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The Galactic Centre is of fundamental astrophysical interest, but existingnear-infrared surveys fall short to cover it adequately. We introduce theGALACTICNUCLEUS survey, a $JHK_s$ imaging survey of the centre of the Milky Waywith a $0.2"$ angular resolution. We present the observations of Field 1 of oursurvey, centred approximately on SgrA* with an approximate size of$7.95'\times3.43'$. We describe the observational set-up and data reductionpipeline and discuss the quality of the data. Finally, we present somepreliminary analysis of the data. The data were acquired with the near-infraredcamera HAWK-I at the ESO VLT. Short readout times in combination with thespeckle holography algorithm allowed us to produce final images with a stable,Gaussian PSF of $0.2"$ FWHM. Astrometric calibration is achieved via the VVVsurvey and photometric calibration is based on the SIRIUS/IRSF survey. Thequality of the data is assessed by comparison between observations of the samefield with different detectors of HAWK-I and at different times. We reach 5sigma detection limits of approximately $J=22$, $H=21$, and $K_s=20$. Thephotometric uncertainties are less than 0.05 at $J<20$, $H<17$ and $K_s<16$. Wedistinguish five stellar populations in the colour-magnitude diagrams; three ofthem appear to belong to foreground spiral arms, and the other two correspondto a high- and a low-extinction star groups at the Galactic Centre. We use ourdata to analyse the near-infrared extinction curve and conclude that it can bedescribed very well by a power-law with an index of $JHK_s=2.30\pm0.08$. We donot find any evidence that this index depends on the position along theline-of-sight, or on the absolute value of the extinction. We produceextinction maps that show the clumpiness of the ISM at the Galactic Centre.Finally, we estimate that the majority of the stars have solar or super-solarmetallicity.

astronomy and astrophysics

GALACTICNUCLEUS: A high angular resolution $JHK_s$ imaging survey of the  Galactic Centre. I. Methodology, performance, and near-infrared extinction  towards the Galactic Centre