Galactic 26Al traces metal loss through hot chimneys

ABSTRACT Radioactive 26Al is an excellent tracer for metal ejection in the Milky Way, and can provide a direct constraint on the modelling of supernova feedback in galaxy evolution. Gamma-ray observations of the 26Al decay line have found high velocities and hence require a significant fraction of the Galactic 26Al in the hot component. At the same time, meteoritic data combined with simulation results suggest that a significant amount of 26Al makes its way into stars before decay. We investigated the distribution into hot and cold channels with a simulation of a Milky-Way-like galaxy with massive-star feedback in superbubbles and with ejecta traced by 26Al. About 30–40 per cent of the ejecta remain hot, with typical cooling times of the order Gyr. 26Al traces the footpoints of a chimney-fed outflow that mixes metals turbulently into the halo of the model galaxy on a scale of at least 50 kpc. The rest diffuses into cold gas ≲ 104 K, and may therefore be quickly available for star formation. We discuss the robustness of the result by comparison to a simulation with a different global flow pattern. The branching ratio into hot and cold components is comparable to that of longer term average results from chemical evolution modelling of galaxies, clusters, and the intracluster medium.

Measuring the growth of structure by matching dark matter haloes to galaxies with VIPERS and SDSS

ABSTRACT We test the history of structure formation from redshift 1 to today by matching galaxies from the VIMOS Public Extragalactic Redshift Survey (VIPERS) and Sloan Digital Sky Survey (SDSS) with dark matter haloes in the MultiDark, Small MultiDark Planck (SMDPL), N-body simulation. We first show that the standard subhalo abundance matching (SHAM) recipe implemented with MultiDark fits the clustering of galaxies well both at redshift 0 for SDSS and at redshift 1 for VIPERS. This is an important validation of the SHAM model at high redshift. We then remap the simulation time steps to test alternative growth histories and infer the growth index γ = 0.6 ± 0.3. This analysis demonstrates the power of using N-body simulations to forward model galaxy surveys for cosmological inference. The data products and code necessary to reproduce the results of this analysis are available online (https://github.com/darklight-cosmology/vipers-sham).

Weak-field general relativistic dynamics and the Newtonian limit

We show that the generally held view that the gravity of weak-field nonrelativistic-velocity sources being invariably almost equivalent to Newtonian gravity (NG) (the “Newtonian limit” approach) is in some instances misleading and in other cases incorrect. A particularly transparent example is provided by comparing the Newtonian and general relativistic analyses of a simple variant of van Stockum’s infinite rotating dust cylinder. We show that some very recent criticisms of our work that had been motivated by the Newtonian limit approach were incorrect and note that no specific errors in our work were found in the critique. In the process, we underline some problems that arise from inappropriate coordinate transformations. As further support for our methodology, we note that our weak-field general relativistic treatment of a model galaxy was vindicated recently by the observations of Xu et al. regarding our prediction that the Milky Way was 19–21 kpc in radius as opposed to the commonly held view that the radius was 15 kpc.

The cluster environments of radio-loud AGN

Radio-loud AGN play an important rôle in galaxy evolution. We need to understand their properties, and the processes that affect their behaviour in order to model galaxy formation and development. We here present preliminary results of an investigation into the cluster environments of radio galaxies. We have found evidence of a strong correlation between radio luminosity and environment richness for low excitation radio galaxies, and no evidence of evolution of the environment with redshift. Conversely, for high excitation radio galaxies, we found no correlation with environment richness, and tentative evidence of evolution of the cluster environment.

The UV upturn phenomenon in the hierarchical universe

Recent studies show that an old stellar population with high metallicity in the monolithic paradigm can explain the UV upturn. Numerical simulations and empirical studies however point out that massive early-type galaxies have evolved hierarchically with an extended star formation history. This obviously has an impact on our traditional understanding on the UV upturn and requires a new investigation on its origin. We report on our investigation on the evolutionary history of model galaxy SEDs in the hierarchical scenario. The use of conventional population models (calibrated to the monolithic picture) in combination with merger trees and extended star formation fails to reproduce the observed UV upturn. If a hierarchical picture is thought to be more realistic than a monolithic one, new calibration on the population models is required.

Building stable stellar systems with ρ as the only datum

Schwarzschild's method to set up a model galaxy is most useful when the distribution in velocity space is unknown. Nevertheless, one has to know beforehand which kind of orbits are spawned by the potential of the model. Moreover, although the system thus generated is in equilibrium, it is not necessarily stable. Here, we present a new method that allows to build up a stable stellar system without any previous knowledge of its distribution in velocity space.

Initial Model Catalogue for Galaxy Evolution

We have computed full hydrochemodynamical evolution for 150 initial models of protogalaxies with our chemodynamical SPH code named GENSO. Various parameters for all models are identical except for a seed for a random number generator. In other words, all models have similar global properties but have the different merging history that leads to a different evolution in each model. Results of the series of computations have two main applications. Firstly, we have an initial model catalogue for subsequent modelling of galaxy evolution. Since the resulting evolution depends strongly on the initial phase of the particle distribution, it is crucial to find a suitable initial model when we model a specific real galaxy in the Universe, notably the Milky Way in our case. We will make a precise chemical and dynamical model of the Milky Way out of 150 models in our initial model catalogue. Secondly, we can obtain a large variety of global histories of physical values such as star formation, metallicity in the ISM and stellar components, and Type II and Ia supernova rates. For example, the resulting total star formation history shows the peak at a high redshift z ∼ 6 and the peak value is ∼280 M⊙ yr–1 Mpc–3. Also, the Type Ia rate obtained has a peak at z ∼ 3.5. All of our results and model catalogue are publicly available from our website for those who wish to model galaxy evolution.

Cloud mass function in a gas rich dwarf galaxy

We study cloud mass function (here after CMF) obtained in a Grape-SPH simulation of model galaxy. The CMF can be fitted by a simple power law, and its power law index is ∼ −2.0, which closes to the observational results.

A search for features in early-type galaxies

We are conducting a search for dust lanes, incipient stellar disks and bars, and other deviations from elliptical symmetry in a sample ∼ 250 early-type galaxies. Division by a model galaxy image is a very powerful enhancement technique for this type of work.

A collision between the Large and Small Magellanic Clouds 2×108 years ago

A number of orbits are obtained for the Large and Small Magellanic Clouds (LMC and SMC) revolving around a model Galaxy with a massive halo. It is suggested that the SMC approached the LMC as close as 3 to 7 kpc about 200 million years ago, if these clouds have been in a binary state for the past 1010 years, and the Magellanic Stream (MS) is due to the gravitational interaction among the triple system of the Galaxy, LMC, and SMC.