Computer Science
Scientific paper
Jan 1993
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=1993phdt........42p&link_type=abstract
Thesis (PH.D.)--UNIVERSITY OF WASHINGTON, 1993.Source: Dissertation Abstracts International, Volume: 54-10, Section: B, page: 52
Computer Science
22
Scientific paper
Narrow-band Hα images of 15 SBb and SBc galaxies form the basis of a survey of star formation properties in barred spiral galaxies. Calibrated, continuum-subtracted images are used to determine integrated Hα luminosities, surface brightness measures, and the spatial and luminosity distribution of H scII regions. Barred spirals display a wide range in their star formation properties. Within the sample, properties tend to fall into two categories correlated largely with Hubble type. SBb galaxies show moderate to virtually no star formation activity in their bars, except in the circumnuclear regions where star formation rates can be extreme. Outside the bar, H scII regions appear concentrated in ring-like structures corresponding to the inner rings of ring galaxies. SBc galaxies generally have luminous H scII regions in their bars, lack circumnuclear starburst regions, and inner rings are much less pronounced. These differences also correlate with the "flat" and "exponential" bar types defined by Elmegreen & Elmegreen (1985). Star formation rates (SFRs) per unit area are found to be enhanced where the bar joins the spiral arms, most noticeably in SBb galaxies. Enhancements range from slight to factors ~3, and the degree of enhancement is often quite different at the two ends of the bar. H scII region luminosity functions (LFs) are compared to those of Kennicutt, Edgar & Hodge (1989). Global LFs in the barred sample are roughly consistent with non-barred galaxies, although among the SBb galaxies there may be be an excess of Type II LFs, which show a break in their power-law slopes. LFs constructed in radial zones show that the H scII region luminosity distributions near the ring structure appear to have strong power-law breaks, but this may be an artifact of crowding. In the SBb galaxies, LFs are steeper in the bars than in the outer disks; in SBc bars, they may be shallower. The LFs in circumnuclear regions may be relatively shallow. Comparison of IRAS fluxes and circumnuclear H alpha emission confirms that the 25 μm "excess" in barred galaxies (Hawarden et al., 1986) is due to vigorous circumnuclear star formation. Furthermore, we find that ~2.3 magnitudes of excess Hα extinction in circumnuclear H scII regions allows the 40-120mum luminosities of all of the sample galaxies to be attributed to star formation. Global SFRs and gas depletion times are found to be consistent with those in non-barred galaxies of similar Hubble type, excluding the circumnuclear regions where derived SFRs are as high as 4-30 M_odot yr^{-1}. If these SFRs are sustained, then depletion timescales for gas within the bar radius are of order a few galactic rotations. Several correlations between bar characteristics and star-formation properties in bars, rings and circumnuclear regions support a scenario of secular evolution.
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