Universität zu Köln

Goldsmith, Paul F., Pineda, Jorge L., Neufeld, David A., Wolfire, Mark G., Risacher, Christophe and Simon, Robert (2018). Velocity-resolved [C II] Emission from Cold Diffuse Clouds in the Interstellar Medium. Astrophys. J., 856 (2). BRISTOL: IOP PUBLISHING LTD. ISSN 1538-4357

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Abstract

We have combined emission from the 158 mu m fine structure transition of C+ observed with the GREAT and upGREAT instruments on SOFIA with 21 cm absorption spectra and visual extinction to characterize the diffuse interstellar clouds found along the lines of sight. The weak [C II] emission is consistent in velocity and line width with the strongest H I component produced by the cold neutral medium. The H I column density and kinetic temperature are known from the 21 cm data and, assuming a fractional abundance of ionized carbon, we calculate the volume density and thermal pressure of each source, which vary considerably, with 27 cm(-3) <= n(H-0) <= 210 cm(-3) considering only the atomic hydrogen along the lines of sight to be responsible for the C+, while 13 cm(-3) <= n(H-0 + H-2) <= 190 cm(-3) including the hydrogen in both forms. The thermal pressure varies widely with 1970 cm(-3) K <= P-th/k <= 10,440 cm(-3) K for H-0 alone and 750 cm(-3) K <= P-th/k <= 9360 cm(-3) K including both H-0 and H-2. The molecular hydrogen fraction varies between 0.10 and 0.67. Photoelectric heating is the dominant heating source, supplemented by a moderately enhanced cosmic ray ionization rate, constrained by the relatively low 45 K to 73 K gas temperatures of the clouds. The resulting thermal balance for the two lower-density clouds is satisfactory, but for the two higher-density clouds, the combined heating rate is insufficient to balance the observed C+ cooling.

Item Type:	Journal Article
Creators:	Creators Email ORCID ORCID Put Code Goldsmith, Paul F. UNSPECIFIED UNSPECIFIED UNSPECIFIED Pineda, Jorge L. UNSPECIFIED UNSPECIFIED UNSPECIFIED Neufeld, David A. UNSPECIFIED UNSPECIFIED UNSPECIFIED Wolfire, Mark G. UNSPECIFIED UNSPECIFIED UNSPECIFIED Risacher, Christophe UNSPECIFIED UNSPECIFIED UNSPECIFIED Simon, Robert UNSPECIFIED UNSPECIFIED UNSPECIFIED
URN:	urn:nbn:de:hbz:38-191799
DOI:	10.3847/1538-4357/aab34e
Journal or Publication Title:	Astrophys. J.
Volume:	856
Number:	2
Date:	2018
Publisher:	IOP PUBLISHING LTD
Place of Publication:	BRISTOL
ISSN:	1538-4357
Language:	English
Faculty:	Unspecified
Divisions:	Unspecified
Subjects:	no entry
Uncontrolled Keywords:	Keywords Language FINE-STRUCTURE EXCITATION; HIGH GALACTIC LATITUDE; ABSORPTION-LINE SURVEY; RAY IONIZATION RATE; MOLECULAR CLOUDS; ZETA-PERSEI; ATOMIC-HYDROGEN; COLLIDING FLOWS; GAS; MODEL Multiple languages Astronomy & Astrophysics Multiple languages
Refereed:	Yes
URI:	http://kups.ub.uni-koeln.de/id/eprint/19179