Context. Feedback from accreting supermassive black holes (SMBHs) is often identified as the main mechanism responsible for regulating star formation in active galactic nucleus (AGN) host galaxies. ...However, the relationships between AGN activity, radiation, winds, and star formation are complex and still far from being understood. Aims. We study scaling relations between AGN properties, host galaxy properties, and AGN winds. We then evaluate the wind mean impact on the global star formation history, taking into account the short AGN duty cycle with respect to that of star formation. Methods. We first collect AGN wind observations for 94 AGN with detected massive winds at sub-pc to kpc spatial scales. We then fold AGN wind scaling relations with AGN luminosity functions, to evaluate the average AGN wind mass-loading factor as a function of cosmic time. Results. We find strong correlations between the AGN molecular and ionised wind mass outflow rates and the AGN bolometric luminosity. The power law scaling is steeper for ionised winds (slope 1.29 ± 0.38) than for molecular winds (0.76 ± 0.06), meaning that the two rates converge at high bolometric luminosities. The molecular gas depletion timescale and the molecular gas fraction of galaxies hosting powerful AGN driven winds are 3–10 times shorter and smaller than those of main sequence galaxies with similar star formation rate (SFR), stellar mass, and redshift. These findings suggest that, at high AGN bolometric luminosity, the reduced molecular gas fraction may be due to the destruction of molecules by the wind, leading to a larger fraction of gas in the atomic ionised phase. The AGN wind mass-loading factor η = ṀOF/SFR is systematically higher than that of starburst driven winds. Conclusions. Our analysis shows that AGN winds are, on average, powerful enough to clean galaxies from their molecular gas only in massive systems at z ≲ 2, i.e. a strong form of co-evolution between SMBHs and galaxies appears to break down for the least massive galaxies.
Using a state-of-the-art semi analytic model for galaxy formation, we investigated in detail the effects of black hole (BH) accretion triggered by disk instabilities (DI) in isolated galaxies on the ...evolution of the AGN population. Specifically, we took on, developed, and expanded the Hopkins & Quataert (2011, MNRAS, 411, 1027) model for the mass inflow following disk perturbations, based on a physical description of nuclear inflows and tested against aimed N-body simulations. We compared the evolution of AGN due to such a DI accretion mode with that arising in a scenario where galaxy interactions (IT mode) produce the sudden destabilization of large quantities of gas feeding the AGN; this constitutes the standard AGN feeding mode implemented in the earliest versions of most semi-analytic models. To study the maximal contribution of DI to the evolution of the AGN population, we extended and developed the DI model to assess the effects of changing the assumed disk surface density profile, and to obtain lower limits for the nuclear star formation rates associated to the DI accretion mode. We obtained the following results: i) For AGN with luminosity M1450 ≳ − 26, the DI mode can provide the BH accretion needed to match the observed AGN luminosity functions up to z ≈ 4.5. In such a luminosity range and redshift, it constitutes a viable candidate mechanism to fuel AGN, and can compete with the IT scenario as the main driver of cosmological evolution of the AGN population. ii) The DI scenario cannot provide the observed abundance of high-luminosity QSO with M1450 ≤ −26 AGN, as well as the abundance of high-redhshift z ≳ 4.5 QSO with M1450 ≤ −24. As found in our earliest works, the IT scenario provides an acceptable match to the observed luminosity functions up to z ≈ 6. iii) The dispersion of the distributions of Eddington ratio λ for low- and intermediate-luminosity AGN (bolometric LAGN = 1043−1045 erg s-1) is predicted to be much smaller in the DI scenario compared to the IT mode. iv) The above conclusions concerning the DI mode are robust with respect to the explored variants of the DI model. We discuss the physical origin of our findings. Finally, we discuss how it is possible to pin down the dominant fueling mechanism of AGN in the low-intermediate luminosity range M1450 ≳ −26 where the DI and the IT modes are both viable candidates as the main drivers of the AGN evolution. We show that an interesting discriminant could be provided by the fraction of AGN with high Eddington ratios λ ≥ 0.5, since it increases with luminosity in the IT case, while the opposite is true in the DI scenario.
