Thursday. Wayne Hu visits IPMU today.
[*]1212.4143
The dependence of the mass-size relation of early-type galaxies on environment in the local Universe
Huertas-Company, .. Mei, Bernardi, ... et al
ETG mass-size relation studied to understand how these galaxies have assembled their mass. One key observational results of the last years is that massive galaxies increased their size by a factor of a few at fixed stellar mass from z~2. Minor mergers have been put forward in hierarchical models as a plausible driver of this size growth. Some of these models, predict a significant environmental dependence in the sense that galaxies residing in more massive haloes tend to be larger than galaxies in lower mass haloes, at fixed stellar mass and redshift. At present observational results of this environmental dependence have been contradictory. In this paper, revisit this issue in the local Universe, by carefully investigating how the sizes of massive ETGs depend on large-scale environment using an updated sample of massive ETGs (>1e11) in different environments - field, group, clusters - from SDSS DR7. Observations do not show any environmental dependence of the sizes of central and satellite ETGs at fixed stellar mass. The size-mass relation of early-type galaxies seems to be universal, independent of the mass of the host halo and of the position of the galaxy in that halo (central or satellite). Compare observational results with two hierarchical models build from Millennium SIm. Find results to broadly agree (w/in 1-2 sigma) with one of the models, but strongly disagree with the other (at 3 sigma), proving how useful environment is in testing galaxy evolution models.
[*]1212.4153
On the multiplicity of supernovae within host galaxies
Anderson, Soto
Investigate nature of multiple supernova hosting galaxies, and the types of events which they produce. Using all known historical supernovae, split host galaxies into samples containing single or multiple events. These samples are then characterized in terms of their relative SNe fractions, and host properties. In multiple SNe hosts the ratio of type Ia to core-collapse events is lower than in single SNe hosts. For core-collapse events there is a suggestion that the ratio of types Ibc to type II events is higher in multiples than within single SNe hosts. This second increase is dominated by an increase in the number of SNIb. Within multiple SNe hosts, SNe of any given type appear to 'prefer' to explode in galaxies that are host to the same type of SN. Also find that multiple SN hosts have higher T-type morphologies [what is that?]. While these results suffer from low number statistics, speculate that their simplest interpretation is that SF within galaxies is generally of an episodic and bursty nature. This leads to the SNe detected within any particular galaxy to be dominated by those with progenitors of a specific age, rather than a random selection from standard relative SNe rates, as the latter would be expected if SF was of a long-term continuous nature. Further discuss the SNe progenitor and SF properties that may be important for understanding these trends, and also comment on a range of important selection effects within the sample.
1212.4157
Ellipsoidal halo finders and implications for models of triaxial halo formation
Despali, Tormen, Sheth
Describe an algorithm for identifying ellipsoidal haloes in numerical simulations, and quantify how the resulting estimates of halo mass and shape differ with respect to spherical halo finders. Haloes become more prolate when fit with ellipsoids, the difference being most pronounced for the more aspherical objects. Although the ellipsoidal mass is systematically larger, this is typically by less than 10% for most of the haloes [?]. However, even this small difference in mass corresponds to a significant difference in shape from the spherical counterpart. Quantify these effects on the initial mass and deformation tensors, on which most models of triaxial collapse are based. By studying the properties of protohaloes in the initial conditions, find that models in which protohaloes are identified in Lagrangian space by three positive eigenvalues of the deformation tensor are are tenable only at the masses well-above M*. The overdensity delta within almost any protohalo is larger than the critical value associated with spherical collapse; this is in good qualitative agreement with models which identify haloes requiring that collapse have occurred along all 3 principal axes, each axis having turned around from the universal expansion at a different time. On average, delta increases as mass M decreases, scaling as delta_c(1+0.2 sigma) with rms scatter 0.2 sigma(M). The mean ellipticity e and prolateness p of the deformation tensor both increase as M decreases.
