376 research outputs found
Near-Infrared Properties of Faint X-rays Sources from NICMOS Imaging in the Chandra Deep Fields
We measure the near-infrared properties of 42 X-ray detected sources from the
Chandra Deep Fields North and South, the majority of which lie within the
NICMOS Hubble Deep Field North and Ultra Deep Field. We detect all 42 Chandra
sources with NICMOS, with 95% brighter than H = 24.5. We find that X-ray
sources are most often in the brightest and most massive galaxies. Neither the
X-ray fluxes nor hardness ratios of the sample show any correlation with
near-infrared flux, color or morphology. This lack of correlation indicates
there is little connection between the two emission mechanisms and is
consistent with the near-infrared emission being dominated by starlight rather
than a Seyfert non-stellar continuum.
Near-infrared X-ray sources make up roughly half of all extremely red (J-H >
1.4) objects brighter than H > 24.5. These red X-ray sources have a range of
hardness ratios similar to the rest of the sample, decreasing the likelihood of
dust-obscured AGN activity as the sole explanation for their red color. Using a
combination of spectroscopic and photometric redshifts, we find the red J-H
objects are at high redshifts (z > 1.5), which we propose as the primary
explanation for their extreme J-H color. Measurement of rest-wavelength
absolute B magnitudes shows that X-ray sources are the brightest optical
objects at all redshifts, which explains their dominance of the bright end of
the red J-H population.Comment: 29 pages, 7 figures, accepted by Ap
A Deep HST Search for Escaping Lyman Continuum Flux at z~1.3: Evidence for an Evolving Ionizing Emissivity
We have obtained deep Hubble Space Telescope far-UV images of 15 starburst
galaxies at z~1.3 in the GOODS fields to search for escaping Lyman continuum
photons. These are the deepest far-UV images m_{AB}=28.7, 3\sigma, 1" diameter)
over this large an area (4.83 arcmin^2) and provide the best escape fraction
constraints for any galaxy at any redshift. We do not detect any individual
galaxies, with 3\sigma limits to the Lyman Continuum (~700 \AA) flux 50--149
times fainter (in f_nu) than the rest-frame UV (1500 \AA) continuum fluxes.
Correcting for the mean IGM attenuation (factor ~2), as well as an intrinsic
stellar Lyman Break (~3), these limits translate to relative escape fraction
limits of f_{esc,rel}<[0.03,0.21]. The stacked limit is
f_{esc,rel}(3\sigma)<0.02. We use a Monte Carlo simulation to properly account
for the expected distribution of IGM opacities. When including constraints from
previous surveys at z~1.3 we find that, at the 95% confidence level, no more
than 8% of star--forming galaxies at z~1.3 can have relative escape fractions
greater than 0.50. Alternatively, if the majority of galaxies have low, but
non-zero, escaping Lyman Continuum, the escape fraction can not be more than
0.04. Both the stacked limits, and the limits from the Monte Carlo simulation
suggest that the average ionizing emissivity (relative to non-ionizing UV
emissivity) at z~1.3 is significantly lower than has been observed in Lyman
Break Galaxies (LBGs) at z~3. If the ionizing emissivity of star-forming
galaxies is in fact increasing with redshift, it would help to explain the high
photoionization rates seen in the IGM at z>4 and reionization of the
intergalactic medium at z>6. [Abridged]Comment: Submitted to ApJ (Nov. 6) Comments Welcome. 11 pages, 8 figure
A Lyman Break Galaxy Candidate at z~9
We report the discovery of a z~9 Lyman Break Galaxy (LBG) candidate, selected
from the NICMOS Parallel Imaging Survey as a J-dropout with J110 - H160 = 1.7.
Spitzer/IRAC photometry reveals that the galaxy has a blue H160 - 3.6 um color,
and a spectral break between 3.6 and 4.5 um. We interpret this break as the
Balmer break, and derive a best-fit photometric redshift of z~9. We use Monte
Carlo simulations to test the significance of this photometric redshift, and
show a 96% probability of z>7. We estimate a lower limit to the comoving number
density of such galaxies at z~9 of phi > 3.8 x 10^{-6} Mpc^{-3}. If the high
redshift of this galaxy is confirmed, this will indicate that the luminous end
of the rest-frame UV luminosity function has not evolved substantially from z~
9 to z~3. Still, some small degeneracy remains between this z~9 model and
models at z~2-3; deep optical imaging (reaching I ~ 29 AB) can rule out the
lower-z models.Comment: Accepted to ApJ Letter
LSST Science Book, Version 2.0
A survey that can cover the sky in optical bands over wide fields to faint
magnitudes with a fast cadence will enable many of the exciting science
opportunities of the next decade. The Large Synoptic Survey Telescope (LSST)
will have an effective aperture of 6.7 meters and an imaging camera with field
of view of 9.6 deg^2, and will be devoted to a ten-year imaging survey over
20,000 deg^2 south of +15 deg. Each pointing will be imaged 2000 times with
fifteen second exposures in six broad bands from 0.35 to 1.1 microns, to a
total point-source depth of r~27.5. The LSST Science Book describes the basic
parameters of the LSST hardware, software, and observing plans. The book
discusses educational and outreach opportunities, then goes on to describe a
broad range of science that LSST will revolutionize: mapping the inner and
outer Solar System, stellar populations in the Milky Way and nearby galaxies,
the structure of the Milky Way disk and halo and other objects in the Local
Volume, transient and variable objects both at low and high redshift, and the
properties of normal and active galaxies at low and high redshift. It then
turns to far-field cosmological topics, exploring properties of supernovae to
z~1, strong and weak lensing, the large-scale distribution of galaxies and
baryon oscillations, and how these different probes may be combined to
constrain cosmological models and the physics of dark energy.Comment: 596 pages. Also available at full resolution at
http://www.lsst.org/lsst/sciboo
CEERS: Spatially Resolved UV and mid-IR Star Formation in Galaxies at 0.2 < z < 2.5: The Picture from the Hubble and James Webb Space Telescopes
We present the mid-IR (MIR) morphologies for 64 star-forming galaxies at
0.210^{9}~M_\odot} using JWST MIRI
observations from the Cosmic Evolution Early Release Science survey (CEERS).
