New 3-D gas density maps of NaI and CaII interstellar absorption within 300pc

TL;DR

This study provides high-resolution 3D maps of interstellar NaI and CaII gas within 300pc of the Sun, revealing the structure of local interstellar clouds and boundaries.

Contribution

It introduces a large catalog of new interstellar absorption measurements and constructs detailed 3D density maps of neutral and ionized gas near the Sun.

Findings

Identification of a neutral gas wall at ~80pc marking the Local Cavity boundary.

Different spatial distributions of NaI and CaII suggest varying ionization and density structures.

The maps improve understanding of the local interstellar medium's structure and boundaries.

Abstract

We present new high resolution (R>50,000) absorption measurements of the NaI doublet (5889 - 5895A) along 482 nearby sight-lines, in addition to 807 new measurements of the CaII K (3933A) absorption line. We have combined these new data with previously reported measurements to produce a catalog of absorptions towards a total of 1857 early-type stars located within 800pc of the Sun. Using these data we have determined the approximate 3-dimensional spatial distribution of neutral and partly ionized interstellar gasdensity within a distance-cube of 300pc from the Sun. All newly recorded spectra were analyzed by means of a multi-component line profile-fitting program, in most cases using simultaneous fits to the line doublets. Normalized absorption profiles were fitted by varying the velocity, doppler width and column density for all intervening interstellar clouds. The resulting total column densities were then used in conjunction with the Hipparcos distances of the target stars to construct inversion maps of the 3-D spatial density distribution of the NaI and CaII bearing gas. A plot of the equivalent width of NaI versus distance reveals a wall of neutral gas at ~80pc that can be associated with the boundary wall to the central rarefied Local Cavity region. In contrast, a similar plot for the equivalent width of CaII shows no sharply increasing absorption at 80pc, but instead we observe a slowly increasing value of CaII equivalent width with increasing sight-line distance sampled.