Frontier Fields: High-redshift Predictions and Early Results
The Frontier Fields program is obtaining deep Hubble and Spitzer Space Telescope images of new "blank" fields and nearby fields gravitationally lensed by massive galaxy clusters. The Hubble images of the lensed fields are revealing nJy sources (AB mag > 31), the faintest galaxies yet observed. The full program will transform our understanding of galaxy evolution in the first 600 million years (z > 9). Previous programs have yielded a dozen or so z > 9 candidates, including perhaps fewer than expected in the Ultra Deep Field and more than expected in shallower Hubble images. In this paper, we present high-redshift (z > 6) number count predictions for the Frontier Fields and candidates in three of the first Hubble images. We show the full Frontier Fields program may yield up to ~70 z > 9 candidates (~6 per field). We base this estimate on an extrapolation of luminosity functions observed between 4 < z < 8 and gravitational lensing models submitted by the community. However, in the first two deep infrared Hubble images obtained to date, we find z ~ 8 candidates but no strong candidates at z > 9. We defer quantitative analysis of the z > 9 deficit (including detection completeness estimates) to future work including additional data. At these redshifts, cosmic variance (field-to-field variation) is expected to be significant (greater than ±50%) and include clustering of early galaxies formed in overdensities. The full Frontier Fields program will significantly mitigate this uncertainty by observing six independent sightlines each with a lensing cluster and nearby blank field.
© 2015 American Astronomical Society. Received 2014 April 30; accepted 2014 December 18; published 2015 February 12. This work is supported by HST archival research program AR-13236. Support for AZ is provided by NASA through Hubble Fellowship grant HST-HF-51334.01-A awarded by STScI. The Frontier Fields are Director's Discretionary programs carried out with the NASA/ESA Hubble Space Telescope and the Spitzer Space Telescope. The Space Telescope Science Institute (STScI) is operated by the Association of Universities for Research in Astronomy, Inc. (AURA) under NASA contract NAS 5-26555. ACS was developed under NASA contract NAS 5-32864. The Spitzer Space Telescope is operated by the Jet Propulsion Laboratory, California Institute of Technology under a contract with NASA. This work utilizes gravitational lensing models produced by PIs Bradac, Ebeling, Zitrin & Merten, Sharon, and Williams funded as part of the HST Frontier Fields program conducted by STScI. The HST image mosaics were produced by the Frontier Fields Science Data Products Team at STScI. We obtained both the images and lens models from the Mikulski Archive for Space Telescopes (MAST). And we thank these teams for all their efforts. We also thank the STScI and SSC directors, their teams implementing the observing programs and reducing the data, and especially the Frontier Fields PI Jennifer Lotz for all of her hard work running this program. Finally, we thank our referee for detailed comments which helped us improve the manuscript. Facilities: HST (WFC3, ACS); Spitzer (IRAC)
Published - 0004-637X_800_2_84.pdf
Submitted - 1405.0011v1.pdf