The Cen A galaxy group: Dynamical mass and missing baryons
Abstract
The nearby elliptical galaxy Centaurus A (Cen A) is surrounded by a flattened system of dwarf satellite galaxies with coherent motions. Using a novel Bayesian approach, we measured the mean rotation velocity vrot and velocity dispersion σint of the satellite system. We found vrot/σint ≃ 0.7, indicating that the satellite system has non-negligible rotational support. Using Jeans' equations, we measured a circular velocity of 258 km s−1 and a dynamical mass of 1.2 × 1013 M⊙ within 800 kpc. In a Λ cold dark matter cosmological context, we found that the Cen A group has a baryon fraction Mb/M200 ≃ 0.035 and is missing ∼77% of the cosmologically available baryons. Consequently, Cen A should have a hot intergalactic medium with a mass of ∼8 × 1011 M⊙, which is more than ∼20 times larger than current X-ray estimates. Intriguingly, the whole Cen A group lies on the baryonic Tully-Fisher relation defined by individual rotationally supported galaxies, as expected in Milgromian dynamics (MOND) with no need of missing baryons.
Based on observations collected at the European Organisation for Astronomical Research in the Southern Hemisphere under the ESO program 0101.A-0193.- Publication:
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Astronomy and Astrophysics
- Pub Date:
- June 2022
- DOI:
- 10.1051/0004-6361/202142351
- arXiv:
- arXiv:2111.10306
- Bibcode:
- 2022A&A...662A..57M
- Keywords:
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- dark matter;
- cosmology: observations;
- galaxies: dwarf;
- galaxies: elliptical and lenticular;
- cD;
- galaxies: halos;
- galaxies: kinematics and dynamics;
- Astrophysics - Astrophysics of Galaxies
- E-Print:
- Accepted for publication in A&