172 research outputs found
A study of the elements copper through uranium in Sirius A: Contributions from STIS and ground-based spectra
We determine abundances or upper limits for all of the 55 stable elements
from copper to uranium for the A1 Vm star Sirius. The purpose of the study is
to assemble the most complete picture of elemental abundances with the hope of
revealing the chemical history of the brightest star in the sky, apart from the
Sun. We also explore the relationship of this hot metallic-line (Am) star to
its cooler congeners, as well as the hotter, weakly- or non-magnetic
mercury-manganese (HgMn) stars. Our primary observational material consists of
{\em Hubble Space Telescope} () spectra taken with the Space Telescope
Imaging Spectrograph (STIS) in the ASTRAL project. We have also used archival
material from the %\citep/{ayr10}. satellite, and from the
Goddard High-Resolution Spectrograph (GHRS), as well as ground-based spectra
from Furenlid, Westin, Kurucz, Wahlgren, and their coworkers, ESO spectra from
the UVESPOP project, and NARVAL spectra retrieved from PolarBase. Our analysis
has been primarily by spectral synthesis, and in this work we have had the
great advantage of extensive atomic data unavailable to earlier workers. We
find most abundances as well as upper limits range from 10 to 100 times above
solar values. We see no indication of the huge abundance excesses of 1000 or
more that occur among many chemically peculiar (CP) stars of the upper main
sequence. The picture of Sirius as a hot Am star is reinforced.Comment: With 6 Figures and 4 Tables; accepted for publication in Ap
Synthetic lethal screening in the mammalian central nervous system identifies Gpx6 as a modulator of Huntington’s disease
Huntington’s disease, the most common inherited neurodegenerative disease, is characterized by a dramatic loss of deep-layer cortical and striatal neurons, as well as morbidity in midlife. Human genetic studies led to the identification of the causative gene, huntingtin. Recent genomic advances have also led to the identification of hundreds of potential interacting partners for huntingtin protein and many hypotheses as to the molecular mechanisms whereby mutant huntingtin leads to cellular dysfunction and death. However, the multitude of possible interacting partners and cellular pathways affected by mutant huntingtin has complicated efforts to understand the etiology of this disease, and to date no curative therapeutic exists. To address the general problem of identifying the disease-phenotype contributing genes from a large number of correlative studies, here we develop a synthetic lethal screening methodology for the mammalian central nervous system, called SLIC, for synthetic lethal in the central nervous system. Applying SLIC to the study of Huntington’s disease, we identify the age-regulated glutathione peroxidase 6 (Gpx6) gene as a modulator of mutant huntingtin toxicity and show that overexpression of Gpx6 can dramatically alleviate both behavioral and molecular phenotypes associated with a mouse model of Huntington’s disease. SLIC can, in principle, be used in the study of any neurodegenerative disease for which a mouse model exists, promising to reveal modulators of neurodegenerative disease in an unbiased fashion, akin to screens in simpler model organisms.National Institute of Neurological Disorders and Stroke (U.S.) (Award R01NS085880)William N. and Bernice E. Bumpus Foundation (Early Career Investigator Innovation Award)JPB FoundationEuropean Molecular Biology Organization (Long-term Fellowship
Z-FIRE: ISM properties of the z = 2.095 COSMOS Cluster
We investigate the ISM properties of 13 star-forming galaxies within the z~2
COSMOS cluster. We show that the cluster members have [NII]/Ha and [OIII]/Hb
emission-line ratios similar to z~2 field galaxies, yet systematically
different emission-line ratios (by ~0.17 dex) from the majority of local
star-forming galaxies. We find no statistically significant difference in the
[NII]/Ha and [OIII]/Hb line ratios or ISM pressures among the z~2 cluster
galaxies and field galaxies at the same redshift. We show that our cluster
galaxies have significantly larger ionization parameters (by up to an order of
magnitude) than local star-forming galaxies. We hypothesize that these high
ionization parameters may be associated with large specific star formation
rates (i.e. a large star formation rate per unit stellar mass). If this
hypothesis is correct, then this relationship would have important implications
for the geometry and/or the mass of stars contained within individual star
clusters as a function of redshift.Comment: 11 pages, 5 figures, accepted for publication in Ap
ZFIRE: The Evolution of the Stellar Mass Tully-Fisher Relation to Redshift 2.0 < Z < 2.5 with MOSFIRE
Using observations made with MOSFIRE on Keck I as part of the ZFIRE survey,
we present the stellar mass Tully-Fisher relation at 2.0 < z < 2.5. The sample
was drawn from a stellar mass limited, Ks-band selected catalog from ZFOURGE
over the CANDELS area in the COSMOS field. We model the shear of the Halpha
emission line to derive rotational velocities at 2.2X the scale radius of an
exponential disk (V2.2). We correct for the blurring effect of a
two-dimensional PSF and the fact that the MOSFIRE PSF is better approximated by
a Moffat than a Gaussian, which is more typically assumed for natural seeing.
