Reionization in the early Universe is likely driven by dwarf galaxies. Using cosmological radiation-hydrodynamic simulations, we study star formation and the escape of Lyman continuum (LyC) photons ...from mini-haloes with $${M_{\rm halo}}\lesssim 10^8\,{\rm M_{\odot }}$$. Our simulations include a new thermo-turbulent star formation model, non-equilibrium chemistry and relevant stellar feedback processes (photoionization by young massive stars, radiation pressure and mechanical supernova explosions). We find that feedback reduces star formation very efficiently in mini-haloes, resulting in the stellar mass consistent with the slope and normalization reported in Kimm & Cen and the empirical stellar mass-to-halo mass relation derived in the local Universe. Because star formation is stochastic and dominated by a few gas clumps, the escape fraction in mini-haloes is generally determined by radiation feedback (heating due to photoionization), rather than supernova explosions. We also find that the photon number-weighted mean escape fraction in mini-haloes is higher (∼20–40 per cent) than that in atomic-cooling haloes, although the instantaneous fraction in individual haloes varies significantly. The escape fraction from Pop III stars is found to be significant ( ≳ 10 per cent) only when the mass is greater than ∼100 M_⊙. Based on simple analytic calculations, we show that LyC photons from mini-haloes are, despite their high escape fractions, of minor importance for reionization due to inefficient star formation. We confirm previous claims that stars in atomic-cooling haloes with masses $$10^8\,{\rm M_{\odot }}\lesssim {M_{\rm halo}}\lesssim 10^{11}\,{\rm M_{\odot }}$$ are likely to be the most important source of reionization.
The growth of a supermassive black hole (BH) is determined by how much gas the host galaxy is able to feed it, which in turn is controlled by the cosmic environment, through galaxy mergers and ...accretion of cosmic flows that time how galaxies obtain their gas, and also by internal processes in the galaxy, such as star formation and feedback from stars and the BH itself. In this paper, we study the growth of a 1012 M⊙ halo at z = 2, which is the progenitor of a group of galaxies at z = 0, and of its central BH by means of a high-resolution zoomed cosmological simulation, the Seth simulation. We study the evolution of the BH driven by the accretion of cold gas in the galaxy, and explore the efficiency of the feedback from supernovae (SNe). For a relatively inefficient energy input from SNe, the BH grows at the Eddington rate from early times, and reaches self-regulation once it is massive enough. We find that at early cosmic times z > 3.5, efficient feedback from SNe forbids the formation of a settled disc as well as the accumulation of dense cold gas in the vicinity of the BH and starves the central compact object. As the galaxy and its halo accumulate mass, they become able to confine the nuclear inflows provided by major mergers and the BH grows at a sustained near-to-Eddington accretion rate. We argue that this mechanism should be ubiquitous amongst low-mass galaxies, corresponding to galaxies with a stellar mass below ≲ 109 M⊙ in our simulations.
An empirically motivated model is presented for accretion-dominated growth of supermassive black holes (SMBH) in galaxies, and the implications are studied for the evolution of the quasar population ...in the Universe. We investigate the core aspects of the quasar population, including space density evolution, evolution of the characteristic luminosity, plausible minimum masses of quasars, the mass function of SMBH and their formation epoch distribution. Our model suggests that the characteristic luminosity in the quasar luminosity function arises primarily as a consequence of a characteristic mass scale above which there is a systematic separation between the black hole and the halo merging rates. At lower mass scales, black hole merging closely tracks the merging of dark haloes. When combined with a declining efficiency of black hole formation with redshift, the model can reproduce the quasar luminosity function over a wide range of redshifts. The observed space density evolution of quasars is well described by formation rates of SMBH above ∽108 M⊙. The inferred mass density of SMBH agrees with that found independently from estimates of the SMBH mass function derived empirically from the quasar luminosity function.
