For a sample of 43 nearby, late-type galaxies, we have investigated the radial variation of both the current star formation rate and the dust-induced UV light attenuation. To do this we have cross-correlated IRAS images and GALEX observations for each of these galaxies and compiled observations of the gas (CO and H I) and metal-abundance gradients found in the literature. We find that attenuation correlates with metallicity. We then use the UV profiles, corrected for attenuation, to study several variants of the Schmidt law and conclude that our results are compatible with a simple law similar to the one of Kennicutt extending smoothly to lower surface densities, but with considerable scatter. We do not detect an abrupt break in the UV light at the threshold radius derived from Hα data (at which the Hα profile shows a break and beyond which only a few H n regions are usually found). We interpret the Ha sudden break not as a change in the star formation regime (as often suggested), but as the vanishingly small number of ionizing stars corresponding to low levels of star formation.
Bibliographical noteFunding Information:
4 Based on observations made with the NASA/ESA Hubble Space Telescope, obtained from the data archive at the Space Telescope Science Institute. STScI is operated by the Association of Universities for Research in Astronomy, Inc. under the NASA contract NAS 5-26555.
We thank Laird Thompson for fruitful discussions and for comments on the manuscript. We also thank J. Condon for providing digital radio images of Arp 118. S. A. L. acknowledges the support of the University of Illinois Research Board and the National Center for Supercomputer Applications (NCSA), which is part of the National Computational Science Alliance. S. A. L. and N. C. H. also acknowledge the use of the Renaissance Education Laboratory and the Numerical Laboratory at the NCSA at the University of Illinois. Y. G.’s research at the Laboratory for Astronomical Imaging in the Astronomy Department at the University of Illinois is funded by NSF grants AST93-20239 and AST96-13999 and by the University of Illinois.
All Science Journal Classification (ASJC) codes
- Astronomy and Astrophysics
- Space and Planetary Science