اشترك بالحزمة الذهبية واحصل على وصول غير محدود شمرا أكاديميا
تسجيل مستخدم جديدLyman-$alpha$ as a tracer of cosmic reionisation in the SPHINX radiation-hydrodynamics cosmological simulation
78
0
0.0
(
0
)
اسأل ChatGPT حول البحث
ﻻ يوجد ملخص باللغة العربية
The Ly$alpha$ emission line is one of the most promising probes of cosmic reionisation but isolating the signature of a change in the ionisation state of the IGM is challenging because of intrinsic evolution and internal radiation transfer effects. We present the first study of the evolution of Ly$alpha$ emitters (LAE) during the epoch of reionisation based on a full radiation-hydrodynamics cosmological simulation that is able to capture both the large-scale process of reionisation and the small-scale properties of galaxies. We predict the Ly$alpha$ emission of galaxies in the $10^3$ cMpc$^3$ SPHINX simulation at $6leq zleq9$ by computing the full Ly$alpha$ radiation transfer from ISM to IGM scales. SPHINX is able to reproduce many observational constraints such as the UV/Ly$alpha$ luminosity functions and stellar mass functions at z $geq$ 6 for the dynamical range probed by our simulation ($M_{rm 1500}gtrsim-18$, $L_{rm Lyalpha}lesssim10^{42}$ erg/s, $M_{star}lesssim10^9$ M$_{odot}$). As intrinsic Ly$alpha$ emission and internal Ly$alpha$ escape fractions barely evolve from $z=6$ to 9, the observed suppression of Ly$alpha$ luminosities with increasing redshift is fully attributed to IGM absorption. For most observable galaxies ($M_{rm 1500}lesssim-16$), the Ly$alpha$ line profiles are slightly shifted to the red due to internal radiative transfer effects which mitigates the effect of IGM absorption. Overall, the enhanced Ly$alpha$ suppression during reionisation traces the IGM neutral fraction $x_{rm HI}$ well but the predicted amplitude of this reduction is a strong function of the Ly$alpha$ peak shift, which is set at ISM/CGM scales. We find that a large number of LAEs could be detectable in very deep surveys during reionisation when $x_{rm HI}$ is still $approx 50%$.
قيم البحث
اقرأ أيضاً
We use the Karl G. Jansky Very Large Array (VLA) to conduct a high-sensitivity survey of neutral hydrogen (HI) absorption in the Milky Way. In combination with corresponding HI emission spectra obtained mostly with the Arecibo Observatory, we detect
a widespread warm neutral medium (WNM) component with excitation temperature <Ts>= 7200 (+1800,-1200) K (68% confidence). This temperature lies above theoretical predictions based on collisional excitation alone, implying that Ly-{alpha} scattering, the most probable additional source of excitation, is more important in the interstellar medium (ISM) than previously assumed. Our results demonstrate that HI absorption can be used to constrain the Ly-{alpha} radiation field, a critical quantity for studying the energy balance in the ISM and intergalactic medium yet notoriously difficult to model because of its complicated radiative transfer, in and around galaxies nearby and at high redshift.
We examine Lyman continuum (LyC) leakage through H II regions regulated by turbulence and radiative feedback in a giant molecular cloud in the context of fully-coupled radiation hydrodynamics (RHD). The physical relations of the LyC escape with H I c
overing fraction, kinematics, spectral hardness, and the emergent Lyman-$alpha$ (Ly$alpha$) line profiles are studied using a series of RHD turbulence simulations performed with RAMSES-RT. The turbulence-regulated mechanism allows ionizing photons to leak out at early times before the onset of supernova feedback. The LyC photons escape through turbulence-generated low column density channels which are evacuated efficiently by radiative feedback via photoheating-induced shocks across the D-type ionization fronts. Ly$alpha$ photons funnel through the photoionized channels along the paths of LyC escape, resulting in a diverse Ly$alpha$ spectral morphology including narrow double-peaked profiles. The Ly$alpha$ peak separation is controlled by the residual H I column density of the channels and the line asymmetry correlates with the porosity and multiphase structure of the H II region. This mechanism through the turbulent H II regions can naturally reproduce the observed Ly$alpha$ spectral characteristics of some of LyC-leaking galaxies. This RHD turbulence-origin provides an appealing hypothesis to explain high LyC leakage from very young ($sim3$ Myr) star-forming galaxies found in the local Universe without need of extreme galactic outflows nor supernova feedback. We discuss the implications of the turbulent H II regions on other nebular emission lines and a possible observational test with the Magellanic System and local blue compact dwarf galaxies as analogs of reionization-era systems.
