Variability of the near-infrared extinction curve towards the Galactic centre

Due to the extreme extinction towards the Galactic centre (A(v) similar to 30 mag), its stellar population is mainly studied in the near-infrared (NIR) regime. Therefore, a proper analysis of the NIR extinction curve is necessary to fully characterise the stellar structure and population of the inner part of the galaxy. Aims. We studied the dependence of the extinction index (alpha(lambda)) in the NIR on the line of sight, wavelength, and extinction. Methods. We used the GALACTICNUCLEUS imaging survey, a high angular resolution catalogue (0.2 '') for the inner part of the Galaxy in JHK(s) and studied the spatial variation in the extinction index. We also applied two independent methods based on red clump stars to compute the extinction index between different bands and its variation with wavelength. Results. We did not detect any significant line-of-sight or extinction variation in a within the studied region in the nuclear stellar disc. The extinction index between JH and HKs differs by 0.19 +/- 0.05. We obtained mean values for the extinction indices alpha(JH)( )= 2.43 +/- 0.03 and alpha(HK), = 2.23 +/- 0.03. The dependence of the extinction index on the wavelength could explain the differences obtained for a d in the literature since it was assumed constant for the NIR regime.© ESO 2019.The research leading to these results has received funding from the European Research Council under the European Union's Seventh Framework Programme (FP7/2007-2013)/ERC grant agreement no [614922]. This work is based on observations made with ESO Telescopes at the La Silla Paranal Observatory under programme IDs 195. B-0283 and 091. B-0418. We thank the sta ff at ESO for their great e ff orts and helpfulness. F. N.-L. acknowledges financial support from a MECD pre-doctoral contract, code FPU14/01700. F. N. acknowledges financial support through Spanish grants ESP2015-65597C4-1-R and ESP2017-86582-C4-1-R (MINECO/FEDER). We acknowledge support from the State Agency for Research of the Spanish MCIU through the Centre of Excellence Severo Ochoa Award of the Instituto de Astrofisica de Andalucia (CSIC) (SEV-2017-0709). N.N. acknowledges support from Sonderforschungsbereich SFB 881 "The Milky Way System" (subproject B8) of the German Research Foundation (DFG).Peer reviewe