Constraints on z ≈ 10 galaxies from the deepest Hubble Space Telescope NICMOS fields

We use all available fields with deep NICMOS imaging to search for J(110)-dropouts (H-160,H-AB less than or similar to 28) at z approximate to 10. Our primary data set for this search is the two J(110) + H-160 NICMOS fields taken in parallel with the Advanced Camera for Surveys (ACS) Hubble Ultra Deep Field (UDF). The 5 sigma limiting magnitudes were similar to 28.6 in J(110) and similar to 28.5 in H-160 (0.'' 6 apertures). Several shallower fields were also used: J(110) + H-160 NICMOS frames available over the Hubble Deep Field (HDF) North, the HDF-South NICMOS parallel, and the ACS UDF (with 5 sigma limiting magnitudes in J(110) and H-160 ranging from 27.0 to 28.2). The primary selection criterion was (J(110) - H-160)(AB) > 1.8. Eleven such sources were found in all search fields using this criterion. Eight of these are clearly ruled out as credible z approximate to 10 sources, either as a result of detections (>2 sigma) blueward of J(110) or their colors redward of the break (H-160 - K similar to 1.5) ( redder than greater than or similar to 98% of lower redshift dropouts). The nature of the three remaining sources could not be determined from the data. This number appears consistent with the expected contamination from low-redshift interlopers. Analysis of the stacked images for the three candidates also suggests some contamination. Regardless of their true redshifts, the actual number of z approximate to 10 sources must be three or fewer. To assess the significance of these results, two lower redshift samples (a z similar to 3.8 B-dropout and z similar to 6 i-dropout sample) were projected to z similar to 7 - 13 using a ( 1 + z)(-1) size scaling (for fixed luminosity). They were added to the image frames and the selection was repeated, giving 15.6 and 4.8 J(110)-dropouts, respectively. This suggests that to the limit of this probe (approximate to 0.3L(z=3)*), there has been evolution from z similar to 3.8 and possibly from z similar to 6. This is consistent with the strong evolution already noted at z similar to 6 and z similar to 7.5 relative to z similar to 3 - 4. Even assuming that three sources from this probe are at z approximate to 10, the rest-frame continuum UV (similar to 1500 angstrom) luminosity density at z similar to 10 ( integrated down to 0.3L(z=3)(*)) is just 0.19(-0.09)(+0.13) times that at z similar to 3.8 (or 0.19(-0.10)(+0.15) times, including the small effect from cosmic variance). However, if none of our sources are at z approximate to 10, this ratio has a 1 sigma upper limit of 0.07.