The effects of metallicity, UV radiation and non-equilibrium chemistry in high-resolution simulations of galaxies

We present a series of hydrodynamic simulations of isolated galaxies with stellar mass of $10^{9} \, \rm{M}_{\odot}$. The models use a resolution of $750 \, \rm{M}_{\odot}$ per particle and include a treatment for the full non-equilibrium chemical evolution of ions and molecules (157 species in total), along with gas cooling rates computed self-consistently using the non-equilibrium abundances. We compare these to simulations evolved using cooling rates calculated assuming chemical (including ionisation) equilibrium, and we consider a wide range of metallicities and UV radiation fields, including a local prescription for self-shielding by gas and dust. We find higher star formation rates and stronger outflows at higher metallicity and for weaker radiation fields, as gas can more easily cool to a cold (few hundred Kelvin) star forming phase under such conditions. Contrary to variations in the metallicity and the radiation field, non-equilibrium chemistry generally has no strong effect on the total star formation rates or outflow properties. However, it is important for modelling molecular outflows. For example, the mass of H$_{2}$ outflowing with velocities $> 50 \, \rm{km} \, \rm{s}^{-1}$ is enhanced by a factor $\sim 20$ in non-equilibrium. We also compute the observable line emission from CII and CO. Both are stronger at higher metallicity, while CII and CO emission are higher for stronger and weaker radiation fields respectively. We find that CII is generally unaffected by non-equilibrium chemistry. However, emission from CO varies by a factor of $\sim 2 - 4$. This has implications for the mean $X_{\rm{CO}}$ conversion factor between CO emission and H$_{2}$ column density, which we find is lowered by up to a factor $\sim 2.3$ in non-equilibrium, and for the fraction of CO-dark molecular gas.Comment: 26 pages, 16 figures, accepted for publication in MNRAS. Minor changes relative to v

On the importance of local sources of radiation for quasar absorption line systems

A generic assumption of ionization models of quasar absorption systems is that radiation from local sources is negligible compared with the cosmological background. We test this assumption and find that it is unlikely to hold for absorbers as rare as H I Lyman limit systems. Assuming that the absorption systems are gas clouds centered on sources of radiation, we derive analytic estimates for the cross-section weighted moments of the flux seen by the absorbers, of the impact parameter, and of the luminosity of the central source. In addition, we compute the corresponding medians numerically. For the one class of absorbers for which the flux has been measured: damped Ly-alpha systems at z~3, our prediction is in excellent agreement with the observations if we assume that the absorption arises in clouds centered on Lyman-break galaxies. Finally, we show that if Lyman-break galaxies dominate the UV background at redshift 3, then consistency between observations of the UV background, the UV luminosity density from galaxies, and the number density of Lyman limit systems requires escape fractions of order 10 percent.Comment: Accepted for publication in the Astrophysical Journal, 11 pages, 1 figure. Version 2: Added alternative method. Decreased fiducial escape fraction to guarantee consistency between observed luminosity density, mean free path, and UV background. This increased the column density above which local radiation is importan

Non-equilibrium chemistry and cooling in the diffuse interstellar medium - I. Optically thin regime

An accurate treatment of the multiphase interstellar medium (ISM) in hydrodynamic galaxy simulations requires that we follow not only the thermal evolution of the gas, but also the evolution of its chemical state, including its molecular chemistry, without assuming chemical (including ionisation) equilibrium. We present a reaction network that can be used to solve for this thermo-chemical evolution. Our model follows the evolution of all ionisation states of the 11 elements that dominate the cooling rate, along with important molecules such as H2 and CO, and the intermediate molecular species that are involved in their formation (20 molecules in total). We include chemical reactions on dust grains, thermal processes involving dust, cosmic ray ionisation and heating and photochemical reactions. We focus on conditions typical for the diffuse ISM, with densities of 10^-2 cm^-3 < nH < 10^4 cm^-3 and temperatures of 10^2 K < T < 10^4 K, and we consider a range of radiation fields, including no UV radiation. In this paper we consider only gas that is optically thin, while paper II considers gas that becomes shielded from the radiation field. We verify the accuracy of our model by comparing chemical abundances and cooling functions in chemical equilibrium with the photoionisation code Cloudy. We identify the major coolants in diffuse interstellar gas to be CII, SiII and FeII, along with OI and H2 at densities nH > 10^2 cm^-3. Finally, we investigate the impact of non-equilibrium chemistry on the cooling functions of isochorically or isobarically cooling gas. We find that, at T < 10^4 K, recombination lags increase the electron abundance above its equilibrium value at a given temperature, which can enhance the cooling rate by up to two orders of magnitude. The cooling gas also shows lower H2 abundances than in equilibrium, by up to an order of magnitude.Comment: 26 pages, 13 figures, accepted for publication in MNRAS. Corrected an error in figure 2. Supplementary material can be found at http://noneqism.strw.leidenuniv.n

Immune function and parasite resistance in male and polymorphic female Coenagrion puella

