36 research outputs found
Tgif1 Counterbalances The Activity Of Core Pluripotency Factors In Mouse Embryonic Stem Cells
Core pluripotency factors, such as Oct4, Sox2, and Nanog, play important roles in maintaining embryonic stem cell (ESC) identity by autoregulatory feedforward loops. Nevertheless, the mechanism that provides precise control of the levels of the ESC core factors without indefinite amplification has remained elusive. Here, we report the direct repression of core pluripotency factors by Tgif1, a previously known terminal repressor of TGF beta/activin/nodal signaling. Overexpression of Tgif1 reduces the levels of ESC core factors, whereas its depletion leads to the induction of the pluripotency factors. We confirm the existence of physical associations between Tgif1 and Oct4, Nanog, and HDAC1/2 and further show the level of Tgif1 is not significantly altered by treatment with an activator/inhibitor of the TGF beta/activin/nodal signaling. Collectively, our findings establish Tgif1 as an integral member of the core regulatory circuitry of mouse ESCs that counterbalances the levels of the core pluripotency factors in a TGF beta/activin/nodal-independent manner.Cancer Prevention Research Institute of Texas (CPRIT) R1106Molecular Bioscience
The Wide Field Spectrograph (WiFeS): Performance and Data Reduction
This paper describes the on-telescope performance of the Wide Field
Spectrograph (WiFeS). The design characteristics of this instrument, at the
Research School of Astronomy and Astrophysics (RSAA) of the Australian National
University (ANU) and mounted on the ANU 2.3m telescope at the Siding Spring
Observatory has been already described in an earlier paper (Dopita et al.
2007). Here we describe the throughput, resolution and stability of the
instrument, and describe some minor issues which have been encountered. We also
give a description of the data reduction pipeline, and show some preliminary
results.Comment: Accepted for publication in Astrophysics & Space Science, 15pp, 11
figure
Cold gas outflows from the Small Magellanic Cloud traced with ASKAP
Feedback from massive stars plays a critical role in the evolution of the
Universe by driving powerful outflows from galaxies that enrich the
intergalactic medium and regulate star formation. An important source of
outflows may be the most numerous galaxies in the Universe: dwarf galaxies.
With small gravitational potential wells, these galaxies easily lose their
star-forming material in the presence of intense stellar feedback. Here, we
show that the nearby dwarf galaxy, the Small Magellanic Cloud (SMC), has atomic
hydrogen outflows extending at least 2 kiloparsecs (kpc) from the star-forming
bar of the galaxy. The outflows are cold, , and may have formed
during a period of active star formation million years (Myr) ago. The
total mass of atomic gas in the outflow is solar masses, , or % of the total atomic gas of the galaxy. The inferred
mass flux in atomic gas alone, , is up to an order of magnitude greater than the star
formation rate. We suggest that most of the observed outflow will be stripped
from the SMC through its interaction with its companion, the Large Magellanic
Cloud (LMC), and the Milky Way, feeding the Magellanic Stream of hydrogen
encircling the Milky Way.Comment: Published in Nature Astronomy, 29 October 2018,
http://dx.doi.org/10.1038/s41550-018-0608-
WALLABY Early Science - I. The NGC 7162 Galaxy Group
We present Widefield ASKAP L-band Legacy All-sky Blind Survey (WALLABY) early
science results from the Australian Square Kilometre Array Pathfinder (ASKAP)
observations of the NGC 7162 galaxy group. We use archival HIPASS and Australia
Telescope Compact Array (ATCA) observations of this group to validate the new
ASKAP data and the data reduction pipeline ASKAPsoft. We detect six galaxies in
the neutral hydrogen (HI) 21-cm line, expanding the NGC 7162 group membership
from four to seven galaxies. Two of the new detections are also the first HI
detections of the dwarf galaxies, AM 2159-434 and GALEXASC J220338.65-431128.7,
for which we have measured velocities of and km s,
respectively. We confirm that there is extended HI emission around NGC 7162
possibly due to past interactions in the group as indicated by the
offset between the kinematic and morphological major axes for NGC 7162A, and
its HI richness. Taking advantage of the increased resolution (factor of
) of the ASKAP data over archival ATCA observations, we fit a tilted
ring model and use envelope tracing to determine the galaxies' rotation curves.
