Nearby Dwarf Irregular Galaxies Research Articles

H II regions in seven dwarf irregular galaxies

view Abstract Citations (60) References (34) Co-Reads Similar Papers Volume Content Graphics Metrics Export Citation NASA/ADS H II Regions in Seven Dwarf Irregular Galaxies Strobel, Nicolas V. ; Hodge, Paul ; Kennicutt, Robert C., Jr. Abstract CCD Hα images are used to study the characteristics of the H II regions of seven nearby dwarf irregular galaxies. Maps and coordinates identify them, and we use the calibrated images to measure the emission- line luminosities of all the H II regions and to determine the H II region luminosity functions for the galaxies. The luminosity functions are all normal, with a mean value for the slope of the power-law fit of -1.5 +/- 0.3. H II region sizes and morphologies are examined, and values for the characteristic size scale, D_0_ , are given; a weak correlation is found with the absolute magnitude of the host galaxy. Publication: The Astrophysical Journal Pub Date: December 1991 DOI: 10.1086/170771 Bibcode: 1991ApJ...383..148S Keywords: Dwarf Galaxies; H Ii Regions; Interstellar Matter; Irregular Galaxies; Nebulae; Astronomical Maps; Charge Coupled Devices; H Alpha Line; Luminosity; Star Formation; Astrophysics; GALAXIES: INTERSTELLAR MATTER; NEBULAE: H II REGIONS full text sources ADS | data products SIMBAD (114) NED (7)

Giant molecular clouds and the CO-to-H2 conversion factor in IC 10

Three molecular clouds have been mapped in the nearby metal-poor dwarf irregular galaxy IC 10 using the Owens Valley Millimeter-Wave Interferometer. The clouds have velocity widths, diameters, temperatures, and masses that are very similar to those of Galactic giant molecular clouds. However, the virial masses are substantially larger than the molecular masses. Two of these clouds obey the size-line width relation established for molecular clouds in the Galaxy and, thus, are probably gravitationally bound. Assuming these two clouds are self-gravitating and adopting a distance of 1 Mpc, the CO-to-H2 conversion factor of IC 10 is 6 x 10 to the 20th/sq cm per (K km/s), twice as large as the Galactic value. Thus, for a given mass of molecular gas, IC 10 is underluminous in CO by only a factor of 2 relative to the Galaxy. This observational result disagrees with recent theoretical predictions that the CO-to-H2 conversion factor should be a strong function of metallicity. 21 refs.

Oxygen abundances in nearby dwarf irregular galaxies

Oxygen abundances are obtained by optical spectrophotometry of H II regions in seven nearby dwarf irregular galaxies. All of these yield oxygen abundances of less than 1/10 of the solar value, and most are in the range of 3-5 percent of the solar value. This suggests that observations of nearby dwarf galaxies may provide an effective means for studying the chemical evolution of low-mass galaxies and, possibly, the primordial helium abundance. A strong correlation is found between the oxygen abundances and absolute magnitudes for nearby irregular galaxies. This correlation will be useful for estimating abundances of irregular galaxies without observable H II regions, and possibly as a distance indicator for irregular galaxies with known abundances. It is inferred from this relationship that infall is no more important in irregular galaxies with extremely large H I halos than in typical irregular galaxies. 72 refs.

THE H II REGIONS OF GR8

ABSTRACT Deep CCD narrow-band Hα imaging of the nearby dwarf irregular galaxy GR8 has revealed a total of 32 H II regions. Positions, Hα luminosities, and sizes of these objects are tabulated. The Hα luminosity function has the same shape as that for more luminous galaxies, except for size of sample effects. Most H II regions detected are at the very low luminosity end of the general luminosity function. The size distribution has an exponential shape, as for other galaxies, with a size scale of 17 pc. The varieties of different structures are discussed and compared to those in larger galaxies. Candidates for the exciting stars can be identified for some of the H II regions; they are very blue, with MB_ = -5 to -6.