Search

Environmental effects are believed to play an important yet poorly understood role in triggering accretion events onto the supermassive black holes (SMBHs) of galaxies (active galactic nuclei; AGNs). Massive clusters, which represent the densest structures in the Universe, provide an excellent laboratory to isolate environmental effects and study their impact on black hole growth. In this work, we critically review observational evidence for the preferential activation of SMBHs in the outskirts of galaxy clusters. We develop a semi-empirical model under the assumption that the incidence of AGN in galaxies is independent of environment. We demonstrate that the model is broadly consistent with recent observations on the AGN halo occupation at z = 0.2, although it may overpredict satellite AGN in massive haloes at that low redshift. We then use this model to interpret the projected radial distribution of X-ray sources around high redshift (z ≈ 1) massive (⁠|$\gt 5 \times 10^{14} \, M_\odot$|⁠) clusters, which show excess counts outside their virial radius. Such an excess naturally arises in our model as a result of sample variance. Up to 20  per cent of the simulated projected radial distributions show excess counts similar to the observations, which are however, because of background/foreground AGN and hence, not physically associated with the cluster. Our analysis emphasizes the importance of projection effects and shows that current observations of z ≈ 1 clusters remain inconclusive on the activation of SMBHs during infall. [ABSTRACT FROM AUTHOR]

Extreme Emission Line Galaxies (EELGs) stand as remarkable objects due to their extremely metal poor environment and intense star formation. Considered as local analogues of high-redshift galaxies in the peak of their star-forming activity, they offer insights into conditions prevalent during the early Universe. Assessment of their stellar and gas properties is therefore of critical importance, which requires the assembly of a considerable sample, comprehending a broad redshift range. The Javalambre-Physics of the Accelerating Universe Astrophysical Survey (JPAS) plays a significant role in assembling such a sample, encompassing ∼8000  |$\rm deg^2$| and employing 54 narrow-band optical filters. The present work describes the development and subsequent application of the tools that will be employed in the forthcoming JPAS spectrophotometric data, allowing for the massive and automated characterization of EELGs that are expected to be identified. This fully automated pipeline (requiring only the object coordinates from users) constructs Spectral Energy Distributions (SEDs) by retrieving virtually all the available multiwavelength photometric data archives, employs SED fitting tools, and identifies optical emission lines. It was applied to the sample of extreme line emitters identified in the miniJPAS Survey, and its derived physical properties such as stellar mass and age, coupled with fundamental relations, mirror results obtained through spectral modelling of SDSS spectra. Thorough testing using galaxies with documented photometric measurements across different wavelengths confirmed the pipeline's accuracy, demonstrating its capability for automated analysis of sources with varying characteristics, spanning brightness, morphology, and redshifts. The modular nature of this pipeline facilitates any addition from the user. [ABSTRACT FROM AUTHOR]

The origin of obscuration in active galactic nuclei (AGNs) is still an open debate. In particular, it is unclear what drives the relative contributions to the line-of-sight column densities from galaxy-scale and torus-linked obscuration. The latter source is expected to play a significant role in Unification Models, while the former is thought to be relevant in both Unification and Evolutionary models. In this work, we make use of a combination of cosmological semi-analytic models and semi-empirical prescriptions for the properties of galaxies and AGN, to study AGN obscuration. We consider a detailed object-by-object modelling of AGN evolution, including different AGN light curves (LCs), gas density profiles, and also AGN feedback-induced gas cavities. Irrespective of our assumptions on specific AGN LC or galaxy gas fractions, we find that, on the strict assumption of an exponential profile for the gas component, galaxy-scale obscuration alone can hardly reproduce the fraction of log (N H/cm−2) ≥ 24 sources at least at z ≲ 3. This requires an additional torus component with a thickness that decreases with luminosity to match the data. The torus should be present in all evolutionary stages of a visible AGN to be effective, although galaxy-scale gas obscuration may be sufficient to reproduce the obscured fraction with 22 < log (N H/cm−2) < 24 (Compton-thin, CTN) if we assume extremely compact gas disc components. The claimed drop of CTN fractions with increasing luminosity does not appear to be a consequence of AGN feedback, but rather of gas reservoirs becoming more compact with decreasing stellar mass. [ABSTRACT FROM AUTHOR]

In this series of papers, we employ several machine learning (ML) methods to classify the point-like sources from the miniJPAS catalogue, and identify quasar candidates. Since no representative sample of spectroscopically confirmed sources exists at present to train these ML algorithms, we rely on mock catalogues. In this first paper, we develop a pipeline to compute synthetic photometry of quasars, galaxies, and stars using spectra of objects targeted as quasars in the Sloan Digital Sky Survey. To match the same depths and signal-to-noise ratio distributions in all bands expected for miniJPAS point sources in the range 17.5 ≤ r < 24, we augment our sample of available spectra by shifting the original r -band magnitude distributions towards the faint end, ensure that the relative incidence rates of the different objects are distributed according to their respective luminosity functions, and perform a thorough modelling of the noise distribution in each filter, by sampling the flux variance either from Gaussian realizations with given widths, or from combinations of Gaussian functions. Finally, we also add in the mocks the patterns of non-detections which are present in all real observations. Although the mock catalogues presented in this work are a first step towards simulated data sets that match the properties of the miniJPAS observations, these mocks can be adapted to serve the purposes of other photometric surveys. [ABSTRACT FROM AUTHOR]

