ALOHA IRDCs molecular line follow-up. I. Gas properties and kinematics

Le résumé fourni par la source

Infrared-dark clouds (IRDCs) are ideal sites for investigating the initial conditions of massive star and cluster formation. The A Lei Of the Habitat and Assembly of Infrared Dark Clouds (ALOHA IRDCs), a Telescope Large Program, has mapped nearby IRDCs utilising the SCUBA-2 continuum camera at the highest achievable sensitivity. Complementary molecular line observations are needed to characterise the physical, kinematic, and chemical properties of the dense gas. James Clerk Maxwell We aim to determine the thermal, kinematic, and chemical properties of clumps identified in the ALOHA IRDCs, and to assess their evolutionary status and level of star-forming activity. We performed single-pointing K-band and W-band observations towards 56 clumps pf ALOHA IRDCs using the Effelsberg 100 m and Yebes 40 m telescopes, respectively. We derived NH_3 kinetic temperatures using the hyperfine group ratio method and identified infall and shock signatures from HCO+$, H^13CO^+, SiO, and HNCO profiles. Water masers and NH$_ 2 D emission were used as complementary tracers of chemical evolution and star formation. The clumps exhibit kinetic temperatures of 15--29,K. We detect NH_2D emission towards 18 sources; the NH_2D centroid velocities are consistent with those of NH_3, indicating the two species trace the same dense gas component. More than half of the clumps display blue-asymmetric HCO+$ profiles, identifying them as infall candidates. Water masers with prominent velocity ranges and variability are detected in 22 sources. Broad SiO emission (gtrsim20, ) indicates strong shocks, while narrower emission ($łesssim6, ) likely traces large-scale interactions or low-velocity shocks. -1 -1 The widespread infall signatures, shock tracers, masers, and NH_2D emission suggest that relatively quiescent, chemically young material can coexist with dynamically active gas affected by early protostellar feedback, providing insight into the coupled physical and chemical evolution of massive IRDC clumps.

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