Rubin-LSST

Abstract:

We study the projected clustering of photometric luminous red galaxies from the DESI Legacy Survey, combining their angular power spectrum, bispectrum, and cross-correlation with maps of the CMB lensing convergence from the Planck satellite. We employ a perturbative bias expansion in Eulerian space to describe the clustering of galaxies, modelling the power spectrum and bispectrum at one-loop and tree level, respectively. This allows us to use the bispectrum to self-consistently calibrate the perturbative bias parameters. We validate this model against an N-body simulation, and show that it can be used up to scales of at least kP max ≃ 0.2 h Mpc-1 and kB max ≃ 0.08 h Mpc-1, saturating the information recovered from the data. We obtain constraints on the amplitude of matter fluctuations σ 8 = 0.761 ± 0.020 and the non-relativistic matter fraction Ω m = 0.307 ± 0.015, as well as the combination S 8 ≡ σ 8 √(Ω m /0.3) = 0.769 ± 0.020. Including the galaxy bispectrum leads to a 10–20% improvement on the cosmological constraints, which are also in good agreement with previous analyses of the same data, and in mild tension with Planck at the ∼2.5σ level. Finally, using the bispectrum allows for a substantially more precise measurement of the bias parameters of this sample, which are in reasonable agreement with existing coevolution relations.

Abstract:

Type Ia supernovae are a cornerstone of modern cosmology, providing first evidence for cosmic acceleration and new tests of dark energy. Son et al. (S25) claim a strong redshift evolution in standardized supernova luminosities driven by supernova progenitor age, with dramatic cosmological implications: rapidly evolving dark energy, decelerating expansion, and a tension with CDM. We show that the underpinning evidence required for this conclusion – the supernova progenitor-age dependence, the redshift-dependent age difference, and their combined impact – is either negligible or relies on effects already corrected for in modern supernova analyses. First, the S25 analysis omits the standard host-galaxy stellar mass correction that captures known environmental dependencies that also correlate with stellar age. Applying this correction to the S25 sample, we find no dependence of standardized supernova brightness on host age. Independent data also show no significant difference at low-redshift in standardized brightness between star-forming galaxies and several Gyr older quiescent galaxies of the same stellar mass. Secondly, the S25 scenario predicts strong redshift evolution of the host-mass effect. Data from the Dark Energy Survey supernova survey measure evolution of , consistent with zero and altering the dark-energy equation-of-state measurement (w) by <0.01 if included. Thirdly, we demonstrate that the claimed Gyr progenitor age difference between nearby and distant supernovae is overstated by factors of three to five largely due to a conflation of host galaxy age with supernova progenitor age. We conclude that type Ia supernova cosmology remains robust for current measurements of dark energy.

Abstract:

We present SNID–SAGE (SuperNova IDentification–Spectral Analysis and Guided Exploration), a framework for supernova spectral classification with both a fully interactive graphical interface and a scriptable command-line pipeline for large-scale processing. The pipeline combines deterministic spectral pre-processing, FFT-based cross-correlation against a curated template library, ranking of candidate matches using a composite quality metric, and consolidation of redshift and classification solutions into a single result with associated quality and confidence estimates. SNID–SAGE includes an upgradeable template library (about 6000 spectra), interactive line identification with velocity measurements, and optional natural-language summaries of classification results. We evaluate SNID–SAGE using two complementary tests: (i) Leave-one-out cross-validation, in which each template spectrum is matched against the remainder of the library; and (ii) large-scale application to WISeREP spectra with valid coverage across the 4000–7000 Å interval, irrespective of spectral type, comprising approximately 46 000 spectra, with redshift validation against known host-galaxy measurements where available. The full validation results and the SNID–SAGE framework are publicly available, supporting integration into spectroscopic survey workflows.