On the Detectability and Measurement of Galactic Bars as a Function of Redshift

Abstract

The cosmic evolution of galactic bars offers key insights into the dynamical history of disk galaxies. However, studies of high-redshift bars are severely hampered by observational effects such as resolution degradation and surface brightness dimming. To quantify these biases and establish a robust methodology of bar detection and measurement for high-redshift galaxies, we develop an automated pipeline integrating isophotal ellipse fitting and Fourier decomposition. We benchmark its performance using a comprehensive set of mock observations generated by artificially redshifting high-quality images of local barred galaxies to match the background and resolution of HST ($z\approx 0.5-3$) and JWST ($z\approx 1-6$) observations. We find that applying standard bar detection criteria derived from local galaxies to high-redshift data results in a severe underestimation of the bar fraction, missing $>50$ of bars at $z>0.5$ in HST imaging and a similar fraction at $z>2$ in JWST imaging. Using adaptive, redshift-dependent criteria optimized via mock data achieves recovery rates above $60$ out to $z\approx 3$ for HST and $z\approx 6$ for JWST. The ellipse fitting method significantly outperforms Fourier decomposition in measurement reliability. While ellipse fitting systematically underestimates bar length by $\sim 4$--$36$ due to surface brightness dimming, this bias is consistent and correctable ($\sigma \approx 0.88$--$2.22$); in contrast, the Fourier method is prone to catastrophic failures ($\sigma \approx 2.40$--$6.14$) in the regime of low signal-to-noise ratio. We propose a standardized workflow that prioritizes mock-derived adaptive criteria and ellipse fitting, providing quantitative correction factors and empirical relations that enable future studies to recover intrinsic bar statistics from raw observations.

32 pages, 20 figures, 10 tables. Submitted to The Astrophysical Journal