Modeling the Stellar Populations in the Canis Major Over-Density: the Relation Between the Old and Young Populations

Abstract

We analyze the stellar populations of the Canis Major stellar over-density, using quantitative color-magnitude diagram (CMD) fitting techniques. The analysis is based on photometry obtained with the Wide Field Imager at the 2.2m telescope at La Silla for several fields near the probable center of the over-density. A modified version of the MATCH software package was applied to fit the observed CMDs, enabling us to constrain the properties of the old and young stellar populations that appear to be present. For the old population we find [Fe/H]~-1.0, a distance of ~7.5 kpc and a line-of-sight depth sigma_los of 1.5+-0.2 kpc and a characteristic age range of 3-6 Gyrs. However, the spread in ages and the possible presence of a ~10 Gyr old population cannot be constrained. The young main-sequence is found to have an age spread; ages must range from a few hundred Myr to 2 Gyr. Because of the degeneracy between distance and metallicity in CMDs the estimates of these parameters are strongly correlated and two scenarios are consistent with the data: if the young stars have a similar metallicity to the old stars, they are equidistant and therefore co-spatial with the old stars; if the young stars have close to solar metallicity they are more distant (~9 kpc). The relatively low metallicity of the old main-sequence favors the interpretation that CMa is the remnant of an accreted dwarf galaxy. Spectroscopic metallicity measurements are needed to determine whether the young main-sequence is co-spatial.

15 pages, 11 figures, (2 additional figures + some textual changes wrt previous version), accepted for publication in Astrophysical Journal

References in corpus (29)

• Maps of Dust IR Emission for Use in Estimation of Reddening and CMBR Foregrounds
• Theoretical isochrones in several photometric systems I. Johnson-Cousins-Glass, HST/WFPC2, HST/NICMOS, Washington, and ESO Imaging Survey filter sets
• The Ghost of Sagittarius and Lumps in the Halo of the Milky Way
• Numerical Methods of Star Formation History Measurement and Applications to Seven Dwarf Spheroidals
• A Low Latitude Halo Stream around the Milky Way
• A dwarf galaxy remnant in Canis Major: the fossil of an in-plane accretion onto the Milky Way
• Outer structure of the Galactic warp and flare: explaining the Canis Major over-density
• A Method for Determining the Star Formation History of a Mixed Stellar Population
• A comprehensive model for the Monoceros tidal stream
• Observations and Implications of the Star Formation History of the LMC
• Non-parametric star formation histories for 5 dwarf spheroidal galaxies of the local group
• A Search for Stars of Very Low Metal Abundance. V. Photoelectric UBV Photometry of Metal-Weak Candidates from the Northern HK Survey
• Elemental Abundance Ratios in Stars of the Outer Galactic Disk. III. Cepheids
• Star Formation Histories from HST Color-Magnitude Diagrams of Six Fields of the LMC
• Spiral structure of the Third Galactic Quadrant and the solution to the Canis Major debate
• Probing the Canis Major stellar over-density as due to the Galactic warp
• A possible age-metallicity relation in the Galactic thick disk?
• The Stellar Content and the Star Formation History of the Local Group Dwarf Galaxy LGS 3
• Detection of the Canis Major galaxy at (l;b)=(244;-8) and in the background of Galactic open clusters
• The Closest View of a Dwarf Galaxy: New Evidence on the Nature of the Canis Major over-density
• The core of the Canis Major galaxy as traced by Red Clump stars
• Detection of a young stellar population in the background of open clusters in the Third Galactic Quadrant
• GaBoDS: The Garching-Bonn Deep Survey -- I. Anatomy of galaxy clusters in the background of NGC 300
• Why the Canis Major overdensity is not due to the Warp: analysis of its radial profile and velocities
• A radial velocity survey of low Galactic latitude structures: I. Kinematics of the Canis Major dwarf galaxy
• Absolute Proper Motion of the Canis Major Dwarf Galaxy Candidate
• The Dog on the Ship: The "Canis Major Dwarf Galaxy" as an Outlying Part of the Argo Star System
• A Canis Major over-density imaging survey. I. Stellar content and star-count maps : A distinctly elongated body of main sequence stars
• Photometry of a Galactic field at l = 232, b = -6. The old open cluster Auner 1, the Norma-Cygnus spiral arm and the signature of the warped Galactic Thick Disk

Cited by in corpus (17)

• The Star Formation Histories of Local Group Dwarf Galaxies I. Hubble Space Telescope / Wide Field Planetary Camera 2 Observations
• The Milky Way's external disc constrained by 2MASS star counts
• Tombaugh 2: The First Open Cluster with a Significant Abundance Spread or Embedded in a Cold Stellar Stream?
• The predicted luminous satellite populations around SMC and LMC-mass galaxies - A missing satellite problem around the LMC?
• Numerical Color-Magnitude Diagram Analysis of SDSS Data and Application to the New Milky Way satellites
• A search for a dark matter annihilation signal towards the Canis Major overdensity with H.E.S.S
• Mapping the Monoceros Ring in 3D with Pan-STARRS1
• On Rings and Streams in the Galactic Anti-Center
• No Excess of RR Lyrae Stars in the Canis Major Overdensity
• Reaffirming the connection between the Galactic stellar warp and the Canis Major overdensity
• Modeling Star counts in the Monoceros stream and the Galactic anti-centre
• Spectroscopic hint of a cold stream in the direction of the globular cluster NGC 1851
• Stellar populations in the Canis Major over-density
• A revised view of the Canis Major stellar overdensity with DECam and Gaia: new evidence of a stellar warp of blue stars
• First Results From the Large Binocular Telescope: Deep Photometry of New dSphs
• Mapping low-latitude stellar substructure with SEGUE photometry
• The Elongated Structure of the Hercules dSph from Deep LBT Imaging