A distribution-function estimate of the Milky Way mass profile from outer halo stars in DESI DR2
Abstract
We present measurements of the Milky Way mass using blue horizontal-branch (BHB) and RR Lyrae (RRL) stars from the second data release of DESI (DR2), covering its first three years of operations. We employ 279 BHBs and 213 RRLs at ∼ 50--$80$\,kpc from the Galactic center, selected from catalogs roughly twice as large as those of DESI DR1, used in our previous mass measurement. We apply the Galactic Mass Estimator (GME), a hierarchical Bayesian framework that assumes power-law forms for the potential and the tracer density, and accounts for distance and velocity uncertainties. Validating the method on 24 AuriDESI mock catalogs (six Auriga halos at four viewing angles), we find that it overestimates the enclosed mass by ∼ 15% at 80\,kpc, and correct our results accordingly. We obtain M(<80 kpc) = 0.64+0.06−0.06 and 0.53+0.05−0.05 × 1012 M⊙ for BHBs and RRLs, respectively, while including Sagittarius stream stars lowers these masses by ∼ 10\%. Extrapolating to 100\,kpc, we obtain M(<100 kpc) = 0.74+0.07−0.07 and 0.62+0.06−0.07 × 1012 M⊙, and anchoring an NFW halo to our GME constraints at 65\,kpc yields virial masses of M200 = 1.12+0.14−0.12 and 0.89+0.11−0.10 × 1012 M⊙. BHBs yield systematically higher masses than RRLs across the full radial range, reflecting the impact of tracer choice even within a single method. This work is part of a wider DESI DR2 Key Project effort to measure the Milky Way mass and constrain systematics arising from different samples and methodologies.
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BibTeX
@misc{medina2026distributionfunction,
title = {{A distribution-function estimate of the Milky Way mass profile from outer halo stars in DESI DR2}},
author = {Gustavo E. Medina and Thomas M. Callingham and Monica Valluri and Alexander H. Riley and Ting S. Li and Jiaxin Han and Leandro Beraldo e Silva and Oleg Y. Gnedin and Amanda Byström and Sergey E. Koposov and Anika Slizewski and Wenting Wang and Gwendolyn M. Eadie and Nathan R. Sandford and Benjamin A. Weaver and Raymond G. Carlberg and J. Aguilar and S. Ahlen and C. Allende Prieto and A. Aviles and F. Beutler and D. Bianchi and D. Brooks and R. Canning and A. Carnero Rosell and F. J. Castander and E. Chaussidon and T. Claybaugh and A. P. Cooper and A. Cuceu and A. de la Macorra and Arjun Dey and Biprateep Dey and P. Doel and S. Ferraro and J. E. Forero-Romero and E. Gaztañaga and Satya Gontcho A Gontcho and G. Gutierrez and H. K. Herrera-Alcantar and M. Ishak and S. Juneau and R. Kehoe and D. Kirkby and A. Kremin and O. Lahav and C. Lamman and M. Landriau and L. Le Guillou and A. Leauthaud and A. Meisner and R. Miquel and S. Nadathur and E. Paillas and N. Palanque-Delabrouille and W. J. Percival and F. Prada and I. Pérez-Ráfols and C. Ravoux and G. Rossi},
howpublished = {arXiv},
year = {2026},
month = nov,
doi = {10.48550/arxiv.2611.05521},
eprint = {2611.05521},
archivePrefix = {arXiv},
url = {https://arxiv.org/abs/2611.05521},
note = {CC BY 4.0},
}
RIS
TY - UNPB
TI - A distribution-function estimate of the Milky Way mass profile from outer halo stars in DESI DR2
AU - Gustavo E. Medina
AU - Thomas M. Callingham
AU - Monica Valluri
AU - Alexander H. Riley
AU - Ting S. Li
AU - Jiaxin Han
AU - Leandro Beraldo e Silva
AU - Oleg Y. Gnedin
AU - Amanda Byström
AU - Sergey E. Koposov
AU - Anika Slizewski
AU - Wenting Wang
AU - Gwendolyn M. Eadie
AU - Nathan R. Sandford
AU - Benjamin A. Weaver
AU - Raymond G. Carlberg
AU - J. Aguilar
AU - S. Ahlen
AU - C. Allende Prieto
AU - A. Aviles
AU - F. Beutler
AU - D. Bianchi
AU - D. Brooks
AU - R. Canning
AU - A. Carnero Rosell
AU - F. J. Castander
AU - E. Chaussidon
AU - T. Claybaugh
AU - A. P. Cooper
AU - A. Cuceu
AU - A. de la Macorra
AU - Arjun Dey
AU - Biprateep Dey
AU - P. Doel
AU - S. Ferraro
AU - J. E. Forero-Romero
AU - E. Gaztañaga
AU - Satya Gontcho A Gontcho
AU - G. Gutierrez
AU - H. K. Herrera-Alcantar
AU - M. Ishak
AU - S. Juneau
AU - R. Kehoe
AU - D. Kirkby
AU - A. Kremin
AU - O. Lahav
AU - C. Lamman
AU - M. Landriau
AU - L. Le Guillou
AU - A. Leauthaud
AU - A. Meisner
AU - R. Miquel
AU - S. Nadathur
AU - E. Paillas
AU - N. Palanque-Delabrouille
AU - W. J. Percival
AU - F. Prada
AU - I. Pérez-Ráfols
AU - C. Ravoux
AU - G. Rossi
PY - 2026
DA - 2026/11/03
PB - arXiv
DO - 10.48550/arxiv.2611.05521
UR - https://arxiv.org/abs/2611.05521
AB - We present measurements of the Milky Way mass using blue horizontal-branch (BHB) and RR Lyrae (RRL) stars from the second data release of DESI (DR2), covering its first three years of operations. We employ 279 BHBs and 213 RRLs at ∼ 50--$80$\,kpc from the Galactic center, selected from catalogs roughly twice as large as those of DESI DR1, used in our previous mass measurement. We apply the Galactic Mass Estimator (GME), a hierarchical Bayesian framework that assumes power-law forms for the potential and the tracer density, and accounts for distance and velocity uncertainties. Validating the method on 24 AuriDESI mock catalogs (six Auriga halos at four viewing angles), we find that it overestimates the enclosed mass by ∼ 15% at 80\,kpc, and correct our results accordingly. We obtain M(<80 kpc) = 0.64^+0.06_−0.06 and 0.53^+0.05_−0.05 × 10^12 M_⊙ for BHBs and RRLs, respectively, while including Sagittarius stream stars lowers these masses by ∼ 10\%. Extrapolating to 100\,kpc, we obtain M(<100 kpc) = 0.74^+0.07_−0.07 and 0.62^+0.06_−0.07 × 10^12 M_⊙, and anchoring an NFW halo to our GME constraints at 65\,kpc yields virial masses of M_200 = 1.12^+0.14_−0.12 and 0.89^+0.11_−0.10 × 10^12 M_⊙. BHBs yield systematically higher masses than RRLs across the full radial range, reflecting the impact of tracer choice even within a single method. This work is part of a wider DESI DR2 Key Project effort to measure the Milky Way mass and constrain systematics arising from different samples and methodologies.
ER -