We find for the Tully-Fisher relation at 2.0 < z < 2.5 that logV2.2 =(2.18 +/-
0.051)+(0.193 +/- 0.108)(logM/Msun - 10) and infer an evolution of the
zeropoint of Delta M/Msun = -0.25 +/- 0.16 dex or Delta M/Msun = -0.39 +/- 0.21
dex compared to z = 0 when adopting a fixed slope of 0.29 or 1/4.5,
respectively. We also derive the alternative kinematic estimator S0.5, with a
best-fit relation logS0.5 =(2.06 +/- 0.032)+(0.211 +/- 0.086)(logM/Msun - 10),
and infer an evolution of Delta M/Msun= -0.45 +/- 0.13 dex compared to z < 1.2
if we adopt a fixed slope. We investigate and review various systematics,
ranging from PSF effects, projection effects, systematics related to stellar
mass derivation, selection biases and slope. We find that discrepancies between
the various literature values are reduced when taking these into account. Our
observations correspond well with the gradual evolution predicted by
semi-analytic models.Comment: 21 pages, 14 figures, 1 appendix. Accepted for publication by Apj,
February 28, 201
ZFIRE: Using H equivalent widths to investigate the in situ initial mass function at z~2
We use the ZFIRE survey (http://zfire.swinburne.edu.au) to investigate the
high mass slope of the initial mass function (IMF) for a mass-complete
(log10(M/M)~9.3) sample of 102 star-forming galaxies at z~2 using
their H equivalent widths (H-EW) and rest-frame optical
colours. We compare dust-corrected H-EW distributions with predictions
of star-formation histories (SFH) from PEGASE.2 and Starburst99 synthetic
stellar population models. We find an excess of high H-EW galaxies that
are up to 0.3--0.5 dex above the model-predicted Salpeter IMF locus and the
H-EW distribution is much broader (10--500 \AA) than can easily be
explained by a simple monotonic SFH with a standard Salpeter-slope IMF. Though
this discrepancy is somewhat alleviated when it is assumed that there is no
relative attenuation difference between stars and nebular lines, the result is
robust against observational biases, and no single IMF (i.e. non-Salpeter
slope) can reproduce the data. We show using both spectral stacking and Monte
Carlo simulations that starbursts cannot explain the EW distribution. We
investigate other physical mechanisms including models with variations in
stellar rotation, binary star evolution, metallicity, and the IMF upper-mass
cutoff. IMF variations and/or highly rotating extreme metal poor stars
(Z~0.1Z) with binary interactions are the most plausible explanations
for our data. If the IMF varies, then the highest H-EWs would require
very shallow slopes (>-1.0) with no one slope able to reproduce the
data. Thus, the IMF would have to vary stochastically. We conclude that the
stellar populations at z~2 show distinct differences from local populations and
there is no simple physical model to explain the large variation in
H-EWs at z~2.Comment: Accepted to MNRAS. 43 pages, 27 Figures. Survey website:
http://zfire.swinburne.edu.au
ZFIRE: A KECK/MOSFIRE Spectroscopic Survey of Galaxies in Rich Environments at z~2
We present an overview and the first data release of ZFIRE, a spectroscopic
redshift survey of star-forming galaxies that utilizes the MOSFIRE instrument
on Keck-I to study galaxy properties in rich environments at . ZFIRE
measures accurate spectroscopic redshifts and basic galaxy properties derived
from multiple emission lines. The galaxies are selected from a stellar mass
limited sample based on deep near infra-red imaging () and
precise photometric redshifts from the ZFOURGE and UKIDSS surveys as well as
grism redshifts from 3DHST. Between 2013--2015 ZFIRE has observed the COSMOS
and UDS legacy fields over 13 nights and has obtained 211 galaxy redshifts over
from a combination of nebular emission lines (such as \Halpha,
\NII, \Hbeta, \OII, \OIII, \SII) observed at 1--2\micron. Based on our
medium-band NIR photometry, we are able to spectrophotometrically flux
calibrate our spectra to \around10\% accuracy. ZFIRE reaches emission
line flux limits of \around with a
resolving power of and reaches masses down to \around10\msol. We
confirm that the primary input survey, ZFOURGE, has produced photometric
redshifts for star-forming galaxies (including highly attenuated ones) accurate
to with outliers. We measure a
slight redshift bias of , and we note that the redshift bias tends to
be larger at higher masses. We also examine the role of redshift on the
derivation of rest-frame colours and stellar population parameters from SED
fitting techniques. The ZFIRE survey extends spectroscopically-confirmed samples across a richer range of environments, here we make available the
first public release of the data for use by the
community.\footnote{\url{http://zfire.swinburne.edu.au}}Comment: Published in ApJ. Data available at http://zfire.swinburne.edu.au,
Code for figures at https://github.com/themiyan/zfire_survey, 31 pages, 24
figure
Large scale structure around a z=2.1 cluster
The most prodigious starburst galaxies are absent in massive galaxy clusters
today, but their connection with large scale environments is less clear at
. We present a search of large scale structure around a galaxy
cluster core at using a set of spectroscopically confirmed galaxies.
