666 research outputs found
High Sensitivity Array Observations of the z=1.87 Sub-Millimeter Galaxy GOODS 850-3
We present sensitive phase-referenced VLBI results on the radio continuum
emission from the z=1.87 luminous submillimeter galaxy (SMG) GOODS 850-3. The
observations were carried out at 1.4 GHz using the High Sensitivity Array
(HSA). Our sensitive tapered VLBI image of GOODS 850-3 at 0.47 x 0.34 arcsec
(3.9 x 2.9 kpc) resolution shows a marginally resolved continuum structure with
a peak flux density of 148 \pm 38 uJy/beam, and a total flux density of 168 \pm
73 uJy, consistent with previous VLA and MERLIN measurements. The derived
intrinsic brightness temperature is > 5 \pm 2 x 10^3 K. The radio continuum
position of this galaxy coincides with a bright and extended near-infrared
source that nearly disappears in the deep HST optical image, indicating a dusty
source of nearly 9 kpc in diameter. No continuum emission is detected at the
full VLBI resolution (13.2 x 7.2 mas, 111 x 61 pc), with a 4-sigma point source
upper limit of 26 uJy/beam, or an upper limit to the intrinsic brightness
temperature of 4.7 x 10^5 K. The extent of the observed continuum source at 1.4
GHz and the derived brightness temperature limits are consistent with the radio
emission (and thus presumably the far-infrared emission) being powered by a
major starburst in GOODS 850-3, with a star formation rate of ~2500 M_sun/yr.
Moreover, the absence of any continuum emission at the full resolution of the
VLBI observations indicates the lack of a compact radio AGN source in this
z=1.87 SMG.Comment: 19 pages, 4 figures, accepted for publication in A
Star Formation in Massive Low Surface Brightness Galaxies
Massive low surface brightness galaxies have disk central surface
brightnesses at least one magnitude fainter than the night sky, but total
magnitudes and masses that show they are among the largest galaxies known. Like
all low surface brightness (LSB) galaxies, massive LSB galaxies are often in
the midst of star formation yet their stellar light has remained diffuse,
raising the question of how star formation is proceeding within these galaxies.
We have undertaken a multi-wavelength study to clarify the structural
parameters and stellar and gas content of these enigmatic systems. The results
of these studies, which include HI, CO, optical, near UV, and far UV images of
the galaxies will provide the most in depth study done to date of how, when,
and where star formation proceeds within this unique subset of the galaxy
population.Comment: to be published in proceeding of IAU 244 - Dark Galaxies and Lost
Baryons IAU Symposiu
Neutral Hydrogen and Star Formation in the Coma-Abell1367 Supercluster
We present preliminary results of a multi-wavelength study focused on the
evolution of spiral galaxies in the UV-optical colour-magnitude (CM) diagram.
By combining HI, UV and optical observations of the Coma-Abell1367 supercluster
we are able to identify galaxies at different stages of their evolution: from
healthy star-forming galaxies, to blue HI-poor spirals and transition objects.
Our analysis shows that galaxies in the transition region are likely to be the
progeny of healthy spirals, whose star-formation has been quenched by the harsh
cluster environment. This result suggests that, at least in clusters of
galaxies, the migration of galaxies from the blue to the red sequence might be
due to environmental processes.Comment: To appear in AIP Conf. Proc., "The Evolution of Galaxies through the
Neutral Hydrogen Window", Feb 1-3 2008, Arecibo, eds. R. Minchin & E.
Momjian. 4 pages, 2 figure
Extragalactic HI Surveys at Arecibo: the Future
Starting in the 1970s, the Arecibo 305m telescope has made seminal
contributions in the field of extragalactic spectroscopy. With the Gregorian
upgrade completed in the late 1990s, the telescope acquired a field of view.
