ZTF SN Ia DR2: Overview

TL;DR

This paper introduces the ZTF SN Ia DR2, the largest homogeneous dataset of spectroscopically classified Type Ia supernovae, enabling detailed studies of SN cosmology and diversity with high-quality light curves and spectra.

Contribution

It provides the first large, homogeneous, and well-characterized low-redshift SN Ia dataset from ZTF, including spectroscopic data, light curves, and host properties, facilitating advanced cosmological analyses.

Findings

Largest SN Ia dataset to date with 3628 objects

Demonstrated a 0.15 mag scatter in the Hubble Diagram

Provided a comprehensive dataset for studying SN Ia diversity and standardization

Abstract

We present the first homogeneous release of several thousand Type Ia supernovae (SNe Ia), all having spectroscopic classification, and spectroscopic redshifts for half the sample. This release, named the "DR2", contains 3628 nearby (z < 0.3) SNe Ia discovered, followed and classified by the Zwicky Transient Facility survey between March 2018 and December 2020. Of these, 3000 have good-to-excellent sampling and 2667 pass standard cosmology light-curve quality cuts. This release is thus the largest SN Ia release to date, increasing by an order of magnitude the number of well characterized low-redshift objects. With the "DR2", we also provide a volume-limited (z < 0.06) sample of nearly a thousand SNe Ia. With such a large, homogeneous and well controlled dataset, we are studying key current questions on SN cosmology, such as the linearity SNe Ia standardization, the SN and host dependencies, the diversity of the SN Ia population, and the accuracy of the current light-curve modeling. These, and more, are studied in detail in a series of articles associated with this release. Alongside the SN Ia parameters, we publish our force-photometry gri-band light curves, 5138 spectra, local and global host properties, observing logs, and a python tool to ease use and access of these data. The photometric accuracy of the "DR2" is not yet suited for cosmological parameter inference, which will follow as "DR2.5" release. We nonetheless demonstrate that the multi-thousand SN Ia Hubble Diagram has a typical 0.15 mag scatter.