Astrophysical surveys rely heavily on the classification of sources as stars, galaxies, or quasars from multiband photometry. Surveys in narrow-band filters allow for greater discriminatory power, but the variety of different types and redshifts of the objects present a challenge to standard template-based methods. In this work, which is part of a larger effort that aims at building a catalogue of quasars from the miniJPAS survey, we present a machine learning-based method that employs convolutional neural networks (CNNs) to classify point-like sources including the information in the measurement errors. We validate our methods using data from the miniJPAS survey, a proof-of-concept project of the Javalambre Physics of the Accelerating Universe Astrophysical Survey (J-PAS) collaboration covering ∼1 deg2 of the northern sky using the 56 narrow-band filters of the J-PAS survey. Due to the scarcity of real data, we trained our algorithms using mocks that were purpose-built to reproduce the distributions of different types of objects that we expect to find in the miniJPAS survey, as well as the properties of the real observations in terms of signal and noise. We compare the performance of the CNNs with other well-established machine learning classification methods based on decision trees, finding that the CNNs improve the classification when the measurement errors are provided as inputs. The predicted distribution of objects in miniJPAS is consistent with the putative luminosity functions of stars, quasars, and unresolved galaxies. Our results are a proof of concept for the idea that the J-PAS survey will be able to detect unprecedented numbers of quasars with high confidence. [ABSTRACT FROM AUTHOR]

Laser Interferometer Space Antenna (LISA) will extend the search for gravitational waves (GWs) at |$0.1\, {-}\, 100$| mHz where loud signals from coalescing binary black holes of |$10^4 \, {-}\, 10^7\, \, \rm {M}_{\odot }$| are expected. Depending on their mass and luminosity distance, the uncertainty in the LISA sky-localization decreases from hundreds of deg2 during the inspiral phase to fractions of a deg2 after the merger. By using the semi-analytical model L-Galaxies applied to the Millennium-I merger trees, we generate a simulated universe to identify the hosts of |$z\, {\le }\, 3$| coalescing binaries with total mass of |$3\, {\times }\, 10^{5}$|⁠ , |$3\, {\times }\, 10^6$|⁠ , and |$3\, {\times }\, 10^7\, \rm {M}_{\odot }$|⁠ , and varying mass ratio. We find that, even at the time of merger, the number of galaxies around the LISA sources is too large (⁠|${\gtrsim }\, 10^2$|⁠) to allow direct host identification. However, if an X-ray counterpart is associated to the GW sources at |$z\, {< }\, 1$|⁠ , all LISA fields at merger are populated by |${\lesssim }\, 10$| active galactic nuclei (AGNs) emitting above |${\sim }\, 10^{-17} \, \rm erg\, cm^{-2}\, s^{-1}$|⁠. For sources at higher redshifts, the poorer sky-localization causes this number to increase up to |${\sim }\, 10^3$|⁠. Archival data from eRosita will allow discarding |${\sim }\, 10{{\ \rm per\ cent}}$| of these AGNs, being too shallow to detect the dim X-ray luminosity of the GW sources. Inspiralling binaries in an active phase with masses |${\lesssim }\, 10^6\, \rm {M}_{\odot }$| at |$z\, {\le }\, 0.3$| can be detected, as early as 10 h before the merger, by future X-ray observatories in less than a few minutes. For these systems, |${\lesssim }\, 10$| AGNs are within the LISA sky-localization area. Finally, the LISA-Taiji network would guarantee the identification of an X-ray counterpart 10 h before merger for all binaries at |$z\, {\lesssim }\, 1$|⁠. [ABSTRACT FROM AUTHOR]

This paper explores the role of small-scale environment (<1 Mpc) in modulating accretion events on to supermassive black holes by studying the incidence of active galactic nuclei (AGNs) in massive clusters of galaxies. A flexible, data-driven semi-empirical model is developed based on a minimal set of parameters and under the zero-order assumption that the incidence of AGNs in galaxies is independent of environment. This is used to predict how the fraction of X-ray selected AGN among galaxies in massive dark matter haloes (⁠|$\gtrsim 3\times 10^{14}\, \mathrm{M}_{\odot }$|⁠) evolves with redshift and reveal tensions with observations. At high redshift, z ∼ 1.2, the model underpredicts AGN fractions, particularly at high X-ray luminosities, |$L_X(\rm 2\rm{-}10\, keV) \gtrsim 10^{44}\, erg \, s^{-1}$|⁠. At low redshift, z ∼ 0.2, the model estimates fractions of moderate luminosity AGN (⁠|$L_X(\rm 2\rm{-}10\, keV) \gtrsim 10^{43}\, erg \, s^{-1}$|⁠) that are a factor of 2–3 higher than the observations. These findings reject the zero-order assumption on which the semi-empirical model hinges and point to a strong and redshift-dependent influence of the small-scale environment on the growth of black holes. Cluster of galaxies appear to promote AGN activity relative to the model expectation at z ∼ 1.2 and suppress it close to the present day. These trends could be explained by the increasing gas content of galaxies towards higher redshift combined with an efficient triggering of AGNs at earlier times in galaxies that fall on to clusters. [ABSTRACT FROM AUTHOR]

The relative roles of mergers and star formation in regulating galaxy growth are still a matter of intense debate. We here present our decode , a new Discrete statistical sEmi-empiriCal mODEl specifically designed to predict rapidly and efficiently, in a full cosmological context, galaxy assembly, and merger histories for any given input stellar mass–halo mass (SMHM) relation. decode generates object-by-object dark matter merger trees (hence discrete) from accurate subhalo mass and infall redshift probability functions (hence statistical) for all subhaloes, including those residing within other subhaloes, with virtually no resolution limits on mass or volume. Merger trees are then converted into galaxy assembly histories via an input, redshift-dependent SMHM relation, which is highly sensitive to the significant systematics in the galaxy stellar mass function and on its evolution with cosmic time. decode can accurately reproduce the predicted mean galaxy merger rates and assembly histories of hydrodynamic simulations and semi-analytical models, when adopting in input their SMHM relations. In this work, we use decode to prove that only SMHM relations implied by stellar mass functions characterized by large abundances of massive galaxies and significant redshift evolution, at least at |$M_\star \gtrsim 10^{11} \, \mathrm{M}_\odot$|⁠ , can simultaneously reproduce the local abundances of satellite galaxies, the galaxy (major merger) pairs since z ∼ 3, and the growth of Brightest Cluster Galaxies. The same models can also reproduce the local fraction of elliptical galaxies, on the assumption that these are strictly formed by major mergers, but not the full bulge-to-disc ratio distributions, which require additional processes. [ABSTRACT FROM AUTHOR]

