%0 Journal Article
%T The hidden heart of the luminous infrared galaxy IC 860 - I. A molecular inflow feeding opaque, extreme nuclear activity
%A A. S. Evans
%A C. Henkel
%A E. Varenius
%A F. Combes
%A G. C. Privon
%A G. Fuller
%A J. Gallagher
%A J. H. Black
%A J. Mangum
%A K. Alatalo
%A K. Kohno
%A K. Sakamoto
%A N. Falstad
%A P. van der Werf
%A R. Beswick
%A S. Aalto
%A S. Garc赤a-Burillo
%A S. Kˋnig
%A S. Mart赤n
%A S. Muller
%A S. M邦hle
%A S. Viti
%J -
%D 2019
%R 10.1051/0004-6361/201935480
%X High-resolution (0.ˋˋ∪03每0.ˋˋ∪09 (9每26 pc)) ALMA (100每350 GHz (<i>竹<i/>3 to 0.8 mm)) and (0.ˋˋ∪04 (11 pc)) VLA 45 GHz measurements have been used to image continuum and spectral line emission from the inner (100 pc) region of the nearby infrared luminous galaxy IC 860. We detect compact (<i>r<i/>ˋ‵ˋ10 pc), luminous, 3 to 0.8 mm continuum emission in the core of IC 860, with brightness temperatures <i>T<i/><sub>B<sub/>ˋ> ˋ160 K. The 45 GHz continuum is equally compact but significantly fainter in flux. We suggest that the 3 to 0.8 mm continuum emerges from hot dust with radius <i>r<i/>ˋ‵ˋ8 pc and temperature <i>T<i/><sub>d<sub/>ˋ‵ˋ280 K, and that it is opaque at millimetre wavelengths, implying a very large H<sub>2<sub/> column density <i>N<i/>(H<sub>2<sub/>)ˋ10<sup>26<sup/>ˋcm<sup>ˋ2<sup/>. Vibrationally excited lines of HCN <i>糸<i/><sub>2<sub/>ˋ=ˋ1f <i>J<i/>ˋ=ˋ4ˋˋˋ3 and 3每2 (HCN-VIB) are seen in emission and spatially resolved on scales of 40每50 pc. The line-to-continuum ratio drops towards the inner <i>r<i/>ˋ=ˋ4 pc, resulting in a ring-like morphology. This may be due to high opacities and matching HCN-VIB excitation- and continuum temperatures. The HCN-VIB emission reveals a north每south nuclear velocity gradient with projected rotation velocities of <i>糸<i/>ˋ=ˋ100ˋkmˋs<sup>ˋ1<sup/> at <i>r<i/>ˋ=ˋ10 pc. The brightest emission is oriented perpendicular to the velocity gradient, with a peak HCN-VIB 3每2 <i>T<i/><sub>B<sub/> of 115 K (above the continuum). Vibrational ground-state lines of HCN 3每2 and 4每3, HC<sup>15<sup/>N 4每3, HCO<sup>+<sup/> 3每2 and 4每3, and CS 7每6 show complex line absorption and emission features towards the dusty nucleus. Redshifted, reversed P-Cygni profiles are seen for HCN and HCO<sup>+<sup/> consistent with gas inflow with <i>糸<i/><sub>in<sub/> ˋ 50 km s<sup>ˋ1<sup/>. Foreground absorption structures outline the flow, and can be traced from the north-east into the nucleus. In contrast, CS 7每6 has blueshifted line profiles with line wings extending out to ˋ180ˋkmˋs<sup>ˋ1<sup/>. We suggest that a dense and slow outflow is hidden behind a foreground layer of obscuring, inflowing gas. The centre of IC 860 is in a phase of rapid evolution where an inflow is building up a massive nuclear column density of gas and dust that feeds star formation and/or AGN activity. The slow, dense outflow may be signaling the onset of feedback. The inner, <i>r<i/>ˋ=ˋ10 pc, IR luminosity may be powered by an AGN or a compact starburst, which then would likely require a top-heavy initial mass function
%U https://www.aanda.org/articles/aa/full_html/2019/07/aa35480-19/aa35480-19.html