Stellar populations in the Canis Major over-density

Abstract

We performed a photometric multicolor survey of the core of the Canis Major over-density at l 244, -8.0, reaching V = 22 and covering 0.3 x 1 degree. The main aim is to unravel the complex mixture of stellar populations toward this Galactic direction, where in the recent past important signatures of an accretion event have been claimed to be detected. While our previous investigations were based on disjointed pointings aimed at revealing the large scale structure of the third Galactic Quadrant, we now focus on a complete coverage of a smaller field centered on the Canis Major over-density. A large wave-length baseline, in the UBVRI bands, allows us to build up a suite of colour colour and colour magnitude diagrams, providing a much better diagnostic tool to disentangle the stellar populations of the region. In fact, the simple use of one colour magnitude diagram, widely employed in all the previous studies defending the existence of the Canis Major galaxy, does not allow one to separate the effects of the different parameters (reddening, age, metallicity, and distance) involved in the interpretation of data, forcing to rely on heavy modeling. In agreement with our previous studies in the same general region of the Milky Way, we recognize a young stellar population compatible with the expected structure and extension of the Local (Orion) and Outer (Norma-Cygnus) spiral arms in the Third Galactic Quadrant. Moreover we interpret the conspicuous intermediate-age metal poor population as belonging to the Galactic thick disk, distorted by the effect of strong disk warping at this latitude, and to the Galactic halo.

9 pages, 12 eps figures (some of them somewhat degraded in resolution), accepted for publication in MNRAS

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• Spectroscopic hint of a cold stream in the direction of the globular cluster NGC 1851
• Galactic structure in the outer disk: the field in the line of sight to the intermediate-age open cluster Tombaugh 1
• CCD $UBV(RI{)}_C$ Photometry of Twenty Open Clusters
• Five old open clusters more in the outer Galactic disk
• The disruption of the low-mass globular cluster E3
• UBVI CCD photometry and star counts in 9 inner disk Galactic star clusters
• The complex stellar populations in the lines of sight to open clusters in the third Galactic quadrant
• Properties of the open cluster Tombaugh 1 from high resolution spectroscopy and uvbyCaH$\beta$ photometry
• A revised view of the Canis Major stellar overdensity with DECam and Gaia: new evidence of a stellar warp of blue stars