The H I Tully-Fisher relation of early-type galaxies

¹ Argelander Institut für Astronomie (AIfA), University of Bonn, Auf dem Hügel 71, 53121 Bonn, Germany
² Max-Planck Institut für Radioastronomie (MPIfR), Auf dem Hügel 69, 53121 Bonn, Germany
³ ASTRON, the Netherlands Institute for Radio Astronomy, Postbus 2, 7990 AA Dwingeloo, The Netherlands
e-mail: oosterloo@astron.nl
⁴ Kapteyn Astronomical Institute, University of Groningen, Postbus 800, 9700 AV Groningen, The Netherlands
⁵ CSIRO Astronomy and Space Science, Australia Telescope National Facility, PO Box 76, Epping, NSW 1710, Australia
⁶ SKA South Africa Radio Astronomy Research Group, 3rd Floor, The Park Park Road Pinelands, 7405, South Africa
⁷ Rhodes University, Department of Physics and Electronics, Rhodes Centre for Radio Astronomy, Techniques & Technologies, PO Box 94, Grahamstown 6140, South Africa
⁸ Sub-Department of Astrophysics, Department of Physics, University of Oxford, Denys Wilkinson Building, Keble Road, Oxford OX1 3RH, UK
⁹ Centre for Astrophysics Research, University of Hertfordshire, Hatfield, Herts AL1 9AB, UK
¹⁰ Laboratoire AIM Paris-Saclay, CEA/IRFU/SAp – CNRS – Université Paris Diderot, 91191 Gif-sur-Yvette Cedex, France
¹¹ European Southern Observatory, Karl-Schwarzschild-Straße 2, 85738 Garching, Germany
¹² Leibniz-Institut für Astrophysik Potsdam (AIP), An der Sternwarte 16, 14482 Potsdam, Germany
¹³ Department of Physics and Astronomy, Macquarie University, Sydney, NSW 2109, Australia
¹⁴ Australian Gemini Office, Australian Astronomical Observatory, PO Box 915, Sydney, NSW 1670, Australia
¹⁵ Max-Planck-Institut für Astrophysik, Karl-Schwarzschild-Straße 1, 85741 Garching, Germany
¹⁶ School of Physics and Astronomy, University of St Andrews, North Haugh, St Andrews KY16 9SS, UK
¹⁷ Sterrewacht Leiden, Leiden University, Postbus 9513, 2300 RA Leiden, The Netherlands

Received: 3 July 2015
Accepted: 14 July 2015

Abstract

We study the H iK-band Tully-Fisher relation and the baryonic Tully-Fisher relation for a sample of 16 early-type galaxies, taken from the ATLAS^3D sample, which all have very regular H i disks extending well beyond the optical body (≳ 5 R_eff). We use the kinematics of these disks to estimate the circular velocity at large radii for these galaxies. We find that the Tully-Fisher relation for our early-type galaxies is offset by about 0.5-0.7 mag from the relation for spiral galaxies, in the sense that early-type galaxies are dimmer for a given circular velocity. The residuals with respect to the spiral Tully-Fisher relation correlate with estimates of the stellar mass-to-light ratio, suggesting that the offset between the relations is mainly driven by differences in stellar populations. We also observe a small offset between our Tully-Fisher relation with the relation derived for the ATLAS^3D sample based on CO data representing the galaxies’ inner regions (≲1 R_eff). This indicates that the circular velocities at large radii are systematically 10% lower than those near 0.5−1 R_eff, in line with recent determinations of the shape of the mass profile of early-type galaxies. The baryonic Tully-Fisher relation of our sample is distinctly tighter than the standard one, in particular when using mass-to-light ratios based on dynamical models of the stellar kinematics. We find that the early-type galaxies fall on the spiral baryonic Tully-Fisher relation if one assumes M/L_K = 0.54 M_⊙/L_⊙ for the stellar populations of the spirals, a value similar to that found by recent studies of the dynamics of spiral galaxies. Such a mass-to-light ratio for spiral galaxies would imply that their disks are 60-70% of maximal. Our analysis increases the range of galaxy morphologies for which the baryonic Tully-Fisher relations holds, strengthening previous claims that it is a more fundamental scaling relation than the classical Tully-Fisher relation.