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Date and Time of the Query: 2019-08-23 T22:19:43 PDT
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For refcode 2018ApJ...854..143B:
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Copyright by American Astronomical Society. Reproduced by permission
2018ApJ...854..143B The Luminous X-Ray Halos of Two Compact Elliptical Galaxies Buote, David A.; Barth, Aaron J. Abstract. 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_&sun;_, with M_BH_ > 1.4 x 10^10^ M_&sun;_ (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_&sun;_), where c_200_ exceeds the mean LambdaCDM 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. Key words: galaxies: elliptical and lenticular, cD, galaxies: formation, galaxies: groups: general, galaxies: individual: Mrk 1216, PGC 032873, X-rays: galaxies
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