High-angular-resolution NIR view of the Orion Bar revealed by Keck/NIRC2
Artikel i vetenskaplig tidskrift, 2023

Context. Nearby photo-dissociation regions (PDRs), where the gas and dust are heated by the far-ultraviolet (FUV) irradiation emitted from stars, are ideal templates with which to study the main stellar feedback processes.
Aims. 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 are among the first targets of the James Webb Space Telescope (JWST) within the framework of the PDRs4All Early Release Science program.
Methods. We employed the subarcsecond resolution accessible with Keck-II NIRC2 and its adaptive optics system to obtain images of the vibrationally excited line H2 1-0 S(1) at 2.12 μm that are more detailed and complete than ever before. H2 1-0 S(1) traces the dissociation front (DF), and the [FeII] and Brγ lines, at 1.64 and 2.16 μm, respectively, trace the ionization front (IF). The former is a powerful tracer of the FUV radiation field strength and gas density distribution at the PDR edge, while the last two trace the temperature and density distribution from the ionized gas to the PDR. We obtained narrow-band filter images in these key gas line diagnostics over ∼40″ at spatial scales of ∼0.1″ (∼0.0002 pc or ∼40 AU at 414 pc).
Results. The Keck/Near Infrared Camera 2 (NIRC2) observations spatially resolve a plethora of irradiated substructures such as ridges, filaments, globules, and proplyds. This portends what JWST should accomplish and how it will complement the highest resolution Atacama Large Millimeter/submillimeter Array (ALMA) maps of the molecular cloud. We observe a remarkable spatial coincidence between the H2 1-0 S(1) vibrational and HCO+ J = 4-3 rotational emission previously obtained with ALMA. This likely indicates the intimate link between these two molecular species and highlights that in high-pressure PDRs, the H/H2 and C+/C/CO transitions zones come closer than in a typical layered structure of a constant density PDR. The H/H2 dissociation front appears as a highly structured region containing substructures with a typical thickness of a few ∼10-3 pc.

Photon-dominated region

ISM: molecules

Infrared: ISM

Författare

Emilie Habart

Institut d'Astrophysique Spatiale

R. Le Gal

Institut de Radioastronomie Millimétrique (IRAM)

Institut de Planétologie et d’Astrophysique de Grenoble (IPAG)

Carlos Alvarez

W. M. Keck Observatory

Els Peeters

Western University

SETI Institute

O. Berné

Institut de Recherche en Astrophysique et Planétologie (IRAP)

M.G. Wolfire

University of Maryland

Javier R. Goicoechea

CSIC - Instituto de Fisica Fundamental (IFF)

Thiébaut-Antoine Schirmer

Chalmers, Rymd-, geo- och miljövetenskap, Astronomi och plasmafysik

E. Bron

Observatoire de Paris

M. Rollig

Universität zu Köln

Astronomy and Astrophysics

0004-6361 (ISSN) 1432-0746 (eISSN)

Vol. 673 A149

Ämneskategorier

Astronomi, astrofysik och kosmologi

Atom- och molekylfysik och optik

DOI

10.1051/0004-6361/202244034

Relaterade dataset

Orion Bar Keck-II/NIRC2 images : J/A+A/673/A149 [dataset]

URI: https://cdsarc.cds.unistra.fr/viz-bin/cat/J/A+A/673/A149

Mer information

Senast uppdaterat

2023-06-21