Dust-Gas Scaling Relations and OH Abundance in the Galactic ISM

Hiep Nguyen; J. R. Dawson; M. A. Miville-Deschenes; Ningyu Tang; Di Li; Carl Heiles; Claire E. Murray; Snežana Stanimirović; Steven J. Gibson; N. M. McClure-Griffiths; Thomas Troland; L. Bronfman; R. Finger

doi:10.3847/1538-4357/aac82b

Dust-Gas Scaling Relations and OH Abundance in the Galactic ISM

Hiep Nguyen, J. R. Dawson, M. A. Miville-Deschenes, Ningyu Tang, Di Li, Carl Heiles, Claire E. Murray, Snežana Stanimirović, Steven J. Gibson, N. M. McClure-Griffiths, Thomas Troland, L. Bronfman, R. Finger

Physics And Astronomy

Research output: Contribution to journal › Article › peer-review

57 Scopus citations

Abstract

Observations of interstellar dust are often used as a proxy for total gas column density N _H. By comparing Planck thermal dust data (Release 1.2) and new dust reddening maps from Pan-STARRS 1 and 2MASS, with accurate (opacity-corrected) H i column densities and newly published OH data from the Arecibo Millennium survey and 21-SPONGE, we confirm linear correlations between dust optical depth τ ₃₅₃, reddening E(B - V), and the total proton column density N _H in the range (1-30) × 10²⁰ cm^-2, along sightlines with no molecular gas detections in emission. We derive an N _H/E(B - V) ratio of (9.4 ± 1.6) × 10²¹ cm^-2 mag^-1 for purely atomic sightlines at , which is 60% higher than the canonical value of Bohlin et al. We report a ∼40% increase in opacity σ ₃₅₃ = τ ₃₅₃/N _H, when moving from the low column density (N _H < 5 × 10²⁰ cm^-2) to the moderate column density (N _H > 5 × 10²⁰ cm^-2) regime, and suggest that this rise is due to the evolution of dust grains in the atomic interstellar medium. Failure to account for H i opacity can cause an additional apparent rise in σ ₃₅₃ of the order of a further ∼20%. We estimate molecular hydrogen column densities from our derived linear relations, and hence derive the OH/H₂ abundance ratio of X _OH ∼ 1 × 10^-7 for all molecular sightlines. Our results show no evidence of systematic trends in OH abundance with in the range ∼ (0.1-10) × 10²¹ cm^-2. This suggests that OH may be used as a reliable proxy for H₂ in this range, which includes sightlines with both CO-dark and CO-bright gas.

Original language	English
Article number	49
Journal	Astrophysical Journal
Volume	862
Issue number	1
DOIs	https://doi.org/10.3847/1538-4357/aac82b
State	Published - Jul 20 2018

Bibliographical note

Publisher Copyright:
© 2018. The American Astronomical Society. All rights reserved.

Funding

J.R.D. is the recipient of an Australian Research Council (ARC) DECRA Fellowship (project number DE170101086). D.L. thanks the supports from the National Key R&D Program of China (2017YFA0402600) and the CAS International Partnership Program (No.114A11KYSB20160008). N.M.-G. acknowledges the support of the ARC through Future Fellowship FT150100024. L.B. acknowledges the support from CONICYT grant PFB06. We are indebted to Professor Mark Wardle for providing us with valuable advice and support. We gratefully acknowledge discussions with Dr. Cormac Purcell and Anita Petzler. Finally, we thank the anonymous referee for comments and criticisms that allowed us to improve the paper.