ABSTRACT
This paper illustrates how mock observational samples of high-redshift galaxies with sophisticated selection criteria can be extracted from the predictions of galics, a hybrid model of ...hierarchical galaxy formation that couples the outputs of large cosmological simulations and semi-analytic recipes, to describe dark matter collapse and the physics of baryons. As an example of this method, we focus on the properties of Lyman-break galaxies at redshift z∼ 3 (hereafter LBGs) in a Λ cold dark matter (ΛCDM) cosmology. With the momaf software package described in a companion paper, we generate a mock observational sample with selection criteria as similar as possible to those implied in the actual observations of z∼ 3 LBGs by Steidel, Pettini & Hamilton. We need to introduce an additional 'maturity' criterion to circumvent subtle effects due to mass resolution in the simulation. We predict a number density of 1.15 arcmin−2 at R≤ 25.5, in good agreement with the observed number density 1.2 ± 0.18 arcmin−2. Our model allows us to study the efficiency of the selection criterion to capture z∼ 3 galaxies. We find that the colour contours designed from models of spectrophotometric evolution of stellar populations are able to select more 'realistic' galaxies issued from models of hierarchical galaxy formation. We quantify the fraction of interlopers (12 per cent) and the selection efficiency (85 per cent), and we give estimates of the cosmic variance. We then study the clustering properties of our model LBGs. They are hosted by haloes with masses ∼1.6 × 1012 M⊙, with a linear bias parameter that decreases with increasing scale from b= 5 to 3. The amplitude and slope of the two-dimensional correlation function is in good agreement with the data. We investigate a series of physical properties: ultraviolet (UV) extinction (a typical factor 6.2 at 1600 Å), stellar masses, metallicities and star formation rates, and we find them to be in general agreement with observed values. The model also allows us to make predictions at other optical and infrared/submillimetre wavelengths, that are easily accessible though queries to a web-interfaced relational data base. Looking into the future of these LBGs, we predict that 75 per cent of them end up as massive ellipticals and lenticulars today, even though only 35 per cent of all our local ellipticals and lenticulars are predicted to have a LBG progenitor. In spite of some shortcomings that come from our simplifying assumptions and the subtle propagation of mass resolution effects, this new 'mock observation' method clearly represents a first step toward a more accurate comparison between hierarchical models of galaxy formation and real observational surveys.
Jet-regulated cooling catastrophe Dubois, Yohan; Devriendt, Julien; Slyz, Adrianne ...
Monthly notices of the Royal Astronomical Society,
12/2010, Letnik:
409, Številka:
3
Journal Article
Recenzirano
Odprti dostop
We present the first implementation of active galactic nuclei (AGN) feedback in the form of momentum-driven jets in an adaptive mesh refinement (AMR) cosmological resimulation of a galaxy cluster. ...The jets are powered by gas accretion on to supermassive black holes (SMBHs) which also grow by mergers. Throughout its formation, the cluster experiences different dynamical states: both a morphologically perturbed epoch at early times and a relaxed state at late times allowing us to study the different modes of black hole (BH) growth and associated AGN jet feedback. BHs accrete gas efficiently at high redshift (z > 2), significantly pre-heating proto-cluster haloes. Gas-rich mergers at high redshift also fuel strong, episodic jet activity, which transports gas from the proto-cluster core to its outer regions. At later times, while the cluster relaxes, the supply of cold gas on to the BHs is reduced leading to lower jet activity. Although the cluster is still heated by this activity as sound waves propagate from the core to the virial radius, the jets inefficiently redistribute gas outwards and a small cooling flow develops, along with low-pressure cavities similar to those detected in X-ray observations. Overall, our jet implementation of AGN feedback quenches star formation quite efficiently, reducing the stellar content of the central cluster galaxy by a factor of 3 compared to the no-AGN case. It also dramatically alters the shape of the gas density profile, bringing it in close agreement with the β model favoured by observations, producing quite an isothermal galaxy cluster for gigayears in the process. However, it still falls short in matching the lower than universal baryon fractions which seem to be commonplace in observed galaxy clusters.
We use the galics hybrid model of galaxy formation to explore the nature of galaxy clustering in the local Universe. We bring the theoretical predictions of our model into the observational plane ...using the momaf software to build mock catalogues which mimic Sloan Digital Sky Survey (SDSS) observations. We measure low- and high-order angular clustering statistic from these mock catalogues, after selecting galaxies the same way as for observations, and compare them directly to estimates from the SDSS data. Note that we also present the first measurements of high-order statistics on the SDSS DR1. We find that our model is in general good agreement with observations in the scale/luminosity range where we can trust the predictions. This range is found to be limited (i) by the size of the dark matter simulation used – which introduces finite volume effects at large scales – and by the mass resolution of this simulation – which introduces incompleteness at apparent magnitudes fainter than r∼ 20. We then focus on the small-scale clustering properties of galaxies and investigate the behaviour of three different prescriptions for positioning galaxies within haloes of dark matter. We show that galaxies are poor tracers of either DM particles or DM substructures, within groups and clusters. Instead, SDSS data tells us that the distribution of galaxies lies somewhat in between these two populations. This confirms the general theoretical expectation from numerical simulations and semi-analytic modelling.
