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Tracing the stellar halo of an early type galaxy out to 25 effective radii

Published online by Cambridge University Press:  09 May 2016

Marina Rejkuba
Marina Rejkuba*
Affiliation:
European Southern Observatory, Karl-Schwarzschild-Strasse 2, 85748 Garching bei München, Germany email: mrejkuba@eso.org
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Abstract

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We have used ACS and WFC3 cameras on board HST to resolve stars in the halo of NGC 5128 out to 140 kpc (25 effective radii, Reff) along the major axis and 70 kpc (13 Reff) along the minor axis. This dataset provides an unprecedented radial coverage of stellar halo properties in any galaxy. Color-magnitude diagrams clearly reveal the presence of the red giant branch stars belonging to the halo of NGC 5128 even in the most distant fields. The V-I colors of the red giants enable us to measure the metallicity distribution in each field and so map the metallicity gradient over the sampled area. The stellar metallicity follows a shallow gradient and even out at 140 kpc (25 Reff) its median value does not go below [M/H]~−1 dex. We observe significant field-to-field metallicity and stellar density variations. The star counts are higher along the major axis when compared to minor axis field located 90 kpc from the galaxy centre, indicating flattening in the outer halo. These observational results provide new important constraints for the assembly history of the halo and the formation of this gE galaxy.

Keywords

galaxies: elliptical and lenticulargalaxies: halosgalaxies: individual (NGC 5128)
Type
Contributed Papers
Information
Proceedings of the International Astronomical Union , Volume 11 , Issue S317: The General Assembly of Galaxy Halos: Structure, Origin and Evolution , August 2015 , pp. 9 - 14
Copyright
Copyright © International Astronomical Union 2016 

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