A Catalog of High-Velocity CIV Mini-BALs in the VLT-UVES and Keck-HIRES Archives

TL;DR

This paper catalogs high-velocity CIV mini-BALs in quasar spectra, revealing their properties, ionization states, and small-scale structures, and discusses implications for quasar outflow models.

Contribution

It provides the first extensive catalog of high-velocity CIV mini-BALs, analyzing their physical characteristics and suggesting a clumpy, inhomogeneous structure of quasar outflows.

Findings

105 mini-BALs identified in 44 quasars

Mini-BALs are highly ionized with small covering fractions

Evidence of inhomogeneous absorbers with small-scale structures

Abstract

We present a catalog of high-velocity CIV $\lambda$ 1548,1551 mini-Broad Absorption Lines (mini-BALs) in the archives of the VLT-UVES and Keck-HIRES spectrographs. We identify high-velocity CIV mini-BALs based on smooth rounded BAL-like profiles with velocity blueshifts $<$ $-$4000 km/s and widths in the range 70 $\lesssim$ FWHM(1548) $\lesssim$ 2000 km/s (for $\lambda$1548 alone). We find 105 mini-BALs in 44 quasars from a total sample of 638 quasars. The fraction of quasars with at least one mini-BAL meeting our criteria is roughly $\sim9$% after correcting for incomplete velocity coverage. However, the numbers of systems rise sharply at lower velocities and narrower FWHMs, suggesting that many outflow lines are missed by our study. All of the systems are highly ionized based on the strong presence of NV and OVI and/or the absence of SiII and CII when within the wavelength coverage. Two of the mini-BAL systems in our catalog, plus three others at smaller velocity shifts, have PV $\lambda$1118,1128 absorption indicating highly saturated CIV absorption and total hydrogen column densities $\gtrsim 10^{22}$ cm$^{-3}$. Most of the mini-BALs are confirmed to have optical depths $\gtrsim$1 with partial covering of the quasar continuum source. The covering fractions are as small as 0.06 in CIV and 0.03 in SiIV , corresponding to outflow absorbing structures $<0.002$ pc across. When multiple lines are measured, the lines of less abundant ions tend to have narrower profiles and smaller covering fractions indicative of inhomogeneous absorbers where higher column densities occur in smaller clumps. This picture might extend to BAL outflows if the broader and generally deeper BALs form in either the largest clumps or collections of many mini-BAL-like clumps that blend together in observed quasar spectra.