Mapping the reddening plane in the Galactic disk through interstellar extinction of open clusters

Abstract

As thousands of new open clusters in the Galaxy have recently been reported with reddening or extinction information, we map the distribution and properties of the MilkyWay’s interstellar material in the Galactic disk as traced by these open clusters. By analyzing the distribution of interstellar extinction for 6215 open clusters located at low Galactic latitude ($\left|b\right|\le 6°$), corresponding to the thin Galactic disk, we identify a reddening plane characterized by a dust layer whose thickness varies with Galactic longitude. By splitting the open clusters sample into several sub-regions of Galactic longitude, we observe that the reddening plane is not perfectly aligned with the formal Galactic plane, but instead varies sinusoidally around the Galactic mid-plane. The maximum and minimum interstellar absorption occur at approximately $42°$ and $222°$, respectively, along the Galactic longitude. Our analysis reveals a noticeable north-south asymmetry in the distribution of interstellar absorption, with a higher proportion of interstellar material below the Galactic plane. We also find that the Sun is located $15.7\pm 7.3$ pc above the reddening plane. The scale height of the open clusters from the reddening plane is estimated to be $z_h=87.3\pm 1.8$ pc. The mean thickness of the absorbing material in the reddening plane, which represents the average extent of the dust layer responsible for interstellar extinction, is found to be about $201\pm 20$ pc. Our findings provide insights into the distribution of interstellar dust, its relationship with the Galactic thin disk, and its implications on the Galactic structure.