An Accurate Distance to High-Velocity Cloud Complex C

TL;DR

This paper precisely measures the distance to the high-velocity cloud Complex C, revealing its mass, size, density, and potential contribution to galactic gas inflow, using high-quality spectral data of stars.

Contribution

It provides the first accurate distance measurement to Complex C using stellar absorption lines, refining its physical properties and galactic impact.

Findings

Distance to Complex C is 10 +/- 2.5 kpc.

Complex C's HI mass is approximately 4.9 million solar masses.

Estimated mass inflow contribution is up to 0.14 solar masses per year.

Abstract

We report an accurate distance of d = 10+/-2.5kpc to the high-velocity cloud Complex C. Using high signal-to-noise Keck/HIRES spectra of two horizontal-branch stars, we have detected CaII K absorption lines from the cloud. Significant non-detections toward a further 3 stars yield robust lower distance limits. The resulting HI mass of Complex C is 4.9^{+2.8}_{-2.2} x 10^6 Msun; a total mass of 8.2^{+4.6}_{-2.6} x 10^6 Msun is implied, after corrections for helium and ionization. At 10kpc, Complex C has physical dimensions 3x15 kpc, and if it is as thick as it is wide, then the average density is log<n> ~ -2.5. We estimate the contribution of Complex C to the mass influx may be as high as ~0.14 Msun/yr.