Thursday, April 11, 2024

Eclipse Fun On Turtle Island


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neo said...

arXiv:2404.06537 (astro-ph)
[Submitted on 9 Apr 2024]
Exploring the nature of dark matter with the extreme galaxy AGC 114905
Pavel E. Mancera Piña, Giulia Golini, Ignacio Trujillo, Mireia Montes
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AGC 114905 is a dwarf gas-rich ultra-diffuse galaxy seemingly in tension with the cold dark matter (CDM) model. Specifically, the galaxy appears to have an extremely low-density halo and a high baryon fraction, while CDM predicts dwarfs to have very dense and dominant dark haloes. The alleged tension relies on the galaxy's rotation curve decomposition, which depends heavily on its inclination. This inclination, estimated from the gas morphology, remains somewhat uncertain. We present unmatched ultra-deep optical imaging of AGC 114905 reaching surface brightness limits μr,lim≈32 mag/arcsec2 (3σ; 10 arcsec × 10 arcsec) obtained with the 10.4-m Gran Telescopio Canarias. With the new imaging, we characterise the galaxy's morphology, surface brightness, colours, and stellar mass profiles in great detail. The stellar disc has a similar extent as the gas, presents spiral arms-like features, and shows a well-defined edge. Stars and gas share similar morphology, and crucially, we find an inclination of 31±2∘, in agreement with the previous determinations. We revisit the rotation curve decomposition of the galaxy, and we explore different mass models in the context of CDM, self-interacting dark matter (SIDM), fuzzy dark matter (FDM) or Modified Newtonian Dynamics (MOND). We find that the latter does not fit the circular speed of the galaxy, while CDM only does so with dark halo parameters rarely seen in cosmological simulations. Within the uncertainties, SIDM and FDM remain feasible candidates to explain the observed kinematics of AGC 114905.

Comments: Submitted to A&A. 17 pages (12 figures) + appendices
Subjects: Astrophysics of Galaxies (astro-ph.GA); Cosmology and Nongalactic Astrophysics (astro-ph.CO)
Cite as: arXiv:2404.06537 [astro-ph.GA]
(or arXiv:2404.06537v1 [astro-ph.GA] for this version)
arXiv:2404.06538 (astro-ph)
[Submitted on 9 Apr 2024]
Refracted Gravity Solutions from Small to Large Scales
Valentina Cesare
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If visible matter alone is present in the Universe, general relativity (GR) and its Newtonian weak field limit (WFL) cannot explain several pieces of evidence, from the largest to the smallest scales. The most investigated solution is the cosmological model Λ cold dark matter (ΛCDM), where GR is valid and two dark components are introduced, dark energy (DE) and dark matter (DM), to explain the ∼70\% and ∼25\% of the mass-energy budget of the Universe, respectively. An alternative approach is provided by modified gravity theories, where a departure of the gravity law from ΛCDM is assumed, and no dark components are included. This work presents refracted gravity (RG), a modified theory of gravity formulated in a classical way where the presence of DM is mimicked by a gravitational permittivity ϵ(ρ) monotonically increasing with the local mass density ρ, which causes the field lines to be refracted in small density environments. Specifically, the flatter the system the stronger the refraction effect and thus, the larger the mass discrepancy if interpreted in Newtonian gravity. RG presented several encouraging results in modelling the dynamics of disk and elliptical galaxies and the temperature profiles of the hot X-ray emitting gas in galaxy clusters and a covariant extension of the theory seems to be promising.

Comments: 32 pages, 9 figures, published on 5th April 2024 in Astronomy 2024, 3(2), 68-99, in the Special Issue "Current Trends in Cosmology"; accepted for publication on 1st April 2024
Subjects: Astrophysics of Galaxies (astro-ph.GA)
Cite as: arXiv:2404.06538 [astro-ph.GA]
(or arXiv:2404.06538v1 [astro-ph.GA] for this version)