NEXUS: Transient Searches and First Results from Year One Observations

Abstract

We describe ongoing efforts of high-redshift transient searches using multi-epoch NIRCam imaging (F200W+F444W) and NIRSpec MSA/PRISM spectroscopy from the NEXUS JWST multi-cycle Treasury program targeting the north ecliptic pole region. The transient search area covers $\sim 61.5\mathrm{arcmi}{\mathrm{n}}^2$ between the reference epoch and each subsequent NEXUS-Deep epoch at a cadence of $\sim 2$~months. In the first year of observations from NEXUS, we detect 68 robust transients, with the host photometric redshift distribution declining rapidly at $z>2$ but extending to $z_{\mathrm{phot}}\approx 6$. In addition, we obtained secure spectroscopic redshifts for 37 transients ($\sim 54\%$) from NIRSpec/PRISM and NIRCam/WFSS, with seventeen at $1<z<2$, eight at $2<z<3$, two at $3<z<4$, and one tentative host association at z = 6.151. Overall, the NEXUS program recovers observed supernova (SN) rates broadly consistent with other SN search programs with JWST. While NEXUS achieves the highest transient detection efficiency, 6.6 SNe per imaging hr ($2.6\times$ COSMOS-SN and $26\times$ JADES-SN), the limited filter coverage (F200W+F444W only) limits robust identification and classification of high-$z$ SNe for deep spectroscopic follow-up. We describe the details of the data reduction and transient detection pipeline, and report the Year-1 transient sample along with their light curves, available MSA spectroscopy, host association, and the raw detection rate. We also describe and release a new PSF photometry package that properly accounts for correlated pixel noise from combining drizzled images.

35 pages, 19 figures, 5 tables. The jwst_psfmc package, designed to account for correlated noise in PSF photometry on drizzled images, is available at https://github.com/mingyangzhuang/jwst_psfmc