A Pride of Satellites in the Constellation Leo? Discovery of the Leo VI Milky Way Satellite Ultra-faint Dwarf Galaxy with DELVE Early Data Release 3

Journal Article · 24 January 2025 · The Astrophysical Journal

DOI: https://doi.org/10.3847/1538-4357/ad9b0c · OSTI ID:2506905

Tan, C. Y. ; Cerny, W. ; Drlica-Wagner, A. ; Pace, A. B. ; Geha, M. ; Ji, A. P. ; Li, T. S. ; Adamów, M. ; Anbajagane, D. ; Bom, C. R. ; Carballo-Bello, J. A. ; Carlin, J. L. ; Chang, C. ; Chaturvedi, A. ; Chiti, A. ; Choi, Y. ; Collins, M. L. M. ; Doliva-Dolinsky, A. ; Ferguson, P. S. ; Gruendl, R. A. ; James, D. J. ; Limberg, G. ; Navabi, M. ; Martínez-Delgado, D. ; Martínez-Vázquez, C. E. ; Medina, G. E. ; Mutlu-Pakdil, B. ; Nidever, D. L. ; Noël, N. E. D. ; Riley, A. H. ; Sakowska, J. D. ; Sand, D. J. ; Sharp, J. ; Stringfellow, G. S. ; Tolley, C. ; Tucker, D. L. ; Vivas, A. K.

Abstract We report the discovery and spectroscopic confirmation of an ultra-faint Milky Way satellite in the constellation of Leo. This system was discovered as a spatial overdensity of resolved stars observed with Dark Energy Camera (DECam) data from an early version of the third data release of the DECam Local Volume Exploration (or DELVE) survey. The low luminosity ( $M_V=-3.56_{-0.37}^{+0.47}$ ; $L_V=2300_{-700}^{+1200}{L}_{\odot }$ ), large size ( $R_{1/2}=90_{-30}^{+30}$ pc), and large heliocentric distance ( $D=111_{-6}^{+9}$ kpc) are all consistent with the population of ultra-faint dwarf galaxies (UFDs). Using Keck/DEIMOS observations of the system, we were able to spectroscopically confirm nine member stars, while measuring a tentative mass-to-light ratio of $700_{-500}^{+1400}{M}_{\odot }/L_{\odot }$ and a nonzero metallicity dispersion of ${\sigma }_{[\mathrm{Fe}/\mathrm{H}]}=0.19_{-0.11}^{+0.14}$ , further confirming Leo VI’s identity as a UFD. While the system has a highly elliptical shape, $ϵ=0.54_{-0.29}^{+0.19}$ , we do not find any conclusive evidence that it is tidally disrupting. Moreover, despite the apparent on-sky proximity of Leo VI to members of the proposed Crater-Leo infall group, its smaller heliocentric distance and inconsistent position in energy–angular momentum space make it unlikely that Leo VI is part of the proposed infall group.

• Research Organization: Arizona U., Astron. Dept. - Steward Observ.; Carnegie Mellon U.; Cerro-Tololo InterAmerican Obs.; Chicago U.; Chicago U., Astron. Astrophys. Ctr.; Chicago U., KICP; Colorado U., CASA; Dartmouth Coll.; Durham U., ICC; Fermi National Accelerator Laboratory (FNAL), Batavia, IL (United States); Gemini Observ., Hilo; IAA, Granada; Illinois U., Urbana (main); Illinois U., Urbana, Astron. Dept.; Montana State U.; NRAO, Tucson; Natl. Solar Observ., Tucson; Rio de Janeiro, CBPF; Sao Paulo U., IAG; Surrey U.; Tampa U.; Tarapaca U.; Toronto U., Astron. Dept.; UC, Berkeley, Astron. Dept.; Unlisted, US, MA; Wisconsin U., Madison; Yale U.
• Sponsoring Organization: US Department of Energy; USDOE
• Grant/Contract Number: 89243024CSC000002
• OSTI ID: 2506905
• Report Number(s): FERMILAB-PUB-24-0358-LDRD-PPD
• Journal Information: The Astrophysical Journal, Journal Name: The Astrophysical Journal Journal Issue: 2 Vol. 979; ISSN 0004-637X
• Publisher: American Astronomical SocietyCopyright Statement
• Country of Publication: United States
• Language: English