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Never knew they existed: Yes, a full workshop: Yes, all the time: Never heard of them: I don't want to start my own business: Been here since it started in the Overcoming Bias days: P Aliens in observable universe: I went back and eliminated all outliers - answers with more than 4 digits or answers in the past - which changed the results to: You can see the exact wordings of the questions on the survey.
The online test does not give you your IQ, and does not, on its own, qualify you for a Mensa membership. However it is useful to evaluate your chances to pass. Test your intelligence quotient with good questions. Our IQ test is suitable for all ages.
Ozy ran bivariate correlations between all the numerical data and recorded all correlations that were significant at the. This year for the first time P Aliens and P Aliens2 are entirely uncorrelated with each other. Time in Community, Time on LW, and IQ are not correlated with anything particularly interesting, suggesting all three fail to change people's views. Results we find amusing: Older people and people with more children have more romantic partners it'd be interesting to see if that holds true for the polyamorous. People who believe in anti-agathics and global catastrophic risk are less likely to believe in a great stagnation presumably because both of the above rely on inventions.
People who spend more time on Less Wrong have lower IQs. Height is, bizarrely, correlated with belief in the supernatural and global catastrophic risk. All political viewpoints are correlated with each other in pretty much exactly the way one would expect. They are also correlated with one's level of belief in God, the supernatural, and religion. There are minor correlations with some of the beliefs and number of partners presumably because polyamory , number of children, and number of languages spoken.
Do people in the effective altruism movement donate more money to charity? Do they donate a higher percent of their income to charity? Are they just generally more altruistic people? Of those , donated nothing to charity, and so had a percent donated of 0. I don't want to draw any conclusions about the community from this because the people who provided both their income numbers and their charity numbers are a highly self-selected sample. But are they more compassionate people in general?
After throwing out the people who said they wanted to give blood but couldn't for one or another reason, I got survey respondents giving me an unambiguous answer yes or no about whether they'd ever given blood. Finally, at the end of the survey I had a question offering respondents a chance to cooperate raising the value of a potential monetary prize to be given out by raffle to a random respondent or defect decreasing the value of the prize, but increasing their own chance of winning the raffle. The story so far - our first survey in found an average IQ of Although IQ fell somewhat the next few years - to in and in - people continued to complain.
These scores confirmed the IQ result on the test. But people still objected that something must be up. This year our IQ has fallen further to no Flynn Effect for us! However it is useful to evaluate your chances to pass the actual Mensa IQ test. It is free, and you can pass it online. We strongly recommend to respect the rules of the test. There is no reason to cheat as this is only for yourself to allow you to judge by yourself whether it is worthwhile to attend the official supervised Mensa IQ test.
The simplest way to reach the pre-test is on the Internet. The test is explained in Luxemburgish, English, German and French. A correlation between the richness of the cluster and its metal content is not supported by observations. In recent years, supernova-driven outflows have received increasing attention as the most plausible explanation for the presence of metals in the ICM.
This naturally establishes a metallicity—mass relationship that is in qualitative agreement with the observations. It also predicts the chemical pollution of the ICM as a side-effect of the outflow. This outflow scenario is not without its problems, however. From a theoretical point of view, a skewness of the IMF towards more massive stars at higher redshift might be expected from simple arguments related to the Jeans scale and to the scale of magnetic support against gravitational collapse Larson In this analysis, we will simply sweep the IMF issue under the carpet by treating the chemical yield as one of the parameters in our model.
Many interesting clues about metal enrichment at high redshift have been found by studying Lyman break galaxies LBGs. Studies of the spectral energy distribution of these objects have shown, somewhat surprisingly, that 20 per cent of these galaxies have been forming stars for more than 1 Gyr Shapley et al. This pushes the onset of star formation in these objects to redshifts in excess of 5. Although there seems to be a general consensus that star-formation activity and hence the chemical pollution of the interstellar medium must have started at high redshift, the question of which galaxies are responsible for this pollution is still controversial.
Some theoretical studies show that elliptical galaxies must have played an important role in establishing the observed abundance of the ICM, but these studies often require, as we noted before, an IMF that is skewed towards more massive stars at high redshift. Other studies Garnett suggest that dwarf galaxies have been the main contributors to the chemical pollution of the intergalactic medium IGM. We test that our model is able to reproduce observations of the number density, the stellar populations and the chemical properties of cluster galaxies, as well as the metal content of the ICM.
We then study which galaxies were primarily responsible for polluting the ICM and when this occurred. The paper is structured as follows: In Section 5 we describe how we set the free parameters of our model and we show the main observational properties that can be fitted. Section 6 and Section 7 present the main results of our investigation on the chemical enrichment history of the ICM and the IGM, and investigate two observational tests that may help to distinguish between different feedback schemes.
Our conclusions are presented in Section 8. As a first step, a suitable target cluster is selected from a previously generated cosmological simulation. The particles in the target cluster and its immediate surroundings are traced back to their Lagrangian region and replaced with a larger number of lower-mass particles.
