The diffuse interstellar band around 8620 {\AA} II. Kinematics and distance of the DIB carrier

TL;DR

This study uses spectroscopic data from GIBS and GES surveys to analyze the kinematics and distances of the DIB 8620 carrier, refining its wavelength, and demonstrating it is located closer than the background stars in the Galactic disk.

Contribution

It provides new measurements of DIB 8620's wavelength, kinematic distances, and confirms its closer proximity to the observer compared to background stars.

Findings

DIB 8620's rest wavelength is 8620.83 Å.

Kinematic distances of DIB carriers are smaller than background stars.

DIB carriers follow Galactic rotation velocities.

Abstract

We aim to make use of the measurements from the Giraffe Inner Bulge Survey (GIBS) and the Gaia$-$ESO survey (GES) to study the kinematics and distance of the carrier of DIB$\,\lambda$8620, as well as other properties. We successfully detected and measured DIB$\,\lambda$8620 in 760 of 4117 GES spectra. Combined with the DIBs measured in GIBS spectra, we confirmed a tight relation between EW and $E(J-K_{\rm S})$ as well as $A_{\rm V}$, with similar fitting coefficients to those found by previous works. With a more accurate sample and the consideration of the solar motion, the rest-frame wavelength of DIB$\,\lambda$8620 was redetermined as 8620.83 \r{A}, with a mean fit error of 0.36 \r{A}. We studied the kinematics of the DIB carriers by tracing their median radial velocities in each field in the local standard of rest ($V_{\rm LSR}$) and into the galactocentric frame ($V_{\rm GC}$), respectively, as a function of the Galactic longitudes. Based on the median $V_{\rm LSR}$ and two Galactic rotation models, we obtained valid kinematic distances of the DIB carriers for nine GIBS and ten GES fields. We also found a linear relation between the DIB$\,\lambda$8620 measured in this work and the near-infrared DIB in APOGEE spectra at $1.5273\,\mu m$. We demonstrate that the DIB carriers can be located much closer to the observer than the background stars based on the following arguments: (i) qualitatively, the carriers occupy in the Galactic longitude$-$velocity diagram typical rotation velocities of stars in the local Galactic disk, while the background stars in the GIBS survey are mainly located in the Galactic bulge; (ii) quantitatively, all the derived kinematic distances of the DIB carriers are smaller than the median distances to background stars in each field.