Using 4MOST to refine the measurement of galaxy properties: A case study of Supernova hosts

TL;DR

This study demonstrates that combining Rubin Observatory photometry with 4MOST spectroscopy significantly improves the accuracy of galaxy property measurements, enhancing supernova classification and cosmological analyses.

Contribution

The paper quantifies how supplementing Rubin photometry with 4MOST spectroscopy reduces uncertainties in galaxy stellar mass measurements, benefiting supernova studies.

Findings

Combining Rubin and 4MOST data halves the uncertainty in galaxy stellar mass for bright galaxies.

Improved mass measurements lead to a 7% enhancement in supernova 'mass step' correction accuracy.

The approach benefits the classification of supernovae and their use as standard candles.

Abstract

The Rubin Observatory's 10-year Legacy Survey of Space and Time will observe near to 20 billion galaxies. For each galaxy the properties can be inferred. Approximately $10^5$ galaxies observed per year will contain Type Ia supernovae (SNe), allowing SN host-galaxy properties to be calculated on a large scale. Measuring the properties of SN host-galaxies serves two main purposes. The first is that there are known correlations between host-galaxy type and supernova type, which can be used to aid in the classification of SNe. Secondly, Type Ia SNe exhibit correlations between host-galaxy properties and the peak luminosities of the SNe, which has implications for their use as standardisable candles in cosmology. We have used simulations to quantify the improvement in host-galaxy stellar mass ($M_\ast$) measurements when supplementing photometry from Rubin with spectroscopy from the 4-metre Multi-Object Spectroscopic Telescope (4MOST) instrument. We provide results in the form of expected uncertainties in $M_\ast$ for galaxies with 0.1 < $z$ < 0.9 and 18 < $r_{AB}$ < 25. We show that for galaxies mag 22 and brighter, combining Rubin and 4MOST data reduces the uncertainty measurements of galaxy $M_\ast$ by more than a factor of 2 compared with Rubin data alone. This applies for elliptical and Sc type hosts. We demonstrate that the reduced uncertainties in $M_\ast$ lead to an improvement of 7\% in the precision of the "mass step" correction. We expect our improved measurements of host-galaxy properties to aid in the photometric classification of SNe observed by Rubin.