The EDIBLES survey
Astronomy and Astrophysics, vol. 681, pp. A6
Abstract
Context. Small linear carbon chain radicals such as C2 and C3 act as both the building blocks and dissociation fragments of larger carbonaceous species. Their rotational excitation traces the temperature and density of local environments. However, these homo-nuclear di- and triatomic species are only accessible through their electronic and vibrational features because they lack a permanent dipole moment, and high signal-to-noise ratio data are necessary as the result of their generally low abundances in the interstellar medium (ISM). Aims. In order to improve our understanding of small carbonaceous species in the ISM, we carried out a sensitive survey of C2 and C3 using the ESO Diffuse Interstellar Bands Large Exploration Survey (EDIBLES) dataset. We also expanded our searches to C4, C5, and the 13C12C isotopologue in the most molecule-rich sightlines. Methods. We fitted synthetic spectra generated following a physical excitation model to the C2 (2-0) Phillips band to obtain the C2 column density (N) as well as the kinetic temperature (Tkin) and number density (n) of the host cloud. The C3 molecule was measured through its à − $ \tilde X$ (000-000) electronic origin band system. We simulated the excitation of this band with a double-temperature Boltzmann distribution. Results. We present the largest combined survey of C2 and C3 to date in which the individual transitions can be resolved. In total, we detected C2 in 51 velocity components along 40 sightlines, and C3 in 31 velocity components along 27 sightlines. Further analysis confirms the two molecules are detected in the same velocity components. We find a very good correlation between N(C2) and N(C3) with a Pearson correlation coefficient r = 0.93 and an average N(C2)/N(C3) ratio of 15.5± 1.4. A comparison with the behaviour of the C2 diffuse interstellar bands (DIBs) shows that there are no clear differences among sightlines with and without detections of C2 and C3. This is in direct contrast to the better-studied non-C2 DIBs, which have reduced strengths in molecule-rich environments, consistent with the idea that the C2 DIBs are indeed a distinguishable DIB family. We also identify, for the first time, the Q(2), Q(3), and Q(4) transitions of the 13C12C (2-0) Phillips band in the stacked average spectrum of molecule-rich sightlines, and estimate the isotopic ratio of carbon 12C/13C to be 79±8, consistent with literature results. At this stage it is not yet possible to identify these transitions in individual sightlines. Our search for the C4 and C5 optical bands was unsuccessful; even in stacked spectra no unambiguous identification could be made.
Authors 17
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Affiliation as printed
Department of Physics and Astronomy, The University of Western Ontario, London, ON N6A 3K7, Canada
Institute for Earth and Space Exploration, The University of Western Ontario, London, ON N6A 3K7, Canada
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Leiden University · Leiden Observatory
Affiliation as printed
Laboratory for Astrophysics, Leiden Observatory, Leiden University, PO Box 9513, 2300 RA Leiden, The Netherlands
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Goddard Space Flight Center · Catholic University of America
Affiliation as printed
Astrochemistry Laboratory, NASA Goddard Space Flight Center, Code 691, 8800 Greenbelt Road, Greenbelt, MD 20771, USA
Department of Physics, The Catholic University of America, Washington, DC 20064, USA
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Leiden University · Leiden Observatory
Affiliation as printed
Laboratory for Astrophysics, Leiden Observatory, Leiden University, PO Box 9513, 2300 RA Leiden, The Netherlands
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Affiliation as printed
Centre d'Etudes et de Recherche de Grasse, ACRI-ST, Av. Nicolas Copernic, Grasse 06130, France
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University of Tehran · Institute for Research in Fundamental Sciences
Affiliation as printed
Department of Physics, University of Tehran, North Karegar Ave, 14395-547 Tehran, Iran
School of Astronomy, Institute for Research in Fundamental Sciences, 19395-5531 Tehran, Iran
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Royal Observatory · European Southern Observatory · UK Astronomy Technology Centre
Affiliation as printed
European Southern Observatory, Alonso de Cordova 3107, Casilla 19001, Vitacura, Santiago, Chile
UK Astronomy Technology Centre, Royal Observatory, Blackford Hill, Edinburgh EH9 3HJ, UK
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Centre National de la Recherche Scientifique · Université Paris Sciences et Lettres · Observatoire de Paris · Laboratoire d’Etudes du Rayonnement et de la Matière en Astrophysique et Atmosphères
Affiliation as printed
LERMA, Observatoire de Paris, PSL Research University, CNRS, Sorbonne Universite's, 92190, Meudon, France
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Leiden University · Leiden Observatory
Affiliation as printed
Leiden Observatory, Leiden University, PO Box 9513, 2300 RA Leiden, The Netherlands
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Affiliation as printed
NASA Ames Research Centre, Space Science & Astrobiology Division, Moffett Field, California, USA
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Leiden University · Leiden Observatory · European Space Research and Technology Centre
Affiliation as printed
ESTEC, ESA, Keplerlaan 1, 2201 AZ Noordwijk, The Netherlands
Leiden Observatory, Leiden University, PO Box 9513, 2300 RA Leiden, The Netherlands
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Centre National de la Recherche Scientifique · Université Paris Sciences et Lettres · Observatoire de Paris · Sorbonne Paris Cité · Galaxies, Etoiles, Physique et Instrumentation · Université Paris Diderot
Affiliation as printed
GEPI, Observatoire de Paris, PSL Research University, CNRS, Université Paris-Diderot, Sorbonne Paris Cité, Place Jules Janssen, 92195 Meudon, France
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Affiliation as printed
Department of Physics and Astronomy, The University of Western Ontario, London, ON N6A 3K7, Canada
Institute for Earth and Space Exploration, The University of Western Ontario, London, ON N6A 3K7, Canada
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Affiliation as printed
Department of Physics and Astronomy, The University of Western Ontario, London, ON N6A 3K7, Canada
Institute for Earth and Space Exploration, The University of Western Ontario, London, ON N6A 3K7, Canada
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Affiliation as printed
School of Chemistry, The University of Nottingham, University Park, Nottingham NG7 2RD, UK
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Affiliation as printed
Lennard-Jones Laboratories, Keele University, ST5 5BG, UK
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Western University · Search for Extraterrestrial Intelligence
Affiliation as printed
Department of Physics and Astronomy, The University of Western Ontario, London, ON N6A 3K7, Canada
Institute for Earth and Space Exploration, The University of Western Ontario, London, ON N6A 3K7, Canada
SETI Institute, 339 Bernardo Ave, Suite 200, Mountain View, CA, 94043, USA
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