Photometric Redshifts with the LSST II: The Impact of Near-Infrared and Near-Ultraviolet Photometry

Abstract

Accurate photometric redshift (photo-$z$) estimates are essential to the cosmological science goals of the Vera C. Rubin Observatory Legacy Survey of Space and Time (LSST). In this work we use simulated photometry for mock galaxy catalogs to explore how LSST photo-$z$ estimates can be improved by the addition of near-infrared (NIR) and/or ultraviolet (UV) photometry from the Euclid, WFIRST, and/or CASTOR space telescopes. Generally, we find that deeper optical photometry can reduce the standard deviation of the photo-$z$ estimates more than adding NIR or UV filters, but that additional filters are the only way to significantly lower the fraction of galaxies with catastrophically under- or over-estimated photo-$z$. For Euclid, we find that the addition of $JH$ $5\sigma$ photometric detections can reduce the standard deviation for galaxies with $z>1$ ($z>0.3$) by $\sim 20\%$ ($\sim 10\%$), and the fraction of outliers by $\sim 40\%$ ($\sim 25\%$). For WFIRST, we show how the addition of deep $YJHK$ photometry could reduce the standard deviation by $\gtrsim 50\%$ at $z>1.5$ and drastically reduce the fraction of outliers to just $\sim 2\%$ overall. For CASTOR, we find that the addition of its $UV$ and $u$-band photometry could reduce the standard deviation by $\sim 30\%$ and the fraction of outliers by $\sim 50\%$ for galaxies with $z<0.5$. We also evaluate the photo-$z$ results within sky areas that overlap with both the NIR and UV surveys, and when spectroscopic training sets built from the surveys' small-area deep fields are used.

21 pages, 16 figures, 4 tables, accepted to AJ

References in corpus (5)

• The Canada-France Imaging Survey: First results from the u-band component
• The Euclid mission design
• Photometric Redshifts with the LSST: Evaluating Survey Observing Strategies
• Scientific Synergy Between LSST and Euclid
• Impact of photometric redshifts on the galaxy power spectrum and BAO scale in the LSST survey

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• Optimising a magnitude-limited spectroscopic training sample for photometric classification of supernovae
• Dark energy reconstruction analysis with artificial neural networks: Application on simulated Supernova Ia data from Rubin Observatory
• Probing bursty star formation by cross-correlating extragalactic background light and galaxy surveys
• Recovered SN Ia rate from simulated LSST images
• Exploring Alternative Cosmologies with the LSST: Simulated Forecasts and Current Observational Constraints
• Chromatic Effects on the PSF and Shear Measurement for the Roman Space Telescope High-Latitude Wide Area Survey
• How limiting is optical follow-up for fast radio burst applications? Forecasts for radio and optical surveys
• Learning Spectral Templates for Photometric Redshift Estimation from Broadband Photometry
• Blending effects on shear measurement synergy between Euclid-like and LSST-like surveys
• TOPz: Photometric redshifts using template fitting applied to the GAMA survey