GALACTICNUCLEUS: A high angular resolution JHKs imaging survey of the Galactic centre. V. Toward the GNS Second Data Release: Methodology, Photometric and Astrometric Performance

TL;DR

The paper introduces GALACTICNUCLEUS DR2, a two-epoch, high-angular-resolution near-infrared survey of the Galactic Center that leverages speckle holography and ground-layer adaptive optics to deliver significantly deeper photometry and markedly improved astrometry. A new data-reduction pipeline with enhanced distortion corrections and jackknife-based error estimates, plus two complementary proper-motion strategies (relative and Gaia-anchored absolute), yields proper-motion accuracies around 0.5 mas/yr and photometric precision of a few percent. Validation on Galactic bar and Arches-cluster regions shows consistency with HST/ Gaia results and demonstrates the ability to detect co-moving groups in the crowded NSD. The DR2 catalogs provide the most precise ground-based GC proper motions to date, enabling detailed studies of NSD dynamics, young star kinematics, and new cluster detections, with strong potential for synergy with JWST and Roman Space Telescope data.

Abstract

The center of the Milky Way is a unique environment of great astrophysical interest, but its extreme crowding and extinction make it difficult to study. The GALACTICNUCLEUS survey, a high-angular-resolution near-infrared imaging program, was designed to overcome these challenges. We present the methodology and first results of its second data release, which includes major improvements in reduction, calibration, and analysis, providing deeper photometry, improved astrometry, and high-precision proper motions across the Nuclear Stellar Disk. Observations were obtained with VLT/HAWK-I in two epochs separated by seven years, using speckle holography and a ground-layer adaptive optics system. Proper motions were derived both relative, by aligning epochs within the survey, and absolute, by tying to the Gaia reference frame. The new release achieves photometry about one magnitude deeper and astrometry about ten times more precise than the first release. Proper motions reach an accuracy of about 0.5 mas/yr relative to Gaia. In the Arches field, our clustering analysis recovers the cluster with mean velocities consistent with HST-based results. The second data release of the GALACTICNUCLEUS survey provides the most precise ground-based proper motion catalogs of the Galactic Center to date, enabling studies of the Nuclear Stellar Disk, young star kinematics, and new stellar cluster detections.

Figures (13)

• Figure 1: GNS survey fields overlaid on a Spitzer/IRAC colour mosaic Stolovy:2006fk.White solid lines indicate the full extent of the GNS. White shaded regions mark the fields analysed in this work, while dotted and dashed outlines denote the fields of view of the GNS I and GNS II pointings, respectively. The black numbers label the individual fields (see Table \ref{['tab:fields']}).Green and blue areas indicate the regions where we computed proper motions: the green area corresponds to a field on the Galactic bar, and the blue solid box corresponds to the GNS fields that overlap with the Arches cluster. The black box shows the coverage of the catalogue from Hosek:2022om.
• Figure 2: Comparison of the $J$, $H$, and $K_s$ luminosity functions for the Galactic bar field (green box in Fig. \ref{['fig:gcview']}), using data from the VVV catalog by Griggio:2024eb (available only for the $J$ and $K_s$ bands), as well as from GNS I (DR1 and DR2) and GNS II.
• Figure 3: Example of the HAWK-I mosaic camera distortion map provided by SCAMP for a GNS II pointing. Colors encode the variation of the pixel scale across the detector.
• Figure 4: Astrometric and photometric uncertainties of the stars in the Galactic bar field (green box in Fig. \ref{['fig:gcview']} using dara from GNS I DR2. Upper row: The gray shaded 2D histograms show the uncertainties estimated by the pipeline for stars of a given magnitude (combined jackknife and PSF uncertainties). The red dots show the uncertainties of stars as estimated from their multiple detections on different detector chips. Lower row: Histograms of the astrometric and photometric uncertainties of bright ($H\leq18$ [mag]) stars measured on different detectors.
• Figure 5: Magnitude residuals between GNS I DR2 and SIRIUS for the $J$, $H$, and $K_s$ bands in the Galactic bar field (see Fig. \ref{['fig:gcview']}). The orange line indicates the mean of the residuals.