J/A+A/685/A75 PDRs4All IV. Orion Bar MRS template spectra (Chown+, 2024)
PDRs4All. IV. An embarrassment of riches:
Aromatic infrared bands in the Orion Bar.
Chown R., Sidhu A., Peeters E., Tielens A.G.G.M., Cami J., Berne O.,
Habart E., Alarcon F., Canin A., Schroetter I., Trahin B., Van De Putte D.,
Abergel A., Bergin E.A., Bernard-Salas J., Boersma C., Bron E.,
Cuadrado S., Dartois E., Dicken D., El-Yajouri M., Fuente A.,
Goicoechea J.R., Gordon K.D., Issa L., Joblin C., Kannavou O., Khan B.,
Lacinbala O., Languignon D., Le Gal R., Maragkoudakis A., Meshaka R.,
Okada Y., Onaka T., Pasquini S., Pound M.W., Robberto M., Roellig M.,
Schefter B., Schirmer T., Vicente S., Wolfire M.G., Zannese M., Aleman I.,
Allamandola L., Auchettl R., Baratta G.A., Bejaoui S., Bera P.P.,
Black J.H., Boulanger F., Bouwman J., Brandl B., Brechignac P.,
Bruenken S., Buragohain M., Burkhardt A., Candian A., Cazaux S.,
Cernicharo J., Chabot M., Chakraborty S., Champion J., Colgan S.W.J.,
Cooke I.R., Coutens A., Cox N.L.J., Demyk K., Meyer J.D., Foschino S.,
Garcia-Lario P., Gavilan L., Gerin M., Gottlieb C.A., Guillard P.,
Gusdorf A., Hartigan P., He J., Herbst E., Hornekaer L., Jaeger C.,
Janot-Pacheco E., Kaufman M., Kemper F., Kendrew S., Kirsanova M.S.,
Klaassen P., Kwok S., Labiano A., Lai T.S.-Y., Lee T.J., Lefloch B.,
Le Petit F., Li A., Linz H., Mackie C.J., Madden S.C., Mascetti J.,
McGuire B.A., Merino P., Micelotta E.R., Misselt K., Morse J.A., Mulas G.,
Neelamkodan N., Ohsawa R., Omont A., Paladini R., Palumbo M.E., Pathak A.,
Pendleton Y.J., Petrignani A., Pino T., Puga E., Rangwala N., Rapacioli M.,
Ricca A., Roman-Duval J., Roser J., Roueff E., Rouille G., Salama F.,
Sales D.A., Sandstrom K., Sarre P., Sciamma-O'Brien E., Sellgren K.,
Shenoy S.S., Teyssier D., Thomas R.D., Togi A., Verstraete L., Witt A.N.,
Wootten A., Zettergren H., Zhang Y., Zhang Z.E., Zhen J.
<Astron. Astrophys. 685, A75 (2024)>
=2024A&A...685A..75C 2024A&A...685A..75C (SIMBAD/NED BibCode)
ADC_Keywords: H II regions ; Infrared sources ; Milky Way ;
Interstellar medium ; Spectroscopy
Keywords: astrochemistry - infrared: ISM - ISM: molecules -
ISM: individual objects: Orion Bar - photon-dominated region (PDR) -
techniques: spectroscopic
Abstract:
Mid-infrared observations of photodissociation regions (PDRs) are
dominated by strong emission features called aromatic infrared bands
(AIBs). The most prominent AIBs are found at 3.3, 6.2, 7.7, 8.6, and
11.2 microns. The most sensitive, highest-resolution infrared spectral
imaging data ever taken of the prototypical PDR, the Orion Bar, have
been captured by JWST. These high-quality data allow for an
unprecedentedly detailed view of AIBs.
We provide an inventory of the AIBs found in the Orion Bar, along with
mid-IR template spectra from five distinct regions in the Bar: the
molecular PDR (i.e. the three H2 dissociation fronts), the atomic PDR,
and the HII region.
We used JWST NIRSpec IFU and MIRI MRS observations of the Orion Bar
from the JWST Early Release Science Program, PDRs4All (ID: 1288). We
extracted five template spectra to represent the morphology and
environment of the Orion Bar PDR. We investigated and characterised
the AIBs in these template spectra. We describe the variations among
them here.
