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Title:
Cold, warm, and hot gas in the late-stage merger NGC 7252
Authors:
Hibbard, J. E.; Guhathakurta, Puragra; van Gorkom, J. H.; Schweizer, Francois
Affiliation:
AA(Columbia Univ., New York, NY, US), AB(Columbia Univ., New York, NY, US), AC(Columbia Univ., New York, NY, US), AD(Columbia Univ., New York, NY, US)
Publication:
The Astronomical Journal, vol. 107, no. 1, p. 67-89 (AJ Homepage)
Publication Date:
01/1994
Category:
Astrophysics
Origin:
STI
NASA/STI Keywords:
GALACTIC ROTATION, GALACTIC STRUCTURE, H I REGIONS, HYDROGEN, INTERSTELLAR GAS, NEUTRAL GASES, STAR FORMATION, ASTRONOMICAL PHOTOMETRY, MOLECULAR GASES, MONATOMIC GASES, RADIO ASTRONOMY, STELLAR MASS, X RAY ASTRONOMY, X RAYS
DOI:
10.1086/116835
Bibliographic Code:
1994AJ....107...67H

Abstract

We present the first observations of the neutral hydrogen distribution and x-ray emission in the prototypical merger remnant NGC 7252, the 'Atoms-for-Peace' galaxy. These data are supplemented by accurate B and R surface photometry, reaching a limit of muB = 26.5 mag/sq arcsec, and images taken through a narrow-band H alpha filter. We find all of the 2 x 109/sq h solar mass of atomic gas to be restricted to the outer, tidal regions of this system (Hzero = 100 h km/s/Mpc). By contrast, the molecular gas traced by the (12)CO(1 approaches zero) map of Wang et al. (1992) is confined to an inner rotating disk of radius 7 seconds and has an H alpha counterpart. The gap between the atomic and molecular gas distributions is filled in by diffuse H alpha emission and perhaps by x-ray emission. The velocity field of the atomic gas in the tidal tails indicates that they are swinging through space in the same sense as the rotation of the inner gas disk. The H I at the apparent base of the northwestern tail seems to be falling back toward the main body of the galaxy, yet there is no H I associated with this main stellar body: This suggests ongoing efficient conversion of the atomic gas into other phases in this region. The H alpha velocity anomalies previously found in the remnant body may be produced in part by the combination of tail-related, noncircular motions and the inner gas-disk rotation. Both tidal tails have bluer B-R colors than the main body of the remnant, with the bluest regions coinciding with peaks in the gas column density. Each tail contains one giant H II region near the end of its optical light distribution. These H II regions are associated with large concentrations of gas and stars that approach the sizes and gas contents of dwarf galaxies. The H I extends beyond the end of the optical tails and reaches projected distances of 62/h kpc east and 120/h kpc northwest from the center. We discuss the possible relevance of these data to : (1) the transformation of merged spirals into ellipticls; (2) the generation of ripples by returning tidal material; and (3) the formation of bound stellar systems from tidally torn material.

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