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X-ray Astronomy Group
Richard Owen, Bob WarwickUniversity of Leicester
The X-ray Morphology and Spectra of Galactic Disks
X-rays from Nearby Galaxies
X-ray Astronomy Group
Introduction
We use XMM-Newton to analyze disk emission from a sample of nearby face-on spiral galaxies.
After exclusion of bright X-ray point sources, we investigate:
• The spectral components in the galactic disk
• The morphology of the residual X-ray emission
• Correlation with NUV emission
X-rays from Nearby Galaxies
X-ray Astronomy Group
Exclusion of bright X-ray point Exclusion of bright X-ray point sources (1)sources (1)
XMM-Newton soft-band (0.3-1 keV) image of M83.
Simulated PSF image of bright point sources.
X-rays from Nearby Galaxies
X-ray Astronomy Group
Exclusion of bright X-ray point Exclusion of bright X-ray point sources (2)sources (2)
Surface brightness cut on simulated image forms source mask.
Tails of PSF extending beyond mask are subtracted to produce residual image.
X-rays from Nearby Galaxies
X-ray Astronomy Group
Galaxies in the sampleGalaxies in the sample
Galaxy M51 M83 M101
Hubble Type Sbc Sc Scd
Distance (Mpc) 7.1 3.7 7.2
D25 (arcmin) 6.9 12.8 28.4
NH (1020 cm-2) 1.3 3.9 1.1
MB -20.3 -19.6 -21.0
Total LX (1039 erg s-1)
(0.3-6 keV)19.4 7.4 8.7
X-rays from Nearby Galaxies
X-ray Astronomy Group
GALEX NUVOM UOM V
M101: Soft X-ray and NUV emission M101: Soft X-ray and NUV emission (1)(1)
Warwick et al 2007
10’ ~ 22.6 kpc
The central 5’ of the soft X-ray image above and NUV map shown
compressed on right with X-ray contours.
0.3-1 keV
X-ray Astronomy Group
M101: Soft X-ray and NUV emission M101: Soft X-ray and NUV emission (2)(2)
The correlation between soft X-ray and emission from the XMM OM UVW1 filter is studied within the central 5’ of M101.
Warwick et al 2007
UVW10.3-1 keV
10’ ~ 22.6 kpc
X-ray Astronomy Group
For 0.2 keV component:
τcool ≈ 1.8 x 108 η½ yr
Not compatible with η~1 due to narrow spiral features in soft X-
ray.
Implies clumpy thin-disk component.
M101: Radial distribution and spectral M101: Radial distribution and spectral analysisanalysis
Warwick et al 2007
Radial distribution: exponential with scalelength 2.6’ (5.4 kpc).
Best fit spectral model: two-temperature mekal, kT ≈ 0.2 and 0.7 keV.
LX (0.3-2 keV) ≈ 2.6 x 1039 erg s-1
X-ray Astronomy Group
M83: Soft X-ray and NUV emission (1)M83: Soft X-ray and NUV emission (1)
Owen et al 2007 (in prep)
12.8’ ~ 13.8 kpc
XMM-Newton soft X-ray and OM UVW1 images of M83 overlaid with soft X-ray contours.
0.3-1 keV
UVW1
X-ray Astronomy Group
M83: Soft X-ray and NUV emission (2)M83: Soft X-ray and NUV emission (2)
Soft X-ray residual and OM UVW1 images are shown overlaid with the bright source mask, showing areas used in correlation analysis.
Owen et al 2007 (in prep)
0.3-1 keV
UVW1
8’ ~ 8.6 kpc
X-ray Astronomy Group
M83: Spectral analysisM83: Spectral analysis
Best fit spectral model: two-temperature mekal with kT ≈ 0.2 and 0.6 keV.
LX (0.3-2 keV) ≈ 1.9 X 1039 erg s-1.
Owen et al 2007 (in prep)
X-ray Astronomy Group
M51: Soft X-ray and NUV emission (1)M51: Soft X-ray and NUV emission (1)
7’ ~ 14 kpc
0.3-1 keV
UVW1
Soft X-ray image and UVW1 image of M51, with X-ray contours shown.
X-rays from Nearby Galaxies
X-ray Astronomy Group
M51: Soft X-ray and NUV emission (2)M51: Soft X-ray and NUV emission (2)
0.3-1 keV
UVW1
Correlation is performed for the regions of M51 not obscured by the source mask, extending out to its D25 radius.
7’ ~ 14 kpc
X-ray Astronomy Group
M51: Spectral analysisM51: Spectral analysis
Best fit spectral model: two-temperature mekal (kT ≈ 0.2, 0.6 keV) with added power-law component (Γ~2.7).
LX (0.3-2 keV) ≈ 5.2 x 1039 erg s-1.
X-rays from Nearby Galaxies
X-ray Astronomy Group
Comparison of soft X-ray versus NUV Comparison of soft X-ray versus NUV correlationscorrelations
M101
M51
M83
Correlations give the best fit gradients:
M51: 0.040 ± 0.005
M83: 0.088 ± 0.010
M101: 0.041 ± 0.005
These must be corrected for extinction in both X-ray and UV. X-rays from Nearby
Galaxies
Extinction corrected
0.038 ± 0.005
0.079 ± 0.010
0.039 ± 0.005
X-ray Astronomy Group
Summary results for diffuse emissionSummary results for diffuse emission
Galaxy M51 M83 M101
Source LX threshold
(1037 erg s-1)5.0 2.0 1.0
Diffuse LX (1039 erg s-
1)(0.3-1 keV)
4.4 1.6 1.7
% attributed to sources
~35 ~25 ~20
Ratio of soft/hard emission
1.5 1.1 3.8
X-ray/UV count-rate ratio
0.038 0.079 0.039
X-rays from Nearby Galaxies
X-ray Astronomy Group
ConclusionsConclusions• X-ray spectra of spiral galaxy disks are typically characterized by two-temperature fits, with kT ≈ 0.2 and 0.6-0.7 keV.
• Diffuse emission can be separated into a clumpy component tracing the spiral arms and a broadly exponential lower halo component.
• In this study we find very good correlation between soft X-ray emission and NUV emission.
• The X-ray/UV count-rate ratio derived is consistent between M51 and M101, but is twice as large in M83.
• We note that the result derived for M83 appears to be due to a genuine soft X-ray excess rather than a UV deficit.
X-rays from Nearby Galaxies