Near-Infrared Properties of Faint X-rays Sources from NICMOS Imaging in the Chandra Deep Fields

摘要

We measure the near-infrared properties of 42 X-ray detected sources from theChandra Deep Fields North and South, the majority of which lie within theNICMOS Hubble Deep Field North and Ultra Deep Field. We detect all 42 Chandrasources with NICMOS, with 95% brighter than H = 24.5. We find that X-raysources are most often in the brightest and most massive galaxies. Neither theX-ray fluxes nor hardness ratios of the sample show any correlation withnear-infrared flux, color or morphology. This lack of correlation indicatesthere is little connection between the two emission mechanisms and isconsistent with the near-infrared emission being dominated by starlight ratherthan a Seyfert non-stellar continuum. Near-infrared X-ray sources make up roughly half of all extremely red (J-H >1.4) objects brighter than H > 24.5. These red X-ray sources have a range ofhardness ratios similar to the rest of the sample, decreasing the likelihood ofdust-obscured AGN activity as the sole explanation for their red color. Using acombination of spectroscopic and photometric redshifts, we find the red J-Hobjects are at high redshifts (z > 1.5), which we propose as the primaryexplanation for their extreme J-H color. Measurement of rest-wavelengthabsolute B magnitudes shows that X-ray sources are the brightest opticalobjects at all redshifts, which explains their dominance of the bright end ofthe red J-H population.