Cosmic Dawn II (CoDa II) is a new, fully-coupled radiation-hydrodynamics simulation of cosmic reionization and galaxy formation and their mutual impact, to redshift $z < 6$. With $4096^3$ particles and cells in a 94 Mpc box, it is large enough to mod
el global reionization and its feedback on galaxy formation while resolving all haloes above $10^8$ M$_{odot}$. Using the same hybrid CPU-GPU code RAMSES-CUDATON as CoDa I in Ocvirk et al. (2016), CoDa II modified and re-calibrated the subgrid star-formation algorithm, making reionization end earlier, at $z gtrsim 6$, thereby better matching the observations of intergalactic Lyman-alpha opacity from quasar spectra and electron-scattering optical depth from cosmic microwave background fluctuations. CoDa II predicts a UV continuum luminosity function in good agreement with observations of high-z galaxies, especially at $z = 6$. As in CoDa I, reionization feedback suppresses star formation in haloes below $sim 2 times 10^9$ M$_{odot}$, though suppression here is less severe, a possible consequence of modifying the star-formation algorithm. Suppression is environment-dependent, occurring earlier (later) in overdense (underdense) regions, in response to their local reionization times. Using a constrained realization of $Lambda$CDM constructed from galaxy survey data to reproduce the large-scale structure and major objects of the present-day Local Universe, CoDa II serves to model both global and local reionization. In CoDa II, the Milky Way and M31 appear as individual islands of reionization, i.e. they were not reionized by the progenitor of the Virgo cluster, nor by nearby groups, nor by each other.
Cosmic Dawn (CoDa) II yields the first statistically-meaningful determination of the relative contribution to reionization by galaxies of different halo mass, from a fully-coupled radiation-hydrodynamics simulation of the epoch of reionization large
enough ($sim$ 100 Mpc) to model global reionization while resolving the formation of all galactic halos above $sim 10^8 M_odot$. Cell transmission inside high-mass haloes is bi-modal -- ionized cells are transparent, while neutral cells absorb the photons their stars produce - and the halo escape fraction $f_{esc}$ reflects the balance of star formation rate (SFR) between these modes. The latter is increasingly prevalent at higher halo mass, driving down $f_{esc}$ (we provide analytical fits to our results), whereas halo escape luminosity, proportional to $f_{esc} times$SFR, increases with mass. Haloes with dark matter masses within $6.10^{8} M_odot < M_h < 3.10^{10} M_odot$ produce $sim 80$% of the escaping photons at z=7, when the Universe is 50% ionized, making them the main drivers of cosmic reionization. Less massive haloes, though more numerous, have low SFRs and contribute less than 10% of the photon budget then, despite their high $f_{esc}$. High mass haloes are too few and too opaque, contributing $<10$% despite their high SFRs. The dominant mass range is lower (higher) at higher (lower) redshift, as mass function and reionization advance together (e.g. at z$=8.5$, x$_{rm HI}=0.9$, $M_h < 5.10^9 M_odot$ haloes contributed $sim$80%). Galaxies with UV magnitudes $M_{AB1600}$ between $-12$ and $-19$ dominated reionization between z$=6$ and 8.
The decline in abundance of Lyman-$alpha$ (Ly$alpha$) emitting galaxies at $z gtrsim 6$ is a powerful and commonly used probe to constrain the progress of cosmic reionization. We use the CoDaII simulation, which is a radiation hydrodynamic simulation
featuring a box of $sim 94$ comoving Mpc side length, to compute the Ly$alpha$ transmission properties of the intergalactic medium (IGM) at $zsim 5.8$ to $7$. Our results mainly confirm previous studies, i.e., we find a declining Ly$alpha$ transmission with redshift and a large sightline-to-sightline variation. However, motivated by the recent discovery of blue Ly$alpha$ peaks at high redshift, we also analyze the IGM transmission on the blue side, which shows a rapid decline at $zgtrsim 6$ of the blue transmission. This low transmission can be attributed not only to the presence of neutral regions but also to the residual neutral hydrogen within ionized regions, for which a density even as low as $n_{rm HI}sim 10^{-9},mathrm{cm}^{-3}$ (sometimes combined with kinematic effects) leads to a significantly reduced visibility. Still, we find that $sim 5%$ of sightlines towards $M_{mathrm{1600AB}}sim -21$ galaxies at $zsim 7$ are transparent enough to allow a transmission of a blue Ly$alpha$ peak. We discuss our results in the context of the interpretation of observations.
سجل دخول لتتمكن من نشر تعليقات
التعليقات
جاري جلب التعليقات
سجل دخول لتتمكن من متابعة معايير البحث التي قمت باختيارها
