Документ взят из кэша поисковой машины. Адрес оригинального документа : http://www.stsci.edu/institute/conference/mergers/images/hcg31.pdf Дата изменения: Wed Oct 4 18:56:32 2006 Дата индексирования: Sun Dec 23 05:52:30 2007 Кодировка: Поисковые слова: clouds

Modes of Star Formation in an Early Universe Laborator y: A First Look at Hickson Compact Group 31 1
Jane Charlton (Penn State), Rupali Chandar (OCIW, JHU), Jayanne English (U Manitoba), Sarah Gallagher (UCLA), Kelsey Johnson (U Virginia), Pat Durrell (YSU), Caryl Gronwall (Penn State), Niel Brandt (Penn state), Debra Elmegreen (Vassar), Michael Eracleous (Penn State), John Hibbard (NRAO), Paul Hickson (UBC), Ann Hornschemeier (NASA Goddard), Sally Hunsberger (Penn State), Karen Knierman (U Arizona), Aparna Maybhate (STScI), John Mulchaey (OCIW), Claudia Mendes Oliveira (U Sao Paulo), Chris Palma (Penn State), Brad Whitmore (STScI), Ann Zabludoff (U Arizona), Stephanie Zonak (U Maryland) We present the first results of our Cycle 15 program to obtain BVI ACS imaging of 12 of the nearest Hickson compact galaxy groups. We are assembling a multiwavelength dataset for these groups, including Spitzer, Chandra, GALEX, Swift/UVOT, VLT, and groundbased imaging and spectroscopy. For selected regions housing the most recent star formation, we will also obtain WFPC2 Uband and ACS Ha images. In the ensemble of 12 groups we expect to study more than 1000 young star clusters for ming inside and outside of galaxies, and more than 4000 old globular clusters in >40 giant galaxies, over 20 tidal features, ~15 AGNs, and widespread intragroup gas. The different modes of star formation that occur amid repeated and ongoing gravitational encounters in these groups must resemble those that occur in the high redshift universe. HCG 31 is an excellent example of multiple simultaneous gravitational encounters. The entire group is embedded in an HI envelope. A merger of galaxies A and C is well underway, while galaxies E and F are tidal dwarf galaxies forming in debris, likely created by a recent encounter with galaxy G.

Figure 3 (above) shows preliminary BV vs. VI colorcolor diagrams, in the Vega system, of point sources. These illustrate that most regions in our ACS image show a wide range of ages, indicating ongoing star formation in the group. The evolutionary track shown begins at 1Myr, but does not take nebular emission into account, which would bring it toward the lower left (dotted line on Galaxy C panel) and into accord with many of the youngest sources in galaxies A, C, and G. Figure 4 (right) shows an expanded view of tidal dwarf galaxy F, which based on kinematics may sur vive the present encounter. Previously, no stellar population older than ~4Myr was detected in this galaxy, but our deeper ACS images do reveal some sources consistent with being old. The red circles in the figure show these older sources, selected to have BV > 0.1 and VI > 0.5.

Figure 1 Three color ACS image of HCG31, made by combining B (F435W), V (F606W), Figure 2 Three color Spitzer image using and I (F814W) images, obtained in August 3.6mm (blue), 4.5mm (green), and 8.0mm 2006. (red). Red implies PAH emission/hot dust.