Families and Clusters of Diffuse Interstellar Bands: a Data-Driven Correlation Analysis

arXiv (Cornell University)

Abstract

More than 500 diffuse interstellar bands (DIBs) have been observed in astronomical spectra, and their signatures and correlations in different environments have been studied over the past decades to reveal clues about the nature of the carriers. We compare the equivalent widths of the DIBs, normalized to the amount of reddening, E_B-V, to search for anti-correlated DIB pairs using a data sample containing 54 DIBs measured in 25 sight lines. This data sample covers most of the strong and commonly detected DIBs in the optical region, and the sight lines probe a variety of ISM conditions. We find that 12.9% of the DIB pairs are anti-correlated, and the lowest Pearson correlation coefficient is r_norm ~ -0.7. We revisit correlation-based DIB families and are able to reproduce the assignments of such families for the well-studied DIBs by applying hierarchical agglomerative and k-means clustering algorithms. We visualize the dissimilarities between DIBs, represented by 1 - r_norm, using multi-dimensional scaling (MDS). With this representation, we find that the DIBs form a rather continuous sequence, which implies that some properties of the DIB carriers are changing gradually following this sequence. We also find at that least two factors are needed to properly explain the dissimilarities between DIBs. While the first factor may be interpreted as related to the ionization properties of the DIB carriers, a physical interpretation of the second factor is less clear and may be related to how DIB carriers interact with surrounding interstellar material.

Authors 12

1. Haoyu Fan corresponding

   Western University

   Affiliation as printed

   Department of Physics and Astronomy, The University of Western Ontario , London, ON N6A 3K7, Canada

   The Institute for Earth and Space Exploration, The University of Western Ontario , London, ON N6A 3K7, Canada

2. Madison Schwartz

   Western University

   Affiliation as printed

   Department of Physics and Astronomy, The University of Western Ontario , London, ON N6A 3K7, Canada

   The Institute for Earth and Space Exploration, The University of Western Ontario , London, ON N6A 3K7, Canada

3. Amin Farhang

   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

4. N. L. J. Cox
   Affiliation as printed

   ACRI-ST , 260 Route du Pin Montard, F-06904 Sophia-Antipolis, France

5. P. Ehrenfreund Aachen Leiden Observatory

   Leiden University · Leiden Observatory

   Affiliation as printed

   Leiden Observatory, Leiden University , Niels Bohrweg 2, NL-2333 CA Leiden, the Netherlands

6. A. Monreal‐Ibero Aachen Leiden Observatory

   Leiden University · Leiden Observatory

   Affiliation as printed

   Leiden Observatory, Leiden University , Niels Bohrweg 2, NL-2333 CA Leiden, the Netherlands

7. Bernard H. Foing Aachen Leiden Observatory

   Leiden University · Leiden Observatory

   Affiliation as printed

   Leiden Observatory, Leiden University , Niels Bohrweg 2, NL-2333 CA Leiden, the Netherlands

8. Farid Salama

   Ames Research Center

   Affiliation as printed

   NASA Ames Research Centre, Space Science & Astrobiology Division , Moffett Field, CA 94035, USA

9. Klay Kulik

   Western University

   Affiliation as printed

   Department of Physics and Astronomy, The University of Western Ontario , London, ON N6A 3K7, Canada

   The Institute for Earth and Space Exploration, The University of Western Ontario , London, ON N6A 3K7, Canada

10. Heather MacIsaac

    Western University

    Affiliation as printed

    Department of Physics and Astronomy, The University of Western Ontario , London, ON N6A 3K7, Canada

    The Institute for Earth and Space Exploration, The University of Western Ontario , London, ON N6A 3K7, Canada

11. Jacco Th. van Loon

    Keele University

    Affiliation as printed

    Lennard-Jones Laboratories, Keele University , Keele, Newcastle ST5 5BG, UK

12. J. Cami

    Western University · Search for Extraterrestrial Intelligence

    Affiliation as printed

    Department of Physics and Astronomy, The University of Western Ontario , London, ON N6A 3K7, Canada

    SETI Institute , 189 Bernardo Ave, Suite 100, Mountain View, CA 94043, USA

    The Institute for Earth and Space Exploration, The University of Western Ontario , London, ON N6A 3K7, Canada