Not All Who Wander Are Lost: Early Excess Demographics in the Volume-limited ZTF DR2 SN Ia Sample

Abstract

Early-time flux excesses in Type Ia supernovae (SNe~Ia) offer a unique insight into their progenitor systems and explosion mechanisms. Although individual early-excess events and larger searches have been reported, demographic studies remain limited by sample size. We present a systematic search for early-time excess emission in a volume-limited sample ($z<0.06$) of SNe~Ia based on the Zwicky Transient Facility Data Release 2 (ZTF DR2). Using ZTF $g$- and $r$-band light curves, we identify candidates showing early-excesses shortly after the explosion time, and we apply conservative coverage and quality requirements to build reliable ``excess'' and ``no-excess'' bump and no-bump catalogs. From an initial sample of 1547 SNe~Ia, our final catalogs contain 42 early-excess and 110 no-excess events. We compare the two populations using SN and host environment parameters from ZTF DR2 and quantify the differences using two-sample statistical tests. We find the strongest differences are in SN light-curve properties: early-excess events have larger SALT2 stretch $x_1$ ($7.91\ddot{I}ƒ$) and larger $r$-band secondary-maximum flux ${\mathcal{F}}_{r_2}$ ($6.25\ddot{I}ƒ$), while differences in SALT2 color $c$ are weak ($0.57\ddot{I}ƒ$). Early-excess events also favor bluer $(g-z{)}_{\mathrm{local}}$ ($3.41\ddot{I}ƒ$) and lower ${\log }_{10}(M_{\ast }/M_{\odot }{)}_{\mathrm{local}}$ ($2.73\ddot{I}ƒ$). Our results connect early excesses with SNe~Ia diversity, and motivate further analyses of upcoming larger samples.

Submitted to Research in Astronomy and Astrophysics (RAA). 23 pages, 6 figures, 4 tables (excluding references and appendices); 35 pages total