The 2MASS galaxy angular power spectrum: Probing the galaxy distribution to Gigaparsec scales

We present an angular power spectrum analysis of the 2 Micron All Sky Survey (2MASS) full release extended source catalogue. The main sample used includes 518 576 galaxies below an extinction-corrected magnitude of Ks =13.5 and limited to |b| > 20◦. The power spectrum results provide an estimate of the galaxy density fluctuations at extremely large scales, r∼ 1000 h −1 Mpc. We compare this with mock predictions constructed from the ΛCDM Hubble Volume mock catalogue. We find that over the range 16 l 6100 the 2MASS Cl is steeper than that for the Hubble Volume model. However, in the linear regime (l 630) there is good agreement between the two. We investigate in detail the effects of possible sources of systematic error. Converting linear power spectrum predictions for the form of the three-dimensional matter power spectrum, P (k), and assuming a flat CDM cosmology, a primordial ns=1 spectrum and negligible neutrino mass, we perform fits to the galaxy angular power spectrum at large linear scales (l 630, corresponding to r∼ 50 h −1 Mpc). We obtain constraints on the galaxy power spectrum shape of Γeff = 0.14±0.02, in good agreement with previous estimates inferred at smaller scales. We also constrain the galaxy power spectrum normalisation to (σ8bK) 2 = 1.36± 0.10; in combination with previous constraints on σ8 we infer a Ks-band bias of bK=1.39±0.12. We are also able to provide weak constraints on Ωmh and Ωb/Ωm. These results are based on the usual assumption that the errors derived from the Hubble Volume mocks are applicable to all other models. If we instead assume that the error is proportional to the Cl amplitude then the constraints weaken; for example it becomes more difficult to reject cosmologies with lower Γeff .