75 research outputs found
The death of massive stars - II. Observational constraints on the progenitors of type Ibc supernovae
The progenitors of many type II core-collapse supernovae have now been
identified directly on pre-discovery imaging. Here we present an extensive
search for the progenitors of type Ibc supernovae in all available
pre-discovery imaging since 1998. There are 12 type Ibc supernovae with no
detections of progenitors in either deep ground-based or Hubble Space Telescope
archival imaging. The deepest absolute BVR magnitude limits are between -4 and
-5. We compare these limits with the observed Wolf-Rayet population in the
Large Magellanic Cloud and estimate a 16 per cent probability we have failed to
detect such a progenitor by chance. Alternatively the progenitors evolve
significantly before core-collapse or we have underestimated the extinction
towards the progenitors. Reviewing the relative rates and ejecta mass estimates
from lightcurve modelling of Ibc SNe, we find both incompatible with Wolf-Rayet
stars with initial masses >25Msun being the only progenitors. We present binary
evolution models that fit these observational constraints. Stars in binaries
with initial masses <20Msun lose their hydrogen envelopes in binary
interactions to become low mass helium stars. They retain a low mass hydrogen
envelope until approximately 10,000 years before core-collapse; hence it is not
surprising that galactic analogues have been difficult to identify.Comment: Accepted by MNRAS. 31 pages, 12 figures, 8 table
The birth place of the type Ic Supernova 2007gr
We report our attempts to locate the progenitor of the peculiar type Ic SN
2007gr in HST pre-explosion images of the host galaxy, NGC 1058. Aligning
adaptive optics Altair/NIRI imaging of SN 2007gr from the Gemini (North)
Telescope with the pre-explosion HST WFPC2 images, we identify the SN position
on the HST frames with an accuracy of 20 mas. Although nothing is detected at
the SN position we show that it lies on the edge of a bright source, 134+/-23
mas (6.9 pc) from its nominal centre. Based on its luminosity we suggest that
this object is possibly an unresolved, compact and coeval cluster and that the
SN progenitor was a cluster member, although we note that model profile fitting
favours a single bright star. We find two solutions for the age of this assumed
cluster; 7-/+0.5 Myrs and 20-30 Myrs, with turn-off masses of 28+/-4 Msun and
12-9 Msun respectively. Pre-explosion ground-based K-band images marginally
favour the younger cluster age/higher turn-off mass. Assuming the SN progenitor
was a cluster member, the turn-off mass provides the best estimate for its
initial mass. More detailed observations, after the SN has faded, should
determine if the progenitor was indeed part of a cluster, and if so allow an
age estimate to within ~2 Myrs thereby favouring either a high mass single star
or lower mass interacting binary progenitor.Comment: 12 pages, 3 figures, resolution of fig 1. has been reduced, some
revision based on referee's comments, Accepted ApJL 27 Nov 200
Identification of Histoplasma-Specific Peptides in Human Urine
Histoplasmosis is a severe dimorphic fungus infection, which is often difficult to diagnose due to similarity in symptoms to other diseases and lack of specific diagnostic tests. Urine samples from histoplasma-antigen-positive patients and appropriate controls were prepared using various sample preparation strategies including immunoenrichment, ultrafiltration, high-abundant protein depletion, deglycosylation, reverse-phase fractions, and digest using various enzymes. Samples were then analyzed by nanospray tandem mass spectrometry. Accurate mass TOF scans underwent molecular feature extraction and statistical analysis for unique disease makers, and acquired MS/MS data were searched against known human and histoplasma proteins. In human urine, some 52 peptides from 37 Histoplasma proteins were identified with high confidence. This is the first report of identification of a large number of Histoplasma-specific peptides from immunoassay-positive patient samples using tandem mass spectrometry and bioinformatics techniques. These findings may lead to novel diagnostic markers for histoplasmosis in human urine
Galaxy Zoo: dust lane early-type galaxies are tracers of recent, gas-rich minor mergers
We present the second of two papers concerning the origin and evolution of
local early-type galaxies exhibiting dust features. We use optical and radio
data to examine the nature of active galactic nucleus (AGN) activity in these
objects, and compare these with a carefully constructed control sample. We find
that dust lane early-type galaxies are much more likely to host emission-line
AGN than the control sample galaxies. Moreover, there is a strong correlation
between radio and emission-line AGN activity in dust lane early-types, but not
the control sample. Dust lane early-type galaxies show the same distribution of
AGN properties in rich and poor environments, suggesting a similar triggering
mechanism. By contrast, this is not the case for early-types with no dust
features. These findings strongly suggest that dust lane early-type galaxies
are starburst systems formed in gas-rich mergers. Further evidence in support
of this scenario is provided by enhanced star formation and black hole
accretion rates in these objects. Dust lane early-types therefore represent an
evolutionary stage between starbursting and quiescent galaxies. In these
objects, the AGN has already been triggered but has not as yet completely
destroyed the gas reservoir required for star formation.Comment: 11 pages, 18 figures, 4 tables, MNRAS (Accepted for publication- 2012
January 19
Galaxy Zoo: dust and molecular gas in early-type galaxies with prominent dust lanes
We study dust and associated molecular gas in 352 nearby early-type galaxies
(ETGs) with prominent dust lanes. 65% of these `dusty ETGs' (D-ETGs) are
morphologically disturbed, suggesting a merger origin. This is consistent with
the D-ETGs residing in lower density environments compared to the controls
drawn from the general ETG population. 80% of D-ETGs inhabit the field
(compared to 60% of the controls) and <2% inhabit clusters (compared to 10% of
the controls). Compared to the controls, D-ETGs exhibit bluer UV-optical
colours (indicating enhanced star formation) and an AGN fraction that is more
than an order of magnitude greater (indicating higher incidence of nuclear
activity). The clumpy dust mass residing in large-scale features is estimated,
using the SDSS r-band images, to be 10^{4.5}-10^{6.5} MSun. A comparison to the
total (clumpy + diffuse) dust masses- calculated using the far-IR fluxes of 15%
of the D-ETGs that are detected by the IRAS- indicates that only ~20% of the
dust resides in these large-scale features. The dust masses are several times
larger than the maximum value expected from stellar mass loss, ruling out an
internal origin. The dust content shows no correlation with the blue
luminosity, indicating that it is not related to a galactic scale cooling flow.
