Elahi, KhMA and Bharadwaj, S and Ghosh, A and Pal, S and Ali, SkS and Choudhuri, S and Chakraborty, A and Datta, A and Roy, N and Choudhury, M and Dutta, P (2023) Towards 21cm intensity mapping at z = 2.28 with uGMRT using the tapered gridded estimator  II. Crosspolarization power spectrum. In: Monthly Notices of the Royal Astronomical Society, 520 (2). pp. 20942108.

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Abstract
Neutral hydrogen (H I) 21cm intensity mapping (IM) offers an efficient technique for mapping the largescale structures in the Universe. We introduce the 'Cross' Tapered Gridded Estimator (Cross TGE), which crosscorrelates two crosspolarizations (RR and LL) to estimate the multifrequency angular power spectrum Cι(Δν). 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 24.4MHzbandwidth uGMRT (upgraded Giant Metrewave Radio Telescope) Band 3 data centred at 432.8 MHz aiming H I IM at z = 2.28. The measured Cι(Δν) 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 2σ upper limit Δ2UL(k) ≤ (58.67)2 mK2 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 H I traces the underlying matter distribution, we have modelled Cι(Δν) to simultaneously estimate the foregrounds and [ΩH IbH I], where ΩH I and bH I are the H I density and linear bias parameters, respectively. We obtain a bestfitting value of [ΩH IbH I]2 = 7.51 × 10−4 ± 1.47 × 10−3 that is consistent with noise. Although the 2σ upper limit [ΩH IbH I]UL ≤ 0.061 is ∼50 times larger than the expected value, this is a considerable improvement over earlier works at this redshift.
Item Type:  Journal Article 

Publication:  Monthly Notices of the Royal Astronomical Society 
Publisher:  Oxford University Press 
Additional Information:  The copyright for this article belongs to the author. 
Keywords:  diffuse radiation; largescale structure of Universe; methods: data analysis; methods: statistical; techniques: interferometric 
Department/Centre:  Division of Physical & Mathematical Sciences > Physics 
Date Deposited:  09 Jul 2023 17:35 
Last Modified:  08 Aug 2023 11:22 
URI:  https://eprints.iisc.ac.in/id/eprint/82096 
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