Understanding the molecular content of galaxies is a critical problem in star formation and galactic evolution. Here we present a new method, based on a Stromgren-type analysis, to calculate the amount of HI that surrounds a molecular cloud irradiated by an isotropic radiation field. We consider both planar and spherical clouds, and H_2 formation either in the gas phase or catalyzed by dust grains. Under the assumption that the transition from atomic to molecular gas is sharp, our method gives the solution without any reference to the photodissociation cross section. We test our results for the planar case against those of a PDR code, and find typical accuracies of about 10%. Our results are also consistent with the scaling relations found in Paper I of this series, but they apply to a wider range of physical conditions. We present simple, accurate analytic fits to our results that are suitable for comparison to observations and to implementation in numerical and semi-analytic models.
Observational measures of the primordial helium mass fraction, $Y_{\rm P}$, are of interest for cosmology and fundamental particle physics. Current measures obtained from H II regions agree with the Standard Model prediction to approximately 1% precision, although these determinations may be affected by systematic uncertainties. This possibility can only be tested by independently measuring the helium abundance in new ways. Here, we propose a novel method to obtain a measurement of $Y_{\rm P}$ using hydrogen and helium recombination line emission from RELHICs: pristine, gas-rich but star-free …
In the last decade, it has become clear that the dust-enshrouded star formation contributes significantly to early galaxy evolution. Detection of dust is therefore essential in determining the properties of galaxies in the high-redshift universe. This requires observations at the (sub-)millimeter wavelengths. Unfortunately, sensitivity and background confusion of single dish observations on the one hand, and mapping efficiency of interferometers on the other hand, pose unique challenges to observers. One promising route to overcome these difficulties is intensity mapping of fluctuations which …
The formation of compact dusty clouds in diffuse interstellar medium (ISM) has been recently proposed and studied by Tsytovich et al. (2014). In the present paper, an effect of the clouds on the rate of H$\to$H$_2$ transition in the ISM is examined. We discuss the mechanisms leading to the formation of the clouds and the creation of gaseous clumps around them, analyze the main processes determining the efficiency of the recombination of atomic hydrogen on dust grains, and estimate the expected enhancement of the global H$_2$ formation due to the presence of the clouds. In conclusion, we argue …
Evidence for dust around supermassive black holes (SMBHs) in the early Universe is strongly suggested by recent observations. However, the accretion mechanism of SMBHs in dusty gas is not well understood yet. We investigate the growth of intermediate-mass black-holes (IMBHs) of $\sim 10^{5}~M_{\odot}$ in dusty clouds by using one-dimensional radiative-hydrodynamics simulations. We find that the accretion of dusty gas onto IMBHs proceeds gently with small fluctuations of the accretion rate, whereas that of pristine gas causes more violent periodic bursts. At dust-to-gas mass ratios similar to t…
We present ALMA, NOEMA, and IRAM-30m/EMIR observations of the high-density tracer molecules HCN, HCO+, and HNC in three of the brightest lensed dusty star-forming galaxies at z~3-3.5, part of the Planck's Dusty GEMS sample, to probe the gas reservoirs closely associated with their exceptional levels of star formation. We obtain robust detections of ten emission lines between J_up=4 and 6, as well as several additional flux upper limits. In PLCK_G244.8+54.9, the brightest source at z=3.0, the HNC(5-4) line emission at 0.1" resolution, together with other spatially-integrated line profiles, sugg…
The first billion years in the evolution of the Universe mark the formation of the first stars, black holes and galaxies. The radiation from the first galaxies plays an important role in determining the final state of primordial gas collapsing in a neighboring halo. This is due to the fact that the primary coolant for primordial gas is molecular hydrogen, which can be dissociated into atomic hydrogen by Lyman-Werner photons in the energy range $11.2 - 13.6$~eV. While cooling by molecular hydrogen leads to Pop. III star formation, cooling by atomic hydrogen can lead to the formation of a superm…
