Carnegie Supernova Project: Fast-Declining Type Ia Supernovae as Cosmological Distance Indicators

TL;DR

This study demonstrates that fast-declining Type Ia SNe Ia, when characterized with the color-stretch parameter $s_{BV}$ or even purely by their maximum-light color $(B_{ m max}-V_{ m max})$, can serve as reliable cosmological distance indicators. Using a CSP Hubble Flow sample of 54 fast decliners and 12 IR SBF-calibrated SNe, the authors apply both the Tripp method and a novel Color method to estimate the Hubble constant, finding consistent $H_0$ values around 75.5–76.7 km s$^{-1}$ Mpc$^{-1}$ across filters. The results show tight color- and color–width relations, with intrinsic dispersions down to ~0.13–0.19 mag in near-IR bands for blue-edge subsamples, and reveal that the Tripp $eta$ parameter for fast decliners encodes temperature-driven color variation rather than purely dust effects. The work suggests fast-declining SNe Ia are valuable distance indicators in the local universe, anchored by non-Cepheid calibrators, and highlights the potential of the Color method as a robust alternative to shape-based corrections.

Abstract

In this paper, the suitability of fast-declining Type Ia supernovae (SNe Ia) as cosmological standard candles is examined utilizing a Hubble Flow sample of 43 of these objects observed by the Carnegie Supernova Project (CSP). We confirm previous suggestions that fast-declining SNe Ia offer a viable method for estimating distances to early-type galaxies when the color-stretch parameter, $s_{BV}$, is used as a measure of the light curve shape. As a test, we employ the Tripp method, which models the absolute magnitude at maximum as a function of light curve shape and color. We calibrate the sample using 12 distance moduli based on published Infrared Surface Brightness Fluctuations to derive a value of the Hubble constant that is in close agreement with the value obtained for the full sample of CSP SNe Ia using the same methodology. We also develop a new and simple method of estimating the distances of fast decliners based only on their colors at maximum (and not light curve shape) and find that it leads to similar results as with using the Tripp method. This "Color" technique is a powerful tool that is unique to fast-declining SNe Ia. We show that the colors of the fast decliners at maximum light are strongly affected by photospheric temperature differences and not solely due to dust extinction, and provide a physical rationale for this effect.

Figures (12)

• Figure 1: (above) Absolute magnitudes, $M_B$, plotted versus the light curve decline rate parameter, $\Delta{\rm m}_{15}(B)$, of SNe Ia observed by the CSP I and CSP-II with $z_{\rm {CMB}} > 0.01$. The K-corrected magnitudes have been adjusted for Milky Way dust reddening, and also for host galaxy dust extinction using the intrinsic color analysis described in detail by burns18. Distance moduli were derived from $z_{\rm {CMB}}$ assuming standard $\Lambda$CDM cosmology and a fixed Hubble constant $H_0 = 72$${\rm km~s}^{-1}~\rm{Mpc}^{-1}$, density parameter $\Omega_m = 0.27$, and cosmological constant parameter $\Omega_\Lambda = 0.73$. Plotted for reference are points for SN 1991bg and the "transitional" SN 1986G. For SN 1991bg, we used the SBF distance modulus for the host, NGC 4374, from tonry01, subtracting 0.16 mag jenson03 to put this on the freedman01 scale. For SN 1986G, we adopted the revised SBF distance of ferrarese07. (below) Same data plotted instead versus the color-stretch parameter, $s_{BV}$.
• Figure 2: Observed ($B_{max} - V_{max}$) pseudocolors for CSP-I and CSP-II SNe Ia plotted versus $s_{BV}$. The black points correspond to the fast-declining, $s_{BV}$$< 0.75$, subsample of CSP SNe with $z_{\rm {CMB}} > 0.01$ and with host galaxy dust reddenings $E(B-V) < 0.15$ mag as estimated via an intrinsic color analysis like that described by burns18. Also plotted as green points are the IR SBF calibrator SNe Ia. Note that the colors for all objects in this plot are corrected for Milky Way dust reddening, but with no correction for host galaxy dust reddening.
• Figure 3: (upper row) Normal and cumulative histograms of the $s_{BV}$ measurements of the CSP Hubble Flow ($z_{\rm {CMB}} > 0.01$) SNe Ia and the IR SBF calibrators (red hatched lines). (middle row) Normal and cumulative histograms of the observed ($B_{max} - V_{max}$) pseudocolors for CSP Hubble Flow SNe Ia and the IR SBF calibrators (red hatched lines). (lower row) Normal and cumulative histograms of the ($B_{max} - V_{max}$) pseudocolors, corrected for host dust reddening, for CSP Hubble Flow SNe Ia and the IR SBF calibrators (red hatched lines). The K-S two-sample test $p$ values are given in the three cumulative histograms.
• Figure 4: Derived absolute magnitudes in $uBgVriYJH$ filters of the CSP SNe Ia with $z_{\rm {CMB}} > 0.01$ plotted against $s_{BV}$. The data are corrected only for Milky Way extinction and the K-correction. The black circles correspond to the subset of SNe for which the host galaxy reddening, $E(B-V)\rm{_{host}}$ is estimated to be less than 0.15 mag (see text for further details).
• Figure 5: Derived absolute magnitudes in $uBgVriYJH$ filters of the CSP SNe Ia with $z_{\rm {CMB}} > 0.01$ plotted against the observed ($B_{max} - V_{max}$) pseudocolor. The data are corrected only for Milky Way extinction and the K-correction. The black circles correspond to the subset of SNe for which the host galaxy reddening, $E(B-V)\rm{_{host}}$, is estimated to be less than 0.15 mag (see text for further details). The arrows in each panel indicate the reddening vectors for host galaxy dust with a color excess of $E(B-V)\rm{_{host}} = 0.2$ mag and $R_V = 2.8$.