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The X-ray Morphology and Spectra of Galactic Disks Richard Owen, Bob Warwick University of Leicester X-rays from Nearby Galaxies Introduction We use XMM-Newton to analyze disk emission from a sample of nearby face-on spiral galaxies.

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the x ray morphology and spectra of galactic disks

The X-ray Morphology and Spectra of Galactic Disks

Richard Owen, Bob Warwick

University of Leicester

X-rays from Nearby Galaxies

slide2

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

slide3

Simulated PSF image of bright point sources.

Exclusion of bright X-ray point sources (1)

XMM-Newton soft-band (0.3-1 keV) image of M83.

X-rays from Nearby Galaxies

slide4

Exclusion of bright X-ray point 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

slide5

Galaxies in the sample

X-rays from Nearby Galaxies

slide6

OM V

OM U

GALEX NUV

M101: Soft X-ray and NUV emission (1)

0.3-1 keV

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.

Warwick et al 2007

slide7

M101: Soft X-ray and NUV emission (2)

UVW1

0.3-1 keV

10’ ~ 22.6 kpc

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

slide8

M101: Radial distribution and spectral analysis

For 0.2 keV component:

τcool ≈ 1.8 x 108η½ yr

Not compatible with η~1 due to narrow spiral features in soft X-ray.

Implies clumpy thin-disk component.

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

Warwick et al 2007

slide9

M83: Soft X-ray and NUV emission (1)

0.3-1 keV

UVW1

12.8’ ~ 13.8 kpc

XMM-Newton soft X-ray and OM UVW1 images of M83 overlaid with soft X-ray contours.

Owen et al 2007 (in prep)

slide10

M83: Soft X-ray and NUV emission (2)

0.3-1 keV

UVW1

8’ ~ 8.6 kpc

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)

slide11

M83: 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)

slide12

M51: Soft X-ray and NUV emission (1)

0.3-1 keV

7’ ~ 14 kpc

UVW1

Soft X-ray image and UVW1 image of M51, with X-ray contours shown.

X-rays from Nearby Galaxies

slide13

M51: Soft X-ray and NUV emission (2)

UVW1

0.3-1 keV

7’ ~ 14 kpc

Correlation is performed for the regions of M51 not obscured by the source mask, extending out to its D25 radius.

slide14

M51: 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

slide15

Comparison of soft X-ray versus NUV correlations

M101

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.

Extinction corrected

0.038 ± 0.005

0.079 ± 0.010

0.039 ± 0.005

M51

X-rays from Nearby Galaxies

slide16

Summary results for diffuse emission

X-rays from Nearby Galaxies

slide17

Conclusions

  • 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