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Testing galaxy formation models with the GHOSTS survey: The stellar halo of M81

Published online by Cambridge University Press:  05 March 2015

A. Monachesi ,
E. Bell ,
D. Radburn-Smith ,
M. Vlajić ,
R. de Jong ,
J. Bailin ,
J. Dalcanton ,
B. Holwerda  and
D. Streich
A. Monachesi
Affiliation:
Department of Astronomy, University of Michigan, 830 Dennison Bldg., 500 Church St., Ann Arbor, MI 48109, USA
E. Bell
Affiliation:
Department of Astronomy, University of Michigan, 830 Dennison Bldg., 500 Church St., Ann Arbor, MI 48109, USA
D. Radburn-Smith
Affiliation:
Department of Astronomy, University of Washington, Seattle, WA 98195, USA
M. Vlajić
Affiliation:
Leibniz-Institut für Astrophysik Potsdam, D-14482 Potsdam, Germany
R. de Jong
Affiliation:
Leibniz-Institut für Astrophysik Potsdam, D-14482 Potsdam, Germany
J. Bailin
Affiliation:
Department of Astronomy, University of Michigan, 830 Dennison Bldg., 500 Church St., Ann Arbor, MI 48109, USA
J. Dalcanton
Affiliation:
Department of Astronomy, University of Washington, Seattle, WA 98195, USA
B. Holwerda
Affiliation:
ESTEC, Keplerlaan 1, 2200 AG Noordwijk, The Netherlands. email: antonela@umich.edu
D. Streich
Affiliation:
Leibniz-Institut für Astrophysik Potsdam, D-14482 Potsdam, Germany
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Abstract

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The GHOSTS survey is the largest study to date of the resolved stellar populations in the outskirts of disk galaxies (Radburn-Smith et al.2011). The sample currently consists of 16 nearby disk galaxies, whose outer disks and halos are imaged with the Hubble Space Telescope (HST). I will present new results obtained from the study of 19 GHOSTS fields in M81's outermost part. The observed fields probe the stellar halo of M81 out to projected distances of ~50 kpc, an unprecedented distance for halo studies outside the Local Group. The 50% completeness levels of the color magnitude diagrams are typically at 2.5 mag below the tip of the red giant branch. When considering only fields located at galactocentric radius R > 15 kpc, we detect no color gradient in the stellar halo of M81. We compare these results with model predictions for the colors of stellar halos formed purely via accretion of satellite galaxies (Bullock & Johnston 2005). When we analyze the cosmologically motivated models in the same way as the HST data, we find that they predict no color gradient for the stellar halos, in good agreement with the observations (see Fig. 1).

Keywords

galaxies: halosgalaxies: individual (M81)galaxies: spiralgalaxies: formation
Type
Contributed Papers
Information
Proceedings of the International Astronomical Union , Volume 10 , Highlights H16: Highlights of Astronomy , August 2012 , pp. 379
Copyright
Copyright © International Astronomical Union 2015 

References

Bullock, J. S. & Johnston, K. V., 2005, ApJ 635, 931CrossRefGoogle Scholar
Radburn-Smith, D. J., et al. 2011, ApJS 195, 18Google Scholar