The superb sensitivity and the spectral and spatial resolution of
these JWST observations reveal many details of the AIB emission and
enable an improved characterization of their detailed profile shapes
and sub-components. The Orion Bar spectra are dominated by the
well-known AIBs at 3.3, 6.2, 7.7, 8.6, 11.2, and 12.7 microns with
well-defined profiles. In addition, the spectra display a wealth of
weaker features and sub-components. The widths of many AIBs show clear
and systematic variations, being narrowest in the atomic PDR template,
but showing a clear broadening in the HII region template while the
broadest bands are found in the three dissociation front templates. In
addition, the relative strengths of AIB (sub-)components vary among
the template spectra as well. All AIB profiles are characteristic of
class A sources as designated by Peeters et al. (2002), except for the
11.2 micron AIB profile deep in the molecular zone, which belongs to
class B_11.2. Furthermore, the observations show that the
sub-components that contribute to the 5.75, 7.7, and 11.2 micron AIBs
become much weaker in the PDR surface layers. We attribute this to the
presence of small, more labile carriers in the deeper PDR layers that
are photolysed away in the harsh radiation field near the surface. The
3.3/11.2 AIB intensity ratio decreases by about 40% between the
dissociation fronts and the HII region, indicating a shift in the
polycyclic aromatic hydrocarbon (PAH) size distribution to larger PAHs
in the PDR surface layers, also likely due to the effects of
photochemistry. The observed broadening of the bands in the molecular
PDR is consistent with an enhanced importance of smaller PAHs since
smaller PAHs attain a higher internal excitation energy at a fixed
photon energy.
Spectral-imaging observations of the Orion Bar using JWST yield key
insights into the photochemical evolution of PAHs, such as the
evolution responsible for the shift of 11.2 micron AIB emission from
class B_11.2 in the molecular PDR to class A_11.2 in the PDR surface
layers. This photochemical evolution is driven by the increased
importance of FUV processing in the PDR surface layers, resulting in a
"weeding out" of the weakest links of the PAH family in these layers.
For now, these JWST observations are consistent with a model in which
the underlying PAH family is composed of a few species: the so-called
'grandPAHs'.
Description:
JWST/MIRI-MRS spectroscopic observations and parameters for five
regions in the Orion Bar are presented.
These are based on observations from the JWST Early Release Science
program PDRs4All: Radiative feedback from massive stars (ID: 1288,
PIs: Berne, Habart, Peeters). These five regions represent the HII
region, the atomic PDR, and three dissociation fronts (DF1, DF2, DF3).
For each region, JWST/MIRI-MRS spectra are provided.
Objects:
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RA (2000) DE Designation(s)
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05 35 22.30 -05 24 33.0 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
sptemp.dat 115 50000 MRS template spectra
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See also:
J/A+A/685/A74 : PDRs4All III. JWST/NIR view of the Orion Bar (Peeters+, 2024)
Byte-by-byte Description of file: sptemp.dat
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Bytes Format Units Label Explanations
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1- 10 F10.7 um lambda [4.9/27.91] Wavelength
12- 31 F20.13 MJy/sr Inu(HII) [141.13/679147.86] HII region MRS template
spectrum (surface brightness)
33- 52 F20.13 MJy/sr Inu(APDR) [316.06/480937.2] Atomic PDR MRS template
spectrum (surface brightness)
54- 73 F20.13 MJy/sr Inu(DF3) [94.88/157221.8] Dissociation Front 3 (DF3)
MRS template spectrum (surface brightness)
75- 94 F20.13 MJy/sr Inu(DF2) [135.14/198845.05] Dissociation Front 2 (DF2)
MRS template spectrum (surface brightness)
96-115 F20.13 MJy/sr Inu(DF1) [194.85/228498.7] Dissociation Front 1 (DF1)
MRS template spectrum (surface brightness)
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Acknowledgements:
Ryan Chown, rchown3(at)uwo.ca
References:
Berne et al., Paper I 2022PASP..134e4301B 2022PASP..134e4301B
Habart et al., Paper II 2024A&A...685A..73H 2024A&A...685A..73H
Peeters et al., Paper III 2024A&A...685A..74P 2024A&A...685A..74P, Cat. J/A+A/685/A74
(End) Ryan Chown [The Ohio State Univ.], Patricia Vannier [CDS] 15-Feb-2024