Proceedings of the International Astronomical Union

Contributed Papers

Detection of a stellar halo in NGC 4244

A. Setha1, R. de Jonga2, J. Dalcantona3 and the GHOSTS team

a1 Harvard-Smithsonian Center for Astrophysics, 60 Garden St., Cambridge, MA 02139 email:

a2 Space Telescope Science Institute

a3 University of Washington


We present the preliminary detection of a stellar halo in the nearby, edge-on galaxy, NGC 4244. Using data from the Hubble Space Telescope's Advanced Camera for Surveys (HST/ACS), we have examined number counts of red giant branch (RGB) stars along the minor axis of the galaxy out to 10 kpc, with a limiting surface brightness of μR ∼ 31 mag/arcsec2. At distances more than 2.5 kpc above the disk, a second stellar component is clearly visible. This component is well fit by either an exponential or a power law. The best-fit exponential scale height is similar to the scale length of the galaxy disk, suggesting that we are indeed detecting a halo component. Furthermore, the color of the RGB stars above 2.5 kpc are significantly bluer than those in the disk, suggesting a more metal-poor population. Outside the local group, this finding represents one of the first detections of a resolved stellar halo in a spiral galaxy.