We present mordor (MORphological DecOmposeR), a new algorithm for structural decomposition of simulated galaxies based on stellar kinematics. The code measures the properties of up to five structural components (a thin/cold and a thick/warm disc, a classical and a secular bulge, and a spherical stellar halo), and determines the properties of a stellar bar (if present). A comparison with other algorithms presented in the literature yields overall good agreement, with mordor displaying a higher flexibility in correctly decomposing systems and identifying bars in crowded environments (e.g. with ongoing fly-bys, often observable in cosmological simulations). We use mordor to analyse galaxies in the TNG50 simulation and find the following: (i) the thick disc component undergoes the strongest evolution in the binding energy-circularity plane, as expected when disc galaxies decrease their turbulent-rotational support with cosmic time; (ii) smaller galaxies (with stellar mass, |$10^{9} \lesssim M_{*}/~\rm M_{\odot }\le 5 \times 10^{9}$|⁠) undergo a major growth in their disc components after z ∼ 1, whereas (iii) the most massive galaxies (⁠|$5 \times 10^{10} \lt M_{*}/~\rm M_{\odot }\le 5\times 10^{11}$|⁠) evolve towards more spheroidal dominated objects down to z  = 0 due to frequent gravitational interactions with satellites; (iv) the fraction of barred galaxies grows rapidly at high redshift and stabilizes below z ∼ 2, except for the most massive galaxies that show a decrease in the bar occupation fraction at low redshift; (v) galaxies with |$M_{*} \sim 10^{11}~~\rm M_{\odot }$| exhibit the highest relative occurrence of bars at z  = 0, in agreement with observational studies. We publicly release mordor and the morphological catalogue of TNG50 galaxies. [ABSTRACT FROM AUTHOR]

We make use of |$z\, {=}\, 0$| samples of strongly barred and unbarred disc galaxies from the TNG100 and TNG50 cosmological hydrodynamical simulations to assess the performance of the simple disc instability criterion proposed by Efstathiou, Lake & Negroponte (1982) (ELN-criterion). We find that strongly barred galaxies generally assemble earlier, are more star dominated in their central regions, and have more massive and more compact discs than unbarred galaxies. The ELN-criterion successfully identifies |${\sim }\, 75$| and |${\sim }\, 80{{ per\ cent}}$| of the strongly barred and the unbarred galaxies, respectively. Strongly barred galaxies that the criterion fails to identify tend to have more extended discs, higher spin values and bars that assembled later than is typical for the bulk of the barred population. The bars in many of these cases appear to be produced by an interaction with a close neighbour (i.e. to be externally triggered) rather than to result from secular growth in the disc. On the other hand, we find that unbarred galaxies misclassified as barred by the ELN-criterion typically have stellar discs similar to those of barred galaxies, although more extended in the vertical direction and less star-dominated in their central regions, possibly reflecting later formation times. In addition, the bulge component of these galaxies is significantly more prominent at early times than in the strongly barred sample. Thus, the ELN-criterion robustly identifies secular bar instabilities in most simulated disc galaxies, but additional environmental criteria are needed to account for interaction-induced bar formation. [ABSTRACT FROM AUTHOR]

We use the magnetic-hydrodynamical simulation TNG50 to study the evolution of barred massive disc galaxies. Massive spiral galaxies are already present as early as z  = 4, and bar formation takes place already at those early times. The bars grow longer and stronger as the host galaxies evolve, with the bar sizes increasing at a pace similar to that of the disc scalelengths. The bar fraction mildly evolves with redshift for galaxies with |$M_{*}\ge 10^{10}\rm M_{\odot }$|⁠ , being greater than |$\sim 40{{\ \rm per\ cent}}$| at 0.5 < z < 3 and |$\sim 30{{\ \rm per\ cent}}$| at z  = 0. When bars larger than a given physical size (⁠|$\ge 2\, \rm kpc$|⁠) or the angular resolution limit of twice the I -band angular PSF FWHM of the HST are considered, the bar fraction dramatically decreases with increasing redshift, reconciling the theoretical predictions with observational data. We find that barred galaxies have an older stellar population, lower gas fractions, and star formation rates than unbarred galaxies. In most cases, the discs of barred galaxies assembled earlier and faster than the discs of unbarred galaxies. We also find that barred galaxies are typical in haloes with larger concentrations and smaller spin parameters than unbarred galaxies. Furthermore, the inner regions of barred galaxies are more baryon-dominated than those of unbarred galaxies but have comparable global stellar mass fractions. Our findings suggest that the bar population could be used as a potential tracer of the buildup of disc galaxies and their host haloes. With this paper, we release a catalogue of barred galaxies in TNG50 at six redshifts between z  = 4 and 0. [ABSTRACT FROM AUTHOR]

