The Variation of the CO to H2Conversion Factor in Two Translucent Clouds
In: The Astrophysical Journal, Jg. 504 (1998-09-01), Heft 1, S. 290-299
Online
serialPeriodical
Zugriff:
The conversion factor, XCO, between the velocity-integrated CO(1-0) antenna temperature, W(CO), and the H2column density, N(H2), is determined for 32 positions in two translucent high-latitude molecular clouds, MBM 40 and MBM 16. XCOis calculated using CH observations of the 2?1/2F= 1-1 hyperfine transition to infer N(H2). The latter quantity, divided by W(CO) yields XCOfor various positions across the clouds. We observed 24 positions in MBM 16, and XCOvalues were derived in the range (1.6-17.3) × 1020cm-2(K km s-1)-1, with a mean value of 7.6 × 1020. Eleven lines of sight were sampled in MBM 40 yielding values of XCOin the range (0.7-9.7) × 1020, with a mean value of 2.6 × 1020. An inverse relationship between XCOand W(CO) may exist, suggesting that the variation in XCOfor these two translucent clouds arises from varying CO abundances. This paper also reports the existence of a broad component in the CH spectra observed throughout much of MBM 16. This component possibly originates in the disturbed outer regions of the cloud where the gas is not gravitationally bound to the core of the cloud. It is unclear how sensitive the CO rotational transitions are to this component, but it is likely that the CO/H2ratio in this broad-line gas is less than 10-5. However, if the CH/H2ratio is the same for the gas in the extended wings as it is for the typical cloud gas, then up to 40% of the cloud mass could be contained in this difficult to trace molecular component.
Titel: |
The Variation of the CO to H2Conversion Factor in Two Translucent Clouds
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Autor/in / Beteiligte Person: | Magnani, Loris ; Onello, Joseph S. ; Adams, Nigel G. ; Hartmann, Dap ; Thaddeus, Patrick |
Link: | |
Zeitschrift: | The Astrophysical Journal, Jg. 504 (1998-09-01), Heft 1, S. 290-299 |
Veröffentlichung: | 1998 |
Medientyp: | serialPeriodical |
ISSN: | 0004-637X (print) ; 1538-4357 (print) |
DOI: | 10.1086/306062 |
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