376 research outputs found
Shocked Molecular Hydrogen in the 3C 326 Radio Galaxy System
The Spitzer spectrum of the giant FR II radio galaxy 3C 326 is dominated by
very strong molecular hydrogen emission lines on a faint IR continuum. The H2
emission originates in the northern component of a double-galaxy system
associated with 3C 326. The integrated luminosity in H2 pure-rotational lines
is 8.0E41 erg/s, which corresponds to 17% of the 8-70 micron luminosity of the
galaxy. A wide range of temperatures (125-1000 K) is measured from the H2 0-0
S(0)-S(7) transitions, leading to a warm H2 mass of 1.1E9 Msun. Low-excitation
ionic forbidden emission lines are consistent with an optical LINER
classification for the active nucleus, which is not luminous enough to power
the observed H2 emission. The H2 could be shock-heated by the radio jets, but
there is no direct indication of this. More likely, the H2 is shock-heated in a
tidal accretion flow induced by interaction with the southern companion galaxy.
The latter scenario is supported by an irregular morphology, tidal bridge, and
possible tidal tail imaged with IRAC at 3-9 micron. Unlike ULIRGs, which in
some cases exhibit H2 line luminosities of comparable strength, 3C 326 shows
little star-formation activity (~0.1 Msun/yr). This may represent an important
stage in galaxy evolution. Starburst activity and efficient accretion onto the
central supermassive black hole may be delayed until the shock-heated H2 can
kinematically settle and coolComment: 27 pages, 7 figures, accepted for publication in the Astrophysical
Journa
The Canada-UK Deep Submillimetre Survey: First Submillimetre Images, the Source Counts, and Resolution of the Background
We present the first results of a deep unbiased submillimetre survey carried
out at 450 and 850 microns. We detected 12 sources at 850 microns, giving a
surface density of sources with 850-micron flux densities > 2.8mJy of of
0.49+-0.16 per square arcmin. The sources constitute 20-30% of the background
radiation at 850 microns and thus a significant fraction of the entire
background radiation produced by stars. This implies, through the connection
between metallicity and background radiation, that a significant fraction of
all the stars that have ever been formed were formed in objects like those
detected here. The combination of their large contribution to the background
radiation and their extreme bolometric luminosities make these objects
excellent candidates for being proto-ellipticals. Optical astronomers have
recently shown that the UV-luminosity density of the universe increases by a
factor of about 10 between z=0 and z=1 and then decreases again at higher
redshifts. Using the results of a parallel submillimetre survey of the local
universe, we show that both the submillimetre source density and background can
be explained if the submillimetre luminosity density evolves in a similar way
to the UV-luminosity density. Thus, if these sources are ellipticals in the
process of formation, they may be forming at relatively modest redshifts.Comment: 8 pages (LATEX), 6 postscript figures, submitted to ApJ Letter
The Canada-UK Deep Submillimetre Survey: The Survey of the 14-hour field
We have used SCUBA to survey an area of 50 square arcmin, detecting 19
sources down to a 3sigma sensitivity limit of 3.5 mJy at 850 microns. We have
used Monte-Carlo simulations to assess the effect of source confusion and noise
on the SCUBA fluxes and positions, finding that the fluxes of sources in the
SCUBA surveys are significantly biased upwards and that the fraction of the 850
micron background that has been resolved by SCUBA has been overestimated. The
radio/submillmetre flux ratios imply that the dust in these galaxies is being
heated by young stars rather than AGN. We have used simple evolution models
based on our parallel SCUBA survey of the local universe to address the major
questions about the SCUBA sources: (1) what fraction of the star formation at
high redshift is hidden by dust? (2) Does the submillimetre luminosity density
reach a maximum at some redshift? (3) If the SCUBA sources are
proto-ellipticals, when exactly did ellipticals form? However, we show that the
observations are not yet good enough for definitive answers to these questions.
