SN Ia Luminosity Research Articles

Carnegie Supernova Project I and II: Measurements of H 0 Using Cepheid, Tip of the Red Giant Branch, and Surface Brightness Fluctuation Distance Calibration to Type Ia Supernovae* *This paper includes data gathered with the 6.5 m Magellan Telescopes located at Las Campanas Observatory, Chile.

We present an analysis of Type Ia supernovae (SNe Ia) from the Carnegie Supernova Project I and II and extend the Hubble diagram from optical to near-infrared wavelengths (uBgVriYJH). We calculate the Hubble constant, H 0, using various distance calibrators: Cepheids, the tip of the red giant branch (TRGB), and surface brightness fluctuations (SBFs). Combining all methods of calibration, we derive H 0 = 71.76 ± 0.58 (stat) ± 1.19 (sys) km s−1 Mpc−1 from the B band and H 0 = 73.22 ± 0.68 (stat) ± 1.28 (sys) km s−1 Mpc−1 from the H band. By assigning equal weight to the Cepheid, TRGB, and SBF calibrators, we derive the systematic errors required for consistency in the first rung of the distance ladder, resulting in a systematic error of 1.2 ∼ 1.3 km s−1 Mpc−1 in H 0. As a result, relative to the statistics-only uncertainty, the tension between the late-time H 0 we derive by combining the various distance calibrators and the early-time H 0 from the cosmic microwave background is reduced. The highest precision in SN Ia luminosity is found in the Y band (0.12 ± 0.01 mag), as defined by the intrinsic scatter (σ int). We revisit SN Ia Hubble residual-host mass correlations and recover previous results that these correlations do not change significantly between the optical and near-infrared wavelengths. Finally, SNe Ia that explode beyond 10 kpc from their host centers exhibit smaller dispersion in their luminosity, confirming our earlier findings. A reduced effect of dust in the outskirts of hosts may be responsible for this effect.

On the Root Cause of the Host “Mass Step” in the Hubble Residuals of Type Ia Supernovae

It is well established that the Hubble residuals of Type Ia supernovae (SNe Ia) show the luminosity step with respect to their host galaxy stellar masses. This “mass step” is taken as an additional correction factor for the SN Ia luminosity standardization. Here we investigate the root cause of the mass step and propose that the bimodal nature of the host age distribution is responsible for the step. In particular, by using the empirical nonlinear mass-to-age relation of local galaxies, we convert the mass function of SN Ia hosts to their age distribution. We find that the age distribution shows clear bimodality: a younger (<6 Gyr) group with lower mass (∼109.5 M Sun) and an older (> 6 Gyr) group with higher mass (∼1010.5 M Sun). On the Hubble residual versus host-mass plane, the two groups create the mass step at ∼1010 M Sun. This leads us to conclude that the host galaxy mass step can be attributed to the bimodal age distribution in relation to a nonlinear relation between galaxy mass and age. We suggest that the mass step is another manifestation of the old “red sequence” and the young “blue cloud” observed in the galactic color–magnitude diagram.

Reconsidering photometric estimation of local star formation environment and its correlation with Type Ia supernova luminosity

ABSTRACT Recent studies on the environmental dependence of Type Ia supernova (SN Ia) luminosity focus on the local environment where the SN exploded, considering that this is more directly linked to the SN progenitors. However, there is a debate about the local environmental, specifically local star formation rate (SFR), dependence of the SN Ia luminosity. A recent study claims that the dependence is insignificant (0.051 ± 0.020 mag; 2.6σ), based on the local SFR measurement by fitting local ugrizy photometry data. However, we find that this photometric local SFR measurement is inaccurate. We argue this based on the theoretical background of SFR measurement and the methodology used to make that claim with their local ugrizy photometry data, especially due to a limited range of extinction parameters used when fitting the data. Therefore, we reanalyse the same host galaxies with the same fitting code, but with more physically motivated extinction treatments and global ugriz photometry of host galaxies. We estimate global stellar mass and SFR. Then, local star formation environments are inferred by using the method which showed that SNe Ia in globally passive galaxies have locally passive environments, while those in globally star-forming low-mass galaxies have locally star-forming environments. We find that there is significant local environmental dependence of SN Ia luminosities: SNe Ia in locally star-forming environments are 0.072 ± 0.021 mag (3.4σ) fainter than those in locally passive environments, even though SN Ia luminosities have been further corrected by the BEAMS with Bias Corrections method that reduces the size of the dependence.

