A Rv map of the Milky Way revealed by LAMOST

TL;DR

This study maps the Rv extinction ratio across the Milky Way using LAMOST data, revealing its distribution, variability, and correlations with interstellar dust properties, which aids in understanding dust evolution and improving extinction corrections.

Contribution

It presents the first large-scale, high-resolution Rv map of the Milky Way derived from optical to mid-infrared data, highlighting spatial variations and environmental correlations.

Findings

Rv distribution peaks around 3.25 with a standard deviation of 0.25

Lower Rv values are found within molecular clouds

Relationships between Rv and dust/gas parameters vary with extinction level

Abstract

The total-to-selective extinction ratio, Rv, is a key parameter for tracing the properties of interstellar dust, as it directly determines the variation of the extinction curve with wavelength. By utilizing accurate color excess measurements from the optical to the mid-infrared range, we have derived Rv values for approximately 3 million stars from the LAMOST data release 7 (DR7) using a forward modeling technique. This extensive dataset enables us to construct a comprehensive two-dimensional Rv map of the Milky Way within the LAMOST footprint at a spatial resolution of ~27.5arcmin. Based on reliable sightlines of E(B-V) > 0.1, we find that Rv exhibits a Gaussian distribution centered around 3.25 with a standard deviation of 0.25. The spatial variability of Rv in the Galactic disk exhibits a wide range, spanning from small scales within individual molecular clouds to large scales up to kiloparsecs. A striking correlation is observed between the distribution of Rv and molecular clouds. Notably, we observe lower Rv values within the regions of nearby molecular clouds compared to their surrounding areas. Furthermore, we have investigated the relationships between Rv and various parameters, including dust temperature, dust emissivity spectral index, column density of atomic and molecular hydrogen, as well as their ratios and the gas-to-dust ratio. We find that these relationships vary with the level of extinction. These analyses provide new insights into the properties and evolution of dust grains in diverse interstellar environments and also hold significant importance for achieving accurate extinction corrections.