arXiv subjects

Louis G. Strolger

Publications and source records attributed to Louis G. Strolger.

3 recordsLinked to original sources

arXiv2025

Revisiting the Mass Step: Environmental Dependence of Type Ia Supernovae in Low-Metallicity Host Galaxies

Despite the tremendous impact of Type Ia supernovae (SNe Ia) on the field of cosmology, their underlying physics are still poorly understood. Studies have found an intriguing correlation between standardized Type Ia supernova (SN Ia) luminosities and host galaxy masses, commonly referred to as the "mass step". SNe Ia in massive galaxies appear systematically brighter than in lower-mass, star-forming hosts after standardization. However, previous analyses use host galaxy mass estimates derived largely from optical data alone and assume parametric forms for host star formation histories (SFHs), both of which are known to misestimate galaxy stellar masses. In this work, we re-examine the mass-step relation with a sample of SN Ia host galaxies complete in broadband optical (3000 Angstrom to 1 micron) and near-infrared (up to 1.8 micron) data, and in some cases including mid-infrared observations (up to 4.5 micron), using Prospector to derive nonparametric SFHs. We find that while the masses for these galaxies have indeed been underestimated, the overall trend in SN Ia luminosity versus host mass remains largely unchanged. We also uncover an environmental metallicity-dependent trend, in which low-metallicity galaxies (Z < -1 Zsol) may drive much of the observed SN Ia luminosity-mass correlation, suggesting that the chemical composition of the SN environment plays a central role in shaping the standardized brightness of SNe Ia.

astro-ph.CO↗

arXiv2014

Three Gravitationally Lensed Supernovae Behind CLASH Galaxy Clusters

We report observations of three gravitationally lensed supernovae (SNe) in the Cluster Lensing And Supernova survey with Hubble (CLASH) Multi-Cycle Treasury program. These objects, SN CLO12Car (z = 1.28), SN CLN12Did (z = 0.85), and SN CLA11Tib (z = 1.14), are located behind three different clusters, MACSJ1720.2+3536 (z = 0.391), RXJ1532.9+3021 (z = 0.345), and Abell 383 (z = 0.187), respectively. Each SN was detected in Hubble Space Telescope (HST) optical and infrared images. Based on photometric classification, we find that SNe CLO12Car and CLN12Did are likely to be Type Ia supernovae (SNe Ia), while the classification of SN CLA11Tib is inconclusive. Using multi-color light-curve fits to determine a standardized SN Ia luminosity distance, we infer that SN CLO12Car was approximately 1.0 +/- 0.2 mag brighter than field SNe Ia at a similar redshift and ascribe this to gravitational lens magnification. Similarly, SN CLN12Did is approximately 0.2 +/- 0.2 mag brighter than field SNe Ia. We derive independent estimates of the predicted magnification from CLASH strong+weak lensing maps of the clusters: 0.83 +/- 0.16 mag for SN CLO12Car, 0.28 +/- 0.08 mag for SN CLN12Did, and 0.43 +/- 0.11 mag for SN CLA11Tib. The two SNe Ia provide a new test of the cluster lens model predictions: we find that the magnifications based on the SN Ia brightness and those predicted by the lens maps are consistent. Our results herald the promise of future observations of samples of cluster-lensed SNe Ia (from the ground or space) to help illuminate the dark-matter distribution in clusters of galaxies, through the direct determination of absolute magnifications.

astro-ph.CO↗

arXiv2012

Evidence for Type Ia Supernova Diversity from Ultraviolet Observations with the Hubble Space Telescope

We present ultraviolet (UV) spectroscopy and photometry of four Type Ia supernovae (SNe 2004dt, 2004ef, 2005M, and 2005cf) obtained with the UV prism of the Advanced Camera for Surveys on the Hubble Space Telescope. This dataset provides unique spectral time series down to 2000 Angstrom. Significant diversity is seen in the near maximum-light spectra (~ 2000--3500 Angstrom) for this small sample. The corresponding photometric data, together with archival data from Swift Ultraviolet/Optical Telescope observations, provide further evidence of increased dispersion in the UV emission with respect to the optical. The peak luminosities measured in uvw1/F250W are found to correlate with the B-band light-curve shape parameter dm15(B), but with much larger scatter relative to the correlation in the broad-band B band (e.g., ~0.4 mag versus ~0.2 mag for those with 0.8 < dm15 < 1.7 mag). SN 2004dt is found as an outlier of this correlation (at > 3 sigma), being brighter than normal SNe Ia such as SN 2005cf by ~0.9 mag and ~2.0 mag in the uvw1/F250W and uvm2/F220W filters, respectively. We show that different progenitor metallicity or line-expansion velocities alone cannot explain such a large discrepancy. Viewing-angle effects, such as due to an asymmetric explosion, may have a significant influence on the flux emitted in the UV region. Detailed modeling is needed to disentangle and quantify the above effects.

astro-ph.HE↗