Astrophys. J., 854, 143-143 (2018/February-3)
The luminous X-ray halos of two compact elliptical galaxies.
BUOTE D.A. and BARTH A.J.
Abstract (from CDS):
There is mounting evidence that compact elliptical galaxies (CEGs) are local analogs of the high-redshift "red nuggets" that are thought to represent progenitors of today's early-type galaxies (ETGs). We report the discovery of extended X-ray emission from a hot interstellar/intragroup medium in two CEGs, Mrk 1216 and PGC 032873, using shallow Chandra observations. We find that PGC 032873 has an average gas temperature of kBT = 0.67 ± 0.06 keV within a radius of 15 kpc and a luminosity Lx = (1.8 ± 0.2) x 1041 erg s–1 within a radius of 100 kpc. For Mrk 1216, which is closer and more luminous (Lx(<100 kpc) = (12.1 ± 1.9) x 1041 erg s–1), we used an entropy-based hydrostatic equilibrium (HE) procedure and obtained a good constraint on the H-band stellar mass-to-light ratio, Mstars/LH = 1.33 ± 0.21 solar, that is in good agreement with stellar dynamical (SD) studies, which supports the HE approximation. We obtain a density slope of 2.22 ± 0.08 within Re that is consistent with other CEGs and normal local ETGs, while the dark matter fraction within Re, fDM = 0.20 ± 0.07 is similar to local ETGs. We constrain the supermasssive black hole mass, MBH = (5 ± 4) x 109 M☉, with MBH > 1.4 x 1010 M☉ (90% confidence), which is consistent with a recent SD measurement. We obtain a halo concentration (c200 = 17.5 ± 6.7) and mass (M200 = (9.6 ± 3.7) x 1012 M☉), where c200 exceeds the mean ΛCDM value (≃7), which is consistent with a system that formed earlier than the general halo population. We suggest that these galaxies should be classified as fossil groups.
© 2018. The American Astronomical Society. All rights reserved.
galaxies: elliptical and lenticular, cD - galaxies: formation - galaxies: groups: general - galaxies: individual: (Mrk 1216, PGC 032873) - X-rays: galaxies
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