What determines satellite galaxy disruption?

In hierarchical structure formation, dark matter halos that merge with larger halos can persist as subhalos. These subhalos are likely hosts of visible galaxies. While the dense halo environment rapidly strips subhalos of their dark mass, the compact luminous material can remain intact for some time, making the correspondence of galaxies with severely stripped subhalos unclear. Many galaxy evolution models assume that satellite galaxies eventually merge with their central galaxy, but this ignores the possibility of satellite tidal disruption. We use a high-resolution $N$-body simulation of cosmological volume to explore satellite galaxy merging/disruption criteria based on dark matter subhalo dynamics. We explore the impact that satellite merging/disruption has on the Halo Occupation Distribution and radial profile of the remnants. Using abundance matching to assign stellar mass/luminosity to subhalos, we compare with observed galaxy clustering, satellite fractions, cluster satellite luminosity functions, finding that subhalos reproduce well these observables on all scales. Our results imply that satellite subhalos corresponding to >0.2L* galaxies must be well-resolved down to 1-3% of their mass at infall to robustly trace the galaxy population. We also explore a simple analytic model based on dynamical friction for satellite galaxy infall, finding good agreement with our subhalo catalog and observations.Comment: 19 pages, 14 figures, accepted for publication in MNRA

Collections for people: museums' stored collections as a public resource

Collections in UK museums grew enormously in the latter half of the 20th century yet museum collections, mostly maintained at public expense, are perceived as an underused resource. The Museums Association’s 2005 report, Collections for the Future1, together with press comments and books such as Treasures on Earth (2002)2 and Fragments of the World (2005)3, brought this issue into sharp focus. Collections for People set out to understand the scale of museum stored collections, and the main parameters of their access and use: • What is the size and nature of collections as a resource? How are they distributed, geographically and among different types of museum? • How much are different types of collection used by people other than museum staff? What sort of people use collections? What do they use them for: research, teaching and learning, creative activities, visits for enjoyment such as store tours? • How do users perceive this service? Do museums actively market collections access? Do they publicise what is in their collections? • How do museums facilitate collections use? What are the factors associated with greater use of collections? What do museums see as the barriers to more use

What triggers black-hole growth? Insights from star formation rates

We present a new semi-analytic model for the common growth of black holes (BHs) and galaxies within a hierarchical Universe. The model is tuned to match the mass function of BHs at z=0 and the luminosity functions of active galactic nuclei (AGNs) at z<4. We use a new observational constraint, which relates the luminosity of AGNs to the star-formation rate (SFR) of their host galaxies. We show that this new constraint is important in various aspects: a) it indicates that BH accretion events are episodic; b) it favours a scenario in which BH accretion is triggered by merger events of all mass ratios; c) it constrains the duration of both merger-induced star-bursts and BH accretion events. The model reproduces the observations once we assume that only 4 per cent of the merger events trigger BH accretion; BHs accretion is not related to secular evolution; and only a few per cent of the mass made in bursts goes into the BH. We find that AGNs with low or intermediate luminosity are mostly being triggered by minor merger events, in broad agreement with observations. Our model matches various observed properties of galaxies, such as the stellar mass function at z<4 and the clustering of galaxies at redshift zero. This allows us to use galaxies as a reliable backbone for BH growth, with reasonable estimates for the frequency of merger events. Other modes of BH accretion, such as disk-instability events, were not considered here, and should be further examined in the future.Comment: accepted to MNRAS, minor changes from version

What Java Developers Know About Compatibility, And Why This Matters

Real-world programs are neither monolithic nor static -- they are constructed using platform and third party libraries, and both programs and libraries continuously evolve in response to change pressure. In case of the Java language, rules defined in the Java Language and Java Virtual Machine Specifications define when library evolution is safe. These rules distinguish between three types of compatibility - binary, source and behavioural. We claim that some of these rules are counter intuitive and not well-understood by many developers. We present the results of a survey where we quizzed developers about their understanding of the various types of compatibility. 414 developers responded to our survey. We find that while most programmers are familiar with the rules of source compatibility, they generally lack knowledge about the rules of binary and behavioural compatibility. This can be problematic when organisations switch from integration builds to technologies that require dynamic linking, such as OSGi. We have assessed the gravity of the problem by studying how often linkage-related problems are referenced in issue tracking systems, and find that they are common

Logahedra: A new weakly relational domain

Weakly relational numeric domains express restricted classes of linear inequalities that strike a balance between what can be described and what can be efficiently computed. Popular weakly relational domains such as bounded differences and octagons have found application in model checking and abstract interpretation. This paper introduces logahedra, which are more expressiveness than octagons, but less expressive than arbitrary systems of two variable per inequality constraints. Logahedra allow coefficients of inequalities to be powers of two whilst retaining many of the desirable algorithmic properties of octagons

What is critique? Towards a sociology of disciplinary heterodoxy in contemporary international law

No abstract available

What Makes the Family of Barred Disc Galaxies So Rich: Damping Stellar Bars in Spinning Haloes

We model and analyse the secular evolution of stellar bars in spinning dark matter (DM) haloes with the cosmological spin lambda ~ 0 -- 0.09. Using high-resolution stellar and DM numerical simulations, we focus on angular momentum exchange between stellar discs and DM haloes of various axisymmetric shapes --- spherical, oblate and prolate. We find that stellar bars experience a diverse evolution which is guided by the ability of parent haloes to absorb angular momentum lost by the disc through the action of gravitational torques, resonant and non-resonant. We confirm the previous claim that dynamical bar instability is accelerated via resonant angular momentum transfer to the halo. Our main findings relate to the long-term, secular evolution of disc-halo systems: with an increasing lambda, bars experience less growth and dissolve after they pass through the vertical buckling instability. Specifically, with an increasing halo spin, (1) The vertical buckling instability in stellar bars colludes with inability of the inner halo to absorb angular momentum --- this emerges as the main factor weakening or destroying bars in spinning haloes; (2) Bars lose progressively less angular momentum, and their pattern speeds level off; (3) Bars are smaller, and for lambda >= 0.06 cease their growth completely following buckling; (4) Bars in lambda > 0.03 haloes have ratio of corotation-to-bar radii, R_CR / R_b > 2, and represent so-called slow bars which do not show offset dust lanes. We provide a quantitative analysis of angular momentum transfer in disc-halo systems, and explain the reasons for absence of growth in fast spinning haloes and its observational corollaries. We conclude that stellar bar evolution is substantially more complex than anticipated, and bars are not as resilient as has been considered so far.Comment: 15 pages., 11 figures, MNRAS, in pres