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Azimuthal and Kinematic Segregation of Neutral and Molecular Gas in Arp 118: The Yin-Yang Galaxy NGC 1144 | | P. N. Appleton
; V. Charmandaris
; Yu Gao
; T. Jarrett
; M. A. Bransford
; | | Date: |
27 Nov 2002 | | Journal: | Astrophys.J. 586 (2003) 112-122 | | Subject: | astro-ph | | Affiliation: | SSC-Caltech), V. Charmandaris (Cornell), Yu Gao (IPAC-Caltech and U. of Massachusetts), T. Jarrett (IPAC-Caltech) and M. A. Bransford (IBM, Rochester | | Abstract: | We present new high-resolution HI observations of the disk of the collisional infrared luminous (L$_{
m IR}=2.2 imes10^{11}$ 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. | | Source: | arXiv, astro-ph/0211585 | | Services: | Forum | Review | PDF | Favorites | |
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