There has been much recent debate over whether the European Union is or should be a ‘militant democratic’ actor in order to respond to democratic backsliding in EU member states. This article argues ...that the EU is a militant democracy in a specific and limited sense, but that this may be normatively undesirable from a democratic perspective. I first develop a definition of militant democracy that focuses on the militant democratic paradox. I argue that the strongest justifications for militant democracy require that two conditions are met: an ‘existential threat condition’ and a ‘necessity condition’. Next, I analyse four ways in which the European Union has been said to be empowered to act in a militant democratic fashion to combat democratic backsliding in EU member states. I show how some, though not all, of these warrant the label ‘militant democracy’. Moving from the descriptive to the normative analysis, I then consider whether the necessity condition can ever be met since there is always the possibility of non-militant responses through forms of EU disintegration. If we accept this argument, EU actors should prioritize robust non-militant measures where possible while pro-democratic member states should disassociate from frankly autocratic member states where non-militant measures fail.
We perform cosmological hydrodynamic simulations to determine to what extent galaxies lose their gas due to photoheating from an ionizing background. We find that the characteristic mass at which ...haloes on average have lost half of their baryons is Mc∼ 6.5 × 109h−1M⊙ at z= 0, which corresponds to a circular velocity of 25 km s−1. This is significantly lower than the filtering mass obtained by the linear theory, which is often used in semi-analytical models of galaxy formation. We demonstrate it is the gas temperature at the virial radius which determines whether a halo can accrete gas. A simple model that follows the merger history of the dark matter progenitors, and where gas accretion is not allowed when this temperature is higher than the virial temperature of the halo, reproduces the results from the simulation remarkably well. This model can be applied to any reionization history, and is easy to incorporate in semi-analytical models.
Galaxies fall into two clearly distinct types: 'blue-sequence' galaxies which are rapidly forming young stars, and 'red-sequence' galaxies in which star formation has almost completely ceased. Most ...galaxies more massive than ... follow the red sequence, while less massive central galaxies lie on the blue sequence. We show that these sequences are created by a competition between star formation-driven outflows and gas accretion on to the supermassive black hole at the galaxy's centre. We develop a simple analytic model for this interaction. In galaxies less massive than ..., young stars and supernovae drive a high-entropy outflow which is more buoyant than any tenuous corona. The outflow balances the rate of gas inflow, preventing high gas densities building up in the central regions. More massive galaxies, however, are surrounded by an increasingly hot corona. Above a halo mass of ..., the outflow ceases to be buoyant and star formation is unable to prevent the build-up of gas in the central regions. This triggers a strongly non-linear response from the black hole. Its accretion rate rises rapidly, heating the galaxy's corona, disrupting the incoming supply of cool gas and starving the galaxy of the fuel for star formation. The host galaxy makes a transition to the red sequence, and further growth predominantly occurs through galaxy mergers. We show that the analytic model provides a good description of galaxy evolution in the EAGLE hydrodynamic simulations. So long as star formation-driven outflows are present, the transition mass scale is almost independent of subgrid parameter choice. (ProQuest: ... denotes formulae/symbols omitted.)
We use the hydrodynamical EAGLE simulation to study the magnitude and origin of the scatter in the stellar mass-halo mass relation for central galaxies. We separate cause and effect by correlating ...stellar masses in the baryonic simulation with halo properties in a matched dark matter only (DMO) simulation. The scatter in stellar mass increases with redshift and decreases with halo mass. At z = 0.1, it declines from 0.25 dex at M..., DMO ... 10... M... to 0.12 dex at M200, DMO ... 10... M..., but the trend is weak above 1012 M... For M..., DMO < 10... M... up to 0.04 dex of the scatter is due to scatter in the halo concentration. At fixed halo mass, a larger stellar mass corresponds to a more concentrated halo. This is likely because higher concentrations imply earlier formation times and hence more time for accretion and star formation, and/or because feedback is less efficient in haloes with higher binding energies. The maximum circular velocity, Vmax, DMO, and binding energy are therefore more fundamental properties than halo mass, meaning that they are more accurate predictors of stellar mass, and we provide fitting formulae for their relations with stellar mass. However, concentration alone cannot explain the total scatter in the M...--M... relation, and it does not explain the scatter in Mstar-Vmax, DMO. Halo spin, sphericity, triaxiality, substructure and environment are also not responsible for the remaining scatter, which thus could be due to more complex halo properties or non-linear/stochastic baryonic effects. (ProQuest: ... denotes formulae/symbols omitted.)
This paper critically engages the legal and political framework for responding to democracy and rule of law backsliding in the EU. I develop a new and original critique of Article 7 TEU based on it ...being democratically illegitimate and normatively incoherent qua itself in conflict with EU fundamental values. Other more incremental and scaleable responses are desirable, and the paper moves on to assess the legitimacy of economic sanctions such as tying access to EU funds to performance on democratic and rule of law indicators or imposing fines on backsliding states. I hold such sanctions to be a priori legitimate, and argue that in some cases economic sanctions are even normatively required, given that EU material support of backsliding member states can amount to material complicity in their backsliding. However, an economic conditionality mechanism would need to be designed to minimize unjust and counterproductive effects. One way to pursue this could be to complement sanctions against the backsliding government with investment for prodemocratic actors in that state.
