photoD with Rubin’s Data Preview 1: First stellar photometric distances and faint blue star deficits

Stellar distances with Rubin’s DP1

¹ Ruđer Bošković Institute, Bijenička cesta 54, 10000 Zagreb, Croatia
² XV. Gymnasium (MIOC), Jordanovac 8, 10000 Zagreb, Croatia
³ Vera C. Rubin Observatory Project Office, 950 N. Cherry Ave., Tucson, AZ 85719, USA
⁴ University of Washington, Dept. of Astronomy, Box 351580, Seattle, WA 98195, USA
⁵ Faculty of Physics, University of Rijeka, Radmile Matejčić 2, Rijeka, Croatia
⁶ Institute for Data-intensive Research in Astrophysics and Cosmology, University of Washington, 3910 15th Avenue NE, Seattle, WA 98195, USA
⁷ McWilliams Center for Cosmology & Astrophysics, Department of Physics, Carnegie Mellon University, Pittsburgh, PA 15213, USA
⁸ Olympic College, 1600 Chester Ave., Bremerton, WA 98337-1699, USA
⁹ INAF – Osservatorio Astronomico di Padova, Vicolo dell‘Osservatorio 5, 35122 Padova, Italy
¹⁰ Department of Physics and Astronomy G. Galilei, University of Padova, Vicolo dell’Osservatorio 3, 35122 Padova, Italy
¹¹ SLAC National Accelerator Laboratory, 2575 Sand Hill Rd., Menlo Park, CA 94025, USA
¹² Université Paris Cité, CNRS/IN2P3, CEA, APC, 4 rue Elsa Morante, 75013 Paris, France
¹³ Yerkes Observatory, 373 W. Geneva St., Williams Bay, WI 53191, USA
¹⁴ Vera C. Rubin Observatory/NSF NOIRLab, 950 N. Cherry Ave., Tucson, AZ 85719, USA
¹⁵ Université Paris Cité, CNRS/IN2P3, APC, 4 rue Elsa Morante, 75013 Paris, France
¹⁶ Kavli Institute for Particle Astrophysics and Cosmology, SLAC National Accelerator Laboratory, 2575 Sand Hill Rd., Menlo Park, CA 94025, USA
¹⁷ NSF NOIRLab, 950 N. Cherry Ave., Tucson, AZ 85719, USA
¹⁸ Université Paris-Saclay, CNRS/IN2P3, IJCLab, 15 Rue Georges Clemenceau, 91405 Orsay, France
¹⁹ Vera C. Rubin Observatory, Avenida Juan Cisternas #1500, La Serena, Chile
²⁰ Sorbonne Université, Université Paris Cité, CNRS/IN2P3, LPNHE, 4 place Jussieu, 75005 Paris, France
²¹ Santa Cruz Institute for Particle Physics and Physics Department, University of California–Santa Cruz, 1156 High St., Santa Cruz, CA 95064, USA
²² Steward Observatory, The University of Arizona, 933 N. Cherry Ave., Tucson, AZ 85721, USA
²³ Université Clermont Auvergne, CNRS/IN2P3, LPCA, 4 Avenue Blaise Pascal, 63000 Clermont-Ferrand, France
²⁴ University of Arizona, Department of Astronomy and Steward Observatory, 933 N. Cherry Ave, Tucson, AZ 85721, USA
²⁵ Department of Astronomy, Yonsei University, 50 Yonsei-ro, Seoul 03722, Republic of Korea
²⁶ Physics Department, University of California, One Shields Avenue, Davis, CA 95616, USA
²⁷ Physics Department, University of California, 366 Physics North, MC 7300 Berkeley, CA 94720, USA
²⁸ Department of Physics, Duke University, Durham, NC 27708, USA
²⁹ Department of Astrophysical Sciences, Princeton University, Princeton, NJ 08544, USA
³⁰ Brookhaven National Laboratory, Upton, NY 11973, USA
³¹ CNRS/IN2P3, CC-IN2P3, 21 avenue Pierre de Coubertin, 69627 Villeurbanne, France
³² NCSA, University of Illinois at Urbana-Champaign, 1205 W. Clark St., Urbana, IL 61801, USA
³³ Department of Physics and Astronomy, Purdue University, 525 Northwestern Ave., West Lafayette, IN 47907, USA
³⁴ National Institute of Standards and Technology, Material Measurement Laboratory, Office of Data and Informatics, Gaithersburg, MD, USA
³⁵ Florida Institute of Technology, 150 W. University Blvd., Melbourne, FL 32901, USA
³⁶ Lawrence Livermore National Laboratory, 7000 East Avenue, Livermore, CA 94550, USA
³⁷ Space Telescope Science Institute, 3700 San Martin Drive, Baltimore, MD 21218, USA
³⁸ Austin Peay State University, Clarksville, TN 37044, USA
³⁹ ASTRON, Oude Hoogeveensedijk 4, 7991 PD, Dwingeloo, The Netherlands
⁴⁰ Fermi National Accelerator Laboratory, PO Box 500, Batavia, IL 60510, USA
⁴¹ Department of Physics, Harvard University, 17 Oxford St., Cambridge, MA 02138, USA
⁴² LSST Discovery Alliance, 933 N. Cherry Ave., Tucson, AZ 85719, USA

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Received: 12 September 2025
Accepted: 28 January 2026

Abstract

Aims. We investigate the utility of Rubin’s Data Preview 1 (DP1) for estimating stellar number density profiles across the Milky Way halo.

Methods. We used stellar broad-band near-UV to near-IR ugrizy photometry released in Rubin’s DP1 to estimate distance and metallicity for blue main sequence stars brighter than r = 24 in three ~1.1 sq. deg. fields at southern Galactic latitudes.

Results. Compared to TRILEGAL simulations of the Galaxy’s stellar content, we found a likely deficit of blue main sequence turn-off stars with 22 < r < 24. We interpreted this discrepancy as a signature of a steeper halo number density profile at galactocentric distances 10–50 kpc than the canonical ~1/r³ profile assumed in TRILEGAL simulations.

Conclusions. This interpretation is consistent with earlier suggestions based on observations of more luminous, but much less numerous, evolved stellar populations, along with a few pencil beam surveys of blue main sequence stars in the northern sky. These results bode well for the future Galactic halo exploration with Rubin’s Legacy Survey of Space and Time (LSST).