Leveraging SN Ia spectroscopic similarity to improve the measurement of H 0

Recent studies suggest spectroscopic differences explain a fraction of the variation in Type Ia supernova (SN Ia) luminosities after light-curve/color standardization. In this work, (i) we empirically characterize the variations of standardized SN Ia luminosities, and (ii) we use a spectroscopically inferred parameter, SIP, to improve the precision of SNe Ia along the distance ladder and the determination of the Hubble constant (H 0). First, we show that the Pantheon+ covariance model modestly overestimates the uncertainty of standardized magnitudes by ∼ 7%, in the parameter space used by the SH0ES Team to measure H 0; accounting for this alone yields H 0 = 73.01 ± 0.92 km s-1 Mpc-1. Furthermore, accounting for spectroscopic similarity between SNe Ia on the distance ladder reduces their relative scatter to ∼ 0.12 mag per object (compared to ∼ 0.14 mag previously). Combining these two findings in the model of SN covariance, we find an overall 14% reduction (to ± 0.85 km s-1 Mpc-1) of the uncertainty in the Hubble constant and a modest increase in its value. Including a budget for systematic uncertainties itemized by Riess et al. (2022a), we report an updated local Hubble constant with ∼ 1.2% uncertainty, H 0 = 73.29 ± 0.90 km s-1 Mpc-1. We conclude that spectroscopic differences among photometrically standardized SNe Ia do not explain the “Hubble tension”. Rather, accounting for such differences increases its significance, as the discrepancy against ΛCDM calibrated by the Planck 2018 measurement rises to 5.7σ.

Do the early galaxies observed by JWST disagree with Planck's CMB polarization measurements?

The recent observations from the James Webb Space Telescope have led to a surprising discovery of a significant density of massive galaxies with masses of M ≥ 1010.5 M ⊙ at redshifts of approximately z ∼ 10. This corresponds to a stellar mass density of roughly ρ * ∼ 106 M ⊙ Mpc-3. Despite making conservative assumptions regarding galaxy formation, this finding may not be compatible with the standard ΛCDM cosmology that is favored by observations of CMB Anisotropies from the Planck satellite. In this paper, we confirm the substantial discrepancy with Planck's results within the ΛCDM framework. Assuming a value of ϵ = 0.2 for the efficiency of converting baryons into stars, we indeed find that the ΛCDM model is excluded at more than 99.7 % confidence level (C.L.). An even more significant exclusion is found for ϵ ∼ 0.1, while a better agreement, but still in tension at more than 95 %, is obtained for ϵ = 0.32.This tension, as already discussed in the literature, could arise either from systematics in the JWST measurements or from new physics. Here, as a last-ditch effort, we point out that disregarding the large angular scale polarization obtained by Planck, which allows for significantly larger values of the matter clustering parameter σ 8, could lead to better agreement between Planck and JWST within the ΛCDM framework. Assuming ΛCDM and no systematics in the current JWST results, this implies either an unknown systematic error in current large angular scale CMB polarization measurements or an unidentified physical mechanism that could lower the expected amount of CMB polarization produced during the epoch of reionization. Interestingly, the model compatible with Planck temperature-only data and JWST observation also favors a higher Hubble constant H 0 = 69.0±1.1 km/s/Mpc at 68% C.L., in better agreement with observations based on SN-Ia luminosity distances.

Phenomenological footprints of Λ varying gravity theories inspired from quantum gravity models in the multi-messenger era

An interesting phenomenological consequence of Λ varying gravity theories inspired by quantum gravity models is reported. The treatment in the present work is quite general and applicable to several different actions with Λ varying, especially those used in RG approaches to quantum gravity. An effective gravitational action with a scale varying cosmological constant, Λ, which depends on the system’s characteristics, like the length and the energy density, is the key feature. If the system is an astrophysical object, like a cluster of galaxies, a black hole, etc, non-negligible corrections arise to several observable quantities. Distinctive footprints could refer to luminosity distance and strong/weak lensing measurements, among others. The present study focuses on the SNIa luminosity distance observable.

