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I'm super excited for our new paper today (by @VoltarCH, @lellifede, @KatjaFah, @satellitegalaxy et al.): https://arxiv.org/abs/2012.08138
The title already states our main finding: "The coherent motion of Cen A dwarf satellite galaxies remains a challenge for ΛCDM cosmology"
The title already states our main finding: "The coherent motion of Cen A dwarf satellite galaxies remains a challenge for ΛCDM cosmology"
The study is a follow-up on our 2018 paper ( https://arxiv.org/abs/1802.00081 ) which cause some debate when we found that of the Centaurus A satellites galaxies which are arranged in a flattened structure, 14 out of 16 have velocities indicative of a rotating plane of satellites.
This is highly unlikely to find in cosmological simulations; less than <0.5% of host galaxies should be surrounded by such an extreme satellite galaxy structure. Baryonic physics doesn't offer an easy way out, so this constitutes a severe challenge to the cosmological model.
We now test our past findings after almost doubling the number of satellites with velocity information. Guess what:
1) the kinematic signal is still present (21/28 sats follow trend)!
2) Its tension with cosmological simulations (we now use Illustris TNG) is at the 0.2% level!
1) the kinematic signal is still present (21/28 sats follow trend)!
2) Its tension with cosmological simulations (we now use Illustris TNG) is at the 0.2% level!
@VoltarCH has a great thread with more details on the paper, so let me just add a couple outtakes. https://twitter.com/VoltarCH/status/1339139097168850946
The orientation that maximizes the kinematic signal aligns with the spatial flattening of the satellite distribution, like a rotating satellite plane.
Dashed line: major axis of sat distr.
Thick green line: minor axis
Dotted lines: indicate where kinematic coherence is maximized
Dashed line: major axis of sat distr.
Thick green line: minor axis
Dotted lines: indicate where kinematic coherence is maximized
Furthermore, while we select the most luminous (or massive) satellite galaxies in the simulations for our main analysis, the results don't change if we instead randomly pick 28 out of N top-ranked sats. The tension with LCDM is robust and not only present for special satellites.
One of the concerns regarding the original study was that there were only 16 satellites with known velocities, i.e.: "we need more data!"
We got more data.
It confirms our previous findings.
We got more data.
It confirms our previous findings.
So, observations don't make this LCDM tension go away in Centaurus A. Combined with similar structures around the MW and M31, we really need to think hard about what we might be missing in our cosmological simulations, or even in the underlying model.
