Artículo de revista
Dust-Gas Scaling Relations and OH Abundance in the Galactic ISM
Fecha
2018Registro en:
Astrophysical Journal, Volumen 862, Issue 1, 2018
15384357
0004637X
10.3847/1538-4357/aac82b
Autor
Nguyen, Hiep
Dawson, J.
Miville-Deschenes, M.
Tang, Ningyu
Li, Di
Heiles, Carl
Murray, Claire
Stanimirović, Snežana
Gibson, Steven
McClure-Griffiths, N.
Troland, Thomas
Bronfman Aguiló, Leonardo
Finger, R.
Institución
Resumen
Observations of interstellar dust are often used as a proxy for total gas column density NH. By
comparing Planck thermal dust data (Release 1.2) and new dust reddening maps from Pan-STARRS
1 and 2MASS (Green et al. 2018), with accurate (opacity-corrected) Hi column densities and newlypublished OH data from the Arecibo Millennium survey and 21-SPONGE, we confirm linear correlations between dust optical depth τ353, reddening E(B−V )and the total proton column density NH
in the range (1–30)×1020cm−2
, along sightlines with no molecular gas detections in emission. We
derive an NH/E(B−V ) ratio of (9.4±1.6)×1021cm−2mag−1
for purely atomic sightlines at |b|>5
◦
,
which is 60% higher than the canonical value of Bohlin et al. (1978). We report a ∼40% increase in
opacity σ353=τ353/NH, when moving from the low column density (NH<5×1020cm−2
) to moderate
column density (NH>5×1020cm−2
) regime, and suggest that this rise is due to the evolution of dust
grains in the atomic ISM. Failure to account for Hi opacity can cause an additional apparent rise in
σ353, of the order of a further ∼20%. We estimate molecular hydrogen column densities NH2
from
our derived linear relations, and hence derive the OH/H2 abundance ratio of XOH∼1×10−7
for all
molecular sightlines. Our results show no evidence of systematic trends in OH abundance with NH2
in the range NH2∼(0.1−10)×1021cm−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.