On the homogeneity of SnIa absolute magnitude in the Pantheon+ sample

ABSTRACT We have analysed the Pantheon+ sample using a new likelihood model that replaces the single Type Ia supernovae (SnIa) absolute magnitude parameter M used in the standard likelihood model of Brout et. al. with two absolute magnitude parameters (M&amp;lt; and M&amp;gt;) and a transition distance (dcrit) that determines the distance at which M changes from M&amp;lt; to M&amp;gt;. The use of this likelihood dramatically changes the quality of fit to the Pantheon+ sample for a Lambda cold dark matter background by Δχ2 = −19.6. The tension between the M&amp;lt; and M&amp;gt; best-fitting values is at a level more than 3σ with a best-fitting dcrit very close to $20\, \mathrm{Mpc}$. The origin of this improvement of fit and M&amp;lt;–M&amp;gt; tension is that the new likelihood model successfully models two signals hidden in the data: (1) the volumetric redshift scatter bias systematic and (2) a mild signal for a change of intrinsic SnIa luminosity at about $20\, \mathrm{Mpc}$. This interpretation of the results is confirmed by truncating the z &amp;lt; 0.01 Hubble diagram data from the Pantheon+ data where the above systematic is dominant and showing that the M&amp;lt;–M&amp;gt; tension decreases from above 3σ to a little less than 2σ. It is also confirmed by performing a Monte Carlo simulation, which shows that the maximum significance of the SnIa luminosity transition ($\Sigma \equiv \frac{|M_{\gt} -M_{\lt} |}{\sqrt{\sigma _{M_{\gt} }^2+\sigma _{M_{\lt} }^2}}$) as obtained from the real SH0ES data is larger than the corresponding maximum significance of $94{{\ \rm per\ cent}}$ of the corresponding homogeneous simulated samples.

Concerning colour: The effect of environment on type Ia supernova colour in the dark energy survey

ABSTRACT Recent analyses have found intriguing correlations between the colour (c) of type Ia supernovae (SNe Ia) and the size of their ‘mass-step’, the relationship between SN Ia host galaxy stellar mass (Mstellar) and SN Ia Hubble residual, and suggest that the cause of this relationship is dust. Using 675 photometrically classified SNe Ia from the Dark Energy Survey 5-yr sample, we study the differences in Hubble residual for a variety of global host galaxy and local environmental properties for SN Ia subsamples split by their colour. We find a 3σ difference in the mass-step when comparing blue (c &amp;lt; 0) and red (c &amp;gt; 0) SNe. We observe the lowest r.m.s. scatter (∼0.14 mag) in the Hubble residual for blue SNe in low mass/blue environments, suggesting that this is the most homogeneous sample for cosmological analyses. By fitting for c-dependent relationships between Hubble residuals and Mstellar, approximating existing dust models, we remove the mass-step from the data and find tentative ∼2σ residual steps in rest-frame galaxy U − R colour. This indicates that dust modelling based on Mstellar may not fully explain the remaining dispersion in SN Ia luminosity. Instead, accounting for a c-dependent relationship between Hubble residuals and global U − R, results in ≤1σ residual steps in Mstellar and local U − R, suggesting that U − R provides different information about the environment of SNe Ia compared to Mstellar, and motivating the inclusion of galaxy U − R colour in SN Ia distance bias correction.

Constraints on Cosmological Parameters with a Sample of Type Ia Supernovae from JWST

We investigate the potential of using a sample of very high-redshift (2 ≲ z ≲ 6) (VHZ) Type Ia supernovae (SNe Ia) attainable by JWST on constraining cosmological parameters. At such high redshifts, the age of the universe is young enough that the VHZ SN Ia sample comprises the very first SNe Ia of the universe, with progenitors among the very first generation of low-mass stars that the universe has made. We show that the VHZ SNe Ia can be used to disentangle systematic effects due to the luminosity distance evolution with redshifts intrinsic to SN Ia standardization. Assuming that the systematic evolution can be described by a linear or logarithmic formula, we found that the coefficients of this dependence can be determined accurately and decoupled from cosmological models. Systematic evolution as large as 0.15 mag and 0.45 mag out to z = 5 can be robustly separated from popular cosmological models for linear and logarithmic evolution, respectively. The VHZ SNe Ia will lay the foundation for quantifying the systematic redshift evolution of SN Ia luminosity distance scales. When combined with SN Ia surveys at comparatively lower redshifts, the VHZ SNe Ia allow for the precise measurement of the history of the expansion of the universe from z ∼ 0 to the epoch approaching reionization.

