GHOSTS: the Nature of Galactic Stellar Halos from Resolved Stellar Populations

• Applicant: Dr. Roelof S. de Jong
• Subject Area: Astrophysics and Astronomy
• Term: from 2009 to 2012
• Project identifier: Deutsche Forschungsgemeinschaft (DFG) - Project number 126360709

• Final Report Year: 2012

Final Report Abstract

In the context of hierarchical galaxy formation, galaxy outskirts are built up through numerous early accretion events; direct fossil record of assembly history of a galaxy is preserved in the ages, mettalicities, kinematics, and spatial distributions of its halo stars. Observations of these extremely faint galaxy outskirts provide a tool for understanding the formation and evolution of disk galaxies. GHOSTS survey (Galaxy Halos, Outer disks, Star clusters, Thick disks, and Substructure) is the largest study of resolved stellar populations in the outskirts of disk galaxies to date, providing colour magnitude diagrams down to 2.5 magnitudes below the tip of the red giant branch. Its depth, high spatial resolution and a careful treatment of contaminants, primarily unresolved distant galaxies, has allowed us to trace stellar haloes down to the effective surface brightness levels of ∼ 30 (V) mag arcsec−2 and distances of ∼ 50 kpc. This is the first time stellar populations outside the Local Group have been charted out to these large galactocentric distances. With GHOSTS data we find that stellar populations in thick disks have increasing scale heights with age. Scale height is also increasing with radius, hinting at flaring disks, which could be related to radial migration of stars. Beyond the break in galaxy disks scale lengths are also increasing with age, again a signature of stellar radial migration. GHOSTS has measured halo properties out to unprecedented distances, reveal flattened haloes with the slope in agreement with the results of numerical simulations, but more compact than predicted by the simulations.

Publications

• (2010). Outer Spiral Disks as Clues to Galaxy Formation and Evolution. Publications of the Astronomical Society of Australia, 27(3), 252-255
  Vlajić, M.
  
• (2011). The GHOSTS survey. I. Hubble space telescope advanced camera for surveys data. The Astrophysical Journal Supplement Series, 195(2), 18
  Radburn-Smith, D. J., de Jong, R. S., Seth, A. C., Bailin, J., Bell, E. F., Brown, T. M., Bullock, J. S., Courteau, S., Dalcanton, J. J., Ferguson, H. C., Goudfrooij, P., Holfeltz, S., Holwerda, B. W., Purcell, C., Sick, J., Streich, D., Vlajić, M. & Zucker, D. B.
  
• (2011). The structure and metallicity gradient in the extreme outer disk of NGC 7793. The Astrophysical Journal, 732(1), 7
  Vlajić, M. , Bland-Hawthorn, J., Freeman, K. C.