A Deep Look at the Ultra-Faint Milky Way Satellite Virgo III with Rubin Observatory Data Preview 2
Abstract
We analyze the ultra-faint Milky Way satellite Virgo III using data from the Vera C. Rubin Observatory Data Preview 2 (DP2). Virgo III was observed in the Rubin "Cosmic Treasure Chest" (M49) First Look field, which contains 924 visits in the u,g,r,i bands comprising ~10.5hrs of exposure time with LSSTCam. These data are considerably deeper than the majority of DP2, with a 5σ limiting magnitude that approaches the expected 10-year depth of LSST (~25.2-26.5mag, depending on band). We report the morphological and stellar population parameters of Virgo III measured with the maximum-likelihood-based package ugali. The depth of the Rubin imaging yields more than a factor of four increase in the number of candidate member stars (N* = 114+11−11) relative to the Virgo III discovery results (N* = 25+5−4), enabling significantly more precise morphological constraints. Our best-fit parameters broadly agree with previous measurements, further confirming that Virgo III has properties that are consistent with an ultra-faint dwarf galaxy (MV = −2.72+0.49−0.70; r1/2 = 53+10−8) located at a heliocentric distance of D⊙ = 151+8−8. We also demonstrate that the depth and photometric quality of the DP2 data are sufficient to separate metal-poor and metal-rich stars in color-color space. We further present period estimates for the three known RR Lyrae member stars derived from the DP2 forced photometry; we use theoretical Period-Luminosity-Metallicity (PLZ) and Period-Wesenheit-Metallicity (PWZ) relations to obtain independent distance estimates. We find that our period and distance estimates are broadly consistent with previous measurements for these RR Lyrae. These results demonstrate the power of LSST data for the discovery and characterization of ultra-faint dwarf galaxies and motivate future searches for new satellites across the southern sky.
Versions
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BibTeX
@misc{pai2026deep,
title = {{A Deep Look at the Ultra-Faint Milky Way Satellite Virgo III with Rubin Observatory Data Preview 2}},
author = {Aashay Pai and Alex Drlica-Wagner and Peter S. Ferguson and William Cerny and Chin Yi Tan and Jeffrey L. Carlin and Yumi Choi and Željko Ivezić and Andrés A. Plazas Malagón and Lauren A. MacArthur and Colin T. Slater and Dan S. Taranu and Brian Yanny},
howpublished = {arXiv},
year = {2026},
month = oct,
doi = {10.48550/arxiv.2607.25044},
eprint = {2607.25044},
archivePrefix = {arXiv},
url = {https://arxiv.org/abs/2607.25044},
note = {CC BY 4.0},
}
RIS
TY - UNPB
TI - A Deep Look at the Ultra-Faint Milky Way Satellite Virgo III with Rubin Observatory Data Preview 2
AU - Aashay Pai
AU - Alex Drlica-Wagner
AU - Peter S. Ferguson
AU - William Cerny
AU - Chin Yi Tan
AU - Jeffrey L. Carlin
AU - Yumi Choi
AU - Željko Ivezić
AU - Andrés A. Plazas Malagón
AU - Lauren A. MacArthur
AU - Colin T. Slater
AU - Dan S. Taranu
AU - Brian Yanny
PY - 2026
DA - 2026/10/16
PB - arXiv
DO - 10.48550/arxiv.2607.25044
UR - https://arxiv.org/abs/2607.25044
AB - We analyze the ultra-faint Milky Way satellite Virgo III using data from the Vera C. Rubin Observatory Data Preview 2 (DP2). Virgo III was observed in the Rubin "Cosmic Treasure Chest" (M49) First Look field, which contains 924 visits in the u,g,r,i bands comprising ~10.5hrs of exposure time with LSSTCam. These data are considerably deeper than the majority of DP2, with a 5σ limiting magnitude that approaches the expected 10-year depth of LSST (~25.2-26.5mag, depending on band). We report the morphological and stellar population parameters of Virgo III measured with the maximum-likelihood-based package ugali. The depth of the Rubin imaging yields more than a factor of four increase in the number of candidate member stars (N_* = 114^+11_−11) relative to the Virgo III discovery results (N_* = 25^+5_−4), enabling significantly more precise morphological constraints. Our best-fit parameters broadly agree with previous measurements, further confirming that Virgo III has properties that are consistent with an ultra-faint dwarf galaxy (M_V = −2.72^+0.49_−0.70; r_1/2 = 53^+10_−8) located at a heliocentric distance of D_⊙ = 151^+8_−8. We also demonstrate that the depth and photometric quality of the DP2 data are sufficient to separate metal-poor and metal-rich stars in color-color space. We further present period estimates for the three known RR Lyrae member stars derived from the DP2 forced photometry; we use theoretical Period-Luminosity-Metallicity (PLZ) and Period-Wesenheit-Metallicity (PWZ) relations to obtain independent distance estimates. We find that our period and distance estimates are broadly consistent with previous measurements for these RR Lyrae. These results demonstrate the power of LSST data for the discovery and characterization of ultra-faint dwarf galaxies and motivate future searches for new satellites across the southern sky.
ER -