Star formation efficiency in the central 1 kiloparsec region of early-type spiral galaxies

It has been reported recently that there are some early-type spiral (Sa-Sab) galaxies with evident star-forming regions that concentrate in their own central 1 kpc. In such central region, is the mechanism of the star formation distinct from that in disks of spiral galaxies? To discover this, we estimate the star formation efficiency (SFE) in this central 1 kpc star-forming region of some early-type spiral galaxies, taking account of the condition required for this 1 kpc region to be self-gravitating. Using two indicators of the present star formation rate (H alpha and infrared luminosity), we estimate the SFE to a few percent. This is equivalent to the observational SFE in the disks of late-type spiral (Sb-) galaxies. This coincidence may support the universality of the mean SFE of spiral galaxies reported in the recent studies, that is, we find no evidence of a distinct mechanism of the star formation in the central 1 kpc region of early-type galaxies. Also, we examine the structure of the central star-forming region and discuss a method for estimating the mass of star-forming regions.