Measuring Cosmological Parameters with Type Ia Supernovae in redMaGiC Galaxies

Abstract

Current and future cosmological analyses with Type Ia supernovae (SNe Ia) face three critical challenges: (i) measuring the redshifts from the SNe or their host galaxies; (ii) classifying the SNe without spectra; and (iii) accounting for correlations between the properties of SNe Ia and their host galaxies. We present here a novel approach that addresses each of these challenges. In the context of the Dark Energy Survey (DES), we analyze an SN Ia sample with host galaxies in the redMaGiC galaxy catalog, a selection of luminous red galaxies. redMaGiC photo-z estimates are expected to be accurate to σ Δz/(1+z) ∼ 0.02. The DES-5YR photometrically classified SN Ia sample contains approximately 1600 SNe, and 125 of these SNe are in redMaGiC galaxies. We demonstrate that redMaGiC galaxies almost exclusively host SNe Ia, reducing concerns relating to classification uncertainties. With this subsample, we find similar Hubble scatter (to within ∼0.01 mag) using photometric redshifts in place of spectroscopic redshifts. With detailed simulations, we show that the bias due to using redMaGiC photo-zs on the measurement of the dark energy equation of state w is up to Δw ∼ 0.01–0.02. With real data, we measure a difference in w when using the redMaGiC photo-zs versus the spec-zs of Δw = 0.005. Finally, we discuss how SNe in redMaGiC galaxies appear to comprise a more standardizable population, due to a weaker relation between color and luminosity (β) compared to the DES-3YR population by ∼5σ. These results establish the feasibility of performing redMaGiC SN cosmology with photometric survey data in the absence of spectroscopic data.

Connecting Infrared Surface Brightness Fluctuation Distances to Type Ia Supernova Hosts: Testing the Top Rung of the Distance Ladder

“…Brout & Scolnic (2021) have argued that this is due to changes in dust properties with increasing galaxy mass. A recent study by Chen et al (2022) suggests that the relation between color and luminosity for SNe Ia found in massive passive hosts is flatter than seen in star-forming galaxies.…”

Designing an Optimal LSST Deep Drilling Program for Cosmology with Type Ia Supernovae

“…Cosmological measurements from SN surveys have historically been achieved with host galaxy spectroscopic redshift measurements (see, e.g., Scolnic et al 2018a;Abbott et al 2019;Brout et al 2022). A recent study (Chen et al 2022) has shown the feasibility of performing SN cosmology using photo-z. Using a set of 125 photometrically classified SNe Ia located in luminous red galaxies with photo-z accuracy similar to the LSST minimal target, a difference in Δw versus spectroscopic redshifts of about 0.005 was found in data and a difference of 0.01-0.02 was found in simulations.…”

Further evidence that galaxy age drives observed type Ia supernova luminosity differences

“…For example, a difference in the mean totalto-selective extinction ratio (𝑅 𝑉 ) such that mean 𝑅 𝑉 = 2.0 in lowmass galaxies and 𝑅 𝑉 = 3.0 in high-mass galaxies can reduce the mass step to ∼ 0.02 mag (Popovic et al 2021a). Such a difference in 𝑅 𝑉 can explain the observed difference in the colour-luminosity coefficient 𝛽 between SNe Ia in low and high mass host galaxies (Sullivan et al 2011;González-Gaitán et al 2021;Chen et al 2022;Kelsey et al 2022), and also account for the observed increase in the step size as a function of SN colour (Brout & Scolnic 2020;Popovic et al 2021a;Kelsey et al 2022) as well as the increase in SN Ia luminosity dispersion as a function of SN colour (Brout & Scolnic 2020;Popovic et al 2021a). Wiseman et al (2022, hereafter W22) explored variations of the Brout & Scolnic (2020) model by simulating the stellar age distributions of galaxies and the delay-time distributions (DTDs) of SNe Ia.…”