NCSA Astronomy Digital Image Library
Project Abstract and Description

An Accurate NH Map of the North Ecliptic Pole

M. Elvis, F. J. Lockman, C. Fassnacht

Contact: Martin Elvis
Email: elvis@cfa.harvard.edu

Number of images in project: 1

References: 1994ApJS...95..413E

Abstract

The Galactic HI column density was measured at 21arcmin angular resolution over an 8 by 9 degree region centered on the North Ecliptic Pole, with the NRAO 140ft telescope and a technique to remove stray radiation (Lockman, Jahoda & McCammon 1986, ApJ, 302, 432).

Over the region NH varies smoothly between 3e20 atoms/cm2 and 8e20 atoms/cm2.

The map is given here. A spin temperature of 250K is assumed. Units are 10^18 atoms/cm2. The center is the NEP at 18 hours +66 degrees.

The paper discusses the structure seen over most of the map on an 0.5 to 1 degree scale. There are other possible sources of interstellar opacity in this direction which may add an equivalent 1e20 atoms/cm2 of HI. We evaluate the effect of uncertainties in the HI column density on inferred X-ray fluxes of extragalactic objects.

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