A FUSE Survey of Interstellar Molecular Hydrogen in the Small and Large Magellanic Clouds

Дата и время публикации : 2001-10-10T22:59:12Z

Авторы публикации и институты :
Jason Tumlinson (University of Colorado)
J. Michael Shull (University of Colorado)
Brian L. Rachford (University of Colorado)
Matthew K. Browning (University of Colorado)
Theodore P. Snow (University of Colorado)
Alex W. Fullerton (UVic,JHU)
Edward B. Jenkins (Princeton)
Blair D. Savage (Wisconsin)
Paul A. Crowther (UCL)
H. Warren Moos (JHU)
Kenneth R. Sembach (STScI)
George Sonneborn (NASA/GSFC)
Donald G. York (Chicago)

Оригинал статьи :http://arxiv.org/abs/astro-ph/0110262v1

Скачать pdf : http://arxiv.org/pdf/astro-ph/0110262v1

Ссылка на журнал-издание: Astrophys.J.566:857-879,2002
Коментарии к статье: 30 pages emulateapj, 14 figures (7 color), 7 tables, accepted for publication in the Astrophysical Journal, figures 11 and 12 compressed at slight loss of quality, see http://casa.colorado.edu/~tumlinso/h2/ for full versions
Первичная категория: astro-ph

Все категории : astro-ph

Краткий обзор статьи: We describe a moderate-resolution FUSE survey of H2 along 70 sight lines to the Small and Large Magellanic Clouds, using hot stars as background sources. FUSE spectra of 67% of observed Magellanic Cloud sources (52% of LMC and 92% of SMC) exhibit absorption lines from the H2 Lyman and Werner bands between 912 and 1120 A. Our survey is sensitive to N(H2) >= 10^14 cm^-2; the highest column densities are log N(H2) = 19.9 in the LMC and 20.6 in the SMC. We find reduced H2 abundances in the Magellanic Clouds relative to the Milky Way, with average molecular fractions <f_H2> = 0.010 (+0.005, -0.002) for the SMC and <f_H2> = 0.012 (+0.006, -0.003) for the LMC, compared with <f_H2> = 0.095 for the Galactic disk over a similar range of reddening. The dominant uncertainty in this measurement results from the systematic differences between 21 cm radio emission and Lya in pencil-beam sight lines as measures of N(HI). These results imply that the diffuse H2 masses of the LMC and SMC are 8 x 10^6 Msun and 2 x 10^6 Msun, respectively, 2% and 0.5% of the H I masses derived from 21 cm emission measurements. The LMC and SMC abundance patterns can be reproduced in ensembles of model clouds with a reduced H2 formation rate coefficient, R ~ 3 x 10^-18 cm^3 s^-1, and incident radiation fields ranging from 10 – 100 times the Galactic mean value. We find that these high-radiation, low-formation-rate models can also explain the enhanced N(4)/N(2) and N(5)/N(3) rotational excitation ratios in the Clouds. We use H2 column densities in low rotational states (J = 0 and 1) to derive a mean kinetic and/or rotational temperature <T_01> = 82 +/- 21 K for clouds with N(H2) >= 10^16 cm^-2, similar to Galactic gas. We discuss the implications of this work for theories of star formation in low-metallicity environments. [Abstract abridged]

Category: Physics