The Zwicky Transient Facility Bright Transient Survey. I. Spectroscopic Classification and the Redshift Completeness of Local Galaxy Catalogs

Abstract

The Zwicky Transient Facility (ZTF) is performing a three-day cadence survey of the visible northern sky (∼3π) with newly found transient candidates announced via public alerts. The ZTF Bright Transient Survey (BTS) is a large spectroscopic campaign to complement the photometric survey. BTS endeavors to spectroscopically classify all extragalactic transients with m peak 18.5 mag in either the g ZTF or r ZTF filters, and publicly announce said classifications. BTS discoveries are predominantly supernovae (SNe), making this the largest flux-limited SN survey to date. Here we present a catalog of 761SNe, classified during the first nine months of ZTF (2018 April 1-2018 December 31). We report BTS SN redshifts from SN template matching and spectroscopic host-galaxy redshifts when available. We analyze the redshift completeness of local galaxy catalogs, the redshift completeness fraction (RCF; the ratio of SN host galaxies with known spectroscopic redshift prior to SN discovery to the total number of SN hosts). Of the 512 host galaxies with SNe Ia, 227 had previously known spectroscopic redshifts, yielding an RCF estimate of 44%±4%. The RCF decreases with increasing distance and decreasing galaxy luminosity (for z<0.05, or ∼200 Mpc, RCF≈0.6). Prospects for dramatically increasing the RCF are limited to new multifiber spectroscopic instruments or wide-field narrowband surveys. Existing galaxy redshift catalogs are only ∼50% complete at r≈16.9 mag. Pushing this limit several magnitudes deeper will pay huge dividends when searching for electromagnetic counterparts to gravitational wave events or sources of ultra-high-energy cosmic rays or neutrinos.

SN2019dge: A Helium-rich Ultra-stripped Envelope Supernova

“…However, the uncertainty in this experiment is the incompleteness of the input galaxy catalog. The redshift completeness fraction (RCF) is≈80% at the lowest redshifts and decreases to≈50% at z=0.05, as measured by the BTS experiment (Fremling et al 2020).…”

“…For the BTS filter, we use only public survey pointings, and reject SNe at low Galactic latitudes (| |   b 7 ) to be consistent with the BTS experiment (Fremling et al 2020). In either the gor r-band light curve, we identify peak light as the brightest detection in the simulated light curve, and require the following:…”

SN 2020bvc: A Broad-line Type Ic Supernova with a Double-peaked Optical Light Curve and a Luminous X-Ray and Radio Counterpart

“…Double-peaked optical light curves have been observed in all types of stripped-envelope SNe: Ic-BL (with SN 2006aj as the prime example), Type Ic (Taddia et al 2016;De et al 2018), Type Ib (Chevalier & Fransson 2008;Mazzali et al 2008;Modjaz et al 2009), and Type IIb (Arcavi et al 2011;Bersten et al 2012Bersten et al , 2018Fremling et al 2020). The leading explanation for double-peaked light curves in these systems is that the progenitor has a nonstandard structure, with a compact core of mass M c and low-mass material with M e =M c extending out to a large radius R e (Bersten et al 2012;Nakar & Piro 2014;Piro 2015), although Sapir & Waxman (2017) have argued that a nonstandard envelope structure is not required.…”

“…In Figure 17, we show early (<4 days) light curves of five nearby (z  0.05) Ic-BL SNe observed as part of ZTF's highcadence surveys, which were spectroscopically classified as part of the ZTF flux-limited (Fremling et al 2020) and volume-limited (De et al 2019) experiments. The light curves shown are from forced photometry on P48 images (Yao et al 2019), and epochs of spectroscopy are marked with an "S." For the two most luminous events, we show the light curve of SN 2006aj for comparison.…”

Early Ultraviolet Observations of Type IIn Supernovae Constrain the Asphericity of Their Circumstellar Material

“…Note-The three first SNe are those for which we were unable to secure enough spectroscopic data in order to include them in our analysis of the CSM geometry (see § 3.3). SN 2018lpu was discovered and classified by the ZTF survey; SN 2018fdt was discovered by the ATLAS survey on 2018-08-14 as ATLAS18tuy (Tonry et al 2018b), also detected by Gaia surveys as Gaia18chl, classified by ZTF (Fremling et al 2018a); SN 2018gwa was discovered (Fremling 2018) and classified (Fremling et al 2018b) by ZTF, also detected by Gaia on 2018-10-05 as Gaia18cxl; The rest of the SNe in the table are all inclded in our analysis of the CSM geometry. SN 2018bwr was discovered by the ATLAS survey on 2018-05-21 as ATLAS18ppb (Tonry et al 2018a), also detected by PS1 and Gaia surveys as PS18aau and Gaia18bpl, classified by ZTF (Fremling & Sharma 2018); SN 2018kag was discovered by the ASAS-SN survey on 2018-12-17 as ASASSN-18abt and classified by Prentice et al (2018); SN 2019qt was discovered (Nordin et al 2019a) and classified (Payne et al 2019) by ZTF, also detected by ATLAS, Gaia and PS1 as ATLAS19btl, Gaia19aid and PS19ahv; SN 2018lnb was discovered and classified by ZTF (Fremling et al 2019a); SN 2019cac was discovered and classified by ZTF (Fremling 2019a), also detected by ATLAS and PS1 as ATLAS19doj and PS19ym; SN 2019cmy was discovered (Nordin et al 2019b) and classified (Fremling et al 2019b) by ZTF, also detected by ATLAS as ATLAS19elx; SN 2019ctt was discovered by ZTF (Nordin et al 2019c) and classified by SCAT (Tucker et al 2019); SN 2019dnz was discovered by ZTF (Fremling 2019b) and classified by TCD (Prentice et al 2019), also detected by ATLAS as ATLAS19hra; SN 2019dde was discovered by ZTF, classified by ZTF (Fremling et al 2019c) and (Cartier et al 2019), also detected by MASTER and PS1 as MASTER OT J142812.05-013615.2 and PS19aaa.…”