1,121 research outputs found
Morphology-dependent trends of galaxy age with environment in Abell 901/902 seen with COMBO-17
We investigate correlations between galaxy age and environment in the Abell
901/2 supercluster for separate morphologies. Using COMBO-17 data, we define a
sample of 530 galaxies, complete at on an area of (Mpc/). We explore several age indicators including an
extinction-corrected residual from the colour-magnitude relation (CMR). As a
result, we find a clear trend of age with density for galaxies of all
morphologies that include a spheroidal component, in the sense that galaxies in
denser environments are older. This trend is not seen among Scd/Irr galaxies
since they all have young ages. However, the trend among the other types is
stronger for fainter galaxies. While we also see an expected age-morphology
relation, we find no evidence for a morphology-density relation at fixed age.Comment: Accepted for publication in MNRAS (Letters
The Tully-Fisher relation of intermediate redshift field and cluster galaxies from Subaru spectroscopy
We have carried out spectroscopic observations in 4 cluster fields using
Subaru's FOCAS multi-slit spectrograph and obtained spectra for 103 bright disk
field and cluster galaxies at . Seventy-seven of these
show emission lines, and 33 provide reasonably-secure determinations of the
galaxies' rotation velocity. The rotation velocities, luminosities, colours and
emission-line properties of these galaxies are used to study the possible
effects of the cluster environment on the star-formation history of the
galaxies. Comparing the Tully-Fisher relations of cluster and field galaxies at
similar reshifts we find no measurable difference in rest-frame -band
luminosity at a given rotation velocity (the formal difference is mag). The colours of the cluster emission line galaxies are only marginally
redder in rest-frame (by mag) than the field galaxies in
our sample. Taken at face value, these results seem to indicate that bright
star-forming cluster spirals are similar to their field counterparts in their
star-formation properties. However, we find that the fraction of disk galaxies
with absorption-line spectra (i.e., with no current star formation) is larger
in clusters than in the field by a factor of --5. This suggests that the
cluster environment has the overall effect of switching off star formation in
(at least) some spiral galaxies. To interpret these observational results, we
carry out simulations of the possible effects of the cluster environment on the
star-formation history of disk galaxies and thus their photometric and
spectroscopic properties. Finally, we evaluate the evolution of the rest-frame
absolute -band magnitude per unit redshift at fixed rotation velocity.Comment: 21 pages, 13 figures, accepted for publication in MNRA
Extremely Red Objects in the Field of QSO 1213-0017: A Galaxy Concentration at z=1.31
We have discovered a concentration of extremely red objects (EROs; R-K>6) in
the field of the z=2.69 quasar QSO 1213-0017 (UM 485), which is significantly
overabundant compared to the field ERO surface density. The optical/near-IR
colors of the EROs and numerous other red galaxies in this field are consistent
with elliptical galaxies at z=1-2. HST optical images for a subset of galaxies
show regular morphologies, most of them being disky or diffuse and without any
obvious evidence for interactions. Ground-based IR images show similar
morphologies, indicating any dust reddening in these objects is spatially
uniform. Optical spectroscopy with the W. M. Keck Telescope has found that four
of the red galaxies lie at =1.31, and a fifth lies in the foreground at
z=1.20. Of the =1.31 galaxies, one is a reddened AGN while the remaining
three have rest-frame UV absorption-line spectra characteristic of old (few
Gyr) stellar populations, similar to the old red galaxy LBDS 53W091 at z=1.55.
