GALACTICNUCLEUS: A high-angular-resolution JHKs imaging survey of the Galactic centre II. First data release of the catalogue and the most detailed CMDs of the GC (1908.10366v1)

Abstract: The high extinction and extreme source crowding of the central regions of the Milky Way are serious obstacles to the study of the structure and stellar population of the Galactic centre (GC). Existing surveys that cover the GC region (2MASS, UKIDSS, VVV, SIRIUS) do not have the necessary high angular resolution. Therefore, a high-angular-resolution survey in the near infrared is crucial to improve the state of the art. Here, we present the GALACTICNUCLEUS catalogue, a near infrared $JHK_s$ high-angular-resolution ($0.2''$) survey of the nuclear bulge of the Milky Way. We explain in detail the data reduction, data analysis, calibration, and uncertainty estimation of the GALACTICNUCLEUS survey. We assess the data quality comparing our results with previous surveys. We obtained accurate $JHK_s$ photometry for $\sim 3.3\times10^6$ stars in the GC detecting around 20 \% in $J$, 65 \% in $H,$ and 90 \% in $K_s$. The survey covers a total area of $\sim0.3$ square degrees, which corresponds to $\sim 6,000$ pc$^2$. The GALACTICNUCLEUS survey reaches 5\,$\sigma$ detections for $J \sim 22$ mag, $H \sim 21$ mag, and $K_s \sim 21$ mag. The uncertainties are below 0.05 mag at $J \sim 21$ mag, $H \sim 19$ mag, and $K_s \sim 18$ mag. The zero point systematic uncertainty is $\lesssim0.04$ mag in all three bands. We present colour-magnitude diagrams for the different regions covered by the survey.

• The paper introduces the GALACTICNUCLEUS catalogue, presenting a high-resolution near-IR survey that maps 3.3 million stars in the Galactic centre despite heavy extinction.
• It employs advanced speckle holography with 0.2'' resolution on HAWK-I at ESO VLT, achieving 5-sigma detections down to J ~22, H, and Ks ~21 mag.
• The study reveals detailed colour-magnitude diagrams that identify key stellar features like the Red Clump and RGB Bump, enhancing our understanding of Galactic evolution.

A High-Resolution Survey of the Galactic Center: The GALACTICNUCLEUS Catalogue

The paper "GALACTICNUCLEUS: A high-angular-resolution $JHK_s$ imaging survey of the Galactic center" by Nogueras-Lara et al. introduces a significant advancement in the paper of the nuclear bulge of the Milky Way through the development and release of the GALACTICNUCLEUS catalogue. This survey was meticulously designed to overcome the challenges posed by high extinction and extreme source crowding in the Galactic center (GC), which have historically hindered detailed structural studies.

Methodology and Key Features

The GALACTICNUCLEUS project employs a high-angular-resolution near-infrared $JHK_s$ survey with a resolution of $0.2''$. The survey encompasses around 0.3 square degrees, translating to approximately 6000 pc$^2$, and provides high-quality photometry for about $3.3 \times 10^6$ stars. The researchers utilized the HAWK-I instrument on the ESO VLT, taking advantage of speckle holography to achieve the required angular resolution amidst the high-density stellar field of the GC.

The survey is characterized by the following specifics:

• The stellar density reached is approximately 600 stars/pc$^2$.
• The data reduction involved custom techniques to account for PSF variations, resulting in an angular resolution of $\sim0.2''$.
• Through careful calibration against the SIRIUS/IRSF GC survey, the systematic uncertainties in photometric zero points were contained within 0.04 mag.
• Detection thresholds for photometric accuracy were established at $J\sim 22$ mag, $H \sim 21$ mag, and $K_s \sim 21$ mag, allowing for 5-sigma detections, which underscore the catalogue’s sensitivity.
• A robust examination assures cosmic completeness of $\sim 80\%$ at $K_s \sim 16$ mag and $H \sim 18$ mag, verified through artificial star tests and earlier high-resolution data comparisons.

Implications and Contributions

The GALACTICNUCLEUS survey contributes notable advancements to the astrophysical community. This catalogue's comprehensive spatial coverage and depth considerably enhance the available data beyond previous surveys such as 2MASS, UKIDSS, and VVV, especially in terms of resolution and sensitivity to fainter and more densely packed objects.

The paper promulgates the first high-resolution color-magnitude diagrams (CMDs) for the inner regions of the Milky Way. These CMDs elucidate various stellar populations within the GC, including features like the Red Clump (RC) and the Red Giant Branch Bump (RGBB), critical for understanding stellar evolution timelines and the distribution of stellar populations across the Galaxy’s center.

Future Prospects

The GALACTICNUCLEUS survey sets a benchmark for similar galactic core surveys and provides a robust base for further research. As data handling techniques and photometric analysis continue to advance, future iterations of such surveys may enhance detection capabilities or explore additional stellar features imperceptible with current methodologies. Moreover, extending such high-resolution studies to other galactic nuclei could illuminate comparative studies between the Milky Way and other galaxies.

Researchers anticipate that sharing the GALACTICNUCLEUS catalogue with the broader community will spur multidisciplinary investigations into GC dynamics, stellar population synthesis, and the underlying physics of galactic nuclei. These collective efforts may unveil new facets of the Milky Way’s complex architecture and evolutionary history.