Diverse stages of star formation in the IRAS 18162-2048 region. Emergence of UV feedback

High-mass star formation remains a major open problem in astrophysics, particularly regarding the transition between deeply embedded protostars and the onset of ionising radiation capable of producing photodissociation regions (PDRs) and compact regions. H ii We aim to characterise the excitation and ionisation conditions of the high-mass star-forming region IRAS 18162-2048, which is where the parsec-scale jet HH80-81 lies. We obtained adaptive optics–assisted integral field spectroscopy in the near-IR K band (1.93-2.47 ) with VLT/SINFONI, complemented by VLA X and C bands (3-6 cm) and ALMA band 3 (∼3.3 mm) observations. We analysed the continuum and line emission to derive visual extinction and excitation conditions and the kinematics of the gas of the region. μ m The near-IR continuum reveals two IR sources, IRS 2 and IRS 7, while the main protostellar core, IRAS 18162-2048, remains undetected up to 2.47 . IRS 7 shows a peculiar hydrogen recombination line (HRL) Brγ profile with a narrow emission component superimposed on a broad absorption feature, consistent with a B2/B3 zero-age main-sequence (ZAMS) star. Extended H_2 emission exhibits a `sawtooth' pattern in the excitation diagram, characteristic of UV radiation in a PDR rather than shock excitation. The radiative transfer model Cloudy reproduces the H_2 ro-vibrational populations for T_ =600 K and n_ =7.9 . The VLA X and C bands observations reveal a compact radio source previously reported as a `stationary condensation' (SC) and coincident with IRS 7. For the first time, we detect IRS 7/SC in millimetre wavelengths. The spectral index in the 3-6 cm and 3.3 mm regime is consistent with optically thin free–free emission. μ m gas H cm^ -3 Our near-IR and radio observations reveal that IRS 7/SC is a B2/B3 ZAMS star that has begun to photo-ionise its environment, giving rise to an extended PDR and a compact region. The coexistence of this source with the deeply embedded protostar IRAS 18162-2048 and other bubble-like structures in the field suggests a multi-generational star-forming environment. Future Space Telescope observations targeting the H_2 pure rotational lines (3-28 ) and other HRLs less affected by extinction will be essential to characterising the cooler molecular and ionised gas to fully disclose the formation history of the region. H ii James Webb μ m