Including the MgII absorber seen in the QSO spectrum, we find five galaxies at
=1.31 spread over 1.5 h_50^{-1} Mpc on the sky. These results suggest we
have discovered a coherent structure of old galaxies at high-redshift, possibly
associated with a massive galaxy cluster.Comment: 37 pages including 11 Postscript figures. To appear in the June 2000
issue of the Astronomical Journa
An Optical/Near-Infrared Study of Radio-Loud Quasar Environments II. Imaging Results
We use optical and near-IR imaging to examine the properties of the
significant excess population of K>=19 galaxies found in the fields of 31 z=1-2
radio-loud quasars by Hall, Green & Cohen (1998). The excess occurs on two
spatial scales: a component at <40'' from the quasars significant compared to
the galaxy surface density at >40'' in the same fields, and a component roughly
uniform to ~100'' significant compared to the galaxy surface density seen in
random-field surveys in the literature. The r-K color distributions of the
excess galaxy populations are indistinguishable and are significantly redder
than the color distribution of the field population.
The excess galaxies are consistent with being predominantly early-type
galaxies at the quasar redshifts, and there is no evidence that they are
associated with intervening MgII absorption systems. The average excess within
0.5 Mpc (~65'') of the quasars corresponds to Abell richness class ~0 compared
to the galaxy surface density at >0.5 Mpc from the quasars, and to Abell
richness class ~1.5 compared to that from the literature.
We discuss the spectral energy distributions (SEDs) of galaxies in fields
with data in several passbands. Most candidate quasar-associated galaxies are
consistent with being 2-3 Gyr old early-types at the quasar redshifts of z~1.5.
However, some objects have SEDs consistent with being 4-5 Gyr old at z~1.5, and
a number of others are consistent with ~2 Gyr old but dust-reddened galaxies at
the quasar redshifts. These potentially different galaxy types suggest there
may be considerable dispersion in the properties of early-type cluster galaxies
at z~1.5. There is also a population of galaxies whose SEDs are best modelled
by background galaxies at z>2.5.Comment: Accepted to ApJ; 54 pages including 30 figures; 2 color GIF files
available separately; also available from
http://www.astro.utoronto.ca/~hall/thesis.htm
The First VLT FORS1 spectra of Lyman-break candidates in the HDF-S and AXAF Deep Field
We report on low-resolution multi-object spectroscopy of 30 faint targets (R
\~ 24-25) in the HDF-S and AXAF deep field obtained with the VLT Focal
Reducer/low dispersion Spectrograph (FORS1). Eight high-redshift galaxies with
2.75< z < 4 have been identified. The spectroscopic redshifts are in good
agreement with the photometric ones with a dispersion at z<2
and at z>2. The inferred star formation rates of the
individual objects are moderate, ranging from a few to a few tens solar masses
per year. Five out of the eight high-z objects do not show prominent emission
lines. One object has a spectrum typical of an AGN. In the AXAF field two
relatively close pairs of galaxies have been identified, with separations of
8.7 and 3.1 proper Mpc and mean redshifts of 3.11 and 3.93, respectively.Comment: 5 pages Latex, with 2 PostScript figures. Astronomy and Astrophysics,
in pres
Chemical Interactions and Cytotoxicity of Terpene and Diluent Vaping Ingredients
Vaping devices have risen in popularity since their inception in 2007. The practice involves using a variety of commercially available devices. Internal heating systems in devices aerosolize e-liquid formulations of complex mixtures including an active ingredient (e.g., THC, CBD, and nicotine), diluents (or cutting agents), solvents, and flavoring agents (e.g., terpenes and aldehydes). The vaping toxicology literature consists of cytotoxicity studies of individual chemicals and commercial formulas. Because of the variation of e-liquid composition, there is a limited understanding of the toxicity of ingredient combinations. This study analyzed the cytotoxic effects after exposure to individual and binary mixtures of a representative terpene (+-R-limonene) and diluent (triethyl citrate) on human lung cell models. Data were analyzed to determine the effects of 97:3 and 80:20% v/v (triethyl citrate/limonene) binary mixtures. BEAS-2B cells, a bronchial epithelial cell, and A549 cells, a type II alveolar epithelial cell, served as models for comparison. LC50 values were calculated and isobolograms were used to assess chemical interactions. Results show that limonene was more cytotoxic than triethyl citrate. Isobolographic analyses confirmed that the 97:3% v/v mixture resulted in an antagonistic chemical interaction. The 80:20% v/v mixture resulted in a similar result. Further testing of different ratios of binary mixtures is needed for chemical interaction screening to inform safety assessments
Constraints On the Size Evolution of Brightest Cluster Galaxies
We measure the luminosity profiles of 16 brightest cluster galaxies (BCGs) at
using high resolution F160W NICMOS and F814W WFPC2 HST imaging.
