1.5 Diffuse interstellar bands from aggregated RVS spectra

Author(s): M. Schultheis, A.G.A. Brown

This FPR presents the parameters of two Diffuse Interstellar Bands (DIBs) identified in stacked spectra from the Gaia Radial Velocity Spectrograph (RVS). DIBs are absorption features seen in optical spectra of stars and extragalactic objects that are probably caused by large and complex molecules in the Galactic interstellar medium (ISM).

In order to isolate the DIB from the stellar features in each individual spectrum, a set of 160 thousand spectra were identified at high Galactic latitudes ($|b|\ge {65}^{\circ }$) covering a range of stellar parameters which are used as DIB-free reference sample. Matching each target spectrum to its closest reference spectrum in stellar parameter space makes it possible to remove the stellar spectrum empirically, without reference to stellar models, leaving a set of 6 million interstellar medium (ISM) spectra. Using the parallax of the star and its Galactic longitude and latitude, we then allocate each ISM spectrum in a voxel (VOlume piXEL) on a contiguous three-dimensional grid with angular size of ${1.8}^{\circ }$ (level 5 HEALPix) leading to a total of $\mathrm{235\hspace{0.17em}428}$ voxels.

Identifying the two DIBs at $862.1$ nm ($\lambda$862.1) and $864.8$ nm ($\lambda$864.8) in the stacked spectra, their shapes are modelled and the central wavelength, width, depth, and equivalent width for each DIB, along with confidence bounds on these measurements calculated.

This FPR contains a parameter table listing the fitted DIB parameters in each voxel and a table containing the stacked ISM spectra in each voxel. The input data for this FPR cover the same time baseline as Gaia DR3.

The data processing and data model for this FPR are described in Gaia Collaboration, Schultheis, M., et al. (2023c).