SImulator of GAlaxy Millimetre/submillimetre Emission (SIGAME): CO emission from massive z=2 main-sequence galaxies

We present SIGAME (SImulator of GAlaxy Millimetre/submillimetre Emission), a new numerical code designed to simulate the 12CO rotational line emission spectrum of galaxies. Using sub-grid physics recipes to post-process the outputs of smoothed particle hydrodynamics (SPH) simulations, a molecular gas phase is condensed out of the hot and partly ionized SPH gas. The gas is subjected to far-UV radiation fields and cosmic ray ionization rates which are set to scale with the local star formation rate volume density. Level populations and radiative transport of the CO lines are solved with the 3-D radiative transfer code LIME. We have applied SIGAME to cosmological SPH simulations of three disc galaxies at z=2 with stellar masses in the range ~(0.5-2)x10^11 Msun and star formation rates ~40-140 Msun/yr. Global CO luminosities and line ratios are in agreement with observations of disc galaxies at z~2 up to and including J=3-2 but falling short of the few existing J=5-4 observations. The central 5 kpc regions of our galaxies have CO 3-2/1-0 and 7-6/1-0 brightness temperature ratios of ~0.55-0.65 and ~0.02-0.08, respectively, while further out in the disc the ratios drop to more quiescent values of ~0.5 and <0.01. Global CO-to-H2 conversion (alpha_CO) factors are ~=1.5 Msun*pc^2/(K km s/1), i.e. ~2-3 times below typically adopted values for disc galaxies, and alpha_CO increases with radius, in agreement with observations of nearby galaxies. Adopting a top-heavy Giant Molecular Cloud (GMC) mass spectrum does not significantly change the results. Steepening the GMC density profile leads to higher global line ratios for J_up>=3 and CO-to-H2 conversion factors [~=3.6 Msun*pc^2/(K km/s)].Comment: 28 pages, 20 figures. Accepted for Publication in MNRAS. Substantial revisions from the previous version, including tests with model galaxies similar to the Milky Way. Improved figures and added table

Revisiting the [C ii]158��m line-intensity mapping power spectrum from the EoR using non-uniform line-luminosity scatter

Detecting the line-intensity mapping (LIM) signal from the galaxies of the Epoch of Reionization is an emerging tool to constrain their role in reionization. Ongoing and upcoming experiments target the signal fluctuations across the sky to reveal statistical and astrophysical properties of these galaxies via signal statistics, e.g., the power spectrum. Here, we revisit the [Cii]158m LIM power spectrum under non-uniform line-luminosity scatter, which has a halo-mass variation of statistical properties. Line-luminosity scatter from a cosmological hydrodynamic and radiative transfer simulation of galaxies at = 6 is considered in this study. We test the robustness of different model frameworks that interpret the impact of the line-luminosity scatter on the signal statistics. We use a simple power-law model to fit the scatter and demonstrate that the mean luminosity-halo mass correlation fit cannot preserve the mean intensity of the LIM signal (hence the clustering power spectrum) under non-uniform scatter. In our case, the mean intensity changes by ∼ 48 per cent compared to the mean correlation fit in contrast to the general case with semianalytic scatter. However, we find that the prediction for the mean intensity from the most-probable fit can be modelled robustly, considering the generalized and more realistic non-uniform scatter. We also explore the possibility of diminishing luminosity bias under non-uniform scatter, affecting the clustering power spectrum, although this phenomenon might not be statistically significant. Therefore, we should adopt appropriate approaches that can consistently interpret the LIM power spectrum from observations

Investigating the [C II\,{\rm \scriptsize II}]-to-H I\,{\rm \scriptsize I} conversion factor and the H I\,{\rm \scriptsize I} gas budget of galaxies at z≈6z\approx 6 with hydrodynamical simulations

One of the most fundamental baryonic matter components of galaxies is the neutral atomic hydrogen (H$\,{\rm \scriptsize I}$). At low redshifts, this component can be traced directly through the 21-cm transition, but to infer H$\,{\rm \scriptsize I}$ gas content of the most distant galaxies, a viable tracer is needed. We here investigate the fidelity of the fine structure transition of the ($^2P_{3/2} - ^2P_{1/3}$) transition of singly-ionized carbon [C$\,{\rm \scriptsize II}$] at $158\,\mu$m as a proxy for H$\,{\rm \scriptsize I}$ in a set simulated galaxies at $z\approx 6$, following the work by Heintz et al. (2021). We select 11,125 star-forming galaxies from the SIMBA simulations, with far-infrared line emissions post-processed and modeled within the SIGAME framework. We find a strong connection between [C$\,{\rm \scriptsize II}$] and H$\,{\rm \scriptsize I}$, with the relation between this [C$\,{\rm \scriptsize II}$]-to-H$\,{\rm \scriptsize I}$ relation ($\beta_{\rm [C\,{\rm \scriptsize II}]}$) being anti-correlated with the gas-phase metallicity of the simulated galaxies. We further use these simulations to make predictions for the total baryonic matter content of galaxies at $z\approx 6$, and specifically the HI gas mass fraction. We find mean values of $M_{\rm HI}/M_\star = 1.4$, and $M_{\rm HI}/M_{\rm bar,tot} = 0.45$. These results provide strong evidence for H$\,{\rm \scriptsize I}$ being the dominant baryonic matter component by mass in galaxies at $z\approx 6$.Comment: 7 pages, 3 figures. Accepted for publication by ApJ

Predictions of the L[CII]_{\rm[CII]}-SFR and [CII_{\rm II}] Luminosity Function at the Epoch of Reionization

