Real or Interloper? The Redshift Likelihoods of z>8 Galaxies in the
  HUDF12
  In the absence of spectra, fitting template model spectra to observed
photometric fluxes, known as Spectral Energy Distribution (SED) fitting, has
become the workhorse for identifying high-z galaxies. In this paper, we present
an analysis of the most recent and possibly most distant galaxies discovered in
the Hubble Ultra Deep Field using a more robust method of redshift estimation
based on Markov Chain Monte Carlo fitting (MCMC), rather than relying on the
redshift of "best fit" models obtained using common chi^2 minimization
techniques. The advantage of MCMC fitting is the ability to accurately estimate
the probability density function of the redshift, as well as any other input
model parameters, allowing us to derive accurate credible intervals by properly
marginalizing over all other input model parameters. We apply our method to 13
recently identified sources and show that, despite claims based on chi^2
minimization, none of these sources can be securely ruled out as low redshift
interlopers given the low signal-to-noise of currently available observations.
We estimate that there is an average probability of 21% that these sources are
low redshift interlopers.
