Blanco DECam Bulge Survey (BDBS) II: Project Performance, Data Analysis, and Early Science Results

TL;DR

The BDBS survey provides extensive photometric data of the Galactic bulge, revealing metallicity distributions, globular cluster properties, and stellar populations, with new insights into bulge enrichment and cluster characteristics.

Contribution

This paper details the survey's data collection, calibration, and early science results, including novel correlations and models for bulge metallicity and globular cluster analysis.

Findings

Strong correlation between (u-i)o and [Fe/H] for bulge giants

Interior bulge fields fit simple closed box enrichment models

Detection of extra-tidal stars and evidence for small He spreads in clusters

Abstract

The Blanco DECam Bulge Survey (BDBS) imaged more than 200 square degrees of the Southern Galactic bulge using the ugrizY filters of the Dark Energy Camera, and produced point spread function photometry of approximately 250 million unique sources. In this paper, we present details regarding the construction and collation of survey catalogs, and also discuss the adopted calibration and dereddening procedures. Early science results are presented with a particular emphasis on the bulge metallicity distribution function and globular clusters. A key result is the strong correlation (sigma ~ 0.2 dex) between (u-i)o and [Fe/H] for bulge red clump giants. We utilized this relation to find that interior bulge fields may be well described by simple closed box enrichment models, but fields exterior to b ~ -6 degrees seem to require a secondary metal-poor component. Applying scaled versions of the closed box model to the outer bulge fields is shown to significantly reduce the strengths of any additional metal-poor components when compared to Gaussian mixture models. Additional results include: a confirmation that the u-band splits the sub-giant branch in M 22 as a function of metallicity, the detection of possible extra-tidal stars along the orbits of M 22 and FSR 1758, and additional evidence that NGC 6569 may have a small but discrete He spread, as evidenced by red clump luminosity variations in the reddest bands. We do not confirm previous claims that FSR 1758 is part of a larger extended structure.