The Zwicky Transient Facility: Science Objectives

TL;DR

The paper presents the Zwicky Transient Facility (ZTF) as a fast, wide-field, 1-m class time-domain survey designed to simulate LSST-scale science on a smaller footprint. It details the hardware, data pipelines, and real-time alert system that enable ambitious programs across supernova physics, multi-messenger astrophysics, cosmology, AGN/TDEs, stellar variability, and small Solar System bodies. It outlines concrete science objectives, anticipated event rates, and the observational cadences needed to achieve them, along with downstream follow-up and astroinformatics needs. The work positions ZTF as a crucial stepping stone to LSST, providing infrastructure, cadence strategies, and a public alert stream that will catalyze community-led discoveries and method development in time-domain astronomy.

Abstract

The Zwicky Transient Facility (ZTF), a public-private enterprise, is a new time domain survey employing a dedicated camera on the Palomar 48-inch Schmidt telescope with a 47 deg$^2$ field of view and 8 second readout time. It is well positioned in the development of time domain astronomy, offering operations at 10% of the scale and style of the Large Synoptic Survey Telescope (LSST) with a single 1-m class survey telescope. The public surveys will cover the observable northern sky every three nights in g and r filters and the visible Galactic plane every night in g and r. Alerts generated by these surveys are sent in real time to brokers. A consortium of universities which provided funding ("partnership") are undertaking several boutique surveys. The combination of these surveys producing one million alerts per night allows for exploration of transient and variable astrophysical phenomena brighter than r $\sim$ 20.5 on timescales of minutes to years. We describe the primary science objectives driving ZTF including the physics of supernovae and relativistic explosions, multi-messenger astrophysics, supernova cosmology, active galactic nuclei and tidal disruption events, stellar variability, and Solar System objects.

Figures (7)

• Figure 1: A collection of flash spectra from iPTF, showing the differing composition of the CSM around core-collapse SNe.
• Figure 2: $r'-i'$ colour distribution of 500 PTF/iPTF core-collapse SN host galaxies, SLSN host galaxies and galaxies from the UltraVISTA survey. The top panel shows the cumulative distribution for all samples at $z<0.7$. SLSN hosts are found in a part of the parameter space that is sparsely populated by galaxies, in general. The average host of an H-poor/-rich SLSN is 0.2/0.15 mag bluer than that of a regular core-collapse SN. Hence, host galaxy properties could be used to identify infant SLSNe in the ZTF alert stream. Figure adapted from Schulze et al., in prep.
• Figure 3: Light curves from the candidate on-axis dirty fireball PTF11agg and the low-luminosity GRB 060218 / Ic-BL SN 2006aj. The rapid decay of PTF11agg is attributed to on-axis fading afterglow. The rise and fade of of SN 2006aj at early times is likely due to shock cooling emission of SN ejecta.
• Figure 4: Redshift distribution of the 2000 expected SN Ia cosmology spectroscopic sample, where the upper redshift limit $z=0.1$ is chosen to mitigate the impact from Malmquist bias. Only supernovae discovered >10 days prior to lightcurve maximum are included.
• Figure 5: Noiseless $6^{\prime\prime}\times6^{\prime\prime}$ composite $gri$ images of 6 simulated gLSNe, their lens galaxies, and their lensed host galaxies, "detected" by ZTF in the simulations of 2018arXiv180910147G. Each image is "taken" exactly one night after the transient is detected as a gLSN candidate based on a light curve fit to the simulated ZTF data. The FWHM of the seeing on the images is $0.1^{\prime\prime}$, and the pixel scale is $0.04^{\prime\prime}$, identical to that of the UVIS channel of the Wide Field Camera 3 (WFC3) on HST.