Recent advances in the determination of some Galactic constants in the Milky Way

Abstract

Abstract.Here we statistically evaluate recent advances in determining the SunGalactic Center distance (R sun ) as well as recent measures of the orbital velocity around the Galactic Center (V lsr ), and the angular rotation parameters of various objects. Recent statistical results point to R sun = 8.0 ± 0.2 kpc, V lsr = 230 ± 3 km/s, and angular rotation at the Sun (ω) near 29 ± 1 km/s/kpc for the gas and stars at the Local Standard of Rest, and near 23 ± 2 km/s/kpc for the spiral pattern itself.This angular difference is similar to what had been predicted by density wave models, along with the observation that the galactic longitude of each spiral arm tracer (dust, cold CO) for each spiral arm becomes reversed across the Galactic Meridian (Vallée 2016b). IntroductionThe value of the distance of the Sun to the Galactic Center, R sun , is one of the fundamental parameters of our Milky Way disk galaxy. Similarly, the value of the circular orbital velocity V lsr , for the Local Standard of Rest at radius R sun around the Galactic Center, is another fundamental parameter. In 1985, the IAU recommended the use of R sun =8.5 kpc and V lsr = 220 km/s. Recent measurements of R sun and V lsr deviate somewhat from this IAU recommendation.Section 2 makes a table of recent measurements of two galactic constants, namely the distance of the Sun to the Galactic Center, and the orbital circular velocity near the Sun around the Galactic Center. Section 3 deals with current angular rotation rates for various galactic features, while Section 4 concludes.

A guided map to the spiral arms in the galactic disk of the Milky Way

“…Yang et al [41] displayed 12 CO J = 1-0 gas for the Perseus and Cygnus arm, for which there is a good match to this model [16].…”

“…Stark & Lee [38] displayed the major 13 CO J = 1-0 clouds for the Cygnus arm (their F arm), being a good match to the four-arm model [16]. Dobbs et al [40] displayed the observed 12 CO J = 1-0 clouds for the Perseus arm and the Cygnus arm, for which there is a good match to this four-arm model [16].…”

“…It took Shapley in the early twentieth Century to separate the sun's position from the Galactic Center's position, by about 20 kpc [2]. Modern observations shows that the Sun is separated from the Galactic Center by about 8.0 kpc, give or take 0.2 kpc [4,11,12]. This allows modern theories to properly present the Sun near but outside a spiral arm in the galaxy.…”

“…The aim here is to provide the observed mean offset in linear width of a tracer t with respect to tracer 12 CO in a typical spiral arm, as well as individual offsets s in each individual arm. Few numerical or analytical theoretical predictions for the Milky Way conform to this offset reversal across the Galactic Meridian.…”

“…For the 12 CO tangent to the Crux-Centaurus arm, the mean of 309.5° has an r.m.s. of 1.0° and s.d.m.…”