Mon. Not. R. Astron. Soc., 452, 99-114 (2015/September-1)
VIMOS mosaic integral-field spectroscopy of the bulge and disc of the early-type galaxy NGC 4697.
SPINIELLO C., NAPOLITANO N.R., COCCATO L., POTA V., ROMANOWSKY A.J., TORTORA C., COVONE G. and CAPACCIOLI M.
Abstract (from CDS):
We present an integral-field study of the internal structure, kinematics and stellar population of the almost edge-on, intermediate-luminosity (L*) elliptical galaxy NGC 4697. We build extended two-dimensional (2D) maps of the stellar kinematics and line strengths of the galaxy up to ∼ 0.7 effective radii (Reff) using a mosaic of eight VIMOS (VIsible Multi-Objects Spectrograph, on the Very Large Telescope) integral-field unit pointings. We find clear evidence for a rotation-supported structure along the major axis from the 2D kinematical maps, confirming the previous classification of this system as a `fast rotator'. We study the correlations between the third and fourth Gauss-Hermite moments of the line-of-sight velocity distribution (LOSVD) h3 and h4 with the rotation parameter (V/σ), and compare our findings to hydrodynamical simulations. We find remarkable similarities to predictions from gas-rich mergers. Based on photometry, we perform a bulge/disc decomposition and study the stellar population properties of the two components. The bulge and the disc show different stellar populations, with the stars in the bulge being older (age_bulge=13.5^+1.4_-1.4 Gyr, age_disc=10.5^+1.6_-2.0Gyr) and more metal poor ([M/H]_bulge = -0.17^+0.12_-0.1, [M/H]_disc = -0.03^+0.02_-0.1). The evidence of a later-formed, more metal-rich disc embedded in an older, more metal poor bulge, together with the LOSVD structure, supports a mass assembly scenario dominated by gas-rich minor mergers and possibly with a late gas-rich major merger that left a previously rapidly rotating system unchanged. The bulge and the disc do not show signs of different stellar initial mass function (IMF) slopes, and both match well with a Milky Way-like IMF.
© 2015 The Authors Published by Oxford University Press on behalf of the Royal Astronomical Society (2015)
galaxies: elliptical and lenticular, cD - galaxies: evolution - galaxies: formation
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