We present the first predictions for the $L_{\rm [CII]}$ - SFR relation and [CII] luminosity function (LF) in the Epoch of Reionization (EoR) based on cosmological hydrodynamics simulations using the SIMBA suite plus radiative transfer calculations via S\'IGAME. The sample consists of 11,137 galaxies covering halo mass $\log M_{\rm halo}\in$[9, 12.4] $M_\odot$, star formation rate SFR$\in$[0.01, 330] $M_\odot$ yr$^{-1}$, and metallicity $<Z_{\rm gas}>_{\rm SFR}\in$[0.1, 0.9] $Z_\odot$. The simulated $L_{\rm [CII]}$-SFR relation is consistent with the range observed, but with a spread of $\simeq$0.3 dex at the high end of SFR ($>$100 $M_\odot$ yr$^{-1}$) and $\simeq$0.6 dex at the lower end, and there is tension between our predictions and the values of $L_{\rm [CII]}$ above 10$^{8.5}$ $L_\odot$ observed in some galaxies reported in the literature. The scatter in the $L_{\rm [CII]}$-SFR relation is mostly driven by galaxy properties, such that at a given SFR, galaxies with higher molecular gas mass and metallicity have higher $L_{\rm [CII]}$. The [CII] LF predicted by SIMBA is consistent with the upper limits placed by the only existing untargeted flux-limited [CII] survey at the EoR (ASPECS) and those predicted by semi-analytic models. We compare our results with existing models and discuss differences responsible for the discrepant slopes in the $L_{\rm [CII]}$-SFR relatiion.Comment: 19 pages, 14 figures, Accepted by Ap

Harmonic Infrared and Raman Spectra in Molecular Environments Using the Polarizable Embedding Model

We present a fully analytic approach to calculate infrared (IR) and Raman spectra of molecules embedded in complex molecular environments modeled using the fragment-based polarizable embedding (PE) model. We provide the theory for the calculation of analytic second-order geometric derivatives of molecular energies and first-order geometric derivatives of electric dipole moments and dipole–dipole polarizabilities within the PE model. The derivatives are implemented using a general open-ended response theory framework, thus allowing for an extension to higher-order derivatives. The embedding-potential parameters used to describe the environment in the PE model are derived through first-principles calculations, thus allowing a wide variety of systems to be modeled, including solvents, proteins, and other large and complex molecular environments. Here, we present proof-of-principle calculations of IR and Raman spectra of acetone in different solvents. This work is an important step toward calculating accurate vibrational spectra of molecules embedded in realistic environments

Challenges and Techniques for Simulating Line Emission

Modeling emission lines from the millimeter to the UV and producing synthetic spectra is crucial for a good understanding of observations, yet it is an art filled with hazards. This is the proceedings of “Walking the Line”, a 3-day conference held in 2018 that brought together scientists working on different aspects of emission line simulations, in order to share knowledge and discuss the methodology. Emission lines across the spectrum from the millimeter to the UV were discussed, with most of the focus on the interstellar medium, but also some topics on the circumgalactic medium. The most important quality of a useful model is a good synergy with observations and experiments. Challenges in simulating line emission are identified, some of which are already being worked upon, and others that must be addressed in the future for models to agree with observations. Recent advances in several areas aiming at achieving that synergy are summarized here, from micro-physical to galactic and circum-galactic scale

L’utilisation des réseaux sociaux (Snapchat, WhatsApp et Instagram) et le cyberbullying

100% des jeunes possèdent un téléphone portable, 99% ont un ordinateur et 97% ont accès à Internet (Waller et al., 2016). Ces nouveaux moyens technologiques font partie de notre quotidien. Depuis l’apparition de ces réseaux, un nouveau mouvement est né : le cyberbullying. Ce harcèlement par Internet consiste à l’utilisation de technologies modernes de communication afin de nuire aux autres de manière délibérée et agressive. Quand les jeunes arrivent en classe, ils apportent avec eux l’entier de leur vécu quotidien, familial ou encore émotionnel. Les problèmes liés à l’utilisation massive de ces réseaux font partie de notre quotidien d’enseignant. Malheureusement, les études faites jusqu’au jour d’aujourd’hui portent en majeure partie sur les élèves entre 13 ans et plus. Mais qu’en est-il des jeunes âgés entre 9 et 12 ans ? Notre travail de recherche porte donc sur l’utilisation des réseaux sociaux (Snapchat, Instagram et WhatsApp) et le cyberbullying. Deux outils différents ont été utilisés lors de cette recherche : des questionnaires afin d’avoir des résultats quantitatifs et deux entretiens afin d’avoir un point de vue qualitatif. Nos résultats montrent que WhatsApp est le réseau social le plus utilisé, suivi d’Instagram en deuxième position et finalement de Snapchat. Les élèves considèrent le nombre de dangers et de conflits sur les réseaux comme très faibles. Ils avouent tout de même donner plus d’informations personnelles sur WhatsApp que sur les autres réseaux choisis dans l’étude. Concernant leur vision du contrôle des parents, ils l’estiment très faible. Cependant, il s’agit uniquement de leur avis, il serait intéressant de savoir la réalité des faits en interrogeant les parents. Les deux sujets interrogés savent définir le cyberbullying et connaissent les différents acteurs agissant au sein de cette forme de harcèlement. Ils sont également conscients des différents risques, conséquences ou sentiments que peut ressentir une cyber-victime mais n’abordent pas du tout ceux concernant le témoin ou le cyber-harceleur. En conclusion, notre recherche montre que les réseaux sociaux font partie intégrante du quotidien d’un grand nombre d’élèves. Il est donc essentiel que les enseignants s’interrogent sur les moyens de gérer les problèmes que ceux-ci peuvent amener en classe mais également les moyens de les éviter