An accurate Galactic N[SUB]H[/SUB] map of the north ecliptic pole

Abstract

The Galactic HI column density was measured at 21 min angular resolution over an 8 deg x 9 deg region centered on the north ecliptic pole. Over the region N<SUB>H</SUB> varies smoothly between 3 x 10<SUP>20</SUP> atoms/sq cm and 8 x 10<SUP>20</SUP> atoms/sq cm; some structure is seen over most of the map on an 0.5 - 1 deg scale. There are other possible sources of interstellar opacity in this direction which may add an equivalent 10<SUP>20</SUP>/sq cm of HI. We evaluate the effect of uncertainties in the HI column density on implied X-ray fluxes of extragalactic objects.