Chandra and XMM-Newton detection of large-scale diffuse X-ray emission from the Sombrero galaxy

Abstract

We present an X‐ray study of the massive edge‐on Sa galaxy, Sombrero (M 104; NGC 4594), based on XMM–Newton and Chandra observations. A list of 62 XMM–Newton and 175 Chandra discrete X‐ray sources is provided, the majority of which are associated with the galaxy. Spectral analysis is carried out for relatively bright individual sources and for an accumulated source spectrum. At energies ≳2 keV, the source‐subtracted X‐ray emission is distributed similarly as the stellar K‐band light and is primarily due to the residual emission from discrete sources. At lower energies, however, a substantial fraction of the source‐subtracted emission arises from diffuse hot gas extending to ∼20 kpc from the galactic centre. The galactic disc shows little X‐ray emission and instead shadows part of the X‐ray radiation from the bulge. The observed diffuse X‐ray emission from the galaxy shows a steep spectrum that can be characterized by an optically thin thermal plasma with temperatures of ∼0.6–0.7 keV, varying little with radius. The diffuse emission has a total luminosity of ∼3 × 1039 erg s−1 in the 0.2–2 keV energy range. This luminosity is significantly smaller than the prediction by current numerical simulations for galaxies as massive as Sombrero. However, such simulations do not include the effect of quiescent stellar feedback (e.g. ejecta from evolving stars and Type Ia supernovae) against the accretion from intergalactic medium. We argue that the stellar feedback likely plays an essential role in regulating the physical properties of hot gas. Indeed, the observed diffuse X‐ray luminosity of Sombrero accounts for at most a few per cent of the expected mechanical energy input from Type Ia supernovae. The inferred gas mass and metal content are also substantially less than those expected from stellar ejecta. We speculate that a galactic bulge wind, powered primarily by Type Ia supernovae, has removed much of the ‘missing’ energy and metal‐enriched gas from the region revealed by the X‐ray observations.

H I in Local Group Dwarf Galaxies and Stripping by the Galactic Halo

“…The solid line is the theoretical density profile for gas whose initial distribution traces the central cusp in the NFW halo (referred to as the low entropy model), while the dotted line represents the density profile which results from an initial gas distribution with a central core of high entropy (Kaufmann et al 2007(Kaufmann et al , 2008. The high entropy model is expected for haloes which have experienced pre-heating feedback early in their histories, and implies a more extended distribution for the hot halo gas, as well as an extended cloud population (Rasmussen et al 2006;Li et al 2007). The remaining density model plotted on Figure 5 is from Sommer-Larsen (2006) and is from high resolution cosmological SPH simulations of a Milky-Way like galaxy in a ΛCDM cosmology.…”

A Deep X-Ray View of the Hot Halo in the Edge-on Spiral Galaxy NGC 891

“…Strickland et al (2004) included two non-starburst edge-on galaxies in their Chandra sample aside from NGC 891 (NGC 6503 and NGC 4244), but both are substantially less massive than NGC 891 and significant X-ray emission was detected in neither. Finally, Li et al (2007) detected diffuse X-ray emission in M104 with a bolometric X-ray luminosity of a few × 10 39 erg s −1 , but M104 is also at least several times more massive than NGC 891 and Li et al (2007) argue that the halo is X-ray underluminous while Bajaja et al (1984) find a relatively small amount of H i in the galaxy.…”

X-raying galaxies: A Chandra legacy

“…Complementary observations from XMM-Newton and Suzaku give consistent results and provide improved spectral information on the hot gas (e.g., refs. 35,36,40,42,43). The morphology of the x-ray emission as well as its correlation with the star formation rate clearly shows that the extraplanar hot gas is primarily heated by the stellar feedback.…”

“…This supersonic wind model depends primarily on two feedback parameters: the integrated energy and mass input rates. However, the model in general fails miserably: It predicts a too low luminosity (by a factor of ∼10 2 ), a too high temperature (a factor of a few), and a too steep radial intensity profile to be consistent with Chandra observations of low L X ∕L B galactic spheroids, in particular those in M31 and M104 (37,43). Only few very low-mass and gas-poor spheroids, hence very faint in x-ray emission, still seem to be consistent with the 1D wind model (e.g., ref.…”