scholarly journals Galactic ionizing photon budget during the epoch of reionization in the Cosmic Dawn II simulation

2020 ◽  
Vol 496 (4) ◽  
pp. 4342-4357 ◽  
Author(s):  
Joseph S W Lewis ◽  
Pierre Ocvirk ◽  
Dominique Aubert ◽  
Jenny G Sorce ◽  
Paul R Shapiro ◽  
...  

ABSTRACT Cosmic Dawn 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 (∼100 Mpc) to model global reionization while resolving the formation of all galactic haloes above ${\sim}10^8 \, {\rm M}_{\odot }$. Cell transmission inside haloes is bi-modal – ionized cells are transparent, while neutral cells absorb the photons their stars produce – and the halo escape fraction fesc reflects the balance of star formation rate (SFR) between these modes. The latter is increasingly prevalent at higher halo mass, driving down fesc (we provide analytical fits to our results), whereas halo escape luminosity, proportional to fesc × SFR, increases with mass. Haloes with dark matter masses within $6\times 10^{8} \, {\rm M}_{\odot }\lt M_{\rm halo}\lt 3 \times 10^{10} \, {\rm M}_{\odot }$ produce ∼80 per cent of the escaping photons at z = 7, when the universe is 50 per cent ionized, making them the main drivers of cosmic reionization. Less massive haloes, though more numerous, have low SFRs and contribute less than 10 per cent of the photon budget then, despite their high fesc. High-mass haloes are too few and too opaque, contributing <10 per cent 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, xH i = 0.9, $M_{\rm halo}\lt 5\times 10^9 \, {\rm M}_{\odot }$ haloes contributed ∼80 per cent). Galaxies with UV magnitudes MAB1600 between −12 and −19 dominated reionization between z = 6 and 8.

2019 ◽  
Vol 15 (S352) ◽  
pp. 234-238
Author(s):  
Donatella Romano ◽  
Zhi-Yu Zhang ◽  
Francesca Matteucci ◽  
Rob J. Ivison ◽  
Padelis P. Papadopoulos

AbstractDetermining the shape of the stellar initial mass function (IMF) and whether it is constant or varies in space and time is the Holy Grail of modern astrophysics, with profound implications for all theories of star and galaxy formation. On a theoretical ground, the extreme conditions for star formation (SF) encountered in the most powerful starbursts in the Universe are expected to favour the formation of massive stars. Direct methods of IMF determination, however, cannot probe such systems, because of the severe dust obscuration affecting their starlight. The next best option is to observe CNO bearing molecules in the interstellar medium at millimetre/ submillimetre wavelengths, which, in principle, provides the best indirect evidence for IMF variations. In this contribution, we present our recent findings on this issue. First, we reassess the roles of different types of stars in the production of CNO isotopes. Then, we calibrate a proprietary chemical evolution code using Milky Way data from the literature, and extend it to discuss extragalactic data. We show that, though significant uncertainties still hamper our knowledge of the evolution of CNO isotopes in galaxies, compelling evidence for an IMF skewed towards high-mass stars can be found for galaxy-wide starbursts. In particular, we analyse a sample of submillimetre galaxies observed by us with the Atacama Large Millimetre Array at the peak of the SF activity of the Universe, for which we measure 13C/18O⋍1. This isotope ratio is especially sensitive to IMF variations, and is little affected by observational uncertainties. At the end, ongoing developments of our work are briefly outlined.


1987 ◽  
Vol 117 ◽  
pp. 413-413
Author(s):  
Richard B. Larson

Current data on the luminosity function of nearby stars allow the possibility that the stellar initial mass function (IMF) is double-peaked and that the star formation rate (SFR) has decreased substantially with time. It is then possible to account for all of the unseen mass in the solar vicinity as stellar remnants. A model for the solar neighborhood has been constructed in which the IMF is bimodal, the SFR is constant for the low-mass mode and strongly decreasing for the high-mass mode, and the mass in remnants is equal to the column density of unseen matter; this model is found to be consistent with all of the available constraints on the evolution and stellar content of the solar neighborhood. In particular, the observed chemical evolution is satisfactorily reproduced without infall. The total SFR in the model decreases roughly with the 1.4 power of the gas content, which is more plausible than the nearly constant SFR required by models with a monotonic IMF.


2020 ◽  
Vol 643 ◽  
pp. A8 ◽  
Author(s):  
C. Gruppioni ◽  
M. Béthermin ◽  
F. Loiacono ◽  
O. Le Fèvre ◽  
P. Capak ◽  
...  

