Ammonia as a Temperature Tracer in the Ultraluminous Galaxy Merger Arp220

Abstract

(abridged) We present ATCA and GBT observations of ammonia (NH3) toward the ultraluminous infrared galaxy (ULIRG) merger Arp220. We detect the NH3 (1,1), (2,2), (3,3), (4,4), (5,5), and (6,6) inversion lines in absorption against the unresolved, (62+/-9)mJy continuum source at 1.2cm. The peak apparent optical depths of the NH3 lines range from ~0.05 to 0.18. The absorption depth of the NH3 (1,1) line is significantly shallower than expected based on the depths of the other transitions, which might be caused by contamination from emission by a hypothetical, cold (<~20K) gas layer with an estimated column density of <~ 2x10^14 cm^-2. The widths of the NH3 absorption lines are ~120-430 km s^-1, in agreement with those of other molecular tracers. We cannot confirm the extremely large linewidths of up to ~1800km s^-1 previously reported. We determine a rotational temperature of (124+/-19)K, corresponding to a kinetic temperature of T_kin=(186+/-55)K. NH3 column densities depend on the excitation temperature. For an excitation temperature of 50K, we estimate (8.4+/-0.5)x10^16cm^-2. The relation scales linearly for possible higher excitation temperatures. In the context of a model with a molecular ring that connects the two nuclei in Arp220, we estimate the H2 gas density to be ~f_V^-0.5 x (1-4)x10^3, (f_V: volume filling factor). In addition to NH3, our ATCA data show an absorption feature adjacent in frequency to the NH3 (3,3) line. If we interpret the line to be from the OH ^2Pi_3/2 J=9/2 F=4-4 transition, it would have a linewidth, systemic velocity, and apparent optical depth similar to what we detect in the NH3 lines. If this association with OH is correct, it marks the first detection of the highly excited (~511K above ground state) ^2Pi_3/2 J=9/2 F=4-4 OH line in an extragalactic object.

31 pages, 6 figures, accepted for publication in the Astrophysical Journal

References in corpus (9)

• Molecular gas in extreme star-forming environments: the starbursts Arp220 and NGC6240 as case studies
• VLBI Images of 49 Radio Supernovae in Arp 220
• SMA Imaging of CO(3-2) Line and 860 micron Continuum of Arp 220 : Tracing the Spatial Distribution of Luminosity
• Is HCN a True Tracer of Dense Molecular Gas in LIRGs and ULIRGs?
• Black hole in the West Nucleus of Arp 220
• Host dynamics and origin of Palomar-Green QSOs
• P-Cygni Profiles of Molecular Lines toward Arp 220 Nuclei
• The Arecibo Arp 220 Spectral Census I: Discovery of the Pre-Biotic Molecule Methanimine and New Cm-wavelength Transitions of Other Molecules
• High-resolution HNC 3-2 SMA observations of Arp220

Cited by in corpus (20)

• Herschel/PACS spectroscopy of NGC 4418 and Arp 220: H2O, H2^{18}O, OH, ^{18}OH, O I, HCN and NH3
• Excited OH+, H2O+, and H3O+ in NGC 4418 and Arp 220
• The Survey of Water and Ammonia in the Galactic Center (SWAG): Molecular Cloud Evolution in the Central Molecular Zone
• Detection of Widespread Hot Ammonia in the Galactic Center
• ATCA Survey of Ammonia in the Galactic Center: The Temperatures of Dense Gas Clumps between SgrA* and SgrB2
• Ammonia Thermometry of Star Forming Galaxies
• Gas Giants in Hot Water: Inhibiting Giant Planet Formation and Planet Habitability in Dense Star Clusters Through Cosmic Time
• Survey of Water and Ammonia in Nearby galaxies (SWAN): Resolved Ammonia Thermometry, Water and Methanol Masers in the Nuclear Starburst of NGC 253
• Kinetic temperature of massive star forming molecular clumps measured with formaldehyde. II. The Large Magellanic Cloud
• Survey of Water and Ammonia in Nearby galaxies (SWAN): Resolved Ammonia Thermometry, and Water and Methanol Masers in IC 342, NGC 6946 and NGC 2146
• Comparing Models for IMF Variation Across Cosmological Time in Milky Way-like Galaxies
• The galaxy-wide stellar initial mass function in the presence of cluster-to-cluster IMF variations
• Hot Ammonia in the Center of the Seyfert 2 galaxy NGC 3079
• High Resolution Observations of Molecular Lines in Arp 220: Kinematics, Morphology, and Limits on the Applicability of the Ammonia Thermometer
• Probing the initial conditions of high-mass star formation -- IV. Gas dynamics and NH${}_2$D chemistry in high-mass precluster and protocluster clumps
• Probing the initial conditions of high-mass star formation. III. Fragmentation and triggered star formation
• Water Masers in the Andromeda Galaxy: I. A Survey for Water Masers, Ammonia, and Hydrogen Recombination Lines
• The Rich JWST Spectrum of the Western Nucleus of Arp 220: Shocked Hot Core Chemistry Dominates the Inner Disk
• Ammonia in the interstellar medium of a starbursting disc at z=2.6
• A Spectral Analysis of the Centimeter Regime of Nearby Galaxies: RRLs, Excited OH, and NH${}_3$