A Study Of The Neutral Hydrogen Content Of Blue Compact Dwarf Galaxies
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Author | : Jeremy A MacHattie |
Publisher | : |
Total Pages | : 294 |
Release | : 2013 |
Genre | : |
ISBN | : |
The results of a study of the neutral hydrogen (HI) content and distribution within a sample of 18 blue compact dwarf galaxies (BCDs) are presented. An investigation of the behaviour of the gas-to-dust ratio (GDR) as a function of metallicity (Z) is also presented. Observations of these BCDs was performed using the Very Large Array (VLA) in 2009, a year in which the array was undergoing a technological upgrade to the the Karl G. Jansky VLA (JVLA). The observations were reduced and images processed using the Astronomical Image Processing Software (AIPS), and data cubes for each galaxy were produced. The results include detections of eleven HI lines (two new detections) and ten background continuum sources (two new discoveries). All detections are at a higher resolution and/or sensitivity than previous measurements. These detections spanned a large range of line widths and HI masses; some masses comparable to those in normal galaxies. Of particular interest was the discovery of a compact absorption feature in the dwarf galaxy Haro 11. A paper submitted to the Monthly Notices of the Royal Astronomical Society (MNRAS) Letters on this discovery is presented. Another significant result was the discovery of a highly extended and massive HI region in the dwarf galaxy CGCG 297-017. For those galaxies with no detected HI line or radio continuum, an upper limit to the flux density was computed, which was used to derive upper limits to the HI mass or star-formation rate (SFR) respectively. Three HI flux density upper limits are new results, and seven continuum flux density upper limits are also new. The GDR-Z relation at low metallicities shows a potential power law or broken power law relation with a turning point at Z=7.96 or Z=8.05. To within error, these turning points and power law indices of the broken power law fits are consistent with other work.
Author | : Jonathan Victor Smoker |
Publisher | : |
Total Pages | : 2930 |
Release | : 1993 |
Genre | : |
ISBN | : |
Author | : B. L. James |
Publisher | : |
Total Pages | : |
Release | : 2010 |
Genre | : |
ISBN | : |
An understanding of Blue Compact Dwarf galaxies (BCDs) and the processes occurring within their chemically un-evolved environments is fundamental in our understanding of the early universe. This thesis presents an investigation into their physical conditions, kinematics, chemical abundances and dust compositions. An optical integral field spectroscopy investigation of two perturbed BCDs, UM420 and UM462, is presented. Emission line maps show that both galaxies display signs of ongoing perturbation and/or interaction. Electron temperatures, densities and chemical abundances are computed from spectra integrated over the whole galaxies and for each area of star formation. A similar yet more complicated analysis is undertaken of the BCD Mrk996, which displays multi-component emission lines. The high excitation energy [O III] \lambda4363 and [N II] \lambda5755 lines are detected only in the inner regions and purely in broad component form, implying unusual excitation conditions. A separate physical analysis of the broad and narrow emission line regions is undertaken, yielding a revised metallicity and N/O ratio typical for the galaxy's metallicity. The mid-IR properties of 19 BCDs are studied through Spitzer spectral and imaging data. The depeletion of PAH emission in BCDs is investigated and found to be due to formation and destruction effects. The [S III] flux ratio is used as a density diagnostic, showing typically low-densities. Maps of PAH emission and radiation field hardness are derived from IRS spectral mapping data. Blackbody fits to IR photometric SEDs typically reveal two dust components. The observed physical and chemical properties of Mrk 996 are successfully reproduced using the photoionisation code MOCASSIN. The best-fit model involved the inclusion of a filling factor and an amorphous carbon dust component with a two-zone dust distribution. A STARBURST99 input spectrum was used, yielding ages consistent with the known young WR stars and old super star clusters within Mrk 996.
Author | : Evan David Skillman |
Publisher | : |
Total Pages | : 440 |
Release | : 1996 |
Genre | : Science |
ISBN | : |
Author | : Bethan Lesley James |
Publisher | : |
Total Pages | : 0 |
Release | : 2010 |
Genre | : |
ISBN | : |
Author | : Gustaaf Adolf Van Moorsel |
Publisher | : |
Total Pages | : 204 |
Release | : 1982 |
Genre | : Astronomy |
ISBN | : |
Author | : S. T. Gottesman |
Publisher | : |
Total Pages | : 21 |
Release | : 1972 |
Genre | : |
ISBN | : |
Interferometric observations at the 21 cm neutral hydrogen emission line have yielded information about the dynamics and structure of the compact galaxy II Zw 40. The neutral hydrogen follows a core-halo distribution with characteristic gaussian half-power widths of 52 arc sec and 350 arc sec. (Author).
Author | : David Theodore Frayer |
Publisher | : |
Total Pages | : 218 |
Release | : 1993 |
Genre | : |
ISBN | : |
Author | : M. Anthony Wong |
Publisher | : |
Total Pages | : 110 |
Release | : 1994 |
Genre | : Interstellar hydrogen |
ISBN | : |
Author | : |
Publisher | : |
Total Pages | : 1142 |
Release | : 1973 |
Genre | : Nuclear energy |
ISBN | : |