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

Abstract

We observed with ALMA three deeply buried nuclei in two galaxies, NGC 4418 and Arp 220, at $\sim$0.2${}^{\prime \prime }$ resolution over a total bandwidth of 67 GHz in $f_{\mathrm{rest}}$ = 215 - 697 GHz. Here we (1) introduce our program, (2) describe our data reduction method for wide-band, high-resolution imaging spectroscopy, (3) analyze in visibilities the compact nuclei with line forests, (4) develop a continuum-based estimation method of dust opacity and gas column density in heavily obscured nuclei, which uses the BGN (buried galactic nuclei) model and is sensitive to $\log (N_{{\mathrm{H}}_2}/{\mathrm{cm}}^{-2})\sim$ 25 - 26 at $\lambda \sim 1$ mm, and (5) present the continuum data and diagnosis of our targets. The three continuum nuclei have major-axis FWHM of $\sim$0.1${}^{\prime \prime }$-0.3${}^{\prime \prime }$ (20-140 pc) aligned to their rotating nuclear disks of molecular gas. However, each nucleus is described better with two or three concentric components than with a single Gaussian. The innermost cores have sizes of 0.05${}^{\prime \prime }$-0.10${}^{\prime \prime }$ (8-40 pc), peak brightness temperatures of ~100-500 K at 350 GHz, and more fractional flux at lower frequencies. The intermediate components correspond to the nuclear disks. They have axial ratios of $\approx$0.5 and hence inclinations $\stackrel{>}{\sim }60$ deg. The outermost elements include the bipolar outflow from Arp 220W. We estimate 1 mm dust opacity of ${\tau }_{\mathrm{d},1mm}\approx 2.2$, $1.2$, and $\stackrel{<}{\sim }0.4$ respectively for NGC 4418, Arp 220W, and Arp 220E. The first two correspond to $\log (N_{\mathrm{H}}/{\mathrm{cm}}^{-2})\sim 26$ for conventional dust-opacity laws, and hence the nuclei are highly Compton thick.

arXiv comment59 pages, 18 figures, 15 tables, accepted for publication in ApJ

References in corpus (56)