[*] 1212.4185
Distant galaxy clusters in the XMM large scale structure survey
Willis et al
Sample of 22 distant (z>0.8) galaxy clusters and cluster candidates from and overlap of XMM, CFHTLS and Spitzer SWIRE surveys. Clusters are selected as extended X-ray sources with an accompanying overdensity of galaxies displaying optical to mid-infrared photometry consistent with z>0.8. Nine clusters confirmed spectroscopic redshifts in the interval 0.8<z<1.2, 4 of which are new. A further 11 candidate cluaters have between 8 and 10 band photometric redshifts in the interval 0.8<z<2.2, while the remaining 2 candidates do not have information in sufficient wavebands to generate a reliable photometric redshift. All candidate clusters are new. These clusters with NIR photometry display evidence for a RS galaxy population, determined either individually or via stacking, whose color is consistent with the expectation of an old, coeval stellar population observed at the cluster redshift. Note that the sample displays a large range of red fraction values indicating that the clusters may be at different stages of red sequence assembly. Compare the observed X-ray emission to the flux expected from a suite of model clusters and find that the sample displays an effective mass limit M200~1e14 Msun with all clusters displaying masses consistent with M200<5e14 Msun. This XMM distant cluster study represents a complete sample of X-ray selected z>0.8 clusters. [really? complete?]
[*]1212.4359
Purring the precision in precision cosmology: how accurate should your data covariance matrix be?
Taylor, Joachimi, Kitching
Parameter estimation in cosmology requires that the likelihood function of the data is accurately known. Assuming that cosmological large-scale structure power spectra data are multivariate Gaussian-distributed, we show the accuracy of parameter estimation is limited by the accuracy of the inverse data covariance matrix - the precision matrix. If the data covariance and precision matrices are estimated by sampling independent realizations of the data, their statistical properties are described by the Wishart and Inverse-Wishart distributions, respectively. Independent of any details of the survey, show that the fractional error on a parameter variance, or FoM, is equal to the fractional variance of the parameter error depends only on the difference between the number of independent realisations and the number of data points, and so can easily diverge. For a 5% error on a parameter error and N_D << 100 data points, a minimum of 200 realisations of the survey are needed, with 10% accuracy for the data covariance. If the number of data-points N_D>>100, need N_S > N_D realizations and a fractional accuracy of <sqrt(2/N_D) in the data covariance. As the number of power spectra data points grows to N_D>1e4-6 this approach will be problematic. We discuss possible ways to relax these conditions: improved theoretical modeling; shrinkage methods; data-compression; simulation and data resampling methods.
[*]1212.4433
Influence of baryonic physics in galaxy simulations: the molecular component
Halle, Combes
Role of baryon physics to solve the main problems encountered by the standard theory at the galactic scale, such as the galaxy stellar mass functions, or the missing satellites problem. The present work aims at investigating in particular the role of the cold and dense molecular phase, which could play a role of gas reservoir in the outer galaxy discs, with low star formation efficiency. Through TreeSPH simulations, implementing the cooling to low temperatures, and the inclusion of the molecular hydrogen component, several feedback efficiencies are studied, and results on the gas morphology and SF are obtained. It is shown that molecular hydrogen allows some slow SF to occur in the outer parts of the discs. This dense and quiescent phase might be a way to store a significant fraction of dark baryons, in a relatively long time-scale, in the complete baryonic cycle, connecting the galaxy discs to host gaseous haloes and to the cosmic filaments.
1212.4452
The escape fraction of ionizing radiation from primordial galaxies
Benson, Venkatesan, Shull
Escape of ionizing radiation from galaxies plays a critical role in the evolution of gas in galaxies, and the heating and ionization history of the IGM. Present semi-analytic calculations of the escape fraction of ionizing radiation for both H and He from primordial galaxies, as well as analytic derivations of these quantities. Consider variations in the galaxy density profile, source type, location, and spectrum, and gas clumping/distribution factors. For sufficiently hard first-light sources, the He ionization fronts closely track or even advance beyond that of hydrogen. Key new results in this work include calculations of the escape fractions for He I and He II ionizing radiation, and the impact of partial ionization from X-rays from early AGN or stellar clusters on the escape fractions from primordial haloes. When factoring in frequency-dependent effects, find that X-rays play an important role in boosting the escape fractions for both H and He, but especially for He II. Briefly discuss the implications of these results for recent observations of the He II reionization epoch at low redshifts, as well as the UV data and emission line signatures from early galaxies anticipated from future satellite missions.
