Hinge Clumps in Interacting Galaxies: Extra-Nuclear Starbursts
Abstract
Hinge clumps are luminous knots of star formation found at the base of tidal features in some interacting galaxies. We use archival Hubble Space Telescope UV/optical/IR images and Chandra X-ray maps along with GALEX UV, Spitzer IR, and ground-based optical/near-IR images to investigate the star forming properties of hinge clumps in a small sample of nearby interacting galaxies. The most extreme of these hinge clumps have star formation rates of 1- 9 solar masses per year, more than that of many normal spiral galaxies. In the HST images, we found remarkably large 70 pc) and luminous sources at the centers of these hinge clumps. If these are individual star clusters they would lie near the top of the `super star cluster' luminosity function of star clusters; alternatively, they may be tightly packed groups of clusters blended together in the HST images. These sources are sometimes embedded in a linear ridge of fainter star clusters, consistent with star formation along a narrow caustic. Comparison to population synthesis modeling indicates that hinge clumps contain a range of stellar ages, consistent with expectations based on models of galaxy interactions, which suggest that star formation may be prolonged in these regions. In the Chandra images, we found strong X-ray emission from several of these hinge clumps. In most cases, this emission is well-resolved with Chandra and has a thermal X-ray spectrum, thus it is likely due to hot gas associated with the star formation. Two of the hinge clumps have point-like X-ray emission much brighter than expected for hot gas; these sources are likely `ultra-luminous X-ray sources' (ULXs) due to accretion disks around black holes. The most extreme of these point sources, in Arp 240, has a hard X-ray spectrum and an absorbed X-ray luminosity greater than 10^41 erg/s, above the luminosity expected by a single high mass X-ray binary. thus it may be either a collection of HMXBs or an intermediate-mass black hole.
- Publication:
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American Astronomical Society Meeting Abstracts #223
- Pub Date:
- January 2014
- Bibcode:
- 2014AAS...22325216S