Astronomy and Astrophysics – Astronomy
Scientific paper
Jun 2006
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2006rmxac..26..183o&link_type=abstract
XI IAU Regional Latin American Meeting of Astronomy (Eds. L. Infante & M. Rubio) Revista Mexicana de Astronomía y Astrofísica (S
Astronomy and Astrophysics
Astronomy
Scientific paper
According to Olano (2004, A&A, 423, 895), the Galaxy is surrounded by a large cloud of high-velocity clouds (HVCs) centered on the Magellanic Clouds, i.e. on the Galactic position (l_c, b_c) = (280°5, -33°9) at a distance from the Sun d_c = 50.1 kpc. This metacloud is translating as a whole with a barycenter velocity V_f similar to the spatial velocity of the Magellanic Clouds, since the HVCs were launched from this moving platform, and expanding from this center due to the original velocities with which the HVCs were ejected from the Clouds. The age T of the metacloud is ≈ 570 Myr. By means of a simplified model of the kinematics of the system of HVCs, we have derived an analytic formula relating the LSR radial velocity ρ of an HVC to its distance d from the Sun: ρ = - V_s sinl cosb - V_f cos(l - l_0) cos(b - b_0) + kd - kd_c (cosb cosb_c cos(l - l_c) + sinb sinb_c) - V_fall, where V_s = 220 km s^{-1} is the velocity of the LSR, l and b are the Galactic coordinates of the HVC, V_f = 282 km s^{-1} and (l_0, b_0) = (78°, 2°) are the stream velocity of the HVCs with respect to the Galactic center and the direction from which the stream of HVCs comes (i.e., the radiant point), k = (1/T) = (1/570) km s^{-1} pc^{-1} and V_{fall} = 133 km s^{-1} is the fall velocity of the HVCs towards the Galactic center. The above equation allows us to determine kinematic distances to the HVCs. We can also apply this equation to evaluate statistically the radius R_m of the metacloud. Equating the theoretical bar{ρ} of the HVCs within the total volume of the metacloud to the observed bar{ρ}, we obtained R_m ≈ 140 kpc. The uncertainties of the distances derived from this equation and its ranges of applicability will be discussed in connection with the ρ - d relations of the HVCs obtained from a dynamical model (Olano 2006, in preparation).
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