The hidden heart of the luminous infrared galaxy IC 860 I. A molecular inflow feeding opaque, extreme nuclear activity

Abstract

High-resolution (0."03 - 0."09) (9 - 26 pc)) ALMA (100 - 350 GHz (3 - 0.8 mm)) and VLA 45 GHz measurements have been used to image continuum and spectral line emission from the inner region of the nearby infrared luminous galaxy IC 860. We detect compact (r=8-10 pc), luminous, mm continuum emission in the core of IC 860, with brightness temperatures $T_{\mathrm{B}}>$ 280 K. The 45 GHz continuum is equally compact, but fainter in flux. We suggest that the 3 to 0.8 mm continuum is opaque at mm-wavelengths, implying a very large H${}_2$ column density $N$(H${}_2$) of 1e26 cm-2, and that it emerges from hot dust with temperature $T_{\mathrm{d}}\sim 280$ K. Vibrationally excited lines of HCN ${\nu }_2$=1f J=4-3 and 3-2 (HCN-VIB) are seen in emission and resolved on scales of 40-50 pc. The HCN-VIB emission reveals a north-south nuclear velocity gradient with projected rotation velocities of v=100 kms${}^{-1}$ at r=10 pc. The brightest HCN-VIB emission is oriented perpendicular to the velocity gradient. Ground state lines of HCN 3-2, 4-3, HC${}^{15}$N 4-3, HCO${}^{+}$ 3-2, 4-3 and CS 7-6, show complex line absorption and emission features. HCN and HCO${}^{+}$ have red-shifted, reversed P-Cygni profiles consistent with gas inflows of $\sim$50 kms${}^{-1}$. The absorption features can be traced from the north-east into the nucleus. In contrast, CS 7-6 shows blue-shifted line wings extending to -180 kms${}^{-1}$. We suggest that a dense and slow outflow is hidden behind a foreground layer of inflowing gas. It appears that the centre of IC 860 is in a phase of rapid evolution where an inflow is building up the nuclear column density of gas. A slow, dense outflow may be signalling the onset of feedback. The inner, r=10 pc, IR luminosity can be powered by an accreting black hole and/or a compact starburst with a top-heavy initial mass function.

13 pages, 9 figures, Accepted for publication in Astronomy and Astrophysics; Language edited

References in corpus (16)

• Mid-IR Galaxy Classification Based on Silicate Obscuration and PAH Equivalent Width
• The close environments of accreting massive black holes are shaped by radiative feedback
• Near-Infrared and Star-forming properties of Local Luminous Infrared Galaxies
• Luminous Infrared Galaxies with the Submillimeter Array: I. Survey Overview and the Central Gas to Dust Ratio
• The evolution of CNO isotopes: a new window on cosmic star-formation history and the stellar IMF in the age of ALMA
• SMA Imaging of CO(3-2) Line and 860 micron Continuum of Arp 220 : Tracing the Spatial Distribution of Luminosity
• Vibrationally Excited HCN in the Luminous Infrared Galaxy NGC 4418
• High resolution observations of HCN and HCO+ J=3-2 in the disk and outflow of Mrk231 -Detection of vibrationally excited HCN in the warped nucleus
• Decoding the stellar fossils of the dusty Milky Way progenitors
• The Arecibo Arp 220 Spectral Census I: Discovery of the Pre-Biotic Molecule Methanimine and New Cm-wavelength Transitions of Other Molecules
• The Discovery of Gas-Rich, Dusty Starbursts in Luminous Reddened Quasars at $z\sim 2.5$ with ALMA
• Subarcsecond international LOFAR radio images of Arp 220 at 150 MHz: A kpc-scale star forming disk surrounding nuclei with shocked outflows
• Resolved Structure of Arp 220 Nuclei at λ~3 mm
• Hidden or missing outflows in highly obscured galaxy nuclei?
• A hidden molecular outflow in the LIRG Zw 049.057
• An extremely low gas-to-dust ratio in the dust-lane lenticular galaxy NGC 5485

