TY - JOUR
T1 - Stellar velocity profiles and line strengths out to four effective radii in the early-type galaxies NGC 3379 and 821
AU - Weijmans, Anne Marie
AU - Cappellari, Michele
AU - Bacon, Roland
AU - De Zeeuw, P. T.
AU - Emsellem, Eric
AU - Falcón-Barroso, Jesús
AU - Kuntschner, Harald
AU - McDermid, Richard M.
AU - Van Den Bosch, Remco C.E.
AU - Van De Ven, Glenn
PY - 2009/9
Y1 - 2009/9
N2 - 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 (Re) 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 ∼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 Re remain constant out to at least 4 Re, 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 Re. 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-Vesc relation: its slope is steeper when a dark matter halo is added to the model.
AB - 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 (Re) 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 ∼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 Re remain constant out to at least 4 Re, 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 Re. 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-Vesc relation: its slope is steeper when a dark matter halo is added to the model.
UR - http://www.scopus.com/inward/record.url?scp=69549135165&partnerID=8YFLogxK
U2 - 10.1111/j.1365-2966.2009.15134.x
DO - 10.1111/j.1365-2966.2009.15134.x
M3 - Article
AN - SCOPUS:69549135165
SN - 0035-8711
VL - 398
SP - 561
EP - 574
JO - Monthly Notices of the Royal Astronomical Society
JF - Monthly Notices of the Royal Astronomical Society
IS - 2
ER -