We investigate a sample of 152 dusty sources at 1:5 < z < 2:5 to understand the connection of enhanced Star-Formation-Rate (SFR) and Black-Hole-Accretion-Rate (BHAR). The sources are Herschel-selected, having stellar masses M*>10^10Msun and SFR (100-1000Msun/yr) elevated(>4?) above the star-forming "main sequence", classifying them as Starbursts (SB). Through a multiwavelength fitting approach (including a dusty torus component), we divided the sample into active SBs (dominated by an AGN emission, SBs-AGN, ? 23% of the sample) and purely star-forming SBs (SBs-SFR). We visually inspected their …
The survey for DUST In Nearby Galaxies with Spitzer (DUSTiNGS) has identified hundreds of candidate dust-producing Asymptotic Giant Branch (AGB) stars in several nearby metal-poor galaxies. We have obtained multi-epoch follow-up observations for these candidates with the Spitzer Space Telescope and measured their infrared (IR) lightcurves. This has allowed us to confirm their AGB nature and investigate pulsation behavior at very low metallicity. We have obtained high-confidence pulsation periods for 88 sources in seven galaxies. We have confirmed DUSTiNGS variable star candidates with a 20% su…
In this paper, an investigation on the relative importance of the thermal gas, radiation, and (minimum-energy) magnetic pressures around $\approx$200 star-forming regions in a sample of nearby normal and luminous infrared galaxies is presented. Given the range of galaxy distances, pressure estimates are made on spatial scales spanning $\sim$0.1$-3$kpc. The ratio of thermal gas-to-radiation pressures does not appear to significantly depend on star formation rate surface density ($Σ_{\rm SFR}$), but exhibits a steady decrease with increasing physical size of the aperture over which the quantitie…
The abundance of molecular hydrogen (H2), the primary coolant in primordial gas, is critical for the thermodynamic evolution and star-formation histories in early protogalaxies. Determining the photodissociation rate of H2 by an incident Lyman-Werner (LW) flux is thus crucial, but prohibitively expensive to calculate on the fly in simulations. The rate is sensitive to the H2 rovibrational distribution, which in turn depends on the gas density, temperature, and incident LW radiation field. We use the publicly available cloudy package to model primordial gas clouds and compare exact photodissoci…
We measure statistically anisotropic signatures imprinted in three-dimensional galaxy clustering using bipolar spherical harmonics (BipoSHs) in both Fourier space and configuration space. We then constrain a well-known quadrupolar anisotropy parameter $g_{2M}$ in the primordial power spectrum, parametrized by $P(\vec{k}) = \bar{P}(k) [ 1 + \sum_{M} g_{2M} Y_{2M}(\hat{k}) ]$, with $M$ determining the direction of the anisotropy. Such an anisotropic signal is easily contaminated by artificial asymmetries due to specific survey geometry. We precisely estimate the contaminated signal and finally s…
Vz-GAL Dusty Star-Forming Galaxies: Revisiting the CO-H2 Conversion Factor Tension
International Max Planck Research School (IMPRS) for Astronomy & Astrophysics（国际天文学与天体物理学马克斯·普朗克高等研究所）；Institute for Astrophysics, University of Cologne（科隆大学天体物理研究所）；Max Planck Institute for Radio Astronomy (MPIfR)（马克斯·普朗克射电天文研究所）；Departement of Space, Earth & Environment, Chalmers University of Technology（查尔姆斯理工大学空间、地球与环境系）；Leiden Observatory, Leiden University（莱顿大学莱顿天文台）；Université de Strasbourg, CNRS, Observatoire astronomique de Strasbourg（斯特拉斯堡大学，法国国家科学研究中心，斯特拉斯堡天文台）；Sorbonne Université, Université Paris 6 and CNRS, Institut d’Astrophysique de Paris（索邦大学，巴黎第六大学及法国国家科学研究中心，巴黎天体物理研究所）；Department of Physics and Astronomy, Rutgers University—New Brunswick（罗格斯大学（新不伦瑞克校区）物理与天文学系）；Department of Physics and Astronomy, University of the Western Cape（西开普大学物理与天文学系）；Institut de Radioastronomie Millimétrique (IRAM)（毫米波射电天文研究所）
We present a new method for estimating the H2 cooling rate in the optically thick regime in simulations of primordial star formation. Our new approach is based on the TreeCol algorithm, which projects matter distributions onto a spherical grid to create maps of column densities for each fluid element in the computational domain. We have improved this algorithm by using the relative gas velocities, to weight the individual matter contributions with the relative spectral line overlaps, in order to properly account for the Doppler effect. We compare our new method to the widely used Sobolev appro…
The fraction of stars in binary systems within star clusters is important for their evolution, but what proportion of binaries form by dynamical processes after initial stellar accretion remains unknown. In previous work, we showed that dynamical interactions alone produced too few low-mass binaries compared to observations. We therefore implement an initial population of binaries in the coupled MHD and direct N-body star cluster formation code Torch. We compare simulations with, and without, initial binary populations and follow the dynamical evolution of the binary population in both sets of…