We find that both color-selected star-forming galaxies (SFGs) and dusty
star-forming galaxies (DSFGs) show significant overdensities around the
cluster. A total of 8 DSFGs (including 3 X-ray luminous active
galactic nuclei, AGNs) and 34 SFGs are found within a 10 arcmin radius
(corresponds to 15 cMpc at ) from the cluster center and within
a redshift range of , which leads to galaxy overdensities of
and . The cluster core and
the extended DSFG- and SFG-rich structure together demonstrate an active
cluster formation phase, in which the cluster is accreting a significant amount
of material from large scale structure while the more mature core may begin to
virialize. Our finding of this DSFG-rich structure, along with a number of
other protoclusters with excess DSFGs and AGNs found to date, suggest that the
overdensities of these rare sources indeed trace significant mass
overdensities. However, it remains puzzling how these intense star formers are
triggered concurrently. Although an increased probability of galaxy
interactions and/or enhanced gas supply can trigger the excess of DSFGs, our
stacking analysis based on 850 m images and morphological analysis based
on rest-frame optical imaging do not show such enhancements of merger fraction
and gas content in this structure.Comment: 11 pages, 4 figures, ApJ accepte
ZFOURGE: Using Composite Spectral Energy Distributions to Characterize Galaxy Populations at 1<z<4
We investigate the properties of galaxies as they shut off star formation
over the 4 billion years surrounding peak cosmic star formation. To do this we
categorize galaxies from into groups based on the shape
of their spectral energy distributions (SEDs) and build composite SEDs with
resolution. These composite SEDs show a variety of spectral shapes
and also show trends in parameters such as color, mass, star formation rate,
and emission line equivalent width. Using emission line equivalent widths and
strength of the 4000\AA\ break, , we categorize the composite SEDs
into five classes: extreme emission line, star-forming, transitioning,
post-starburst, and quiescent galaxies. The transitioning population of
galaxies show modest H emission (\AA) compared to
more typical star-forming composite SEDs at
(\AA). Together with their smaller sizes (3 kpc vs. 4 kpc)
and higher S\'ersic indices (2.7 vs. 1.5), this indicates that morphological
changes initiate before the cessation of star formation. The transitional group
shows a strong increase of over one dex in number density from to
, similar to the growth in the quiescent population, while
post-starburst galaxies become rarer at . We calculate average
quenching timescales of 1.6 Gyr at and 0.9 Gyr at and
conclude that a fast quenching mechanism producing post-starbursts dominated
the quenching of galaxies at early times, while a slower process has become
more common since .Comment: Accepted for publication in The Astrophysical Journa
Z-FIRE: ISM PROPERTIES OF THE z=2.095 COSMOS CLUSTER
We investigate the ISM properties of 13 star-forming galaxies within the z~ 2 COSMOS cluster. We show that the cluster members have [N ii]/Halpha and [O iii]/Hbeta emission-line ratios similar to z~ 2 field galaxies, yet systematically different emission-line ratios (by ~0.17 dex) from the majority of local star-forming galaxies. We find no statistically significant difference in the [N ii]/Halpha and [O iii]/Hbeta line ratios or ISM pressures among the z~ 2 cluster galaxies and field galaxies at the same redshift. We show that our cluster galaxies have significantly larger ionization parameters (by up to an order of magnitude) than local star-forming galaxies. We hypothesize that these high ionization parameters may be associated with large specific star formation rates (SFRs; i.e., a large SFR per unit stellar mass). If this hypothesis is correct, then this relationship would have important implications for the geometry and/or the mass of stars contained within individual star clusters as a function of redshift
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