Cited by in corpus (35)

• Cool Outflows in Galaxies and their Implications
• The Galaxy Activity, Torus and Outflow Survey (GATOS) I. ALMA images of dusty molecular tori in Seyfert galaxies
• SUPER-II: Spatially resolved ionized gas kinematics and scaling relations in z~2 AGN host galaxies
• A hard X-ray view of Luminous and Ultra-luminous Infrared Galaxies in GOALS: I - AGN obscuration along the merger sequence
• A Hard X-ray Test of HCN Enhancements as a Tracer of Embedded Black Hole Growth
• Star formation and nuclear activity in luminous infrared galaxies: An infrared through radio review
• CON-quest: Searching for the most obscured galaxy nuclei
• Comprehensive Broadband X-ray and Multiwavelength Study of Active Galactic Nuclei in Local 57 Ultra/luminous Infrared Galaxies Observed with NuSTAR and/or Swift/BAT
• ALMA Observations of Multiple-CO and C Lines Toward the Active Galactic Nucleus of NGC 7469: X-Ray-dominated Region Caught in the Act
• Outflows from Super Star Clusters in the Central Starburst of NGC253
• Deciphering the imprint of AGN feedback in Seyfert galaxies: Nuclear-scale molecular gas deficits
• ALMA resolves the remarkable molecular jet and rotating wind in the extremely radio-quiet galaxy NGC 1377
• The Obscured Nucleus and Shocked Environment of VV 114E Revealed by JWST/MIRI Spectroscopy
• Enhanced UV radiation and dense clumps in Mrk231's molecular outflow
• GOALS-JWST: Pulling Back the Curtain on the AGN and Star Formation in VV 114
• GOALS-JWST: Gas Dynamics and Excitation in NGC7469 revealed by NIRSpec
• Ray-tracing simulations and spectral models of X-ray radiation in dusty media
• A Multiwavelength view of IC 860: What Is in Action inside Quenching Galaxies
• A Detailed Look at the Most Obscured Galactic Nuclei in the Mid-Infrared
• The Role of AGN in Luminous Infrared Galaxies from the Multiwavelength Perspective
• AGN-driven galactic outflows: comparing models to observations
• SUNRISE: The rich molecular inventory of high-redshift dusty galaxies revealed by broadband spectral line surveys
• Arp 220: New Observational Insights into the Structure and Kinematics of the Nuclear Molecular Disks and Surrounding Gas
• Deeply Buried Nuclei in the Infrared-Luminous Galaxies NGC 4418 and Arp 220: I. ALMA Observations at $\lambda =$1.4-0.4 mm and Continuum Analysis
• Discovery of Methanimine Megamasers Toward Compact Obscured Galaxy Nuclei
• The Opaque Heart of the Galaxy IC 860: Analogous Protostellar, Kinematics, Morphology, and Chemistry
• CON-quest II. Spatially and spectrally resolved HCN/HCO+ line ratios in local luminous and ultraluminous infrared galaxies
• Extremely Buried Nucleus of IRAS 17208$-$0014 Observed at Sub-Millimeter and Near-Infrared Wavelengths
• What powers galactic outflows: nuclear starbursts or AGN?
• APEX and NOEMA observations of H${}_2$S in nearby luminous galaxies and the ULIRG Mrk~231 -- Is there a relation between dense gas properties and molecular outflows?
• Investigating starburst-driven neutrino emission from galaxies in the Great Observatories All-Sky LIRG Survey
• Forming Stars in a Dual AGN Host: Molecular and Ionized Gas in the Nearby, Luminous Infrared Merger, Mrk 266
• An Imaging and Spectroscopic Exploration of the Dusty Compact Obscured Nucleus Galaxy Zw~049.057
• A technique to select the most obscured galaxy nuclei
• Molecular gas dynamics around nuclei of galaxies