The Spitzer Space Telescope First Look Survey: Neutral Hydrogen Emission

Abstract

The Spitzer Space Telescope (formerly SIRTF) extragalactic First Look Survey covered about 5 deg2 centered on (J2000.0) α=17h18m, δ=59deg30' in order to characterize the infrared sky with high sensitivity. We used the 100 m Green Bank Telescope to image the 21 cm Galactic H I emission over a 3deg×3deg square, covering this position with an effective angular resolution of 9.8 arcmin and a velocity resolution of 0.62 km s-1. In the central square degree of the image the average column density is NHI=2.5×1020 cm-2 with an rms fluctuation of 0.3×1020 cm-2. The Galactic H I in this region has a very interesting structure. There is a high-velocity cloud, several intermediate-velocity clouds (one of which is probably part of the Draco Nebula), and narrow-line low-velocity filaments. The H I emission shows a strong and detailed correlation with dust. Except for the high-velocity cloud, all features in the NH I map have counterparts in an E(B-V) map derived from infrared data. Relatively high E(B-V)/NH I ratios in some directions suggest the presence of molecular gas. The best diagnostic of such regions is the peak H I line brightness temperature, not the total NH I: directions where Tb>12 K have E(B-V)/NH I significantly above the average value. The data corrected for stray radiation have been released via the World Wide Web.