arXiv subjects

Jiangang Kang

Publications and source records attributed to Jiangang Kang.

6 recordsLinked to original sources

arXiv2025

Estimating constraints on cosmological parameters via the canonical and the differential redshift drift with SKA HI 21-cm observations

Redshift drift effect, an observational probe that indenpendent of cosmological models, presents unique applications in specific cosmological epoch. By quantifying redshift drift signal , researchers can determine the rate of the Universe's accelerated expansion and impose constraints on cosmological models and parameters. This study evaluates the precision in cosmological parameters estimation derived from this signal via HI 21cm signal, that observed by the Square Kilometre Array (SKA) telescope, with spectral resolutions of 0.001 Hz and 0.002 Hz over an observational period of $ΔT = 0.5$ year, utilizing two established techniques: the canonical redshift drift and the differential redshift drift method. The primary objective of this project is to ascertain the rate of cosmic acceleration and establish a solid foundation for real-time cosmology. The results reveal that both the two methods impose highly precise constraints on cosmological parameters, with accuracy reaching the level of millimeter per second (mm/s) or better. However, the canonical method provides relatively less stringent compared to the differential approach. Furthermore, when solely constraining the matter density parameter $Ω_m$, the strategy can be adapted to the canonical method. Nonetheless, the differential method exhibits clear advantages when simultaneously constraining the matter density parameter $Ω_m$ and the equation of state of dark energy. These findings validate SKA's capability in detecting redshift drift and refining observational cosmology and indicates the effect can offer superior diagnostic capabilities compared to other techniques, provided that appropriate observational equipment or sufficient observational time is employed.

astro-ph.CO↗

arXiv2025

Redshift drift effect through the observation of HI 21cm signal with SKA

This study presents the findings of using the Square Kilometre Array (SKA) telescope to measure redshift drift via the HI 21cm signal, employing semi-annual observational interval within redshift around z $\sim$ 1 with main goal is to directly gauge the universe's expansion acceleration rate with millimeter-per-second (mm/s) precision. The SKA can detect over a billion HI 21cm emissions from individual galaxies to the redshift z $\sim$ 2 and thousands of absorption lines from Damped Lyman-alpha (DLA) systems against bright quasars to the redshift z $\sim$ 13, with the sensitivity limit of 100 mJy. By utilizing SKA's high spectral resolution settings (0.001, 0.002, 0.005, 0.01 Hz) to detect redshift drift, particularly focusing on the 0.001 and 0.002 Hz configuration, one aims to achieve the necessary mm/s in precision measurement by the 0.5-year observation period. The velocity drift rate, crucially determined by the two operational regimes within 0.01 to 0.21 mm/s and 0.031 to 0.17 mm/s, respectively, exceeds the theoretical accuracy limit of 1.28 mm/s. The analysis thoroughly restricts cosmological parameters related to dark energy using the Sandage-Loeb (SL) signal from the HI 21cm emission and absorption lines. It estimates $\rm H_0$ of about 70 km/s/Mpc, $\rm Ω_m$ near 0.3, with w close to -1, $\rm w_0$ around -1, and $\rm w_a$ approaching -0.1. These results strongly endorse the SL effect as an effective method for confirming cosmic acceleration and exploring the dark sector in real-time cosmology with the SKA.

astro-ph.CO↗

arXiv2024

Toward a direct measurement of the cosmic acceleration: The pilot observation of H I 21cm absorption line at FAST

This study presents results on detecting neutral atomic hydrogen (HI) 21cm absorption in the spectrum of PKS1413+135 at redshift $z=0.24670041$. The observation was conducted by FAST, with a spectral resolution of 10 Hz, using 10 minutes of observing time. The global spectral profile is examined by modeling the absorption line using a single Gaussian function with a resolution of 10 kHz within a 2 MHz bandwidth. The goal is to determine the rate of the latest cosmic acceleration by directly measuring redshift evolution of H I 21 cm absorption line with Hubble flow towards a same background Quasar over a decade or longer time span. This will serve as a detectable signal generated by the accelerated expansion of the Universe at redshift $z < 1$, referred to as redshift drift $\dot{z}$ or the SL effect. The measured HI gas column density in this DLA system is approximately equivalent to the initial observation value, considering uncertainties of the spin temperature of a spiral host galaxy. The high signal-to-noise ratio of 57, obtained at a 10 kHz resolution, strongly supports the feasibility of using the H I 21 cm absorption line in DLA systems to accurately measure the redshift drift rate at a precision level of around $10^{-10}$ per decade.

astro-ph.CO↗

arXiv2022

Extragalactic HI survey with FAST : First look of the pilot survey results

As first data release of a pilot extragalactic HI survey with Five-hundred-meter Aperture Spherical radio Telescope (FAST),we extracted 544 extragalaxies from three-dimensional(3D) spectral data to perform interactive searching and computing, yielding global parameters for these detections, extending redshift ranges of HI 21cm line up to z = 0.04 ,which covers part of the sky region in right ascension(R.A. or $α$) and declination(Dec or $δ$) range $00^{\rm h} 47^{\rm m}< \rm R.A.(J2000)<23^{\rm h}22^{\rm m}$ and $+24^{\circ}<\rm Dec.(J2000) <+43^{\circ}$ . The S/N of 544 HI detections are greater than 5 flagged with code 1 to 4 based on baseline qualities or RFI contamination. Besides, we find 16 of which without any counterparts in the existing galaxy catalogs. The catalog can give a guidence for the future HI observation with FAST.

astro-ph.GA↗

arXiv2021

Reconstructing a non-linear interaction in the dark sector with cosmological observations

In this work we model two non-linear directly interacting scenarios in dark sector of the universe with the dimensionless parameter $α$ and $β$, which dominate the energy exchange between dark energy and dark matter. The central goal of this investigation is to research the interacting model and discuss the cosmological implications based on the current observational datasets. The class of the interaction is generally characterized by a coupling function $Q\propto H(z)ρ_x$, $x$ denotes the energy density of dark matter or dark energy. The constrained results we obtained indicate that the direct interaction in cosmic dark sector is favored by various observational data and the key effects on CMB power spectrum and linear matter power spectrum appear compared to $Λ$CDM standard paradigm. Finally, we discuss in depth the effect of different neutrino mass hierarchy on matter power spectrum and the variation of the ratio of CMB temperature power spectrum $C_{\ell}^{TT}$ and matter power spectrum $P(k)$ when the $ΔN_{eff}= N-3.046$ from 0.5 to 2, respectively.

astro-ph.CO↗

arXiv2019

Cosmological constraints on ultra-light axion fields

Ultra-light axions (ULAs) with mass less than 10^-20 eV have interesting behaviors that may contribute to either dark energy or dark matter at different epochs of the Universe. Its properties can be explored by cosmological observations, such as expansion history of the Universe, cosmic large-scale structure, cosmic microwave background, etc. In this work, we study the ULAs with a mass around 10^-33 eV, which means the ULA field still rolls slowly at present with the equation of state w=-1 as dark energy. In order to investigate the mass and other properties of this kind of ULA field, we adopt the measurements of Type Ia supernova (SN Ia), baryon acoustic oscillation (BAO), and Hubble parameter H(z). The Markov Chain Monte Carlo (MCMC) technique is employed to perform the constraints on the parameters. Finally, by exploring four cases of the model, we find that the mass of this ULA field is about 3x10^-33 eV if assuming the initial axion field phi_i=M_pl. We also investigate a general case by assuming phi_i< M_pl and find that the fitting results of phi_i/M_pl are consistent with or close to 1 for the datasets we use.

astro-ph.CO↗