TRIGONOMETRIC PARALLAXES OF MASSIVE STAR-FORMING REGIONS. VI. GALACTIC STRUCTURE, FUNDAMENTAL PARAMETERS, AND NONCIRCULAR MOTIONS

By M. J. Reid, K. Menten, X. Zheng, A. Brunthaler, L. Moscadelli, Y. Xu, Bingqing Zhang, M. Sato, M. Honma, T. Hirota and 4 more. 2009

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We are using the Very Long Baseline Array and the Japanese VLBI Exploration of Radio Astronomy project to measure trigonometric parallaxes and proper motions of masers found in high-mass star-forming regions across the Milky Way. Early results from 18 sources locate several spiral arms. The Perseus spiral arm has a pitch angle of 16° ± 3°, which favors four rather than two spiral arms for the Galaxy. Combining positions, distances, proper motions, and radial velocities yields complete three-dimensional kinematic information. We find that star-forming regions on average are orbiting the Galaxy ≈15 km s−1 slower than expected for circular orbits. By fitting the measurements to a model of the Galaxy, we estimate the distance to the Galactic center R0 = 8.4 ± 0.6 kpc and a circular rotation speed Θ0 = 254 ± 16 km s−1. The ratio Θ0/R0 can be determined to higher accuracy than either parameter individually, and we find it to be 30.3 ± 0.9 km s−1 kpc−1, in good agreement with the angular rotation rate determined from the proper motion of Sgr A*. The data favor a rotation curve for the Galaxy that is nearly flat or slightly rising with Galactocentric distance. Kinematic distances are generally too large, sometimes by factors greater than 2; they can be brought into better agreement with the trigonometric parallaxes by increasing Θ0/R0 from the IAU recommended value of 25.9 km s−1 kpc−1 to a value near 30 km s−1 kpc−1. We offer a “revised” prescription for calculating kinematic distances and their uncertainties, as well as a new approach for defining Galactic coordinates. Finally, our estimates of Θ0 and Θ0/R0, when coupled with direct estimates of R0, provide evidence that the rotation curve of the Milky Way is similar to that of the Andromeda galaxy, suggesting that the dark matter halos of these two dominant Local Group galaxy are comparably massive.

Subfields: Astronomy and Astrophysics

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Citations in the corpus

Fundamental Parameters of the Milky Way Galaxy Based on VLBI Astrometry (2012, methodology): “If Vˇ = 5.25 km s 1 is adopted to this relation, the star-forming regions lag behind the Galactic rotation by 14 km s 1, confirming the earlier suggestion by Reid et al. (2009b).”
THE MILKY WAY'S CIRCULAR-VELOCITY CURVE BETWEEN 4 AND 14 kpc FROM APOGEE DATA (2012, background): “The recent measurement of Vc = 254 ± 16 km s −1, from the kinematics of masers in the Galactic disk (Reid et al. 2009), was shown to have an overly optimistic precision by Bovy et al. (2009a), who concluded from a more general model for the distribution function of the masers that these data only…”
Colloquium: Annual modulation of dark matter (2013, background): “=3 p v (16) is the most probable speed, with an approximate value of 235 km=s (Kerr and Lynden-Bell, 1986; Bovy, Hogg, and Rix, 2009; McMillan and Binney, 2009; Reid et al., 2009) (see Sec.”
Gaseous Galaxy Halos (2012, background): “The Milky Way has a total mass of ∼ 2× 1012 M (Reid et al., 2009; Kalberla et al., 2007), and ideally we would discuss only galaxies of this mass for comparison.”
Molecular Clouds in the Milky Way (2015, methodology): “Of course, these studies are also improving our knowledge of the Galactic kinematics, leading to more accurate methods for determining kinematic distances (Reid et al. 2009).”
The observed spiral structure of the Milky Way (2014, methodology): “A flat rotation curve (Reid et al. 2009b, 2014; Brunthaler et al. 2011) and the rotation curve of Brand & Blitz (1993, hereafter BB93) are adopted in calculating the kinematic distances.”
TIMING MEASUREMENTS OF THE RELATIVISTIC BINARY PULSAR PSR B1913+16 (2010, background): “Using R0 = 8.4 ± 0.6 kpc for the distance to the galactic center and Θ0 = 254 ± 16 km s−1 for the circular velocity of the local standard of rest (Ghez et al. 2008; Gillessen et al. 2009; Reid et al. 2009), and d = 9.9± 3.1 kpc for the pulsar distance (Weisberg et al. 2008), we obtain the kinematic ”
The RMS survey : Galactic distribution of massive star formation (2013, methodology): “…et al. 2000) with a Galactic radius of 4.4 6 The luminosities presented by Mottram et al. (2011b) were estimated using kinematic distances derived from the Brand & Blitz (1993) rotation curve and so have been rescaled to the kinematic distances derived from the Reid et al. (2009) rotation model.”
A novel determination of the local dark matter density (2009, neutral): “[24]; we compare against the compilation of velocities with respect to the local standard of rest velocities, or the heliocentric velocities, versus the parallax inferred distances, having gauged out the estimated average value for proper motion components.”
TRIGONOMETRIC PARALLAXES OF HIGH MASS STAR FORMING REGIONS: THE STRUCTURE AND KINEMATICS OF THE MILKY WAY (2014, methodology): “The Bovy et al. (2009) re-analysis of our preliminary data employed a different ap- proach than that of Reid et al. (2009b).”
A DIRECT DYNAMICAL MEASUREMENT OF THE MILKY WAY'S DISK SURFACE DENSITY PROFILE, DISK SCALE LENGTH, AND DARK MATTER PROFILE AT 4 kpc ≲ R ≲ 9 kpc (2013, background): “Such constraints exists, e.g., from the measurement of the Oort constants (e.g., Feast & Whitelock 1997), from the kinematics of masers in the disk of the Milky Way (Reid et al. 2009; Bovy et al. 2009), or from the kinematics of stars throughout the disk (Bovy et al. 2012a).”
The Bar and Spiral Structure Legacy (BeSSeL) Survey: Mapping the Milky Way with VLBI Astrometry† (2011, methodology): “A description that takes into account these two effects and gives (in general) more accurate kinematic distances, and a more realistic distance uncertainty estimate is also presented in Reid et al. (2009b).”
The ATLASGAL survey: a catalog of dust condensations in the Galactic plane (2013, positive): “Our estimate ofa 0.32◦ scale-height corresponds to 47 pc at 8.4 kpc (Reid et al. 2009), which is the same as derived by Beuther et al. (2012).”
THE WISE CATALOG OF GALACTIC H ii REGIONS (2013, methodology): “…et al. 2007; (19) Moellenbrock et al. 2009; (20) Moscadelli et al. 2009; (21) Niinuma et al. 2011; (22) Oh et al. 2010; (23) Reid et al. 2009a; (24) Reid et al. 2009c; (25) Rygl et al. 2010; (26) Rygl et al. 2012; (27) Sanna et al. 2009; (28) Sanna et al. 2012; (29) Sato et al. 2008; (30) Sato…”