Examinando por Autor "Amram P."
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Ítem Dark matter fraction derived from the M31 rotation curve(EDP Sciences, 0025-02) Hammer F.; Yang Y.B.; Amram P.; Chemin L.; Mamon G.A.; Wang J.L.; Akib I.; Jiao Y.J.; Wang H.F.Mass estimates of a spiral galaxy derived from its rotation curve must account for the galaxy's past accretion history. There are several lines of evidence indicating that M31 experienced a major merger 2 to 3 Gyr ago. In this work, we generated a dynamical model of M31 as a merger remnant that reproduces most of its properties, including from the central bar to the outskirts. The model accounts for M31's past major merger and reproduces the details of its rotation curve, including its 14 kpc bump and the observed increase of velocity beyond 25 kpc. We find non-equilibrium and oscillatory motions in the gas of the merger-remnant outskirts caused by material in a tidal tail returning to the merger remnant. A total dynamical M31 mass of 4.5× 1011 M⊙ within 137 kpc was obtained after scaling it to the observed HI rotation curve. Within this radial distance, we find that 68% of the total dynamical mass is dark. © The Authors 2025.Ítem Dark matter fraction derived from the M31 rotation curve(EDP Sciences, 0025-02) Hammer F.; Yang Y.B.; Amram P.; Chemin L.; Mamon G.A.; Wang J.L.; Akib I.; Jiao Y.J.; Wang H.F.Mass estimates of a spiral galaxy derived from its rotation curve must account for the galaxy's past accretion history. There are several lines of evidence indicating that M31 experienced a major merger 2 to 3 Gyr ago. In this work, we generated a dynamical model of M31 as a merger remnant that reproduces most of its properties, including from the central bar to the outskirts. The model accounts for M31's past major merger and reproduces the details of its rotation curve, including its 14 kpc bump and the observed increase of velocity beyond 25 kpc. We find non-equilibrium and oscillatory motions in the gas of the merger-remnant outskirts caused by material in a tidal tail returning to the merger remnant. A total dynamical M31 mass of 4.5× 1011 M⊙ within 137 kpc was obtained after scaling it to the observed HI rotation curve. Within this radial distance, we find that 68% of the total dynamical mass is dark. © The Authors 2025.Ítem MHONGOOSE discovery of a gas-rich low surface brightness galaxy in the Dorado group(EDP Sciences, 2024-10) Maccagni F.M.; De Blok W.J.G.; Mancera Piña P.E.; Ragusa R.; Iodice E.; Spavone M.; Mcgaugh S.; Oman K.A.; Oosterloo T.A.; Koribalski B.S.; Kim M.; Adams E.A.K.; Amram P.; Bosma A.; Bigiel F.; Brinks E.; Chemin L.; Combes F.; Gibson B.; Healy J.; Holwerda B.W.; Józsa G.I.G.; Kamphuis P.; Kleiner D.; Kurapati S.; Marasco A.; Spekkens K.; Veronese S.; Walter F.; Zabel N.; Zijlstra A.We present the discovery of a low-mass, gas-rich low surface brightness galaxy in the Dorado group, at a distance of 17.7 Mpc. Combining deep MeerKAT 21-cm observations from the MeerKAT Hi Observations of Nearby Galactic Objects: Observing Southern Emitters (MHONGOOSE) survey with deep photometric images from the VST Early-type Galaxy Survey (VEGAS) we find a stellar and neutral atomic hydrogen (H i) gas mass of M∗ = 2:23 × 106M⊙ and MHI = 1:68 × 106 M⊙, respectively. This low surface brightness galaxy is the lowest-mass Hi detection found in a group beyond the local Universe (D ≳ 10 Mpc). The dwarf galaxy has the typical overall properties of gas-rich low surface brightness galaxies in the Local group, but with some striking differences. Namely, the MHONGOOSE observations reveal a very low column density (∼ 1018-19 cm-2) Hi disk with asymmetrical morphology possibly supported by rotation and higher velocity dispersion in the centre. There, deep optical photometry and UV observations suggest a recent enhancement of the star formation. Found at galactocentric distances where in the Local Group dwarf galaxies are depleted of cold gas (at a projected distance of 390 kpc from the group centre), this galaxy is likely on its first orbit within the Dorado group. We discuss the possible environmental effects that may have caused the formation of the Hi disk and the enhancement of star formation (SF), highlighting the short-lived phase (a few hundreds million years) of the gaseous disk, before either SF or hydrodynamical forces will deplete the gas of the galaxy.