• The chemical composition of the Sun
• A Cosmological Framework for the Co-Evolution of Quasars, Supermassive Black Holes, and Elliptical Galaxies: I. Galaxy Mergers & Quasar Activity
• Planck 2013 results. XI. All-sky model of thermal dust emission
• The SCUBA Local Universe Galaxy Survey I: First Measurements of the Submillimetre Luminosity and Dust Mass Functions
• Obscured Active Galactic Nuclei
• Self-similarity and scaling behavior of IR emission from radiatively heated dust: I. Theory
• Mid-IR Galaxy Classification Based on Silicate Obscuration and PAH Equivalent Width
• GOALS: The Great Observatories All-Sky LIRG Survey
• The SCUBA Local Universe Galaxy Survey II. 450 micron data - evidence for cold dust in bright IRAS Galaxies
• Compton-thick Accretion in the local Universe
• The Evolution of ISM Mass Probed by Dust Emission -- ALMA Observations at z = 0.3 to 2
• Ultra-Luminous Infrared Mergers: Elliptical Galaxies in Formation?
• The Interstellar dust properties of nearby galaxies
• Cold Molecular Outflows in the Local Universe
• Planck Early Results: Thermal dust in Nearby Molecular Clouds
• A cosmic abundance standard: chemical homogeneity of the solar neighbourhood and the ISM dust-phase composition
• Counterrotating Nuclear Disks in Arp 220
• Mid-Infrared Properties of Nearby Luminous Infrared Galaxies I: Spitzer IRS Spectra for the GOALS Sample
• UVMULTIFIT: A versatile tool for fitting astronomical radio interferometric data
• ALMA observations of molecular tori around massive black holes
• Herschel/PACS spectroscopy of NGC 4418 and Arp 220: H2O, H2^{18}O, OH, ^{18}OH, O I, HCN and NH3
• Elusive Active Galactic Nuclei
• 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
• The radio spectra of the compact sources in Arp 220: A mixed population of supernovae and supernova remnants
• ALMA Resolves the Nuclear Disks of Arp 220
• P-Cygni Profiles of Molecular Lines toward Arp 220 Nuclei
• Starburst in the Ultra-luminous Galaxy Arp 220 - Constraints from Observations of Radio Recombination Lines and Continuum
• The Submillimeter Array 1.3 mm line survey of Arp 220
• Submillimeter Interferometry of the Luminous Infrared Galaxy NGC 4418: A Hidden Hot Nucleus with an Inflow and an Outflow
• High-Resolution Radio Continuum Measurements of the Nuclear Disks of Arp 220
• High Spatial Resolution Imaging of Arp 220 from 3 - 25 microns
• Chandra Observations of Extended X-ray Emission in Arp 220
• Extreme dust disks in Arp 220 as revealed by ALMA
• CON-quest: Searching for the most obscured galaxy nuclei
• Exploring the molecular chemistry and excitation in obscured luminous infrared galaxies: An ALMA mm-wave spectral scan of NGC 4418
• Subarcsecond international LOFAR radio images of Arp 220 at 150 MHz: A kpc-scale star forming disk surrounding nuclei with shocked outflows
• The unbearable opaqueness of Arp 220
• A high-resolution mm and cm study of the obscured LIRG NGC 4418 - A compact obscured nucleus fed by in-falling gas?
• The hidden heart of the luminous infrared galaxy IC 860 I. A molecular inflow feeding opaque, extreme nuclear activity
• Nuclear gas dynamics in Arp 220 - sub-kiloparsec scale atomic hydrogen disks
• A hard X-ray constraint on the presence of an AGN in the ultra-luminous infrared galaxy Arp220
• Molecular gas and dust properties of galaxies from the Great Observatories All-sky LIRG Survey
• Studying Faint Ultra Hard X-ray Emission from AGN in GOALS LIRGs with Swift BAT
• ALMA Astrochemical Observations of the Infrared-Luminous Merger NGC 3256
• Resolved Structure of Arp 220 Nuclei at λ~3 mm
• The population of SNe/SNRs in the starburst galaxy Arp 220. A self-consistent analysis of 20 years of VLBI monitoring
• ALMA Spatially-resolved Dense Molecular Gas Survey of Nearby Ultraluminous Infrared Galaxies
• Arp220: extinction and merger-induced star formation
• 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
• Arp 220: New Observational Insights into the Structure and Kinematics of the Nuclear Molecular Disks and Surrounding Gas
• Dust masses, compositions, and luminosities in the nuclear disks and the diffuse circumnuclear medium of Arp220
• An atomic hydrogen bridge fueling NGC 4418 with gas from VV 655
• VV 655 and NGC 4418: Implications of an interaction for the evolution of a LIRG

Cited by in corpus (8)

• GOALS-JWST: Pulling Back the Curtain on the AGN and Star Formation in VV 114
• No evidence of AGN features in the nuclei of Arp 220 from JWST/NIRSpec IFS
• Warm Molecular Gas in the Central Parsecs of the Buried Nucleus of NGC 4418 Traced with the Fundamental CO Ro-vibrational Absorptions
• The Rich JWST Spectrum of the Western Nucleus of Arp 220: Shocked Hot Core Chemistry Dominates the Inner Disk
• Investigating starburst-driven neutrino emission from galaxies in the Great Observatories All-Sky LIRG Survey
• Systematic Study of the Inner Structure of Molecular Tori in Nearby U/LIRGs using Velocity Decomposition of CO Rovibrational Absorption Lines
• The Binding Energies of Atoms on Amorphous Silicate Dust: A Computational Study
• Implication of a galaxy-scale negative feedback by one of the most powerful multi-phase outflows in a hyper-luminous infrared galaxy at the intermediate redshift