Near-IR Explorations of the Diffuse Interstellar Medium
Gail Zasowski, Johns Hopkins University
One of the longest standing puzzles of galactic astronomy and astrochemistry is the nature of the Diffuse Interstellar Bands (DIBs). These seemingly ubiquitous ISM absorption features are seen superimposed on the spectra of stars, galaxies, and quasars, but despite nearly a century of study, no physical carrier has been positively identified. The vast majority of our knowledge of DIBs is from optical data, as the first near-IR H-band features, detected towards a handful of stars, were not published until 2011. I will describe a new project that increases the number of these detections by orders of magnitude and, contrary to most DIB studies to date, characterizes them to use as tools for understanding the Galactic ISM on large scales. The dataset comprises high resolution, H-band spectra from the Apache Point Observatory Galactic Evolution Experiment (APOGEE, part of the SDSS-III), which takes advantage of the reduced effects of extinction at IR wavelengths to probe stars throughout the Galactic bulge, disk, and halo, homogeneously sampling a wide range of ISM environment. I will discuss how this catalog of near-IR DIBs is being used to map the DIB carrier's distribution within the Milky Way and to relate it to other Galactic ISM tracers. I will also present new statistical analyses of quasar and galaxy spectra that probe weak, high-latitude optical DIBs. These analyses demonstrate the power of large datasets to provide new insights into the properties of these poorly-understood feature carriers and the ISM in which they reside.
