Red giants in the outer halo of the elliptical galaxy NGC 5128 / Centaurus A

Abstract

We used VIMOS on VLT to perform $V$ and $I$ band imaging of the outermost halo of NGC 5128 / Centaurus A ($(m-M{)}_0=27.91\pm 0.08$), 65 kpc from the galaxy's center and along the major axis. The stellar population has been resolved to $I_0\approx 27$ with a $50\%$ completeness limit of $I_0=24.7$, well below the tip of the red-giant branch (TRGB), which is seen at $I_0\approx 23.9$. The surface density of NGC 5128 halo stars in our fields was sufficiently low that dim, unresolved background galaxies were a major contaminant in the source counts. We isolated a clean sample of red-giant-branch (RGB) stars extending to $\approx 0.8$ mag below the TRGB through conservative magnitude and color cuts, to remove the (predominantly blue) unresolved background galaxies. We derived stellar metallicities from colors of the stars via isochrones and measured the density falloff of the halo as a function of metallicity by combining our observations with HST imaging taken of NGC 5128 halo fields closer to the galaxy center. We found both metal-rich and metal-poor stellar populations and found that the falloff of the two follows the same de Vaucouleurs' law profiles from $\approx 8$ kpc out to $\approx$ 70 kpc. The metallicity distribution function (MDF) and the density falloff agree with the results of two recent studies of similar outermost halo fields in NGC 5128. We found no evidence of a "transition" in the radial profile of the halo, in which the metal-rich halo density would drop rapidly, leaving the underlying metal-poor halo to dominate by default out to greater radial extent, as has been seen in the outer halo of two other large galaxies. If NGC 5128 has such a transition, it must lie at larger galactocentric distances.

Accepted for publication in A&A. 11 pages, including 14 figures and 1 table

References in corpus (4)

• The Metal-Poor Halo of the Andromeda Spiral Galaxy (M31)
• A 2dF spectroscopic study of globular clusters in NGC 5128: Probing the formation history of the nearest giant Elliptical
• The Kinematics and Dynamics of the Globular Clusters and the Planetary Nebulae of NGC 5128
• Tracing the outer halo in a giant elliptical to 25 Reff

Cited by in corpus (7)

• A Recent Major Merger Tale for the Closest Giant Elliptical Galaxy Centaurus A
• Astrophysical Distance Scale II. Application of the JAGB Method: A Nearby Galaxy Sample
• The Strikingly Metal-Rich Halo of the Sombrero Galaxy
• The outermost stellar halo of NGC 5128 (Centaurus A): Radial structure
• A too-many dwarf galaxy satellites problem in the M83 group
• Individual element sensitivity for stellar evolutionary isochrones
• The Metallicity Distribution Function in Outer Halo Fields of Simulated Elliptical Galaxies Compared to Observations of NGC 5128