We present zELDA (redshift Estimator for Line profiles of Distant Lyman Alpha emitters), an open source code to fit Lyman α (Ly α) line profiles. The main motivation is to provide the community with an easy to use and fast tool to analyse Ly α line profiles uniformly to improve the understating of Ly α emitting galaxies. zELDA is based on line profiles of the commonly used 'shell-model' pre-computed with the full Monte Carlo radiative transfer code LyaRT. Via interpolation between these spectra and the addition of noise, we assemble a suite of realistic Ly α spectra which we use to train a deep neural network.We show that the neural network can predict the model parameters to high accuracy (e.g. ≲ 0.34 dex H  i column density for R ∼ 12 000) and thus allows for a significant speedup over existing fitting methods. As a proof of concept, we demonstrate the potential of zELDA by fitting 97 observed Ly α line profiles from the LASD data base. Comparing the fitted value with the measured systemic redshift of these sources, we find that Ly α determines their rest frame Ly α wavelength with a remarkable good accuracy of ∼0.3 Å (⁠|$\sim 75\,\, {\rm km\, s}^{-1}$|⁠). Comparing the predicted outflow properties and the observed Ly α luminosity and equivalent width, we find several possible trends. For example, we find an anticorrelation between the Ly α luminosity and the outflow neutral hydrogen column density, which might be explained by the radiative transfer process within galaxies. [ABSTRACT FROM AUTHOR]

We explore how to mitigate the clustering distortions in Lyman α emitter (LAE) samples caused by the misidentification of the Lyman α (⁠|$\rm {Ly}\,\alpha$|⁠) wavelength in their |$\rm {Ly}\,\alpha$| line profiles. We use the |$\rm {Ly}\,\alpha$| line profiles from our previous LAE theoretical model that includes radiative transfer in the interstellar and intergalactic mediums. We introduce a novel approach to measure the systemic redshift of LAEs from their |$\rm {Ly}\,\alpha$| line using neural networks. In detail, we assume that for a fraction of the whole LAE population their systemic redshift is determined precisely through other spectral features. We then use this subset to train a neural network that predicts the |$\rm {Ly}\,\alpha$| wavelength given an |$\rm {Ly}\,\alpha$| line profile. We test two different training sets: (i) the LAEs are selected homogeneously and (ii) only the brightest LAE is selected. In comparison with previous approaches in the literature, our methodology improves significantly the accuracy in determining the |$\rm {Ly}\,\alpha$| wavelength. In fact, after applying our algorithm in ideal |$\rm {Ly}\,\alpha$| line profiles, we recover the clustering unperturbed down to |$1\, {\rm cMpc}\, h^{-1}$|⁠. Then, we test the performance of our methodology in realistic |$\rm {Ly}\,\alpha$| line profiles by downgrading their quality. The machine learning technique using the uniform sampling works well even if the |$\rm {Ly}\,\alpha$| line profile quality is decreased considerably. We conclude that LAE surveys such as HETDEX would benefit from determining with high accuracy the systemic redshift of a subpopulation and applying our methodology to estimate the systemic redshift of the rest of the galaxy sample. [ABSTRACT FROM AUTHOR]

We study the mass assembly and spin evolution of supermassive black holes (BHs) across cosmic time as well as the impact of gravitational recoil on the population of nuclear and wandering BHs (wBHs) by using the semi-analytical model L-Galaxies  run on top of Millennium merger trees. We track spin changes that BHs experience during both coalescence events and gas accretion phases. For the latter, we assume that spin changes are coupled with the bulge assembly. This assumption leads to predictions for the median spin values of z  = 0 BHs that depend on whether they are hosted by pseudo-bulges, classical bulges or ellipticals, being |$\overline{a} \sim 0.9$|⁠ , 0.7 and 0.4, respectively. The outcomes of the model display a good consistency with |$z \le 4$| quasar luminosity functions and the |$z = 0$| BH mass function, spin values, and BH correlation. Regarding the wBHs, we assume that they can originate from both the disruption of satellite galaxies (orphan wBH) and ejections due to gravitational recoils (ejected wBH). The model points to a number density of wBHs that increases with decreasing redshift, although this population is always |$\rm {\sim}2\, dex$| smaller than the one of nuclear BHs. At all redshifts, wBHs are typically hosted in |$\rm {\it M}_{halo} \gtrsim 10^{13} \, M_{\odot }$| and |$\rm {\it M}_{stellar} \gtrsim 10^{10} \, M_{\odot }$|⁠ , being orphan wBHs the dominant type. Besides, independently of redshift and halo mass, ejected wBHs inhabit the central regions (⁠|${\lesssim}\rm 0.3{\it R}_{200}$|⁠) of the host DM halo, while orphan wBH linger at larger scales (⁠|${\gtrsim}\rm 0.5{\it R}_{200}$|⁠). Finally, we find that gravitational recoils cause a progressive depletion of nuclear BHs with decreasing redshift and stellar mass. Moreover, ejection events lead to changes in the predicted local BH–bulge relation, in particular for BHs in pseudo-bulges, for which the relation is flattened at |$\rm {\it M}_{bulge} \gt 10^{10.2}\, M_{\odot }$| and the scatter increase up to |${\sim}\rm 3\, dex$|⁠. [ABSTRACT FROM AUTHOR]

In the near future galaxy surveys will target Lyman alpha emitting galaxies (LAEs) to unveil the nature of dark energy. It has been suggested that the observability of LAEs is coupled to the large-scale properties of the intergalactic medium. Such coupling could introduce distortions into the observed clustering of LAEs, adding a new potential difficulty to the interpretation of upcoming surveys. We present a model of LAEs that incorporates Ly α radiative transfer processes in the interstellar and intergalactic medium. The model is implemented in the GALFORM semi-analytic model of galaxy of formation and evolution. We find that the radiative transfer inside galaxies produces selection effects over galaxy properties. In particular, observed LAEs tend to have low metallicities and intermediate star formation rates. At low redshift we find no evidence of a correlation between the spatial distribution of LAEs and the intergalactic medium properties. However, at high redshift the LAEs are linked to the line of sight velocity and density gradient of the intergalactic medium. The strength of the coupling depends on the outflow properties of the galaxies and redshift. This effect modifies the clustering of LAEs on large scales, adding non-linear features. In particular, our model predicts modifications to the shape and position of the baryon acoustic oscillation peak. This work highlights the importance of including radiative transfer physics in the cosmological analysis of LAEs. [ABSTRACT FROM AUTHOR]