No correlation is found with the age of the recent starburst, suggesting that
the dust is accreted directly in the merger rather than being produced in situ
by the triggered star formation. Using molecular gas-to-dust ratios of ETGs in
the literature we estimate that the median current and initial molecular gas
fraction are ~1.3% and ~4%, respectively. Recent work suggests that the merger
activity in nearby ETGs largely involves minor mergers (mass ratios between
1:10 and 1:4). If the IRAS-detected D-ETGs form via this channel, then the
original gas fractions of the accreted satellites are 20%-44%. [Abridged]Comment: 11 pages, 18 figures, 1 table, MNRAS (Accepted for publication- 2012
March 19
Anatomy of a post-starburst minor merger: a multi-wavelength WFC3 study of NGC 4150
(Abridged) We present a spatially-resolved near-UV/optical study of NGC 4150,
using the Wide Field Camera 3 (WFC3) on board the Hubble Space Telescope.
Previous studies of this early-type galaxy (ETG) indicate that it has a large
reservoir of molecular gas, exhibits a kinematically decoupled core (likely
indication of recent merging) and strong, central H_B absorption (indicative of
young stars). The core of NGC 4150 shows ubiquitous near-UV emission and
remarkable dusty substructure. Our analysis shows this galaxy to lie in the
near-UV green valley, and its pixel-by-pixel photometry exhibits a narrow range
of near-UV/optical colours that are similar to those of nearby E+A
(post-starburst) galaxies. We parametrise the properties of the recent star
formation (age, mass fraction, metallicity and internal dust content) in the
NGC 4150 pixels by comparing the observed near-UV/optical photometry to stellar
models. The typical age of the recent star formation (RSF) is around 0.9 Gyrs,
consistent with the similarity of the near-UV colours to post-starburst
systems, while the morphological structure of the young component supports the
proposed merger scenario. The RSF metallicity, representative of the
metallicity of the gas fuelling star formation, is around 0.3 - 0.5 Zsun.
Assuming that this galaxy is a merger and that the gas is sourced mainly from
the infalling companion, these metallicities plausibly indicate the gas-phase
metallicity (GPM) of the accreted satellite. Comparison to the local mass-GPM
relation suggests (crudely) that the mass of the accreted system is around
3x10^8 Msun, making NGC 4150 a 1:20 minor merger. A summation of the pixel RSF
mass fractions indicates that the RSF contributes about 2-3 percent of the
stellar mass. This work reaffirms our hypothesis that minor mergers play a
significant role in the evolution of ETGs at late epochs.Comment: 28 pages, 2 tables, accepted for publication in Ap
The Hubble Space Telescope Wide Field Camera 3 Early Release Science data: Panchromatic Faint Object Counts for 0.2-2 microns wavelength
We describe the Hubble Space Telescope (HST) Wide Field Camera 3 (WFC3) Early
Release Science (ERS) observations in the Great Observatories Origins Deep
Survey (GOODS) South field. The new WFC3 ERS data provide calibrated, drizzled
mosaics in the UV filters F225W, F275W, and F336W, as well as in the near-IR
filters F098M (Ys), F125W (J), and F160W (H) with 1-2 HST orbits per filter.
Together with the existing HST Advanced Camera for Surveys (ACS) GOODS-South
mosaics in the BViz filters, these panchromatic 10-band ERS data cover 40-50
square arcmin at 0.2-1.7 {\mu}m in wavelength at 0.07-0.15" FWHM resolution and
0.090" Multidrizzled pixels to depths of AB\simeq 26.0-27.0 mag (5-{\sigma})
for point sources, and AB\simeq 25.5-26.5 mag for compact galaxies.