We investigate for the first time the effects of a warm dark matter (WDM) power spectrum on the statistical properties of galaxies using a semi-analytic model of galaxy formation. The WDM spectrum we ...adopt as a reference case is suppressed - compared to the standard cold dark matter (CDM) case - below a cut-off scale ≈1 Mpc corresponding (for thermal relic WDM particles) to a mass mX
= 0.75 keV. This ensures consistency with present bounds provided by the microwave background Wilkinson Microwave Anisotropy Probe data and by the comparison of hydrodynamical N-body simulations with observed Lyman-α forest. We run our fiducial semi-analytic model with such a WDM spectrum to derive galaxy luminosity functions (in B, UV and K bands) and the stellar mass distributions over a wide range of cosmic epochs, to compare with recent observations and with the results in the CDM case. The predicted colour distribution of galaxies in the WDM model is also checked against the data. When compared with the standard CDM case, the luminosity and stellar mass distributions we obtain assuming a WDM spectrum are characterized by (i) flattening of the faint-end slope and (ii) sharpening of the cut-off at the bright end for z≲ 0.8. We discuss how the former result is directly related to the smaller number of low-mass haloes collapsing in the WDM scenario, while the latter is related to the smaller number of satellite galaxies accumulating in massive haloes at a low redshift, thus suppressing the accretion of small lumps on the central, massive galaxies. These results shows how adopting a WDM power spectrum may contribute to solving two major problems of CDM galaxy formation scenarios, namely, the excess of predicted faint (low-mass) galaxies at low and - most of all - high redshifts, and the excess of bright (massive) galaxies at low redshifts.
Recent advances in observations have provided a wealth of measurements of the expansions of outflows in galactic disks out to large radii in a variety of galactic hosts. To provide an updated ...baseline for the interpretation of such data, and to assess to what extent the present status of the modeling is consistent with the existing observations, we provide a compact two-dimensional description for the expansion of active galactic nucleus (AGN)-driven shocks in realistic galactic disks with exponential gas density profiles in a disk geometry. We derive solutions for the outflow expansion and the mass outflow rates in different directions with respect to the plane of the disk. These are expressed in terms of the global properties of the host galaxy and of the central AGN to allow for an easy and direct comparison with existing observations in a variety of galactic hosts with measured properties, and out to distances of ∼10 kpc from the center. The results are compared with a state-of-the-art compilation of observed outflows in 19 galaxies with different measured gas and dynamical mass, allowing for a detailed, one-by-one comparison with the model predictions. The agreement we obtain for a wide range of host galaxy gas mass ( ) and AGN bolometric luminosity ( ) provides a quantitative systematic test for the modeling of AGN-driven outflows in galactic disks. We also consider a larger sample of 48 objects in galaxies with no reliable measurements of the gas and dynamical mass. In this case, we perform a comparison of the model predictions for different bins of AGN luminosities assuming different reference values for the gas mass and dynamical mass derived from average scaling relations. Finally, we reconsider the AGN wind scaling laws empirically derived by many authors in light of the results from our updated models. The encouraging, quantitative agreement of the model predictions with a wide set of existing observations constitutes a baseline for the interpretation of forthcoming data, and for a more detailed treatment of AGN feedback in galaxy formation models.
We use deep Herschel observations taken with both PACS and SPIRE imaging cameras to estimate the dust mass of a sample of galaxies extracted from the GOODS-S, GOODS-N and the COSMOS fields. We divide ...the redshift–stellar mass (Mstar)–star formation rate (SFR) parameter space into small bins and investigate average properties over this grid. In the first part of the work we investigate the scaling relations between dust mass, stellar mass and SFR out to z = 2.5. No clear evolution of the dust mass with redshift is observed at a given SFR and stellar mass. We find a tight correlation between the SFR and the dust mass, which, under reasonableassumptions, is likely a consequence of the Schmidt-Kennicutt (S-K) relation. The previously observed correlation between the stellar content and the dust content flattens or sometimes disappears when considering galaxies with the same SFR. Our finding suggests that most of the correlation between dust mass and stellar mass obtained by previous studies is likely a consequence of the correlation between the dust mass and the SFR combined with the main sequence, i.e., the tight relation observed between the stellar mass and the SFR and followed by the majority of star-forming galaxies. We then investigate the gas content as inferred from dust mass measurements. We convert the dust mass into gas mass by assuming that the dust-to-gas ratio scales linearly with the gas metallicity (as supported by many observations). For normal star-forming galaxies (on the main sequence) the inferred relation between the SFR and the gas mass (integrated S-K relation) broadly agrees with the results of previous studies based on CO measurements, despite the completely different approaches. We observe that all galaxies in the sample follow, within uncertainties, the same S-K relation. However, when investigated in redshift intervals, the S-K relation shows a moderate, but significant redshift evolution. The bulk of the galaxy population at z ~ 2 converts gas into stars with an efficiency (star formation efficiency, SFE = SFR/Mgas, equal to the inverse of the depletion time) about 5 times higher than at z ~ 0. However, it is not clear what fraction of such variation of the SFE is due to an intrinsic redshift evolution and what fraction is simply a consequence of high-z galaxies having, on average, higher SFR, combined with the super-linear slope of the S-K relation (while other studies find a linear slope). We confirm that the gas fraction (fgas = Mgas/(Mgas + Mstar)) decreases with stellar mass and increases with the SFR. We observe no evolution with redshift once Mstarand SFR are fixed. We explain these trends by introducing a universal relation between gas fraction, stellar mass and SFR that does not evolve with redshift, at least out to z ~ 2.5. Galaxies move across this relation as their gas content evolves across the cosmic epochs. We use the 3D fundamental fgas–Mstar–SFR relation, along with the evolution of the main sequence with redshift, to estimate the evolution of the gas fraction in the average population of galaxies as a function of redshift and as a function of stellar mass: we find that Mstar ≳ 1011 M⊙ galaxies show the strongest evolution at z ≳ 1.3 and a flatter trend at lower redshift, while fgas decreases more regularly over the entire redshift range probed in Mstar ≲ 1011 M⊙ galaxies, in agreement with a downsizing scenario.
We compute the non-thermal emissions produced by relativistic particles accelerated by the shocks driven by the active galactic nucleus (AGN) in NGC 1068, and we compare the model predictions with ...the observed γ-ray and radio spectra. The former is produced by pion decay, inverse Compton scattering, and bremsstrahlung, while the latter is produced by synchrotron radiation. We derive the γ-ray and radio emissions by assuming the standard acceleration theory, and we discuss how our results compare with those corresponding to other commonly assumed sources of γ-ray and radio emissions, like supernova remnants (SNR) or AGN jets. We find that the AGN-driven shocks observed in the circumnuclear molecular disk of NGC 1068 provide a contribution to the γ-ray emission comparable to that provided by the starburst activity when standard particle acceleration efficiencies are assumed, while the shocks can yield the whole γ-ray emission only when the parameters describing the acceleration efficiency and the proton coupling with the molecular gas are tuned to values larger than those assumed in standard, SNR-driven shocks. We discuss the range of acceleration efficiencies (for protons and electrons) and of proton calorimetric fractions required to account for the observed γ-ray emission in the AGN outflow model. We further compare the neutrino flux expected in our model with constraints from current experiments, and we provide predictions for the detections by the upcoming KM3NeT neutrino telescope. This analysis strongly motivates observations of NGC 1068 at ≳TeV energies with current and future Cherenkov telescopes in order to gain insight into the nature of the γ-rays source.
We derive the contribution to the extragalactic gamma-ray background (EGB) from active galactic nuclei (AGN) winds and star-forming galaxies by including a physical model for the γ-ray emission ...produced by relativistic protons accelerated by AGN-driven and supernova-driven shocks into a state-of-the-art semi-analytic model of galaxy formation. This is based on galaxy interactions as triggers of AGN accretion and starburst activity and on expanding blast waves as the mechanism to communicate outwards the energy injected into the interstellar medium by the active nucleus. We compare the model predictions with the latest measurement of the EGB spectrum performed by the Large Area Telescope (LAT) on board the Fermi Gamma-ray Space Telescope (Fermi) in the range between 100 MeV and 820 GeV. We find that AGN winds can provide ~35 ± 15% of the observed EGB in the energy interval Eγ = 0.1–1 GeV, for ~73 ± 15% at Eγ = 1–10 GeV, and for ~60 ± 20% at Eγ ≳10 GeV. The AGN wind contribution to the EGB is predicted to be larger by a factor of ~3–5 than that provided by star-forming galaxies (quiescent plus starburst) in the hierarchical clustering scenario. The cumulative γ-ray emission from AGN winds and blazars can account for the amplitude and spectral shape of the EGB, assuming the standard acceleration theory, and AGN wind parameters that agree with observations. We also compare the model prediction for the cumulative neutrino background from AGN winds with the most recent IceCube data. We find that for AGN winds with accelerated proton spectral index p = 2.2–2.3, and taking into account internal absorption of γ-rays, the Fermi-LAT and IceCube data could be reproduced simultaneously.
