ar X iv : a st ro - p h / 05 03 11 6 v 2 1 7 M ar 2 00 5 Constraints on z ≈ 10 Galaxies from the Deepest HST NICMOS 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 were the two J 110 + H 160 NICMOS parallel fields taken with the Advanced Camera for Surveys (ACS) Hubble Ultra Deep Field (HUDF). The 5σ 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 HUDF (with 5σ 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 were clearly ruled out as credible z ≈ 10 sources, either as a result of detections (> 2σ) 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 3 remaining sources could not be determined from the data. The number appears consistent with the expected contamination from low-redshift interlopers. Analysis of the stacked images for the 3 candidates also suggests some contamination. Regardless of their true redshifts, the actual number of z ≈ 10 sources must be ≤ 3. 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 ∼ 8 − 12 using a (1 + z) −1 size scaling (for fixed luminosity). They were added to the image frames, and the selection repeated, giving 15.6 and 4.8 J 110-dropouts, respectively. This suggests that to the limit of this probe (≈ 0.3L * z=3) there has been evolution from z ∼ 3.8 and possibly from z ∼ 6. This