Search

Stellar prolate rotation in dwarf galaxies is rather uncommon, with only two known galaxies in the Local Group showing such feature (Phoenix and And II). Cosmological simulations show that in massive early-type galaxies prolate rotation likely arises from major mergers. However, the origin of such kinematics in the dwarf galaxies regime has only been explored using idealized simulations. Here we made use of hydrodynamical cosmological simulations of dwarfs galaxies with stellar mass between $3\times10^5$ and $5\times10^8$ M$_{\odot}$ to explore the formation of prolate rotators. Out of $27$ dwarfs, only one system showed clear rotation around the major axis, whose culprit is a major merger at $z=1.64$, which caused the transition from an oblate to a prolate configuration. Interestingly, this galaxy displays a steep metallicity gradient, reminiscent of the one measured in Phoenix and And II: this is the outcome of the merger event that dynamically heats old, metal-poor stars, and of the centrally concentrated residual star formation. Major mergers in dwarf galaxies offer a viable explanation for the formation of such peculiar systems, characterized by steep metallicity gradients and prolate rotation., 5 pages, 3 figures

We use Gaia DR2 systemic proper motions of 45 satellite galaxies to constrain the mass of the Milky Way using the scale free mass estimator of Watkins et al. (2010). We first determine the anisotropy parameter $\beta$, and the tracer satellites' radial density index $\gamma$ to be $\beta$=$-0.67^{+0.45}_{-0.62}$ and $\gamma=2.11\pm0.23$. When we exclude possible former satellites of the Large Magellanic Cloud, the anisotropy changes to $\beta$=$-0.21^{+0.37}_{-0.51}$. We find that the index of the Milky Way's gravitational potential $\alpha$, which is dependent on the mass itself, is the parameter with the largest impact on the mass determination. Via comparison with cosmological simulations of Milky Way-like galaxies, we carried out a detailed analysis of the estimation of the observational uncertainties and their impact on the mass estimator. We found that the mass estimator is biased when applied naively to the satellites of simulated Milky Way halos. Correcting for this bias, we obtain for our Galaxy a mass of $0.58^{+0.15}_{-0.14}\times10^{12}$M$_\odot$ within 64 kpc, as computed from the inner half of our observational sample, and $1.43^{+0.35}_{-0.32}\times10^{12}$M$_\odot$ within 273 kpc, from the full sample; this latter value extrapolates to a virial mass of $M_\mathrm{vir\,\Delta=97}$=$1.51^{+0.45}_{-0.40} \times 10^{12}M_{\odot}$ corresponding to a virial radius of R$_\mathrm{vir}$=$308\pm29$ kpc. This value of the Milky Way mass lies in-between other mass estimates reported in the literature, from various different methods., Comment: 17 pages, 10 figures, 2 tables. Accepted for publication in MNRAS

We continue to investigate the dynamics of collisionless systems of particles interacting via additive $r^{-\alpha}$ interparticle forces. Here we focus on the dependence of the radial-orbit instability on the force exponent $\alpha$. By means of direct $N$-body simulations we study the stability of equilibrium radially anisotropic Osipkov-Merritt spherical models with Hernquist density profile and with $1\leq\alpha0.3$, so they are never flatter than an E7 system., Comment: 12 pages, 6 figures

We explore for the first time the effect of self-interacting dark matter (SIDM) on the dark matter (DM) and baryonic distribution in massive galaxies formed in hydrodynamical cosmological simulations, including explicit baryonic physics treatment. A novel implementation of Super-Massive Black Hole (SMBH) formation and evolution is used, as in Tremmel et al.(2015, 2016), allowing to explicitly follow SMBH dynamics at the center of galaxies. A high SIDM constant cross-section is chosen, $\sigma$=10 $\rm cm^2/gr$, to amplify differences from CDM models. Milky Way-like galaxies form a shallower DM density profile in SIDM than they do in CDM, with differences already at 20 kpc scales. This demonstrates that even for the most massive spirals the effect of SIDM dominates over the adiabatic contraction due to baryons. Strikingly, the dynamics of SMBHs differs in the SIDM and reference CDM case. SMBHs in massive spirals have sunk to the centre of their host galaxy in both the SIDM and CDM run, while in less massive galaxies about 80$\%$ of the SMBH population is off-centered in the SIDM case, as opposed to the CDM case in which $\sim$90$\%$ of SMBHs have reached their host's centre. SMBHs are found as far as $\sim$9 kpc away from the centre of their host SIDM galaxy. This difference is due to the increased dynamical friction timescale caused by the lower DM density in SIDM galaxies compared to CDM, resulting in 'core stalling'. This pilot work highlights the importance of simulating in a full hydrodynamical context different DM models combined to SMBH physics to study their influence on galaxy formation., Comment: 10 pages, 6 figures, matches accepted version (MNRAS, April 27 2017)

