Dark Energy Survey Year 1 results: measurement of the galaxy angular power spectrum

We use data from the first-year observations of the DES collaboration to measure the galaxy angular power spectrum (APS), and search for its BAO feature. We test our methodology in a sample of 1800 DES Y1-like mock catalogues. We use the pseudo-C_ℓ method to estimate the APS and the mock catalogues to estimate its covariance matrix. We use templates to model the measured spectra and estimate template parameters firstly from the C_ℓ's of the mocks using two different methods, a maximum likelihood estimator and a Markov Chain Monte Carlo, finding consistent results with a good reduced χ². Robustness tests are performed to estimate the impact of different choices of settings used in our analysis. Finally, we apply our method to a galaxy sample constructed from DES Y1 data specifically for LSS studies. This catalogue comprises galaxies within an effective area of 1318 deg² and 0.6 < z < 1.0. We find that the DES Y1 data favour a model with BAO at the 2.6 σ C.L. However, the goodness of fit is somewhat poor, with χ²/(d.o.f.) = 1.49. We identify a possible cause showing that using a theoretical covariance matrix obtained from C_ℓ's that are better adjusted to data results in an improved value of χ²/(dof) = 1.36 which is similar to the value obtained with the real-space analysis. Our results correspond to a distance measurement of D_A(z_eff = 0.81)/r_d = 10.65 ± 0.49, consistent with the main DES BAO findings. This is a companion paper to the main DES BAO article showing the details of the harmonic space analysis.