901 research outputs found
Gas-Rich Companions of Isolated Galaxies
We have used the VLA to search for gaseous remnants of the galaxy formation
process around six extremely isolated galaxies. We found two distinct HI clouds
around each of two galaxies in our sample (UGC 9762 & UGC 11124). These clouds
are rotating and appear to have optical counterparts, strongly implying that
they are typical dwarf galaxies. The companions are currently weakly
interacting with the primary galaxy, but have short dynamical friction
timescales (~1 Gyr) suggesting that these triple galaxy systems will shortly
collapse into one massive galaxy. Given that the companions are consistent with
being in circular rotation about the primary galaxy, and that they have small
relative masses, the resulting merger will be a minor one. The companions do,
however, contain enough gas that the merger will represent a significant
infusion of fuel to drive future star formation, bar formation, or central
activity, while building up the mass of the disk thus making these systems
important pieces of the galaxy formation and evolution process.Comment: Corrected dynamical friction calculation error. Revised discussion &
conclusions. 7 pages, 4 tables, 6 figures, to appear in May 1999 Astronomical
Journa
Structure and Star Formation in NGC 925
We present the results from an optical study of the stellar & star formation
properties of NGC 925 using the WIYN 3.5m telescope. Images in B,V,R, & H-alpha
reveal a galaxy that is fraught with asymmetries. From isophote fits we
discover that the bar center is not coincident with the center of the outer
isophotes nor with the dynamical center (from Pisano et al. 1998). Cuts across
the spiral arms reveal that the northern arms are distinctly different from the
southern arm. The southern arm not only appears more coherent, but the peaks in
stellar and H-alpha emission are found to be coincident with those of the HI
distribution, while no such consistency is present in the northern disk. We
also examine the gas surface density criterion for massive star formation in
NGC 925, and find that its behavior is more consistent with that for irregular
galaxies, than with late-type spirals. In particular, star formation persists
beyond the radius at which the gas surface density falls below the predicted
critical value for star formation for late-type spirals. Such properties are
characteristic of Magellanic spirals, but are present at a less dramatic level
in NGC 925, a late-type spiral.Comment: accepted for publication in the August 2000 Astronomical Journal 12
pages, 3 tables, 14 figure
High-Velocity Clouds in the Nearby Spiral Galaxy M 83
We present deep HI 21-cm and optical observations of the face-on spiral
galaxy M 83 obtained as part of a project to search for high-velocity clouds
(HVCs) in nearby galaxies. Anomalous-velocity neutral gas is detected toward M
83, with 5.6x10^7 Msolar of HI contained in a disk rotating 40-50 km/s more
slowly in projection than the bulk of the gas. We interpret this as a
vertically extended thick disk of neutral material, containing 5.5% of the
total HI within the central 8 kpc. Using an automated source detection
algorithm to search for small-scale HI emission features, we find eight
distinct, anomalous-velocity HI clouds with masses ranging from 7x10^5 to
1.5x10^7 Msolar and velocities differing by up to 200 km/s compared to the HI
disk. Large on-disk structures are coincident with the optical spiral arms,
while unresolved off-disk clouds contain no diffuse optical emission down to a
limit of 27 r' mag per square arcsec. The diversity of the thick HI disk and
larger clouds suggests the influence of multiple formation mechanisms, with a
galactic fountain responsible for the slowly-rotating disk and on-disk discrete
clouds, and tidal effects responsible for off-disk cloud production. The mass
and kinetic energy of the HI clouds are consistent with the mass exchange rate
predicted by the galactic fountain model. If the HVC population in M 83 is
similar to that in our own Galaxy, then the Galactic HVCs must be distributed
within a radius of less than 25 kpc.Comment: 30 pages, 23 figures; accepted for publication in ApJ. Some figures
have been altered to reduce their siz
A higher-order entity formed by the flexible assembly of RAP1 with TRF2
Essonne committee of the Ligue contre le cancer M18756 M22897 Foundation ARC pour la Recherche sur le Cancer SFI20121205503International audienceTelomere integrity is essential to maintain genome stability, and telomeric dysfunctions are associated with cancer and aging pathologies. In human, the shelterin complex binds TTAGGG DNA repeats and provides capping to chromosome ends. Within shel-terin, RAP1 is recruited through its interaction with TRF2, and TRF2 is required for telomere protection through a network of nucleic acid and protein interactions. RAP1 is one of the most conserved shelterin proteins although one unresolved question is how its interaction may influence TRF2 properties and regulate its capacity to bind multiple proteins. Through a combination of biochemical, biophysical and structural approaches, we unveiled a unique mode of assembly between RAP1 and TRF2. The complete interaction scheme between the full-length proteins involves a complex biphasic interaction of RAP1 that directly affects the binding properties of the assembly. These results reveal how a non-DNA binding protein can influence the properties of a DNA-binding partner by mutual conformational adjustments
Anomalous HI in NGC 2997
We present deep HI observations of the moderately inclined spiral galaxy, NGC
2997. The goal of these observations was to search for HI clouds in the
vicinity of NGC 2997 analogous to the high velocity clouds of the Milky Way and
gain insight into their origins. We find evidence for the presence of a
galactic fountain as well as the accretion of intragalactic material, however
we do not identify any large clouds of HI far from the disk of the galaxy. NGC
2997 has a thick, lagging HI disk that is modeled with a vertical velocity
gradient of 18-31 km/s/kpc. Anomalous velocity HI clouds with masses of order
10^7 Msun, which cannot be explained by galactic fountain models allow us to
estimate a lower limit to the accretion of extragalactic gas of 1.2 Msun/yr.
