Spectrophotometric redshifts for $mathrm{zsim1}$ galaxies and predictions for number densities with WFIRST and Euclid. (arXiv:1903.08705v1 [astro-ph.GA])
<a href="http://arxiv.org/find/astro-ph/1/au:+Joshi_B/0/1/0/all/0/1">Bhavin A. Joshi</a>, <a href="http://arxiv.org/find/astro-ph/1/au:+Cohen_S/0/1/0/all/0/1">Seth Cohen</a>, <a href="http://arxiv.org/find/astro-ph/1/au:+Windhorst_R/0/1/0/all/0/1">Rogier A. Windhorst</a>, <a href="http://arxiv.org/find/astro-ph/1/au:+Jansen_R/0/1/0/all/0/1">Rolf Jansen</a>, <a href="http://arxiv.org/find/astro-ph/1/au:+Pirzkal_N/0/1/0/all/0/1">Norbert Pirzkal</a>, <a href="http://arxiv.org/find/astro-ph/1/au:+Hathi_N/0/1/0/all/0/1">Nimish P. Hathi</a>
We investigate the accuracy of 4000AA/Balmer-break based redshifts by
combining Hubble Space Telescope ({it HST}) grism data with photometry. The
grism spectra are from the Probing Evolution And Reionization Spectroscopically
(PEARS) survey with {it HST} using the G800L grism on the Advanced Camera for
Surveys (ACS). The photometric data come from a compilation by the 3D-HST
collaboration of imaging from multiple surveys (notably CANDELS and 3D-HST). We
show evidence that spectrophotometric redshifts (SPZs) typically improve on the
accuracy of photometric redshifts by $sim$16–60%. We show that the
robustness of the SPZ is directly related to the fidelity of the D4000
measurement. We also estimate the accuracy of continuum-based redshifts, i.e.,
for galaxies that do not contain strong emission lines, based on the grism data
alone ($sigma^mathrm{NMAD}_{Delta z/(1+z)}{lesssim}0.06$). Given that
future space-based observatories like WFIRST and Euclid will spend a
significant fraction of time on slitless spectroscopic observations, we
estimate number densities for objects with a redshift accuracy $leq$0.02. We
predict $sim$8200 galaxies/degree$^2$ for galaxies with D4000$>$1.1 and a
redshift accuracy of $leq$2% to a limit of $i_{AB}$$sim$24 mag. This is
emph{especially} important in the absence of an accompanying rich photometric
dataset like the existing one for the CANDELS fields, where redshift accuracy
from future surveys will rely only on the presence of a feature like the
4000AA/Balmer breaks or the presence of emission lines within the grism
spectra.
We investigate the accuracy of 4000AA/Balmer-break based redshifts by
combining Hubble Space Telescope ({it HST}) grism data with photometry. The
grism spectra are from the Probing Evolution And Reionization Spectroscopically
(PEARS) survey with {it HST} using the G800L grism on the Advanced Camera for
Surveys (ACS). The photometric data come from a compilation by the 3D-HST
collaboration of imaging from multiple surveys (notably CANDELS and 3D-HST). We
show evidence that spectrophotometric redshifts (SPZs) typically improve on the
accuracy of photometric redshifts by $sim$16–60%. We show that the
robustness of the SPZ is directly related to the fidelity of the D4000
measurement. We also estimate the accuracy of continuum-based redshifts, i.e.,
for galaxies that do not contain strong emission lines, based on the grism data
alone ($sigma^mathrm{NMAD}_{Delta z/(1+z)}{lesssim}0.06$). Given that
future space-based observatories like WFIRST and Euclid will spend a
significant fraction of time on slitless spectroscopic observations, we
estimate number densities for objects with a redshift accuracy $leq$0.02. We
predict $sim$8200 galaxies/degree$^2$ for galaxies with D4000$>$1.1 and a
redshift accuracy of $leq$2% to a limit of $i_{AB}$$sim$24 mag. This is
emph{especially} important in the absence of an accompanying rich photometric
dataset like the existing one for the CANDELS fields, where redshift accuracy
from future surveys will rely only on the presence of a feature like the
4000AA/Balmer breaks or the presence of emission lines within the grism
spectra.
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