Triggered/sequential star formation? A multi-phase ISM study around the prominent IRDC G18.93-0.03

Context. Triggered star formation has been discussed for many years, and evidence for the formation of stars and cores triggered by Hii regions is under debate. Aims. We investigate the imprints of an expanding Hii region on a pre-existing starless clumps. Methods. We selected an infrared dark filament spanning 0.8 ◦ . One portion of this filament, G18.93-0.03 is a prominent dust complex, with the molecular clump G18.93/m being IR dark from near-IR wavelength up to 160 μm. Spitzer composite images show an IR bubble spatially associated with G18.93-0.03. We use GRS 13 CO and IRAM 30 m H 13 CO + data to disentangle the large and small scale spatial structure of the region. From ATLASGAL submm data we calculate the gas mass, while we use the H 13 CO + line width to estimate its virial mass. To study the IR properties of G18.93/ mw e useHerschel data and produce temperature maps from fitting the spectral energy distribution. With the MAGPIS 20 cm and SuperCOSMOS Hα data we trace the ionized gas, and the VGPS Hi survey provides information on the atomic hydrogen gas. Results. We show that the bubble is spatially associated with G18.93, located at a kinematic near distance of 3.6 kpc. The total gas