TheSpitzer Space TelescopeFirst Look Survey: Neutral Hydrogen Emission

The Spitzer Space Telescope (formerly SIRTF) extragalactic First-Look Surveycovered about 5 square degrees centered on J2000 17:18 +59:30 in order tocharacterize the infrared sky with high sensitivity. We used the 100-m GreenBank Telescope to image the 21cm Galactic HI emission over a 3x3 degree fieldcovering this position with an effective angular resolution of 9.8 arcmin and avelocity resolution of 0.62 km/s. In the central square degree of the image theaverage column density is N(HI) = 2.5 x 10^{20} cm-2 with an rms fluctuation of0.3 x 10^{20}. The Galactic HI in this region has a very interesting structure.There is a high-velocity cloud, several intermediate-velocity clouds (one ofwhich is probably part of the Draco nebula), and narrow-line low velocityfilaments. The HI emission shows a strong and detailed correlation with dust.Except for the high-velocity cloud, all features in the HI map havecounterparts in an E(B-V) map derived from infrared data. Relatively highE(B-V)/N(HI) ratios in some directions suggest the presence of molecular gas.The best diagnostic of such regions is the peak HI line brightness temperature,not the total N(HI): directions where Tb > 12 K have E(B-V)/N(HI) significantlyabove the average value. The data corrected for stray radiation have beenreleased via the Web.