We analyse the properties of strongly barred disc galaxies using the TNG100 simulation, a cosmological hydrodynamical realization of the IllustrisTNG suite. We identify 270 disc galaxies at z  = 0 in the stellar mass range |$M_{*}=10^{10.4-11}\, {\rm M_{\odot }}$|⁠ , of which 40 per cent are barred. Of the detected bars, more than half are strong. We find that the fraction of barred galaxies increases with stellar mass, in agreement with observational results. Strongly barred galaxies exhibit, overall, lower gas-to-stellar mass ratios compared to unbarred galaxies. The majority of barred galaxies are quenched (sSFR ∼ 10−11.7 yr−1), whereas unbarred galaxies continue to be active (sSFR ∼ 10−10.3 yr−1) on the main sequence of star-forming galaxies. We explore the evolution of strongly barred and unbarred galaxies to investigate their formation and quenching histories. We find that strong bars form between 0.5 < z < 1.5, with more massive galaxies hosting older bars. Strong bars form in galaxies with an early-established prominent disc component, undergoing periods of enhanced star formation and black hole accretion, possibly assisted by cosmological inflows. Unbarred galaxies, on the other hand, assemble most of their mass and disc component at late times. The nuclear region of strongly barred galaxies quenches shortly after bar formation, while unbarred galaxies remain active across time. Our findings are indicative of bar quenching, possibly assisted by nuclear feedback processes. We conclude that the cosmological environment, together with small-scale feedback processes, determine the chances of a galaxy to form a bar and to rapidly quench its central region. [ABSTRACT FROM AUTHOR]

We present flareon (Fast Lyman α Radiative Escape from Outflowing Neutral gas), a public python package that delivers fast and accurate |$\rm {Ly}\,\alpha$| escape fractions and line profiles over a wide range of outflow geometries and properties. The code incorporates different algorithms, such as interpolation and machine learning to predict |$\rm {Ly}\,\alpha$| line properties from a pre-computed grid of outflow configurations based on the outputs of a Monte Carlo radiative transfer code. Here we describe the algorithm, discuss its performance and illustrate some of its many applications. Most notably, flareon can be used to infer the physical properties of the outflowing medium from an observed |$\rm {Ly}\,\alpha$| line profile, including the escape fraction, or it can be run over millions of objects in a galaxy formation model to simulate the escape of |$\rm {Ly}\,\alpha$| photons in a cosmological volume. [ABSTRACT FROM AUTHOR]

Bars are a key factor in the long-term evolution of spiral galaxies, in their unique role in redistributing angular momentum and transporting gas and stars on large scales. The Eris-suite simulations are cosmological zoom-in, N -body, smoothed-particle hydrodynamic simulations built to follow the formation and evolution of a Milky-Way-sized galaxy across the build-up of the large-scale structure. Here we analyse and describe the outcome of two particular simulations taken from the Eris suite – ErisBH and Eris2k – which mainly differ in the prescriptions employed for gas cooling, star formation, and feedback from supernovae and black holes. Our study shows that the enhanced effective feedback in Eris2k, due to the collective effect of the different micro-physics implementations, results in a galaxy that is less massive than its ErisBH counterpart till z  ∼ 1. However, when the stellar content is large enough so that global dynamical instabilities can be triggered, the galaxy in Eris2k develops a stronger and more extended bar with respect to ErisBH. We demonstrate that the structural properties and time evolution of the two bars are very different. Our results highlight the importance of accurate sub-grid prescriptions in cosmological zoom-in simulations of the process of galaxy formation and evolution, and the possible use of a statistical sample of barred galaxies to assess the strength of the stellar feedback. [ABSTRACT FROM AUTHOR]

We study the cosmological build-up of pseudo-bulges using the L-Galaxies  semi-analytical model for galaxy formation with a new approach for following separately the assembly of classical bulges and pseudo-bulges. Classical bulges are assumed to be the result of violent processes (i.e. mergers and starbursts), while the formation of pseudo-bulges is connected to the secular growth of discs. We apply the model to both the Millennium and the Millennium II simulations, in order to study our results across a wide range of stellar masses (⁠|$\rm 10^{7}\!-\!10^{11.5}\, {\rm M}_{\odot }$|⁠). We find that z  = 0 pseudo-bulges mainly reside in galaxies of |$\mathit{ M}_{\rm stellar} \, {\sim }\, 10^{10}\!-\!10^{10.5}\, {\rm M}_{\odot }$| (⁠|$\mathit{ M}_{\rm halo} \, {\sim }\, 10^{11.5}\!-\!10^{12}\, {\rm M}_{\odot }$|⁠) and we recover structural properties of these objects (e.g. sizes and bulge-to-total ratios) that are in good agreement with observational results. Tracing their formation history, we find that pseudo-bulges assembled in galaxies with a very quiet merger history, as opposed to the host galaxies of classical bulges. Regarding the bulge structure, we find that |$\, {\sim }\, 30{{\ \rm per\ cent}}$| of the galaxies with a predominant pseudo-bulge feature a composite structure, hosting both a pseudo- and a classical bulge component. The classical component typically constitutes |${\sim }\, 10{{\ \rm per\ cent}}$| of the total bulge galaxy mass. When looking at the properties of the host galaxies, we find that z  = 0 pseudo-bulges are hosted by main-sequence galaxies, characterized by a stellar population which is generally younger compared to the one of the hosts of classical bulges. [ABSTRACT FROM AUTHOR]

