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HST ACS/HRC imaging of the intergalactic HII regions in NGC 1533

Published online by Cambridge University Press:  01 August 2006

J. K. Werk ,
M. E. Putman ,
G. R. Meurer ,
E. V. Ryan-Weber  and
M. S. Oey
J. K. Werk
Affiliation:
Department of Astronomy, University of Michigan, Ann Arbor, MI, USA; jwerk@umich.edu
M. E. Putman
Affiliation:
Department of Astronomy, University of Michigan, Ann Arbor, MI, USA; jwerk@umich.edu
G. R. Meurer
Affiliation:
Department of Astronomy and Physics, Johns Hopkins University, Baltimore, MD, USA
E. V. Ryan-Weber
Affiliation:
Institute of Astronomy, University of Cambridge, Cambridge, CB3 OHK, UK
M. S. Oey
Affiliation:
Department of Astronomy, University of Michigan, Ann Arbor, MI, USA; jwerk@umich.edu
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Abstract

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Intergalactic HII regions, far from the confines of a galactic disk, represent a mode of star formation in low-density gas outside of galaxies. The figure below (left) shows an R-band continuum image of NGC 1533 from the SINGG Hα survey (Meurer et al. 2006) overlaid with HI contours and the location of three intergalactic HII regions discovered by Ryan-Weber et al. (2004). The HI contours are 1.6, 2.0, 2.4, 2.8, 3.2 and 4.0 ×1020 cm−2 and have a resolution of ~1′. ACS/HRC images of the intergalactic HII regions (right) are composites of UV, V, and I bands. The half-light radii of the clusters associated with regions 1, 2, and 5 are 24.7, 21.7, and 17.0 pc, respectively, at the distance to NGC 1533 (21 Mpc; Tonry et al. 2001). Assuming a Salpeter IMF with Mup = 100, Hα/UV ratios indicate a small number of ionizing O stars relative to the total number of UV-emitting O and B stars. These young (4-6 Myr), intergalactic stellar populations lend valuable insight to our understanding of the methods by which star formation is triggered and may even represent the first episodes of star formation in emerging galaxies.

Type
Contributed Papers
Information
Proceedings of the International Astronomical Union , Volume 2 , Symposium S237: Triggered Star Formation in a Turbulent ISM , August 2006 , pp. 493
Copyright
Copyright © International Astronomical Union 2007

References

Meurer, et al. 2006, ApJS 165, 307CrossRefGoogle Scholar
Ryan-Weber, et al. 2004, AJ 127, 1431CrossRefGoogle Scholar
Tonry, et al. 2001, ApJ 421, 681CrossRefGoogle Scholar