2014ApJ...784..107Z

The formation of hypercompact (HC) H II regions is an important stage in massive star formation. Spectral line and continuum observations can explore its dynamic conditions. We present high angular resolution observations carried out with the Submillimeter Array (SMA) and the Very Large Array (VLA) toward the HC H II region G35.58-0.03. With the 1.3 mm SMA and 1.3 cm VLA, we detected a total of about 25 transitions of 8 different species and their isotopologues (CO, CH₃CN, SO₂, CH₃CCH, OCS, CS, H, and NH₃). G35.58-0.03 consists of an HC H II core with electron temperature T_e^* ≥ 5500 K, emission measure EM ~1.9x10⁹ pc/cm6, local volume electron density n_e= 3.3x10⁵/cm3, and a same width of radio recombination line FWHM ~ 43.2 km/s for both H30α and H38β at its intrinsic core size ∼3714 AU. The H30α line shows evidence of an ionized outflow driving a molecular outflow. Based on the derived Lyman continuum flux, there should be an early-type star equivalent to O6.5 located inside the H II region. From the continuum spectral energy distribution from 3.6 cm, 2.0 cm, 1.3 cm, 1.3 mm and 0.85 mm to 0.45 mm, we distinguished the free-free emission (25% ∼ 55%) from the warm dust component (75% ∼ 45%) at 1.3 mm. The molecular envelope shows evidence of infall and outflow with an infall rate of 0.05 M_☉/yr and a mass loss rate of 5.2x10^–3 M_☉/yr. The derived momentum (∼0.05 M_☉ km/s) is consistent between the infalling and outflowing gas per year. It is suggested that the infall is predominant and the envelope mass of dense core is increasing rapidly, but the accretion in the inner part might already be halted.