87 research outputs found
Warm Molecular Hydrogen Emission in Normal Edge-On Galaxies NGC 4565 and NGC 5907
We have observed warm molecular hydrogen in two nearby edge-on disk galaxies,
NGC 4565 and NGC 5907, using the Spitzer high-resolution infrared spectrograph.
The 0-0 S(0) 28.2 micron and 0-0 S(1) 17.0 micron pure rotational lines were
detected out to 10 kpc from the center of each galaxy on both sides of the
major axis, and in NGC 4565 the S(0) line was detected at r = 15 kpc on one
side. This location lies beyond a steep drop in the radio continuum emission
from cosmic rays in the disk. Despite indications that star formation activity
decreases with radius, the H2 excitation temperature and the ratio of the H2
line and the far-IR luminosity surface densities, Sigma_L(H2}/Sigma_L(TIR},
change very little as a function of radius, even into the diffuse outer region
of the disk of NGC 4565. This suggests that the source of excitation of the H2
operates over a large range of radii, and is broadly independent of the
strength and relative location of UV emission from young stars. Although
excitation in photodissociation regions is the most common explanation for the
widespread H2 emission, cosmic ray heating or shocks cannot be ruled out. The
inferred mass surface densities of warm molecular hydrogen in both edge-on
galaxies differ substantially, being 4(-60) M_solar/pc^2 and 3(-50)
M_solar/pc^2 at r = 10 kpc for NGC 4565 and NGC 5907, respectively. The higher
values represent very unlikely point-source upper limits. The point source case
is not supported by the observed emission distribution in the spectral slits.
These mass surface densities cannot support the observed rotation velocities in
excess of 200 km/s. Therefore, warm molecular hydrogen cannot account for dark
matter in these disk galaxies, contrary to what was implied by a previous ISO
study of the nearby edge-on galaxy NGC 891.Comment: Accepted for publication in the Astronomical Journal (20 pages, 17
figures, 7 tables
IRAC Observations of M81
IRAC images of M81 show three distinct morphological constituents: a smooth
distribution of evolved stars with bulge, disk, and spiral arm components; a
clumpy distribution of dust emission tracing the spiral arms; and a pointlike
nuclear source. The bulge stellar colors are consistent with M-type giants, and
the disk colors are consistent with a slightly younger population. The dust
emission generally follows the blue and ultraviolet emission, but there are
large areas that have dust emission without ultraviolet and smaller areas with
ultraviolet but little dust emission. The former are presumably caused by
extinction, and the latter may be due to cavities in the gas and dust created
by supernova explosions. The nucleus appears fainter at 8 um than expected from
ground-based 10 um observations made four years ago.Comment: ApJS in press (Spitzer special issue); 15 pages, 3 figures. Changes:
unused references removed, numbers and labels in Table 1 change
The Evolution of the Star Formation Rate of Galaxies at 0.0 < z < 1.2
We present the 24 micron rest-frame luminosity function (LF) of star-forming
galaxies in the redshift range 0.0 < z < 0.6 constructed from 4047
spectroscopic redshifts from the AGN and Galaxy Evolution Survey of 24 micron
selected sources in the Bootes field of the NOAO Deep Wide-Field Survey. This
sample provides the best available combination of large area (9 deg^2), depth,
and statistically complete spectroscopic observations, allowing us to probe the
evolution of the 24 micron LF of galaxies at low and intermediate redshifts
while minimizing the effects of cosmic variance. In order to use the observed
24 micron luminosity as a tracer for star formation, active galactic nuclei
(AGNs) that could contribute significantly at 24 micron are identified and
excluded from our star-forming galaxy sample based on their mid-IR spectral
energy distributions or the detection of X-ray emission. The evolution of the
24 micron LF of star-forming galaxies for redshifts of z < 0.65 is consistent
with a pure luminosity evolution where the characteristic 24 micron luminosity
evolves as (1+z)^(3.8+/-0.3). We extend our evolutionary study to encompass 0.0
< z < 1.2 by combining our data with that of the Far-Infrared Deep
Extragalactic Legacy Survey. Over this entire redshift range the evolution of
the characteristic 24 micron luminosity is described by a slightly shallower
power law of (1+z)^(3.4+/-0.2). We find a local star formation rate density of
(1.09+/-0.21) x 10^-2 Msun/yr/Mpc^-3, and that it evolves as (1+z)^(3.5+/-0.2)
over 0.0 < z < 1.2. These estimates are in good agreement with the rates using
optical and UV fluxes corrected for the effects of intrinsic extinction in the
observed sources. This agreement confirms that star formation at z <~ 1.2 is
robustly traced by 24 micron observations and that it largely occurs in
obscured regions of galaxies. (Abridged)Comment: ApJ, in press, 16 pages 9 figure
UV-to-FIR analysis of Spitzer/IRAC sources in the Extended Groth Strip II: Photometric redshifts, Stellar masses and Star formation rates
Based on the ultraviolet to far-infrared photometry already compiled and
presented in a companion paper (Barro et al. 2011a, Paper I), we present a
detailed SED analysis of nearly 80,000 IRAC 3.6+4.5 micron selected galaxies in
the Extended Groth Strip. We estimate photometric redshifts, stellar masses,
and star formation rates separately for each galaxy in this large sample. The
catalog includes 76,936 sources with [3.6] < 23.75 (85% completeness level of
the IRAC survey) over 0.48 square degrees. The typical photometric redshift
accuracy is Delta z/(1+z)=0.034, with a catastrophic outlier fraction of just
2%. We quantify the systematics introduced by the use of different stellar
population synthesis libraries and IMFs in the calculation of stellar masses.
