16 μm Imaging around the Hubble Deep Field-North with the Spitzer IRS

We present a pilot study of 16 μm imaging within the GOODS northern field. Observations were obtained using the ``peak-up'' imaging capability of the Spitzer IRS. We survey 35 arcmin² to an average 3 σ depth of 0.075 mJy and detect 149 sources. The survey partially overlaps the area imaged at 15 μm by the ISO, and we demonstrate that our photometry and galaxy number counts are consistent with its measurements. We infer the total infrared luminosity of 16 μm detections using a comparison to local templates and find a wide range of L_IR, from ~10⁹ to 10¹² L_solar. Approximately 1/5 of the detected sources have counterparts in the Chandra 2 Ms catalog, and we show that the hard-band (2-8 keV) detected sources are likely to have strong active galactic nucleus (AGN) contributions to the X-ray flux. The ultradeep sensitivity of Chandra implies that some X-ray detections may be purely starbursting objects. We examine the 16 to 24 μm flux ratio and conclude that it shows evidence for the detection of redshifted polycyclic aromatic hydrocarbon (PAH) emission at z~0.5 and z>0.8.

Based on observations obtained with the Spitzer Space Telescope, which is operated by JPL, California Institute of Technology, for the National Aeronautics and Space Administration.

The IRS is a collaborative venture between Cornell University and Ball Aerospace Corporation that was funded by NASA through JPL.