PDRs4All

Astronomy and Astrophysics, vol. 714, pp. A4

Abstract

Context. Conspicuous excess emission is present in the near-infrared (NIR) region in various objects, including reflection nebulae, planetary nebulae, and nearby galaxies. However, the spatial distribution and spectral shape of the excess emission remain poorly understood. Aims. We studied the NIR continuum emission spectroscopically and obtained its spatial distribution relative to the aromatic infrared band (AIB) at 3.3 µm in the Orion Bar prototypical photodissociation region (PDR). We aim to characterize its spectral shape and discuss its origin. Methods. We employed 3D spectroscopic data of the Orion Bar taken with the integrated field unit of NIRSpec on JWST from the Early Release Science program “PDRs4All.” Contribution from the foreground ionized gas was estimated using the Cloudy code and subtracted. The observed regions were divided into nine physically distinct regions and an average spectrum was derived for each region. Results. The nine regions, including the ionized gas, atomic PDR, and molecular PDR, clearly show remaining continuum in the region 1–4.5 µm. The continuum at wavelengths longer than 2.7 µm shows good correlations with the 3.3 µm AIB, while the correlation of the continuum at 1.2 µm is not significant. We further find that the NIR continuum in the Orion Bar can be approximated by a summation of two blackbodies. The low-temperature component correlates with the AIB well, while the high-temperature component does not. The average spectra also show absorption features at 3.0 and 4.27 µm, which are attributed to the presence in the spectra of water ice and CO 2 ice. Conclusions. We discuss possible origins of the NIR continuum, among which recurrent fluorescence from carbon clusters better explains the observed low-temperature component. The presence of ice species suggests a contribution from a deeper layer of the PDR along the line of sight producing characteristic ice absorption features.

Authors 16

1. Takashi Onaka

   The University of Tokyo

   Affiliation as printed

   Department of Astronomy, Graduate School of Science, The University of Tokyo

2. Emmanuel Dartois

   Centre National de la Recherche Scientifique · Université Paris-Saclay · Institut des Sciences Moléculaires d'Orsay

   Affiliation as printed

   Institut des Sciences Moléculaires d’Orsay, Université Paris-Saclay, CNRS

3. E. Peeters

   Western University · Search for Extraterrestrial Intelligence

   Affiliation as printed

   Carl Sagan Center, SETI Institute

   Department of Physics & Astronomy, The University of Western Ontario

   Institute for Earth and Space Exploration, The University of Western Ontario

4. Olivier Berné

   Centre National de la Recherche Scientifique · Université Toulouse III - Paul Sabatier · Institut de Recherche en Astrophysique et Planétologie

   Affiliation as printed

   Institut de Recherche en Astrophysique et Planétologie, Université Toulouse III – Paul Sabatier, CNRS, CNES

5. E. Habart

   Centre National de la Recherche Scientifique · Université Paris-Saclay · Institut d'Astrophysique Spatiale

   Affiliation as printed

   Institut d’Astrophysique Spatiale, Université Paris-Saclay, CNRS

6. Christiaan Boersma

   Ames Research Center

   Affiliation as printed

   NASA Ames Research Center

7. J. Cami

   Western University · Search for Extraterrestrial Intelligence

   Affiliation as printed

   Carl Sagan Center, SETI Institute

   Department of Physics & Astronomy, The University of Western Ontario

   Institute for Earth and Space Exploration, The University of Western Ontario

8. Asunción Fuente

   Centro de Astrobiología

   Affiliation as printed

   Centro de Astrobiología (CSIC-INTA),Ctra de Torrejón a Ajaalvir

9. Javier R. Goicoechea

   Consejo Superior de Investigaciones Científicas · Instituto de Física Fundamental

   Affiliation as printed

   Instituto de Física Fundamental (CSIC)

10. Ozan Lacinbala

    Centre National de la Recherche Scientifique · Université Paris-Saclay · Institut des Sciences Moléculaires d'Orsay

    Affiliation as printed

    Institut des Sciences Moléculaires d’Orsay, Université Paris-Saclay, CNRS

11. Yoko Okada

    University of Cologne

    Affiliation as printed

    I. Physikalisches Institut der Universität zu Köln

12. Alexander G. G. M. Tielens Aachen Leiden Observatory

    Leiden University · Leiden Observatory · University of Maryland, College Park

    Affiliation as printed

    Astronomy Department, University of Maryland

    Leiden Observatory, Leiden University

13. Dries Van De Putte

    Western University

    Affiliation as printed

    Department of Physics & Astronomy, The University of Western Ontario

    Institute for Earth and Space Exploration, The University of Western Ontario

14. F. Boulanger

    Centre National de la Recherche Scientifique · Université Paris Sciences et Lettres · École Normale Supérieure - PSL · Sorbonne Université · Laboratoire de Physique de l'Ecole Normale Supérieure

    Affiliation as printed

    Laboratoire de Physique de l’École Normale Supérieure, ENS, Université PSL, CNRS, Sorbonne Université, Université de Paris

15. Thomas Pino

    Centre National de la Recherche Scientifique · Université Paris-Saclay · Institut des Sciences Moléculaires d'Orsay

    Affiliation as printed

    Institut des Sciences Moléculaires d’Orsay, Université Paris-Saclay, CNRS

16. Yong Zhang

    Sun Yat-sen University

    Affiliation as printed

    School of Physics and Astronomy, Sun Yat-sen University