Optimal Filter Systems for Photometric Redshift Estimation
Benítez, N.; Moles, M.; Aguerri, J. A. L.;Alfaro, E.; Broadhurst, T.; Cabrera-Caño, J.;Castander, F. J.; Cepa, J.; Cerviño, M.;Cristóbal-Hornillos, D.; Fernández-Soto, A.;González Delgado, R. M.; Infante, L.; Márquez, I.;Martínez, V. J.; Masegosa, J.; DelOlmo, A.;Perea, J.; Prada, F.; Quintana, J. M.;Sánchez, S. F.. Optimal Filter Systems for Photometric Redshift Estimation. The Astrophysical Journal Letters. 2009, Vol. Volume 692, Issue 1, pp. L5-L8 (2009)., p. -2009.
In the coming years, several cosmological surveys will rely on imaging
data to estimate the redshift of galaxies, using traditional filter
systems with 4-5 optical broad bands; narrower filters improve the
spectral resolution, but strongly reduce the total system throughput. We
explore how photometric redshift performance depends on the number of
filters n<SUB>f</SUB> , characterizing the survey depth by the fraction
of galaxies with unambiguous redshift estimates. For a combination of
total exposure time and telescope imaging area of 270 hr m<SUP>2</SUP>,
4-5 filter systems perform significantly worse, both in completeness
depth and precision, than systems with n<SUB>f</SUB> gsim 8 filters. Our
results suggest that for low n<SUB>f</SUB> the color-redshift
degeneracies overwhelm the improvements in photometric depth, and that
even at higher n<SUB>f</SUB> the effective photometric redshift depth
decreases much more slowly with filter width than naively expected from
the reduction in the signal-to-noise ratio. Adding near-IR observations
improves the performance of low-n<SUB>f</SUB> systems, but still the
system which maximizes the photometric redshift completeness is formed
by nine filters with logarithmically increasing bandwidth (constant
resolution) and half-band overlap, reaching ~0.7 mag deeper, with 10%
better redshift precision, than 4-5 filter systems. A system with 20
constant-width, nonoverlapping filters reaches only ~0.1 mag shallower
than 4-5 filter systems, but has a precision almost three times better,
δz = 0.014(1 + z) versus δz = 0.042(1 + z). We briefly
discuss a practical implementation of such a photometric system: the
ALHAMBRA Survey.
In the coming years, several cosmological surveys will rely on imaging
data to estimate the redshift of galaxies, using traditional filter
systems with 4-5 optical broad bands; narrower filters improve the
spectral resolution, but strongly reduce the total system throughput. We
explore how photometric redshift performance depends on the number of
filters n<SUB>f</SUB> , characterizing the survey depth by the fraction
of galaxies with unambiguous redshift estimates. For a combination of
total exposure time and telescope imaging area of 270 hr m<SUP>2</SUP>,
4-5 filter systems perform significantly worse, both in completeness
depth and precision, than systems with n<SUB>f</SUB> gsim 8 filters. Our
results suggest that for low n<SUB>f</SUB> the color-redshift
degeneracies overwhelm the improvements in photometric depth, and that
even at higher n<SUB>f</SUB> the effective photometric redshift depth
decreases much more slowly with filter width than naively expected from
the reduction in the signal-to-noise ratio. Adding near-IR observations
improves the performance of low-n<SUB>f</SUB> systems, but still the
system which maximizes the photometric redshift completeness is formed
by nine filters with logarithmically increasing bandwidth (constant
resolution) and half-band overlap, reaching ~0.7 mag deeper, with 10%
better redshift precision, than 4-5 filter systems. A system with 20
constant-width, nonoverlapping filters reaches only ~0.1 mag shallower
than 4-5 filter systems, but has a precision almost three times better,
δz = 0.014(1 + z) versus δz = 0.042(1 + z). We briefly
discuss a practical implementation of such a photometric system: the
ALHAMBRA Survey.