TY - JOUR
T1 - Dust and gas in the magellanic clouds from the heritage herschel key project. II. Gas-to-dust ratio variations across interstellar medium phases
AU - Roman-Duval, J.
AU - Gordon, K.D.
AU - Meixner, M.M.
AU - Bot, C.
AU - Bolatto, A.D.
AU - Hughes, A.M.
AU - Wong, T.
AU - Babler, B.L.
AU - Bernard, J.P.
AU - Clayton, G.C.
AU - Fukui, Y.
AU - Galametz, M.
AU - Galliano, F.
AU - Glover, S.C.O.
AU - Hony, S.
AU - Israël, F.P.
AU - Jameson, K.
AU - Lebouteiller, V.
AU - Min-Young, L.E.E.
AU - Li, A.
AU - Madden, S.C.
AU - Misselt, K.A.
AU - Montiel, E.J.
AU - Okumura, K.
AU - Onishi, T.
AU - Panuzzo, P.
AU - Reach, W.T.
AU - Rémy-Ruyer, A.
AU - Robitaille, T.P.
AU - Rubio, M.
AU - Sauvage, M.A.
AU - Seale, J.P.
AU - Sewiło, M.M.
AU - Staveley-Smith, Lister
AU - Zhukovska, S.V.
PY - 2014
Y1 - 2014
N2 - © 2014. The American Astronomical Society. All rights reserved. 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), HI 21 cm, CO, and Hiα observations. In the diffuse atomic interstellar medium (ISM), we derive the GDR as the slope of the dust-gas relation and find GDRs of 380-130 +250 ± 3 in the LMC, and 1200-420 +1600 ± 120 in the SMC, not including helium. The atomic-to-molecular transition is located at dust surface densities of 0.05 M⊙ pc-2 in the LMC and 0.03 M⊙ 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 6 × 1020 cm-2 K-1 km-1 s in the LMC (Z = 0.5 Z⊙) at 15 pc resolution, and 4 × 1021 cm-2 K-1 km-1 s in the SMC (Z = 0.2 Z⊙) 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. Our analysis demonstrates that obtaining robust ISM masses remains a non-trivial endeavor even in the local Universe using state-of-the-art maps of thermal dust emission.
AB - © 2014. The American Astronomical Society. All rights reserved. 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), HI 21 cm, CO, and Hiα observations. In the diffuse atomic interstellar medium (ISM), we derive the GDR as the slope of the dust-gas relation and find GDRs of 380-130 +250 ± 3 in the LMC, and 1200-420 +1600 ± 120 in the SMC, not including helium. The atomic-to-molecular transition is located at dust surface densities of 0.05 M⊙ pc-2 in the LMC and 0.03 M⊙ 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 6 × 1020 cm-2 K-1 km-1 s in the LMC (Z = 0.5 Z⊙) at 15 pc resolution, and 4 × 1021 cm-2 K-1 km-1 s in the SMC (Z = 0.2 Z⊙) 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. Our analysis demonstrates that obtaining robust ISM masses remains a non-trivial endeavor even in the local Universe using state-of-the-art maps of thermal dust emission.
U2 - 10.1088/0004-637X/797/2/86
DO - 10.1088/0004-637X/797/2/86
M3 - Article
SN - 0004-637X
VL - 797
SP - 1
EP - 24
JO - The Astrophysical Journal
JF - The Astrophysical Journal
IS - 2
ER -