113 research outputs found
On the Nature of the NGC 1275 System
Sub-arcsecond images, taken in B, R, and H-Alpha filters, and area
spectroscopy obtained with the WIYN 3.5-m telescope provide the basis for an
investigation of the unusual structures in the stellar body and ionized gas in
and around the Perseus cluster central galaxy, NGC 1275. Our H-Alpha filter is
tuned to gas at the velocity of NGC 1275, revealing complex, probably
unresolved, small-scale features in the extended ionized gas, located up to
50/h kpc from NGC 1275. The mean H-Alpha surface brightness varies little along
the outer filaments; this, together with the complex excitation state
demonstrated by spectra, imply that the filaments are likely to be tubes, or
ribbons, of gas. The morphology, location and inferred physical parameters of
the gas in the filaments are consistent with a model whereby the filaments form
through compression of the intracluster gas by relativistic plasma emitted from
the active nucleus of NGC 1275. Imaging spectroscopy with the Densepak fiber
array on WIYN suggests partial rotational support of the inner component of low
velocity ionized gas. We confirm and extend evidence for features in the
stellar body of NGC 1275, and identify outer stellar regions containing very
blue, probably very young, star clusters. We interpret these as evidence for
recent accretion of a gas-rich system, with subsequent star formation. We
suggest that two main processes, which may be causally connected, are
responsible for the rich phenomenology of the NGC 1275 system -- NGC 1275
experienced a recent merger/interaction with a group of gas-rich galaxies, and
recent outflows from its AGN have compressed the intracluster gas, and perhaps
the gas in the infalling galaxies, to produce a complex web of filaments.
(Abridged)Comment: AJ, accepted; a recommended full resolution version is available at
http://www.astro.wisc.edu/~chris/pera.p
A Search for Time Variation of the Fine Structure Constant
A method offering an order of magnitude sensitivity gain is described for
using quasar spectra to investigate possible time or space variation in the
fine structure constant, alpha. Applying the technique to a sample of 30
absorption systems, spanning redshifts 0.5 < z< 1.6, obtained with the Keck I
telescope, we derive limits on variations in alpha over a wide range of epochs.
For the whole sample Delta(alpha)/alpha = -1.1 +/- 0.4 x 10^{-5}. This
deviation is dominated by measurements at z > 1, where Delta(alpha)/alpha =
-1.9 +/- 0.5 x 10^{-5}. For z < 1, Delta(alpha)/alpha = -0.2 +/- 0.4 x 10^{-5},
consistent with other known constraints. Whilst these results are consistent
with a time-varying alpha, further work is required to explore possible
systematic errors in the data, although careful searches have so far not
revealed any.Comment: 4 pages, 1 figure, accepted for publication in Physical Review
Letter
Galaxy morphology and evolution from SWAN Adaptive Optics imaging
We present the results from adaptive optics (AO) assisted imaging in the Ks
band of an area of 15 arcmin^2 for SWAN (Survey of a Wide Area with NACO). We
derive the high resolution near-IR morphology of ~400 galaxies up to Ks~23.5 in
the first 21 SWAN fields around bright guide stars, carefully taking into
account the survey selection effects and using an accurate treatment of the
anisoplanatic AO PSF. The detected galaxies are sorted into two morphological
classes according to their Sersic index. The extracted morphological properties
and number counts of the galaxies are compared with the predictions of
different galaxy formation and evolution models, both for the whole galaxy
population and separately for late-type and early-type galaxies. This is one of
the first times such a comparison has been done in the near-IR, as AO
observations and accurate PSF modeling are needed to obtain reliable
morphological classification of faint field galaxies at these wavelengths. For
early-type galaxies we find that a pure luminosity evolution model, without
evidence for relevant number and size evolution, better reproduces the observed
properties of our Ks-selected sample than current semi-analytic models based on
the hierarchical picture of galaxy formation. In particular, we find that the
observed flattening of elliptical galaxy counts at Ks~20 is quantitatively in
good agreement with the prediction of the pure luminosity evolution model that
was calculated prior to the observation. For late-type galaxies, while both
models are able to reproduce the number counts, we find some hints of a
possible size growth. These results demonstrate the unique power of AO
observations to derive high resolution details of faint galaxies' morphology in
the near-IR and drive studies of galaxy evolution.Comment: 15 pages, 10 figures. A&A, in press. Final version with corrected
typo