Accurate cosmology from upcoming weak lensing surveys relies on knowledge of the total matter power spectrum at per cent level at scales k < 10 h Mpc^−1, for which modelling the impact of baryonic ...physics is crucial. We compare measurements of the total matter power spectrum from the Horizon cosmological hydrodynamical simulations: a dark-matter-only run, one with full baryonic physics, and another lacking active galactic nucleus (AGN) feedback. Baryons cause a suppression of power at k ≃ 10 h Mpc^−1 of |${\lt}15{{\ \rm per\ cent}}$| at |$z$| = 0, and an enhancement of a factor of a few at smaller scales due to the more efficient cooling and star formation. The results are sensitive to the presence of the highest mass haloes in the simulation and the distribution of dark matter is also impacted up to a few per cent. The redshift evolution of the effect is non-monotonic throughout |$z$| = 0−5 due to an interplay between AGN feedback and gas pressure, and the growth of structure. We investigate the effectiveness of an analytic ‘baryonic correction model’ in describing our results. We require a different redshift evolution and propose an alternative fitting function with four free parameters that reproduces our results within |$5{{\ \rm per\ cent}}$|. Compared to other simulations, we find the impact of baryonic processes on the total matter power spectrum to be smaller at |$z$| = 0. Correspondingly, our results suggest that AGN feedback is not strong enough in the simulation. Total matter power spectra from the Horizon simulations are made publicly available at https://www.horizon-simulation.org/catalogues.html.
ABSTRACT
We set constraints on the dark matter halo mass and concentration of ∼22 000 individual galaxies visible both in $\rm{H}\, {\small I}$ (from the ALFALFA survey) and optical light (from the ...Sloan Digital Sky Survey). This is achieved by combining two Bayesian models, one for the $\rm{H}\, {\small I}$ line width as a function of the stellar and neutral hydrogen mass distributions in a galaxy using kinematic modelling, and the other for the galaxy’s total baryonic mass using the technique of inverse subhalo abundance matching. We hence quantify the constraining power on halo properties of spectroscopic and photometric observations, and assess their consistency. We find good agreement between the two sets of posteriors, although there is a sizeable population of low-line width galaxies that favour significantly smaller dynamical masses than expected from abundance matching (especially for cuspy halo profiles). Abundance matching provides significantly more stringent bounds on halo properties than the $\rm{H}\, {\small I}$ line width, even with a mass–concentration prior included, although combining the two provides a mean gain of 40 per cent for the sample when fitting an NFW profile. We also use our kinematic posteriors to construct a baryonic mass–halo mass relation, which we find to be near power law, and with a somewhat shallower slope than expected from abundance matching. Our method demonstrates the potential of combining photometric and spectroscopic observations to precisely map out the dark matter distribution at the galaxy scale using upcoming $\rm{H}\, {\small I}$ surveys such as the SKA.
ABSTRACT
Rotation curves are the key observational manifestation of the dark matter distribution around late-type galaxies. In a halo model context, the precision of constraints on halo parameters is ...a complex function of properties of the measurements as well as properties of the galaxy itself. Forthcoming surveys will resolve rotation curves to varying degrees of precision, or measure their integrated effect in the $\mathrm{H}\, \small {\rm I}$ linewidth. To ascertain the relative significance of the relevant quantities for constraining halo properties, we study the information on halo mass and concentration as quantified by the Kullback–Leibler divergence of the kinematics-informed posterior from the uninformative prior. We calculate this divergence as a function of the different types of spectroscopic observation, properties of the measurement, galaxy properties, and auxiliary observational data on the baryonic components. Using the SPARC (Spitzer Photometry & Accurate Rotation Curves) sample, we find that fits to the full rotation curve exhibit a large variation in information gain between galaxies, ranging from ~1 to ~11 bits. The variation is predominantly caused by the vast differences in the number of data points and the size of velocity uncertainties between the SPARC galaxies. We also study the relative importance of the minimum $\mathrm{H}\, \small {\rm I}$ surface density probed and the size of velocity uncertainties on the constraining power on the inner halo density slope, finding the latter to be significantly more important. We spell out the implications of these results for the optimization of galaxy surveys aiming to constrain galaxies’ dark matter distributions, highlighting the need for precise velocity measurements.
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