Linear relation between HI circular velocity and stellar velocity dispersion in early-type galaxies, and slope of the density profiles

Paolo Serra*, Tom Oosterloo, Michele Cappellari, Milan den Heijer, Gyula I. G. Jozsa

*Corresponding author for this work

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Abstract

We report a tight linear relation between the HI circular velocity measured at 6 R-e and the stellar velocity dispersion measured within 1 R-e for a sample of 16 early-type galaxies with stellar mass between 10(10) and 10(11) M-circle dot. The key difference from previous studies is that we only use spatially resolved v(circ)(H I) measurements obtained at large radius for a sizeable sample of objects. We can therefore link a kinematical tracer of the gravitational potential in the dark-matter dominated outer regions of galaxies with one in the inner regions, where baryons control the distribution of mass. We find that v(cir)c(H I) = 1.33 sigma(e) with an observed scatter of just 12 per cent. This indicates a strong coupling between luminous and dark matter from the inner-to the outer regions of early-type galaxies, analogous to the situation in spirals and dwarf irregulars. The v(circ)(H I)-sigma(e) relation is shallower than those based on v(circ) measurements obtained from stellar kinematics and modelling at smaller radius, implying that v(circ) declines with radius - as in bulge-dominated spirals. Indeed, the value of v(circ)(H I) is typically 25 per cent lower than the maximum v(circ) derived at similar to 0.2 R-e from dynamical models. Under the assumption of power-law total density profiles. rho proportional to r(-gamma), our data imply an average logarithmic slope = 2.18 +/- 0.03 across the sample, with a scatter of 0.11 around this value. The average slope and scatter agree with recent results obtained from stellar kinematics alone for a different sample of early-type galaxies.
Original languageEnglish
Pages (from-to)1382-1389
Number of pages8
JournalMonthly Notices of the Royal Astronomical Society
Volume460
Issue number2
DOIs
Publication statusPublished - 1-Aug-2016

Keywords

  • galaxies: elliptical and lenticular, cD
  • galaxies: kinematics and dynamics
  • galaxies: structure
  • TO-LIGHT RATIO
  • SUPERMASSIVE BLACK-HOLES
  • TULLY-FISHER RELATION
  • DARK-MATTER HALOES
  • SURFACE BRIGHTNESS GALAXIES
  • ATLAS(3D) PROJECT
  • SPIRAL GALAXIES
  • ROTATION CURVES
  • MASS-DISTRIBUTION
  • NEUTRAL HYDROGEN

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