Volume 610, February 2018
|Number of page(s)||23|
|Section||Catalogs and data|
|Published online||07 March 2018|
GALACTICNUCLEUS: A high angular resolution JHKs imaging survey of the Galactic centre
I. Methodology, performance, and near-infrared extinction towards the Galactic centre★
Instituto de Astrofísica de Andalucía (CSIC),
Glorieta de la Astronomía s/n,
2 European Southern Observatory (ESO), Casilla 19001, Vitacura, Santiago, Chile
3 European Southern Observatory (ESO), Karl-Schwarzschild-Straße 2, 85748 Garching, Germany
4 Leiden Observatory, Leiden University, Postbus 9513, 2300 RA Leiden, The Netherlands
5 The University of Chicago, The Department of Astronomy and Astrophysics, 5640 S. Ellis Ave, Chicago, IL 60637, USA
6 Miyagi University of Education, Aoba-ku, 980-0845 Sendai, Japan
7 Departamento de Astrofísica, Centro de Astrobiología (CSIC-INTA), Ctra. Torrejón a Ajalvir km 4, 28850 Torrejón de Ardoz, Spain
8 Max-Planck Institute for Astronomy, Königstuhl 17, 69117 Heidelberg, Germany
Accepted: 14 November 2017
Context. The Galactic centre (GC) is of fundamental astrophysical interest, but existing near-infrared surveys fall short covering it adequately, either in terms of angular resolution, multi-wavelength coverage, or both. Here we introduce the GALACTICNUCLEUS survey, a JHKs imaging survey of the centre of the Milky Way with a 0.2″ angular resolution. Aims. The purpose of this paper is to present the observations of Field 1 of our survey, centred approximately on SgrA* with an approximate size of 7.95′ × 3.43′. We describe the observational set-up and data reduction pipeline and discuss the quality of the data. Finally, we present the analysis of the data.
Methods. The data were acquired with the near-infrared camera High Acuity Wide field K-band Imager (HAWK-I) at the ESO Very Large Telescope (VLT). Short readout times in combination with the speckle holography algorithm allowed us to produce final images with a stable, Gaussian PSF (point spread function) of 0.2″ FWHM (full width at half maximum). Astrometric calibration is achieved via the VISTA Variables in the Via Lactea (VVV) survey and photometric calibration is based on the SIRIUS/Infrared Survey Facility telescope (IRSF) survey. The quality of the data is assessed by comparison between observations of the same field with different detectors of HAWK-I and at different times.
Results. We reach 5σ detection limits of approximately J = 22, H = 21, and Ks = 20. The photometric uncertainties are less than 0.05 at J ≲ 20, H ≲ 17, and Ks ≲ 16. We can distinguish five stellar populations in the colour-magnitude diagrams; three of them appear to belong to foreground spiral arms, and the other two correspond to high- and low-extinction star groups at the GC. We use our data to analyse the near-infrared extinction curve and find some evidence for a possible difference between the extinction index between J − H and H − Ks. However, we conclude that it can be described very well by a power law with an index of αJHKs = 2.30 ± 0.08. We do not find any evidence that this index depends on the position along the line of sight, or on the absolute value of the extinction. We produce extinction maps that show the clumpiness of the ISM (interstellar medium) at the GC. Finally, we estimate that the majority of the stars have solar or super-solar metallicity by comparing our extinction-corrected colour-magnitude diagrams with isochrones with different metallicities and a synthetic stellar model with a constant star formation.
Key words: Galaxy: nucleus / dust, extinction / Galaxy: center / stars: horizontal-branch
Extinction maps as well as their corresponding uncertainty maps (Figs. 28, 30 and 31) are only available at the CDS via anonymous ftp to cdsarc.u-strasbg.fr (220.127.116.11) or via http://cdsarc.u-strasbg.fr/viz-bin/qcat?J/A+A/610/A83
© ESO 2018
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