The Hubble Missing Globular Cluster Survey. III. Astro-photometric catalogs, artificial-star tests, and improved absolute proper motions

Abstract

The Hubble Missing Globular Cluster Survey (MGCS) has taken one of the last opportunities to complete the census of Galactic globular clusters (GCs) started by past Hubble Space Telescope (HST) programs, securing high-resolution data for 34 GCs never observed before by HST. The previous papers of the series have highlighted the astrometric and photometric potential of the project by analyzing a subsample of targets. We present, and release to the community, the official astro-photometric catalogs of the MGCS for all GCs imaged by this project. We describe the data reduction using state-of-the-art techniques designed for HST. We discuss the photometric calibration and show, for the first time, the synergy with the Gaia catalog to ensure homogeneous photometry across our data set. We compute artificial-star tests that can be used to assess systematics and the completeness level of our data. We combined HST and Gaia data to refine the absolute PMs of our GCs, reaching a precision $\sim$3 times better than that of Gaia alone. We used these new PMs to update (and to determine for the first time for six systems) the associations between GCs and their putative galaxy progenitors. This work continues decades-long efforts of large Treasury programs in sharing precise and accurate atlases to the community for studying GCs across a wide range of scientific endeavors.

Figures (9)

• Figure 1: Comparison of our photometry with that in the Gaia synthetic-photometry catalog. In each row ($=$camera/filter), the first two panels from the left show the HST-Gaia magnitude difference for all stars in all our GCs as a function of magnitude and color, respectively. The red line is set to 0 as a reference, while the light-blue lines are set at the median (solid line) $\pm$ 1$\sigma$ (dashed lines) magnitude difference for all GCs. The third panel from the left shows the average zero-point difference for each cluster. Finally, the last panel on the right shows the magnitude trend after the photometric correction.
• Figure 2: Overview of the artificial-star tests for the GC ESO-452-11. Panel (a) shows the input CMD for the ACS/WFC data. Black dots are taken from the observed catalog, while gray points are artificial stars in input. Panel (b) presents the Hess diagram of recovered stars, color-coded by the completeness level as in the colorbar at the top. The analogs of these plots for the WFC3/UVIS parallel field are provided in panels (c) and (d). Panels (e) and (f) display the Hess diagrams of the spatial completeness in the ACS/WFC region. The former is color-coded according to the average completeness level, while the latter is color-coded according to the F606W magnitude at which the completeness level reaches the 50%. The $x$- and $y$-axis units are WFC3/UVIS pixels (units in the plot labels are omitted for clarity). Similarly, panels (g) and (h) show the spatial completeness in the WFC3/UVIS region.
• Figure 3: Completeness level for the GC ESO-452-11 as a function of F606W magnitude (instrumental at the top and calibrated at the bottom) for the ACS/WFC (black line) and WFC3/UVIS (red line) data. The 50% completeness level is highlighted with a gray, dashed line.
• Figure 4: Absolute PMs for a sample of GCs in our program. For each GC (two for each row), from left to right we present: the VPD of the Gaia DR3 PMs; the VPD of the PMs from GaiaHub; and a calibrated CMD. In the rightmost CMD, stars in red are likely cluster members according to their PM (made with an arbitrary magnitude-dependent PM selection). This Figure includes examples of a very-crowded region (Palomar 8); a well-populated, moderately-crowded field (ESO-452-11); a loose GC in a sparse field (Bliss 1); and a cluster observed with the WFC3/IR camera (UKS 1).
• Figure 5: Projections (left panel: $E$ versus $L_z$; right panel: $L_\perp$ versus $L_z$) of the integral-of-motion space for the GCs analyzed in our work, color-coded according to the association with their progenitor (see legend in the right panel). The gray points represent all other GCs included in the repository of Pace2025OJAp....8E.142P as a reference.