Abstract
We investigate the connection between the star formation rate (SFR) of galaxies and their central black hole accretion rate (BHAR) using the eagle cosmological hydrodynamical simulation. We ...find, in striking concurrence with recent observational studies, that the 〈SFR〉–BHAR relation for an active galactic nucleus (AGN)-selected sample produces a relatively flat trend, whilst the 〈BHAR〉–SFR relation for an SFR-selected sample yields an approximately linear trend. These trends remain consistent with their instantaneous equivalents even when both SFR and BHAR are time averaged over a period of 100 Myr. There is no universal relationship between the two growth rates. Instead, SFR and BHAR evolve through distinct paths that depend strongly on the mass of the host dark matter halo. The galaxies hosted by haloes of mass M
200 ≲ 1011.5 M⊙ grow steadily, yet black holes (BHs) in these systems hardly grow, yielding a lack of correlation between SFR and BHAR. As haloes grow through the mass range 1011.5 ≲ M
200 ≲ 1012.5 M⊙ BHs undergo a rapid phase of non-linear growth. These systems yield a highly non-linear correlation between the SFR and BHAR, which are non-causally connected via the mass of the host halo. In massive haloes (M
200 ≳ 1012.5 M⊙), both SFR and BHAR decline on average with a roughly constant scaling of SFR/BHAR ∼ 103. Given the complexity of the full SFR–BHAR plane built from multiple behaviours, and from the large dynamic range of BHARs, we find the primary driver of the different observed trends in the 〈SFR〉–BHAR and 〈BHAR〉–SFR relationships are due to sampling considerably different regions of this plane.
The rapid growth phase of supermassive black holes McAlpine, Stuart; Bower, Richard G; Rosario, David J ...
Monthly notices of the Royal Astronomical Society,
12/2018, Letnik:
481, Številka:
3
Journal Article
ABSTRACT
We introduce the Assembly of high-ResoluTion Eagle-simulations of MIlky Way-type galaxieS (artemis) simulations, a new set of 42 zoomed-in, high-resolution (baryon particle mass of $\approx ...2\times 10^4 \, {\rm M}_{\odot }\, h^{-1}$), hydrodynamical simulations of galaxies residing in haloes of Milky Way mass, simulated with the eagle galaxy formation code with re-calibrated stellar feedback. In this study, we analyse the structure of stellar haloes, specifically the mass density, surface brightness, metallicity, colour, and age radial profiles, finding generally very good agreement with recent observations of local galaxies. The stellar density profiles are well fitted by broken power laws, with inner slopes of ≈−3, outer slopes of ≈−4, and break radii that are typically ≈20–40 kpc. The break radii generally mark the transition between in situ formation and accretion-driven formation of the halo. The metallicity, colour, and age profiles show mild large-scale gradients, particularly when spherically averaged or viewed along the major axes. Along the minor axes, however, the profiles are nearly flat, in agreement with observations. Overall, the structural properties can be understood by two factors: that in situ stars dominate the inner regions and that they reside in a spatially flattened distribution that is aligned with the disc. Observations targeting both the major and minor axes of galaxies are thus required to obtain a complete picture of stellar haloes.
The brighter galaxies reionized the Universe Sharma, Mahavir; Theuns, Tom; Frenk, Carlos ...
Monthly Notices of the Royal Astronomical Society Letters,
05/2016, Letnik:
458, Številka:
1
Journal Article
Recenzirano
Odprti dostop
Hydrogen in the Universe was (re)ionized between redshifts z ≈ 10 and z ≈ 6. The nature of the sources of the ionizing radiation is hotly debated, with faint galaxies below current detection limits ...regarded as prime candidates. Here, we consider a scenario in which ionizing photons escape through channels punctured in the interstellar medium by outflows powered by starbursts. We take account of the observation that strong outflows occur only when the star formation density is sufficiently high, and estimate the galaxy-averaged escape fraction as a function of redshift and luminosity from the resolved star formation surface densities in the eagle cosmological hydrodynamical simulation. We find that the fraction of ionizing photons that escape from galaxies increases rapidly with redshift, reaching values of 5–20 per cent at z > 6, with the brighter galaxies having higher escape fractions. Combining the dependence of escape fraction on luminosity and redshift with the observed luminosity function, we demonstrate that galaxies emit enough ionizing photons to match the existing constraints on reionization while also matching the observed ultraviolet-background post-reionization. Our findings suggest that galaxies above the current Hubble Space Telescope detection limit emit half of the ionizing radiation required to reionize the Universe.
We present results from a subset of simulations from the ‘Evolution and Assembly of GaLaxies and their Environments’ (eagle) suite in which the formulation of the hydrodynamics scheme is varied. We ...compare simulations that use the same subgrid models without recalibration of the parameters but employing the standard gadget flavour of smoothed particle hydrodynamics (SPH) instead of the more recent state-of-the-art anarchy formulation of SPH that was used in the fiducial eagle runs. We find that the properties of most galaxies, including their masses and sizes, are not significantly affected by the details of the hydrodynamics solver. However, the star formation rates of the most massive objects are affected by the lack of phase mixing due to spurious surface tension in the simulation using standard SPH. This affects the efficiency with which AGN activity can quench star formation in these galaxies and it also leads to differences in the intragroup medium that affect the X-ray emission from these objects. The differences that can be attributed to the hydrodynamics solver are, however, likely to be less important at lower resolution. We also find that the use of a time-step limiter is important for achieving the feedback efficiency required to match observations of the low-mass end of the galaxy stellar mass function.
PDF