We find systematic offsets ranging from 0.1 to 0.4 dex, with a typical scatter
of 0.3 dex. We also provide UV- and IR-based SFRs for all sample galaxies,
based on several sets of dust emission templates and SFR indicators. We
evaluate the systematic differences and goodness of the different SFR
estimations using the deep FIDEL 70 micron data available in the EGS. Typical
random uncertainties of the IR-bases SFRs are a factor of two, with
non-negligible systematic effects at z1.5 observed when only MIPS 24
micron data is available. All data products (SEDs, postage stamps from imaging
data, and different estimations of the photometric redshifts, stellar masses,
and SFRs of each galaxy) described in this and the companion paper are publicly
available, and they can be accessed through our the web-interface utility
Rainbow-navigatorComment: 39 pages, 22 figures, Accepted for publication in ApJ. Access the
Rainbow Database at: http://rainbowx.fis.ucm.e
Mid-IR Luminosities and UV/Optical Star Formation Rates at z<1.4
UV continuum and mid-IR emission constitute two widely used star formation
indicators at intermediate and high redshifts. We study 2430 galaxies with
z<1.4 in the Extended Groth Strip with MIPS 24 mic observations from FIDEL,
spectroscopy from DEEP2, and UV, optical, and near-IR photometry from AEGIS.
The data are coupled with stellar population models and Bayesian SED fitting to
estimate dust-corrected SFRs. In order to probe the dust heating from stellar
populations of various ages, the derived SFRs were averaged over various
timescales--from 100 Myr for "current" SFR to 1--3 Gyr for long-timescale SFRs.
These SED-based UV/optical SFRs are compared to total infrared luminosities
extrapolated from 24 mic observations. We find that for the blue, actively star
forming galaxies the correlation between the IR luminosity and the UV/optical
SFR shows a decrease in scatter when going from shorter to longer SFR-averaging
timescales. We interpret this as the greater role of intermediate age stellar
populations in heating the dust than what is typically assumed. This holds over
the entire redshift range. Many so-called green valley galaxies are simply
dust-obscured actively star-forming galaxies. However, there exist 24
mic-detected galaxies, some with L>10^11 L_sun, yet with little current star
formation. For them a reasonable amount of dust absorption of stellar light is
sufficient to produce the observed levels of IR. In our sample optical and
X-ray AGNs do not contribute on average more than ~50% to the mid-IR
luminosity, and we see no evidence for a large population of "IR excess"
galaxies (Abridged).Comment: Accepted for publication in ApJ. Content identical to arXiv version
1. No color figure
The impact of bars on the mid-infrared dust emission of spiral galaxies: global and circumnuclear properties
We study the mid-infrared properties of a sample of 69 nearby spiral
galaxies, selected to avoid Seyfert activity contributing a significant
fraction of the central energetics, or strong tidal interaction, and to have
normal infrared luminosities. These observations were obtained with ISOCAM,
which provides an angular resolution of the order of 10 arcsec (half-power
diameter of the point spread function) and low-resolution spectro-imaging
information. Between 5 and 18 microns, we mainly observe two dust phases,
aromatic infrared bands and very small grains, both out of thermal equilibrium.
