We present an analysis of the X-ray emission from a large sample of ultraviolet ( UV ) selected , star forming galaxies with 0.74 < z < 1.32 in the Hubble Deep Field North ( HDF-N ) region .
By excluding all sources with significant detected X-ray emission in the 2 Ms Chandra observation we are able to examine the properties of galaxies for which the dominant emission in both UV and X-ray is expected to be predominantly due to star formation .
Stacking the X-ray flux from 216 galaxies in the soft and hard bands produces significant detections ( 14.9 \sigma and 3.2 \sigma , respectively ) .
The derived mean 2–10 keV rest-frame luminosity is 2.97 \pm 0.26 \times 10 ^ { 40 } erg s ^ { -1 } , corresponding to an X-ray derived star formation rate ( SFR ) of 6.0 \pm 0.6 M _ { \sun } ~ { } \mathrm { yr } ^ { -1 } .
Comparing the X-ray value with the mean UV derived SFR , uncorrected for attenuation , we find that the average UV attenuation correction factor is \sim 3 .
By binning the galaxy sample according to UV magnitude and colour , and stacking the observed frame soft band X-ray flux in each bin , correlations between UV and X-ray emission are examined .
We find a strong positive correlation between X-ray emission and rest-frame UV emission , consistent with a strict linear relationship , L _ { \mathrm { X } } \propto \mathrm { L } _ { \mathrm { UV } } , at the 90 per cent level .
A correlation between the ratio of X-ray-to-UV emission and UV colour is also seen , such that \mathrm { L } _ { \mathrm { X } } / \mathrm { L } _ { \mathrm { UV } } increases for redder galaxies .
We find no direct relation between X-ray flux and UV colour .
Given that X-ray emission offers a view of star formation regions that is relatively unaffected by extinction , results such as these can be used to evaluate the effects of dust on the UV emission from high- z galaxies .
For instance , using the observed correlation between UV colour excess and the ratio of X-ray-to-UV emission – a measure of UV obscuration – we derive a relationship for estimating UV attenuation corrections as a function of colour excess .
The observed relation is inconsistent with the Calzetti et al .
( 7 ) reddening law which over predicts the range in UV attenuation corrections by a factor of \sim 100 for the UV selected z \sim 1 galaxies in this sample .