Infall, outflow, and rotation in the G19.61-0.23 hot molecular core

Aims. We carried out sub-arcsecond resolution observations towards the high-mass star formation region G19.61−0.23, in both continuum and molecular line emission. While the centimeter continuum images, representing ultra compact HII regions, will be discussed in detail in a forthcoming paper, here we focus on the (sub)mm emission, devoting special attention to the hot molecular core (HMC). Methods. A set of multi wavelength continuum and molecular line emission data between 6 cm and 890 μm were obtained with the Very Large Array, Nobeyama Millimeter Array, Owens Valley Radio Observatory millimeter array, and Submillimeter Array (SMA). These data were analyzed in conjunction with previously published data. Results. Our SMA observations resolve the HMC into three cores whose masses are on the order of 10^1−10^3 M_⊙. No submm core exhibits detectable free-free emission in the centimeter regime, but appear to be associated with masers and thermal line emission from complex organic molecules. Towards the most massive core, SMA1, the CH_3CN (18_K−17_K) lines provide hints of rotation about the axis of a jet/outflow traced by H_2O maser and H^(13)CO^+(1−0) line emission. Inverse P-Cygni profiles of the ^(13)CO (3−2) and C^(18)O (3−2) lines seen towards SMA1 indicate that the central high-mass (proto)star(s) is (are) still gaining mass with an accretion rate ≥3 × 10^(−3) M_⊙ yr^(−1). Owing to the linear scales and high accretion rate, we hypothesize that we are observing an accretion flow towards a star cluster in the making, rather than towards a single massive star.