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Probing highly obscured, self-absorbed galaxy nuclei with vibrationally excited HCN

Susanne Aalto (Institutionen för rymd- och geovetenskap, Radioastronomi och astrofysik) ; S. Martin ; Francesco Costagliola (Institutionen för rymd- och geovetenskap, Radioastronomi och astrofysik) ; E. Gonzalez-Alfonso ; Sebastien Muller (Institutionen för rymd- och geovetenskap, Onsala rymdobservatorium) ; K. Sakamoto ; G. A. Fuller ; S. Garcia-Burillo ; P. van der Werf ; R. Neri ; M. Spaans ; F. Combes ; S. Viti ; S. Muhle ; L. Armus ; A. Evans ; E. Sturm ; J. Cernicharo ; C. Henkel ; T. R. Greve
Astronomy and Astrophysics (0004-6361). Vol. 584 (2015),
[Artikel, refereegranskad vetenskaplig]

We present high resolution (0.'' 4) IRAM PdBI and ALMA mm and submm observations of the (ultra) luminous infrared galaxies ((U)LIRGs) IRAS 17208-0014, Arp220, IC 860 and Zw049.057 that reveal intense line emission from vibrationally excited (nu(2) = 1) J = 3-2 and 4-3 HCN. The emission is emerging from buried, compact (r < 17-70 pc) nuclei that have very high implied mid-infrared surface brightness >5 x 10(13) L-circle dot kpc(-2). These nuclei are likely powered by accreting supermassive black holes (SMBHs) and/or hot (>200 K) extreme starbursts. Vibrational, nu(2) = 1, lines of HCN are excited by intense 14 mu m mid-infrared emission and are excellent probes of the dynamics, masses, and physical conditions of (U)LIRG nuclei when H-2 column densities exceed 10(24) cm(-2). It is clear that these lines open up a new interesting avenue to gain access to the most obscured AGNs and starbursts. Vibrationally excited HCN acts as a proxy for the absorbed mid-infrared emission from the embedded nuclei, which allows for reconstruction of the intrinsic, hotter dust SED. In contrast, we show strong evidence that the ground vibrational state (. = 0), J = 3-2 and 4-3 rotational lines of HCN and HCO+ fail to probe the highly enshrouded, compact nuclear regions owing to strong self-and continuum absorption. The HCN and HCO+ line profiles are double-peaked because of the absorption and show evidence of non-circular motions-possibly in the form of in-or outflows. Detections of vibrationally excited HCN in external galaxies are so far limited to ULIRGs and early-type spiral LIRGs, and we discuss possible causes for this. We tentatively suggest that the peak of vibrationally excited HCN emission is connected to a rapid stage of nuclear growth, before the phase of strong feedback.

Nyckelord: galaxies: evolution, galaxies: active, galaxies: nuclei, galaxies

Denna post skapades 2016-01-21. Senast ändrad 2016-04-11.
CPL Pubid: 231055


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Denna publikation är ett resultat av följande projekt:

Molecules as Diagnostic Tools for Active and Obscured Galaxies (VR//2011-4143)