Smith, Beverly J. and Struck, Curtis and Hancock, Mark and Giroux, Mark L. and Appleton, Philip N. and Charmandaris, Vassilis and Reach, William and Hurlock, Sabrina and Hwang, Jeong-Sun (2008) Stochastic "beads on a string" in the accretion tail of Arp 285. Astronomical Journal, 135 (6). pp. 2406-2423. ISSN 0004-6256 http://resolver.caltech.edu/CaltechAUTHORS:20090427-111331515
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We present Spitzer infrared, Galaxy Evolution Explorer UV, and Sloan Digitized Sky Survey and Southeastern Association for Research in Astronomy optical images of the peculiar interacting galaxy pair Arp 285 (NGC 2856/4), and compare with a new numerical model of the interaction. We estimate the ages of clumps of star formation in these galaxies using population synthesis models, carefully considering the uncertainties on these ages. This system contains a striking example of "beads on a string": a series of star-formation complexes ~1 kpc apart. These "beads" are found in a tail-like feature that is perpendicular to the disk of NGC 2856, which implies that it was formed from material accreted from the companion NGC 2854. The extreme blueness of the optical/UV colors and redness of the mid-infrared colors implies very young stellar ages (~4-20 Myr) for these star-forming regions. Spectral decomposition of these "beads" shows excess emission above the modeled stellar continuum in the 3.6 μm and 4.5 μm bands, indicating either contributions from interstellar matter to these fluxes or a second older stellar population. These clumps have –12.0 < M_B < –10.6, thus they are less luminous than most dwarf galaxies. Our model suggests that bridge material falling into the potential of the companion overshoots the companion. The gas then piles up at apogalacticon before falling back onto the companion, and star formation occurs in the pile-up. There was a time delay of ~500 Myr between the point of closest approach between the two galaxies and the initiation of star formation in this feature. A luminous (M_B ~ –13.6) extended (FWHM ~ 1.3 kpc) "bright spot" is visible at the northwestern edge of the NGC 2856 disk, with an intermediate stellar population (400-1500 Myr). Our model suggests that this feature is part of a expanding ripple-like "arc" created by an off-center ring-galaxy-like collision between the two disks.
|Additional Information:||© 2008 The American Astronomical Society. Received 2007 September 5; accepted 2008 February 24; published 2008 May 15. We thank the Spitzer, GALEX, and SDSS teams for making this research possible. This research was supported by NASA Spitzer grant 1263924, NSF grant AST-0097616, NASA LTSA grant NAG5-13079, and NASA GALEX grant GALEXGI04- 0000-0026. V. C. acknowledges partial support from the EU ToK grant 39965. We thank Jayaram Chengalur for providing us with an electronic copy of the Hi data. We also acknowledge Amanda Moffett and Chris Carver for help with system administration. This research has made use of the NASA/IPAC Extragalactic Database (NED) which is operated by the Jet Propulsion Laboratory, California Institute of Technology, under contract with the National Aeronautics and Space Administration.|
|Subject Keywords:||galaxies: individual (Arp 285); galaxies: interactions; galaxies: starburst|
|Usage Policy:||No commercial reproduction, distribution, display or performance rights in this work are provided.|
|Deposited By:||Tony Diaz|
|Deposited On:||09 Jul 2009 23:56|
|Last Modified:||26 Dec 2012 10:58|
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