The EDIBLES survey III. C2-DIBs and their profiles

Abstract

The so-called C2-DIBs are a class of very weak bands that fall in the blue part of the optical spectrum and are associated with high column densities of the C2 molecule. DIB profile structures constrain potential molecular carriers, but their measurement requires high S/N and spectra and the use of sightlines without Doppler splitting, as typical for a single-cloud situation. Spectra from the ESO Diffuse Interstellar Bands Large Exploration Survey (EDIBLES) conducted at the VLT (ESO/Paranal) were explored to identify single-cloud and high C2 column sightlines, extract the corresponding C2-DIBs and study their strengths and profiles, and to investigate in detail any sub-structures. The target selection was made based on profile-fitting of the Sodium doublets and the detection of C2 lines. The C2 (2-0) Phillips system was fitted using a physical model of the host cloud. C2 column densities, temperatures as well as gas densities were derived for each sightline. 18 known C2-DIBs and 8 strong non-C2 DIBs were extracted towards 8 targets, comprising 7 single-cloud and one multi-cloud line-of-sights. Correlational studies revealed a tight association of the former group with the C2 columns, whereas the non-C2 DIBs are primarily correlated with reddening. We report three new weak diffuse band candidates. We show for the first time that at least 14 C2-DIBs exhibit spectral sub-structures which are consistent with unresolved rotational branches of molecular carriers. The variability of their peak separations among the bands for a given sightline implies that their carriers are different molecules with quite different sizes. We also illustrate how profiles of the same DIB vary among targets and as a function of physical parameters and provide tables defining the sub-structures to be compared with future models and experimental results.

arXiv comment19 pages, 15 figures, accepted for publication in A&A

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Cited by in corpus (18)

• The Apache Point Observatory Catalog of Optical Diffuse Interstellar Bands
• Polyacenes and diffuse interstellar bands
• The EDIBLES survey IV. Cosmic ray ionization rates in diffuse clouds from near-ultraviolet observations of interstellar OH${}^{+}$
• Galactic extinction laws: II. Hidden in plain sight, a new interstellar absorption band at 7700 Å broader than any known DIB
• CRIRES high-resolution near-infrared spectroscopy of diffuse interstellar band profiles. Detection of 12 new DIBs in the YJ band and the introduction of a combined ISM sight line and stellar analysis approach
• Survey of very broad Diffuse Interstellar Bands
• The EDIBLES survey V: Line profile variations in the $\lambda \lambda$5797, 6379, and 6614 diffuse interstellar bands as a tool to constrain carrier sizes
• Updated extraction of the APOGEE 1.5273 μm diffuse interstellar band: a Planck view on the carrier depletion in dense cores
• High-speed stars. II. An unbound star, young stars, bulge metal-poor stars, and Aurora candidates
• The diffuse interstellar band around 8620 Å II. Kinematics and distance of the DIB carrier
• First detection of $A$--$X$ (0,0) bands of interstellar C${}_2$ and CN
• The EDIBLES Survey. VII. A survey of C2 and C3 in interstellar clouds
• Correlation between UV resilience and wavelength of narrow DIBs
• Theoretical studies of carbon isotopic fractionation in reactions of C with C${}_2$: dynamics, kinetics, and isotopologue equilibria
• Transmission of the AtmosPhere for AStronomical data: TAPAS upgrade
• The Pristine Inner Galaxy Survey (PIGS) VI: Different vertical distributions between two DIBs at 442.8 nm and 862.1 nm
• The EDIBLES survey VI. Searching for time variations of interstellar absorption features
• Families and Clusters of Diffuse Interstellar Bands: a Data-Driven Correlation Analysis