Astronomy and Astrophysics – Astrophysics – Galaxy Astrophysics
Scientific paper
2011-11-15
Astronomy and Astrophysics
Astrophysics
Galaxy Astrophysics
67 pages; 18 figures; aastex; accepted to ApJ; higher quality figures (1, 2, 9, 18) are available at http://astro.uchicago.edu
Scientific paper
We have determined column densities of H I and/or H_2 for sight lines in the Magellanic Clouds from archival HST and FUSE spectra of H I Lyman-alpha and H_2 Lyman-band absorption. Together with some similar data from the literature, we now have absorption-based N(H I) and/or N(H_2) for 285 LMC and SMC sight lines (114 with a detection or limit for both species) -- enabling more extensive, direct, and accurate determinations of molecular fractions, gas-to-dust ratios, and elemental depletions in these two nearby, low-metallicity galaxies. For sight lines where the N(H I) estimated from 21 cm emission is significantly higher than the value derived from Lyman-alpha absorption (presumably due to emission from gas beyond the target stars), integration of the 21 cm profile only over the velocity range seen in Na I or H_2 absorption generally yields much better agreement. Conversely, N(21 cm) can be lower than N(Ly-alpha) by factors of 2--3 in some LMC sight lines -- suggestive of small-scale structure within the 21 cm beam(s) and/or some saturation in the emission. The mean gas-to-dust ratios obtained from N(H_tot)/E(B-V) are larger than in our Galaxy, by factors of 2.8--2.9 in the LMC and 4.1--5.2 in the SMC -- i.e., factors similar to the differences in metallicity. The N(H_2)/E(B-V) ratios are more similar in the three galaxies, but with considerable scatter within each galaxy. These data may be used to test models of the atomic-to-molecular transition at low metallicities and predictions of N(H_2) based on comparisons of 21 cm emission and the IR emission from dust.
Welty Daniel E.
Wong Tony
Xue Rongrong
No associations
LandOfFree
Interstellar H I and H_2 in the Magellanic Clouds: An Expanded Sample Based on UV Absorption-Line Data does not yet have a rating. At this time, there are no reviews or comments for this scientific paper.
If you have personal experience with Interstellar H I and H_2 in the Magellanic Clouds: An Expanded Sample Based on UV Absorption-Line Data, we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and Interstellar H I and H_2 in the Magellanic Clouds: An Expanded Sample Based on UV Absorption-Line Data will most certainly appreciate the feedback.
Profile ID: LFWR-SCP-O-67703