177 research outputs found
The Ultraviolet View of the Magellanic Clouds from GALEX: A First Look at the LMC Source Catalog
The Galaxy Evolution Exporer (GALEX) has performed unprecedented imaging
surveys of the Magellanic Clouds (MC) and their surrounding areas including the
Magellanic Bridge (MB) in near-UV (NUV, 1771-2831\AA) and far-UV (FUV,
1344-1786\AA) bands at 5" resolution. Substantially more area was covered in
the NUV than FUV, particularly in the bright central regions, because of the
GALEX FUV detector failure. The 5 depth of the NUV imaging varies
between 20.8 and 22.7 (ABmag). Such imaging provides the first sensitive view
of the entire content of hot stars in the Magellanic System, revealing the
presence of young populations even in sites with extremely low star-formation
rate surface density like the MB, owing to high sensitivity of the UV data to
hot stars and the dark sky at these wavelengths.
The density of UV sources is quite high in many areas of the LMC and SMC.
Crowding limits the quality of source detection and photometry from the
standard mission pipeline processing. We performed custom-photometry of the
GALEX data in the MC survey region ( from the LMC,
from the SMC). After merging multiple detections of sources in overlapping
images, the resulting catalog we have produced for the LMC contains nearly 6
million unique NUV point sources within 15 and is briefly presented
herein. This paper provides a first look at the GALEX MC survey and highlights
some of the science investigations that the entire catalog and imaging dataset
will make possible.Comment: 16 pages, 8 figures; J. Adv. Space Res. (2013
Astronomical CCD Imaging at UMR: An Interim Report
Progress towards the modernization and update of the UMR observatory through the implementation of astronomical CCD technology is detailed. Preliminary image data is presented, specifically: globular cluster M13 and the lunar surface. An evaluation of the Santa Barbara Instrument Group’s (SBIG) ST-6 CCD camera is presented; bias frames, dark frames, and flat-fields are all examined. A custom optical assembly for instrument focusing and housing BVRI photometry and RGB colorimetry filters is described. The ST60PS data acquisition program, provided by SBIG, is reviewed. Additional work towards the development of a custom image processing utility program is mentioned. Finally, optical telescope collimation and polar alignment issues are discussed
HIIphot: Automated Photometry of HII Regions Applied to M51
We have developed a robust, automated method, hereafter designated HIIphot,
which enables accurate photometric characterization of HII regions while
permitting genuine adaptivity to irregular source morphology. HIIphot utilizes
object-recognition techniques to make a first guess at the shapes of all
sources then allows for departure from such idealized ``seeds'' through an
iterative growing procedure. Photometric corrections for spatially coincident
diffuse emission are derived from a low-order surface fit to the background
after exclusion of all detected sources. We present results for the
well-studied, nearby spiral M51 in which 1229 HII regions are detected above
the 5-sigma level. A simple, weighted power-law fit to the measured H-alpha
luminosity function (HII LF) above log L_H-alpha = 37.6 gives alpha =
-1.75+/-0.06, despite a conspicuous break in the HII LF observed near L_H-alpha
= 10^38.9. Our best- fit slope is marginally steeper than measured by Rand
(1992), perhaps reflecting our increased sensitivity at low luminosities and to
notably diffuse objects. HII regions located in interarm gaps are
preferentially less luminous than counterparts which constitute M51's
grand-design spiral arms and are best fit with a power-law slope of alpha =
-1.96+/-0.15. We assign arm/interarm status for HII regions based upon the
varying surface brightness of diffuse emission as a function of position
throughout the image. Using our measurement of the integrated flux contributed
by resolved HII regions in M51, we estimate the diffuse fraction to be
approximately 0.45 -- in agreement with the determination of Greenawalt et al.
(1998). Automated processing of degraded datasets is undertaken to gauge
systematic effects associated with limiting spatial resolution and sensitivity.Comment: 41 pages, 14 figures, Postscript version with high-resolution figures
at ftp://ftp.aoc.nrao.edu/staff/dthilker/preprint
Exploring extreme conditions for star formation: a deep search for molecular gas in the Leo ring
We carry out sensitive searches for the CO J=1-0 and J=2-1 lines in the giant
extragalactic HI ring in Leo to investigate the star formation process within
environments where gas metallicities are close to solar but physical conditions
are different than those typical of bright galaxy disks. Our aim is to check
the range of validity of known scaling relations. We use the IRAM-30m telescope
to observe eleven regions close to HI gas peaks or where sparse young massive
stars have been found. For all pointed observations we reached a spectral noise
between 1 and 5~mK for at least one observed frequencies at 2~km/s spectral
resolution. We marginally detect two CO J=1-0 lines in the star forming region
Clump~1 of the Leo ring, whose radial velocities are consistent with those of
Halpha lines but line widths are much smaller than observed for virialized
molecular clouds of similar mass in galaxies. The low signal-to-noise ratio,
the small line widths and the extremely low number densities suggest that a
more standard population of molecular clouds, still undetected, might be in
place. Using upper limits to the CO lines, the most sensitive pointed
observations show that the molecular gas mass surface density is lower than
expected from the extrapolation of the molecular Kennicutt-Schmidt relation
established in the disk of galaxies. The sparse stellar population in the ring,
possibly forming ultra diffuse dwarf galaxies, might then be the result of a
short molecular gas depletion time in this extreme environment.}Comment: 11 pages, 7 figures, accepted for publication in A&
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