Lyman-α emitters (LAEs) are a promising target to probe the large-scale structure of the Universe at high redshifts, z  ≳ 2. However, their detection is sensitive to radiative transfer effects that depend on local astrophysical conditions. Thus, modeling the bulk properties of this galaxy population remains challenging for theoretical models. Here we develop a physically motivated scheme to predict LAEs in cosmological simulations. The escape of Lyα photons is computed using a Monte Carlo radiative transfer code that outputs a Lyα escape fraction. To speed up the process of assigning escape fractions to individual galaxies, we employ fitting formulae that approximate the full Monte Carlo results within an accuracy of 10 per cent for a broad range of column densities, gas metallicities, and gas bulk velocities. We apply our methodology to the semi-analytical model galform on a large N -body simulation. The Lyα photons escape through an outflowing neutral gas medium, implemented assuming different geometries. This results in different predictions for the typical column density and outflow velocities of the LAE population. To understand the impact of radiative transfer on our predictions, we contrast our models against a simple abundance matching assignment. Our full models populate LAEs in less massive haloes than what is obtained with abundance matching. Overall, radiative transfer effects result in better agreement when confronting the properties of LAEs against observational measurements. This suggests that incorporating the effects of Lyα radiative transfer in the analysis of this galaxy population, including their clustering, can be important for obtaining an unbiased interpretation of future data sets. [ABSTRACT FROM AUTHOR]

We look into the abundance of Dual AGN (active galactic nucleus) in the largest hydrodynamical simulation from the Evolution and Assembly of GaLaxies and their Environment (EAGLE) project. We define a Dual AGN as two active black holes (BHs) with a separation below 30 kpc. We find that only 1 per cent of AGN with L HX ≥ 1042 erg s−1 are part of a Dual AGN system at |$z$|  = 0.8–1. During the evolution of a typical binary BH system, the rapid variability of the hard X-ray luminosity on Myr time-scales severely limits the detectability of Dual AGN. To quantify this effect, we calculate a probability of detection, t on/ t 30, where t 30 is the time in which the two BHs are separated at distances below 30 kpc and t on, the time that both AGNs are visible (e.g. when both AGNs have L HX ≥ 1042 erg s−1) in this period. We find that the average fraction of visible Dual systems is 3 per cent. The visible Dual AGN distribution as a function of BH separation presents a pronounced peak at ∼20 kpc that can be understood as a result of the rapid orbital decay of the host galaxies after their first encounter. We also find that 75 per cent of the host galaxies have recently undergone or are undergoing a merger with stellar mass ratio ≥0.1. Finally, we find that the fraction of visible Dual AGN increases with redshift as found in observations. [ABSTRACT FROM AUTHOR]

We use the semi-analytical model of galaxy formation GALFORM to characterize an indirect signature of active galactic nucleus (AGN) feedback in the environment of radio galaxies at high redshifts. The predicted environment of radio galaxies is denser than that of radio-quiet galaxies with the same stellar mass. This is consistent with observational results from the CARLA survey. Our model shows that the differences in environment are due to radio galaxies being hosted by dark matter haloes that are ∼1.5 dex more massive than those hosting radio-quiet galaxies with the same stellar mass. By running a control simulation in which AGN feedback is switched off, we identify AGN feedback as the primary mechanism affecting the build up of the stellar component of radio galaxies, thus explaining the different environment in radio galaxies and their radio-quiet counterparts. The difference in host halo mass between radio-loud and radio-quiet galaxies translates into different galaxies populating each environment. We predict a higher fraction of passive galaxies around radio-loud galaxies compared to their radio-quiet counterparts. Furthermore, such a high fraction of passive galaxies shapes the predicted infrared luminosity function in the environment of radio galaxies in a way that is consistent with observational findings. Our results suggest that the impact of AGN feedback at high redshifts and environmental mechanisms affecting galaxies in high halo masses can be revealed by studying the environment of radio galaxies, thus providing new constraints on galaxy formation physics at high redshifts. [ABSTRACT FROM AUTHOR]

It has been proposed that close interactions with satellite galaxies can significantly perturb the morphology of the main galaxy. However, the dynamics of an already formed bar following the interaction with the external environment has not been studied in detail in a fully cosmological context. In this work, analysing the cosmological zoom-in simulation Eris2k, we study the effects that a very unequal-mass flyby crossing the stellar disc has on the stability of the pre-existing bar. We characterize the evolution of the bar strength and length showing that the perturbation exerted by the flyby shuffles the orbits of stars for less than one Gyr. After this time, the bar shows a remarkable resilience, reforming with properties comparable to those it had before the interaction. Our work shows that close unequal-mass encounters, the most frequent interactions occurring during the evolution of cosmic structures, have (i) an overall minor impact on the global evolution of the bar in the long term, still (ii) the effect is destructive, and (iii) a very weak interaction is sufficient to dismantle a strong bar leading to its “apparent death”. As a consequence, due to the non-negligible duration of the bar-less period, a fraction of observed spiral galaxies classified as non-barred could be prone to bar formation. [ABSTRACT FROM AUTHOR]