Ítem Possible origins of anomalous Ha I gas around MHONGOOSE galaxy, NGC 5068(EDP Sciences, 2024-07) Healy J.; De Blok W.J.G.; Maccagni F.M.; Amram P.; Chemin L.; Combes F.; Holwerda B.W.; Kamphuis P.; Pisano D.J.; Schinnerer E.; Spekkens K.; Verdes-Montenegro L.The existing reservoirs of neutral atomic hydrogen gas (HI) in galaxies are insufficient to have maintained the observed levels of star formation without some kind of replenishment. This refuelling of the H I reservoirs is likely to occur at column densities an order of magnitude lower than previous observational limits (NHI, limit ∼ 1019 cm-2 at a 30″ resolution over a linewidth of 20 km s-1). In this paper, we present recent deep HI observations of NGC 5068, a nearby isolated star-forming galaxy observed by MeerKAT as part of the MHONGOOSE survey. With these new data, we were able to detect low column density HI around NGC 5068 with a 3σ detection limit of NHI = 6.4 × 1017 cm-2 at a 90″ resolution over a 20 km s-1 linewidth. The high sensitivity and resolution of the MeerKAT data reveal a complex morphology of the HI in this galaxy, a regularly rotating inner disk coincident with the main star-forming disk of the galaxy, a warped outer disk of low column density gas (NHI < 9 × 1019 cm-2), in addition to clumps of gas on the north-western side of the galaxy. We employed a simple two disk model that described the inner and outer disks, which enabled us to identify anomalous gas that deviates from the rotation of the main galaxy. The morphology and the kinematics of the anomalous gas suggest a possible extra-galactic origin. We explore a number of possible origin scenarios that may explain the anomalous gas, and conclude that fresh accretion is the most likely scenario.Ítem The Milky Way accretion history compared to cosmological simulations: From bulge formation to dwarf galaxy infall(EDP Sciences, 0024-12) Hammer F; Jiao Y.J.; Mamon G.A; Yang Y.B; Akib I.; Amram P.; Wang H.F.; Wang J.L; Chemin L.Galactic halos are known to grow hierarchically, inside out. This implies a correlation between the infall lookback time of satellites and their binding energy. Cosmological simulations predict a linear relation between the infall lookback time and the logarithm of the binding energy, with a small scatter. Gaia measurements of the bulk proper motions of globular clusters and dwarf satellites of the Milky Way are sufficiently accurate to establish the kinetic energies of these systems. Assuming the gravitational potential of the Milky Way, we can deduce the binding energies of the dwarf satellites and those of the galaxies that were previously accreted by the Milky Way. This can be compared to cosmological simulations for the first time. The relation of the infall lookback time versus binding energy we found in a cosmological simulation matches that for the early accretion events when the simulated total Milky Way mass within 21 kpc was rescaled to 2 1011 M. This agrees well with previous estimates from globular cluster kinematics and from the rotation curve. However, the vast majority of the dwarf galaxies are clear outliers to this rescaled relation, unless they are very recent infallers. In other words, the very low binding energies of most dwarf galaxies compared to Sgr and previous accreted galaxies suggests that most of them were accreted much later than 8 or even 5 Gyr ago. We also found that the subhalo systems in some cosmological simulations are too dynamically hot when they are compared to identified Milky Way substructures. This leads to an overestimated impact of satellites on the Galaxy rotation curve. © 2024 EDP Sciences. All rights reserved.