eCite Digital Repository

The ACS nearby galaxy survey treasury. II. Young stars and their relation to Hα and UV Emission timescales in the M81 Outer Disk


Gogarten, SM and Dalcanton, JJ and Williams, BF and Seth, AC and Dolphin, A and Weisz, D and Skillman, E and Holtzman, J and Cole, AA and Girardi, L and de Jong, RS and Karachentsev, ID and Olsen, K and Rosema, K, The ACS nearby galaxy survey treasury. II. Young stars and their relation to Hα and UV Emission timescales in the M81 Outer Disk, The Astrophysical Journal, 691, (1) pp. 115-130. ISSN 0004-637X (2009) [Refereed Article]

Restricted - Request a copy

Copyright Statement

Copyright 2009 The American Astronomical Society

Official URL:

DOI: doi:10.1088/0004-637X/691/1/115


We have obtained resolved stellar photometry from Hubble Space Telescope Advanced Camera for Surveys observations of a field in the outer disk of M81 as part of ANGST. Motivated by the recent discovery of extended UV disks around many nearby spiral galaxies, we use the observed stellar population to derive the recent star formation histories of five ~ 0.5 kpc-sized regions within this field. These regions were selected on the basis of their UV luminosity from GALEX and include two HII regions, two regions that are UV-bright but Hα-faint, and one "control" region faint in both UV and Hα. We estimate our effective star formation rate detection limit at ~2 x 104 M yr1, which is lower than that of GALEX for regions of this size. As expected, the HII regions contain massive main-sequence stars (in the mass range 18-27 M, based on our best extinction estimates), while similar massive main-sequence stars are lacking in the UV-bright/Hα-faint regions. The observations are consistent with stellar ages ≲ 10 Myr in the H II regions, and≳ 16 Myr in the UV-bright/Hα-faint regions. All regions but the control have formed ~ 104 M of stars over the past ~ 65 Myr. Thus, our results, for at least one small area in the outer disk of M81, are consistent with an age difference being sufficient to explain the observed discrepancy between star forming regions detected in Hα and those detected exclusively in UV. However, our data cannot conclusively rule out other explanations, such as a strongly truncated initial mass function.

Item Details

Item Type:Refereed Article
Keywords:galaxies: evolution; galaxies: individual (M81); galaxies: spiral; galaxies: stellar content; H II regions
Research Division:Physical Sciences
Research Group:Astronomical sciences
Research Field:Cosmology and extragalactic astronomy
Objective Division:Expanding Knowledge
Objective Group:Expanding knowledge
Objective Field:Expanding knowledge in the physical sciences
UTAS Author:Cole, AA (Professor Andrew Cole)
ID Code:56318
Year Published:2009
Web of Science® Times Cited:49
Deposited By:Physics
Deposited On:2009-04-21
Last Modified:2014-12-01

Repository Staff Only: item control page