There are, for example, acceptable models in which 10 times as much
high-redshift star formation is hidden by dust as is seen at optical
wavelengths, but also acceptable ones in which the amount of hidden star
formation is less than that seen optically. There are acceptable models in
which very little star formation occurred before a redshift of three (as might
be expected in models of hierarchical galaxy formation), but also ones in which
30% of the stars have formed by this redshift. The key to answering these
questions are measurements of the dust temperatures and redshifts of the SCUBA
sources.Comment: 41 pages (latex), 17 postscript figures, to appear in the November
issue of the Astronomical Journa
The Redshift One LDSS-3 Emission line Survey (ROLES) II: Survey method and z~1 mass-dependent star-formation rate density
Motivated by suggestions of 'cosmic downsizing', in which the dominant
contribution to the cosmic star formation rate density (SFRD) proceeds from
higher to lower mass galaxies with increasing cosmic time, we describe the
design and implementation of the Redshift One LDSS3 Emission line Survey
(ROLES). ROLES is a K-selected (22.5 < K_AB < 24.0) survey for dwarf galaxies
[8.5<log(M*/Msun)< 9.5] at 0.89 < z < 1.15 drawn from two extremely deep fields
(GOODS-S and MS1054-FIRES). Using the [OII]3727 emission line, we obtain
redshifts and star-formation rates (SFRs) for star-forming galaxies down to a
limit of ~0.3 Msun/yr. We present the [OII] luminosity function measured in
ROLES and find a faint end slope of alpha_faint ~ -1.5, similar to that
measured at z~0.1 in the SDSS. By combining ROLES with higher mass surveys, we
measure the SFRD as a function of stellar mass using [OII] (with and without
various empirical corrections), and using SED-fitting to obtain the SFR from
the rest-frame UV luminosity for galaxies with spectroscopic redshifts. Our
best estimate of the corrected [OII]-SFRD and UV SFRD both independently show
that the SFRD evolves equally for galaxies of all masses between z~1 and z~0.1.
The exact evolution in normalisation depends on the indicator used, with the
[OII]-based estimate showing a change of a factor of ~2.6 and the UV-based a
factor of ~6. We discuss possible reasons for the discrepancy in normalisation
between the indicators, but note that the magnitude of this uncertainty is
comparable to the discrepancy between indicators seen in other z~1 works. Our
result that the shape of the SFRD as a function of stellar mass (and hence the
mass range of galaxies dominating the SFRD) does not evolve between z~1 and
z~0.1 is robust to the choice of indicator. [abridged]Comment: Resubmitted to MNRAS following first referee report. 20 pages, 16
figures. High resolution version available at
http://astro.uwaterloo.ca/~dgilbank/papers/roles2.pd
THE fmos-cosmos survey of star-forming galaxies at Z 1.6. II. The mass-metallicity relation and the dependence on star formation rate and dust extinction
We investigate the relationships between stellar mass, gas-phase oxygen abundance (metallicity), star formation rate (SFR), and dust content of star-forming galaxies at z 1.6 using Subaru/FMOS spectroscopy in the COSMOS field. The mass-metallicity (MZ) relation at z 1.6 is steeper than the relation observed in the local universe. The steeper MZ relation at z 1.6 is mainly due to evolution in the stellar mass where the MZ relation begins to turnover and flatten. This turnover mass is 1.2 dex larger at z 1.6. The most massive galaxies at z 1.6 (1011 M) are enriched to the level observed in massive galaxies in the local universe. The MZ relation we measure at z 1.6 supports the suggestion of an empirical upper metallicity limit that does not significantly evolve with redshift. We find an anti-correlation between metallicity and SFR for galaxies at a fixed stellar mass at z 1.6, which is similar to trends observed in the local universe. We do not find a relation between stellar mass, metallicity, and SFR that is independent of redshift; rather, our data suggest that there is redshift evolution in this relation. We examine the relation between stellar mass, metallicity, and dust extinction, and find that at a fixed stellar mass, dustier galaxies tend to be more metal rich. From examination of the stellar masses, metallicities, SFRs, and dust extinctions, we conclude that stellar mass is most closely related to dust extinction
A One Health investigation of Salmonella enterica serovar Wangata in north-eastern New South Wales, Australia, 2016-2017
