| タイトル | The X-Ray Luminosity Functions of Field Low-Mass X-Ray Binaries in Early-Type Galaxies: Evidence for a Stellar Age Dependence |
| 本文（外部サイト） | http://hdl.handle.net/2060/20150023315 |
| 著者（英） | Fragos, T.; Sivakoff, G. R.; Bauer, F. E.; Yukita, M.; Brandt, W. N.; Tzanavaris, P.; Alexander, D. M.; Ptak, A.; Lehmer, B. D.; Berkeley, M.; Basu-Zych, A.; Hornschemeier, A. E.; Kalogera, V.; Zezas, A. |
| 著者所属（英） | NASA Goddard Space Flight Center |
| 発行日 | 2014-05-12 |
| 言語 | eng |
| 内容記述 | We present direct constraints on how the formation of low-mass X-ray binary (LMXB) populations in galactic fields depends on stellar age. In this pilot study, we utilize Chandra and Hubble Space Telescope (HST) data to detect and characterize the X-ray point source populations of three nearby early-type galaxies: NGC 3115, 3379, and 3384. The luminosity-weighted stellar ages of our sample span approximately equal to 3-10 Gyr. X-ray binary population synthesis models predict that the field LMXBs associated with younger stellar populations should be more numerous and luminous per unit stellar mass than older populations due to the evolution of LMXB donor star masses. Crucially, the combination of deep Chandra and HST observations allows us to test directly this prediction by identifying and removing counterparts to X-ray point sources that are unrelated to the field LMXB populations, including LMXBs that are formed dynamically in globular clusters, Galactic stars, and background AGN/galaxies. We find that the "young" early-type galaxy NGC 3384 (approximately equals 2-5 Gyr) has an excess of luminous field LMXBs (L(sub x) approximately greater than (5-10) 10(exp 37) erg s(exp -1)) per unit K-band luminosity (L(sub K); a proxy for stellar mass) than the "old" early-type galaxies NGC 3115 and 3379 (approximately equals 8-10 Gyr), which results in a factor of 2-3 excess of L(sub X)/L(sub K) for NGC 3384. This result is consistent with the X-ray binary population synthesis model predictions; however, our small galaxy sample size does not allow us to draw definitive conclusions on the evolution field LMXBs in general. We discuss how future surveys of larger galaxy samples that combine deep Chandra and HST data could provide a powerful new benchmark for calibrating X-ray binary population synthesis models. |
| NASA分類 | Astrophysics |
| レポートNO | GSFC-E-DAA-TN24309 |
| 権利 | Copyright, Distribution as joint owner in the copyright |
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