Journal
ASTROPHYSICAL JOURNAL
Volume 793, Issue 1, Pages -Publisher
IOP PUBLISHING LTD
DOI: 10.1088/0004-637X/793/1/40
Keywords
galaxies: evolution; galaxies: fundamental parameters; galaxies: ISM; galaxies: star formation
Categories
Funding
- NSF [AST-0607007, AST-1107390]
- Brinson Foundation
- National Science Council (NSC) of Taiwan [NSC 100-2112-M-001-006-MY3]
- Ministry of Science and Technology (MOST) of Taiwan [MOST 103-2112-M-001-032-MY3]
- GALEX Guest Investigator program under NASA [NNX07AJ12G, NNX07AJ41G, NNX08AL67G, NNX09AF79G, NNX10AI03G]
- Alfred P. Sloan Foundation
- National Science Foundation
- U.S. Department of Energy
- NASA
- Japanese Monbukagakusho
- Max Planck Society
- Higher Education Funding Council for England
- U.S. Department of Energy Office of Science
- NASA [NNX10AI03G, 99072, NNX08AL67G, 133130, NNX09AF79G, 118656] Funding Source: Federal RePORTER
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We present first results of the study of a set of exceptional H I sources identified in the 40% ALFALFA extragalactic H I survey catalog alpha.40 as both being H I massive (M-H I > 10(10) M-circle dot) and having high gas fractions for their stellar masses: the HIghMass galaxy sample. We analyze UV- and optical-broadband and H alpha images to understand the nature of their relatively underluminous disks in optical and to test whether their high gas fractions can be tracked to higher dark matter halo spin parameters or late gas accretion. Estimates of their star formation rates (SFRs) based on spectral energy distribution fitting agree within uncertainties with the Ha luminosity inferred current massive SFRs. The H II region luminosity functions, parameterized as dN/d log L alpha L-alpha, have standard slopes at the luminous end (alpha similar to -1). The global SFRs demonstrate that the HIghMass galaxies exhibit active ongoing star formation (SF) with moderate SF efficiency but, relative to normal spirals, a lower integrated SFR in the past. Because the SF activity in these systems is spread throughout their extended disks, they have overall lower SFR surface densities and lower surface brightness in the optical bands. Relative to normal disk galaxies, the majority of HIghMass galaxies have higher H alpha equivalent widths and are bluer in their outer disks, implying an inside-out disk growth scenario. Downbending double exponential disks are more frequent than upbending disks among the gas-rich galaxies, suggesting that SF thresholds exist in the downbending disks, probably as a result of concentrated gas distribution.
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