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

Abstract

Methods: We obtained adaptive optics-assisted integral field spectroscopy in the near-infrared (IR) $K$ band ($1.93-2.47\mu \mathrm{m}$) with VLT/SINFONI, complemented by VLA X and C bands (3$-$6 cm) and ALMA band 3 ($\sim$3.3 mm) observations. Results: The near-IR continuum reveals two infrared sources, IRS 2 and IRS 7, while the main protostellar core IRAS 18162-2048 remains undetected up to $2.47\mu \mathrm{m}$. IRS 7 shows a peculiar Hydrogen Recombination Line Br$\gamma$ profile with a narrow emission component superimposed on a broad absorption feature, consistent with a B2/B3 zero-age main-sequence 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 $T_{\mathrm{gas}}=600$ K and $n_{\mathrm{H}}=7.9\times 10^3\mathrm{c}{\mathrm{m}}^{-3}$. 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 mm wavelengths. The spectral index in the 3$-$6 cm and 3.3 mm regime is consistent with optically thin free-free emission. Conclusions: Our near-IR and radio observations reveal that IRS 7/SC is a B2/B3 ZAMS star that has begun to photoionise its environment, giving rise to an extended PDR and a compact \ion{H}{ii} region. The coexistence of this source with the deeply embedded protostar IRAS 18162-2048 and other bubble-like structures in the field, suggests a multigenerational star-forming environment. Future \textit{James Webb Space Telescope} observations targeting the H${}_2$ pure rotational lines ($3-28\mu \mathrm{m}$) and other HRLs less affected by extinction will be essential to characterise the cooler molecular and ionised gas to fully disclose the formation history of the region.

arXiv commentAccepted in A&A. This version is after language editor corrections

References in corpus (42)

• The Disk Substructures at High Angular Resolution Project (DSHARP): I. Motivation, Sample, Calibration, and Overview
• CASA, the Common Astronomy Software Applications for Radio Astronomy
• A Unified Representation of Gas-Phase Element Depletions in the Interstellar Medium
• A multi-scale multi-frequency deconvolution algorithm for synthesis imaging in radio interferometry
• X-Shooter spectroscopy of young stellar objects: IV -- Accretion in low-mass stars and sub-stellar objects in Lupus
• SINFONI - Integral Field Spectroscopy at 50 milli-arcsecond resolution with the ESO VLT
• A Magnetized Jet from a Massive Protostar
• Photodissociation and X-Ray Dominated Regions
• The RMS Survey: Critical Tests of Accretion Models for the Formation of Massive Stars
• The Luminosity Functions and Timescales of MYSOs and Compact HII regions
• A near IR imaging survey of intermediate and high-mass young stellar outflow candidates
• The Ratio of Ortho- to Para-H2 in Photodissociation Regions
• A search for ionized jets towards massive young stellar objects
• VLT K-band spectroscopy of massive stars deeply embedded in IRAS sources with UCHII colours
• The circumstellar disk, envelope, and bi-polar outflow of the Massive Young Stellar Object W33A
• Jets from Young Stars
• A near-IR spectroscopic survey of massive jets towards EGOs
• Triggered Star Formation by Massive Stars
• Forming an Early O-type Star Through Gas Accretion?
• ALMA reveals sequential high-mass star formation in the G9.62+0.19 complex
• The Highly Collimated Radio Jet of HH 80-81: Structure and Non-Thermal Emission
• Triggered Star Formation
• Resolving the Circumstellar Disk Around the Massive Protostar Driving the HH 80-81 Jet
• Mid-infrared PAH and H2 emission as a probe of physical conditions in extreme PDRs
• Molecular jets driven by high-mass protostars: a detailed study of the IRAS 20126+4104 jet
• A measure of the size of the magnetospheric accretion region in TW Hydrae
• The PhotoDissociation Region Toolbox: Software and Models for Astrophysical Analysis
• Star Formation Under the Outflow: The Discovery of a Non-Thermal Jet from OMC-2 FIR 3 and its Relationship to the Deeply Embedded FIR 4 Protostar
• Excitation of Molecular Hydrogen in the Orion Bar Photodissociation Region From a Deep Near-Infrared IGRINS Spectrum
• Protostellar Outflows at the EarliesT Stages (POETS). I. Radio thermal jets at high resolution nearby H${}_2$O maser sources
• Tracing jet emission at the base of a high-mass YSO. First AMBER/VLTI observations of the Brγemission in IRAS 13481-6124
• Modeling the accretion disk around the high-mass protostar GGD 27-MM1
• Measuring the ionisation fraction in a jet from a massive protostar
• Centimeter continuum observations of the northern head of the HH 80/81/80N jet: revising the actual dimensions of a parsec scale jet
• Unveiling a cluster of protostellar disks around the massive protostar GGD27 MM1
• Star Formation Signatures in the Condensation Downstream of HH 80N
• Parsec-scale jets driven by high-mass young stellar objects. Connecting the au- and the parsec-scale jet in IRAS 13481-6124
• Fluorescent H_2 Emission Lines from the Reflection Nebula NGC 7023 Observed with IGRINS
• Hydrogen permitted lines in the first near-IR spectra of Th 28 microjet: accretion or ejection tracers?
• Near-Infrared Observations of Outflows and YSOs in the Massive Star-Forming Region AFGL 5180
• NIR jets from a clustered region of massive star formation: Morphology and composition in the IRAS 18264-1152 region
• Imaging of HH80-81 jet in the NIR shock tracers H${}_2$ and [Fe II]