Population of that field of view with a seven-feed array at L-band (ALFA)
increased by nearly one order of magnitude its survey speed. As a result, much
of the extragalactic astronomy time of the telescope is now allocated to survey
projects, which are briefly discussed. The next technical development stage for
the 305m telescope is foreseen as that of a 40 beam system that would take
advantage of phased array technology: AO40. This would further speed up the
survey performance of the telescope. It is shown how the figure of merit for
survey speed of AO40 would be comparable with that of SKA-precursor facilities,
planned for operation in the next decade. A number of scientifically desirable
new surveys that would become possible with AO40 are briefly discussed.Comment: To appear in AIP Conference Proceedings, "The Evolution of Galaxies
through the Neutral Hydrogen Window", Feb 1-3 2008, Arecibo, Puerto Rico,
eds. R. Minchin & E. Momjian. 6 pages including 1 figur
Conference Summary: HI Science in the Next Decade
The atomic hydrogen (HI) 21cm line measures the gas content within and around
galaxies, traces the dark matter potential and probes volumes and objects that
other surveys do not. Over the next decade, 21cm line science will exploit new
technologies, especially focal plane and aperture arrays, and will see the
deployment of Epoch of Reionization/Dark Age detection experiments and Square
Kilometer Array (SKA) precursor instruments. Several experiments designed to
detect and eventually to characterize the reionization history of the
intergalactic medium should deliver first results within two-three years time.
Although "precision cosmology" surveys of HI in galaxies at z ~ 1 to 3 require
the full collecting area of the SKA, a coherent program of HI line science
making use of the unique capabilities of both the existing facilities and the
novel ones demonstrated by the SKA precursors will teach us how many gas rich
galaxies there really are and where they reside and will yield fundamental
insight into how galaxies accrete gas, form stars and interact with their
environment.Comment: To appear in AIP Conference Proceedings, "The Evolution of Galaxies
through the Neutral Hydrogen Window", Feb 1-3 2008, Arecibo, Puerto Rico,
eds. R. Minchin & E. Momjian. 8 page
Extreme sensitivity of hearing to decreases of ICP in Menière's disease
We report the case of a Menière's disease patient affected by normal pressure hydrocephalus (NPH) who presented a cerebrospinal fluid (CSF) pressure-dependent hearing impairment after shunting. This side-effect was not only reversible and reproducible but occurred at a high opening pressure when the valve setting was lowered by only 0.7mmHg (10mmH2O). This observation suggests that hearing in Menière's disease might be very sensitive to small reductions of intracranial pressure (ICP) and that these patients should be informed of this potential risk, which can compromise the efficacy of the shun
HI Structure Observations of Reionization and Dark Energy
This proceeding concentrates on the BAO signature of dark energy, and how the
SKA dark energy case has been complicated by the emergence of HI structure
experiments modeled after the Epoch of Reionization observatories. The purpose
of the conference talk was to review the current status of the Murchison
Widefield Array (MWA), and show the applications of HI structure observations
for both reionization and dark energy measurements. Since the status of the MWA
is changing weekly, please see the website www.haystack.mit.edu/ast/arrays/mwa/
for the current status. This proceedings will instead concentrate on HI
structure observations, their applicability to reionization and cosmography,
and the implications for the SKA and future HI structure observations of dark
energy.Comment: Proceeding from The Evolution of Galaxies through the Neutral
Hydrogen Window, Arecibo, 2008, AIP Conference Proceedings, Volume 103
Resolving distance ambiguities towards 6.7 GHz methanol masers
Distances to most star forming regions are determined using kinematics,
through the assumption that the observed radial velocity arises from the motion
of the source with respect to the Sun resulting from the differential rotation
of Galaxy. The primary challenge associated with the application of this
technique in the inner Galaxy is the kinematic distance ambiguity. In this
work, we aim to resolve the kinematic distance ambiguity towards a sample of
6.7 GHz methanol masers, which are signposts of the early stages of massive
star formation. We measured 21 cm HI absorption spectra using the Very Large
Array in C and CnB configurations. A comparison of the maximum velocity of HI
absorption with the source velocity and tangent point velocity was used to
resolve the kinematic distance ambiguity. We resolved the distance ambiguity
towards 41 sources. Distance determinations that are in conflict with previous
measurements are discussed. The NE2001 spiral arm model is broadly consistent
with the locations of the star forming complexes. We find that the use of
vertical scale height arguments to resolve the distance ambiguity can lead to
erroneous classifications for a significant fraction of sources.Comment: Accepted by Astronomy & Astrophysic
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