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.

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

References in corpus (29)

• Maps of Dust IR Emission for Use in Estimation of Reddening and CMBR Foregrounds
• A large stellar evolution database for population synthesis studies. I. Scaled solar models and isochrones
• Tracing Galaxy Formation with Stellar Halos I: Methods
• Minor mergers and the size evolution of elliptical galaxies
• The Two Phases of Galaxy Formation
• A large stellar evolution database for population synthesis studies. II. Stellar models and isochrones for an alpha-enhanced metal distribution
• Homogeneous Photometry for Star Clusters and Resolved Galaxies. II. Photometric Standard Stars
• Tip of the Red Giant Branch Distances. II. Zero-Point Calibration
• WFPC2 Observations of the Hubble Deep Field-South
• The Local Group and other neighboring galaxy groups
• The Distance to NGC 5128 (Centaurus A)
• The Halo Stars in NGC 5128. III: An Inner-Halo Field and the Metallicity Distribution
• The Metal-Poor Halo of the Andromeda Spiral Galaxy (M31)
• The Metallicity Distribution in the Halo Stars of NGC 5128: Implications for Galaxy Formation
• The Planetary Nebula System and Dynamics in the Outer Halo of NGC 5128
• Deep ACS Imaging of the Halo of NGC 5128: Reaching the Horizontal Branch
• A 2dF spectroscopic study of globular clusters in NGC 5128: Probing the formation history of the nearest giant Elliptical
• The Ages, Metallicities and Alpha Element Enhancements of Globular Clusters in the Elliptical NGC 5128: A Homogeneous Spectroscopic Study with Gemini/GMOS
• A Young Blue Tidal Stream in NGC 5128
• The Leo Elliptical NGC 3379: A Metal-Poor Halo Emerges
• The Globular Cluster System of NGC 5128 I. Survey and Catalogs
• The Kinematics of the Globular Cluster System of NGC 5128 with a New, Large Sample of Radial Velocity Measurements
• The Kinematics and Dynamics of the Globular Clusters and the Planetary Nebulae of NGC 5128
• How old are the stars in the halo of NGC 5128 (Centaurus A)?
• Tracing the outer halo in a giant elliptical to 25 Reff
• HST Photometry for the Halo Stars in the Leo Elliptical NGC 3377
• The Nature of the Halo Population of NGC 5128 Resolved with NICMOS on the Hubble Space Telescope
• The Outer Halo of the Nearest Giant Elliptical: A VLT/VIMOS Survey of the Resolved Stellar Populations in Centaurus A to 85 kpc
• Resolving the Stellar Population of the Standard Elliptical Galaxy NGC3379

Cited by in corpus (8)

• Dual Stellar Halos in the Standard Elliptical Galaxy M105 and Formation of Massive Early-Type Galaxies
• 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