Comment: Accepted to MNRAS. 43 pages, 27 Figures. Survey website:
http://zfire.swinburne.edu.au
Investigation of the potential effects of transportation and lairage on the contamination of pig carcasses with Yersinia enterocolitica
Pathogenic Yersinia enterocolitica is frequently isolated from pig tonsils, but can also be found in the feces and lymph nodes of infected animals; which represent potential sources for the surface carcass contamination during slaughter. The aim of the study was to investigate the respective effects of the transportation and lairage steps on the overall contamination of the carcass, taking also into account the contamination of their environment. Each Trial was conducted in two abattoirs, whose environmental contamination was assessed. In each abattoir, 6 trucks and 6 lairage pens were sampled in duplicate at the end of the day, for 5 consecutive days, in spring and autumn. Four groups of 8 pigs from the Anses Specific Pathogen-Free herd (SPF) were mixed with conventional pigs for different contact times during transportation (1h) or lairage (2, 4 or 8h) prior to slaughter, and one group had no contact with other pigs. Each group of SPF pigs was sampled at the end of the slaughter line for the presence of pathogenic Y. enterocolitica for internal (tonsils, caecal content, mesenteric lymph nodes) and external (carcass surface) contamination. Samples were placed in ITC broth for enrichment at 25°C for 48h. Broth was streaked on CIN plates. After 24H at 30°C, typical colonies were streaked on YeCM plates. Biochemical tests were done to confirm Y. enterocolitica and to identify the biotype. The environmental contamination of trucks and lairage was very low. Y. enterocolitica was only detected in 11/240 lairage swabs. All internal and external samples from SPF pigs mixed with conventional pigs during transportation or lairage were negative after slaughter. Four tonsils of the SPF pigs slaughtered directly on the slaughter line after 4 hours of activity, with no prior contact with conventional pigs, and one of the corresponding surface carcasses, were found positive in one abattoir. In our experimental conditions with SPF pigs, we were not able to demonstrate contamination by contact with conventional pigs during transportation and lairage steps, whose environmental contamination appeared to be scarce. Limited cross contaminations were observed during the slaughter process, which emphasizes the importance of good hygiene procedures to limit carcass contamination by pathogenic Y. enterocolitica
The Evolution of the Field and Cluster Morphology-Density Relation for Mass-Selected Samples of Galaxies
The Sloan Digital Sky Survey (SDSS) and photometric/spectroscopic surveys in
the GOODS-South field (the Chandra Deep Field-South, CDFS) are used to
construct volume-limited, stellar mass-selected samples of galaxies at
redshifts 0<z<1. The CDFS sample at 0.6<z<1.0 contains 207 galaxies complete
down to M=4x10^10 Msol (for a ``diet'' Salpeter IMF), corresponding to a
luminosity limit for red galaxies of M_B=-20.1. The SDSS sample at
0.020<z<0.045 contains 2003 galaxies down to the same mass limit, which
corresponds to M_B=-19.3 for red galaxies. Morphologies are determined with an
automated method, using the Sersic parameter n and a measure of the residual
from the model fits, called ``bumpiness'', to distinguish different
morphologies. These classifications are verified with visual classifications.
In agreement with previous studies, 65-70% of the galaxies are located on the
red sequence, both at z~0.03 and at z~0.8. Similarly, 65-70% of the galaxies
have n>2.5. The fraction of E+S0 galaxies is 43+/-3%$ at z~0.03 and 48+/-7% at
z~0.8, i.e., it has not changed significantly since z~0.8. When combined with
recent results for cluster galaxies in the same redshift range, we find that
the morphology-density relation for galaxies more massive than 0.5M* has
remained constant since at least z~0.8. This implies that galaxies evolve in
mass, morphology and density such that the morphology-density relation does not
change. In particular, the decline of star formation activity and the
accompanying increase in the stellar mass density of red galaxies since z~1
must happen without large changes in the early-type galaxy fraction in a given
environment.Comment: 16 pages, 13 figures, 2 tables. Updated to match journal version.
Will appear in ApJ (vol. 670, p. 206
A Spectroscopic Redshift Measurement for a Luminous Lyman Break Galaxy at z=7.730 using Keck/MOSFIRE
We present a spectroscopic redshift measurement of a very bright Lyman break
galaxy at z=7.7302+-0.0006 using Keck/MOSFIRE. The source was pre-selected
photometrically in the EGS field as a robust z~8 candidate with H=25.0 mag
based on optical non-detections and a very red Spitzer/IRAC [3.6]-[4.5]
broad-band color driven by high equivalent width [OIII]+Hbeta line emission.
The Lyalpha line is reliably detected at 6.1 sigma and shows an asymmetric
profile as expected for a galaxy embedded in a relatively neutral
inter-galactic medium near the Planck peak of cosmic reionization. The line has
a rest-frame equivalent width of EW0=21+-4 A and is extended with
V_FWHM=360+90-70 km/s. The source is perhaps the brightest and most massive z~8
Lyman break galaxy in the full CANDELS and BoRG/HIPPIES surveys, having
assembled already 10^(9.9+-0.2) M_sol of stars at only 650 Myr after the Big
Bang. The spectroscopic redshift measurement sets a new redshift record for
galaxies. This enables reliable constraints on the stellar mass, star-formation
rate, formation epoch, as well as combined [OIII]+Hbeta line equivalent widths.
The redshift confirms that the IRAC [4.5] photometry is very likely dominated
by line emission with EW0(OIII+Hbeta)= 720-150+180 A. This detection thus adds
to the evidence that extreme rest-frame optical emission lines are a ubiquitous
feature of early galaxies promising very efficient spectroscopic follow-up in
the future with infrared spectroscopy using JWST and, later, ELTs.Comment: 6 pages, 4 figures, small updates to match ApJL accepted versio
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