NASA/IPAC EXTRAGALACTIC DATABASE
Date and Time of the Query: 2019-08-25 T07:36:15 PDT
Help | Comment | NED Home

For refcode 1999ApJ...519...55Y:
Retrieve 35 NED objects in this reference.
Please click here for ADS abstract

NED Abstract

Copyright by American Astronomical Society. Reproduced by permission
1999ApJ...519...55Y The Luminosity Functions and Size Distributions of H II Regions in Irregular Galaxies ABIGAIL J. YOUNGBLOOD AND DEIDRE A. HUNTER Lowell Observatory, 1400 West Mars Hill Road, Flagstaff, AZ 86001; ayoungbl@brynmawr.edu, dah@lowell.edu Received 1998 December 1; accepted 1999 February 9 ABSTRACT CCD H{alpha} images were used to study the properties of H II regions in 29 normal Im galaxies and six blue compact dwarf/starburst irregulars. The H{alpha} emission line fluxes were measured and used to construct luminosity functions for each galaxy. For most galaxies, the luminosity function is well represented by a power law. Only two of the 29 Im galaxies have supergiant H II regions, which is probably a result of the small size and small total numbers of H II regions in irregular galaxies. BCDs and starburst galaxies, on the other hand, do not always have supergiant H II regions but may have them even if only a few regions are present. Comparison of the cumulative composite H II luminosity function with that of spiral galaxies shows that the irregulars in our sample do not have an unusually large population of supergiant H II regions relative to the galactic luminosity. Thus, these galaxies will not suffer a disproportionate amount of disruption by the concentration of massive stars within such regions. However, in BCD/starburst galaxies there is an excess of H II regions with luminosities greater than 10^38^ ergs s^-1^ compared to Im and Sc galaxies relative to the luminosities of the host galaxies. Most of the H II region luminosity in normal Im galaxies comes from small regions and that in BCD/starburst galaxies from moderately large regions. Over 80% of the H II region luminosity in irregulars is found in complexes of H II regions typically with summed luminosities equivalent to <=10 Orion nebulae. Two types of luminosity functions were observed: those that exhibit turnover and those that do not. Those that do exhibit turnover have an average slope of -1.5+/-0.1, and those that do not exhibit turnover tend to be complete to fainter levels, have lower upper luminosity cutoffs, have fewer H II regions, and have shallower slopes of -1.0+/-0.1. If the luminosity function is universal for a galaxy type, this difference suggests the possibility of a break in the luminosity function corresponding to H II regions ionized by single stars and H II regions ionized by clusters of stars. However, we cannot exclude the possibility that the two groups of galaxies are different in terms of their global star formation properties. Diameters of H II regions were also measured and diameter distributions were constructed for each of the galaxies. The diameter distribution was fitted with an exponential and the characteristic diameter D_0_ was measured for each galaxy, although this fit did not characterize the distribution very well in most galaxies. The weak correlation between D_0_ and the absolute blue magnitude of the galaxy suggested by others is confirmed to be very weak. Subject headings: galaxies: irregular-galaxies: ISM-galaxies: starburst- H II regions
Retrieve 35 NED objects in this reference.
Please click here for ADS abstract

Back to NED Home