Molecular gas in spiral galaxies: a new warm phase at large galactocentric distances?

Details Molecular gas in spiral galaxies: a new warm phase at large galactocentric distances? Molecular gas in spiral galaxies: a new warm phase at large galactocentric distances?

2002-08-29

arxiv.org/abs/astro-ph/0208535v1

Astrophys.J. 579 (2002) 270-274; Erratum-ibid. 583 (2003) 524

Astronomy and Astrophysics

Astrophysics

In press at ApJ. 14 pages, 1 b&w figure

Scientific paper

10.1086/342872

There is now strong evidence suggesting that the 12CO J = 1-0 transition, widely used to trace H2 gas, significantly underestimates its mass in metal-poor regions. In spiral disks such regions are found in large galactocentric distances where we show that any unaccounted H2 gas phase is likely to be diffuse (~5-20 cm^-3) and warmer (T(kin) ~ 50-100 K) than the cool (T(kin) ~ 15-20 K) CO-luminous one. Moreover we find that a high value of the H2 formation rate on grains, suggested by recent observational work, can compensate for the reduction of the available grain surface in the metal-poor part of typical galactic disks and thus enhance this CO-poor H2 component which may be contributing significantly to the mass and pressure of spiral disks beyond their optical radius.

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