The emergence of a large-scale stellar bar is one of the most striking features in disc galaxies. By means of state-of-the-art cosmological zoom-in simulations, we study the formation and evolution of bars in Milky Way-like galaxies in a fully cosmological context, including the physics of gas dissipation, star formation and supernova feedback. Our goal is to characterize the actual trigger of the non-axisymmetric perturbation that leads to the strong bar observable in the simulations at z = 0, discriminating between an internal/secular and an external/tidal origin. To this aim, we run a suite of cosmological zoom-in simulations altering the original history of galaxy–satellite interactions at a time when the main galaxy, though already barunstable, does not feature any non-axisymmetric structure yet. We find that the main effect of a late minor merger and of a close fly-by is to delay the time of bar formation and those two dynamical events are not directly responsible for the development of the bar and do not alter significantly its global properties (e.g. its final extension).We conclude that, once the disc has grown to a mass large enough to sustain global non-axisymmetric modes, then bar formation is inevitable. [ABSTRACT FROM AUTHOR]

We present ELDAR, a new method that exploits the potential of medium- and narrow-band filter surveys to securely identify active galactic nuclei (AGN) and determine their redshifts. Our methodology improves on traditional approaches by looking for AGN emission lines expected to be identified against the continuum, thanks to the width of the filters. To assess its performance, we apply ELDAR to the data of the ALHAMBRA (Advance Large Homogeneous Area Medium Band Redshift Astronomical) survey, which covered an effective area of 2.38 deg2 with 20 contiguous medium-band optical filters down to F814W ≃ 24.5. Using two different configurations of ELDAR in which we require the detection of at least two and three emission lines, respectively, we extract two catalogues of type-I AGN. The first is composed of 585 sources (79 per cent of them spectroscopically unknown) down to F814W = 22.5 at zphot > 1, which corresponds to a surface density of 209 deg-2. In the second, the 494 selected sources (83 per cent of them spectroscopically unknown) reach F814W= 23 at zphot > 1.5, for a corresponding number density of 176 deg-2. Then, using samples of spectroscopically known AGN in the ALHAMBRA fields, for the two catalogues we estimate a completeness of 73 per cent and 67 per cent, and a redshift precision of 1.01 per cent and 0.86 per cent (with outliers fractions of 8.1 per cent and 5.8 per cent). At z > 2, where our selection performs best, we reach 85 per cent and 77 per cent completeness and we find no contamination from galaxies. [ABSTRACT FROM AUTHOR]

We simulate neutralino dark matter (χDM) haloes from their initial collapse, at ~ earth mass, up to a few percent solar. Our results confirm that the density profiles of the first haloes are described by a ~r-1.5 power law. As haloes grow in mass, their density profiles evolve significantly. In the central regions, they become shallower and reach on average ~r-1, the asymptotic form of an NFW profile. Using non-cosmological controlled simulations, we observe that temporal variations in the gravitational potential caused by major mergers lead to a shallowing of the inner profile. This transformation is more significant for shallower initial profiles and for a higher number of merging systems. Depending on the merger details, the resulting profiles can be shallower or steeper than NFW in their inner regions. Interestingly, mergers have a much weaker effect when the profile is given by a broken power law with an inner slope of -1 (such as NFW or Hernquist profiles). This offers an explanation for the emergence of NFW-like profiles: after their initial collapse, r-1.5 χDM haloes suffer copious major mergers, which progressively shallows the profile. Once an NFW-like profile is established, subsequent merging does not change the profile anymore. This suggests that halo profiles are not universal but rather a combination of (1) the physics of the formation of the microhaloes and (2) their early merger history - both set by the properties of the dark matter particle - as well as (3) the resilience of NFW-like profiles to perturbations. [ABSTRACT FROM AUTHOR]

We analyse the outputs of the cosmological 'zoom-in' hydrodynamical simulation ErisBH to study a strong stellar bar which naturally emerges in the late evolution of the simulated Milky Way-type galaxy. We focus on the analysis of the formation and evolution of the bar and on its effects on the galactic structure, the gas distribution and the star formation. A large central region in the ErisBH disc becomes bar unstable after z ∼ 1.4, but a clear bar starts to grow significantly only after z ≃ 0.4, possibly triggered by the interaction with a massive satellite. At z ≃ 0.1, the bar stabilizes and reaches its maximum radial extent of l ≈ 2.2 kpc. As the bar grows, it becomes prone to buckling instability. The actual buckling event, observable at z ≃ 0.1, results in the formation of a boxy-peanut bulge clearly discernible at z = 0. During its early growth, the bar exerts a strong torque on the gas and drives gas inflows that enhance the nuclear star formation on sub-kpc scales. Later on, as the bar reaches its maximum length and strength, the gas within its extent is nearly all consumed into stars, leaving behind a gasdepleted region in the central ∼2 kpc. Observations would more likely identify a prominent, large-scale bar at the stage when the galactic central region has already been gas depleted, giving a hint at the fact that bar-driven quenching may play an important role in the evolution of disc-dominated galaxies. [ABSTRACT FROM AUTHOR]

We present a new zoom-in hydrodynamical simulation, 'ErisBH', which features the same initial conditions, resolution, and sub-grid physics as the close Milky Way-analogue 'Eris' (Guedes et al. 2011), but it also includes prescriptions for the formation, growth and feedback of supermassive black holes. This enables a detailed study of black hole evolution and the impact of active galactic nuclei (AGN) feedback in a late-type galaxy. At z = 0, the main galaxy of ErisBH hosts a central black hole of 2.6 × 106M☉, which correlates to the bulge mass and the galaxy's central velocity dispersion similarly to what is observed in the Milky Way and in pseudobulges. During its evolution, the black hole grows mostly through mergers with black holes brought in by accreted satellite galaxies and very little by gas accretion (due to the modest amount of gas that reaches the central regions). AGN feedback is weak and it affects only the central 1-2 kpc. Yet, it limits the growth of the bulge, which results in a rotation curve that, in the inner ~10 kpc, is flatter than that of Eris. We find that ErisBH is more prone to instabilities than Eris, due to its smaller bulge and larger disc. At z ~ 0.3, an initially small bar grows to be of a few disc scalelengths in size. The formation of the bar causes a small burst of star formation in the inner few hundred pc, provides new gas to the central black hole and causes the bulge to have a boxy/peanut morphology by z = 0. [ABSTRACT FROM AUTHOR]