Salmonella enterica serovar Wangata (S. Wangata) is an important cause of endemic salmonellosis in Australia, with human infections occurring from undefined sources. This investigation sought to examine possible environmental and zoonotic sources for human infections with S. Wangata in north-eastern New South Wales (NSW), Australia. The investigation adopted a One Health approach and was comprised of three complimentary components: a case–control study examining human risk factors; environmental and animal sampling; and genomic analysis of human, animal and environmental isolates. Forty-eight human S. Wangata cases were interviewed during a 6-month period from November 2016 to April 2017, together with 55 Salmonella Typhimurium (S. Typhimurium) controls and 130 neighbourhood controls. Indirect contact with bats/flying foxes (S. Typhimurium controls (adjusted odds ratio (aOR) 2.63, 95% confidence interval (CI) 1.06–6.48)) (neighbourhood controls (aOR 8.33, 95% CI 2.58–26.83)), wild frogs (aOR 3.65, 95% CI 1.32–10.07) and wild birds (aOR 6.93, 95% CI 2.29–21.00) were statistically associated with illness in multivariable analyses. S. Wangata was detected in dog faeces, wildlife scats and a compost specimen collected from the outdoor environments of cases’ residences. In addition, S. Wangata was detected in the faeces of wild birds and sea turtles in the investigation area. Genomic analysis revealed that S. Wangata isolates were relatively clonal. Our findings suggest that S. Wangata is present in the environment and may have a reservoir in wildlife populations in north-eastern NSW. Further investigation is required to better understand the occurrence of Salmonella in wildlife groups and to identify possible transmission pathways for human infections.Whole genome sequencing for this project was supported by the NSW Public Health Pathogen Genomics Consortium,
CIDM-PH, NSW Health
X-ray properties of radio-selected star forming galaxies in the Chandra-COSMOS survey
X-ray surveys contain sizable numbers of star forming galaxies, beyond the
AGN which usually make the majority of detections. Many methods to separate the
two populations are used in the literature, based on X-ray and multiwavelength
properties. We aim at a detailed test of the classification schemes and to
study the X-ray properties of the resulting samples. We build on a sample of
galaxies selected at 1.4 GHz in the VLA-COSMOS survey, classified by Smolcic et
al. (2008) according to their optical colours and observed with Chandra. A
similarly selected control sample of AGN is also used for comparison. We review
some X-ray based classification criteria and check how they affect the sample
composition. The efficiency of the classification scheme devised by Smolcic et
al. (2008) is such that ~30% of composite/misclassified objects are expected
because of the higher X-ray brightness of AGN with respect to galaxies. The
latter fraction is actually 50% in the X-ray detected sources, while it is
expected to be much lower among X-ray undetected sources. Indeed, the analysis
of the stacked spectrum of undetected sources shows, consistently, strongly
different properties between the AGN and galaxy samples. X-ray based selection
criteria are then used to refine both samples. The radio/X-ray luminosity
correlation for star forming galaxies is found to hold with the same
X-ray/radio ratio valid for nearby galaxies. Some evolution of the ratio may be
possible for sources at high redshift or high luminosity, tough it is likely
explained by a bias arising from the radio selection. Finally, we discuss the
X-ray number counts of star forming galaxies from the VLA- and C-COSMOS surveys
according to different selection criteria, and compare them to the similar
determination from the Chandra Deep Fields. The classification scheme proposed
here may find application in future works and surveys.Comment: 15 pages, 7 figures, 3 table
Spitzer Reveals Hidden Quasar Nuclei in Some Powerful FR II Radio Galaxies
We present a Spitzer mid-infrared survey of 42 Fanaroff-Riley class II radio
galaxies and quasars from the 3CRR catalog at redshift z<1. All of the quasars
and 45+/-12% of the narrow-line radio galaxies have a mid-IR luminosity of
nuLnu(15 micron) > 8E43 erg/s, indicating strong thermal emission from hot dust
in the active galactic nucleus. Our results demonstrate the power of Spitzer to
unveil dust-obscured quasars. The ratio of mid-IR luminous narrow-line radio