The number and mass of these clouds have implications for cosmological
simulations of large scale structure and the presence of dark matter halos. We
have used values from the the literature to estimate a star formation rate of 5
+/- 1 Msun/yr and to derive a new distance to NGC 2997 of 12.2 +/- 0.9 Mpc
using published Tully-Fisher relations.Comment: 29 pages, 11 figures, accepted for publication in Ap
CHILES: HI morphology and galaxy environment at z=0.12 and z=0.17
We present a study of 16 HI-detected galaxies found in 178 hours of
observations from Epoch 1 of the COSMOS HI Large Extragalactic Survey (CHILES).
We focus on two redshift ranges between 0.108 <= z <= 0.127 and 0.162 <= z <=
0.183 which are among the worst affected by radio frequency interference (RFI).
While this represents only 10% of the total frequency coverage and 18% of the
total expected time on source compared to what will be the full CHILES survey,
we demonstrate that our data reduction pipeline recovers high quality data even
in regions severely impacted by RFI. We report on our in-depth testing of an
automated spectral line source finder to produce HI total intensity maps which
we present side-by-side with significance maps to evaluate the reliability of
the morphology recovered by the source finder. We recommend that this become a
common place manner of presenting data from upcoming HI surveys of resolved
objects. We use the COSMOS 20k group catalogue, and we extract filamentary
structure using the topological DisPerSE algorithm to evaluate the \hi\
morphology in the context of both local and large-scale environments and we
discuss the shortcomings of both methods. Many of the detections show disturbed
HI morphologies suggesting they have undergone a recent interaction which is
not evident from deep optical imaging alone. Overall, the sample showcases the
broad range of ways in which galaxies interact with their environment. This is
a first look at the population of galaxies and their local and large-scale
environments observed in HI by CHILES at redshifts beyond the z=0.1 Universe.Comment: 23 pages, 12 figures, 1 interactive 3D figure, accepted to MNRA
Comparison of Acquisition Parameters and Breast Dose in Digital Mammography and Screen-Film Mammography in the American College of Radiology Imaging Network Digital Mammographic Imaging Screening Trial
The purpose of our study was to compare the technical performance of full-field digital mammography (FFDM) and screen-film mammography
Observing the Evolution of the Universe
How did the universe evolve? The fine angular scale (l>1000) temperature and
polarization anisotropies in the CMB are a Rosetta stone for understanding the
evolution of the universe. Through detailed measurements one may address
everything from the physics of the birth of the universe to the history of star
formation and the process by which galaxies formed. One may in addition track
the evolution of the dark energy and discover the net neutrino mass.
We are at the dawn of a new era in which hundreds of square degrees of sky
can be mapped with arcminute resolution and sensitivities measured in
microKelvin. Acquiring these data requires the use of special purpose
telescopes such as the Atacama Cosmology Telescope (ACT), located in Chile, and
the South Pole Telescope (SPT). These new telescopes are outfitted with a new
generation of custom mm-wave kilo-pixel arrays. Additional instruments are in
the planning stages.Comment: Science White Paper submitted to the US Astro2010 Decadal Survey.
Full list of 177 author available at http://cmbpol.uchicago.ed
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