See Change : VLT spectroscopy of a sample of high-redshift Type Ia supernova host galaxies

Williams, S. C. and Hook, I. M. and Hayden, B. and Nordin, Jakob and Aldering, G. and Boone, K. and Goobar, A. and Lidman, C. E. and Perlmutter, S. and Rubin, David and Ruiz-Lapuente, P. and Saunders, C. (2020) See Change : VLT spectroscopy of a sample of high-redshift Type Ia supernova host galaxies. Monthly Notices of the Royal Astronomical Society, 495 (4). pp. 3859-3880. ISSN 0035-8711

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Abstract

The Supernova Cosmology Project has conducted the `See Change' programme, aimed at discovering and observing high-redshift (1.13 $\leq$ z $\leq$ 1.75) Type Ia supernovae (SNe Ia). We used multi-filter Hubble Space Telescope (HST) observations of massive galaxy clusters with sufficient cadence to make the observed SN Ia light curves suitable for a cosmological probe of dark energy at z > 0.5. As part of the See Change programme, we obtained ground-based spectroscopy of each discovered transient and/or its host galaxy. Here we present Very Large Telescope (VLT) spectra of See Change transient host galaxies, deriving their redshifts, and host parameters such as stellar mass and star formation rate. Of the 39 See Change transients/hosts that were observed with the VLT, we successfully determined the redshift for 26, including 15 SNe Ia at z > 0.97. This new sample of SNe Ia with multi-colour light curves is the largest to date at these redshifts. We show that even in passive environments, it is possible to recover secure redshifts for the majority of SN hosts out to z = 1.5. We find that with typical exposure times of 3 - 4 hrs on an 8m-class telescope we can recover ~75% of SN Ia redshifts in the range of 0.97 <z <1.5. Furthermore, we show that the combination of HST photometry and VLT spectroscopy is able to provide estimates of host galaxy stellar mass that are sufficiently accurate for use in a mass-step correction in the cosmological analysis.