Constraints onz ≈ 10 Galaxies from the DeepestHubble Space TelescopeNICMOS Fields

We use all available fields with deep NICMOS imaging to search for J 110 -dropouts ( H 160,AB ≲ 28) at z ≈ 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 σ limiting magnitudes were ~28.6 in J 110 and ~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 σ 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 ≈ 10 sources, either as a result of detections (>2 σ) blueward of J 110 or their colors redward of the break ( H 160 - K ~ 1.5) (redder than ≳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 ≈ 10 sources must be three or fewer. To assess the significance of these results, two lower redshift samples (a z ~ 3.8 B -dropout and z ~ 6 i -dropout sample) were projected to z ~ 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 (≈0.3 L ), there has been evolution from z ~ 3.8 and possibly from z ~ 6. This is consistent with the strong evolution already noted at z ~ 6 and z ~ 7.5 relative to z ~ 3-4. Even assuming that three sources from this probe are at z ≈ 10, the rest-frame continuum UV (~1500 Å) luminosity density at z ~ 10 (integrated down to 0.3 L ) is just 0.19 times that at z ~ 3.8 (or 0.19 times, including the small effect from cosmic variance). However, if none of our sources are at z ≈ 10, this ratio has a 1 σ upper limit of 0.07.