Star Formation Properties of Barred Spiral Galaxies

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Session 23 -- Starburst Activity in External Galaxies
Oral presentation, Monday, 30, 1994, 2:00-3:30

[23.01] Star Formation Properties of Barred Spiral Galaxies

A. C. Phillips (Univ. Washington \& Lick Observatory)

\def\Halpha{{H$\alpha$}} \def\HIIR{{{\sc H\thinspace ii} region}} \def\micron{{\rm $\mu$m}}

Narrow-band \Halpha\ images of 15 SBb and SBc galaxies are used to survey star formation properties of barred spiral galaxies. Integrated \Halpha\ luminosities and surface brightness measures, as well as the spatial and luminosity distribution of \HIIR s, are determined.

Barred spirals display a wide range in their star formation properties. Within the sample, properties tend to fall into two categories, which roughly correlate with Hubble type as well as the ``flat'' and ``exponential'' bar types of Elmegreen \& Elmegreen (1985). SBb galaxies show moderate to virtually no star formation activity in their bars, except in the circumnuclear regions where star formation rates (SFRs) can be extreme. SBc galaxies generally have luminous \HIIR s in their bars and lack circumnuclear starbursts. Outside the bar, \HIIR s appear concentrated in ring-like structures, particularly in the SBb cases. SFRs per unit area are generally enhanced where the bar joins the spiral arms, especially in SBb galaxies; enhancements range from slight to factors $\sim$3, and may be quite different at the two bar ends.

\HIIR\ luminosity functions (LFs) are compared to those of Kennicutt, Edgar \& Hodge (1989). Global LFs in the barred sample are consistent with non-barred galaxies, although the SBb galaxies may have an excess of Type II LFs, which show a break in their power-law slopes. LFs constructed in radial zones show that the \HIIR\ 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.

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.

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