Aims. We present the detailed characterisation of a sample of 56 sources serendipitously detected in ALMA band 7 as part of the ALMA Large Program to INvestigate CII at Early Times (ALPINE). These sources, detected in COSMOS and ECDFS, have been used to derive the total infrared luminosity function (LF) and to estimate the cosmic star formation rate density (SFRD) up to z ≃ 6. Methods. We looked for counterparts of the ALMA sources in all the available multi-wavelength (from HST to VLA) and photometric redshift catalogues. We also made use of deeper UltraVISTA and Spitzer source lists and maps to identify optically dark sources with no matches in the public catalogues. We used the sources with estimated redshifts to derive the 250 μm rest-frame and total infrared (8–1000 μm) LFs from z ≃ 0.5 to 6. Results. Our ALMA blind survey (860 μm flux density range: ∼0.3–12.5 mJy) allows us to further push the study of the nature and evolution of dusty galaxies at high-z, identifying luminous and massive sources to redshifts and faint luminosities never probed before by any far-infrared surveys. The ALPINE data are the first ones to sample the faint end of the infrared LF, showing little evolution from z ≃ 2.5 to z ≃ 6, and a “flat” slope up to the highest redshifts (i.e. 4.5 <  z <  6). The SFRD obtained by integrating the luminosity function remains almost constant between z ≃ 2 and z ≃ 6, and significantly higher than the optical or ultra-violet derivations, showing a significant contribution of dusty galaxies and obscured star formation at high-z. About 14% of all the ALPINE serendipitous continuum sources are found to be optically and near-infrared (near-IR) dark (to a depth Ks ∼ 24.9 mag). Six show a counterpart only in the mid-IR and no HST or near-IR identification, while two are detected as [C II] emitters at z ≃ 5. The six HST+near-IR dark galaxies with mid-IR counterparts are found to contribute about 17% of the total SFRD at z ≃ 5 and to dominate the high-mass end of the stellar mass function at z >  3.


1999 ◽  
Vol 190 ◽  
pp. 8-14
Author(s):  
F.D.A. Hartwick

We use observations and evolutionary models of local objects to interpret a recent determination of the star-formation history of the universe. By fitting the global star-formation rate, the model predicts the ratio of spheroid to disk mass of ~1, an intergalactic medium (IGM) whose mass is ~2.3 times the mass in stars, and whose metallicity is ~0.1 Z⊙.


2019 ◽  
Vol 486 (2) ◽  
pp. 1718-1740 ◽  
Author(s):  
Genaro Suárez ◽  
Juan José Downes ◽  
Carlos Román-Zúñiga ◽  
Miguel Cerviño ◽  
César Briceño ◽  
...  

Abstract The stellar initial mass function (IMF) is an essential input for many astrophysical studies but only in a few cases has it been determined over the whole cluster mass range, limiting the conclusions about its nature. The 25 Orionis group (25 Ori) is an excellent laboratory for investigating the IMF across the entire mass range of the population, from planetary-mass objects to intermediate/high-mass stars. We combine new deep optical photometry with optical and near-infrared data from the literature to select 1687 member candidates covering a 1.1° radius area in 25 Ori. With this sample we derived the 25 Ori system IMF from 0.012 to 13.1 M⊙. This system IMF is well described by a two-segment power law with Γ = −0.74 ± 0.04 for m &lt; 0.4 M⊙ and Γ = 1.50 ± 0.11 for m ≥ 0.4 M⊙. It is also well described over the whole mass range by a tapered power-law function with Γ = 1.10 ± 0.09, mp = 0.31 ± 0.03 and β = 2.11 ± 0.09. The best lognormal representation of the system IMF has mc = 0.31 ± 0.04 and σ = 0.46 ± 0.05 for m &lt; 1 M⊙. This system IMF does not present significant variations with the radii. We compared the resultant system IMF as well as the brown dwarf/star ratio of 0.16 ± 0.03 that we estimated for 25 Ori with that of other stellar regions with diverse conditions and found no significant discrepancies. These results support the idea that general star-formation mechanisms are probably not strongly dependent on environmental conditions. We found that the substellar and stellar objects in 25 Ori do not have any preferential spatial distributions and confirmed that 25 Ori is a gravitationally unbound stellar association.


2019 ◽  
Vol 14 (S351) ◽  
pp. 204-207
Author(s):  
Jun Kumamoto ◽  
Michiko S. Fujii ◽  
Ataru Tanikawa

AbstractGravitational wave direct detections suggest that 30 M⊙ binary black holes (BBHs) commonly exist in the universe. One possible formation scenario of such BBHs is dynamical three-body encounters in dense star clusters. We performed a series of direct N-body simulations with a mass of 2500 and 10000 M⊙ and found a new channel for the formation of BBHs which is dominant in open clusters. In open clusters, the core-collapse time is shorter than in globular clusters, and therefore massive main-sequence (MS) binaries can form before they evolve to BHs. These MS binaries experience common envelope evolution and evolve to hard BBHs, which can merge within the Hubble time. The number of BBH mergers per unit mass obtained from our simulations reached 20–50 % of that for globular clusters, assuming an initial cluster mass function. Thus, open clusters can be a dominant formation site of hard BBHs.