Renal function and the effects of vericiguat in patients with worsening heart failure with reduced ejection fraction:insights from the VICTORIA (Vericiguat Global Study in Subjects with HFrEF) trial
AIMS: Vericiguat reduced the primary composite outcome of cardiovascular death or heart failure (HF) hospitalization in patients with worsening HF with reduced ejection fraction (HFrEF) and a lower limit of baseline estimated glomerular filtration rate (eGFR) of 15âmL/min/1.73âm(2). We evaluated the relationship between the efficacy of vericiguat and baseline and subsequent changes in renal function. METHODS AND RESULTS: In VICTORIA, core laboratory serum creatinine was measured at baseline (n = 4956) and weeks 16, 32, and 48. Worsening renal function (WRF), defined as an increase â„0.3 mg/dL in creatinine from baseline to week 16, was assessed via a Cox model with respect to subsequent primary events. Mean age was 69âyears, 24% were female, and mean baseline eGFR was 61âmL/min/1.73âm(2). During 48âweeks of treatment, the trajectories in eGFR and creatinine with vericiguat were similar to placebo (P = 0.50 and 0.18). The beneficial effects of vericiguat on the primary outcome were not influenced by baseline eGFR (interaction P = 0.48). WRF occurred in 15% of patients and was associated with worse outcomes (adjusted hazard ratio 1.28, 95% confidence interval 1.11â1.47; Pâ<â0.001), but the beneficial effects of vericiguat on the primary outcome were similar in patients with or without WRF (interaction P = 0.76). CONCLUSION: Renal function trajectories were similar between vericiguatâ and placeboâtreated patients and the beneficial effects of vericiguat on the primary outcome were consistent across the full range of eGFR and irrespective of WRF
Simulations of Mixed Morphology Supernova Remnants With Anisotropic Thermal Conduction
We explore the role of anisotropic thermal conduction on the evolution of
supernova remnants through interstellar media with a range of densities via
numerical simulations. We find that a remnant expanding in a dense environment
can produce centre-bright hard x-ray emission within 20 kyr, and centre-bright
soft x-ray emission within 60 kyr of the supernova event. In a more tenuous
environment, the appearance of a centre-bright structure in hard x-rays is
delayed until about 60 kyr. The soft x-ray emission from such a remnant may not
become centre bright during its observable lifetime. This can explain the
observations that show that mixed-morphology supernova remnants preferentially
occur close to denser, molecular environments. Remnants expanding into denser
environments tend to be smaller, making it easier for thermal conduction to
make larger changes in the temperatures of their hot gas bubbles. We show that
the lower temperatures make it very favorable to use high-stage ions as
diagnostics of the hot gas bubbles in SNRs. In particular, the distribution of
O VIII transitions from shell-bright at early epochs to centre-bright at later
epochs in the evolution of an SNR expanding in a dense ISM when the physics of
thermal conduction is included.Comment: 8 pages, 5 figures, submitted to Monthly Notice
A multiorganism pipeline for antiseizure drug discovery:Identification of chlorothymol as a novel Îł-aminobutyric acidergic anticonvulsant
OBJECTIVE:Current medicines are ineffective in approximately one-third of people with epilepsy. Therefore, new antiseizure drugs are urgently needed to address this problem of pharmacoresistance. However, traditional rodent seizure and epilepsy models are poorly suited to high-throughput compound screening. Furthermore, testing in a single species increases the chance that therapeutic compounds act on molecular targets that may not be conserved in humans. To address these issues, we developed a pipeline approach using four different organisms. METHODS:We sequentially employed compound library screening in the zebrafish, Danio rerio, chemical genetics in the worm, Caenorhabditis elegans, electrophysiological analysis in mouse and human brain slices, and preclinical validation in mouse seizure models to identify novel antiseizure drugs and their molecular mechanism of action. RESULTS:Initially, a library of 1690 compounds was screened in an acute pentylenetetrazol seizure model using D rerio. From this screen, the compound chlorothymol was identified as an effective anticonvulsant not only in fish, but also in worms. A subsequent genetic screen in C elegans revealed the molecular target of chlorothymol to be LGC-37, a worm Îł-aminobutyric acid type A (GABAA ) receptor subunit. This GABAergic effect was confirmed using in vitro brain slice preparations from both mice and humans, as chlorothymol was shown to enhance tonic and phasic inhibition and this action was reversed by the GABAA receptor antagonist, bicuculline. Finally, chlorothymol exhibited in vivo anticonvulsant efficacy in several mouse seizure assays, including the 6-Hz 44-mA model of pharmacoresistant seizures. SIGNIFICANCE:These findings establish a multiorganism approach that can identify compounds with evolutionarily conserved molecular targets and translational potential, and so may be useful in drug discovery for epilepsy and possibly other conditions
