The C iv linewidth distribution for quasars and its implications for broad-line region dynamics and virial mass estimation

We perform an extensive analysis of the C IV 1549 line in three large spectroscopic surveys of quasars. Differing approaches for fitting the C IV line can be found in the literature, and we compare the most common methods to highlight the relative systematics associated with each. We choose the line-fitting procedure that results in a symmetric profile for the C IV line and gives accurate fits to local emission features around the line, and use this approach to measure the width of the C IV line in spectra from the Sloan Digital Sky Survey (SDSS) and 2dF QSO Redshift (2QZ) and 2dF SDSS LRG And QSO (2SLAQ) surveys.