TY - JOUR
T1 - The opacity of spiral galaxy disks
T2 - IX. Dust and gas surface densities
AU - Holwerda, B. W.
AU - Allen, R. J.
AU - de Blok, W. J. G.
AU - Bouchard, A.
AU - Gonzalez-Lopezlira, R. A.
AU - van der Kruit, P. C.
AU - Leroy, A.
PY - 2013/3
Y1 - 2013/3
N2 - Our aim is to explore the relation between gas, atomic and molecular, and dust in spiral galaxies. Gas surface densities are from atomic hydrogen and CO line emission maps. To estimate the dust content, we use the disk opacity as inferred from the number of distant galaxies identified in twelve HST/WFPC2 fields of ten nearby spiral galaxies. The observed number of distant galaxies is calibrated for source confusion and crowding with artificial galaxy counts and here we verify our results with sub-mm surface brightnesses from archival Herschel-SPIRE data. We find that the opacity of the spiral disk does not correlate well with the surface density of atomic (H I) or molecular hydrogen (H-2) alone implying that dust is not only associated with the molecular clouds but also the diffuse atomic disk in these galaxies. Our result is a typical dust-to-gas ratio of 0.04, with some evidence that this ratio declines with galactocentric radius, consistent with recent Herschel results. We discuss the possible causes of this high dust-to-gas ratio; an over-estimate of the dust surface-density, an under-estimate of the molecular hydrogen density from CO maps or a combination of both. We note that while our value of the mean dust-to-gas ratio is high, it is consistent with the metallicity at the measured radii if one assumes the Pilyugin & Thuan (2005) calibration of gas metallicity. (C) 2013 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim
AB - Our aim is to explore the relation between gas, atomic and molecular, and dust in spiral galaxies. Gas surface densities are from atomic hydrogen and CO line emission maps. To estimate the dust content, we use the disk opacity as inferred from the number of distant galaxies identified in twelve HST/WFPC2 fields of ten nearby spiral galaxies. The observed number of distant galaxies is calibrated for source confusion and crowding with artificial galaxy counts and here we verify our results with sub-mm surface brightnesses from archival Herschel-SPIRE data. We find that the opacity of the spiral disk does not correlate well with the surface density of atomic (H I) or molecular hydrogen (H-2) alone implying that dust is not only associated with the molecular clouds but also the diffuse atomic disk in these galaxies. Our result is a typical dust-to-gas ratio of 0.04, with some evidence that this ratio declines with galactocentric radius, consistent with recent Herschel results. We discuss the possible causes of this high dust-to-gas ratio; an over-estimate of the dust surface-density, an under-estimate of the molecular hydrogen density from CO maps or a combination of both. We note that while our value of the mean dust-to-gas ratio is high, it is consistent with the metallicity at the measured radii if one assumes the Pilyugin & Thuan (2005) calibration of gas metallicity. (C) 2013 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim
KW - dust, extinctione
KW - galaxies: ISM
KW - galaxies: spiral
KW - galaxies: structure
KW - ISM: structur
KW - opacity
KW - STAR-FORMATION LAW
KW - GIANT MOLECULAR CLOUDS
KW - SYNTHETIC FIELD METHOD
KW - SMALL-MAGELLANIC-CLOUD
KW - SPECTRAL ENERGY-DISTRIBUTION
KW - RADIAL EXTINCTION PROFILES
KW - LARGE-SCALE DISSOCIATION
KW - DIGITAL-SKY-SURVEY
KW - NEARBY GALAXIES
KW - SEEING GALAXIES
UR - http://adsabs.harvard.edu/abs/2013AN....334..268H
U2 - 10.1002/asna.201211713
DO - 10.1002/asna.201211713
M3 - Article
SN - 0004-6337
VL - 334
SP - 268
EP - 281
JO - Astronomische Nachrichten
JF - Astronomische Nachrichten
IS - 3
ER -