A Uniform Type Ia Supernova Distance Ladder with the Zwicky Transient Facility: Absolute Calibration Based on the Tip of the Red Giant Branch Method

The current Cepheid-calibrated distance ladder measurement of H 0 is reported to be in tension with the values inferred from the cosmic microwave background (CMB), assuming standard cosmology. However, some tip of the red giant branch (TRGB) estimates report H 0 in better agreement with the CMB. Hence, it is critical to reduce systematic uncertainties in local measurements to understand the Hubble tension. In this paper, we propose a uniform distance ladder between the second and third rungs, combining Type Ia supernovae (SNe Ia) observed by the Zwicky Transient Facility (ZTF) with a TRGB calibration of their absolute luminosity. A large, volume-limited sample of both calibrator and Hubble flow SNe Ia from the same survey minimizes two of the largest sources of systematics: host-galaxy bias and nonuniform photometric calibration. We present results from a pilot study using the existing TRGB distance to the host galaxy of ZTF SN Ia SN 2021rhu (aka ZTF21abiuvdk) in NGC7814. Combining the ZTF calibrator with a volume-limited sample from the first data release of ZTF Hubble flow SNe Ia, we infer H 0 = 76.94 ± 6.4 km s−1 Mpc−1, an 8.3% measurement. The error budget is dominated by the single object calibrating the SN Ia luminosity in this pilot study. However, the ZTF sample includes already five other SNe Ia within ∼20 Mpc for which TRGB distances can be obtained with the Hubble Space Telescope. Finally, we present the prospects of building this distance ladder out to 80 Mpc with James Webb Space Telescope observations of more than 100 ZTF SNe Ia.

A very low central oxygen mass in the peculiar type Ia SN 2010lp: further diversity at the low-luminosity end of SNe Ia

ABSTRACT A nebular spectrum of the peculiar, low-luminosity type Ia supernova 2010lp is modelled in order to estimate the composition of the inner ejecta and to illuminate the nature of this event. Despite having a normally declining light curve, SN 2010lp was similar spectroscopically to SN 1991bg at early times. However, it showed a very unusual double-peaked [O i] $\lambda \lambda \, 6300,6363$ emission at late times (Taubenberger et al.). Modelling of the nebular spectrum suggests that a very small amount of oxygen (∼0.05 M⊙), expanding at very low speed (≲ 2000 km s−1) is sufficient to reproduce the observed emission. The rest of the nebula is not too dissimilar from SN 1991bg, except that SN 2010lp is slightly more luminous. The double-peaked [O i] emission suggests that SN 2010lp may be consistent with the merger or collision of two low-mass white dwarfs. The low end of the SN Ia luminosity sequence is clearly populated by diverse events, where different channels may contribute.

