arXiv subjects

Junhyuk Son

Publications and source records attributed to Junhyuk Son.

8 recordsLinked to original sources

arXiv2026

Which Type Ia supernova observables best indicate the ages of their progenitor stars?

Type Ia supernovae (SNe Ia) observables, such as the light-curve shape and the colour, are expected to contain information about the progenitor star. In this work, we explore this information, with a particular focus on the age of the SN Ia progenitor star. For this, we construct the SN Ia progenitor age distribution (SPAD) and compare it to the observed distributions of light-curve shape (x1) and the colour (c) parameters in a volume-limited SN Ia sample. We find that SPAD and the x1 distribution share a common shape: a young/high-x1 peak and an old/low-x1 bump in the tail, and this shape varies systematically with redshift. In contrast, this behaviour is not evident in the c distribution. We then examine the correlation of the local age at the SN Ia explosion site, used as a proxy for the progenitor age, with x1 and c. The local age and x1 are well correlated (the linear correlation coefficient ~ -0.71), whereas the local age and c show no significant correlation (the coefficient ~ 0.08). Furthermore, we find that the x1 distribution systematically evolves with the local age. Lastly, we demonstrate that an empirical mapping approach based on SPAD successfully reproduces the observed x1 distribution across different redshift bins. Taken together, our results suggest that the light-curve shape distribution indicates progenitor age at the population level more robustly than the colour does. In particular, younger progenitors are more likely to have higher-x1 SNe Ia. We discuss an application for creating a more homogeneous sample of SNe Ia in terms of progenitor age across a wide redshift range without the Malmquist bias, thereby improving the accuracy of cosmological constraints derived from SNe Ia.

astro-ph.HE↗

arXiv2026

Still non-accelerating: age-bias correction in supernova cosmology is robust to host-progenitor age mapping

We re-examine the claim by Wiseman et al. (2026) that progenitor-age bias has a negligible impact on cosmological inferences from Type Ia supernovae (SNe Ia). We show that their inferred host-age-Hubble residual (HR) slope is severely underestimated because their combined SN Ia sample spans an unusually wide redshift range ($0.04 < z < 0.42$), over which the mean host age evolves by $\sim$\,3 Gyr. As a result, SNe Ia spanning substantial host-age differences are effectively assigned similar HR values prior to regression, artificially flattening the inferred age-HR relation. In addition, their application of the Pantheon+ host-mass correction further suppresses the slope, but the underlying dust model is highly incompatible with the measured dust attenuation curves of galaxies. We also demonstrate that our age bias correction is robust to uncertainties in host-progenitor age mapping arising from different choices of the SN Ia delay-time distribution. The reduced progenitor-age evolution argued by Wiseman et al. (2026) must, by the same logic, be accompanied by a steeper inferred progenitor-age-HR slope. When these two effects are consistently combined in computing the redshift-dependent magnitude correction, the final correction, and hence the resulting cosmological impact, remain largely unchanged from Son et al. (2025).

astro-ph.CO↗

arXiv2026

Strong Progenitor Age Bias in Supernova Cosmology. III. Progenitor Age as the Physical Origin of the Type Ia Supernova Magnitude Steps with Host Properties

The standardized magnitude of a type Ia supernova (SN Ia) correlates with host-galaxy properties, and a host mass-step correction is now routinely included in SN Ia luminosity standardization. Given that host mass cannot directly influence SN Ia luminosity, the root cause of the step must be another latent parameter associated with host mass. Identifying this driver is essential because different host properties evolve differently with redshift, so corrections based on them can lead to divergent cosmological inferences. In recent years, direct and extensive age measurements have revealed a significant relation between host age and Hubble residual (HR). Here, using a new dataset, we confirm that this relation arises from the age dependence of the SN Ia luminosity standardization process and the resulting overcorrection. Specifically, we show that while the mass-step correction reduces the age bias by about half, the host age-bias correction fully eliminates the mass step, supporting a progenitor-age origin of the host-age--HR relation. We further demonstrate that the SN Ia magnitude steps with host mass (and specific star formation rate; sSFR) emerge from a nonlinear, step-like relation between mass (and sSFR) and progenitor age, combined with a linear progenitor-age--HR relation: the SN Ia magnitude steps are therefore projected manifestations of an underlying dependence on progenitor age. Taken together, our results show that progenitor age is the primary driver of both the strong host-age--HR relation and the apparent host-mass and host-sSFR steps.

astro-ph.GA↗

arXiv2026

How Robust is the Cosmic Distance with Tip of Red Giant Branch against Stellar Population Variations?

