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Title

Evidence for two phases of galaxy formation from radial trends in the globular cluster system of NGC 1407

Author(s)

Forbes, Duncan A.;  Spitler, Lee R.;  Strader, Jay;  Romanowsky, Aaron J.;  Brodie, Jean P.;  Foste, Caroline

Abstract

Here we present the colours of individual globular clusters (GCs) around the massive elliptical galaxy NGC 1407 out to a projected galactocentric radius of 140 kpc or 17 galaxy effective radii (Re). Such data are a proxy for the halo metallicity. We find steep, and similar, metallicity gradients of ∼ –0.4 dex per dex for both the blue (metal-poor) and red (metal-rich) GC subpopulations within 5–8.5 Re (40–70 kpc). At larger radii the mean GC colours (metallicity) are constant. A similar behaviour is seen in a wide-field study of M87’s GC system, and in our own Galaxy. We interpret these radial metallicity trends to indicate an inner region formed by early in-situ dissipative processes and an outer halo formed by ongoing accretion of low mass galaxies and their GCs. These results provide observational support for the model of galaxy formation whereby massive galaxies form inside-out in two phases. We have also searched the literature for other massive early-type galaxies with reported GC metallicity gradients in their inner regions. No obvious correlation with galaxy mass or environment is found but the sample is currently small.

Publication type

Journal article

Research centre

Swinburne University of Technology. Faculty of Information and Communication Technologies. Centre for Astrophysics and Supercomputing

Source

Monthly Notices of the Royal Astronomical Society, Vol. 413, no. 4 (Jun 2011), pp. 2943-2949

Publication year

2011

FOR Code(s)

0201 Astronomical and Space Sciences

Keyword(s)

Galaxies;  Galaxy formation;  Globular clusters;  NGC 1407;  Star clusters

Publisher

Wiley-Blackwell Publishing

ISSN

0035-8711

Publisher URL

http://dx.doi.org/10.1111/j.1365-2966.2011.18373.x

Copyright

Copyright © 2011 The Authors. Journal compilation copyright © 2011 Royal Astronomical Society. The accepted manuscript is reproduced in accordance with the copyright policy of the publisher. The definitive publication is available at www.interscience.wiley.com.

Full text

Peer reviewed