Background: Colour polymorphisms are widespread and one of the prime examples is the colour polymorphism in female coenagrionid damselflies: one female morph resembles the male colour (andromorph) while one, or more, female morphs are described as typically female (gynomorph). However, the selective pressures leading to the evolution and maintenance of this polymorphism are not clear. Here, based on the hypothesis that coloration and especially black patterning can be related to resistance against pathogens, we investigated the differences in immune function and parasite resistance between the different female morphs and males. Results: Our studies of immune function revealed no differences in immune function between the female morphs but between the sexes in adult damselflies. In an experimental infection females infected shortly after emergence showed a higher resistance against a fungal pathogen than males, however female morphs did not differ in resistance. In a field sample of adult damselflies we did not find differences in infection rates with watermites and gregarines. Conclusion: With respect to resistance and immune function 'andromorph' blue females of Coenagrion puella do not resemble the males. Therefore the colour polymorphism in coenagrionid damselflies is unlikely to be maintained by differences in immunity

Mapping the Cosmic Web with Ly-alpha Emission

We use a high-resolution cosmological simulation to predict the distribution of HI Ly-alpha emission from the low-redshift (z<0.5) intergalactic medium (IGM). Our simulation can be used to reliably compute the emission from optically thin regions of the IGM but not that of self-shielded gas. We therefore consider several models that bracket the expected emission from self-shielded regions. Most galaxies are surrounded by extended (>10^2 kpc) ``coronae'' of optically thin gas with Ly-alpha surface brightness close to the expected background. Most of these regions contain smaller cores of dense, cool gas. Unless self-shielded gas is able to cool to T<10^4.1 K, these cores are much brighter than the background. The Ly-alpha coronae represent ``cooling flows'' of IGM gas accreting onto galaxies. We also estimate the number of Ly-alpha photons produced through the reprocessing of stellar ionizing radiation in the interstellar medium of galaxies; while this mechanism is responsible for the brightest Ly-alpha emission, it occurs on small physical scales and can be separated using high-resolution observations. In all cases, we find that Ly-alpha emitters are numerous (with a space density ~0.1 h^3 Mpc^-3) and closely trace the filamentary structure of the IGM, providing a new way to map gas inside the cosmic web.Comment: 4 pages, 3 figures, accepted by ApJ

Interviewer Effects on Nonresponse

In face-to-face surveys interviewers play a crucial role in making contact with and gaining cooperation from sample units. While some analyses investigate the influence of interviewers on nonresponse, they are typically restricted to single-country studies. However, interviewer training, contacting and cooperation strategies as well as survey climates may differ across countries. Combining call-record data from the European Social Survey (ESS) with data from a detailed interviewer questionnaire on attitudes and doorstep behavior we find systematic country differences in nonresponse processes, which can in part be explained by differences in interviewer characteristics, such as contacting strategies and avowed doorstep behavior.

Size and Causes of the Occupational Gender Wage-gap in the Netherlands

Research from the United States consistently shows that female-dominated occupations generally yield lower wages than male-dominated occupations. Using detailed occupational data, this study analyses the size andcauses of this occupational genderwage-gap in the Dutch labourmarket using multi-levelmodelling techniques.The analyses showthat bothmen andwomen earn lowerwages if they are employed in female-dominated occupations. This especially indicates the signi¢cance of gender inWestern labour markets, since overall levels of wage inequality are relatively small in the Netherlands compared to, for example, the United Kingdom and the United States. Di¡erences in required responsibility are particularly important in accounting for this occupational wage-gap. Nonetheless, we find large wage penalties for working in a female-dominated instead of a maledominated occupation for occupations that require high levels of education, skills, and responsibility.

The scatter and evolution of the global hot gas properties of simulated galaxy cluster populations

We use the cosmo-OWLS suite of cosmological hydrodynamical simulations to investigate the scatter and evolution of the global hot gas properties of large simulated populations of galaxy groups and clusters. Our aim is to compare the predictions of different physical models and to explore the extent to which commonly-adopted assumptions in observational analyses (e.g. self-similar evolution) are violated. We examine the relations between (true) halo mass and the X-ray temperature, X-ray luminosity, gas mass, Sunyaev-Zel'dovich (SZ) flux, the X-ray analogue of the SZ flux ($Y_X$) and the hydrostatic mass. For the most realistic models, which include AGN feedback, the slopes of the various mass-observable relations deviate substantially from the self-similar ones, particularly at late times and for low-mass clusters. The amplitude of the mass-temperature relation shows negative evolution with respect to the self-similar prediction (i.e. slower than the prediction) for all models, driven by an increase in non-thermal pressure support at higher redshifts. The AGN models predict strong positive evolution of the gas mass fractions at low halo masses. The SZ flux and $Y_X$ show positive evolution with respect to self-similarity at low mass but negative evolution at high mass. The scatter about the relations is well approximated by log-normal distributions, with widths that depend mildly on halo mass. The scatter decreases significantly with increasing redshift. The exception is the hydrostatic mass-halo mass relation, for which the scatter increases with redshift. Finally, we discuss the relative merits of various hot gas-based mass proxies.Comment: 31 pages (21 before appendices), 19 figures, 12 tables, accepted by MNRAS after minor revisio

Loading Stark-decelerated molecules into electrostatic quadrupole traps

Beams of neutral polar molecules in a low-field seeking quantum state can be slowed down using a Stark decelerator, and can subsequently be loaded and confined in electrostatic quadrupole traps. The efficiency of the trap loading process is determined by the ability to couple the decelerated packet of molecules into the trap without loss of molecules and without heating. We discuss the inherent difficulties to obtain ideal trap loading, and describe and compare different trap loading strategies. A new "split-endcap" quadrupole trap design is presented that enables improved trap loading efficiencies. This is experimentally verified by comparing the trapping of OH radicals using the conventional and the new quadrupole trap designs