MOND-like behavior in the Dirac–Milne universe

Aims.Observational data show that the observed luminous matter is not sufficient to explain several features of the present universe, from gravitational structure formation to the rotational velocities in galaxies and clusters. The mainstream explanation is that the missing mass, although gravitationally active, interacts very weakly with ordinary matter. Competing explanations involve changing the laws of gravity at low accelerations, as in MOdified Newtonian Dynamics (MOND). Here, we suggest that the Dirac-Milne cosmology, a matter-antimatter symmetric cosmology where the two components repel each other, is capable of accounting for such an apparent modification of the Newtonian law, without invoking dark matter.Methods.Using a simple analytical approximation and 1D and 3D simulations, we study rotation curves and virial velocities and compare the mass observed in the simulations to the mass derived assuming Newtonian gravity. Using a modified version of theRAMSEScode, we study the Faber-Jackson scaling relation and the intensity of the additional gravitational field created by antimatter clouds.Results.We show that, in the Dirac-Milne universe, rotation curves are generically flat beyond a characteristic distance of ≈2.5 virial radii, and that the Tully-Fisher and Faber-Jackson scaling relations with an exponent ≈3 are satisfied. We show that the mass derived from the rotation curves assuming Newtonian gravity is systematically overestimated compared to the mass really present. In addition, the Dirac-Milne universe, featuring a polarization between its matter and antimatter components, presents a behavior similar to that of MOND, characterized by an additional surface gravity compared to the Newtonian case. We show that in the Dirac-Milne universe, at the present epoch, the intensity of the additional gravitational fieldgamdue to the presence of clouds of antimatter is on the order of a few 10−11m s−2, similar to the characteristic acceleration of MOND. We study the evolution of this additional accelerationgamand show that it depends on the redshift, and it is therefore not a fundamental constant.Conclusions.Combined with its known concordance properties on the SNIa luminosity distance, age, nucleosynthesis, and structure formation, the Dirac-Milne cosmology may then represent an interesting alternative to the standard cosmological model ΛCDM, MOND, and other scenarios for explaining the dark matter (or missing gravity) and dark energy conundrum.

Artificial neural network spectral light curve template for type Ia supernovae and its cosmological constraints

The spectral energy distribution (SED) sequence for type Ia supernovae (SN Ia) is modeled by an artificial neural network. The SN Ia luminosity is characterized as a function of phase, wavelength, a color parameter and a decline rate parameter. After training and testing the neural network, the SED sequence could give both the spectrum with wavelength range from 3000 Åto 8000 Åand the light curve with phase from 20 days before to 50 days after the maximum luminosity for the supernovae with different colors and decline rates. Therefore, we call this the Artificial Neural Network Spectral Light Curve Template (ANNSLCT) model. We retrain the Joint Light-curve Analysis (JLA) supernova sample by using the ANNSLCT model and obtain the parameters for each supernova to make a constraint on the cosmological [Formula: see text]CDM model. We find that the best fitting values of these parameters are very close to those from the JLA sample trained with the Spectral Adaptive Lightcurve Template 2 (SALT2) model. It is expectable that the ANNSLCT model has potential to analyze more SN Ia multi-color light curves measured in future observation projects.

Pantheon update on a model-independent analysis of cosmological supernova data

We present an update of our previous work, necessitated by availability of a significantly improved dataset. The work is a model-independent analysis of the cosmological supernova (type Ia) data, where function families are fit to the data in form of luminosity distance as function of redshift, that is, d L(z); and subsequently time-derivatives of the scale function a(t) are analytically derived, but as functions of z, without making assumptions about the theory of gravity or the contents of the Universe. This gives, e.g. the redshift value at which the Universe goes over from deceleration to acceleration, as z t = 0.54 ± 0.04 for a flat Universe. In the update, we switch to a more modern fit criterion and also take into account the uncertainty in the calibration of the SNIa luminosities. If a theory of gravity is assumed, our results allow determination of the density of the Universe as function of z, from which conclusions about the contents of the Universe can be drawn. We update the previous work’s result where this was done for Einstein gravity, finding a lower-limit on the dark energy (DE) fraction, ΩDE > 0.46; and here we do this also for Starobinsky gravity, where we can find a Starobinsky parameter that can eliminate the need for DE.

The dependence of Type Ia Supernovae salt2 light-curve parameters on host galaxy morphology