Funders	Funder number
National Key Basic Research Program of China	2017YFA0402600
College of Arts and Sciences, University of Nebraska-Lincoln	FT150100024, 114A11KYSB20160008
Australian Research Council	DE170101086
Comisión Nacional de Investigación Científica y Tecnológica	PFB06

Keywords

ISM: clouds
ISM: molecules
dust
extinction

ASJC Scopus subject areas

Astronomy and Astrophysics
Space and Planetary Science

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10.3847/1538-4357/aac82b

Cite this

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title = "Dust-Gas Scaling Relations and OH Abundance in the Galactic ISM",

abstract = "Observations of interstellar dust are often used as a proxy for total gas column density N H. By comparing Planck thermal dust data (Release 1.2) and new dust reddening maps from Pan-STARRS 1 and 2MASS, with accurate (opacity-corrected) H i column densities and newly published OH data from the Arecibo Millennium survey and 21-SPONGE, we confirm linear correlations between dust optical depth τ 353, reddening E(B - V), and the total proton column density N H in the range (1-30) × 1020 cm-2, along sightlines with no molecular gas detections in emission. We derive an N H/E(B - V) ratio of (9.4 ± 1.6) × 1021 cm-2 mag-1 for purely atomic sightlines at , which is 60% higher than the canonical value of Bohlin et al. We report a ∼40% increase in opacity σ 353 = τ 353/N H, when moving from the low column density (N H < 5 × 1020 cm-2) to the moderate column density (N H > 5 × 1020 cm-2) regime, and suggest that this rise is due to the evolution of dust grains in the atomic interstellar medium. Failure to account for H i opacity can cause an additional apparent rise in σ 353 of the order of a further ∼20%. We estimate molecular hydrogen column densities from our derived linear relations, and hence derive the OH/H2 abundance ratio of X OH ∼ 1 × 10-7 for all molecular sightlines. Our results show no evidence of systematic trends in OH abundance with in the range ∼ (0.1-10) × 1021 cm-2. This suggests that OH may be used as a reliable proxy for H2 in this range, which includes sightlines with both CO-dark and CO-bright gas.",

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T1 - Dust-Gas Scaling Relations and OH Abundance in the Galactic ISM

AU - Nguyen, Hiep

AU - Dawson, J. R.

AU - Miville-Deschenes, M. A.

AU - Tang, Ningyu

AU - Li, Di

AU - Heiles, Carl

AU - Murray, Claire E.

AU - Stanimirović, Snežana

AU - Gibson, Steven J.

AU - McClure-Griffiths, N. M.

AU - Troland, Thomas

AU - Bronfman, L.

AU - Finger, R.

PY - 2018/7/20

Y1 - 2018/7/20

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AB - Observations of interstellar dust are often used as a proxy for total gas column density N H. By comparing Planck thermal dust data (Release 1.2) and new dust reddening maps from Pan-STARRS 1 and 2MASS, with accurate (opacity-corrected) H i column densities and newly published OH data from the Arecibo Millennium survey and 21-SPONGE, we confirm linear correlations between dust optical depth τ 353, reddening E(B - V), and the total proton column density N H in the range (1-30) × 1020 cm-2, along sightlines with no molecular gas detections in emission. We derive an N H/E(B - V) ratio of (9.4 ± 1.6) × 1021 cm-2 mag-1 for purely atomic sightlines at , which is 60% higher than the canonical value of Bohlin et al. We report a ∼40% increase in opacity σ 353 = τ 353/N H, when moving from the low column density (N H < 5 × 1020 cm-2) to the moderate column density (N H > 5 × 1020 cm-2) regime, and suggest that this rise is due to the evolution of dust grains in the atomic interstellar medium. Failure to account for H i opacity can cause an additional apparent rise in σ 353 of the order of a further ∼20%. We estimate molecular hydrogen column densities from our derived linear relations, and hence derive the OH/H2 abundance ratio of X OH ∼ 1 × 10-7 for all molecular sightlines. Our results show no evidence of systematic trends in OH abundance with in the range ∼ (0.1-10) × 1021 cm-2. This suggests that OH may be used as a reliable proxy for H2 in this range, which includes sightlines with both CO-dark and CO-bright gas.

KW - ISM: clouds

KW - ISM: molecules

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KW - extinction

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ER -

Dust-Gas Scaling Relations and OH Abundance in the Galactic ISM

Abstract

Bibliographical note

Funding

Keywords

ASJC Scopus subject areas

Access to Document

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