The Luminous X-Ray Halos of Two Compact Elliptical Galaxies

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 k(B)T = 0.67 +/- 0.06 keV within a radius of 15 kpc and a luminosity L-x = (1.8 +/- 0.2) x 10(41) erg s(-1) within a radius of 100 kpc. For Mrk 1216, which is closer and more luminous (L-x(<100 kpc) = (12.1 +/- 1.9) x 10(41) 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, M-stars/L-H = 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 R-e that is consistent with other CEGs and normal local ETGs, while the dark matter fraction within R-e, f(DM) = 0.20 +/- 0.07 is similar to local ETGs. We constrain the supermasssive black hole mass, M-BH = (5 +/- 4) x 10(9) M-circle dot, with M-BH > 1.4 x 10(10)M(circle dot) (90% confidence), which is consistent with a recent SD measurement. We obtain a halo concentration (c(200) = 17.5 +/- 6.7) and mass (M-200 = (9.6 +/- 3.7) x 10(12)M(circle dot)), where c(200) exceeds the mean Lambda CDM value (approximate to 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.