James Webb Space Telescope Feed Post

The JWST Discovery of the Triply-imaged Type Ia "Supernova H0pe" and Observations of the Galaxy Cluster PLCK G165.7+67.0

The Arc 1a galaxy group at z ~ 2.2. Photometric redshift fits identify a compact galaxy overdensity at z ~ 2.2 that surrounds the spectroscopically confirmed Arcs 1a and NS 46 consisting of a total of 6 objects. These include the multiply imaged Arcs 3, 4, 6, and 15, as well a singly imaged lensed galaxy located only 20 kpc away from Arc 1a and NS 46. Each galaxy exhibits a highly clumpy morphology consistent with cosmic-noon starbursts, and if their redshifts are correct, they may be interacting given their ~20 kpc physical separations (after demagnification according to our lens model). Abstract: A Type Ia supernova (SN) at z=1.78 was discovered in James Webb Space Telescope Near Infrared Camera imaging of the galaxy cluster PLCK G165.7+67.0 (G165; z=0.35). The SN is situated 1.5-2kpc from its host galaxy Arc 2 and appears in three different locations as a result of gravitational lensing by G165. These data can yield a value for Hubble's constant using time delays from this multiply-imaged SN Ia that we call "SN H0pe." Over the entire field we identified 21 image multiplicities, confirmed five of them using Near-Infrared Spectrograph (NIRspec), and constructed a new lens model that gives a total mass within 600kpc of (2.6±0.3)×1014 M?. The photometry uncovered a galaxy overdensity at Arc 2's redshift. NIRSpec confirmed six member galaxies, four of which surround Arc 2 with relative velocity ?900 km s-1 and projected physical extent ?33 kpc. Arc 2 dominates the stellar mass ((5.0±0.1)×1011 M?), which is a factor of ten higher than other members of this compact galaxy group. These other group members have specific star formation rates (sSFR) of 2-260Gyr-1 derived from the Ha-line flux corrected for stellar absorption, dust extinction, and slit losses. Another group centered on the dusty star forming galaxy Arc 1 is at z=2.24. The total SFR for the Arc 1 group (gtrsim M? yr-1) translates to a supernova rate of ~1 SNe yr-1, suggesting that regular monitoring of this cluster may yield additional SNe.