Obscured Starburst Activity in High Redshift Clusters and Groups
Using Spitzer-MIPS 24um imaging and Keck spectroscopy we examine the nature
of the obscured star forming population in three clusters and three groups at
z~0.9. These six systems are components of the Cl1604 supercluster, the largest
structure imaged by Spitzer at redshifts near unity. We find that the average
density of 24um-detected galaxies within the Cl1604 clusters is nearly twice
that of the surrounding field and that this overdensity scales with the
cluster's dynamical state. The 24um-bright members often appear optically
unremarkable and exhibit only moderate [OII] line emission due to severe
obscuration. Their spatial distribution suggests they are an infalling
population, but an examination of their spectral properties, morphologies and
optical colors indicate they are not simply analogs of the field population
that have yet to be quenched. Using stacked composite spectra, we find the
24um-detected cluster and group galaxies exhibit elevated levels of Balmer
absorption compared to galaxies undergoing normal, continuous star formation. A
similar excess is not observed in field galaxies with equivalent infrared
luminosities, indicating a greater fraction of the detected cluster and group
members have experienced a burst of star formation in the recent past compared
to their counterparts in the field. Our results suggest that gas-rich galaxies
at high redshift experience a temporary increase in their star formation
activity as they assemble into denser environments. Using HST-ACS imaging we
find that disturbed morphologies are common among the 24um-detected cluster and
group members and become more prevalent in regions of higher galaxy density. We
conclude that mergers are the dominant triggering mechanism responsible for the
enhanced star formation found in the Cl1604 groups, while a mix of harassment
and mergers are likely driving the activity of the cluster galaxies.Comment: 18 pages, 19 figures, submitted to Ap
The Team Keck Treasury Redshift Survey of the GOODS-North Field
We report the results of an extensive imaging and spectroscopic survey in the
GOODS-North field completed using DEIMOS on the Keck II telescope. Observations
of 2018 targets in a magnitude-limited sample of 2911 objects to R=24.4 yield
secure redshifts for a sample of 1440 galaxies and AGN plus 96 stars. In
addition to redshifts and associated quality assessments, our catalog also
includes photometric and astrometric measurements for all targets detected in
our R-band imaging survey of the GOODS-North region. We investigate various
sources of incompleteness and find the redshift catalog to be 53% complete at
its limiting magnitude. The median redshift of z=0.65 is lower than in similar
deep surveys because we did not select against low-redshift targets. Comparison
with other redshift surveys in the same field, including a complementary
Hawaii-led DEIMOS survey, establishes that our velocity uncertainties are as
low as 40 km/s for red galaxies and that our redshift confidence assessments
are accurate. The distributions of rest-frame magnitudes and colors among the
sample agree well with model predictions out to and beyond z=1. We will release
all survey data, including extracted 1-D and sky-subtracted 2-D spectra, thus
providing a sizable and homogeneous database for the GOODS-North field which
will enable studies of large scale structure, spectral indices, internal galaxy
kinematics, and the predictive capabilities of photometric redshifts.Comment: 17 pages, 18 figures, submitted to AJ; v2 minor changes; see survey
database at http://www2.keck.hawaii.edu/realpublic/science/tksurvey
HETDEX pilot survey for emission-line galaxies - I. Survey design, performance, and catalog
We present a catalog of emission-line galaxies selected solely by their
emission-line fluxes using a wide-field integral field spectrograph. This work
is partially motivated as a pilot survey for the upcoming Hobby-Eberly
Telescope Dark Energy Experiment (HETDEX). We describe the observations,
reductions, detections, redshift classifications, line fluxes, and counterpart
information for 397 emission-line galaxies detected over 169 sq.arcmin with a
3500-5800 Ang. bandpass under 5 Ang. full-width-half-maximum (FWHM) spectral
resolution. The survey's best sensitivity for unresolved objects under
photometric conditions is between 4-20 E-17 erg/s/sq.cm depending on the
wavelength, and Ly-alpha luminosities between 3-6 E42 erg/s are detectable.
