Photometric redshifts for the Pan-STARRS1 survey

Abstract

We present a robust approach to estimating the redshift of galaxies using Pan-STARRS1 photometric data. Our approach is an application of the algorithm proposed for the SDSS Data Release 12. It uses a training set of 2 313 724 galaxies for which the spectroscopic redshift is obtained from SDSS, and magnitudes and colours are obtained from the Pan-STARRS1 Data Release 2 survey. The photometric redshift of a galaxy is then estimated by means of a local linear regression in a 5D magnitude and colour space. Our approach achieves an average bias of Δ̅z̅n̅o̅r̅m̅ = −1.92 × 10−4, a standard deviation of σ(Δznorm) = 0.0299, and an outlier rate of Po = 4.30% when cross-validating the training set. Even though the relation between each of the Pan-STARRS1 colours and the spectroscopic redshifts is noisier than for SDSS colours, the results obtained by our approach are very close to those yielded by SDSS data. The proposed approach has the additional advantage of allowing the estimation of photometric redshifts on a larger portion of the sky (∼3/4 vs ∼1/3). The training set and the code implementing this approach are publicly available at the project website.

A sample of Fast Radio Bursts discovered and localised with MeerTRAP at the MeerKAT telescope

“…Unfortunately, all four galaxies lack redshift estimates in the literature. We used the data-driven local linear regression technique in a 5D magnitude and colour space developed by Beck et al (2016) for the Sloan Digital Sky Survey DR12 and applied to PS1 DR2 by Tarrío & Zarattini (2020) to estimate photometric redshifts for the host galaxy candidates.…”

“…In particular, we used the PS1 DR2 stack photometry data for the galaxy candidates, i.e. the r -band Kron magnitude and the four Kron colours (g -r, r -i, i -z, z -y), as input for the software and the training data set 10 provided by Tarrío & Zarattini (2020). As shown by those authors, using the Kron colours instead of the aperture colours results in essentially the same redshift estimates.…”

The detection of cluster magnetic fields via radio source depolarisation

“…For sources outside of the Legacy Survey, we calculated the photometric redshift using the Pan-STARRS grizy bands. We followed the method and used the code provided by Tarrío & Zarattini (2020), which estimates redshifts through local linear regression in a five-dimensional colour and magnitude space. The five-dimensional space consists of (r, g-r, r-i, i-z, z-y) where the letters indicate the extinction corrected Kron magnitudes (Kron 1980) of galaxies in the PanSTARRS grizy bands.…”

“…The five-dimensional space consists of (r, g-r, r-i, i-z, z-y) where the letters indicate the extinction corrected Kron magnitudes (Kron 1980) of galaxies in the PanSTARRS grizy bands. The correction for interstellar extinction used the maps from Schlegel et al (1998) and is described in detail in Section 2.3 of Tarrío & Zarattini (2020). To compute the photo- Notes.…”

“…metric redshifts from the Pan-STARRS band, we found the 100 nearest neighbours in the five-dimensional space for each source, from a training set composed of 2 313 724 galaxies with spectroscopic redshifts, constructed by Tarrío & Zarattini (2020). The redshift was computed for all sources where at least four out of five colours were available.…”