High angular resolution near-IR view of the Orion Bar revealed by Keck/NIRC2

Abstract

Nearby Photo-Dissociation Regions (PDRs), where the gas and dust are heated by the far UV-irradiation emitted from stars, are ideal templates to study the main stellar feedback processes. With this study we aim to probe the detailed structures at the interfaces between ionized, atomic, and molecular gas in the Orion Bar. This nearby prototypical strongly irradiated PDR will be among the first targets of the James Webb Space Telescope (JWST) within the framework of the PDRs4All Early Release Science program. We employed the sub-arcsec resolution accessible with Keck-II NIRC2 and its adaptive optics system to obtain the most detailed and complete images, ever performed, of the vibrationally excited line H${}_2$ 1-0 S(1) at 2.12~$\mu$m, tracing the dissociation front, and the [FeII] and Br$\gamma$ lines, at 1.64 and 2.16~$\mu$m respectively, tracing the ionization front. We obtained narrow-band filter images in these key gas line diagnostic over $\sim 40^{\prime \prime }$ at spatial scales of $\sim$0.1${}^{\prime \prime }$ ($\sim$0.0002~pc or $\sim$40~AU at 414~pc). The Keck/NIRC2 observations spatially resolve a plethora of irradiated sub-structures such as ridges, filaments, globules and proplyds. A remarkable spatial coincidence between the H${}_2$ 1-0 S(1) vibrational and HCO${}^{+}$ J=4-3 rotational emission previously obtained with ALMA is observed. This likely indicates the intimate link between these two molecular species and highlights that in high pressure PDR the H/H${}_2$ and C${}^{+}$/C/CO transitions zones come closer as compared to a typical layered structure of a constant density PDR. This is in agreement with several previous studies that claimed that the Orion Bar edge is composed of very small, dense, highly irradiated PDRs at high thermal pressure immersed in a more diffuse environment.

References in corpus (50)

• The distance to the Orion Nebula
• A model for atomic and molecular interstellar gas: The Meudon PDR code
• The evolution of amorphous hydrocarbons in the ISM: dust modelling from a new vantage point
• A Disk of Young Stars at the Galactic Center as Determined by Individual Stellar Orbits
• The global dust modelling framework THEMIS (The Heterogeneous dust Evolution Model for Interstellar Solids)
• The Gould's Belt Distances Survey (GOBELINS) II. Distances and structure towards the Orion Molecular Clouds
• Photodissociation and X-Ray Dominated Regions
• The chemistry of vibrationally excited H2 in the interstellar medium
• Compression and ablation of the photo-irradiated cloud the Orion Bar
• 3D shape of Orion A from Gaia DR2
• Herschel/HIFI observations of [CII] and [13CII] in PDRs
• Velocity-resolved [CII] emission and [CII]/FIR Mapping along Orion with Herschel
• The chemistry of ions in the Orion Bar I. - CH+, SH+, and CF+: The effect of high electron density and vibrationally excited H2 in a warm PDR surface
• HAWC+/SOFIA Multiwavelength Polarimetric Observations of OMC-1
• Structure of photodissociation fronts in star-forming regions revealed by observations of high-J CO emission lines with Herschel
• Orion's Bar: Physical Conditions across the Definitive H+ / H0 / H2 Interface
• A MUSE map of the central Orion Nebula (M 42)
• PDRs4All: A JWST Early Release Science Program on radiative feedback from massive stars
• H_2 Pure Rotational Lines in the Orion Bar
• Expanding bubbles in Orion A: [CII] observations of M42, M43, and NGC 1977
• 3D simulations of globules and pillars formation around HII regions: turbulence and shock curvature
• Waves on the surface of the Orion molecular cloud
• Tearing the Veil: interaction of the Orion Nebula with its neutral environment
• Spatial variation of the cooling lines in the Orion Bar from Herschel/PACS
• FEEDBACK: a SOFIA Legacy Program to Study Stellar Feedback in Regions of Massive Star Formation
• Effects of Magnetic Fields on Photoionised Pillars and Globules
• The Orion Fingers: Near-IR Adaptive Optics Imaging of an Explosive Protostellar Outflow
• Deviations from He I Case B Recombination Theory and Extinction Corrections in the Orion Nebula
• Modelling clumpy PDRs in 3D - Understanding the Orion Bar stratification
• PDR Model Mapping of Physical Conditions via Spitzer/IRS Spectroscopy of H2: Theoretical Success toward NGC 2023-South
• Carbon recombination lines in the Orion Bar
• Spatially resolved images of reactive ions in the Orion Bar
• Constraining physical conditions for the PDR of Trumpler 14 in the Carina Nebula
• Rotationally Warm Molecular Hydrogen in the Orion Bar
• SOC program for dust continuum radiative transfer
• Excitation of Molecular Hydrogen in the Orion Bar Photodissociation Region From a Deep Near-Infrared IGRINS Spectrum
• Near-Infrared Spectroscopy of Photodissociation Regions: The Orion Bar and Orion S
• The initial gas-phase sulfur abundance in the Orion Molecular Cloud from sulfur radio recombination lines
• Maps of Magnetic Field Strength in the OMC-1 using HAWC+ FIR Polarimetric data
• A Near-infrared Survey of UV-excited Molecular Hydrogen in Photodissociation Regions
• Spatial distribution of FIR rotationally excited CH+ and OH emission lines in the Orion Bar PDR
• Herschel survey and modelling of externally-illuminated photoevaporating protoplanetary disks
• HIFI observations of warm gas in DR21: Shock versus radiative heating
• Direct estimation of electron density in the Orion Bar PDR from mm-wave carbon recombination lines
• Self-generated ultraviolet radiation in molecular shock waves II. CH+ and the interpretation of emission from shock ensembles
• The KOSMA-$\tau$ PDR Model -- I. Recent updates to the numerical model of photo-dissociated regions
• Dynamical effects of the radiative stellar feedback on the H I-to-H2 transition
• Merged H/H2 and C+/C/CO transitions in the Orion Bar
• A JWST Preview: Adaptive-Optics Images of H${}_2$, Br-$\gamma$, and K-continuum in Carina's Western Wall
• Tracing PAH Size in Prominent Nearby Mid-Infrared Environments

Cited by in corpus (10)

• PDRs4All III: JWST's NIR spectroscopic view of the Orion Bar
• PDRs4All II: JWST's NIR and MIR imaging view of the Orion Nebula
• HCN emission from translucent gas and UV-illuminated cloud edges revealed by wide-field IRAM 30m maps of Orion B GMC: Revisiting its role as tracer of the dense gas reservoir for star formation
• PDRs4All XI. Detection of infrared CH${}^{+}$ and CH${}_3^{+}$ rovibrational emission in the Orion Bar and disk d203-506: evidence of chemical pumping
• The extremely sharp transition between molecular and ionized gas in the Horsehead nebula
• PDRs4All VI: Probing the Photochemical Evolution of PAHs in the Orion Bar Using Machine Learning Techniques
• PDRs4All. X. ALMA and JWST detection of neutral carbon in the externally irradiated disk d203-506: Undepleted gas-phase carbon
• PDRs4All. XII. FUV-driven formation of hydrocarbon radicals and their relation with PAHs
• Near infrared view on the photodissociation regions S255, S257, NGC7538 and S140
• PDRs4All XVII: Formation and excitation of HD in photodissociation regions. Application to the Orion Bar