galaxies to quasars indicates a mean dust covering fraction of 0.56+/-0.15,
assuming relatively isotropic emission. We analyze Spitzer spectra of the 14
mid-IR luminous narrow-line radio galaxies thought to host hidden quasar
nuclei. Dust temperatures of 210-660 K are estimated from single-temperature
blackbody fits to the low and high-frequency ends of the mid-IR bump. Most of
the mid-IR luminous radio galaxies have a 9.7 micron silicate absorption trough
with optical depth <0.2, attributed to dust in a molecular torus. Forbidden
emission lines from high-ionization oxygen, neon, and sulfur indicate a source
of far-UV photons in the hidden nucleus. However, we find that the other
55+/-13% of narrow-line FR II radio galaxies are weak at 15 micron, contrary to
single-population unification schemes. Most of these galaxies are also weak at
30 micron. Mid-IR weak radio galaxies may constitute a separate population of
nonthermal, jet-dominated sources with low accretion powerComment: 34 pages, 8 figures, ApJ submitte
CFHT Legacy Ultraviolet Extension (CLUE): Witnessing Galaxy Transformations up to 7 Mpc from Rich Cluster Cores
Using the optical data from the Wide component of the CFHT Legacy Survey, and
new ultraviolet data from GALEX, we study the colours and specific star
formation rates (SSFR) of ~100 galaxy clusters at 0.16<z<0.36, over areas
extending out to radii of r~7Mpc. We use a multicolour, statistical background
subtraction method to study the galaxy population at this radius; thus our
results pertain to those galaxies which constitute an excess over the average
field density. We find that the average SSFR, and its distribution, of the
star-forming galaxies (with SFR>0.7 M_sun/yr at z~0.2 and SFR>1.2 M_sun/yr at
z~0.3) have no measurable dependence on the cluster-centric radius, and are
consistent with the field values. However, the fraction of galaxies with SFR
above these thresholds, and the fraction of optically blue galaxies, are lower
for the overdense galaxy population in the cluster outskirts compared with the
average field value, at all stellar masses M*>10^{9.8} M_sun and at all radii
out to at least 7Mpc. Most interestingly, the fraction of blue galaxies that
are forming stars at a rate below our UV detection limit is much higher in all
radial bins around our cluster sample, compared with the general field value.
This is most noticeable for massive galaxies M*>10^{10.7} M_sun; while almost
all blue field galaxies of this mass have detectable star formation, this is
true for less than 20% of the blue cluster galaxies, even at 7Mpc from the
cluster centre. Our results support a scenario where galaxies are pre-processed
in locally overdense regions, in a way that reduces their SFR below our UV
detection limit, but not to zero.Comment: MNRAS accepte
The Evolution of [OII] Emission from Cluster Galaxies
We investigate the evolution of the star formation rate in cluster galaxies.
We complement data from the CNOC1 cluster survey (0.15<z<0.6) with measurements
from galaxy clusters in the 2dF galaxy redshift survey (0.05<z<0.1) and
measurements from recently published work on higher redshift clusters, up to
almost z=1. We focus our attention on galaxies in the cluster core, ie.
galaxies with r<0.7h^{-1}_{70}Mpc. Averaging over clusters in redshift bins, we
find that the fraction of galaxies with strong [OII] emission is < 20% in
cluster cores, and the fraction evolves little with redshift. In contrast,
field galaxies from the survey show a very strong increase over the same
redshift range. It thus appears that the environment in the cores of rich
clusters is hostile to star formation at all the redshifts studied. We compare
this result with the evolution of the colours of galaxies in cluster cores,
first reported by Butcher & Oemler (1984). Using the same galaxies for our
analysis of the [OII] emission, we confirm that the fraction of blue galaxies,
which are defined as galaxies 0.2 mag bluer in the rest frame B-V than the red
sequence of each cluster, increases strongly with redshift. Since the colours
of galaxies retain a memory of their recent star formation history, while
emission from the [OII] line does not, we suggest that these two results can
best be reconciled if the rate at which the clusters are being assembled is
higher in the past, and the galaxies from which it is being assembled are
typically bluer.Comment: 8 pages, 7 figures, accepted for publication in MNRA
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