Journal Article

Global properties of ‘ordinary’ early-type galaxies: photometry and spectroscopy of stars and globular clusters in NGC 4494

Caroline Foster, Lee R. Spitler, Aaron J. Romanowsky, Duncan A. Forbes, Vincenzo Pota, Kenji Bekki, Jay Strader, Robert N. Proctor, Jacob A. Arnold and Jean P. Brodie

in Monthly Notices of the Royal Astronomical Society

Published on behalf of The Royal Astronomical Society

Volume 415, issue 4, pages 3393-3416
Published in print August 2011 | ISSN: 0035-8711
Published online August 2011 | e-ISSN: 1365-2966 | DOI: http://dx.doi.org/10.1111/j.1365-2966.2011.18965.x
Global properties of ‘ordinary’ early-type galaxies: photometry and spectroscopy of stars and globular clusters in NGC 4494

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We present a comprehensive analysis of the spatial, kinematic and chemical properties of stars and globular clusters (GCs) in the ‘ordinary’ elliptical galaxy NGC 4494 using data from the Keck and Subaru telescopes. We derive galaxy surface brightness and colour profiles out to large galactocentric radii. We compare the latter to metallicities derived using the near-infrared Calcium Triplet. We obtain stellar kinematics out to ∼3.5 effective radii. The latter appear flattened or elongated beyond ∼1.8 effective radii in contrast to the relatively round photometric isophotes. In fact, NGC 4494 may be a flattened galaxy, possibly even an S0, seen at an inclination of ∼45°. We publish a catalogue of 431 GC candidates brighter than i0= 24 based on the photometry, of which 109 are confirmed spectroscopically and 54 have measured spectroscopic metallicities. We also report the discovery of three spectroscopically confirmed ultra-compact dwarfs around NGC 4494 with measured metallicities of −0.4 ≲[Fe/H]≲−0.3. Based on their properties, we conclude that they are simply bright GCs. The metal-poor GCs are found to be rotating with similar amplitude as the galaxy stars, while the metal-rich GCs show marginal rotation. We supplement our analysis with available literature data and results. Using model predictions of galaxy formation, and a suite of merger simulations, we find that many of the observational properties of NGC 4494 may be explained by formation in a relatively recent gas-rich major merger. Complete studies of individual galaxies incorporating a range of observational avenues and methods such as the one presented here will be an invaluable tool for constraining the fine details of galaxy formation models, especially at large galactocentric radii.

Keywords: galaxies: abundances; galaxies: haloes; galaxies: individual: NGC 4494; galaxies: kinematics and dynamics; galaxies: star clusters: general

Journal Article.  18443 words.  Illustrated.

Subjects: Astronomy and Astrophysics

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