We use the large catalogues of haloes available for the Millennium Simulation to test whether recently merged haloes exhibit stronger large-scale clustering than other haloes of the same mass. This effect could help us to understand the very strong clustering of quasars at high redshift. However, we find no statistically significant excess bias for recently merged haloes over the redshift range , with the most massive haloes showing an excess of at most ∼5 per cent. We also consider galaxies extracted from a semi-analytic model built on the Millennium Simulation. At fixed stellar mass, we find an excess bias of per cent for recently merged objects, decreasing with increasing stellar mass. The fact that recently merged galaxies are found in systematically more massive subhaloes than other galaxies of the same stellar mass accounts for about half of this signal, and perhaps more for high-mass galaxies. The weak merger bias of massive systems suggests that objects of merger-driven nature do not cluster significantly differently from other objects of the same characteristic mass over the range . We discuss the implications of these results for the interpretation of quasar clustering data with respect to quasar duty cycles, visibility times and evolution in the black hole–host mass relation. [ABSTRACT FROM AUTHOR]

We study the spatial distribution of X-ray selected active galactic nuclei (AGN) in the framework of hierarchical coevolution of supermassive black holes and their host galaxies and dark matter haloes. To this end, we have applied the theoretical model developed by Croton et al., De Lucia & Blaizot and Marulli et al. to the output of the Millennium Run and obtained hundreds of realizations of past light cones from which we have extracted realistic mock AGN catalogues that mimic the Chandra deep fields. We find that the model AGN number counts are in fair agreement with observations both in the soft and in the hard X-ray bands, except at fluxes , where the model systematically overestimates the observations. However, a large fraction of these faint objects are typically excluded from the spectroscopic AGN samples of the Chandra fields. We find that the spatial two-point correlation function predicted by the model is well described by a power-law relation out to , in close agreement with observations. Our model matches the correlation length r0 of AGN in the Chandra Deep Field-North but underestimates it in the Chandra Deep Field-South. When fixing the slope to , as in Gilli et al., the statistical significance of the mismatch is 2σ–2.5σ, suggesting that the predicted cosmic variance, which dominates the error budget, may not account for the different correlation length of the AGN in the two fields. However, the overall mismatch between the model and the observed correlation function decreases when both r0 and γ are allowed to vary, suggesting that more realistic AGN models and a full account of all observational errors may significantly reduce the tension between AGN clustering in the two fields. While our results are robust to changes in the model prescriptions for the AGN light curves, the luminosity dependence of the clustering is sensitive to the different light-curve models adopted. However, irrespective of the model considered, the luminosity dependence of the AGN clustering in our mock fields seems to be weaker than in the real Chandra fields. The significance of this mismatch needs to be confirmed using larger data sets. [ABSTRACT FROM AUTHOR]

We use semi-analytic modelling on top of the Millennium simulation to study the joint formation of galaxies and their embedded supermassive black holes. Our goal is to test scenarios in which black hole accretion and quasar activity are triggered by galaxy mergers, and to constrain different models for the light curves associated with individual quasar events. In the present work, we focus on studying the spatial distribution of simulated quasars. At all luminosities, we find that the simulated quasar two-point correlation function is fit well by a single power law in the range , but its normalization is a strong function of redshift. When we select only quasars with luminosities within the range typically accessible by today's quasar surveys, their clustering strength depends only weakly on luminosity, in agreement with observations. This holds independently of the assumed light-curve model, since bright quasars are black holes accreting close to the Eddington limit, and are hosted by dark matter haloes with a narrow mass range of a few . Therefore, the clustering of bright quasars cannot be used to disentangle light-curve models, but such a discrimination would become possible if the observational samples can be pushed to significantly fainter limits. Overall, our clustering results for the simulated quasar population agree rather well with observations, lending support to the conjecture that galaxy mergers could be the main physical process responsible for triggering black hole accretion and quasar activity. [ABSTRACT FROM AUTHOR]

We model the cosmological co-evolution of galaxies and their central supermassive black holes (BHs) within a semi-analytical framework developed on the outputs of the Millennium Simulation. This model, described in detail by Croton et al. and De Lucia and Blaizot, introduces a ‘radio mode’ feedback from active galactic nuclei (AGN) at the centre of X-ray emitting atmospheres in galaxy groups and clusters. Thanks to this mechanism, the model can simultaneously explain: (i) the low observed mass dropout rate in cooling flows; (ii) the exponential cut-off in the bright end of the galaxy luminosity function and (iii) the bulge-dominated morphologies and old stellar ages of the most massive galaxies in clusters. This paper is the first of a series in which we investigate how well this model can also reproduce the physical properties of BHs and AGN. Here we analyse the scaling relations, the fundamental plane and the mass function of BHs, and compare them with the most recent observational data. Moreover, we extend the semi-analytic model to follow the evolution of the BH mass accretion and its conversion into radiation, and compare the derived AGN bolometric luminosity function with the observed one. While we find for the most part a very good agreement between predicted and observed BH properties, the semi-analytic model underestimates the number density of luminous AGN at high redshifts, independently of the adopted Eddington factor and accretion efficiency. However, an agreement with the observations is possible within the framework of our model, provided it is assumed that the cold gas fraction accreted by BHs at high redshifts is larger than at low redshifts. [ABSTRACT FROM AUTHOR]