Distribution of the high-velocity clouds in the Galactic halo

Abstract

Context. There is a connection between the kinematics and sky distribution of the high velocity clouds (HVCs) and the spatial velocity and orbital plane of the Magellanic Clouds (MCs) that allow us to conclude that most HVCs were ejected from the Clouds, some hundreds of Myrs ago, probably by an encounter between the Large (LMC) and Small Magellanic Cloud (SMC). Aims. Based on the idea that HVCs have progenitors in the MCs, we attempt determine theoretical distances to the HVCs using observed data of the sky positions and radial velocities, and thus to map the spatial distribution of the HVCs. Methods. i) In the context of a kinematical model we have found an analytical formula that gives the distance of an HVC; ii) we have developed two dynamical models in order to study the orbits of the HVCs under the gravitational forces exerted by the Galaxy and the MCs and forces of resistance due to the movement of the HVCs through the Galactic gaseous disk. We have adopted the gravitational potential of the Milky Way given by a dark matter halo (Model 1) plus a massive thick disk partially composed by dark matter (Model 2). By means of a fitting to certain Galactic, MC and HVC conditions we have obtained values for the free parameters of the Models. We have obtained the dynamical distances to the HVCs by constructing the theoretical relationship between the radial velocity and the distance in the line of sight of each HVC. Results. The HVCs can be divided into three major groups: Population MS, Population W and Population A−C. Population MS comprises the Magellanic stream and the leading arm of the Magellanic system. The HVCs of this population are dispersed around the MCs within a volume of ≈200 kpc × 200 kpc × 60 kpc. Population W is situated at a mean distance of ≈15 kpc from the Sun, and has been braked by the gas of the Galactic disk. Population A−C includes Complexes A, C, H, L, M, and ACHVC. The dynamical models give two solutions for the distance of each HVC of Population A−C. The near-distance solutions place Population A−C at ≈6 kpc from the Sun, showing that this chain of HVCs started to interact with the outer parts of the Galactic gaseous disk about 100 Myr ago. While, the spatial distribution of Population A−C represented with the far distances has the shape of a gigantic ring with a radius of ≈125 kpc. Our results support the idea that the LMC-SMC encounter triggered a period of star formation bursts, in which part of the LMC bar was probably formed. The interactions of a few 10 5 massive stars formed in this era with the then-existing low metallicity ISM of the MCs would have created the HVCs

The Gould Belt

“…Although the distances to these clouds are poorly known, it is assumed that they are associated with the Magellan flow [106,107].…”

Three-dimensional orientation of compact high velocity clouds

“…Uncertainties arise from determining the escape fraction of ionizing UV photons, though the patchiness of the disk interstellar gas ceases to be of concern for |z| > 10 kpc (Bland-Hawthorn & Putman 2001;Peek et al 2007). Olano (2008) uses a putative origin to constrain distances of CHVCs spatially associated with the Magellanic complexes (also Peek et al 2008;Saul et al 2012). Distance constraints based on cloud kinematics assume a terminal velocity for HVCs (Benjamin & Danly 1997) or rely on differential drag due to the interaction with the background medium (Peek et al 2007).…”

Capture of field stars by giant interstellar clouds: the formation of moving stellar groups

“…According to the theory of density waves, the gas clouds are comprised and strongly decelerated when they enter the spiral density wave (Roberts 1969(Roberts , 1970. Another phenomenon that can accelerate gas of huge regions of the Galactic disc and form such giant clouds is the fall of highvelocity clouds (HVCs) on the Galactic disc (see Olano 2004Olano , 2008 and references therein).…”