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

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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.

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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.

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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

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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.

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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.

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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

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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.

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