The X-ray Morphology and Spectra of Galactic Disks   R. Owen, R. Warwick The X-ray Universe 2008

Introduction We use XMM-Newton to analyze disk emission from a sample of nearby face-on spiral galaxies. After excluding the bright X-ray point sources, we investigate:   Spectral components in the galactic disk Morphology of the residual X-ray emission Correlation with NUV emission Link between residual X-ray emission and star formation in disk. The X-ray Universe 2008

Sample of galaxies Galaxy M51 M74 M83 M101 NGC300 Type Sbc Sc Scd Sd Distance /Mpc 8.4 9.7 3.7 7.2 2.0 D25/arcmin 11.2 10.5 12.9 26.9 21.8 NH/1020cm-2 1.8 4.8 3.9 1.1 3.6 LX/1039 ergs-1 (0.3-6 keV) 19.4* 8.5 7.4 8.7 0.5   *includes LLAGN The X-ray Universe 2008

Exclusion of bright X-ray point sources   Residual emission from M83 after exclusion of bright point sources. XMM-Newton soft band (0.3-1 keV) image of M83. Simulated PSF image of bright point sources. Source mask created from simulated image. The X-ray Universe 2008

M83: spectral and radial analysis   Radial distribution: exponential with scalelength 0.79’ (0.85 kpc) 2-temperature mekal fit : kT ~ 0.2, 0.6 keV. LX (0.3-1 keV) ≈ 1.6 x 1039 ergs-1 Unresolved soft X-ray emission (0.3-1 keV) in M83. Chandra log N-log S: 2/3 of residual emission truly diffuse. Owen & Warwick (2008, in prep.) The X-ray Universe 2008

M83: Soft X-ray and NUV emission GALEX NUV 0.3-1 keV   12.8’ ~ 13.8 kpc XMM-Newton soft X-ray and GALEX NUV images of M83 overlaid with soft X-ray contours. The X-ray Universe 2008

M83: X-ray / NUV correlation 0.3-1 keV GALEX   8’ ~ 8.6 kpc Soft X-ray residual and GALEX NUV images are shown overlaid with the bright source mask, showing areas used in correlation analysis. Correlation gradient: 18.3 ± 2.7 (arbitrary units) The X-ray Universe 2008

M101: X-ray / NUV correlation GALEX 0.3-1 keV   10’ ~ 22.6 kpc Correlation gradient: 12.8 ± 1.2 (extinction corrected, arbitrary units) Warwick et al. (2007) The X-ray Universe 2008

M51: X-ray / NUV correlation GALEX 0.3-1 keV   10’ ~ 24.5 kpc Correlation gradient: 18.2 ± 1.3 (extinction corrected, arbitrary units) The X-ray Universe 2008

M74: X-ray / NUV correlation GALEX 0.3-1 keV   10’ ~ 25.3 kpc Correlation gradient: 12.0 ± 0.9 (extinction corrected, arbitrary units) The X-ray Universe 2008

NGC300: X-ray / NUV correlation GALEX 0.3-1 keV   10’ ~ 6.2 kpc Correlation gradient: 1.7 ± 0.4 (extinction corrected, arbitrary units) The X-ray Universe 2008

Radial distribution of X-ray emission M83: scalelength = 0.79’ (0.85 kpc) M101: scalelength = 2.6’ (5.4 kpc)   X-ray SFR M51: scalelength = 0.72’ (1.76 kpc) M74: scalelength = 0.92’ (2.33 kpc)

Spectral components of galaxy sample   2-temperature fit: kT ≈ 0.2, 0.6 keV. Soft/hard component ratio = 1.3 LX (0.3-1 keV) ≈ 1.6 x 1039 ergs-1 2-temperature fit: kT ≈ 0.2, 0.7 keV. Soft/hard component ratio = 3.8 LX (0.3-1 keV) ≈ 1.7 x 1039 ergs-1 2-temperature fit: kT ≈ 0.2, 0.65 keV. Soft/hard component ratio = 1.5 LX (0.3-1 keV) ≈ 4.4 x 1039 ergs-1 2-temperature fit: kT ≈ 0.2, 0.6 keV. Soft/ hard component ratio = 6.0 LX (0.3-1 keV) ≈ 2.1 x 1039 ergs-1 The X-ray Universe 2008

X-ray properties of galaxy sample NGC300 Type Sbc Sc Scd Sd Diffuse LX (1039 ergs-1, 0.3-1 keV) 4.4 1.6 2.1 1.7 N/A Soft / hard ratio 1.5 1.3 6.0 3.8 X-ray/NUV correlation gradient 18.2 18.3 12.0 12.8 Star formation rate* (10-8Mοyr-1pc-2) 3.54 4.22 0.80 0.73 0.32   *Munoz-Mateos et al (2007). The X-ray Universe 2008

Results: Comparison with SFR Radial scalelength of X-ray emission across galactic disk is shorter than SFR. X-ray/NUV correlation shows X-ray deficit at low SFR. Temperature of diffuse emission increases as SFR increases.   Possible interpretation: The efficiency of X-ray emission from supernova shocks and stellar winds depends on density of gas in surrounding environment. Towards outside edge of disk, X-ray emission falls off faster than SFR as density of environment is lower. These trends agree with HMXB luminosity/SFR relationship derived by Grimm, Gilfanov & Sunyaev (2003). The X-ray Universe 2008

Conclusions We have used XMM-Newton to examine diffuse X-ray emission from a sample of nearby face-on spiral galaxies. Spectral analysis of the disks gives two-temperature thermal fits at kT ~ 0.2, 0.6 keV, with higher temperature gas found in systems with higher SFR. Diffuse X-ray emission declines with radius over a shorter scalelength than SFR. Strong correlation is found between X-ray and NUV emission across the galactic disks, with an X-ray deficit found in systems with lower SFR. Quantitative relationship with SFR still in development, physical explanation fits discovered trends across sample.   The X-ray Universe 2008