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 G'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 chi(2). 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 deg(2) and 0.6 < z < 1.0. We find that the DES Y1 data favour a model with BAO at the 2.6 sigma C.L. However, the goodness of fit is somewhat poor, with chi(2)/(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 chi(2)/(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.