Stellar velocity profiles and line strengths out to four effective radii in the early-type galaxies NGC 3379 and 821

Anne-Marie Weijmans*, Michele Cappellari, Roland Bacon, P. T. de Zeeuw, Eric Emsellem, Jesus Falcon-Barroso, Harald Kuntschner, Richard M. McDermid, Remco C. E. van den Bosch, Glenn van de Ven

*Corresponding author for this work

Research output: Contribution to journalArticlepeer-review

107 Citations (Scopus)

Abstract

We use the integral-field spectrograph SAURON to measure the stellar line-of-sight velocity distribution and absorption line strengths out to four effective radii (R(e)) in the early-type galaxies NGC 3379 and 821. With our newly developed observing technique, we can now probe these faint regions in galaxies that were previously not accessible with traditional long-slit spectroscopy. We make optimal use of the large field-of-view and high throughput of the spectrograph: by adding the signal of all similar to 1400 lenslets into one spectrum, we obtain sufficient signal-to-noise in a few hours of observing time to reliably measure the absorption line kinematics and line strengths out to large radius.

We find that the line strength gradients previously observed within 1 R(e) remain constant out to at least 4 R(e), which puts constraints on the merger histories of these galaxies. The stellar halo populations are old and metal poor. By constructing orbit-based Schwarzschild dynamical models, we find that dark matter is necessary to explain the observed kinematics in NGC 3379 and 821, with 30-50 per cent of the total matter being dark within 4 R(e). The radial anisotropy in our best-fitting halo models is less than in our models without halo, due to differences in orbital structure. The halo also has an effect on the Mg b-V(esc) relation: its slope is steeper when a dark matter halo is added to the model.

Original languageEnglish
Pages (from-to)561-574
Number of pages14
JournalMonthly Notices of the Royal Astronomical Society
Volume398
Issue number2
DOIs
Publication statusPublished - 11 Sept 2009

Keywords

  • EXTRA LIGHT
  • dark matter
  • ORBITAL STRUCTURE
  • galaxies: elliptical and lenticular
  • galaxies: individual: NGC 821
  • DARK-MATTER HALOS
  • galaxies: kinematics and dynamics
  • LICK INDEXES
  • MULTI-GAUSSIAN EXPANSION
  • LENTICULAR GALAXIES
  • SAURON PROJECT
  • ELLIPTIC GALAXIES
  • LENS ACS SURVEY
  • cD
  • POPULATION SYNTHESIS
  • galaxies: individual: NGC 3379
  • galaxies: haloes

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