These particles are then perturbed using the same fluctuation field as in the parent simulation, but now extended to smaller scales reflecting the increase in resolution. Outside the high-resolution region, particles of variable mass, increasing with distance, are displaced on a spherical grid whose spacing grows with distance from the high-resolution region and that extends to the box size of the parent simulation. This method allows us to concentrate the computational effort on the cluster of interest and, at the same time, to maintain a faithful representation of the large-scale density and velocity of the parent simulation.
We will exclude these haloes from the analysis. The cluster simulation used in this work was carried out by Barbara Lanzoni as part of her PhD thesis and is described in Lanzoni et al. This used the same resimulation technique as the cluster simulation. The simulation was performed using a parallel p3m code Macfarland et al. The parent cosmological simulation is characterized by the following parameters: The numerical parameters of the simulations used in this work are summarized in Table 1. Numerical parameters for the simulations used.
The prescriptions adopted for the different physical processes included in our model are described in more detail in the next section. In this section we summarize how the semi-analytic model is grafted on to the high-resolution N -body simulation. The techniques we employ in this work are similar to those used by Springel et al. In standard semi-analytic models, all galaxies are located within dark matter haloes. Haloes are usually identified in a simulation using a standard friends-of-friends FOF algorithm with a linking length of 0.
The novelty of the analysis technique developed by Springel et al. This means that the dark matter halo within which a galaxy forms is still followed even after it is accreted by a larger object.
The algorithm used to identify subhaloes subfind is described in detail by Springel et al. The algorithm decomposes a given halo into a set of disjoint and self-bound subhaloes, identified as locally overdense regions in the density field of the background halo. De Lucia et al. As in De Lucia et al. An important change due to the inclusion of subhaloes is a new nomenclature for the different kinds of galaxies present in the simulation.
This galaxy is fed by gas cooling from the surrounding hot halo medium. These galaxies were previously central galaxies of another halo, which then merged to form the larger object. Because the core of the parent halo is still intact, the positions and velocities of these halo galaxies can be accurately determined. Note that gas is no longer able to cool on to halo galaxies.
Dark matter subhaloes lose mass and are eventually destroyed as a result of tidal stripping effects. A galaxy that is no longer identified with a subhalo is called a satellite. The position of the satellite is tracked using the position of the most bound particle of the subhalo before it was disrupted.
This improvement is mainly attributed to a more realistic estimate of the merger rate: This produces first-ranked galaxies that are too bright when compared with observational data. Our treatment of the physical processes driving galaxy evolution is similar to the one adopted in Kauffmann et al. Many prescriptions have been modified in order to properly take into account the exchange of metals between the different phases. We also include metallicity-dependent cooling rates and luminosities.
The details of our implementation are described below. Gas cooling is treated as in Kauffmann et al. It is assumed that the hot gas within dark matter haloes initially follows the dark matter distribution. The cooling radius is defined as the radius for which the local cooling time is equal to the age of the Universe at that epoch. At early times and for low-mass haloes, the cooling radius can be larger than the virial radius. It is then assumed that the hot gas condenses out on a halo dynamical time.
If the cooling radius lies within the virial radius, the gas is assumed to cool quasi-statically and the cooling rate is modelled by a simple inflow equation. Note that the cooling rates are strongly dependent on the temperature of the gas and on its metallicity. At lower temperatures line cooling from heavy elements dominates mainly iron in the 10 6 —10 7 K regime, with oxygen significant at lower temperatures.
The net effect of using metallicity-dependent cooling rates is an overall increase of the brightness of galaxies, because cooling is more efficient. This effect is strongest in low-mass haloes. As in previous models Kauffmann et al.
Note that following Springel et al. The mass of a subhalo, on the other hand, is defined in terms of the total number of particles it contains. The virial velocity of a subhalo is fixed at the velocity that it had just before infall. There are observational indications, however, that low-mass galaxies convert gas into stars less efficiently than high-mass galaxies Kauffmann et al. More importantly, perhaps, the above prescription leads to gas fractions that are essentially independent of the mass of the galaxy.
The theoretical and observational understanding of how the feedback process operates is far from complete. One major uncertainty is whether the reheated gas leaves the halo. This will depend on a number of factors, including the velocity to which the gas is accelerated, the amount of intervening gas, the fraction of energy lost by radiative processes, and the depth of the potential well of the halo. On the observational side, evidence in support of the existence of outflows from galaxies has grown rapidly in the last few years Heckman et al.
In many cases, the observed gas velocities exceed the escape velocity of the parent galaxies; this material will then escape from the galaxies and will be injected into the intergalactic medium. Different methods to estimate the outflow rate suggest that it is comparable to the star-formation rate. These observational results indicate that the outflows preferentially occur in smaller galaxies. This provides a natural explanation for the observed relation between galaxy luminosity and metallicity. An accurate implementation of the feedback process is beyond the capabilities of present numerical codes.
