Gas flow models in the Milky Way embedded bars

Abstract

Context. The gas distribution and dynamics in the inner Galaxy present many unknowns, such as the origin of the asymmetry of the lv-diagram of the Central Molecular Zone (CMZ). On the other hand, there is recent evidence in the stellar component of the presence of a nuclear bar that may be slightly lopsided. Aims. Our goal is to characterize the nuclear bar observed in 2MASS maps and to study the gas dynamics in the inner Milky Way taking into account this secondary bar. Methods. We have derived a realistic mass distribution by fitting the 2MASS star count map with a model including three components (disk, bulge and nuclear bar) and we have simulated the gas dynamics in the deduced gravitational potential using a sticky-particles code.Results. Our simulations of the gas dynamics successfully reproduce the main characteristics of the Milky Way for a bulge orientation of 20• -35• with respect to the Sun-Galactic Center (GC) line and a pattern speed of 30-40 km s −1 kpc −1 . In our models the Galactic Molecular Ring (GMR) is not an actual ring but the inner parts of the spiral arms, while the 3-kpc arm and its far side counterpart are lateral arms that extend around the bar. Our simulations reproduce, for the first time, the parallelogram shape of the lv-diagram of the CMZ as the gas response to the nuclear bar. This bar should be oriented by an angle of ∼60• -75• with respect to the Sun-GC line and its mass amounts to (2-5.5) 10 9 M . We show that the observed asymmetry of the CMZ cannot be due to lopsidedness of the nuclear bar as suggested by the 2MASS maps. Conclusions. We do not find clear evidence of lopsidedness in the stellar potential. We propose that the observed asymmetry of the central gas layer can be due to the infalling of gas into the CMZ in the l = 1.3• -complex.

Stochastic non-circular motion and outflows driven by magnetic activity in the Galactic bulge region

“…Based on the above consideration and finding, Binney et al (1991) showed that a bar-like potential naturally reproduces the noncircular motion by comparing observed and calculated l − v (Galactic longitude -line-of-sight velocity from the Local Standard of Rest; LSR, hereafter) diagrams. The streaming motion driven by the bar potential provides an only viable explanation on the parallelogram, which has been explicitly discussed in literatures (Blitz 1994;Koda & Wada 2002;Rodriguez-Fernandez & Combes 2008;Baba, Saitoh & Wada 2010;Molinari et al 2011).…”

“…Rodriguez-Fernandez & Combes (2008) presented the first numerical simulations for the parallelogram. Their Figure 14 shows a simulated parallelogram to be compared to the CMZ, while their result is yet crude at best with no detailed fitting to the gas distribution in the l-v diagram.…”

“…Their conclusion indicates that the bar potential alone cannot reproduce the asymmetry of the CMZ or the high-z CO features including the 1.3 • complex. The difficulty in explaining the CMZ makes a contrast with the large-scale simulations in the bar potential over several kpc, which successfully reproduce the 3-kpc arm and other major features outside the central kpc (e.g., Rodriguez-Fernandez & Combes 2008).…”

Large scale IRAM 30 m CO-observations in the giant molecular cloud complex W43

“…Figure 5b shows the kinematic distance curve for our case at 30 • Galactic longitude. This works only for the circular orbits in the spiral arms and not the elliptical orbits in the Galactic bar (see Rodríguez-Fernández & Combes 2008;Rodríguez-Fernández 2011).…”

The onset of high-mass star formation in the direct vicinity of the Galactic mini-starburst W43

“…This region is very luminous with L ∼ 3 × 10 6 L , and it contains sources at different evolutionary stages from a Wolf-Rayet cluster to active young star-forming cores (e.g., Blum et al 1999;Motte et al 2003). Nguyen Luong et al (2011) recently discussed several broad velocity components in that regions and suggested that this whole complex might have formed via converging gas flows due to its special location at the interface of the Galactic bar with the inner Scutum spiral arm (Benjamin et al 2005;López-Corredoira et al 2007;Rodriguez-Fernandez & Combes 2008). Different velocity components were also identified in atomic HI emission and absorption (Liszt et al 1993).…”