Effect of Inclination of Galaxies on Photometric Redshift

TL;DR

This study reveals that galaxy inclination significantly affects photometric redshift accuracy due to reddening and extinction, and proposes correction methods to mitigate this bias.

Contribution

It demonstrates the impact of galaxy inclination on photo-z errors and introduces PCA-based correction techniques for more accurate galaxy property estimation.

Findings

Photo-z bias increases with galaxy inclination.

Inclination can be represented by a principal component resembling an extinction curve.

Correction methods reduce inclination-induced errors in galaxy properties.

Abstract

The inclination of galaxies induces both reddening and extinction to their observed spectral energy distribution, which in turn impact the derived properties of the galaxies. Here we report a significant dependence of the error in photometric redshift (photo-z) on the inclination of disk galaxies from the Sloan Digital Sky Survey. The bias in the photo-z based on the template-fitting approach increases from -0.015 in face-on to 0.021 in edge-on galaxies. A Principal Component Analysis on the full sample of photometry reveals the inclination of the galaxies to be represented by the 2nd mode. The corresponding eigenspectrum resembles an extinction curve. The isolation of the inclination effect in a low-order mode demonstrates the significant reddening induced on the observed colors, leading to the over-estimated photo-z in galaxies of high inclinations. We present approaches to correct the photo-z and the other properties of the disk galaxies against the inclination effect.