In this paper, we describe: a) the scientific rationale, and the data taking
plus reduction procedures of the panchromatic 10-band ERS mosaics; b) the
procedure of generating object catalogs across the 10 different ERS filters,
and the specific star-galaxy separation techniques used; and c) the reliability
and completeness of the object catalogs from the WFC3 ERS mosaics. The
excellent 0.07-0.15" FWHM resolution of HST/WFC3 and ACS makes star- galaxy
separation straightforward over a factor of 10 in wavelength to AB\simeq 25-26
mag from the UV to the near-IR, respectively.Comment: 51 pages, 71 figures Accepted to ApJS 2011.01.2
A WFC3 study of globular clusters in NGC 4150 - an early-type minor merger
We combine near-ultraviolet (NUV; 2250 {\AA}) and optical (U, B, V, I)
imaging from the Wide Field Camera 3 (WFC3), on board the Hubble Space
Telescope (HST), to study the globular cluster (GC) population in NGC 4150, a
sub-L* (M_B ~ -18.48 mag) early-type minor-merger remnant in the Coma I cloud.
We use broadband NUV-optical photometry from the WFC3 to estimate individual
ages, metallicities, masses and line-of-sight extinctions [E_(B-V)] for 63
bright (M_V < -5 mag) GCs in this galaxy. In addition to a small GC population
with ages greater than 10 Gyr, we find a dominant population of clusters with
ages centred around 6 Gyr, consistent with the expected peak of stellar mass
assembly in faint early-types residing in low-density environments. The old and
intermediate-age GCs in NGC 4150 are metal-poor, with metallicities less than
0.1 ZSun, and reside in regions of low extinction (E_(B-V) < 0.05 mag). We also
find a population of young, metal-rich (Z > 0.3 ZSun) clusters that have formed
within the last Gyr and reside in relatively dusty (E_(B-V) > 0.3 mag) regions
that are coincident with the part of the galaxy core that hosts significant
recent star formation. Cluster disruption models (in which ~80-90% of objects
younger than a few 10^8 yr dissolve every dex in time) suggest that the bulk of
these young clusters are a transient population.Comment: Submitted to MNRAS Letter
SNAPSHOT USA 2019 : a coordinated national camera trap survey of the United States
This article is protected by copyright. All rights reserved.With the accelerating pace of global change, it is imperative that we obtain rapid inventories of the status and distribution of wildlife for ecological inferences and conservation planning. To address this challenge, we launched the SNAPSHOT USA project, a collaborative survey of terrestrial wildlife populations using camera traps across the United States. For our first annual survey, we compiled data across all 50 states during a 14-week period (17 August - 24 November of 2019). We sampled wildlife at 1509 camera trap sites from 110 camera trap arrays covering 12 different ecoregions across four development zones. This effort resulted in 166,036 unique detections of 83 species of mammals and 17 species of birds. All images were processed through the Smithsonian's eMammal camera trap data repository and included an expert review phase to ensure taxonomic accuracy of data, resulting in each picture being reviewed at least twice. The results represent a timely and standardized camera trap survey of the USA. All of the 2019 survey data are made available herein. We are currently repeating surveys in fall 2020, opening up the opportunity to other institutions and cooperators to expand coverage of all the urban-wild gradients and ecophysiographic regions of the country. Future data will be available as the database is updated at eMammal.si.edu/snapshot-usa, as well as future data paper submissions. These data will be useful for local and macroecological research including the examination of community assembly, effects of environmental and anthropogenic landscape variables, effects of fragmentation and extinction debt dynamics, as well as species-specific population dynamics and conservation action plans. There are no copyright restrictions; please cite this paper when using the data for publication.Publisher PDFPeer reviewe
The Protective Action Encoding of Serotonin Transients in the Human Brain
The role of serotonin in human brain function remains elusive due, at least in part, to our inability to measure rapidly the local concentration of this neurotransmitter. We used fast-scan cyclic voltammetry to infer serotonergic signaling from the striatum of fourteen brains of human patients with Parkinson's disease. Here we report these novel measurements and show that they correlate with outcomes and decisions in a sequential investment game. We find that serotonergic concentrations transiently increase as a whole following negative reward prediction errors, while reversing when counterfactual losses predominate. This provides initial evidence that the serotonergic system acts as an opponent to dopamine signaling, as anticipated by theoretical models. Serotonin transients on one trial were also associated with actions on the next trial in a manner that correlated with decreased exposure to poor outcomes. Thus, the fluctuations observed for serotonin appear to correlate with the inhibition of over-reactions and promote persistence of ongoing strategies in the face of short-term environmental changes. Together these findings elucidate a role for serotonin in the striatum, suggesting it encodes a protective action strategy that mitigates risk and modulates choice selection particularly following negative environmental events
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