Astronomy and Astrophysics – Astronomy
Scientific paper
Feb 1995
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=1995pasp..107..204b&link_type=abstract
Publications of the Astronomical Society of the Pacific, v.107, p.204
Astronomy and Astrophysics
Astronomy
1
Scientific paper
This dissertation adds to the body of research concerning the structure of galaxies by investigating the distribution of luminous and dark matter in edge-on spiral galaxies. Such galaxies have several unique properties, including that they provide for a nearly unambiguous separation of the disk's vertical (minor-axis or "z") and radial (major-axis or "R") distributions and that they permit an easy separation of distributions layered with respect to the mid-plane, such as dust and stellar populations. In order to study starlight in the region of the dust lane, which is a conspicuous component of edge-on spirals that severely extincts visual light, I observe these galaxies at near-infrared wavelengths. These wavelengths are optimum for lowering the dust extinction while maximizing the sensitivity to starlight from the dynamically-important old-disk population. An essential part of this study was the operation and calibration of the near-infrared camera used to make the observations, and I report on tests that show that the systematic and relative uncertainties in the photometry are on the order of 0.1m down to 18m arcsec^-2. I analyze an Sc galaxy, NGC 5907, and an Sbc galaxy, NGC 4013, producing a bulge/disk decomposition for each from H-band (1.68 microns) surface photometry. Both are fit reasonably well with a model consisting of a modified-Hubble profile bulge and a two-function disk consisting of an exponential in the radial dimension and a hyperbolic secant in the vertical dimension. The scale lengths of the disks are significantly smaller than those measured using visual observations, which is consistent with the disks being optically thick at visual wavelengths. I report the first measurements on the size and shape of the bulge of NGC 5907. I also report on the bulge of NGC 4013 which appears remarkably small unless I use a "hollow-disk" fit, which produces a brighter bulge consistent with the classification of Sbc. Even so, the diameter of the hollow region is much smaller than the diameter obtained from visual observations. Finally, I am able to model the inner rotation curve of NGC 5907, which has not been successfully done using visual surface photometry. I still must invoke a halo of dark matter to model the outer rotation curve, and I demonstrate that the dark matter contributes about twice the mass at the periphery of the visible disk than does the luminous matter. (SECTION: Dissertation Summaries)
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