Due to their low surface brightness, dwarf galaxies are particularly susceptible to tidal forces. The expected degree of disturbance depends on the assumed gravity law and whether they have a dominant dark halo. This makes dwarf galaxies useful for testing different gravity models.
In this project, we use the Fornax Deep Survey (FDS) dwarf galaxy catalogue to compare the properties of dwarf galaxies in the Fornax Cluster with those predicted by the Lambda cold dark matter (ΛCDM) standard model of cosmology and Milgromian dynamics (MOND). We construct a test particle simulation of the Fornax system. We then use the MCMC method to fit this to the FDS distribution of tidal susceptibility η (half-mass radius divided by theoretical tidal radius), the fraction of dwarfs that visually appear disturbed as a function of η, and the distribution of projected separation from the cluster centre. This allows us to constrain the η value at which dwarfs should get destroyed by tides.
Accounting for an r′-band surface brightness limit of 27.8 magnitudes per square arcsec, the required stability threshold is ηdestr=0.25+0.07−0.03 in ΛCDM and 1.88+0.85−0.53 in MOND. The ΛCDM value is in tension with previous N-body dwarf galaxy simulations, which indicate that ηdestr≈1. Our MOND N-body simulations indicate that ηdestr=1.70±0.30, which agrees well with our MCMC analysis of the FDS.
We therefore conclude that the observed deformations of dwarf galaxies in the Fornax Cluster and the lack of low surface brightness dwarfs towards its centre are incompatible with ΛCDM expectations but well consistent with MOND.
E. Asencio, I. Banik, S. Mieske, A. Venhola, P. Kroupa, H. Zhao, "The distribution and morphologies of Fornax Cluster dwarf galaxies suggest they lack dark matter" arXiv:2208.02265 (August 3, 2022) (accepted for publication in MNRAS).
N-body dwarf galaxy simulations
ReplyDeletecomputer simulations can generate any result you demand
You put rules for the game in the simulations. If the simulations match reality, your rules have to be fairly close to the mark.
ReplyDeleteHuh, it's hard enough to get these huge complex models to run at all without erroring off to infinity. So it's equally hard to believe that someone has their fingers on the scales to get a predetermined result. But you can run the simulation multiple times and pick the result that you like.
ReplyDeletebtw
ReplyDelete[Submitted on 8 Aug 2022]
Searching for New Physics with DarkLight at the ARIEL Electron-Linac
E Cline (for the DarkLight Collaboration)
The search for a dark photon holds considerable interest in the physics community. Such a force carrier would begin to illuminate the dark sector. Many experiments have searched for such a particle, but so far it has proven elusive. In recent years the concept of a low mass dark photon has gained popularity in the physics community. Of particular recent interest is the 8Be and 4He anomaly, which could be explained by a new fifth force carrier with a mass of 17 MeV/c2. The proposed DarkLight experiment would search for this potential low mass force carrier at ARIEL in the 10-20 MeV e+e− invariant mass range. This proceeding will focus on the experimental design and physics case of the DarkLight experiment.
Comments: 7 pages, 4 figures, to be submitted as part of the proceedings on "New Scientific Opportunities with the TRIUMF ARIEL e-linac"
Subjects: Nuclear Experiment (nucl-ex)
Cite as: arXiv:2208.04120 [nucl-ex]
the hunt for x17 still being carried out in 8 Aug 2022
x17 = bigfoot ?
ReplyDelete"x17 = bigfoot?"
ReplyDeletePretty much. There are plausible alternative explanations for the data giving rise to the X17 hypothesis (I don't recall off the cuff what they were, but I blogged them, something about nuclear structure I think), and further experiments have pretty much ruled it out.
Also, there are a variety of fairly tight experimental constraints on dark photons such as one announced today: https://arxiv.org/abs/2208.04496
I don't usually blog dark photon exclusion papers because the possibility is fairly unlikely and because each individual paper usually only excludes a fairly narrow range.
One of these days, I may do a review post on exclusions of various kinds of dark matter particle hypotheses since the literature does a poor job of aggregating them.
Contra the X17 hypothesis:
ReplyDeletehttps://dispatchesfromturtleisland.blogspot.com/2020/08/new-analysis-disfavors-x17-particle.html
https://dispatchesfromturtleisland.blogspot.com/2019/11/hungarian-scientists-almost-surely.html
https://www.physicsforums.com/threads/new-force-of-nature-discovered.980792/
Comments at: https://dispatchesfromturtleisland.blogspot.com/2020/06/standard-model-neutrino-properties.html
Matt Strassler explained some of the problems with the hypothesis in November 2019. https://profmattstrassler.com/2019/11/25/has-a-new-force-of-nature-been-discovered/
See also https://en.wikipedia.org/wiki/X17_particle
The mass is far too low for a proposed tetraquark explanation of the kind made here (even though it wouldn't proposed a new fundamental boson):
https://arxiv.org/abs/2006.01018
A least three papers have explained the experimental data used as a basis for the X17 hypothesis without new physics:
https://arxiv.org/abs/2005.10643
https://arxiv.org/abs/2003.05722
https://arxiv.org/abs/2001.08995
X17 hypothesis (I don't recall off the cuff what they were, but I blogged them, something about nuclear structure I think), and further experiments have pretty much ruled it out.
ReplyDelete[Submitted on 8 Aug 2022]
Searching for New Physics with DarkLight at the ARIEL Electron-Linac
E Cline (for the DarkLight Collaboration)
only some of the parameter space for x17
it's also looking for dark photons
the exciting thing is New Physics with DarkLight at the ARIEL Electron-Linac
should give definitely on x17 near future