1995 ◽  
Vol 164 ◽  
pp. 389-389
Author(s):  
M. Haywood ◽  
A.C. Robin ◽  
O. Bienaymé

We have analyse star-count data in the direction of the Galactic Poles using a model of stellar population synthesis (Robin & Crézé (1986), Bienaymé, Robin & Crézé (1987)). The HR diagram for disc stars in the model is computed for a given star formation rate history and initial mass function (Haywood, 1994). In a paper submitted to A&A (Haywood et al.), we give a detailed investigation of the effects of these two functions on the simulated star-counts, and compare these with observed V, B-V data from V=5 to 22. We have obtained new constraints on the SFR, which we show has remained constant (to within a factor <3) since the disc formation, and on the IMF in the intermediate mass range (1-2 M⊙). Finally, we also obtain new constraint on the increase of vertical velocity dispersion with age. We state that if the disc does not containt any dynamically important dark mass, then this relation saturates at value smaller than 21 km.s−1.


2010 ◽  
Vol 6 (S275) ◽  
pp. 3-10
Author(s):  
I. Felix Mirabel

AbstractSignificant historic cosmic evolution for the formation rate of stellar black holes is inferred from current theoretical models of the evolution of massive stars, the multiple observations of compact stellar remnants in the near and distant universe, and the cosmic chemical evolution. The mean mass of stellar black holes, the fraction of black holes/neutron stars, and the fraction of black hole high mass X-ray binaries (BH-HMXBs)/solitary black holes increase with redshift. The energetic feedback from large populations of BH-HMXBs form in the first generations of star burst galaxies has been overlooked in most cosmological models of the reionization epoch of the universe. The powerful radiation, jets, and winds from BH-HMXBs heat the intergalactic medium over large volumes of space and keep it ionized until AGN take over. It is concluded that stellar black holes constrained the properties of the faintest galaxies at high redshifts. I present here the theoretical and observational grounds for the historic cosmic evolution of stellar black holes. Detailed calculations on their cosmic impact are presented elsewhere (Mirabel, Dijkstra, Laurent, Loeb, & Pritchard 2011).


Author(s):  
Pierre Ocvirk ◽  
Joseph S W Lewis ◽  
Nicolas Gillet ◽  
Jonathan Chardin ◽  
Dominique Aubert ◽  
...  

Abstract The high redshift Lyman-α forest, in particular the Gunn-Peterson trough, is the most unambiguous signature of the neutral to ionized transition of the intergalactic medium (IGM) taking place during the Epoch of Reionization (EoR). Recent studies have shown that reproducing the observed Lyman-α opacity distributions after overlap required a non-monotonous evolution of cosmic emissivity: rising, peaking at z∼6, and then decreasing onwards to z=4. Such an evolution is puzzling considering galaxy buildup and the cosmic star formation rate are still continously on the rise at these epochs. Here, we use new RAMSES-CUDATON simulations to show that such a peaked evolution may occur naturally in a fully coupled radiation-hydrodynamical framework. In our fiducial run, cosmic emissivity at z&gt;6 is dominated by a low mass (${\rm M_{DM}}&lt;2 \times 10^9 \rm M_{\odot }$), high escape fraction halo population, driving reionization, up to overlap. Approaching z=6, this population is radiatively suppressed due to the rising ionizing UV background, and its emissivity drops. In the meantime, the high mass halo population builds up and its emissivity rises, but not fast enough to compensate the dimming of the low mass haloes, because of low escape fractions. The combined ionizing emissivity of these two populations therefore naturally results in a rise and fall of the cosmic emissivity, from z=12 to z=4, with a peak at z∼6. An alternative run, which features higher escape fractions for the high mass haloes and later suppression at low mass, leads to overshooting the ionizing rate, over-ionizing the IGM and therefore too low Lyman-α opacities.


2020 ◽  
Vol 500 (1) ◽  
pp. L37-L41
Author(s):  
Saili Dutta ◽  
Nishikanta Khandai

ABSTRACT We present the conditional H i (neutral hydrogen) mass function (HIMF) conditioned on observed optical properties, Mr (r-band absolute magnitude), and Cur (u − r colour), for a sample of 7709 galaxies from Arecibo Legacy Fast ALFA (40 per cent data release – α.40) which overlaps with a common volume in SDSS DR7. Based on the conditional HIMF, we find that the luminous red, luminous blue, and faint blue populations dominate the total HIMF at the high-mass end, knee, and the low-mass end, respectively. We use the conditional HIMF to derive the underlying distribution function of ΩH i (H i density parameter), p(ΩH i), in the colour–magnitude plane of galaxies. The distribution, p(ΩH i), peaks in the blue cloud at $\mathit{ M_{{r}}}^{\text{max}}=-19.25, \mathit{ C_{{ur}}}^{\text{max}}=1.44$ but is skewed. It has a long tail towards faint blue galaxies, and luminous red galaxies. We argue that p(ΩH i) can be used to reveal the underlying relation between cold gas, stellar mass, and the star formation rate in an unbiased way, that is, the derived relation does not suffer from survey or sample selection.


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