Azimuthal and Kinematic Segregation of Neutral and Molecular Gas in Arp 118: The Yin-Yang Galaxy NGC 1144

Abstract

We present new high-resolution HI observations of the disk of the collisional infrared luminous (L${}_{\mathrm{IR}}=2.2\times 10^{11}$ L$_{\sun}$) galaxy NGC 1144, which reveal an apparent large-scale azimuthal and kinematic segregation of neutral hydrogen relative to the molecular gas distribution. Even among violently collisional galaxies, the CO/HI asymmetry in NGC 1144 is unusual, both in the inner regions, and in the outer disk. We suggest that we are observing Arp 118 at a special moment, shortly after a high-speed collision between NGC 1144 and its elliptical companion NGC 1143. HI emission with an average molecular fraction f${}_{mol}$ $<$ 0.5 is observed on one side (NW) of the rotating disk of NGC 1144, while the other side (SE) is dominated by dense molecular complexes in which f${}_{mol}$ is almost unity. The interface region between the warm-- and cool--cloud dominated regions, lies on a deep spiral-like dust-lane which we identify as a shock-wave responsible for the relative shift in the dominance of HI and H${}_2$ gas. A strong shock being fed by diffuse HI clouds with unusually large ($>$ 400 km s${}^{-1}$) rotational velocities can explain: 1) the CO/HI asymmetries, 2) a large velocity jump (185 km s${}^{-1}$) across the arm as measured by HI absorption against a radio bright continuum source which straddles the arm, and 3) the asymmetric distribution of star formation and off-nuclear molecular gas resulting from likely streaming motions associated with the strong-shock. The new results provide for the first time a coherent picture of Arp 118's many peculiarities, and underlines the potentially complex changes in the gas-phase that can accompany large gravitational perturbations of gas-rich galaxies.

arXiv comment20 pages, two tables, 9 Figures

References in corpus (20)

• Gasdynamics and Starbursts in Major Mergers
• Rotating Nuclear Rings and Extreme Starbursts in Ultraluminous Galaxies
• H I, H II, and R-Band Observations of a Galactic Merger Sequence
• The BIMA Survey of Nearby Galaxies (BIMA SONG): I. The Radial Distribution of CO Emission in Spiral Galaxies
• Abundant Molecular Gas in Tidal Dwarf Galaxies: On-going Galaxy Formation
• Molecular Gas Depletion and Starbursts in Luminous Infrared Galaxy Mergers
• Molecular Gas and Nuclear Activity in Ultraluminous Infrared Galaxies with Double Nuclei
• Cold gas and star formation in a merging galaxy sequence
• Radio Supernovae as Distance Indicators
• Large-Scale Asymmetry of Rotation Curves in Lopsided Spiral Galaxies
• Nature of widely separated ultraluminous infrared galaxies
• Arp 302: Non-starburst Luminous Infrared Galaxies
• Mid-IR and CO Observations of the IR/X-Ray Luminous Seyfert I Galaxy NGC985: The Making or Breaking of a ULIRG?
• Plasma and Warm Dust in the Collisional Ring Galaxy VIIZw466 from VLA and ISO Observations
• Molecular Gas in the Spectacular Ring Galaxy NGC 1144
• Spiral Molecular Front in Galaxies: Quick Transition from Atomic to Molecular Hydrogen in Spiral Arms
• Gas Distribution and Starburst Activity in the Widely Separated Interacting Galaxies NGC 6670
• Progressive Star Bursts and High Velocities in the Infrared Luminous, Colliding Galaxy Arp 118
• Distorted HI Gas in the Widely Separated LIRG Arp 256
• The HI and Ionized Gas Disk of the Seyfert Galaxy NGC 1144 = Arp 118: A Violently Interacting Galaxy with Peculiar Kinematics

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