A method to calculate the local density distribution of the Galaxy from the Tycho-Gaia Astrometric Solution data

Abstract

New and more reliable distances and proper motions of a large number of stars in the Tycho-Gaia Astrometric Solution (TGAS) catalogue allow to calculate the local matter density distribution more precisely than earlier.We devised a method to calculate the stationary gravitational potential distribution perpendicular to the Galactic plane by comparing the vertical probability density distribution of a sample of observed stars with the theoretical probability density distribution computed from their vertical coordinates and velocities. We applied the model to idealised test stars and to the real observational samples. Tests with two mock datasets proved that the method is viable and provides reasonable results.Applying the method to TGAS data we derived that the total matter density in the Solar neighbourhood is 0.09 ± 0.02 M pc −3 being consistent with the results from literature. The matter surface density within |z| ≤ 0.75 kpc is 42 ± 4 M pc −2 . This is slightly less than the results derived by other authors but within errors is consistent with previous estimates. Our results show no firm evidence for significant amount of dark matter in the Solar neighbourhood. However, we caution that our calculations at |z| ≤ 0.75 kpc rel on an extrapolation from the velocity distribution function calculated at |z| ≤ 25 pc. This extrapolation can be very sensitive to our assumption that the stellar motions are perfectly decoupled in R and z, and to our assumption of equilibrium. Indeed, we find that ρ(z) within |z| ≤ 0.75 kpc is asymmetric with respect to the Galactic plane at distances |z| = 0.1 − 0.4 kpc indicating that the density distribution may be influenced by density perturbations.

Stellar Mass Distribution and Star Formation History of the Galactic Disk Revealed by Mono-age Stellar Populations from LAMOST

“…Assuming a gas density of 0.05 M ⊙ /pc 3 as widely adopted (Holmberg & Flynn 2000;Flynn et al 2006), the expected mass density of baryon matter (star and gas) in the nearby disk plane within a few hundred parsec is thus 0.109 M ⊙ /pc 3 (0.104 M ⊙ /pc 3 for Chabrier IMF). Such a value is consistent well with the local total mass density yielded by stellar dynamics, which suggest a typical value of 0.1 M ⊙ /pc 3 (Bienayme et al 1987;Kuijken & Gilmore 1989c;Pham 1997;Holmberg & Flynn 2000;Read 2014;McKee et al 2015;Widmark & Monari 2017;Kipper et al 2018). Our results thus leave little room for the existence of a meaningful amount of dark matter in the nearby disk mid-plane.…”

A method to calculate gravitational accelerations within discrete localized regions in the Milky Way

“…By selecting a region around a point in a galaxy containing several tens of thousands stars and calculating orbits of these stars it is possible to calculate gravitational potential derivatives at a given point rather precisely. This paper continues our previous work (Kipper et al 2018) where only Solar neighbourhood in 1D was studied. With Gaia complete solution data the entire MW covered by sufficiently precise Gaia data can be analysed.…”

The origin of interstellar asteroidal objects like 1I/2017 U1 ‘Oumuamua

“…This makes the object unambiguously unbound on an en-passant orbit through the Solar system (de la Fuente Marcos & de la Fuente Marcos 2017; Bannister et al 2017), not unlike the prediction by Moro-Martín, Turner & Loeb (2009). The absence of a tail indicates that the object is probably rock-like (Meech 2018), which, together with its unusual elongated shape (∼ 35 by 230 m reported by Meech et al 2017a, and explained by Fitzsimmons et al (2018) and Domokos et al (2017)) and rapid spin (with an 8.10 ± 0.02 hour period, see Jewitt et al 2017;Bolin et al 2018), has been hosted by a star for an extensive period of time (Katz 2018;Hoang et al 2018). In this period it may have lost most of its volatiles and ice by sputtering (Meech 2018; Emain: spz@strw.leidenuniv.nl Fitzsimmons et al 2018).…”