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PreprintarXiv licencearXiv

Supernova Cousins: The Intrinsic Dispersion and Environmental Dependence of Type Ia Supernovae in Galaxy Groups with TITAN

  • Allison Blum
  • Erik R. Peterson
  • David O. Jones
  • R. Brent Tully
  • Elijah G. Marlin
  • Yukei S. Murakami
  • Jack W. Tweddle
  • Dillon Brout
  • Mitchell Dixon
  • Stephen J. Smartt
Open at sourcePDFDOICite

Abstract

At low redshift, scatter in the Type Ia supernova (SN Ia) Hubble diagram is increased by peculiar velocities (PVs) and correlations between SN distances and their host-galaxy environments, limiting the precision of cosmological distance measurements. We investigate these effects using 1086 spectroscopically-confirmed SNe Ia from the Type Ia Supernova Trove from ATLAS in the Nearby Universe (TITAN) sample in the redshift range 0.01<z<0.05. We identify 314 group-associated SNe, including 80 SN "cousins" occurring in different galaxies within 32 common groups. We first examine whether using the group-averaged redshifts of SNe in galaxy groups can mitigate PV-induced scatter; however, we find that the Hubble residual scatter increases slightly from 0.184+0.017−0.009 mag using individual host-galaxy redshifts to 0.200+0.016−0.015 mag using group-averaged redshifts. For the sample of SN cousins, we next analyze pairwise differences in their distances and compare their scatter to the Hubble residual scatter of the full SN sample. For analysis variants that limit line-of-sight differences in distance modulus between cousins, we find ∼30-40% lower scatter from SN cousins at significances of 2.3-2.8σ. We also find tentative evidence that these differences in scatter may be driven by the youngest groups, with a 2σ reduction in scatter for groups with high fractions of spiral galaxies. These results suggest that SN cousins may provide a novel route for increasing SN Ia distance precision and understanding the role of host-galaxy and group properties on SN Ia distance measurements.

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Cite

BibTeXRIS
BibTeX
@misc{blum2026supernova,
  title = {{Supernova Cousins: The Intrinsic Dispersion and Environmental Dependence of Type Ia Supernovae in Galaxy Groups with TITAN}},
  author = {Allison Blum and Erik R. Peterson and David O. Jones and R. Brent Tully and Elijah G. Marlin and Yukei S. Murakami and Jack W. Tweddle and Dillon Brout and Mitchell Dixon and Stephen J. Smartt},
  howpublished = {arXiv},
  year = {2026},
  month = sep,
  doi = {10.48550/arxiv.2609.13525},
  eprint = {2609.13525},
  archivePrefix = {arXiv},
  url = {https://arxiv.org/abs/2609.13525},
}
RIS
TY  - UNPB
TI  - Supernova Cousins: The Intrinsic Dispersion and Environmental Dependence of Type Ia Supernovae in Galaxy Groups with TITAN
AU  - Allison Blum
AU  - Erik R. Peterson
AU  - David O. Jones
AU  - R. Brent Tully
AU  - Elijah G. Marlin
AU  - Yukei S. Murakami
AU  - Jack W. Tweddle
AU  - Dillon Brout
AU  - Mitchell Dixon
AU  - Stephen J. Smartt
PY  - 2026
DA  - 2026/09/11
PB  - arXiv
DO  - 10.48550/arxiv.2609.13525
UR  - https://arxiv.org/abs/2609.13525
AB  - At low redshift, scatter in the Type Ia supernova (SN Ia) Hubble diagram is increased by peculiar velocities (PVs) and correlations between SN distances and their host-galaxy environments, limiting the precision of cosmological distance measurements. We investigate these effects using 1086 spectroscopically-confirmed SNe Ia from the Type Ia Supernova Trove from ATLAS in the Nearby Universe (TITAN) sample in the redshift range 0.01<z<0.05. We identify 314 group-associated SNe, including 80 SN "cousins" occurring in different galaxies within 32 common groups. We first examine whether using the group-averaged redshifts of SNe in galaxy groups can mitigate PV-induced scatter; however, we find that the Hubble residual scatter increases slightly from 0.184^+0.017_−0.009 mag using individual host-galaxy redshifts to 0.200^+0.016_−0.015 mag using group-averaged redshifts. For the sample of SN cousins, we next analyze pairwise differences in their distances and compare their scatter to the Hubble residual scatter of the full SN sample. For analysis variants that limit line-of-sight differences in distance modulus between cousins, we find ∼30-40% lower scatter from SN cousins at significances of 2.3-2.8σ. We also find tentative evidence that these differences in scatter may be driven by the youngest groups, with a 2σ reduction in scatter for groups with high fractions of spiral galaxies. These results suggest that SN cousins may provide a novel route for increasing SN Ia distance precision and understanding the role of host-galaxy and group properties on SN Ia distance measurements.
ER  -