分类： 天文学 >> 天文学 提交时间： 2023-02-19
摘要： Current standard astrophysical models struggle to explain the tentative detection of the 21 cm absorption trough centered at $z\sim17$ measured by the EDGES low-band antenna. However, it has been shown that the EDGES results are consistent with an extrapolation of a declining UV luminosity density, following a simple power-law of deep Hubble Space Telescope observations of $4 < z < 9$ galaxies. We here explore the conditions by which the EDGES detection is consistent with current reionization and post-reionization observations, including the volume-averaged neutral hydrogen fraction of the intergalactic medium at $z\sim6-8$, the optical depth to the cosmic microwave background, and the integrated ionizing emissivity at $z\sim5$. By coupling a physically motivated source model derived from radiative transfer hydrodynamic simulations of reionization to a Markov Chain Monte Carlo sampler, we find that high contribution from low-mass halos along with high photon escape fractions are required to simultaneously reproduce the high-redshift (cosmic dawn) and low-redshift (reionization) existing constraints. Low-mass faint-galaxies dominated models produce a flatter emissivity evolution that results in an earlier onset of reionization with gradual and longer duration, and higher optical depth. Our results provide insights on the role of faint and bright galaxies during cosmic reionization, which can be tested by upcoming surveys with the James Webb Space Telescope.
分类： 天文学 >> 天文学 提交时间： 2023-02-19
摘要： Using the novel semi-numerical code for reionization AMBER, we model the patchy kinetic Sunyaev-Zel'dovich (kSZ) effect by directly specifying the reionization history with the redshift midpoint $z_\mathrm{mid}$, duration $\Delta_\mathrm{z}$, and asymmetry $A_\mathrm{z}$. We further control the ionizing sources and radiation through the minimum halo mass $M_\mathrm{h}$ and the radiation mean free path $\lambda_\mathrm{mfp}$. AMBER reproduces the free electron number density and the patchy kSZ power spectrum of radiation-hydrodynamic simulations at the target resolution ($1\,{\rm Mpc}/h$) with matched reionization parameters. With a suite of $(2\,{\rm Gpc}/h)^3$ simulations using AMBER, we first constrain the redshift midpoint $6.08$ is needed to ensure an end of reionization before $z=5.5$). We show that constraints on the asymmetry require $\sim 0.1\,\mu k^2$ measurement accuracy at multipoles other than $\ell=3000$. Finally, we find that the amplitude and shape of the kSZ spectrum are only weakly sensitive to $M_h$ under a fixed reionization history and radiation mean-free path.
分类： 天文学 >> 天文学 提交时间： 2023-02-19
Satoshi Kikuta
Yuichi Matsuda
Shigeki Inoue
Charles C. Steidel
Renyue Cen
Zheng Zheng
Hidenobu Yajima
Rieko Momose
Masatoshi Imanishi
Yutaka Komiyama
摘要： We present UV and Ly$\alpha$ radial surface brightness (SB) profiles of Ly$\alpha$ emitters (LAEs) at $z=2.84$ detected with the Hyper Suprime-Cam (HSC) on the Subaru Telescope. The depth of our data, together with the wide field coverage including a protocluster, enable us to study the dependence of Ly$\alpha$ halos (LAHs) on various galaxy properties, including Mpc-scale environments. UV and Ly$\alpha$ images of 3490 LAEs are extracted, and stacking the images yields SB sensitivity of $\sim1\times10^{-20}\mathrm{~erg~s^{-1}~cm^{-2}~arcsec^{-2}}$ in Ly$\alpha$, reaching the expected level of optically thick gas illuminated by the UV background at $z\sim3$. Fitting of the two-component exponential function gives the scale-lengths of $1.56\pm0.01$ and $10.4\pm0.3$ pkpc. Dividing the sample according to their photometric properties, we find that while the dependence of halo scale-length on environment outside of the protocluster core is not clear, LAEs in the central regions of protoclusters appear to have very large LAHs which could be caused by combined effects of source overlapping and diffuse Ly$\alpha$ emission from cool intergalactic gas permeating the forming protocluster core irradiated by active members. For the first time, we identify ``UV halos'' around bright LAEs which are probably due to a few lower-mass satellite galaxies. Through comparison with recent numerical simulations, we conclude that, while scattered Ly$\alpha$ photons from the host galaxies are dominant, star formation in satellites evidently contributes to LAHs, and that fluorescent Ly$\alpha$ emission may be boosted within protocluster cores at cosmic noon and/or near bright QSOs.
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