The heterogeneous sample is drawn from a variety of surveys: seven from
clusters in the Einstein Medium Sensitivity Survey, five from the Las Campanas
Distant Cluster Survey and its northern hemisphere precursor, and the remaining
four from traditional optical surveys. We find that the surface brightness
profiles of all but three of these BCGs are well described by a standard de
Vaucouleurs () profile out to at least and that the
biweight-estimated NICMOS effective radius of our high redshift BCGs ( kpc for km s Mpc, ) is times smaller than that measured for a local
BCG sample. If high redshift BCGs are in dynamical equilibrium and satisfy the
same scaling relations as low redshift ones, this change in size would
correspond to a mass growth of a factor of 2 since . However, the
biweight-estimated WFPC2 effective radius of our sample is 18 5.1 kpc,
which is fully consistent with the local sample. While we can rule out mass
accretion rates higher than a factor of 2 in our sample, the discrepancy
between our NICMOS and WFPC2 results, which after various tests we describe
appears to be physical, does not yet allow us to place strong constraints on
accretion rates below that level.Comment: ApJ accepted (566, 1, February 2002), 12 pages, uses emulateapj5.st
On the Optimization of Broad-Band Photometry for Galaxy Evolution Studies
We have derived the uncertainties to be expected in the derivation of galaxy
physical properties (star formation history, age, metallicity, reddening) when
comparing broad-band photometry to the predictions of evolutionary synthesis
models. We have obtained synthetic colors for a large sample (9000) of
artificial galaxies assuming different star formation histories, ages,
metallicities, reddening values, and redshifts. The colors derived have been
perturbed by adopting different observing errors, and compared back to the
evolutionary synthesis models grouped in different sets. The comparison has
been performed using a combination of Monte Carlo simulations, a Maximum
Likelihood Estimator and Principal Component Analysis. After comparing the
input and derived output values we have been able to compute the uncertainties
and covariant degeneracies between the galaxy physical properties as function
of (1) the set of observables available, (2) the observing errors, and (3) the
galaxy properties themselves. In this work we have considered different sets of
observables, some of them including the standard Johnson/Cousins (UBVRI) and
Sloan Digital Sky Survey (SDSS) bands in the optical, the 2 Micron All Sky
Survey (2MASS) bands in the near-infrared, and the Galaxy Evolution Explorer
(GALEX) bands in the UV, at three different redshifts, z=0.0, 0.7, and 1.4.
This study is intended to represent a basic tool for the design of future
projects on galaxy evolution, allowing an estimate of the optimal band-pass
combinations and signal-to-noise ratios required for a given scientific
objective.Comment: 20 pages, 9 postscript figures, 3 tables, accepted for publication in
A
COVID-19 labour market shocks and their inequality implications for financial wellbeing
Using an online survey of Australian residents, we elicit the potential impacts of COVID-19 related labour market shocks on a validated measure of financial wellbeing. Experiencing a reduction in hours and earnings, entering into unemployment or having to file for unemployment benefits during the pandemic are strongly and significantly associated with decreases in financial wellbeing of around 29% or 18 points on the financial wellbeing scale of 0-100, despite various government measures to reduce such effects. Unconditional quantile regression analyses indicate that the negative COVID-19 labour market effects are felt the most by people in the lowest percentiles of the financial wellbeing distribution. Counterfactual distributional analyses and distribution regression indicate a shifting of the financial wellbeing distribution leftwards brought on by those suffering any of the above-mentioned labour market shocks, indicating potential dramatic increases in financial wellbeing disadvantage and inequality
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