ﻻ يوجد ملخص باللغة العربية
We examine spectral properties of the ionising continua, the Lyman-break, and the Ly-a and HeII 1640 recombination lines in starbursts. The transition from primordial galaxies to currently observed metallicities, is examined. For the average properties of starbursts, the main findings are: 1) The Lyman continuum flux increases with decreasing metallicity. For a universal Salpeter IMF from 1-100 Msun the enhancement reaches typically a factor of ~3 between solar metallicity and Pop III objects. 2) While for metallicities Z >~ 1/50 Zsun the amplitude of the Lyman-break depends little on Z, a reduction by a factor ~2 is found at lower Z, due to the strong increase of the average stellar temperature. 3) Using theoretical models and empirical constraints we discuss the expected evolution of the hardness of He+ to H ionising photons with metallicity and possible uncertainties. We also provide a simple estimate of the possible impact of hot WR like stars on Q(He+)/Q(H) at very low metallicities. 4) Calibrations for star formation rate determinations from various recombination lines at all metallicities and for various IMFs are derived. For young bursts the maximum Ly-a equivalent width is shown to increase strongly with decreasing metallicity for the same IMF. However, for well known reasons, the Ly-a emission predicted likely represents an upper limit. Non-negligible HeII 1640 emission due to stellar photoionisation appears to be limited to very low metallicities and Population III objects.(abridged abstract)
We present a new photometric search for high-z galaxies hosting Population III (PopIII) stars based on deep intermediate-band imaging observations obtained in the Subaru Deep Field (SDF), by using Suprime-Cam on the Subaru Telescope. By combining our
Population III galaxies, made partly or exclusively of metal-free stars, are predicted to exist at high redshifts and may produce very strong Lya emission. A substantial fraction of these Lya photons are likely absorbed in the intergalactic medium at
Deep optical spectroscopic surveys of galaxies provide us a unique opportunity to investigate rest-frame ultra-violet (UV) emission line properties of galaxies at ${z sim 2-4.5}$. Here we combine VLT/MUSE Guaranteed Time Observations of the Hubble De
Using the VLT we have obtained high quality spectra of about 70 high redshift (1- 4.6) galaxies within the FORS Deep Field (FDF). As expected most of them turn out to be (bright) starburst galaxies and the observed spectra agree with synthetic ones.
Recent literature suggests that there are two modes through which galaxies grow their stellar mass - a normal mode characterized by quasi-steady star formation, and a highly efficient starburst mode possibly triggered by stochastic events such as gal