Akos Bogdan, Laurence P. David, Christine Jones, William R. Forman, Ralph P. Kraft
The presence of warm X-ray emitting gas is nearly ubiquitous in massive early-type galaxies. However, much less is known about the X-ray gas content and physical status of the warm gas in low-mass ellipticals. In the present paper we study the X-ray gas content of four low-mass elliptical galaxies using archival Chandra X-ray observations. The sample galaxies, NGC821, NGC3379, NGC4278, and NGC4697, have approximately identical K-band luminosities, and hence stellar masses, yet their X-ray appearance is strikingly different. We conclude that the unresolved emission in NGC821 and NGC3379 is built up from the multitude of faint compact objects, such as coronally active binaries (ABs) and cataclysmic variables (CVs). Despite the non-detection of warm X-ray gas, these galaxies may host low density, hence low luminosity X-ray gas components, which undergo an SN Ia driven outflow. We detect warm X-ray gas with temperature of kT ~ 0.6 keV in the central ~35 arcsec (~2.8 kpc) region of NGC4278. We demonstrate that the X-ray gas exhibits a bipolar morphology in the northeast-southwest direction, indicating that the X-ray gas may be outflowing from the galaxy. The mass and energy budget of the outflow can be maintained by evolved stars and Type Ia Supernovae (SNe Ia), respectively. The X-ray gas in NGC4697 has an average temperature of kT ~ 0.3-0.4 keV, and has a significantly broader distribution than the stellar light. From the parameters of the warm X-ray gas, we conclude that the gas in NGC4697 is most likely in hydrostatic equilibrium, although a subsonic outflow may be present.
View original:
http://arxiv.org/abs/1206.2434
No comments:
Post a Comment