ABSTRACT Type Ia Supernovae (SNe Ia) are widely used to measure distances in the Universe. Despite the recent progress achieved in SN Ia standardization, the Hubble diagram still shows some remaining intrinsic dispersion. The remaining scatter in supernova luminosity could be due to the environmental effects that are accounted for as mass step correction in the current cosmological analyses. In this work, we compare the local and global colour (U − V), the local star formation rate, and the host stellar mass to the host galaxy morphology. The observed trends suggest that the host galaxy morphology is a relevant parameter to characterize the SN Ia environment. Therefore, we study the influence of host galaxy morphology on light-curve parameters of SNe Ia from the pantheon cosmological supernova sample. We determine the Hubble morphological type of host galaxies for a subsample of 330 SNe Ia. We confirm that the salt2 stretch parameter x1 depends on the host morphology with the p-value ∼10−14. The supernovae with lower stretch value are hosted mainly by elliptical and lenticular galaxies. No correlation for the salt2 colour parameter c is found. We also examine Hubble diagram residuals for supernovae hosted by ‘early-type’ and ‘late-type’ morphological groups of galaxies. The analysis reveals that the mean distance modulus residual in early-type galaxies is smaller than the one in late-type galaxies, which means that early-type galaxies contain brighter supernovae after stretch and colour corrections. However, we do not observe any difference in the residual dispersion for these two morphological groups. The obtained results are in the line with other analyses showing environmental dependence of SN Ia light-curve parameters and luminosity. We confirm the importance of including a host galaxy parameter into the standardization procedure of SNe Ia for further cosmological studies.

A novel early dark energy model

We present a theoretical study of an early dark energy (EDE) model. The equation of state ω(z) evolves during the thermal history in a framework of a Friedmann-Lemaitre-Robertson-Walker Universe, following an effective parametrization that is a function of redshift z. We explore the evolution of the system from the radiation domination era to the late times, allowing the EDE model to have a non-negligible contribution at high redshift (as opposed to the cosmological constant that only plays a role once the structure is formed) with a very little input to the Big Bang Nucleosynthesis, and to do so, the equation of state mimics the radiation behaviour, but being subdominant in terms of its energy density. At late times, the equation of state of the dark energy model asymptotically tends to the fiducial value of the De Sitter domination epoch, providing an explanation for the accelerated expansion of the Universe at late times, emulating the effect of the cosmological constant. The proposed model has three free parameters, that we constrain using SNIa luminosity distances, along with the CMB shift parameter and the deceleration parameter calculated at the time of dark energy - matter equality. With full knowledge of the best fit for our model, we calculate different observables and compare these predictions with the standardΛCDM model. Besides the general consent of the community with the cosmological constant, there is no fundamental reason to choose that particular candidate as dark energy. Here, we open the opportunity to consider a more dynamical model, that also accounts for the late accelerated expansion of the Universe.

Evidence for Cosmic Acceleration Is Robust to Observed Correlations between Type Ia Supernova Luminosity and Stellar Age

Abstract Type Ia supernovae (SNe Ia) are powerful standardizable candles for constraining cosmological models and provided the first evidence of the accelerated expansion of the universe. Their precision derives from empirical correlations, now measured from &gt;1000 SNe Ia, between their luminosities, light-curve shapes, colors, and most recently with the stellar mass of their host galaxy. As mass correlates with other galaxy properties, alternative parameters have been investigated to improve SN Ia standardization though none have been shown to significantly alter the determination of cosmological parameters. We re-examine a recent claim, based on 34 SN Ia in nearby passive host galaxies, of a 0.05 mag Gyr−1 dependence of standardized SN Ia luminosity on host age, which, if extrapolated to higher redshifts, would be a bias up to 0.25 mag, challenging the inference of dark energy. We reanalyze this sample of hosts using both the original method and a Bayesian hierarchical model and find after a fuller accounting of the uncertainties the significance of a dependence on age to be ≤2σ and ∼1σ after the removal of a single poorly sampled SN Ia. To test the claim that a trend seen in old stellar populations can be applied to younger ages, we extend our analysis to a larger sample that includes young hosts. We find the residual dependence of host age (after all standardization typically employed for cosmological measurements) to be consistent with zero for 254 SNe Ia from the Pantheon sample, ruling out the large but low significance trend seen in passive hosts.

