http://arxiv.org/abs/2111.10240
Damped Lyman-{\alpha} Absorber(DLA) of HI 21cm system is an ideal probe to directly measure cosmic acceleration in real-time cosmology via Sandage-Loeb(SL) test. During short observations toward two DLAs in the commissioning progress of FAST, we manage to exhibit an HI 21cm absorption feature from PKS1413+135 spectrum with our highest resolution up to 100Hz, validating the frequency consistency under different resolutions and bandwidths. We make a Gaussian fitting to extract the spectral features, employ relativistic receding velocity in high-precision velocity measurement, introduce two indicators to describe the fitted velocity uncertainty, and ultimately give a redshift constraint of z = 0.24671595 {\pm} 0.00000015 in accord with most literature. But our redshift error is still three magnitudes larger than theoretical cosmic acceleration over a decade. Though our first attempt has some flaws in time recording and diode settings, it still proves the correctness of our data process. For a higher-resolution radio observation, we propose five main challenges: (1) an accurate astrometric method to optimize Doppler correction; (2) a precise timing standard in data recording; (3) a statistical sample set of DLAs with prominent absorptions; (4) a widely accepted standard of velocity uncertainty; (5) an improved baseline fitting to detect faint macro changes from sharp noisy interference. With close corporation among the community, our quest for cosmic acceleration would advance firmly in the thorny path.
C. Lu, K. Jiao, T. Zhang, et. al.
Mon, 22 Nov 21
11/53
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