SALT/RSS Longslit Spectroscopy of the NGC 1140 Starburst

Type Conference Paper
Names Eric B. Burgh, J. S. Gallagher, K. H. Nordsieck, J. W. Percival, M. P. Smith, D. O'Donoghue, D. A. Buckley, N. S. Loaring
Proceedings Title Bulletin of the American Astronomical Society
Conference Name American Astronomical Society, AAS Meeting #208, #14.03
Volume 38
Pages 93
Date June 1, 2006
Library Catalog NASA ADS
Abstract We present a long-slit spectrum of the amorphous starbursting dwarf galaxy NGC 1140 taken by the Robert Stobie Spectrograph of the Southern African Large Telescope during its commissioning phase in November 2005. A 1.2 arcsecond wide longslit oriented along the major axis in conjunction with a volume phase holographic grating were used to produce a 800 Angstrom wide spectrum, centered on H-alpha, with a resolving power of 5500. Twelve minutes of data were obtained. Emission features from H-alpha, [NII], [SII] and HeI were observed. The peak of the emission features is observed to be 2 arcseconds north of the stellar continuum, consistent with HST imaging of the galaxy, and a bright knot of gas with a velocity offset of 100 km/s is detected about 18 arcseconds south of the continuum peak. The emission lines are well-resolved with FWHM 80-100 km/s in the inner galaxy, typical of intensely star-forming regions, while FWHM 100-140 km/s are seen in the outer galaxy, suggesting a possible galactic wind. The complex velocity field is consistent with the merger model for NGC 1140. The intensity ratio of the [SII] doublet, 6717/6731 is 1.3, indicating a low electron density, and thus modest thermal pressure despite the galaxy's starburst status. The H-alpha/[SII] ratio, which is an indicator of the presence of shocks,varies along the slit with a maximum of 8 at the peak of the gaseous emission and dropping to nearly 2 at the edges of the galaxy, with a value of 3 for the offset knot of gas. Thus shocks could play a role in the outer galaxy, while the knot is more likely a star forming region. We interpret our results in the context of a starburst induced by the merger of two low mass galaxies, as previously discussed by Hunter et al. (1994, ApJS, 91, 79).
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