Background: There are three well-studied cases of planes of satellite galaxies, i.e. flattened arrangements of satellite galaxies that show coherent dynamics reminiscent of rotation: Milky Way, Andromeda, and Centaurus A. Each of these is in tension with ΛCDM expectations.
A few months ago Karachentsev & Kroupa (2024, ) highlighted the NGC4490 system as another case where the surrounding dwarf companions are in a spatially flattened arrangement and show a strong kinematic correlation. ui.adsabs.harvard.edu/abs/2024MNRAS.…
Another new paper, lead by my @AIP_Potsdam PhD student Jamie Kanehisa (with @VoltarCH).
We identified a serious "Too Many Dwarf Galaxies" problem, not for a specific host but for the whole MATLAS survey targeting 150 fields around early-type hosts.
MATLAS () is a deep imaging survey targeting massive galaxies beyond the Local Volume. matlas.astro.unistra.fr/WP/
In MATLAS' 150 fields around these early-type hosts, a total of 2210 dwarf candidates were found. Not all of these are bona fide satellite galaxies, but between 57% and ~80% of those with velocity measurements are within 500km/s of their hosts and thus confirmed likely satellites
Paper day! I'm thrilled about the extensive new work by Salvatore Taibi, postdoc in my group (incl S. Khoperskov, @GalacticRAVE @satellitegalaxy). We study the observed Vast Polar Structure (VPOS) of the Milky Way and end up with a weirdly puzzling result. arxiv.org/abs/2310.13521
There are many papers looking at the planes of satellite galaxies problem via cosmological simulations. This approach is of limited utility to learn about the origin of the observed sat. planes. We instead focus on empirically investigating the MW’s satellite plane, the VPOS.
Our approach is motivated by an earlier study by @michelle_lmc, who compared the on- and off-plane satellite galaxies of the Andromeda galaxy, and found them to not show any marked differences. ui.adsabs.harvard.edu/abs/2015ApJ...…
To those of you interested in the controversy over the wide binary stars test of MOND, with some papers finding MOND behavior and another excluding MOND at extremely high sigma, let me summarize in a🧵what the discussion among the teams seems to have settled on here at #MONDat40:
Context: You can test the the law of gravity in the low acceleration regime via wide binary stars. This is relevant for Modified Newtonian Dynamics (MOND), which should act at accelerations around and below a0≈1.2×10−10 m/s2, where gravity is stronger than expected from Newton.
Here at #MONDat40, we heard three conflicting WB study results:
Kyu-Hyun Chae and independently Xavier Hernandez find agreement with MOND: a deviation from Newtonian expectations for wide-enough binaries.
Indanil Banik et al. find no MOND-like behavior & report 16 sigma tension.
Planes of satellite galaxies vs. LCDM. There’s a lot of literature on this debate. Since it would be a shame if relevant papers wouldn’t be cited and old arguments needlessly repeated, now is as good a time as any to go over some common methodological issues to look out for.
Planes of satellites are spatially flattened arrangements with coherent kinematics; potentially co-rotating. The latter seems the case for many of the 11 classical MW satellite galaxies. To measure tension with LCDM, one looks for similarly extreme structures in simulated systems
Matching only either the observed flattening or the kinematic coherence does not provide a good estimate of the frequency of analogs in simulations. The intriguing property is that the observe system is both flattened & correlated. ui.adsabs.harvard.edu/abs/2020MNRAS.…ui.adsabs.harvard.edu/abs/2014MNRAS.…
Paper day! "The Milky Way’s Disk of Classical Satellite Galaxies in Light of Gaia DR2", accepted in MNRAS, is out on the arXiv today: arxiv.org/abs/1911.05081
The paper is a whopping 20 pages long, so let me summarize the key takeaways here.
We know since Lynden-Bell (1976) and Kunkel & Demers (1976) that the distribution of known Milky Way satellite galaxies, especially the 11 brightest ones, is highly flattened. They form a disk/plane perpendicular to the MW.
Proper motion (PM) measurements have indicated that many of these satellites also orbit along this plane in the same direction (i.e. co-orbit).
Which is a problem for our standard model of cosmology LCDM, where similarly coherent satellite systems are very rare.