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

2. 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

3. 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
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4. 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

5. 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.)
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6. 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

7. 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)
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8. 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)
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9. M51: X-ray / NUV correlation
GALEX
0.3-1 keV
10’ ~ 24.5 kpc
Correlation gradient: 18.2 ± 1.3 (extinction corrected, arbitrary units)
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10. M74: X-ray / NUV correlation
GALEX
0.3-1 keV
10’ ~ 25.3 kpc
Correlation gradient: 12.0 ± 0.9 (extinction corrected, arbitrary units)
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11. NGC300: X-ray / NUV correlation
GALEX
0.3-1 keV
10’ ~ 6.2 kpc
Correlation gradient: 1.7 ± 0.4 (extinction corrected, arbitrary units)
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12. 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)

13. 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
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14. X-ray properties of galaxy sample
NGC300
Type
Sbc Sc
Scd Sd
Diffuse LX (1039 ergs-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).
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15. 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).
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16. 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