X-ray emission from the stellar population in M 32

Abstract

Using Chandra observations, we study the X-ray emission of the stellar population in the compact dwarf elliptical galaxy M 32. The proximity of M 32 allows one to resolve all bright point sources with luminosities higher than 8 × 10 33 erg s −1 in the 0.5-7 keV band. The remaining (unresolved) emission closely follows the galaxy's optical light and is characterized by an emissivity per unit stellar mass of ∼4.3 × 10 27 erg s −1 M −1 in the 2-10 keV energy band. The spectrum of the unresolved emission above a few keV smoothly joins the X-ray spectrum of the Milky Way's ridge measured with RXTE and INTEGRAL. These results strongly suggest that weak discrete X-ray sources (accreting white dwarfs and active binary stars) provide the bulk of the "diffuse" emission of this gas-poor galaxy. Within the uncertainties, the average X-ray properties of the M 32 stars are consistent with those of the old stellar population in the Milky Way. The inferred cumulative soft X-ray (0.5-2 keV) emissivity is however smaller than is measured in the immediate Solar vicinity in our Galaxy. This difference is probably linked to the contribution of young (age 1 Gyr) stars, which are abundant in the Solar neighborhood but practically absent in M 32. Combining Chandra, RXTE and INTEGRAL data, we obtain a broad-band (0.5-60 keV) X-ray spectrum of the old stellar population in galaxies.

The Massive Survey. Iv. The X-Ray Halos of the Most Massive Early-Type Galaxies in the Nearby Universe

“…However, given the relatively high stellar mass (high K-band luminosity) of the MASSIVE galaxies, it should not be surprising given that the expected X-ray luminosity for the AB/CV population is over an order of magnitude lower than the gas components measured here based on the typical L L K X ratio for the AB/CV population located in Local Group galaxies (e.g., Revnivtsev et al 2007). For those sources with multiple observations, the spectra were not combined into one single spectrum, but instead the spectra were modeled simultaneously.…”

Discovery of Hot Gas in Outflow in NGC 3379

“…More recently, Revnivtsev et al (2008) have suggested a different interpretation for the unresolved emission: using the full data set as in the present work, they derive a radial profile of the 0.5Y2.0 keV emission, cleaned of detected sources, which they compare with the K-band profile. Based on this comparison they conclude that all of the unresolved emission observed in NGC 3379 can be attributed to the emission of stellar sources, with no evidence of a truly diffuse ISM.…”

“…In this paper we present our analysis of the diffuse /unresolved X-ray emission component of this galaxy. This analysis leads us to conclude that in addition to the unresolved emission of faint LMXBs and other stellar sources ( Revnivtsev et al 2008), a hot ISM is likely to be present in the central 800 pc of NGC 3379.…”

Accretion and nuclear activity in Virgo early-type galaxies

“…Revnivtsev et al 2007). We exploit conversely the result obtained by Revnivtsev et al (2008): they show that the old stars contribution to the X-ray emission of early-type galaxies (per unit stellar luminosity in the K band) displays a small scatter (less than a factor of 2) around the value they measured for NGC 3379,…”