Low-velocity shocks traced by extended SiO emission along the W43 ridges: witnessing the formation of young massive clusters

摘要: The formation of high-mass stars is tightly linked to that their parental clouds. We here focus on the high-density parts W43, a molecular cloud undergoing an efficient event formation. structure studied with column density image derived from Herschel continuum maps obtained at 70, 160, 250, 350, and 500 micron. identify two high-column filamentary clouds, quoted as W43-MM1 W43-MM2 ridges, which both account for 1.5x10^4 Msun gas mass above 10^23 cm-2 within areas 5 14pc^2, respectively. used N_2H^+ 1--0 line confirm ridges are structures coherent in velocity gravitationally bound, despite large dispersion ~5 kms widths. most intriguing result W43 program bright wide-spread SiO 2--1 emission: 1--11 K kms$ stretching area ~28 pc^2. Concentrated toward immediate surroundings, it leads total luminosity L_SiO 2-1 ~4 10^4 kpc^2pc^2. measured steep relation between extent SiO~2--1 lines propose use distinguish low-velocity shocks observed more classical high-velocity ones associated outflows young stellar objects. state-of-the-art shock models demonstrate ( 10^4-10^5 cm^-3) shocked suggests could be forming via colliding flows driven by gravity accompanied shocks. This mechanism may initial conditions massive clusters these ridges.