Astronomy and Astrophysics – Astronomy
Scientific paper
Jan 2010
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2010aas...21541106f&link_type=abstract
American Astronomical Society, AAS Meeting #215, #411.06; Bulletin of the American Astronomical Society, Vol. 42, p.240
Astronomy and Astrophysics
Astronomy
Scientific paper
In order to determine whether composite starburst-AGN galaxies demonstrate any radio properties distinct from starbursts and AGNs, we studied 156 infrared objects for which spectroscopic and VLBI or LBA radio data was available. We found that 19 of 28 (68%) optically classified AGN had a compact radio core, 16 of 55 (29%) optically classified starburst had a compact radio core, and only 8 of 52 (15%) optically classified composites had a compact radio core. Thus, there appears to be a depletion of compact radio cores among composites, an unexpected result considering that in previous classification schemes, composites were often classified as LINERs. We calculate that there is <1% chance that such an uneven distribution of compact radio cores would randomly occur if composites were AGNs, and that there is a 7% chance that this distribution would occur if composites were starbursts. The latter is a small but significant percentage, and it is probably a lower bound, considering that some of the optically classified starbursts with compact radio cores may actually be obscured AGN. In addition, we find that the compact radio core luminosity of composites tends to be in between that of starbursts and AGNs, supporting the hypothesis that composites may possess a mixture of starburst and AGN phenomena. Thus, these results, though not enough to decisively confirm the existence of composites as a distinct class, certainly lend support to such a conclusion, and suggest that composite galaxies may be an interesting area of future research. This research was undertaken at the Institute for Astronomy at the University of Hawaii as part of a Research Experience for Undergraduates (REU) program funded by the National Science Foundation.
Fornasini Francesca
Kewley Lisa J.
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