The Pristine Inner Galaxy Survey (PIGS) – VI. Different vertical distributions between two DIBs at 442.8 nm and 862.1 nm

Abstract

ABSTRACT Although diffuse interstellar bands (DIBs) were discovered over 100 yr ago, for most of them, their origins are still unknown. Investigation on the correlations between different DIBs is an important way to study the behaviour and distributions of their carriers. Based on stacking thousands of spectra from the Pristine Inner Galaxy Survey, we study the correlations between two DIBs at 442.8 nm (λ442.8) and 862.1 nm (λ862.1), as well as the dust grains, in a range of latitude spanning ∼22° ($4^{\circ }\, {\lt }\, |b|\, {\lt }\, 15^{\circ }$) toward the Galactic Centre ($|\ell |\, {\lt }\, 11^{\circ }$). Tight linear intensity correlations can be found between λ442.8, λ862.1, and dust grains for $|b|\, {\lt }\, 12^{\circ }$ or $E(B\, {-}\, V)\, {\gt }\, 0.3$ mag. For $|b|\, {\gt }\, 12^{\circ }$, λ442.8 and λ862.1 present larger relative strength with respect to the dust grains. A systematic variation of the relative strength between λ442.8 and λ862.1 with |b| and $E(B\, {-}\, V)$ concludes that the two DIBs do not share a common carrier. Furthermore, the carrier of λ862.1 is more abundant at high latitudes than that of λ442.8. This work can be treated as an example showing the significance and potentials to the DIB research covering a large latitude range.