Universität zu Köln

Gonzalez-Alfonso, E., Fischer, J., Bruderer, S., Ashby, M. L. N., Smith, H. A., Veilleux, S., Mueller, H. S. P., Stewart, K. P. and Sturm, E. (2018). Outflowing OH+ in Markarian 231: The Ionization Rate of the Molecular Gas. Astrophys. J., 857 (1). BRISTOL: IOP PUBLISHING LTD. ISSN 1538-4357

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Abstract

The oxygen-bearing molecular ions OH+, H2O+, and H3O+ are key species that probe the ionization rate of (partially) molecular gas that is ionized by X-rays and cosmic-rays permeating the interstellar medium. We report Herschel far-infrared and submillimeter spectroscopic observations of OH+ in Mrk. 231, showing both ground-state P-Cygni profiles, and excited line profiles with blueshifted absorption wings extending up to approximate to 1000 km s(-1). In addition, OH+ probes an excited component peaking at central velocities, likely arising from the torus probed by the OH centimeter-wave megamaser. Four lines of H2O+ are also detected at systemic velocities, but H3O+ is undetected. Based on our earlier OH studies, we estimate an abundance ratio of OH OH+ similar to 5-10 for the outflowing components and approximate to 20 for the torus, and an OH+ abundance relative to H nuclei of greater than or similar to 10(-7). We also find high OH+/H2O+ and OH+/H3O+ ratios; both are greater than or similar to 4 in the torus and greater than or similar to 10-20 in the outflowing gas components. Chemical models indicate that these high OH+ abundances relative to OH, H2O+, and H3O+ are characteristic of gas with a high ionization rate per unit density, zeta/nH similar to (1-5) x 10(-17) cm(3) s(-1) and similar to(1-2) x 10(-16) cm(3) s(-1) for the above components, respectively, an ionization rate of zeta similar to (0.5-2) x 10(-12) s(-1), and a low molecular fraction, fH(2) similar to 0.25. X-rays appear to be unable to explain the inferred ionization rate, and thus we suggest that low-energy (10-400 MeV) cosmic-rays are primarily responsible for the ionization, with <(M)over dot>(CR) similar to 0.01 M-circle dot yr(-1) and <(E)over dot>(CR) similar to 10(44) erg. s(-1); the latter corresponds to similar to 1% of the luminosity of the active galactic nucleus and is similar to the energetics of the molecular outflow. We suggest that cosmic-rays accelerated in the forward shock associated with the molecular outflow are responsible for the ionization, as they diffuse through the outflowing molecular phase downstream.

Item Type:	Journal Article
Creators:	Creators Email ORCID ORCID Put Code Gonzalez-Alfonso, E. UNSPECIFIED UNSPECIFIED UNSPECIFIED Fischer, J. UNSPECIFIED UNSPECIFIED UNSPECIFIED Bruderer, S. UNSPECIFIED UNSPECIFIED UNSPECIFIED Ashby, M. L. N. UNSPECIFIED UNSPECIFIED UNSPECIFIED Smith, H. A. UNSPECIFIED UNSPECIFIED UNSPECIFIED Veilleux, S. UNSPECIFIED UNSPECIFIED UNSPECIFIED Mueller, H. S. P. UNSPECIFIED UNSPECIFIED UNSPECIFIED Stewart, K. P. UNSPECIFIED UNSPECIFIED UNSPECIFIED Sturm, E. UNSPECIFIED UNSPECIFIED UNSPECIFIED
URN:	urn:nbn:de:hbz:38-189511
DOI:	10.3847/1538-4357/aab6b8
Journal or Publication Title:	Astrophys. J.
Volume:	857
Number:	1
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 ACTIVE GALACTIC NUCLEI; RAY DOMINATED REGIONS; COLOGNE DATABASE; STAR-FORMATION; GALAXY; CHEMISTRY; WINDS; SPECTROSCOPY; ABSORPTION; SIGNATURES Multiple languages Astronomy & Astrophysics Multiple languages
Refereed:	Yes
URI:	http://kups.ub.uni-koeln.de/id/eprint/18951