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Dust and Gas in the Magellanic Clouds from the HERITAGE Herschel Key Project. II. Gas-to-Dust Ratio Variations across ISM Phases | Julia Roman-Duval
; Karl Gordon
; Margaret Meixner
; Caroline Bot
; Alberto D. Bolatto
; Annie Hughes
; Tony Wong
; Brian Babler
; Jean-Philippe Bernard
; Geoffrey Clayton
; Yasuo Fukui
; Maud Galametz
; Frederic Galliano
; Simon C. O. Glover
; Sacha Hony
; Frank Israel
; Katherine Jameson
; Vianney Lebouteiller
; Min-Young Lee
; Aigen Li
; Suzanne C. Madden
; Karl Misselt
; Edward Montiel
; K. Okumura
; Toshikazu Onishi
; Pasquale Panuzzo
; William Reach
; A Remy-Ruyer
; Thomas Robitaille
; Monica Rubio
; Marc Sauvage
; Jonathan Seale
; Marta Sewilo
; Lister Staveley-Smith
; Svitlana Zhukovska
; | Date: |
17 Nov 2014 | Abstract: | The spatial variations of the gas-to-dust ratio (GDR) provide constraints on
the chemical evolution and lifecycle of dust in galaxies. We examine the
relation between dust and gas at 10-50 pc resolution in the Large and Small
Magellanic Clouds (LMC and SMC) based on Herschel far-infrared (FIR), H I 21
cm, CO, and Halpha observations. In the diffuse atomic ISM, we derive the
gas-to-dust ratio as the slope of the dust-gas relation and find gas-to-dust
ratios of 380+250-130 in the LMC, and 1200+1600-420 in the SMC, not including
helium. The atomic-to-molecular transition is located at dust surface densities
of 0.05 Mo pc-2 in the LMC and 0.03 Mo pc-2 in the SMC, corresponding to AV ~
0.4 and 0.2, respectively. We investigate the range of CO-to-H2 conversion
factor to best account for all the molecular gas in the beam of the
observations, and find upper limits on XCO to be 6x1020 cm-2 K-1 km-1 s in the
LMC (Z=0.5Zo) at 15 pc resolution, and 4x 1021 cm-2 K-1 km-1 s in the SMC
(Z=0.2Zo) at 45 pc resolution. In the LMC, the slope of the dust-gas relation
in the dense ISM is lower than in the diffuse ISM by a factor ~2, even after
accounting for the effects of CO-dark H2 in the translucent envelopes of
molecular clouds. Coagulation of dust grains and the subsequent dust emissivity
increase in molecular clouds, and/or accretion of gas-phase metals onto dust
grains, and the subsequent dust abundance (dust-to-gas ratio) increase in
molecular clouds could explain the observations. In the SMC, variations in the
dust-gas slope caused by coagulation or accretion are degenerate with the
effects of CO-dark H2. Within the expected 5--20 times Galactic XCO range, the
dust-gas slope can be either constant or decrease by a factor of several across
ISM phases. Further modeling and observations are required to break the
degeneracy between dust grain coagulation, accretion, and CO-dark H2. | Source: | arXiv, 1411.4552 | Services: | Forum | Review | PDF | Favorites |
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