Soft X-ray emission from the inner disk of M33

Abstract

We present a study, based on archival XMM-Newton observations, of the extended X-ray emission associated with the inner disk of M33. After the exclusion of point sources with L_X > 2 x 10^{35} erg/s (0.3-6 keV), we investigate the morphology and spectrum of the residual X-ray emission. This residual emission has a soft X-ray spectrum which can be fitted with a two-temperature thermal model, with kT = 0.2 keV and 0.6 keV. The soft X-ray surface brightness distribution shows a strong correlation with FUV emission, indicative of a close connection between recent star-formation activity and the production of soft X-rays. Within 3.5 kpc of the nucleus of M33, the soft X-ray and FUV surface brightness distributions exhibit similar radial profiles. This implies that the ratio of the soft X-ray luminosity (0.3-2.0 keV) to the star formation rate (SFR) per unit disk area remains fairly constant within this inner disk region. We derive a value for this ratio of 1-1.5 x 10^{39} (erg/s)/(M_sun/yr), consistent with previous studies. In the same region, the ratio of soft X-ray luminosity to stellar mass (derived from K-band photometry) is 4 x 10^{28} erg/s/M_sun, a factor of 5-10 higher than is typical of dwarf elliptical galaxies, suggesting that 10-20% of the unresolved emission seen in M33 may originate in its old stellar population. The remainder of the soft X-ray emission is equally split between two spatial components, one which closely traces the spiral arms of the galaxy and the other more smoothly distributed across the inner disk of M33. The former must represent a highly clumped low-filling factor component linked to sites of recent or ongoing star formation, whereas the distribution of the latter gives few clues as to its exact origin.

13 pages, 4 figures, 5 tables. Accepted for publication in MNRAS

References in corpus (19)

• The GALEX Ultraviolet Atlas of Nearby Galaxies
• X-ray source populations in galaxies
• Specific SFR profiles in nearby spiral galaxies: quantifying the inside-out formation of disks
• X-ray luminosity function of faint point sources in the Milky Way
• A multi-scale study of infrared and radio emission from Scd galaxy M33
• Neon and Oxygen Abundances in M33
• Universal X-ray emissivity of the stellar population in early-type galaxies: unresolved X-ray sources in NGC 3379
• Identifying XMM-Newton observations affected by solar wind charge exchange - Part I
• X-ray emission from the extended disks of spiral galaxies
• Unresolved emission and ionized gas in the bulge of M31
• Resolving the Galactic X-ray background
• X-ray emission from the stellar population in M32
• Chandra ACIS Survey of M33 (ChASeM33): A First Look
• Bar imprints on the inner gas kinematics of M33
• The X-ray binary population in M33: I. Source list and luminosity function
• The Chandra ACIS Survey of M33 (ChASeM33): Investigating the Hot Ionized Medium in NGC604
• An XMM-Newton view of M101 - III. Diffuse X-ray emission
• The Chandra ACIS Survey of M33 (ChASeM33): Transient X-ray Sources Discovered in M33
• The X-ray binary population in M33: II. X-ray spectra and variability

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