UGC8802: A Massive Disk Galaxy in Formation - Astrophysics > Cosmology and Nongalactic AstrophysicsReport as inadecuate

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Abstract: We report new observations of the galaxy UGC8802 obtained through GASS, theGALEX Arecibo SDSS Survey, which show this galaxy to be in a remarkableevolutionary state. UGC8802 GASS35981 is a disk galaxy with stellar massM*=2x10^10 Msolar which appears to contain an additional 2.1x10^10 Msolar of HIgas. New millimeter observations with the IRAM 30m telescope indicate amolecular gas mass only a tenth this large. Using deep long-slit spectroscopy,we examine the spatially resolved star formation rate and metallicity profilesof GASS35981 for clues to its history. We find that the star formation surfacedensity in this galaxy is low Sigma SFR=0.003 Msolar-yr-kpc^2 and that thestar formation is spread remarkably evenly across the galaxy. The low moleculargas masses measured in our three IRAM pointings are largely consistent with thetotal star formation measured within the same apertures. Our MMT long-slitspectrum reveals a sharp drop in metallicity in the outer disk of GASS35981.The ratio of current star formation rate to existing stellar mass surfacedensity in the outer disk is extremely high, implying that all the stars musthave formed within the past ~1Gyr. At current star formation rates, however,GASS35981 will not consume its HI reservoir for another 5-7 Gyr. Despite itsexceptionally large gas fraction for a galaxy this massive, GASS35981 has aregular rotation curve and exhibits no sign of a recent interaction or merger.We speculate that GASS35981 may have acquired its gas directly from theinter-galactic medium, and that it and other similar galaxies identified in theGASS survey may provide rare local glimpses of gas accretion processes thatwere more common during the prime epoch of disk galaxy formation at z~1.

Author: Sean M. Moran JHU, Guinevere Kauffmann, Timothy M. Heckman, Javier Gracia-Carpio, Amelie Saintonge, Barbara Catinella, Jing Wang,


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