Amazing stuff!
"Preview data from the recently completed ... Vera C. Rubin Observatory in Chile point to a wave of discoveries that may complete the census of the Milky Way’s neighboring galaxies — including its faintest companions.
Using newly available data from the observatory ... researchers identified two previously unknown companions of the Milky Way, an early indicator that the observatory’s advanced technology could reveal the hundreds of faint companions thought to be hiding around Earth’s home galaxy.
Large galaxies are often orbited by satellites — small galaxies or star clusters — but many are extremely faint and difficult to find. There are about 65 known satellite galaxies of the Milky Way, yet there is speculation that hundreds more Milky Way satellites remain undetected. ..."
From the abstract:
"We present the discovery of Aquarius IV (Rubin J2201−0234)—the first ultra-faint Milky Way (MW) satellite to be identified using data from the Vera C. Rubin Observatory.
This system was detected at ∼8σ significance using Rubin Early Data Preview 2 (EDP2) photometry and independently confirmed at ∼6σ significance in archival Dark Energy Camera imaging.
Jointly fitting its morphology and distance, we find that Aquarius IV is a low-luminosity (), compact ( pc; arcmin) stellar system in the outer Galactic halo (D⊙ = ). Its stellar population is consistent with an ancient, metal-poor stellar isochrone (τ = 13 Gyr, Z = 0.0001).
These properties closely resemble those of the smallest and faintest confirmed ultra-faint dwarf galaxies (UFDs), though a globular cluster classification is not ruled out. Given the small number of detected member stars in Rubin EDP2, deeper imaging and spectroscopy will be critical for determining the properties and classification of Aquarius IV at higher confidence."
Discovery of the Distant, Ultra-faint Milky Way Satellite Aquarius IV with the Vera C. Rubin Observatory Early Data Preview 2 (open access)
Figure 1.
Top
Left: Smoothed spatial distribution of isochrone-filtered stars in a small region surrounding Aquarius IV.
Center: EDP2 color coadd image of a much smaller region centered on Aquarius IV.
Right: CMD of stars located within of Aquarius IV ...
Bottom
Left: Radial density profile of isochrone-filtered stars. The best-fit Plummer model is shown in blue.
Center: Spatial distribution of stars in a region centered on Aquarius IV, colored by ugali membership probability; stars with probabilities pi < 0.05 are shown in gray.
Right: CMD of the same stars shown in the bottom-center panel. The brightest red giant branch star candidate (g0 ≈ 18; × symbol) is rule
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