The SAMI Galaxy Survey: The Low-Redshift Stellar Mass Tully-Fisher Relation

TL;DR

This study uses 2D spatially resolved Halpha velocity maps from the SAMI Galaxy Survey to analyze the low-redshift stellar mass Tully-Fisher relation, revealing how kinematic asymmetry affects scatter and emphasizing the importance of integral field spectroscopy.

Contribution

It introduces an adaptation of kinemetry to quantify kinematic asymmetry and demonstrates its correlation with TFR scatter, highlighting the advantages of 2D kinematic data over slit spectroscopy.

Findings

Kinematic asymmetry correlates with increased TFR scatter, especially at low stellar masses.

Aligning slits with photometric rather than kinematic axes increases scatter.

Integral field spectroscopy improves rotation velocity estimates by reducing slit misalignment effects.

Abstract

We investigate the Tully-Fisher Relation (TFR) for a morphologically and kine- matically diverse sample of galaxies from the SAMI Galaxy Survey using 2 dimensional spatially resolved Halpha velocity maps and find a well defined relation across the stellar mass range of 8.0 < log(M*) < 11.5. We use an adaptation of kinemetry to parametrise the kinematic Halpha asymmetry of all galaxies in the sample, and find a correlation between scatter (i.e. residuals off the TFR) and asymmetry. This effect is pronounced at low stellar mass, corresponding to the inverse relationship between stellar mass and kinematic asymmetry found in previous work. For galaxies with log(M*) < 9.5, 25 +/- 3% are scattered below the root mean square (RMS) of the TFR, whereas for galaxies with log(M*) > 9.5 the fraction is 10 +/- 1% We use 'simulated slits' to directly compare our results with those from long slit spectroscopy and find that aligning slits with the photometric, rather than the kinematic, position angle, increases global scatter below the TFR. Further, kinematic asymmetry is correlated with misalignment between the photometric and kinematic position angles. This work demonstrates the value of 2D spatially resolved kinematics for accurate TFR studies; integral field spectroscopy reduces the underestimation of rotation velocity that can occur from slit positioning off the kinematic axis.