This paper explores the X-ray properties of ‘ normal ’ galaxies using a shallow ( 2-10 ksec ) XMM- Newton survey covering an area of \approx 1.5 deg ^ { 2 } .
The X-ray survey overlaps with the 2dF Galaxy Redshift Survey .
Compared with previous studies this has the advantage that high quality spectra and spectral classifications ( early , late type ) exist for all galaxies to b _ { j } = 19.4 .
Moreover , sources with optical spectra revealing powerful AGNs can easily be discarded from the normal galaxy sample used here .
In particular , we present stacking analysis results for about 200 galaxies from the 2dF Galaxy Redshift Survey at a mean redshift of z \approx 0.1 .
We detect a strong signal for the whole sample ( \approx 6 \sigma ) in the soft 0.5-2 keV band corresponding to a flux of \approx 7 \times 10 ^ { -16 } erg sec ^ { -1 } cm ^ { -2 } and a luminosity of \approx 2 \times 10 ^ { 40 } erg sec ^ { -1 } .
A statistically significant signal is also detected for both the early and late galaxy sub-samples with X-ray luminosities of \approx 3 \times 10 ^ { 40 } and \approx 5 \times 10 ^ { 39 } erg sec ^ { -1 } respectively .
In contrast , no signal is detected in the hard 2-8 keV band for any of the above samples .
The mean L _ { X } / L _ { B } ratio of the spiral galaxy sample is found to be consistent with both local ( < 100 Mpc ) and distant ( z \approx 1 ) samples ( after accounting for differences in L _ { B } ) suggesting little or no evolution of the X-ray emission mechanisms relative to the optical .
The 0.5-2 keV XRB contribution of the spiral galaxy sub-sample at z \approx 0.1 is estimated to be 0.4 per cent in broad agreement with the XRB fractions estimated in previous studies .
Assuming that star-forming galaxies evolve with redshift as ( 1 + z ) ^ { k } the present data combined with previous studies suggest k < 3 .
The k values are constrained by the relatively low fraction of the soft X-ray background that remains unresolved by deep surveys ( 6–26 % ) .
Higher k values will result in an overproduction of the soft X-ray background given the fraction already attributed to AGN , groups and clusters .
The mean X-ray emissivity of spiral galaxies at z \approx 0.1 is also estimated and is found to be consistent within the uncertainties with that of local H II galaxy samples .
Using the mean X-ray emissivity of the spiral galaxy sub-sample we estimate a global star-formation density of 0.009 \pm 0.007 M _ { \odot } yr ^ { -1 } at z \approx 0.1 .
Although the uncertainty is large this is lower than previous results based on galaxy samples selected at different wavelengths .
Nevertheless , given the large uncertainties involved in converting X-ray luminosity to star-formation rate the agreement is surprising .