Context. There have been recent claims that a significant fraction of type 2 AGN accrete close to or even above the Eddington limit. In type 2 AGN, the bolometric luminosity (Lb) is generally ...inferred from the OIII emission line luminosity (LOIII). The key issue in estimating the bolometric luminosity in these AGN, is therefore to know the bolometric correction to be applied to LOIII. A complication arises from the observed LOIII being affected by extinction, most likely from dust within the narrow line region. The extinction-corrected OIII luminosity ($L^{\rm c}_{\rm OIII}$) is a better estimator of the nuclear luminosity than LOIII. However, only the bolometric correction to be applied to the uncorrected LOIII has been evaluated so far. Aims. This paper is devoted to estimating the bolometric correction $C_{\rm OIII}=L_{\rm b}$/$L^{\rm c}_{\rm OIII}$ for deriving the Eddington ratios for the type 2 AGN in a sample of SDSS objects. Methods. We collected 61 sources from the literature with reliable estimates of both $L^{\rm c}_{\rm OIII}$ and X-ray luminosities (LX). To estimate COIII, we combined the observed correlation between $L^{\rm c}_{\rm OIII}$ and LX with the X-ray bolometric correction. Results. In contrast to previous studies, we found a linear correlation between $L^{\rm c}_{\rm OIII}$ and LX. We estimated COIII using an earlier luminosity-dependent X-ray bolometric correction, and we found a mean value of COIII in the luminosity ranges log LOIII = 38–40, 40–42, and 42–44 of 87, 142, and 454, respectively. We used it to calculate the Eddington ratio distribution of type 2 SDSS AGN at $0.3<z<0.4$ and found that these sources are not accreting near their Eddington limit, contrary to previous claims.
We investigate galaxy formation in models with dark matter (DM) constituted by sterile neutrinos. Given their large parameter space, defined by the combinations of sterile neutrino mass and mixing ...parameter with active neutrinos, we focus on models with , consistent with the tentative 3.5 keV line detected in several X-ray spectra of clusters and galaxies. We consider (1) two resonant production models with and , to cover the range of mixing parameters consistent with the 3.5 keV line; (2) two scalar-decay models, representative of the two possible cases characterizing such a scenario: a freeze-in and a freeze-out case. We also consider thermal warm DM with particle mass . Using a semianalytic model, we compare the predictions for the different DM scenarios with a wide set of observables. We find that comparing the predicted evolution of the stellar mass function, the abundance of satellites of Milky Way-like galaxies, and the global star formation history of galaxies with observations does not allow us to disentangle the effects of the baryonic physics from those related to the different DM models. On the other hand, the distribution of the stellar-to-halo mass ratios, the abundance of faint galaxies in the UV luminosity function at , and the specific star formation and age distribution of local, low-mass galaxies constitute potential probes for the DM scenarios considered. We discuss how future observations with upcoming facilities will enable us to rule out or to strongly support DM models based on sterile neutrinos.
An increasing amount of observational evidence supports the notion that there are two modes of star formation: a quiescent mode in disk-like galaxies and a starburst mode, which is generally ...interpreted as driven by merging. Using a semi-analytic model of galaxy formation, we derive the relative contribution to the cosmic star formation rate density of quiescently star forming and starburst galaxies, predicted under the assumption that starburst events are triggered by galaxy encounters (merging and fly-by kind) during their merging histories. We show that, within this framework, quiescently star forming galaxies dominate the cosmic star formation rate density at all redshifts. The contribution of the burst-dominated star forming galaxies increases with redshift, starting from ≲5% at low redshift (z ≲ 0.1) to ~20% at z ≥ 5. We estimated that the fraction of the final (z = 0) galaxy stellar mass that is formed through the burst component of star formation is ~10% for 1010 M⊙ ≤ M∗ ≤ 1011.5 M⊙. Selected according to their distance from the galaxy main sequence, starburst galaxies account for ~10% of the star formation rate density in the redshift interval 1.5 < z < 2.5, i.e., at the cosmic peak of the star formation activity.
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