GALAXIES M32 AND NGC 5102 CONFIRM A NEAR-INFRARED SPECTROSCOPIC CHRONOMETER

Journal Article · Thu Jan 20 04:00:00 EST 2011 · Astrophysical Journal Letters

DOI:https://doi.org/10.1088/2041-8205/727/1/L15· OSTI ID:21560562

Miner, Jesse; Cecil, Gerald ^[1]; Rose, James A ^[2]

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1. Infrared Telescope Facility, which is operated by the University of Hawaii under Cooperative Agreement no. NNX-08AE38A with the National Aeronautics and Space Administration, Science Mission Directorate, Planetary Astronomy Program. (United States)
2. Department of Physics and Astronomy, University of North Carolina, Chapel Hill, NC 27516 (United States)

We present near-infrared (NIR) IRTF/SpeX spectra of the intermediate-age galaxy M32 and the post-starburst galaxy NGC 5102. We show that features from thermally pulsing asymptotic giant branch (TP-AGB) and main-sequence turnoff (MSTO) stars yield similar ages to those derived from optical spectra. The TP-AGB can dominate the NIR flux of a coeval stellar population between {approx}0.1 and {approx}2 Gyr, and the strong features of (especially C-rich) TP-AGB stars are useful chronometers in integrated light studies. Likewise, the Paschen series in MSTO stars is strongly dependent on age and is an indicator of a young stellar component in integrated spectra. We define four NIR spectroscopic indices to measure the strength of absorption features from both C-rich TP-AGB stars and hydrogen features in main-sequence stars, in a preliminary effort to construct a robust chronometer that probes the contributions from stars in different evolutionary phases. By comparing the values of the indices measured in M32 and NGC 5102 to those in the Maraston stellar population synthesis models for various ages and metallicities, we show that model predictions for the ages of the nuclei of M32 and NGC 5102 agree with previous results obtained from integrated optical spectroscopy and color-magnitude diagram analysis of the giant branches. The indices discriminate between an intermediate-age population of {approx}3-4 Gyr, a younger population of {approx}<1 Gyr, and can also detect the signatures of very young {approx}<100 Myr populations.

• OSTI ID: 21560562
• Journal Information: Astrophysical Journal Letters, Journal Name: Astrophysical Journal Letters Journal Issue: 1 Vol. 727; ISSN 2041-8205
• Country of Publication: United States
• Language: English

Related Subjects

79 ASTRONOMY AND ASTROPHYSICS
ELECTROMAGNETIC RADIATION
EVOLUTION
GALAXIES
INFRARED RADIATION
INFRARED SPECTRA
MAIN SEQUENCE STARS
NEAR INFRARED RADIATION
RADIATIONS
SPECTRA
SPECTROSCOPY
STARS