Dark matter and visible baryons in M33

Abstract

In this paper we present new measurements of the gas kinematics in M33 using the CO J=1-0 line. The resulting rotational velocities complement previous 21-cm line data for a very accurate and extended rotation curve. The implied dark matter mass, within the total gaseous extent, is a factor 5 higher than the visible baryonic mass. Dark matter density profiles with an inner cusp as steep as R^{-1}, are compatible with M33 data. The dark matter concentrations required for fitting the M33 rotation curve are very low but marginally consistent with halos forming in a standard Cold Dark Matter cosmology. The M33 virialized dark halo is at least 50 times more massive than the visible baryons and its size is comparable with the M33-M31 separation. Inner cusps as steep as R^{-1.5} are ruled out, while halo models with a large size core of constant density are consistent with the M33 data. A central spheroid of stars is needed and we evaluate its dynamical mass range. Using accurate rotational velocity gradients and the azimuthally averaged baryonic surface densities, we show that a disk instability can regulate the star formation activity in M33. Considering the gaseous surface density alone, the predicted outer star formation threshold radius is consistent with the observed drop of the H-alpha surface brightness if a shear rate criterion is used. The classical Toomre criterion predicts correctly the size of the unstable region only when the stellar or dark halo gravity, derived in this paper, is added to that of the gaseous disk.Comment: 14 pages, MNRAS in pres

Dynamical signatures of a ΛCDM-halo and the distribution of the baryons in M 33

“…M 33 is in fact one of the very few objects for which it has been possible to combine a high quality and high resolution extended rotation curve (Corbelli & Salucci 2000) with a well determined distance (assumed in this paper to be D = 840 kpc, Freedman et al 1991;Gieren et al 2013), and with an overwhelming quantity of data across the electromagnetic spectrum. Previous analyses have shown that the HI and CO velocity fields are very regular and cannot be explained by Newtonian dynamic without including a massive dark matter halo (Corbelli 2003). On the other hand, the dark matter density distribution inside the halo is still debated because of the unconstrained value of the mass-to-light ratio of the stellar disk.…”

Dynamical friction and scratches of orbiting satellite galaxies on host systems

“…The dynamical mass including a dark halo of the satellite galaxies, the LMC and M33 is still uncertain by a factor of 10 (e.g. Corbelli 2003;Seigar 2011;Kallivayalil et al 2013;van der Marel & Kallivayalil 2014). As indicated by Equation (6) and shown in Figure 4, the amplitude of the induced density is proportional to the satellite mass.…”

“…Corbelli (2003) found that dark halo mass out to 17 kpc from the center of M33 is ∼ 5 × halo surrounding M33 of (2.2 ± 0.1) × 10 11 M⊙ from the HI rotation curve. We assume that the mass and size of M33 are MM33 = 10 11 M⊙ and l = 17kpc, respectively.…”

Control of galactic scale star formation by gravitational instability or midplane pressure?

“…The apparent stability of the M33 disk was raised by Padoan in his talk at this conference as a counterargument to the theory of gravitational instability, with a citation to Corbelli (2003). Examination of that paper shows that the star forming disk of M33 is indeed stable if only the gas is considered.…”

“…Examination of that paper shows that the star forming disk of M33 is indeed stable if only the gas is considered. However, Corbelli (2003) also performed a simplified analysis including the stellar surface density, and concluded that the entire star-forming disk is indeed Toomre unstable if the stellar contribution is accounted for (see her Fig. 8).…”