We use the NIHAO simulations to investigate the effects of baryonic physics on the time evolution of Dark Matter central density profiles. The sample is made of $\approx 70$ independent high resolution hydrodynamical simulations of galaxy formation and covers a wide mass range: 1e10< Mhalo, Comment: 11 pages, 13 figures. Corrected typo in table 2 (middle row) with respect to the version published in MNRAS

We use the recently proposed scale-free mass estimators to determine the masses of the Milky Way (MW) and Andromeda (M31) galaxy in a dark matter only Constrained Local Universe Simulation. While these mass estimators work rather well for isolated spherical host systems, we examine here their applicability to a simulated binary system with a unique satellite population similar to the observed satellites of MW and M31. We confirm that the scale-free estimators work also very well in our simulated Local Group galaxies with the right number of satellites which follow the observed radial distribution. In the isotropic case and under the assumption that the satellites are tracking the total gravitating mass, the power-law index of the radial satellite distribution N(< r) ∝r3−γ is directly related to the host’s mass profile M(< r) ∝r1−α as α=γ− 2. The use of this relation for any given γ leads to highly accurate mass estimations which is a crucial point for observer, since they do not know a priori the mass profile of the MW and M31 haloes. We discuss possible bias in the mass estimators and conclude that the scale-free mass estimators can be satisfactorily applied to the real MW and M31 system.

Using Constrained Local UniversE Simulations (CLUES) of the formation of the Local Group in a cosmological context we investigate the recently highlighted problem that the majority of the most massive dark subhaloes of the Milky Way are too dense to host any of its bright satellites. In particular, we examine the influence of baryonic processes and find that they leave a twofold effect on the relation between the peak of the rotation curve and its position (Vmax and Rmax). Satellites with a large baryon fraction experience adiabatic contraction thus decreasing Rmax while leaving Vmax more or less unchanged. Subhaloes with smaller baryon fractions undergo a decrease in Vmax possibly due to outflows of material. Furthermore, the situation of finding subhaloes in simulations that lie outside the confidence interval for possible hosts of the bright MW dwarf spheroidals, appears to be far more prominent in cosmologies with a high sigma8 normalisation and depends on the mass of the host. We conclude that the problem cannot be simply solved by including baryonic processes and hence demands further investigations.

We analysed the relationship between coffee and alcohol intake, smoking and risk of multiple pregnancies using data from a case-control study on risk factors for multiple births conducted in Italy. Cases were 133 women who delivered multiple births not related to treatment for infertility (33 monozygotic and 100 dizygotic twins). Controls were 395 women admitted for normal delivery at the same clinic where cases had been identified. The odds ratios (OR) of multiple pregnancy were 1.5[95% confidence interval (CI) 0.8-2.8] and 2.0 (95% CI 1.0-3.7) for women drinking respectively one to two or three or more cups of coffee per day in comparison with non-coffee drinkers. Considering separately dizygotic and monozygotic pregnancies, the estimated OR were respectively for women drinking three or more cups of coffee, 1.7 and 3.1 for dizygotic and monozygotic pregnancies. The risk of multiple pregnancy tended to be higher in women drinking >or= 15 alcohol drinks per week: in comparison with tea-totallers the estimated OR for drink > or = 15 glasses per week were 2.3 and 2.6 respectively for dizygotic and monozygotic pregnancies. Heavy smokers (> or = 10 cigarettes per day) were at increased risk of multiple pregnancy: in comparison with never smokers, the estimated OR for multiple pregnancy was 1.6 (95% CI 0.9-2.7). Considering separately the two groups of multiple pregnancy, the OR of dizygotic and monozygotic pregnancy were 1.4 (95% CI 0.8-2.5) and 2.4 (95% CI 0.9-6.1) for women smoking > or = 10 cigarettes/day, but the trend in risk with number of cigarettes smoked per day and duration of the habit was not significant.