X-Ray Irradiated Molecular Clouds in Active Galactic Nuclei

Details X-Ray Irradiated Molecular Clouds in Active Galactic Nuclei X-Ray Irradiated Molecular Clouds in Active Galactic Nuclei

Dec 1992

adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=1992aas...181.3503m&link_type=abstract

American Astronomical Society, 181st AAS Meeting, #35.03; Bulletin of the American Astronomical Society, Vol. 24, p.1172

Astronomy and Astrophysics

Astronomy

1

Scientific paper

Vibrationally-excited molecular hydrogen emission appears to be quite common in Seyfert galaxies (\eg Kawara, Nishida & Gregory 1987, Ap. J. 321, L35). High spatial resolution observations show that this emission is typically extended on ~ 100 pc size scales. Hence it does not arise in the parsec-scale obscuring tori postulated to exist around AGNs. This H_2 emission has been ascribed to circumnuclear starbursts or shocks generated by a wind from the AGN impacting on the ISM of the galaxy. Here we examine whether molecular clouds irradiated by X-rays from the AGN are capable of producing the observed molecular hydrogen emission. We consider this problem in a somewhat more general framework than Krolik & Lepp (1989, Ap.J. 347, 179). A power-law radiation field extending from E ~ 1-100 keV, attenuated by an intervening column density N_att, is assumed incident on the clouds. We consider a range of fluxes and cloud densities, and calculate the ionization, thermal balance, and a simplified molecular scheme. X-ray photoionization dominates over Compton scattering for N_attlta 10(24) cm(-2) . Both the ionization and atomic fractions can be substantial. We delineate the X-ray flux/cloud density regime where X-ray pumped H_2 emission is significant and compare our results with observations.

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