J/A+A/673/A149 Orion Bar Keck-II/NIRC2 images (Habart+, 2023)
High-angular-resolution NIR view of the Orion Bar revealed by Keck/NIRC2.
Habart E., Le Gal R., Alvarez C., Peeters E., Berne O., Wolfire M.G.,
Goicoechea J.R., Schirmer T., Bron E., Rollig M.
<Astron. Astrophys. 673, A149 (2023)>
=2023A&A...673A.149H 2023A&A...673A.149H (SIMBAD/NED BibCode)
ADC_Keywords: Star Forming Region ; Infrared
Keywords: infrared: ISM - photon-dominated regions - ISM: molecules
Abstract:
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.
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.
We employed the subarcsecond resolution accessible with Keck-II NIRC2
and its adaptive optics system to obtain images of the vibrationally
excited line H_2+ 1-0 S(1) at 2.12um 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 2.16um,
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" (∼0.0002pc or ∼40AU at 414pc).
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 ∼1*10-3pc.
Description:
Emission maps of Orion Bar are taken in imaging mode using
Keck-II/Near Infrared Camera 2 (NIRC2). We observe a representative
field-of-view (FoV) of 40"x40' of the Orion Bar centered on
RA=05:35:20.662, DEC=-05:25:19.38 (J2000) with a pixel size of 0.04".
Observations were obtained in the narrow-band filters H2 v=1-0
(λc=2.128um, {DELTA}λ=0.034um), [FeII]
(λc=1.645um, {DELTA}λ=0.026um), and Brγ
(λc=2.168um, {DELTA}λ=0.0326um). We also obtained
observations in the Kcont (λc = 2.271um, {DELTA}λ =
0.033 um) and Hcont (λc = 1.580um, {DELTA}λ = 0.023um)
filters to subtract the continuum from the H2 v=1-0, Brγ, and
[FeII] line maps, respectively. The full width at half maximum (FWHM)
of the point-spread function (PSF) was ∼0.11". The flux-calibrated
science maps are in erg/cm2/s/sr. We assigned an accuracy of about
25% to the measurements of the line intensity.
Objects:
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RA (2000) DE Designation(s)
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05 35 20.66 -05 25 19.38 Orion Bar = NAME Ori Bar
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File Summary:
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FileName Lrecl Records Explanations
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ReadMe 80 . This file
list.dat 127 6 Information on fits images
fits/* . 6 Individual fits images
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Byte-by-byte Description of file: list.dat
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Bytes Format Units Label Explanations
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1- 9 F9.5 deg RAdeg Right Ascension of center (J2000)
10- 18 F9.5 deg DEdeg Declination of center (J2000)
20- 22 I3 --- Nx Number of pixels along X-axis
24- 26 I3 --- Ny Number of pixels along Y-axis
28- 31 I4 Kibyte size Size of FITS file
33- 68 A36 --- FileName Name of FITS file, in subdirectory fits
70-127 A58 --- Title Title of the FITS file
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Acknowledgements:
Emilie Habart, emilie.habart(at)ias.u-psud.fr
(End) Patricia Vannier [CDS] 07-May-2023