The tip of the red giant branch (TRGB) provides a key standard candle for extragalactic distance measurements and for refining the Hubble constant. We test its robustness by quantifying how metallicity, $α$-element enhancement, age, and initial helium abundance modulate the TRGB luminosity, using synthetic composite color--magnitude diagrams in the $I$ and $F814W$ bands. We find that metallicity and $α$-element enhancement are the primary drivers of TRGB variation, while age introduces only a modest effect and helium abundance is negligible. At fixed age and helium content, increasing the mean metallicity by 0.5 dex or the $α$-element enhancement by 0.3 dex produces the well-known systematic dimming of 0.046 and 0.050 mag, respectively, in $M_I^{\rm TRGB}$, and of 0.093 and 0.044 mag, respectively, in $M_{F814W}^{\rm TRGB}$. By comparison, changes in age of 3~Gyr and in initial helium abundance of 0.10 yield minor luminosity shifts, with average changes of 0.031 and 0.009~mag, respectively, in $M_I^{\rm TRGB}$, and of 0.035 and 0.027 mag, respectively, in $M_{F814W}^{\rm TRGB}$, substantially smaller than those caused by variations in metallicity or $α$-element enhancement. For mixed stellar populations under typical stellar-halo metallicity conditions, the net variation in $M_I^{\rm TRGB}$ arising from each combination of the $α$-element enhancement, age, and initial helium abundance remains below 0.028~mag, well within reported systematic uncertainties. Together, these results reaffirm the TRGB as a highly robust distance indicator and support its continued use as an independent anchor for precision cosmology in the era of the Hubble-tension debate.

astro-ph.GA↗

arXiv2025

Strong Progenitor Age-bias in Supernova Cosmology. II. Alignment with DESI BAO and Signs of a Non-Accelerating Universe

Supernova (SN) cosmology is based on the key assumption that the luminosity standardization process of Type Ia SNe remains invariant with progenitor age. However, direct and extensive age measurements of SN host galaxies reveal a significant (5.5σ) correlation between standardized SN magnitude and progenitor age, which is expected to introduce a serious systematic bias with redshift in SN cosmology. This systematic bias is largely uncorrected by the commonly used mass-step correction, as progenitor age and host galaxy mass evolve very differently with redshift. After correcting for this age-bias as a function of redshift, the SN dataset aligns more closely with the w0waCDM model recently suggested by the DESI BAO project from a combined analysis using only BAO and CMB data. This result is further supported by an evolution-free test that uses only SNe from young, coeval host galaxies across the full redshift range. When the three cosmological probes (SNe, BAO, CMB) are combined, we find a significantly stronger (> 9σ) tension with the ΛCDM model than that reported in the DESI papers, suggesting a time-varying dark energy equation of state in a currently non-accelerating universe.

astro-ph.CO↗

arXiv2025

Strong progenitor age bias in supernova cosmology. I. Robust and ubiquitous evidence from a larger sample of host galaxies in a broader redshift range

Type Ia supernovae (SNe Ia) serve as the most crucial standardizable candles in cosmology, providing direct measurements of the universe's expansion history. However, it is well-known that the post-standardization brightness of SNe Ia is influenced by the properties of their host galaxies, such as mass and star formation rate, both of which are closely related to progenitor age. In this study, by measuring the stellar population ages of SN host galaxies, we reaffirm the ubiquitous and robust correlation between SN Ia luminosity and host age, showing that this host property dependence arises primarily from stellar population age of the host galaxy. This analysis was conducted using an expanded sample of over 300 hosts across a broad redshift range up to $z \sim 0.4$, ensuring sufficient statistical significance of the result. To quantify the relationship between host age and Hubble residual (HR), we employed two linear regression techniques: LINMIX, which assumes a Gaussian age error, and Bayesian hierarchical linear regression, which utilizes a full posterior for the age error. Both models demonstrate a robust correlation between host age and HR, with high statistical significance approaching $5.5 σ$. While our new regression analyses yield the slopes that are similar or slightly shallower compared to our previous results, the significance of these slopes has notably increased. These findings robustly validate our previous suggestions that post-standardization SN Ia luminosity varies with progenitor age, which is currently not properly accounted for in SN cosmology.

astro-ph.GA↗

arXiv2023

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 ($\sim 10^{9.5}{\rm M}_{\rm sun}$) and an older ($>$ 6 Gyr) group with higher mass ($\sim 10^{10.5}{\rm M}_{\rm sun}$). On the Hubble residual versus host mass plane, the two groups create the mass-step at $\sim 10^{10}{\rm M}_{\rm sun}$. 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.

astro-ph.GA↗

arXiv2022

Evidence for strong progenitor age dependence of type Ia supernova luminosity standardization process

Supernova (SN) cosmology is based on the assumption that the width-luminosity relation (WLR) and the color-luminosity relation (CLR) in the type Ia SN luminosity standardization would not show {absolute magnitude differences} with progenitor age. Unlike this expectation, recent age datings of stellar populations in host galaxies have shown significant correlations between progenitor age and Hubble residual (HR). Here we show that this correlation originates from a strong progenitor age dependence of the zero-points of the WLR and the CLR, in the sense that SNe from younger progenitors are fainter each at given light-curve parameters $x_1$ and $c$. This $4.6σ$ result is reminiscent of Baade's discovery of the zero-point variation of the Cepheid period-luminosity relation with age, and, as such, causes a serious systematic bias with redshift in SN cosmology. Other host properties show substantially smaller and insignificant offsets in the WLR and CLR for the same dataset. We illustrate that the differences between the high-$z$ and low-$z$ SNe in the WLR and CLR, and in HR after the standardization, are fully comparable to those between the correspondingly young and old SNe at intermediate redshift, indicating that the observed dimming of SNe with redshift may well be an artifact of over-correction in the luminosity standardization. When this systematic bias with redshift is properly taken into account, there is little evidence left for an accelerating universe, in discordance with other probes, urging the follow-up investigations with larger samples at different redshift bins.

astro-ph.GA↗