Dalcanton, Julianne J. and Williams, Benjamin F. and Melbourne, Jason L. and Girardi, Léo and Dolphin, Andy and Rosenfield, Philip A. and Boyer, Martha L. and De Jong, Roelof S. and Gilbert, Karoline M. and Marigo, Paola and Olsen, Knut and Seth, Anil C. and Skillman, Evan (2012) Resolved Near-infrared Stellar Populations in Nearby Galaxies. Astrophysical Journal Supplement Series, 198 (1). p. 6. ISSN 0067-0049 http://resolver.caltech.edu/CaltechAUTHORS:20120130-152228592
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We present near-infrared (NIR) color-magnitude diagrams (CMDs) for the resolved stellar populations within 26 fields of 23 nearby galaxies (≲ 4 Mpc), based on images in the F110W and F160W filters taken with the Wide-Field Camera 3 (WFC3) on the Hubble Space Telescope (HST). The CMDs are measured in regions spanning a wide range of star formation histories, including both old dormant and young star-forming populations. We match key NIR CMD features with their counterparts in more familiar optical CMDs, and identify the red core helium-burning (RHeB) sequence as a significant contributor to the NIR flux in stellar populations younger than a few 100 Myr old. The strength of this feature suggests that the NIR mass-to-light ratio can vary significantly on short timescales in star-forming systems. The NIR luminosity of star-forming galaxies is therefore not necessarily proportional to the stellar mass. We note that these individual RHeB stars may also be misidentified as old stellar clusters in images of nearby galaxies. For older stellar populations, we discuss the CMD location of asymptotic giant branch (AGB) stars in the HST filter set and explore the separation of AGB subpopulations using a combination of optical and NIR colors. We empirically calibrate the magnitude of the NIR tip of the red giant branch in F160W as a function of color, allowing future observations in this widely adopted filter set to be used for distance measurements. We also analyze the properties of the NIR red giant branch (RGB) as a function of metallicity, showing a clear trend between NIR RGB color and metallicity. However, based on the current study, it appears unlikely that the slope of the NIR RGB can be used as an effective metallicity indicator in extragalactic systems with comparable data. Finally, we highlight issues with scattered light in the WFC3, which becomes significant for exposures taken close to a bright Earth limb.
|Additional Information:||© 2012 American Astronomical Society. Received 2011 May 13; accepted 2011 September 28; published 2011 December 22. The authors are very happy to acknowledge helpful discussions with Ben Weiner about scattered light in WFC3/IR. Aaron Dotter is warmly thanked for supplying theoretical RGB sequences, as is Jason Kalirai for providing information helpful for WFC3/IR calibration and processing. As always, we thank Alison Vick for her support in scheduling and executing these observations. The anonymous referee is thanked for providing useful, detailed comments on this very long paper. J. J. D. thanks the Max Planck Institute für Astronomie for their hospitality while writing part of this paper. L.G. and P.M. acknowledge support from contract ASI-INAF I/009/10/0. This work was supported by the Space Telescope Science Institute through SNAP-11719, and used additional data products produced through GO-10915 and AR-10945.|
|Subject Keywords:||galaxies: abundances; galaxies: distances and redshifts; galaxies: dwarf; galaxies: irregular; galaxies: stellar content; infrared: stars; stars: AGB and post-AGB; stars: carbon|
|Official Citation:||Resolved Near-infrared Stellar Populations in Nearby Galaxies Julianne J. Dalcanton et al. 2012 ApJS 198 6|
|Usage Policy:||No commercial reproduction, distribution, display or performance rights in this work are provided.|
|Deposited By:||Jason Perez|
|Deposited On:||31 Jan 2012 19:23|
|Last Modified:||26 Dec 2012 14:45|
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