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Near-Infrared Molecular Hydrogen Emission from the Central Regions of Galaxies: Regulated Physical Conditions in the Interstellar Medium
The central regions of many interacting and early-type spiral galaxiesare actively forming stars. This process affects the physical andchemical properties of the local interstellar medium, as well as theevolution of the galaxies. We observed near-infrared H2emission lines: v=1-0 S(1), 3-2 S(3), 1-0 S(0), and 2-1 S(1) from thecentral ~1 kpc regions of the archetypical starburst galaxies M82 andNGC 253 and the less dramatic but still vigorously star-forming galaxiesNGC 6946 and IC 342. Like the far-infrared continuum luminosity, thenear-infrared H2 emission luminosity can directly trace theamount of star formation activity because the H2 emissionlines arise from the interaction between hot and young stars and nearbyneutral clouds. The observed H2 line ratios show that boththermal excitation and nonthermal excitation are responsible for theemission lines but that the great majority of the near-infraredH2 line emission in these galaxies arises from energy statesexcited by ultraviolet fluorescence. The derived physical conditions,e.g., far-ultraviolet radiation field and gas density, from [C II] and[O I] lines and far-infrared continuum observations when used as inputsto photodissociation models also explain the luminosity of the observedH2 1-0 S(1) line. The ratio of the H2 1-0 S(1)line to far-IR continuum luminosity is remarkably constant over a broadrange of galaxy luminosities:LH2/LFIR~=10-5, in normallate-type galaxies (including the Galactic center), in nearby starburstgalaxies, and in luminous IR galaxies (LIRGs:LFIR>1011 Lsolar). Examining thisconstant ratio in the context of photodissociation region models, weconclude that it implies that the strength of the incident UV field ontypical molecular clouds follows the gas density at the cloud surface.
| The H II regions of M101. I - an atlas of 1264 emission regions
A previous survey of the H II regions in M101 (Hodge and Kennicutt) hasbeen extended by a series of CCD images and image tube plates of thegalaxy, approximately tripling the number of known emission regions.This paper provides maps and a catalog of a total of 1264 H II regionsin M101.
| Images in the rocket ultraviolet - Photometry of M101
It is pointed out that ultraviolet imagery of spiral galaxies is asensitive probe of the large-scale morphology of the star-formingregions and the associated interstellar dust. A rocket-borneRitchey-Chretien telescope was employed to obtain three ultravioletimages of the Sc 1 galaxy M101 (NGC 5457). The present investigation isconcerned with the procedures for reduction and absolute calibration ofthe obtained images and an analysis in terms of discrete sources.Attention is also given to the radial variation and the azimuthalvariation of disk and arms. It is found that the emission from M101 inthe UV bandpass is dominated by extreme Population I, in the form ofdiscrete OB/H II complexes.
| Evidence for Composition Gradients across the Disks of Spiral Galaxies
Abstract image available at:http://adsabs.harvard.edu/abs/1971ApJ...168..327S
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