On the Analysis of DLA Kinematics

TL;DR

This paper critiques previous analyses of damped Lyman-alpha (DLA) kinematics, highlighting biases introduced by certain data treatment methods that may have compromised earlier results.

Contribution

It identifies specific biases in past DLA kinematic studies caused by improper data excision, emphasizing the need for unbiased analysis methods.

Findings

Previous analyses are biased against low and high NHI sightlines.

Biases exclude low velocity width DLA sightlines.

These biases may have affected the validity of earlier conclusions.

Abstract

We discuss two mistreatments of damped Lya (DLA) kinematic analysis that were first performed by Haehnelt, Steinmetz, & Rauch (1998; hereafter HSR98) and have recently been repeated by Hong et al. (2010; arXiv:1008.4242v1, arXiv:1008.4242v2; hereafter H10). Each mistreatment led to the improper excising of simulated absorption profiles. Specifically, their analyses are strictly biased against DLA sightlines that have low HI column density log NHI < 20.5, very high NHI values, and (for all NHI) sightlines with low velocity width Dv (<30 km/s for HSR98; <[20-30] km/s for H10). None of these biases exist in the observational analysis. We suspect these mistreatments compromise the results that followed. Hopefully this posting will prevent their repetition in the future.