Table 2
Synopsis of velocity-integrated column densities of CH, HF, and OH on the sightline to W49 N.
| υ | N(CH ) | N(HF ) | N(OH ) | fH_2d | N(HF)∕N(CH)e | N(OH)∕N(CH)e | |
|---|---|---|---|---|---|---|---|
| [km s−1 ] | [1013 cm−2] | ||||||
| Local gas | (−3, +5) |  |
 |
 |
 |
 |
 |
| Perseusa | (+5, +20) |  |
 |
 |
 |
 |
 |
| Interarm | (+20, +30) |  |
 |
 |
 |
 |
 |
| Sgrb | (+30, +45) |  |
 |
 |
 |
 |
 |
| Sgrc | (+45, +70) |  |
 |
 |
 |
 |
 |
Notes. Error estimates are based on the normalized
χ2
of the fits shown in Fig. 2, and
on a 5% uncertainty in the continuum levels.
(a)
Analysis and error estimates inaccurate (velocity
interval contains hot-core environment of unknown
excitation, HF absorption is partially saturated).
(b)
Near- and far-side crossing of Sagittarius spiral arm.
(c) Far-side crossing.
(d) Molecular hydrogen
fractions 
are derived
from HF (with N(HF)∕N(H2) = 1.4 × 10−8)
and from HI λ21 cm
data, (Winkel et al. 2017, further references therein).
(e)
Bayesian error estimates (accounting for the correlation
between the column densities of the reported ratios).
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