The Luminous X-Ray Halos of Two Compact Elliptical Galaxies

Abstract

There is mounting evidence that compact elliptical galaxies (CEGs) are local analogs of the high-redshift "red nuggets" 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 archival Chandra observations. We find that PGC 032873 has an average gas temperature $k_{B}T=0.67\pm 0.06$ keV within a radius of 15 kpc, and a luminosity $L_{\mathrm{x}}=(1.8\pm 0.2)\times 10^{41}$ erg s${}^{-1}$ within a radius of 100kpc. For Mrk 1216, which is closer and more luminous $[L_{\mathrm{x}}(<100\mathrm{kpc})=(12.1\pm 1.9)\times 10^{41}$ erg s${}^{-1}]$, we performed a spatially resolved spectral analysis in 7 annuli out to a radius of 73 kpc. Using an entropy-based hydrostatic equilibrium (HE) procedure, we obtain a good constraint on the $H$-band stellar mass-to-light ratio, $M_{\mathrm{stars}}/L_H=1.33\pm 0.21$ solar, in good agreement with stellar dynamical (SD) studies, which supports the HE approximation. We obtain a density slope $2.22\pm 0.08$ within $R_e$ consistent with other CEGs and normal local ETGs, while the dark matter (DM) fraction within $R_e$, $f_{\mathrm{DM}}=0.20\pm 0.07$, is similar to local ETGs. We place a constraint on the SMBH mass, $M_{\mathrm{BH}}=(5\pm 4)\times 10^9{M}_{\odot }$, with a 90% upper limit of $M_{\mathrm{BH}}=1.4\times 10^{10}{M}_{\odot }$, consistent with a recent SD measurement. We obtain a halo concentration $(c_{200}=17.5\pm 6.7)$ and mass [$M_{200}=(9.6\pm 3.7)\times 10^{12}{M}_{\odot }$], where $c_{200}$ exceeds the mean $\Lambda$CDM value ($\approx 7$), consistent with a system that formed earlier than the general halo population. We suggest that these galaxies, which reside in group-scale halos, should be classified as fossil groups. (Abridged)

10 pages, 6 figures, Accepted for Publication in The Astrophysical Journal, minor changes

References in corpus (12)

• Scaling Properties of a Complete X-ray Selected Galaxy Group Sample
• Chi-square and Poissonian Data: Biases Even in the High-Count Regime and How to Avoid them
• Radial metal abundance profiles in the intra-cluster medium of cool-core galaxy clusters, groups, and ellipticals
• Small scatter and nearly-isothermal mass profiles to four half-light radii from two-dimensional stellar dynamics of early-type galaxies
• Hunting for Supermassive Black Holes in Nearby Galaxies with the Hobby-Eberly Telescope
• Two new confirmed massive relic galaxies: red nuggets in the present-day Universe
• The structural and dynamical properties of compact elliptical galaxies
• Weighing the Quiescent Central Black Hole in an Elliptical Galaxy with X-ray Emitting Gas
• Hydrostatic Gas Constraints on Supermassive Black Hole Masses: Implications for Hydrostatic Equilibrium and Dynamical Modelling in a Sample of Early-Type Galaxies
• A Black Hole Mass Determination for the Compact Galaxy Mrk 1216
• Digging for red nuggets: discovery of hot halos surrounding massive, compact, relic galaxies
• The Unusually High Halo Concentration of the Fossil Group NGC 6482: Evidence for Weak Adiabatic Contraction

Cited by in corpus (11)

• Hot Atmospheres, Cold Gas, AGN Feedback and the Evolution of Early Type Galaxies: a Topical Perspective
• The Extremely High Dark Matter Halo Concentration of the Relic Compact Elliptical Galaxy Mrk 1216
• Correlations between supermassive black holes, hot atmospheres, and the total masses of early type galaxies
• Digging for red nuggets: discovery of hot halos surrounding massive, compact, relic galaxies
• An ALMA Gas-dynamical Mass Measurement of the Supermassive Black Hole in the Local Compact Galaxy UGC 2698
• Radial X-ray profiles of simulated galaxies: Contributions from hot gas and XRBs
• Black Hole Feeding and Feedback in a Compact Galaxy
• Diversifying halo structures in two-component self-interacting dark matter models via mass segregation
• X-ray properties of massive compact relic galaxies
• Spectral study of X-ray sources in some galaxies recently observed by Chandra
• Chemical Enrichment of Isolated Relic Galaxy Mrk1216