A SPECTROSCOPIC AND PHOTOMETRIC EXPLORATION OF THE C/M RATIO IN THE DISK OF M31

Journal Article · Tue Sep 01 00:00:00 EDT 2015 · Astrophysical Journal

DOI:https://doi.org/10.1088/0004-637X/810/1/60· OSTI ID:22525501

Hamren, Katherine M.; Rockosi, Constance M.; Guhathakurta, Puragra; Smith, Graeme H.; Toloba, Elisa; Dorman, Claire E. ^[1]; Boyer, Martha L. ^[2]; Dalcanton, Julianne J.; Lewis, Alexia R.; Williams, Benjamin F.; Weisz, Daniel R. ^[3]; Gregersen, Dylan; Seth, Anil C. ^[4]; Girardi, Léo ^[5]

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1. Department of Astronomy and Astrophysics, University of California Santa Cruz, 1156 High Street, Santa Cruz, CA 95064 (United States)
2. Observational Cosmology Lab, Code 665, NASA Goddard Space Flight Center, Greenbelt, MD 20771 (United States)
3. Department of Astronomy, Box 351580, University of Washington, Seattle, WA 98195 (United States)
4. Department of Physics and Astronomy, University of Utah, Salt Lake City, UT 84112 (United States)
5. Osservatorio Astronomico di Padova-INAF, Vicolo dell'Osservatorio 5, I-35122 Padova (Italy)

We explore the ratio (C/M) of carbon-rich to oxygen-rich thermally pulsing asymptotic giant branch (TP-AGB) stars in the disk of M31 using a combination of moderate-resolution optical spectroscopy from the Spectroscopic Landscape of Andromeda’s Stellar Halo survey and six-filter Hubble Space Telescope photometry from the Panchromatic Hubble Andromeda Treasury survey. Carbon stars were identified spectroscopically. Oxygen-rich M-stars were identified using three different photometric definitions designed to mimic, and thus evaluate, selection techniques common in the literature. We calculate the C/M ratio as a function of galactocentric radius, present-day gas-phase oxygen abundance, stellar metallicity, age (via proxy defined as the ratio of TP-AGB stars to red giant branch, stars), and mean star formation rate over the last 400 Myr. We find statistically significant correlations between log(C/M) and all parameters. These trends are consistent across different M-star selection methods, though the fiducial values change. Of particular note is our observed relationship between log(C/M) and stellar metallicity, which is fully consistent with the trend seen across Local Group satellite galaxies. The fact that this trend persists in stellar populations with very different star formation histories indicates that the C/M ratio is governed by stellar properties alone.

• OSTI ID: 22525501
• Journal Information: Astrophysical Journal, Vol. 810, Issue 1; Other Information: Country of input: International Atomic Energy Agency (IAEA); ISSN 0004-637X
• Country of Publication: United States
• Language: English

Related Subjects

79 ASTROPHYSICS
COSMOLOGY AND ASTRONOMY
ASYMPTOTIC SOLUTIONS
CARBON
CARBON STARS
CORRELATIONS
ELEMENT ABUNDANCE
EMISSION SPECTROSCOPY
GALAXIES
GIANT STARS
METALLICITY
OXYGEN
PHOTOMETRY
RESOLUTION
SATELLITES
STAR EVOLUTION
TELESCOPES