Warm Molecular Gas in the Central Parsecs of the Buried Nucleus of NGC 4418 Traced with the Fundamental CO Ro-vibrational Absorptions

Abstract

We investigated the inner buried nucleus of a nearby luminous infrared galaxy NGC 4418 using high-resolution spectroscopy of fundamental carbon monoxide (CO) ro-vibrational absorptions around $4.67\mu$m for the first time. This method allowed us to examine the physical and kinematical properties in the hot inner region of this nucleus. We detected a series of both very deep (partly saturated) ${}^{12}$CO and moderately deep (optically thin) ${}^{13}$CO absorption lines and inferred a large column density ($N_{H2}=(5\pm 3)\times 10^{23}$ cm${}^{-2}$ in front of the $5\mu$m photosphere) of warm ($T_{\mathrm{ex}}\simeq 170$ K) molecular gas by assuming an isothermal plane-parallel slab illuminated by a compact background MIR-emitting source. We modeled that the warm CO absorber almost covers the central heating source and that it is an inner layer around the $5\mu$m photosphere (at $r=$several pc) of a compact shroud of gas and dust ($d\sim 100$ pc). The width of the absorption lines ($110$ km s${}^{-1}$) and their small deviation from the systemic velocity ($<10$ km s${}^{-1}$) are consistent with a warm and turbulent layer with little bulk motion in the radial direction.

arXiv comment18 pages, 3 figures, 2 tables, accepted for publication in ApJ

References in corpus (49)

• emcee: The MCMC Hammer
• AGN Dusty Tori: I. Handling of Clumpy Media
• The Critical Density and the Effective Excitation Density of Commonly Observed Molecular Dense Gas Tracers
• Diagnostics of irradiated gas in galaxy nuclei. I: A Far-ultraviolet and X-ray dominated region code
• Mid-IR Galaxy Classification Based on Silicate Obscuration and PAH Equivalent Width
• NICMOS Imaging of Infrared-Luminous Galaxies
• High resolution mid-infrared spectroscopy of ultraluminous infrared galaxies
• Herschel/PACS spectroscopy of NGC 4418 and Arp 220: H2O, H2^{18}O, OH, ^{18}OH, O I, HCN and NH3
• Vibrationally Excited HCN in the Luminous Infrared Galaxy NGC 4418
• Deep Mid-Infrared Silicate Absorption as a Diagnostic of Obscuring Geometry Toward Galactic Nuclei
• AKARI IRC infrared 2.5-5 micron spectroscopy of a large sample of luminous infrared galaxies
• The obscured mid-infrared continuum of NGC 4418: a dust- and ice-enshrouded AGN
• The Detection of Crystalline Silicates in Ultra-Luminous Infrared Galaxies
• The Deep Silicate Absorption Feature in IRAS 08572+3915 and Other Infrared Galaxies
• Systematic infrared 2.5-5 micron spectroscopy of nearby ultraluminous infrared galaxies with AKARI
• Submillimeter Interferometry of the Luminous Infrared Galaxy NGC 4418: A Hidden Hot Nucleus with an Inflow and an Outflow
• Infrared Molecular Starburst Fingerprints in Deeply Obscured (U)LIRG Nuclei
• Dust in active galactic nuclei. Mid-infrared T-ReCS/Gemini spectra using the new RedCan pipeline
• Local Luminous Infrared Galaxies. I. Spatially resolved observations with Spitzer/IRS
• The far-infrared emitting region in local galaxies and QSOs: Size and scaling relations
• The opaque nascent starburst in NGC 1377: Spitzer SINGS observations
• High-J CO SLEDs in nearby infrared bright galaxies observed by Herschel-PACS
• Direct measurements of carbon and sulfur isotope ratios in the Milky Way
• Near-infrared and Millimeter Constraints on the Nuclear Energy Source of the Infrared Luminous Galaxy NGC 4418
• 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
• Luminous HC3N line emission in NGC4418 - buried AGN or nascent starburst?
• A high-resolution mm and cm study of the obscured LIRG NGC 4418 - A compact obscured nucleus fed by in-falling gas?
• Detection of strongly processed ice in the central starburst of NGC4945
• The Compact Nucleus of the Deep Silicate Absorption Galaxy NGC 4418
• The Interstellar Medium of IRAS 08572+3915 NW: H3+ and Warm High Velocity CO
• ALMA Observations of Nearby Luminous Infrared Galaxies with Various AGN Energetic Contributions Using Dense Gas Tracers
• High-velocity neon line emission from the ULIRG IRAS F00183-7111: revealing the optically obscured base of a nuclear outflow
• Hidden or missing outflows in highly obscured galaxy nuclei?
• ALMA Multiple-Transition Observations of High Density Molecular Tracers in Ultraluminous Infrared Galaxies
• ALMA Investigation of Vibrationally Excited HCN/HCO+/HNC Emission Lines in the AGN-Hosting Ultraluminous Infrared Galaxy IRAS 20551-4250
• The radio core structure of the luminous infrared galaxy NGC 4418
• The Greenhouse Effect in Buried Galactic Nuclei and the Resonant HCN Vibrational Emission
• The silicate absorption profile in the ISM towards the heavily obscured nucleus of NGC 4418
• Nuclear activity in nearby galaxies: Mid-infrared imaging with the VLT
• Infrared Spectroscopy of CO Ro-vibrational Absorption Lines toward the Obscured AGN IRAS 08572+3915
• Modelling the Spoon IRS diagnostic diagram
• A deep look at the nuclear region of UGC 5101 through high angular resolution mid-IR data with GTC/CanariCam
• The Near-Infrared CO Absorption Band as a Probe to the Innermost Part of an AGN Obscuring Material
• The Nature of Deeply Buried Ultraluminous Infrared Galaxies: A Unified Model for Highly Obscured Dusty Galaxy Emission
• AKARI Infrared Camera Observations of the 3.3 μm PAH feature in Swift/BAT AGNs
• Deeply Buried Nuclei in the Infrared-Luminous Galaxies NGC 4418 and Arp 220: I. ALMA Observations at $\lambda =$1.4-0.4 mm and Continuum Analysis
• Extremely Buried Nucleus of IRAS 17208$-$0014 Observed at Sub-Millimeter and Near-Infrared Wavelengths
• Probing dynamics and thermal properties inside molecular tori with CO rovibrational absorption lines

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• Probing the Infrared/Radio correlation of the full IRAS Revised Bright Galaxy Sample with MeerKAT and the VLA
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