The MIRI bands span the MIR (7.7--21~m), enabling us to measure the
effective radii () and S\'{e}rsic indexes of these SFGs at
rest-frame 6.2 and 7.7 m, which contains strong emission from Polycyclic
aromatic hydrocarbon (PAH) features, a well-established tracer of star
formation in galaxies. We define a ``PAH-band'' as the MIRI bandpass that
contains these features at the redshift of the galaxy. We then compare the
galaxy morphologies in the PAH-bands to those in rest-frame Near-UV (NUV) using
HST ACS/F435W or ACS/F606W and optical/near-IR using HST WFC3/F160W imaging
from UVCANDELS and CANDELS, where the NUV-band and F160W trace the profile of
(unobscured) massive stars and the stellar continuum, respectively. The
of galaxies in the PAH-band are slightly smaller (10\%)
than those in F160W for galaxies with at
, but the PAH-band and F160W have a similar fractions of light within
1 kpc. In contrast, the of galaxies in the NUV-band are larger,
with lower fractions of light within 1 kpc compared to F160W for galaxies at
. Using the MIRI data to estimate the surface
density, we find the correlation between the surface
density and stellar mass has a steeper slope than that of the
surface density and stellar mass, suggesting more massive
galaxies having increasing amounts of obscured fraction of star formation in
their inner regions. This paper demonstrates how the high-angular resolution
data from JWST/MIRI can reveal new information about the morphology of
obscured-star formation.Comment: 28 pages, 11 figures, Accepted by Ap
Susceptibility to chronic mucus hypersecretion, a genome wide association study
Background: Chronic mucus hypersecretion (CMH) is associated with an increased frequency of respiratory infections, excess lung function decline, and increased hospitalisation and mortality rates in the general population. It is associated with smoking, but it is unknown why only a minority of smokers develops CMH. A plausible explanation for this phenomenon is a predisposing genetic constitution. Therefore, we performed a genome wide association (GWA) study of CMH in Caucasian populations.Methods: GWA analysis was performed in the NELSON-study using the Illumina 610 array, followed by replication and metaanalysis in 11 additional cohorts. In total 2,704 subjects with, and 7,624 subjects without CMH were included, all current or former heavy smokers (>= 20 pack-years). Additional studies were performed to test the functional relevance of the most significant single nucleotide polymorphism (SNP).Results: A strong association with CMH, consistent across all cohorts, was observed with rs6577641 (p = 4.25610(-6), OR = 1.17), located in intron 9 of the special AT-rich sequence-binding protein 1 locus (SATB1) on chromosome 3. The risk allele (G) was associated with higher mRNA expression of SATB1 (4.3610 29) in lung tissue. Presence of CMH was associated with increased SATB1 mRNA expression in bronchial biopsies from COPD patients. SATB1 expression was induced during differentiation of primary human bronchial epithelial cells in culture.Conclusions: Our findings, that SNP rs6577641 is associated with CMH in multiple cohorts and is a cis-eQTL for SATB1, together with our additional observation that SATB1 expression increases during epithelial differentiation provide suggestive evidence that SATB1 is a gene that affects CMH.</p
Nuclear Calcium Signaling Controls Expression of a Large Gene Pool: Identification of a Gene Program for Acquired Neuroprotection Induced by Synaptic Activity
Synaptic activity can boost neuroprotection through a mechanism that requires synapse-to-nucleus communication and calcium signals in the cell nucleus. Here we show that in hippocampal neurons nuclear calcium is one of the most potent signals in neuronal gene expression. The induction or repression of 185 neuronal activity-regulated genes is dependent upon nuclear calcium signaling. The nuclear calcium-regulated gene pool contains a genomic program that mediates synaptic activity-induced, acquired neuroprotection. The core set of neuroprotective genes consists of 9 principal components, termed Activity-regulated Inhibitor of Death (AID) genes, and includes Atf3, Btg2, GADD45β, GADD45γ, Inhibin β-A, Interferon activated gene 202B, Npas4, Nr4a1, and Serpinb2, which strongly promote survival of cultured hippocampal neurons. Several AID genes provide neuroprotection through a common process that renders mitochondria more resistant to cellular stress and toxic insults. Stereotaxic delivery of AID gene-expressing recombinant adeno-associated viruses to the hippocampus confers protection in vivo against seizure-induced brain damage. Thus, treatments that enhance nuclear calcium signaling or supplement AID genes represent novel therapies to combat neurodegenerative conditions and neuronal cell loss caused by synaptic dysfunction, which may be accompanied by a deregulation of calcium signal initiation and/or propagation to the cell nucleus
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