The Gaia-ESO Survey: Extracting diffuse interstellar bands from cool
  star spectra, DIB-based interstellar medium line-of-sight structures at the
  kpc scale
  We study how diffuse interstellar bands (DIBs) measured toward
distance-distributed target stars can be used to locate dense interstellar (IS)
clouds in the Galaxy and probe a line-of-sight (LOS) kinematical structure, a
potential useful tool when gaseous absorption lines are saturated or not
available in the spectral range. Cool target stars are numerous enough for this
purpose. We have devised automated DIB fitting methods appropriate to cool star
spectra and multiple IS components. The data is fitted with a combination of a
synthetic stellar spectrum, a synthetic telluric transmission, and empirical
DIB profiles. In parallel, stellar distances and extinctions are estimated
self-consistently by means of a 2D Bayesian method, from
spectroscopically-derived stellar parameters and photometric data. We have
analyzed Gaia-ESO Survey (GES) and previously recorded spectra that probe
between $\sim$ 2 and 10 kpc long LOS in five different regions of the Milky
Way. Depending on the observed spectral intervals, we extracted one or more of
the following DIBs: $\lambda\lambda$ 6283.8, 6613.6 and 8620.4. For each field,
we compared the DIB strengths with the Bayesian distances and extinctions, and
the DIB Doppler velocities with the HI emission spectra. For all fields, the
DIB strength and the target extinction are well correlated. In case of targets
widely distributed in distance, marked steps in DIBs and extinction radial
distance profiles match with each other and broadly correspond to the expected
locations of spiral arms. For all fields, the DIB velocity structure agrees
with HI emission spectra and all detected DIBs correspond to strong NaI lines.
This illustrates how DIBs can be used to locate the Galactic interstellar gas
and to study its kinematics at the kpc scale.
