Evidence for a Rotational Component in the Circumgalactic Medium of Nearby Galaxies*

Abstract

Abstract We present results of a study comparing the relative velocity of Lyα absorbers to the rotation velocity of nearby galaxy disks in the local universe (z ≤ 0.03). We have obtained rotation curves via long-slit spectroscopy of eight galaxies with the Southern African Large Telescope, and combine this data set with an additional 16 galaxies with data from the literature. Each galaxy appears within 3R vir of a QSO sightline with archival Cosmic Origin Spectrograph spectra. We study the velocity orientation of absorbers with respect to nearby galaxy’s rotation, and compare with results from both the Steidel et al. monolithic halo model and a new cylindrical Navarro–Frenk–White galaxy halo model to interpret these data in the context of probing 3D galaxy halos via 1D QSO absorption-line spectroscopy. Relative to these models, we find that up to 59% ± 5% of Lyα absorbers have velocities consistent with corotation. We find the Lyα corotation fraction to decrease with galaxy luminosity (L*) and impact parameter in a model-independent fashion. We report that both anti-rotating absorbers and those found near luminous galaxies (L ≳ 0.5L*) mostly have low Doppler b-parameters (b ≲ 50 km s−1). Absorbers consistent with corotation show a wide range of Doppler b-parameters. Finally, we find a strong anticorrelation between corotation fraction and galaxy inclination, which is at odds with recent metal-line kinematic studies and suggests the kinematic and geometric distribution of the circumgalactic medium is complex and multiphase.