H i Kinematics and Mass Distribution of Messier 33

Abstract

A new deep Hi survey of the galaxy Messier 33 is presented, based on observations obtained at the Dominion Radio Astrophysical Observatory. We observe a perturbed outer gas distribution and kinematics in M33, and confirm the disk warping as a significant kinematical twist of the major axis of the velocity field, though no strong tilt is measured, in agreement with previous work. Evidence for a new low brightness Hi component with anomalous velocity is reported. It harbours a large velocity scatter, as its kinematics both exceeds and lags the rotation of the disk, and leaks in the forbidden velocity zone of apparent counter-rotation. The observations also reveal wide and multiple peak Hi profiles which can be partly explained by crowded orbits in the framework of the warp model. Asymmetric motions are identified in the velocity field, as possible signatures of a lopsided potential and the warp. The mass distribution modeling of the hybrid Hα-Hi rotation curve favours a cuspy dark matter halo with a concentration in disagreement with the ΛCDM dark halo mass-concentration relationship. The total mass enclosed in 23 kpc is 8 10 10 M , of which 11% are stars and gas. At the virial radius of the cuspy halo, the resulting total mass is 5 10 11 M , but with a baryonic mass fraction of 2% only. This strongly suggests a more realistic radius encompassing the total mass of M33 well smaller than the virial radius of the halo, maybe comparable to the size of the Hi disk.

CLUES about M33: the reversed radial stellar age gradient in the outskirts of Triangulum galaxy

“…A warped disc component can be seen in the edge-on view, similarly to the warped disc reported in observations of M33 (e.g. Corbelli & Schneider 1997;Kam et al 2017). Moreover, similar to the observed M33, our simulated counterpart shows well defined spiral features, clearly visible in the face-on gas density plot.…”

“…Spiral features and a thin warped disc of gas are visible, in agreement with observational data (e.g. Corbelli & Schneider 1997;Kam et al 2017). and stellar mass, and the Tully-Fisher relation; meaning we can have a degree of confidence in our analysis.…”

“…In order to compare more quantitatively with observational results, we present in Tab.1 the virial and stellar mass of the M33 candidate, and we compare these values with the observational M33 data reported in Corbelli et al (2014) and Kam et al (2017). For the simulation, the virial mass is computed as the total mass within the virial radius at z = 0, while the stellar mass is the sum of all the star particles found within the galaxy and its halo.…”

The M31/M33 tidal interaction: a hydrodynamic simulation of the extended gas distribution

“…The mass of M33 we adopt is lower than traditional estimates based on the modelling of its observed rotation curve. Using this approach, Kam et al (2017) estimate a virial mass for M33 of ∼ 5 × 10 11 M (see also Corbelli et al 2014) . As discussed by these authors, however, with a baryonic mass of order 10 10 M , the baryonic:total mass fraction in M33 is only 2 percent, well below the typical value for disc galaxies (∼ 7 percent; e.g.…”

A multiscale study of star formation in Messier 33

“…where V F(x, y) is the radial velocity at position (x, y) as given by the velocity field, V sys = −180 km s −1 (Kam et al 2017), i = 53.9 • , and θ = 201.3 • . The tilted ring model from Kam et al (2017) shows the position angle of the galaxy to be constant at a value of 201.3 • out to radius R = 30 arcmin. Over the same radial range, the inclination varies linearly from a value of 53.2 • at the centre to 54.6 • .…”