This survey method complements narrowband and color-selection techniques in the
search for high redshift galaxies with its different selection properties and
large volume probed. The four survey fields within the COSMOS, GOODS-N, MUNICS,
and XMM-LSS areas are rich with existing, complementary data. We find 104
galaxies via their high redshift Ly-alpha emission at 1.9<z<3.8, and the
majority of the remainder objects are low redshift [OII]3727 emitters at
z<0.56. The classification between low and high redshift objects depends on
rest frame equivalent width, as well as other indicators, where available.
Based on matches to X-ray catalogs, the active galactic nuclei (AGN) fraction
amongst the Ly-alpha emitters (LAEs) is 6%. We also analyze the survey's
completeness and contamination properties through simulations. We find five
high-z, highly-significant, resolved objects with full-width-half-maximum sizes
>44 sq.arcsec which appear to be extended Ly-alpha nebulae. We also find three
high-z objects with rest frame Ly-alpha equivalent widths above the level
believed to be achievable with normal star formation, EW(rest)>240 Ang.Comment: 45 pages, 36 figures, 5 tables, submitted to ApJ
The Evolution of Ly-alpha Emitting Galaxies Between z = 2.1 and z = 3.1
We describe the results of a new, wide-field survey for z=3.1 Ly-alpha
emission-line galaxies (LAEs) in the Extended Chandra Deep Field South
(ECDF-S). By using a nearly top-hat 5010 Angstrom filter and complementary
broadband photometry from the MUSYC survey, we identify a complete sample of
141 objects with monochromatic fluxes brighter than 2.4E-17 ergs/cm^2/s and
observers-frame equivalent widths greater than ~ 80 Angstroms (i.e., 20
Angstroms in the rest-frame of Ly-alpha). The bright-end of this dataset is
dominated by x-ray sources and foreground objects with GALEX detections, but
when these interlopers are removed, we are still left with a sample of 130 LAE
candidates, 39 of which have spectroscopic confirmations. This sample overlaps
the set of objects found in an earlier ECDF-S survey, but due to our filter's
redder bandpass, it also includes 68 previously uncataloged sources. We confirm
earlier measurements of the z=3.1 LAE emission-line luminosity function, and
show that an apparent anti-correlation between equivalent width and continuum
brightness is likely due to the effect of correlated errors in our
heteroskedastic dataset. Finally, we compare the properties of z=3.1 LAEs to
LAEs found at z=2.1. We show that in the ~1 Gyr after z~3, the LAE luminosity
function evolved significantly, with L* fading by ~0.4 mag, the number density
of sources with L > 1.5E42 ergs/s declining by ~50%, and the equivalent width
scale-length contracting from 70^{+7}_{-5} Angstroms to 50^{+9}_{-6} Angstroms.
When combined with literature results, our observations demonstrate that over
the redshift range z~0 to z~4, LAEs contain less than ~10% of the
star-formation rate density of the universe.Comment: 39 pages, 12 figures, Accepted to Ap
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