Rossa, Jörn and Laine, Seppo and van der Marel, Roeland P. and Mihos, J. Christopher and Hibbard, John E. and Böker, Torsten and Zabludoff, Ann I. (2007) The Toomre Sequence Revisited with HST NICMOS: Nuclear Brightness Profiles and Colors of Interacting and Merging Galaxies. Astronomical Journal, 134 (6). pp. 2124-2147. ISSN 0004-6256 http://resolver.caltech.edu/CaltechAUTHORS:20091117-102040704
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We discuss the near-infrared (NIR) properties of the nuclei in the 11 merging galaxies of the Toomre sequence, based on high spatial resolution J, H, and K imaging data using NICMOS on board the Hubble Space Telescope (HST). The observations are less affected by dust extinction than our previous HST WFPC2 observations and offer higher spatial resolution than existing ground-based NIR data. Nuclear positions are generally found to be consistent with those reported from data in other wave bands. In NGC 7764A we detect for the first time two nuclei with a separation of about 260 pc, consistent with its placement in the middle of the merging sequence. We see a marginal trend for the nuclei to become bluer with advancing merger stage, which we attribute to a dispersal of dust at late times in the merging process. Our data also indicate a statistically significant trend for the nuclei in the sequence to become more luminous, within an aperture of fixed physical size and after correcting for dust extinction, with advancing merger stage. We derive K-band surface brightness profiles for those nuclei for which the morphology allows a meaningful isophotal analysis, and fit the profiles with a "Nuker" law for comparison with other samples of galaxies observed with HST. The majority of the nuclei have steep profiles that can be characterized as power-law type. In general, the Toomre-sequence galaxies tend to have steeper profiles and higher central luminosity surface densities than E/S0 galaxies. Our findings can be explained if the Toomre-sequence galaxies have newly formed stars that are concentrated toward their centers. We derive V - K color profiles for the nuclei to further address this possibility, but find that the large amounts of dust extinction complicate their interpretation. Overall, our results are consistent with the generic predictions of N-body simulations of spiral galaxy mergers. If left to evolve and fade for several gigayears, it is possible that the properties of the Toomre-sequence nuclei would resemble the properties of the nuclei of normal E/S0 galaxies. Our results therefore support the view that mergers of spiral galaxies can lead to the formation of early-type galaxies.
|Additional Information:||© 2007 The American Astronomical Society. Received 2006 July 14; accepted 2007 August 20. Support for proposal 9402 was provided by NASA through a grant from the Space Telescope Science Institute, which is operated by the Association of Universities for Research in Astronomy, Inc., under NASA contract NAS5-26555. We thank Nick Scoville for kindly providing us with the drizzled NGC 2623 images, and Daisuke Iono for providing us with the unpublished coordinates of the CO measurements of the nuclei of NGC 6621 and NGC 7592.We would also like to thank the anonymous referee for a very constructive and detailed report, which helped to improve the clarity and contents of the paper. R. P. v. d. M. carried out part of this research at the Kavli Institute for Theoretical Physics in Santa Barbara, supported in part by the National Science Foundation under grant PHY 99-07949. A. I. Z. is grateful for the hospitality and support of the Aspen Center for Physics, the Kavli Institute for Theoretical Physics, and the New York University Physics Department and Center for Cosmology and Particle Physics during her sabbatical year. This research has made use of the NASA/IPAC Extragalactic Database, which is operated by the Jet Propulsion Laboratory, California Institute of Technology, under contract with the National Aeronautics and Space Administration. This publication makes use of data products from the Two Micron All Sky Survey, which is a joint project of the University Of Massachusetts and the Infrared Processing and Analysis Center/California Institute of Technology, funded by the National Aeronautics and Space Administration and the National Science Foundation.|
|Subject Keywords:||galaxies : evolution; galaxies : formation; galaxies : interactions; galaxies : nuclei; galaxies : spiral|
|Official Citation:||The Toomre Sequence Revisited with HST NICMOS: Nuclear Brightness Profiles and Colors of Interacting and Merging Galaxies Jörn Rossa, Seppo Laine, Roeland P. van der Marel, J. Christopher Mihos, John E. Hibbard, Torsten Böker, and Ann I. Zabludoff 2007 The Astronomical Journal 134 2124-2147 doi: 10.1086/522782|
|Usage Policy:||No commercial reproduction, distribution, display or performance rights in this work are provided.|
|Deposited By:||Tony Diaz|
|Deposited On:||25 Nov 2009 19:07|
|Last Modified:||26 Dec 2012 11:34|
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