Spitzer Space Telescope - Directors Discretionary Time Proposal #293

The nature of JD0910+46: a candidate z~10 galaxy

Principal Investigator: Nial Tanvir 
Institution: University of Leicester

Co-Investigators:
Andrew Levan, University of Warwick
James Rhoads, Arizona State University
Andrew Fruchter, Space Telescope Science Institute
Malcolm Bremer, University of Bristol
Robert Priddey, University of Hertfordshire
Jens Hjorth, University of Copenhagen
Evert Rol, University of Leicester
Pall Jakobsson, University of Hertfordshire 


Science Category: Cosmology/High-z
Observing Modes: IRAC Mapping  
Hours Approved: 2.2

Abstract: The earliest galaxies in the Universe should have formed at very high
redshifts, z>10, based both on models of hierarchical structure
formation, and on observations of the microwave background polarization
by WMAP that require significant ionization of the intergalactic medium
before z=10. However, direct observation of sources at z>7 remains
highly challenging due to their scarcity and faintness. We recently
identified a bright, spatially extended J-band dropout, JD0910+46, that
is an promising candidate for a z>10 galaxy. Its spectral energy
distribution is more extreme than any previously reported: It is
undetected in J, with a very red J-H color, yet is quite blue in H-K. It
appears to be the best candidate to date for a z>10 galaxy: These colors
are natural for a Lyman break, but model SEDs of either "old" or dusty
galaxies at more moderate redshifts (z~3) cannot easily reproduce the
observed combination of red J-H and blue H-K color. Yet we do not feel
the case for z>10 can be adequately resolved with existing optical and
NIR data alone.  Spitzer/IRAC photometry will convincingly distinguish
between different models and so elucidate the nature of this remarkable
source. Should it turn out to be at a lower redshift it will provide an
important example of the kinds of interloper which may contaminate
samples of high-z candidates based on the dropout technique.