The Blanco DECam Bulge Survey. I. The Survey Description and Early Results

Abstract

The Blanco Dark Energy Camera (DECam) Bulge survey is a Vera Rubin Observatory (LSST) pathfinder imaging survey, spanning $\sim 200$ sq. deg. of the Southern Galactic bulge, $-2^{\circ }<$b$<-13^{\circ }$ and $-11^{\circ }<$l$<+11^{\circ }$. We have employed the CTIO-4m telescope and the Dark Energy Camera (DECam) to image a contiguous $\sim 200$ sq. deg. region of the relatively less reddened Southern Galactic bulge, in SDSS $u$ + Pan-STARRS$grizy$. Optical photometry with its large colour baseline will be used to investigate the age and metallicity distributions of the major structures of the bulge. Included in the survey footprint are 26 globular clusters imaged in all passbands. Over much of the bulge, we have Gaia DR2 matching astrometry to $i\sim 18$, deep enough to reach the faint end of the red clump. This paper provides the background, scientific case, and description of the survey. We present an array of new reddening-corrected colour-magnitude diagrams that span the extent of Southern Galactic bulge. We argue that a population of massive stars in the blue loop evolutionary phase, proposed to lie in the bulge, are instead at $\sim 2$ kpc from the Sun and likely red clump giants in the old disk. A bright red clump near $(l,b)=(+8^{\circ },-4^{\circ })$ may be a feature in the foreground disk, or related to the long bar reported in earlier work. We also report the first map of the blue horizontal branch population spanning the BDBS field of regard, and our data does not confirm the reality of a number of proposed globular clusters in the bulge.

19 pages, 13 figures; MNRAS in press; revision corrects some errors and omissions

References in corpus (16)

• The Gaia mission
• The UKIRT Infrared Deep Sky Survey (UKIDSS)
• The Milky Way Tomography with SDSS: II. Stellar Metallicity
• Stellar Proper Motions in the Galactic Bulge from deep HST ACS/WFC Photometry
• The GIRAFFE Inner Bulge Survey (GIBS) III. Metallicity distributions and kinematics of 26 Galactic bulge fields
• Light, Alpha, and Fe-Peak Element Abundances in the Galactic Bulge
• The Bulge Radial Velocity Assay (BRAVA): I. Techniques and a Rotation Curve
• Tracing the long bar with red-clump giants
• The Long Bar in the Milky Way. Corroboration of an old hypothesis
• A Sequoia in the Garden: FSR 1758 - Dwarf Galaxy or Giant Globular Cluster?
• The long Galactic bar as seen by UKIDSS Galactic Plane Survey
• A parametric description of the 3D structure of the Galactic Bar/Bulge using the VVV survey
• The Chemical Composition of the Galactic Bulge and Implications for its Evolution
• The inner two degrees of the Milky Way. Evidence of a chemical difference between the Galactic Center and the surrounding inner bulge stellar populations
• Mapping the stellar age of the Milky Way bulge with the VVV. I. The method
• Mapping the Interstellar Reddening and Extinction towards Baade's Window Using Minimum Light Colors of ab-type RR Lyrae Stars. Revelations from the De-reddened Color-Magnitude Diagrams

Cited by in corpus (9)

• The Ages of Galactic Bulge Stars with Realistic Uncertainties
• Modeling the chemical enrichment history of the Bulge Fossil Fragment Terzan 5
• Blanco DECam Bulge Survey (BDBS) III: A new view of the double red clump in the Milky Way bulge through luminosity and color distribution
• Rubin Observatory LSST Stars Milky Way and Local Volume Star Clusters Roadmap
• Using LSST Microlensing to Constrain Dark Compact Objects in Spherical and Disk Configurations
• He-star donor AM CVn stars and their progenitors as LISA sources
• Blanco DECam Bulge Survey (BDBS) V. Cleaning the foreground populations from Galactic bulge colour-magnitude diagrams using Gaia EDR3
• Spectroscopic Observations of Obscured Populations in the Inner Galaxy: 2MASS-GC02, Terzan 4, and the 200 km/s stellar peak
• Blanco DECam Bulge Survey (BDBS) IV: Metallicity Distributions and Bulge Structure from 2.6 Million Red Clump Stars