skip to main content
OSTI.GOV title logo U.S. Department of Energy
Office of Scientific and Technical Information

Title: WHEELS OF FIRE. IV. STAR FORMATION AND THE NEUTRAL INTERSTELLAR MEDIUM IN THE RING GALAXY AM0644-741

Abstract

We combine data from the Australia Telescope National Facility and Swedish ESO Submillimeter Telescope to investigate the neutral interstellar medium (ISM) in AM0644-741, a large and robustly star-forming ring galaxy. The galaxy's ISM is concentrated in the 42 kpc diameter starburst ring, but appears dominated by atomic gas, with a global molecular fraction (f{sub mol}) of only 0.062 {+-} 0.005. Apart from the starburst peak, the gas ring appears stable against the growth of gravitational instabilities (Q{sub gas} = 3-11). Including the stellar component lowers Q overall, but not enough to make Q < 1 everywhere. High star formation efficiencies (SFEs) follow from the ring's low H{sub 2} content. AM0644-741's star formation law is highly peculiar: H I obeys a Schmidt law while H{sub 2} is uncorrelated with star formation rate density. Photodissociation models yield low volume densities in the ring, especially in the starburst quadrant (n {approx} 2 cm{sup -3}), implying a warm neutral medium dominated ISM. At the same time, the ring's pressure and ambient far-ultraviolet radiation field lead to the expectation of a predominantly molecular ISM. We argue that the ring's high SFE, low f{sub mol} and n, and peculiar star formation law follow from the ISM'smore » {approx}> 100 Myr confinement time in the starburst ring, which amplifies the destructive effects of embedded massive stars and supernovae. As a result, the ring's molecular ISM becomes dominated by small clouds, causing M{sub H{sub 2}} to be significantly underestimated by {sup 12}CO line fluxes: in effect, X{sub CO} >> X{sub Gal} despite the ring's {>=}solar metallicity. The observed H I is primarily a low-density photodissociation product, i.e., a tracer rather than a precursor of massive star formation. Such an 'over-cooked' ISM may be a general characteristic of evolved starburst ring galaxies.« less

Authors:
;  [1];  [2]
  1. Department of Physics, Georgia Southern University, Statesboro, GA 30460-8031 (United States)
  2. Department of Physics and Astronomy, University of New Mexico, Albuquerque, NM 87131 (United States)
Publication Date:
OSTI Identifier:
21587456
Resource Type:
Journal Article
Journal Name:
Astrophysical Journal
Additional Journal Information:
Journal Volume: 739; Journal Issue: 2; Other Information: DOI: 10.1088/0004-637X/739/2/97; Country of input: International Atomic Energy Agency (IAEA); Journal ID: ISSN 0004-637X
Country of Publication:
United States
Language:
English
Subject:
79 ASTROPHYSICS, COSMOLOGY AND ASTRONOMY; DISSOCIATION; FAR ULTRAVIOLET RADIATION; GALAXIES; GRAVITATIONAL INSTABILITY; INTERACTIONS; SUPERNOVAE; BINARY STARS; ELECTROMAGNETIC RADIATION; ERUPTIVE VARIABLE STARS; INSTABILITY; PLASMA INSTABILITY; RADIATIONS; STARS; ULTRAVIOLET RADIATION; VARIABLE STARS

Citation Formats

Higdon, James L., Higdon, Sarah J. U., and Rand, Richard J. WHEELS OF FIRE. IV. STAR FORMATION AND THE NEUTRAL INTERSTELLAR MEDIUM IN THE RING GALAXY AM0644-741. United States: N. p., 2011. Web. doi:10.1088/0004-637X/739/2/97; COUNTRY OF INPUT: INTERNATIONAL ATOMIC ENERGY AGENCY (IAEA).
Higdon, James L., Higdon, Sarah J. U., & Rand, Richard J. WHEELS OF FIRE. IV. STAR FORMATION AND THE NEUTRAL INTERSTELLAR MEDIUM IN THE RING GALAXY AM0644-741. United States. doi:10.1088/0004-637X/739/2/97; COUNTRY OF INPUT: INTERNATIONAL ATOMIC ENERGY AGENCY (IAEA).
Higdon, James L., Higdon, Sarah J. U., and Rand, Richard J. Sat . "WHEELS OF FIRE. IV. STAR FORMATION AND THE NEUTRAL INTERSTELLAR MEDIUM IN THE RING GALAXY AM0644-741". United States. doi:10.1088/0004-637X/739/2/97; COUNTRY OF INPUT: INTERNATIONAL ATOMIC ENERGY AGENCY (IAEA).
@article{osti_21587456,
title = {WHEELS OF FIRE. IV. STAR FORMATION AND THE NEUTRAL INTERSTELLAR MEDIUM IN THE RING GALAXY AM0644-741},
author = {Higdon, James L. and Higdon, Sarah J. U. and Rand, Richard J.},
abstractNote = {We combine data from the Australia Telescope National Facility and Swedish ESO Submillimeter Telescope to investigate the neutral interstellar medium (ISM) in AM0644-741, a large and robustly star-forming ring galaxy. The galaxy's ISM is concentrated in the 42 kpc diameter starburst ring, but appears dominated by atomic gas, with a global molecular fraction (f{sub mol}) of only 0.062 {+-} 0.005. Apart from the starburst peak, the gas ring appears stable against the growth of gravitational instabilities (Q{sub gas} = 3-11). Including the stellar component lowers Q overall, but not enough to make Q < 1 everywhere. High star formation efficiencies (SFEs) follow from the ring's low H{sub 2} content. AM0644-741's star formation law is highly peculiar: H I obeys a Schmidt law while H{sub 2} is uncorrelated with star formation rate density. Photodissociation models yield low volume densities in the ring, especially in the starburst quadrant (n {approx} 2 cm{sup -3}), implying a warm neutral medium dominated ISM. At the same time, the ring's pressure and ambient far-ultraviolet radiation field lead to the expectation of a predominantly molecular ISM. We argue that the ring's high SFE, low f{sub mol} and n, and peculiar star formation law follow from the ISM's {approx}> 100 Myr confinement time in the starburst ring, which amplifies the destructive effects of embedded massive stars and supernovae. As a result, the ring's molecular ISM becomes dominated by small clouds, causing M{sub H{sub 2}} to be significantly underestimated by {sup 12}CO line fluxes: in effect, X{sub CO} >> X{sub Gal} despite the ring's {>=}solar metallicity. The observed H I is primarily a low-density photodissociation product, i.e., a tracer rather than a precursor of massive star formation. Such an 'over-cooked' ISM may be a general characteristic of evolved starburst ring galaxies.},
doi = {10.1088/0004-637X/739/2/97; COUNTRY OF INPUT: INTERNATIONAL ATOMIC ENERGY AGENCY (IAEA)},
journal = {Astrophysical Journal},
issn = {0004-637X},
number = 2,
volume = 739,
place = {United States},
year = {2011},
month = {10}
}