On this sample, we show that the global F15/F7 colors of galaxies are very
uniform, the only increase being found in early-type strongly barred galaxies,
consistent with previous IRAS studies. The F15/F7 excesses are unambiguously
due to galactic central regions where bar-induced starbursts occur. However,
the existence of strongly barred early-type galaxies with normal circumnuclear
colors indicates that the relationship between a distortion of the
gravitational potential and a central starburst is not straightforward. As the
physical processes at work in central regions are in principle identical in
barred and unbarred galaxies, and since this is where the mid-infrared activity
is mainly located, we investigate the mid-infrared circumnuclear properties of
all the galaxies in our sample. We show how surface brightnesses and colors are
related to both the available molecular gas content and the mean age of stellar
populations contributing to dust heating. Therefore, the star formation history
in galactic central regions can be constrained by their position in a
color-surface brightness mid-infrared diagram.Comment: 22 pages, 25 figures, accepted for publication in A&A ; small errors
corrected and references update
Infrared Array Camera (IRAC) Observations of M81
Infrared Array Camera (IRAC) images of M81 show three distinct morphological constituents: a smooth distribution of evolved stars with bulge, disk, and spiral arm components; a clumpy distribution of dust emission tracing the spiral arms; and a pointlike nuclear source. The bulge stellar colors are consistent with M-type giants, and the disk colors are consistent with a slightly younger population. The dust emission generally follows the blue and ultraviolet emission, but there are large areas that have dust emission without ultraviolet and smaller areas with ultraviolet but little dust emission. The former are presumably caused by extinction, and the latter may be due to cavities in the gas and dust created by supernova explosions. The nucleus appears fainter at 8 μm than expected from ground-based 10 μm observations made 4 years ago
Modeling working memory: An interference model of complex span
This article introduces a new computational model for the complex-span task, the most popular task for studying working memory. SOB-CS is a two-layer neural network that associates distributed item representations with distributed, overlapping position markers. Memory capacity limits are explained by interference from a superposition of associations. Concurrent processing interferes with memory through involuntary encoding of distractors. Free time in-between distractors is used to remove irrelevant representations, thereby reducing interference. The model accounts for benchmark findings in four areas: (1) effects of processing pace, processing difficulty, and number of processing steps; (2) effects of serial position and error patterns; (3) effects of different kinds of item-distractor similarity; and (4) correlations between span tasks. The model makes several new predictions in these areas, which were confirmed experimentally
Convalescent plasma in patients admitted to hospital with COVID-19 (RECOVERY): a randomised controlled, open-label, platform trial
Background:
Many patients with COVID-19 have been treated with plasma containing anti-SARS-CoV-2 antibodies. We aimed to evaluate the safety and efficacy of convalescent plasma therapy in patients admitted to hospital with COVID-19.
Methods:
This randomised, controlled, open-label, platform trial (Randomised Evaluation of COVID-19 Therapy [RECOVERY]) is assessing several possible treatments in patients hospitalised with COVID-19 in the UK. The trial is underway at 177 NHS hospitals from across the UK. Eligible and consenting patients were randomly assigned (1:1) to receive either usual care alone (usual care group) or usual care plus high-titre convalescent plasma (convalescent plasma group). The primary outcome was 28-day mortality, analysed on an intention-to-treat basis. The trial is registered with ISRCTN, 50189673, and ClinicalTrials.gov, NCT04381936.
Findings:
Between May 28, 2020, and Jan 15, 2021, 11558 (71%) of 16287 patients enrolled in RECOVERY were eligible to receive convalescent plasma and were assigned to either the convalescent plasma group or the usual care group. There was no significant difference in 28-day mortality between the two groups: 1399 (24%) of 5795 patients in the convalescent plasma group and 1408 (24%) of 5763 patients in the usual care group died within 28 days (rate ratio 1·00, 95% CI 0·93–1·07; p=0·95). The 28-day mortality rate ratio was similar in all prespecified subgroups of patients, including in those patients without detectable SARS-CoV-2 antibodies at randomisation. Allocation to convalescent plasma had no significant effect on the proportion of patients discharged from hospital within 28 days (3832 [66%] patients in the convalescent plasma group vs 3822 [66%] patients in the usual care group; rate ratio 0·99, 95% CI 0·94–1·03; p=0·57). Among those not on invasive mechanical ventilation at randomisation, there was no significant difference in the proportion of patients meeting the composite endpoint of progression to invasive mechanical ventilation or death (1568 [29%] of 5493 patients in the convalescent plasma group vs 1568 [29%] of 5448 patients in the usual care group; rate ratio 0·99, 95% CI 0·93–1·05; p=0·79).
Interpretation:
In patients hospitalised with COVID-19, high-titre convalescent plasma did not improve survival or other prespecified clinical outcomes.
Funding:
UK Research and Innovation (Medical Research Council) and National Institute of Health Research
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