An asymmetric explosion mechanism may explain the diversity of Si ii linewidths in Type Ia supernovae

ABSTRACT Near maximum brightness, the spectra of Type Ia supernovae (SNe Ia) present typical absorption features of Silicon II observed at roughly $6100$ and $5750\, \mathring{\rm A}$. The two-dimensional distribution of the pseudo-equivalent widths (pEWs) of these features is a useful tool for classifying SNe Ia spectra (Branch plot). Comparing the observed distribution of SNe on the Branch plot to results of simulated explosion models, we find that one-dimensional models fail to cover most of the distribution. In contrast, we find that tardis radiative transfer simulations of the white dwarf head-on collision models along different lines of sight almost fully cover the distribution. We use several simplified approaches to explain this result. We perform order-of-magnitude analysis and model the opacity of the Si ii lines using local thermodynamic equilibrium and non-local thermodynamic equilibrium approximations. Introducing a simple toy model of spectral feature formation, we show that the pEW is a good tracer for the extent of the absorption region in the ejecta. Using radiative transfer simulations of synthetic SN ejecta, we reproduce the observed Branch plot distribution by varying the luminosity of the SN and the Si density profile of the ejecta. We deduce that the success of the collision model in covering the Branch plot is a result of its asymmetry, which allows for a significant range of Si density profiles along different viewing angles, uncorrelated with a range of 56Ni yields that cover the observed range of SN Ia luminosity. We use our results to explain the shape and boundaries of the Branch plot distribution.

Supernova Magnitude Evolution and PAge Approximation

Abstract The evidence of environmental dependence of SN Ia luminosity has inspired recent discussion about whether the late-universe cosmic acceleration is still supported by supernova data. We adopt the ΔHR/Δage parameter, which describes the dependence of supernova absolute magnitude on the age of supernova progenitor, as an additional nuisance parameter. Using the Pantheon supernova data, a lower bound ≥12 Gyr on the cosmic age, and a Gaussian prior on the Hubble constant, we reconstruct the cosmic expansion history. Within the flat Λ cold dark matter framework, we still find a 5.6σ detection of cosmic acceleration. This is because a matter-dominated decelerating universe would be too young to accommodate observed old stars with age ≳12 Gyr. A decelerating but non-flat universe is marginally consistent with the data, however, only in the presence of a negative spatial curvature ∼2 orders of magnitude beyond the current constraint from cosmic microwave background data. Finally, we propose a more general parameterization based on the cosmic age (PAge), which is not directly tied to the dark energy concept and hence is ideal for a null test of the cosmic acceleration. We find that, for a magnitude evolution rate ΔHR/Δage ≲ 0.3 mag/5.3 Gyr, a spatially flat and decelerating PAge universe is fully consistent with the supernova data and the cosmic age bound, and has no tension with the geometric constraint from the observed cosmic microwave background acoustic angular scales.

Hubble Space Telescope Observations of Mira Variables in the SN Ia Host NGC 1559: An Alternative Candle to Measure the Hubble Constant

Abstract We present year-long, near-infrared Hubble Space Telescope (HST) WFC3 observations used to search for Mira variables in NGC 1559, the host galaxy of the Type Ia supernova (SN Ia) SN 2005df. This is the first dedicated search for Miras, highly evolved low-mass stars, in an SN Ia host, and subsequently the first calibration of the SN Ia luminosity using Miras in a role historically played by Cepheids. We identify a sample of 115 O-rich Miras with P &lt; 400 days based on their light-curve properties. We find that the scatter in the Mira period–luminosity relation (PLR) is comparable to Cepheid PLRs seen in SN Ia host galaxies. Using a sample of O-rich Miras discovered in NGC 4258 with HSTF160W and its maser distance, we measure a distance modulus for NGC 1559 of (statistical) (systematic) mag. Based on the light curve of the normal, well-observed, low-reddening SN 2005df, we obtain a measurement of the fiducial SN Ia absolute magnitude of mag. With the Hubble diagram of SNe Ia we find km s−1 Mpc−1. Combining the calibration from the NGC 4258 megamaser and the Large Magellanic Cloud detached eclipsing binaries gives a best value of km s−1 Mpc−1. This result is within 1σ of the Hubble constant derived using Cepheids and multiple calibrating SNe Ia. This is the first of four expected calibrations of the SN Ia luminosity from Miras that should reduce the error in H 0 via Miras to ∼3%. In light of the present Hubble tension and JWST, Miras have utility in the extragalactic distance scale to check Cepheid distances or calibrate nearby SNe in early-type host galaxies that would be unlikely targets for Cepheid searches.