Systematic uncertainties on DESI Tully-Fisher distances constrained with integral field spectroscopy
Abstract
The Tully-Fisher (TF) relation is an empirical tool for estimating distances to spiral galaxies. Dark Energy Spectroscopic Instrument (DESI) Peculiar Velocity (PV) Survey uses photometric position angles (PAs) to place its fibers along the semi-major axis of the galaxy and infer maximum rotational velocities for ≈ 53,000 spiral galaxies. Systematic errors may arise if the photometric PA differs from the kinematic PA measured from velocity fields. tractor We aim to quantify the systematic uncertainty in DESI-TF distance estimates introduced by the use of photometric PAs and assess the impact of photometric--kinematic PA misalignment on derived distances. We analyzed a curated sample of 215 nearby galaxies from the PISCO and AMUSING surveys. For consistency with the DESI-PV survey, we estimated the maximum rotational velocity at 0.4,R_26. We estimated the TF distance using three different sets of parameters. We obtained kinematic parameters using PaFit from . For the global photometric parameters, we relied on data available from the Siena Galaxy Atlas SGA-2020 drawn from photometry and we also used photometry as an additional photometric approach. Cappellari Software tractor HostPhot Approximately 28% of our sample exhibit a photometric-kinematic PA misalignment $>10^̧irc$. The bias in distance is +1.98,Mpc with a skewed residual distribution dominated by outliers. The overall standard deviation (σ) for the estimated distance is 19.35, The misaligned galaxies show twice the dispersion compared to aligned galaxies. The mean percentage error (MPE) is 2.8 % ± 1.96 (SE) throughout the sample. Kinematic constraints from integral field spectroscopy (IFS) reveal a low positive median bias approx1.98 , but high galaxy-to-galaxy scatter in DESI-TF distances, particularly for misaligned galaxies. Because DESI-TF targets lack kinematic PA measurements, we recommend a global fractional uncertainty of ≈ 3.5% for DESI-TF distances. When kinematic information is available, aligned galaxies with photometric-kinematic PA offsets $<10^̧irc$ are consistent with a ≈ 1% uncertainty, while strongly misaligned or kinematically incomplete systems warrant an upper threshold of ≈ 10%. Mpc