arXiv subjects

Yukei Murakami

Publications and source records attributed to Yukei Murakami.

4 recordsLinked to original sources

arXiv2026

Old Universe, Young SNe Ia: A Statistical Analysis of Type Ia Supernova Progenitor Age from 6,983 TITAN Host Galaxies, and Implications for Cosmology

Correlations between standardized Type Ia supernova (SN Ia) luminosities and host-galaxy properties are routinely modeled to avoid bias in cosmological parameter inference. A recent hypothesis attributes these correlations to progenitor-age variations and, combined with a strong ($\sim$5-6 Gyr) age evolution between low- and high-redshift samples, could alter cosmological conclusions. We test this scenario using the SN Ia host galaxies of TITAN DR1, the largest low-redshift sample of its kind to date (6,983 hosts; 0 $\lesssim$ z $\lesssim$ 0.15). Progenitor ages are estimated by combining host-galaxy star-formation histories (SFHs) with empirical delay-time distributions. The SFHs are constrained via spectral energy distribution (SED) fitting of photometry spanning ultraviolet (UV) to mid-infrared (MIR) wavelengths, enabling robust separation of dusty star-forming and quiescent systems. The resulting progenitor-age distribution has a mean of 3.5 Gyr, substantially younger than predicted by strong-evolution models. It is strongly peaked near 2.2 Gyr, predominantly from star-forming hosts (60% of the sample), with a smaller, broader component centered near 6.0 Gyr from quiescent systems. Restricting to high-mass galaxies (in order to isolate progenitor effects from the mass-step), the age difference between host types reduces to 3.3 Gyr which, under the age-dependence hypothesis, would imply a 0.10 mag luminosity offset, inconsistent with observed standardized magnitudes. We infer a modest 1.5 Gyr evolution in mean progenitor age over cosmic time which, combined with observed age-Hubble-residual (HR) relations, yields a maximum redshift-dependent bias of $\Delta$HR = $-0.007^{+0.012}_{-0.014}$ mag, consistent with zero. We find no evidence for a large, unmodeled progenitor-age systematic beyond what is already captured, to good approximation, by standard host-mass corrections.

astro-ph.CO↗

arXiv2025

The CosmoVerse White Paper: Addressing observational tensions in cosmology with systematics and fundamental physics

The standard model of cosmology has provided a good phenomenological description of a wide range of observations both at astrophysical and cosmological scales for several decades. This concordance model is constructed by a universal cosmological constant and supported by a matter sector described by the standard model of particle physics and a cold dark matter contribution, as well as very early-time inflationary physics, and underpinned by gravitation through general relativity. There have always been open questions about the soundness of the foundations of the standard model. However, recent years have shown that there may also be questions from the observational sector with the emergence of differences between certain cosmological probes. In this White Paper, we identify the key objectives that need to be addressed over the coming decade together with the core science projects that aim to meet these challenges. These discordances primarily rest on the divergence in the measurement of core cosmological parameters with varying levels of statistical confidence. These possible statistical tensions may be partially accounted for by systematics in various measurements or cosmological probes but there is also a growing indication of potential new physics beyond the standard model. After reviewing the principal probes used in the measurement of cosmological parameters, as well as potential systematics, we discuss the most promising array of potential new physics that may be observable in upcoming surveys. We also discuss the growing set of novel data analysis approaches that go beyond traditional methods to test physical models. [Abridged]

astro-ph.CO↗

arXiv2023

A Low-Mass Helium Star Progenitor Model for the Type Ibn SN 2020nxt

A growing number of supernovae (SNe) are now known to exhibit evidence for significant interaction with a dense, pre-existing, circumstellar medium (CSM). SNe Ibn comprise one such class that can be characterised by both rapidly evolving light curves and persistent narrow He I lines. The origin of such a dense CSM in these systems remains a pressing question, specifically concerning the progenitor system and mass-loss mechanism. In this paper, we present multi-wavelength data of the Type Ibn SN 2020nxt, including $HST$/STIS ultraviolet spectra. We fit the data with recently updated CMFGEN models designed to handle configurations for SNe Ibn. The UV coverage yields strong constraints on the energetics and, when combined with the CMFGEN models, offer new insight on potential progenitor systems. We find the most successful model is a $\lesssim4 {\rm M}_\odot$ helium star that lost its $\sim 1\,{\rm M}_\odot$ He-rich envelope in the years preceding core collapse. We also consider viable alternatives, such as a He white dwarf merger. Ultimately, we conclude at least some SNe Ibn do not arise from single, massive ($>30 {\rm M}_\odot$) Wolf-Rayet-like stars.

astro-ph.HE↗

arXiv2022

A Comprehensive Measurement of the Local Value of the Hubble Constant with 1 km/s/Mpc Uncertainty from the Hubble Space Telescope and the SH0ES Team

We report observations from HST of Cepheids in the hosts of 42 SNe Ia used to calibrate the Hubble constant (H0). These include all suitable SNe Ia in the last 40 years at z<0.01, measured with >1000 orbits, more than doubling the sample whose size limits the precision of H0. The Cepheids are calibrated geometrically from Gaia EDR3 parallaxes, masers in N4258 (here tripling that Cepheid sample), and DEBs in the LMC. The Cepheids were measured with the same WFC3 instrument and filters (F555W, F814W, F160W) to negate zeropoint errors. We present multiple verifications of Cepheid photometry and tests of background determinations that show measurements are accurate in the presence of crowding. The SNe calibrate the mag-z relation from the new Pantheon+ compilation, accounting here for covariance between all SN data, with host properties and SN surveys matched to negate differences. We decrease the uncertainty in H0 to 1 km/s/Mpc with systematics. We present a comprehensive set of ~70 analysis variants to explore the sensitivity of H0 to selections of anchors, SN surveys, z range, variations in the analysis of dust, metallicity, form of the P-L relation, SN color, flows, sample bifurcations, and simultaneous measurement of H(z). Our baseline result from the Cepheid-SN sample is H0=73.04+-1.04 km/s/Mpc, which includes systematics and lies near the median of all analysis variants. We demonstrate consistency with measures from HST of the TRGB between SN hosts and NGC 4258 with Cepheids and together these yield 72.53+-0.99. Including high-z SN Ia we find H0=73.30+-1.04 with q0=-0.51+-0.024. We find a 5-sigma difference with H0 predicted by Planck+LCDM, with no indication this arises from measurement errors or analysis variations considered to date. The source of this now long-standing discrepancy between direct and cosmological routes to determining the Hubble constant remains unknown.

astro-ph.CO↗