Using these we estimate the dynamical masses and find, as expected, high dark
matter fractions of for all group members. The
ASKAP data are publicly available.Comment: 20 pages, 11 figures, accepted for publication in MNRA
Neutral hydrogen (H I) gas content of galaxies at z â 0.32
We use observations made with the Giant Metrewave Radio Telescope (GMRT) to probe the neutral hydrogen (H I) gas content of field galaxies in the VIMOS VLT Deep Survey (VVDS) 14h field at z â 0.32. Because the HI emission from individual galaxies is too faint to detect at this redshift, we use an HI spectral stacking technique using the known optical positions and redshifts of the 165 galaxies in our sample to co-add theirHI spectra and thus obtain the average HI mass of the galaxies. Stacked HI measurements of 165 galaxies show that âł95 per cent of the neutral gas is found in blue, star-forming galaxies. Among these galaxies, those having lower stellar mass are more gas rich than more massive ones. We apply a volume correction to our HI measurement to evaluate the HI gas density at zâ0.32 asΩHI = (0.50 ± 0.18) Ă 10-3 in units of the cosmic critical density. This value is in good agreement with previous results at z < 0.4, suggesting no evolution in the neutral hydrogen gas density over the last ~4Gyr. However the z â 0.32 gas density is lower than that at z ~ 5 by at least a factor of two.This research was funded by an Australian Indian Strategic Research Fund (AISRF) grant. This fund was jointly administered by the Department of Innovation, Industry, Science and Research in Australia and by the Department of Science and Technology in India. The project title was âGas in Galaxies in the Distant Pastâ. Parts of this research were conducted by the Australian Research Council Centre of Excellence for All-sky Astrophysics (CAASTRO), through project number CE110001020. Funding for the SDSS and SDSSâII has been provided by the Alfred P. Sloan Foundation,
the Participating Institutions, the National Science Foundation, the
U.S. Department of Energy, the National Aeronautics and Space Administration, the Japanese Monbukagakusho, the Max Planck Society and the Higher Education Funding Council for England
WSCLEAN: an implementation of a fast, generic wide-field imager for radio astronomy
Astronomical wide-field imaging of interferometric radio data is computationally expensive, especially for the large data volumes created by modern non-coplanar many-element arrays. We present a new wide-field interferometric imager that uses the w-stacking algorithm and can make use of the w-snapshot algorithm. The performance dependences of CASA's w-projection and our new imager are analysed and analytical functions are derived that describe the required computing cost for both imagers. On data from the Murchison Widefield Array, we find our new method to be an order of magnitude faster than w-projection, as well as being capable of full-sky imaging at full resolution and with correct polarization correction. We predict the computing costs for several other arrays and estimate that our imager is a factor of 2-12 faster, depending on the array configuration. We estimate the computing cost for imaging the lowfrequency Square Kilometre Array observations to be 60 PetaFLOPS with current techniques. We find that combining w-stacking with the w-snapshot algorithm does not significantly improve computing requirements over pure w-stacking. The source code of our new imager is publicly released
The Look-back Time Evolution of Far-Ultraviolet Flux from the Brightest Cluster Elliptical Galaxies at z < 0.2
We present the GALEX UV photometry of the elliptical galaxies in Abell
clusters at moderate redshifts (z < 0.2) for the study of the look-back time
evolution of the UV upturn phenomenon. The brightest elliptical galaxies (M_r <
-22) in 12 remote clusters are compared with the nearby giant elliptical
galaxies of comparable optical luminosity in the Fornax and Virgo clusters. The
sample galaxies presented here appear to be quiescent without signs of massive
star formation or strong nuclear activity, and show smooth, extended profiles
in their UV images indicating that the far-UV (FUV) light is mostly produced by
hot stars in the underlying old stellar population. Compared to their
counterparts in nearby clusters, the FUV flux of cluster giant elliptical
galaxies at moderate redshifts fades rapidly with ~ 2 Gyrs of look-back time,
and the observed pace in FUV - V color evolution agrees reasonably well with
the prediction from the population synthesis models where the dominant FUV
source is hot horizontal-branch stars and their progeny. A similar amount of
color spread (~ 1 mag) in FUV - V exists among the brightest cluster elliptical
galaxies at z ~ 0.1, as observed among the nearby giant elliptical galaxies of
comparable optical luminosity.Comment: Accepted for publication in the Special GALEX ApJ Supplement,
December 200
WALLABY Pilot Survey: Hydra Cluster Galaxies UV and HI morphometrics
Galaxy morphology in atomic hydrogen (HI) and in the ultra-violet (UV) are
closely linked. This has motivated their combined use to quantify morphology
over the full H i disk for both H i and UV imaging. We apply galaxy
morphometrics: Concentration, Asymmetry, Gini, M20 and
Multimode-Intensity-Deviation statistics to the first moment-0 maps of the
WALLABY survey of galaxies in the Hydra cluster center. Taking advantage of
this new HI survey, we apply the same morphometrics over the full HI extent on
archival GALEX FUV and NUV data to explore how well HI truncated, extended
ultraviolet disk (XUV) and other morphological phenomena can be captured using
pipeline WALLABY data products. Extended HI and UV disks can be identified
relatively straightforward from their respective concentration. Combined with
WALLABY HI, even the shallowest GALEX data is sufficient to identify XUV disks.
Our second goal is to isolate galaxies undergoing ram-pressure stripping in the
H i morphometric space. We employ four different machine learning techniques, a
decision tree, a k-nearest neighbour, a support-vector machine, and a random
forest. Up to 80% precision and recall are possible with the Random Forest
giving the most robust results.Comment: 17 figures, 12 figures, 7 tables, accepted by MNRA