Outer rotation curve of the Galaxy with VERA. III. Astrometry of IRAS 07427−2400 and test of the density-wave theory

Abstract

We report the trigonometric parallax of IRAS 07427−2400 with VERA to be 0.185 ± 0.027 mas, corresponding to a distance of 5.41$^{+0.92}_{-0.69}\:$kpc. The result is consistent with the previous result of 5.32$^{+0.49}_{-0.42}\:$kpc obtained by Choi et al. (2014, ApJ, 790, 99) within error. To remove the effect of internal maser motions (e.g., random motions), we observed six maser features associated with IRAS 07427−2400 and determined systematic proper motions of the source by averaging proper motions of the six maser features. The obtained proper motions are (μαcos δ, μδ) = (−1.79 ± 0.32, 2.60 ± 0.17) mas yr−1 in equatorial coordinates, while Choi et al. (2014) showed (μαcos δ, μδ) = (−2.43 ± 0.02, 2.49 ± 0.09) mas yr−1 with one maser feature. Our astrometry results place the source in the Perseus arm, the nearest main arm in the Milky Way. Using our result with previous astrometry results obtained from observations of the Perseus arm, we conducted direct (quantitative) comparisons between 27 astrometry results and an analytic gas dynamics model based on the density-wave theory, obtaining two results. First is the pitch angle of the Perseus arm determined by VLBI astrometry, 11 $_{.}^{\circ}$1 ± 1 $_{.}^{\circ}$4, differing from what is determined by the spiral potential model (probably traced by stars), ∼ 20°. The second is an offset between a dense gas region and the bottom of the spiral potential model. The dense gas region traced by VLBI astrometry is located downstream of the spiral potential model, which was previously confirmed in the nearby grand-design spiral galaxy M 51 in Egusa, Koda, and Scoville (2011, ApJ, 726, 85).

Determination of the Rotation Curve of the Milky Way Using the 21 cm Hi Emission Line

“…The proper motions of red clump giant stars were also used to derive the rotation curve of the Galaxy [18]. Recently, observations of maser sources from VERA (VLBI Experiment for Radio Astrometry) are used to study the rotation curve of the Milky Way [19,20]. We also estimated the mass of the Milky Way within a radius of R=50 kpc to be ~ 5.615 × 10 11 M⊙, whereas the mass of visible matter within a radius of R=15 kpc is found to be ~ 1.65 × 10 11 M⊙.…”

Debris of Gaia-Sausage-Enceladus that made a H I hole in the Milky Way ≈20 million years ago

“…6D (position-velocity) phase space information was obtained for the SFRs and stars by analyzing VLBI and Gaia astrometric data. For astrometric data reductions, we followed procedures [31][32][33][34] in which coordinates (α, δ, J2000), parallax, LSR velocity and proper motion of each source are used. The required Galactic and solar motion parameters are given in Extended Data Table 2, and those associated with the source are defined in Extended Data Table 3.…”

Spiral Structure Boosts Star Formation in Disk Galaxies

“…The enhancement on SFE for the giant molecular clouds located on the spiral arms of NGC 6946 is more definitive (Rebolledo et al 2012), but the same does not seem to hold for NGC 628, whose SFE is similar in its arm and inter-arm regions (Foyle et al 2010;Kreckel et al 2016). The spiral arms of the Milky Way also appear to have little or no effect on the SFE (Eden et al 2015;Ragan et al 2016), despite the evidence that the spirals affect the distribution and kinematics of the dense gas (Sakai et al 2015). This complexity may be traced to the fact that although shocks raise the gas density they also introduce turbulent and streaming motions, which prevent cloud collapse and curtail SFE (Meidt et al 2013;Leroy et al 2017).…”