As a result, published simulation results offer little indication of appropriate recipes for treating galactic winds. In this paper we experiment with three different simplified prescriptions for feedback and study whether they lead to different observational signatures. For all the other galaxies halo and satellite galaxies , we assume that the material reheated to the virial temperature of the subhalo is then kinematically stripped and added to the hot component of the main halo.
In hierarchical models of galaxy formation, galaxies and their associated dark matter haloes form through merging and accretion. The formula applies to satellites of mass M sat orbiting at a radius R vir in a halo of virial velocity V vir. For the satellite galaxy mass we use the value of M vir corresponding at the last time the galaxy was a central galaxy either of a halo or of a subhalo. When a small satellite merges with the central galaxy, its stellar mass and cold mass are simply transferred to the central galaxy and the photometric properties are updated accordingly.
In particular we transfer the stellar mass of the merged galaxy to the bulge of the central galaxy and update the photometric properties of this galaxy. If the mass ratio between the stellar component of the merging galaxies is larger than 0. In addition we assume that the merger consumes all the gas left in the two merging galaxies in a single burst.
The stars formed in this burst are also added to the bulge. Note that since the galaxy is fed by a cooling flow, it can grow a new disc later on. The stellar population synthesis models are used to generate look-up tables of the luminosity of a single burst of fixed mass, as a function of the age of the stellar population and as a function of its metallicity. When updating the photometric properties of our model galaxies, we interpolate between these tables using a linear interpolation in t and log Z. It is assumed that stars form with the same metallicity as the cold gas.
We have adopted a Salpeter IMF with upper and lower mass cut-offs of and 0. The most important sources of uncertainty in our model predictions are thus the IMF which affects the luminosity quite strongly and the associated yield which influences the colours. Attenuation of starlight by dust affects the colours of galaxies.
The properties of dust are dependent on a number of factors such as the star-formation rate, that regulates the rate of creation, heating and destruction of dust grains and the distribution of dust and metals within gas clouds. For a single galaxy, all these factors can be taken into account, and it is then possible to model the effect of dust on the galaxy's spectrum.
However, the level of detail that is required goes far beyond the capabilities of our present code. We therefore adopt a dust model that is based on the macroscopic properties of galaxies, i. We assume that a yield Y of heavy elements is produced per solar mass of gas converted into stars. All the metals are instantaneously returned to the cold phase note that this means that we are assuming a mixing efficiency of per cent. We also assume that a fraction R of the mass in stars is returned to the cold gas.
Metals are then exchanged between the different gas phases depending on the feedback model see Section 4. In the retention model, the metals contained in the reheated gas are put in the hot component and can subsequently cool to further enrich the cold phase. In the ejection and wind schemes, the metals can be ejected outside the halo. The ejected metals are reincorporated into the hot halo gas on a halo dynamical time see equation 3.
In more massive systems, the metals contained in the reheated gas are mixed with the hot component of the main halo. For simplicity, we do not consider schemes in which metals are selectively ejected from galaxies. When a satellite galaxy merges, its stars, cold gas and metals are simply added to those of the central galaxy.
Schematic representation of how mass is exchanged between the different phases considered in our models in the absence of accretion from outside.
Each arrow is accompanied by a name indicating the physical process driving the mass exchange. Metals follow the same routes as the mass. Note that the above equations assume that material is being ejected outside haloes. The practical implementation of the prescriptions is described in detail in Springel et al.
For each new snapshot, we estimate the merger time-scales of satellite galaxies that have entered a given halo. The merger clock is reset if the halo containing the satellites merges with a larger system. A new halo may form. In this case its hot gas mass is initialized to the value f b M vir. In this case the accreted baryons are effectively added to the hot component using equation 5. Two haloes can merge. In this case both the ejected component and the hot component of the lower mass halo are added to the hot component of the remnant halo.
The ejected component of the remnant halo remains outside the halo but is reduced by a factor given by equation 3. The cooling rate is assumed to be constant between two successive simulation outputs.
All my life, everyone I've ever hired to work for me, I have trusted my gut. In this plot we only consider the metals ejected from galaxies that reside within the virial radius of the cluster at the present day. This improvement is mainly attributed to a more realistic estimate of the merger rate: Unnamed has promised to analyze the "Extra Credit: If galaxy groups had the same gas fractions as clusters, the observed X-ray background at 0. The top panel shows the fraction of metals in the cluster at the present day as a function of the redshift when they were first incorporated into the ICM. Of the of you, only
The differential equations given above are solved using smaller time-steps 50 between each pair of simulation snapshots. We also check that we get the right normalization and slope for the Tully—Fisher relation. Properties of a Milky-Way-type galaxy in our simulation. The value of the parameter R can be directly estimated from stellar evolution theory for a given choice of IMF. Population synthesis models show that this recycled fraction is roughly independent of metallicity and lies in the range 0.