The distance to Complex M and the Intermediate Velocity Arch

The Intermediate Velocity Arch is an association of H I clouds lying within the broad limits I approximate to 110 degrees - 210 degrees, b approximate to 50 degrees - 80 degrees. We use high-resolution optical, and single-dish 21-cm, observations of 10 early-type halo star sightlines in this region to establish distance limits (0.4 less than or equal to z less than or equal to 3.5 kpc) for seven IVCs that are part of the Arch. We re-examine a previous determination of upper and lower distance limits on the IVC Complex M using the closely aligned halo stars ED +38 2182 and HD 93521. Our H I spectra show no evidence of emission from Complex M, leading us to conclude that, while an upper distance limit of z less than or equal to 3.5 kpc may be established, no useful lower distance determination can be made. Our new H I observations allow new limits to be established on the metallicity of Complex M, and show C, O and Si variations with respect to solar abundances in the range +/-0.3 dex.