Jeans modelling of the Milky Way’s nuclear stellar disc

Abstract

The nuclear stellar disc (NSD) is a flattened stellar structure that dominates the gravitational potential of the Milky Way at Galactocentric radii 30 ≲ R ≲ 300 pc. In this paper, we construct axisymmetric Jeans dynamical models of the NSD based on previous photometric studies and we fit them to line-of-sight kinematic data of APOGEE and SiO maser stars. We find that (i) the NSD mass is lower but consistent with the mass independently determined from photometry by Launhardt et al. (2002). Our fiducial model has a mass contained within spherical radius r = 100 pc of $M(r<100\, {\rm pc}) = 3.9 \pm 1 \times 10^8 \, \rm M_\odot$ and a total mass of $M_{\rm NSD} = 6.9 \pm 2 \times 10^8 \, \rm M_\odot$. (ii) The NSD might be the first example of a vertically biased disc, i.e. with ratio between the vertical and radial velocity dispersion σz/σR > 1. Observations and theoretical models of the star-forming molecular gas in the central molecular zone suggest that large vertical oscillations may be already imprinted at stellar birth. However, the finding σz/σR > 1 depends on a drop in the velocity dispersion in the innermost few tens of parsecs, on our assumption that the NSD is axisymmetric, and that the available (extinction corrected) stellar samples broadly trace the underlying light and mass distributions, all of which need to be established by future observations and/or modelling. (iii) We provide the most accurate rotation curve to date for the innermost 500 pc of our Galaxy.

Composite bulges – II. Classical bulges and nuclear discs in barred galaxies: the contrasting cases of NGC 4608 and NGC 4643

“…Assuming no strong gradients in M/L and a total galaxy stellar mass of 6.2 × 10 10 M (Section 3), the nuclear disc has a stellar mass of ∼7 × 10 9 M . This is about seven times the mass estimated for Milky Way's nuclear disc (∼1 × 10 9 M ; Nogueras-Lara et al 2020; Sormani et al 2020). The stellar-population analysis of the MUSE data in Bittner et al (2020) indicates that the nuclear disc is old (∼10.5 Gyr) -but slightly less so than the stars in the B/P bulge (∼11.5 Gyr) in which it is embedded.…”

The nuclear stellar disc of the Milky Way: A dynamically cool and metal-rich component possibly formed from the central molecular zone

“…We used data from Paper I, where part of the foreground population was excluded using colour cut H−K s. To remove the remaining foreground sources that might affect our results, we applied more restrictive cuts following previous studies on the NSD and the innermost bulge (e.g. Nogueras-Lara et al 2018bSormani et al 2020). Given the high differential extinction (Nogueras-Lara et al 2020b) and its variation on arcsecond scales in the Galactic centre (GC, Nogueras-Lara et al 2018a), we applied different H−K s cuts for each of the considered regions.…”

“…The red dashed line shows the colour cut used to remove foreground stars from the Galactic disc and the innermost bulge following previous work (e.g. Nogueras-Lara et al 2018aSormani et al 2020).…”

“…This figure shows the surface density ratio of the bulge/bar model from Sect. 4.2 of Launhardt et al (2002) to the sum of the fiducial NSD model (model 3) of Sormani et al (2020), the best fitting NSC model of Chatzopoulos et al (2015), and the bulge/bar model in Launhardt et al (2002). Assuming that the probability of a given star ending up in our sample is independent of the star belonging to the bar/bulge or to the NSD, this ratio can be taken as a crude estimation of the expected contamination due to bulge/bar stars in the sample along each line of sight.…”

“…use the kinematics of APOGEE stars to trace the rotation velocity of the nuclear disc (∼120 km s −1 ), suggesting that the NSD is kinematically cool with a small vertical extent of 50 pc and a truncation radius of R ∼ 150 pc (see also Gallego-Cano et al 2020). In addition, these authors show that the NSD is rotating with similar velocities as the molecular gas in the central molecular zone (CMZ), thus indicating that these two components could be linked together and that the stars in the NSD could originate from the dense CMZ gas (Sormani et al 2020). With additional data from APOGEE DR16 (Ahumada et al 2020) and SiO maser data of AGB stars in the inner Galaxy from Messineo et al (2005), Sormani et al (2020) fit axisymmetric Jeans dynamical models and determine the total mass of the NSD of M NSD = 6.9±2×10 8 M , which is lower than the photometric mass found by Launhardt et al (2002).…”