Towards 21-cm intensity mapping at z=2.28 with uGMRT using the tapered gridded estimator - II. Cross-polarization power spectrum

Neutral hydrogen (H I ) 21-cm intensity mapping (IM) offers an efficient technique for mapping the large-scale structures in the Universe. We introduce the Cross' Tapered Gridded Estimator (Cross TGE), which cross-correlates two cross-polarizations (RR and LL) to estimate the multifrequency angular power spectrum C-l(delta nu). We expect this to mitigate several effects like noise bias, calibration errors, etc., which affect the Total' TGE that combines the two polarizations. Here, we apply the Cross TGE on 24 . 4 -MHz-bandwidth uGMRT (upgraded Giant Metrewave Radio Telescope) Band 3 data centred at 432 . 8 MHz aiming H I IM at z = 2.28. The measured C-l(delta nu) is modelled to yield maximum likelihood estimates of the foregrounds and the spherical power spectrum P(k) in several k bins. Considering the mean squared brightness temperature fluctuations, we report a 2 sigma upper limit delta(2)(UL) (k) <= (58 . 67)(2) mK(2) at k = 0 . 804 Mpc( -1), which is a factor of 5.2 improvement on our previous estimate based on the Total TGE. Assuming that the HI traces the underlying matter distribution, we have modelled C-l(delta nu) to simultaneously estimate the foregrounds and [omega(HI)b(HI)], where omega(HI) and b(HI) are the H I density and linear bias parameters, respectively. We obtain a best-fitting value of [omega(HI)b(HI)](2) = 7 . 51 x 10(-4) +/- 1 . 47 x 10(-3) that is consistent with noise. Although the 2 sigma upper limit [omega(HI)b(HI)](UL) <= 0 . 061 is similar to 50 times larger than the expected value, this is a considerable improvement over earlier works at this redshift.

Automated summary

Neutral hydrogen (H I) 21-cm intensity mapping is an efficient technique for mapping large-scale structures in the Universe. The Cross' Tapered Gridded Estimator (Cross TGE) is introduced to estimate the multifrequency angular power spectrum and mitigate various effects. The application of Cross TGE on uGMRT Band 3 data yields improved upper limits and best-fitting values for foregrounds and parameters.