COOL-LAMPS. VI. Lens Model and New Constraints on the Properties of COOL J1241+2219, a Bright z = 5 Lyman Break Galaxy and its z = 1 Cluster Lens

We present a strong lensing analysis of COOL J1241+2219, the brightest known gravitationally lensed galaxy at z ≥ 5, based on new multiband Hubble Space Telescope (HST) imaging data. The lensed galaxy has a redshift of z = 5.043, placing it shortly after the end of the “Epoch of Reionization,” and an AB magnitude z AB = 20.47 mag (Khullar et al.). As such, it serves as a touchstone for future research of that epoch. The high spatial resolution of HST reveals internal structure in the giant arc, from which we identify 15 constraints and construct a robust lens model. We use the lens model to extract the cluster mass and lensing magnification. We find that the mass enclosed within the Einstein radius of the z = 1.001 cluster lens is M(<5.″77)=1.079−0.007+0.023×1013M☉ , significantly lower than other known strong lensing clusters at its redshift. The average magnification of the giant arc is 〈μ arc〉 = 76−20+40 , a factor of 2.4−0.7+1.4 greater than previously estimated from ground-based data; the flux-weighted average magnification is 〈μ arc〉 = 92−31+37 . We update the current measurements of the stellar mass and star formation rate (SFR) of the source for the revised magnification to log(M⋆/M⊙)= 9.7 ± 0.3 and SFR = 10.3−4.4+7.0 M ⊙ yr−1, respectively. The powerful lensing magnification acting upon COOL J1241+2219 resolves the source and enables future studies of the properties of its star formation on a clump-by-clump basis. The lensing analysis presented here will support upcoming multiwavelength characterization with HST and JWST data of the stellar mass assembly and physical properties of this high-redshift lensed galaxy

The Most Rapidly Declining Type I Supernova 2019bkc/ATLAS19dqr

We report observations of the hydrogen-deficient supernova (SN) 2019bkc/ATLAS19dqr. With B- and r-band decline between peak and 10 days post peak of Dm10 (B) = 5.24. 0.07 mag and Dm10 (r) = 3.85. 0.10 mag, respectively, SN.2019bkc is the most rapidly declining SN I discovered so far. While its closest matches are the rapidly declining SN.2005ek and SN. 2010X, the light curves and spectra of SN.2019bkc show some unprecedented characteristics. SN.2019bkc appears "hostless," with no identifiable host galaxy near its location, although it may be associated with the galaxy cluster MKW1 at z.=.0.02. We evaluate a number of existing models of fast-evolving SNe, and we find that none of them can satisfactorily explain all aspects of SN.2019bkc observations

Dependence of Cosmological Constraints on Gray Photometric Zero-point Uncertainties of Supernova Surveys

Type Ia supernova (SN) measurements of the Hubble constant, H _0 ; cosmic mass density, Ω _M ; and dark energy equation-of-state parameter, w , rely on heterogeneous SN surveys across three decades of observation. These distinct surveys may have undiagnosed, relative photometric zero-point errors. We determine the sensitivities of the SH0ES+Pantheon+ cosmological constraints to unknown gray systematics in the photometric zero-point calibration between the 19 surveys that comprise the Pantheon+ SN compendium. Varying the surveys’ gray zero-points simultaneously with cosmological parameters, we determine that the SH0ES+Pantheon+ measurement of H _0 is robust against gray intersurvey photometric miscalibration. Specifically, uncalibrated intersurvey systematics could represent a source of uncertainty no larger than 0.39 km s ^−1 Mpc ^−1 for H _0 . This modest increase in H _0 uncertainty could not account for the 7 km s ^−1 Mpc ^−1 “Hubble tension” between the SH0ES measurement of H _0 and the Planck ΛCDM-based inference of H _0 . However, the SH0ES+Pantheon+ best-fit values of Ω _M and w are not robust against gray zero-point error, slipping by up to 0.16 and −0.63. Because measurements of Ω _M and w depend on intrasurvey cross-band calibration, the hypothetical gray miscalibration underestimates the sensitivity of these measurements to zero-point miscalibration. Because the Pantheon+ compendium contains many surveys that share low- z Hubble flow (HF) and Cepheid-paired SNe, intersurvey photometric calibration errors do not significantly impede the joint use of SH0ES and Pantheon+ to measure H _0 to 1% accuracy. However, H _0 constraints that rely on one HF survey but numerous galactic distance calibration surveys are susceptible to intersurvey photometric miscalibration

Measurement of telescope transmission using a Collimated Beam Projector

International audienceThe number of type Ia supernova observations will see a significant growth within the next decade, especially thanks to the Legacy Survey of Space and Time undertaken by the Vera Rubin Observatory in Chile. With this rise, the statistical uncertainties will decrease and the flux calibration will become the main uncertainty for the characterization of dark energy. The uncertainty over the telescope transmission is a major systematic when measuring SNe Ia colors. Here we introduce the Collimated Beam Projector (CBP), a device that can measure the transmission of a telescope and its filters. Composed of a tunable monochromatic light source and optics to provide a parallel output beam this device is able to measure with high precision the filter transmissions. In the following, we will show how measuring precisely a telescope transmission can also improve the precision of the dark energy parameters. As an example, we will present the first results of the CBP in the context of the StarDice experiment

Measurement of telescope transmission using a Collimated Beam Projector

International audienceThe number of type Ia supernova observations will see a significant growth within the next decade, especially thanks to the Legacy Survey of Space and Time undertaken by the Vera Rubin Observatory in Chile. With this rise, the statistical uncertainties will decrease and the flux calibration will become the main uncertainty for the characterization of dark energy. The uncertainty over the telescope transmission is a major systematic when measuring SNe Ia colors. Here we introduce the Collimated Beam Projector (CBP), a device that can measure the transmission of a telescope and its filters. Composed of a tunable monochromatic light source and optics to provide a parallel output beam this device is able to measure with high precision the filter transmissions. In the following, we will show how measuring precisely a telescope transmission can also improve the precision of the dark energy parameters. As an example, we will present the first results of the CBP in the context of the StarDice experiment