The gas-to-extinction ratio and the gas distribution in the Galaxy
Abstract We investigate the relation between the optical extinction (A V ) and the hydrogen column density (N H) determined from X-ray observations of a large sample of Galactic sightlines towards 35 supernova remnants, 6 planetary nebulae and 70 X-ray binaries for which N H was determined in the li...
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| Vydáno v: | Monthly notices of the Royal Astronomical Society Ročník 471; číslo 3; s. 3494 - 3528 |
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| Hlavní autoři: | , , , |
| Médium: | Journal Article |
| Jazyk: | angličtina |
| Vydáno: |
Oxford University Press
01.11.2017
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| Témata: | |
| ISSN: | 0035-8711, 1365-2966 |
| On-line přístup: | Získat plný text |
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| Shrnutí: | Abstract
We investigate the relation between the optical extinction (A
V
) and the hydrogen column density (N
H) determined from X-ray observations of a large sample of Galactic sightlines towards 35 supernova remnants, 6 planetary nebulae and 70 X-ray binaries for which N
H was determined in the literature with solar abundances. We derive an average ratio of 〈N
H/A
V
〉 = (2.08 ± 0.02) × 1021 H cm−2 mag−1 for the whole Galaxy. We find no correlation between 〈N
H/A
V
〉 and the number density of hydrogen, the distance away from the Galactic Centre and the distance above or below the Galactic plane. The 〈N
H/A
V
〉 ratio is generally invariant across the Galaxy, with 〈N
H/A
V
〉 = (2.04 ± 0.05) × 1021 H cm−2 mag−1 for the first and fourth Galactic quadrants and 〈N
H/A
V
〉 = (2.09 ± 0.03) × 1021 H cm−2 mag−1 for the second and third Galactic quadrants. We also explore the distribution of hydrogen in the Galaxy by enlarging our sample with additional 74 supernova remnants for which both N
H and distances are known. We find that, between the Galactic radius of 2 and 10 kpc, the vertical distribution of hydrogen can be roughly described by a Gaussian function with a scaleheight of h = 75.5 ± 12.4 pc and a mid-plane density of n
H(0) = 1.11 ± 0.15 cm−3, corresponding to a total gas surface density of ∑gas ∼ 7.0 M⊙ pc−2. We also compile N
H from 19 supernova remnants and 29 X-ray binaries for which N
H was determined with subsolar abundances. We obtain 〈N
H/A
V
〉 = (2.47 ± 0.04) × 1021 H cm−2 mag−1 which exceeds that derived with solar abundances by ∼20 per cent. We suggest that in future studies one may simply scale N
H derived from subsolar abundances by a factor of ∼1.2 when converting to N
H of solar abundances. |
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| ISSN: | 0035-8711 1365-2966 |
| DOI: | 10.1093/mnras/stx1580 |