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： High-dimensional data sets are expected from the next generation of large-scale surveys. These data sets will carry a wealth of information about the early stages of galaxy formation and cosmic reionization. Extracting the maximum amount of information from the these data sets remains a key challenge. Current simulations of cosmic reionization are computationally too expensive to provide enough realizations to enable testing different statistical methods, such as parameter inference. We present a non-Gaussian generative model of reionization maps that is based solely on their summary statistics. We reconstruct large-scale ionization fields (bubble spatial distributions) directly from their power spectra (PS) and Wavelet Phase Harmonics (WPH) coefficients. Using WPH, we show that our model is efficient in generating diverse new examples of large-scale ionization maps from a single realization of a summary statistic. We compare our model with the target ionization maps using the bubble size statistics, and largely find a good agreement. As compared to PS, our results show that WPH provide optimal summary statistics that capture most of information out of a highly non-linear ionization fields.
分类： 天文学 >> 天文学 提交时间： 2023-02-19
摘要： While cosmological dark matter-only simulations relying solely on gravitational effects are comparably fast to compute, baryonic properties in simulated galaxies require complex hydrodynamic simulations that are computationally costly to run. We explore the merging of an extended version of the equilibrium model, an analytic formalism describing the evolution of the stellar, gas, and metal content of galaxies, into a machine learning framework. In doing so, we are able to recover more properties than the analytic formalism alone can provide, creating a high-speed hydrodynamic simulation emulator that populates galactic dark matter haloes in N-body simulations with baryonic properties. While there exists a trade-off between the reached accuracy and the speed advantage this approach offers, our results outperform an approach using only machine learning for a subset of baryonic properties. We demonstrate that this novel hybrid system enables the fast completion of dark matter-only information by mimicking the properties of a full hydrodynamic suite to a reasonable degree, and discuss the advantages and disadvantages of hybrid versus machine learning-only frameworks. In doing so, we offer an acceleration of commonly deployed simulations in cosmology.
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