[*]1212.4143
The dependence of the mass-size relation of early-type galaxies on environment in the local Universe
Huertas-Company, .. Mei, Bernardi, ... et al
ETG mass-size relation studied to understand how these galaxies have assembled their mass. One key observational results of the last years is that massive galaxies increased their size by a factor of a few at fixed stellar mass from z~2. Minor mergers have been put forward in hierarchical models as a plausible driver of this size growth. Some of these models, predict a significant environmental dependence in the sense that galaxies residing in more massive haloes tend to be larger than galaxies in lower mass haloes, at fixed stellar mass and redshift. At present observational results of this environmental dependence have been contradictory. In this paper, revisit this issue in the local Universe, by carefully investigating how the sizes of massive ETGs depend on large-scale environment using an updated sample of massive ETGs (>1e11) in different environments - field, group, clusters - from SDSS DR7. Observations do not show any environmental dependence of the sizes of central and satellite ETGs at fixed stellar mass. The size-mass relation of early-type galaxies seems to be universal, independent of the mass of the host halo and of the position of the galaxy in that halo (central or satellite). Compare observational results with two hierarchical models build from Millennium SIm. Find results to broadly agree (w/in 1-2 sigma) with one of the models, but strongly disagree with the other (at 3 sigma), proving how useful environment is in testing galaxy evolution models.
[*]1212.4153
On the multiplicity of supernovae within host galaxies
Anderson, Soto
Investigate nature of multiple supernova hosting galaxies, and the types of events which they produce. Using all known historical supernovae, split host galaxies into samples containing single or multiple events. These samples are then characterized in terms of their relative SNe fractions, and host properties. In multiple SNe hosts the ratio of type Ia to core-collapse events is lower than in single SNe hosts. For core-collapse events there is a suggestion that the ratio of types Ibc to type II events is higher in multiples than within single SNe hosts. This second increase is dominated by an increase in the number of SNIb. Within multiple SNe hosts, SNe of any given type appear to 'prefer' to explode in galaxies that are host to the same type of SN. Also find that multiple SN hosts have higher T-type morphologies [what is that?]. While these results suffer from low number statistics, speculate that their simplest interpretation is that SF within galaxies is generally of an episodic and bursty nature. This leads to the SNe detected within any particular galaxy to be dominated by those with progenitors of a specific age, rather than a random selection from standard relative SNe rates, as the latter would be expected if SF was of a long-term continuous nature. Further discuss the SNe progenitor and SF properties that may be important for understanding these trends, and also comment on a range of important selection effects within the sample.
1212.4157
Ellipsoidal halo finders and implications for models of triaxial halo formation
Despali, Tormen, Sheth
Describe an algorithm for identifying ellipsoidal haloes in numerical simulations, and quantify how the resulting estimates of halo mass and shape differ with respect to spherical halo finders. Haloes become more prolate when fit with ellipsoids, the difference being most pronounced for the more aspherical objects. Although the ellipsoidal mass is systematically larger, this is typically by less than 10% for most of the haloes [?]. However, even this small difference in mass corresponds to a significant difference in shape from the spherical counterpart. Quantify these effects on the initial mass and deformation tensors, on which most models of triaxial collapse are based. By studying the properties of protohaloes in the initial conditions, find that models in which protohaloes are identified in Lagrangian space by three positive eigenvalues of the deformation tensor are are tenable only at the masses well-above M*. The overdensity delta within almost any protohalo is larger than the critical value associated with spherical collapse; this is in good qualitative agreement with models which identify haloes requiring that collapse have occurred along all 3 principal axes, each axis having turned around from the universal expansion at a different time. On average, delta increases as mass M decreases, scaling as delta_c(1+0.2 sigma) with rms scatter 0.2 sigma(M). The mean ellipticity e and prolateness p of the deformation tensor both increase as M decreases.
[*] 1212.4185
Distant galaxy clusters in the XMM large scale structure survey
Willis et al
Sample of 22 distant (z>0.8) galaxy clusters and cluster candidates from and overlap of XMM, CFHTLS and Spitzer SWIRE surveys. Clusters are selected as extended X-ray sources with an accompanying overdensity of galaxies displaying optical to mid-infrared photometry consistent with z>0.8. Nine clusters confirmed spectroscopic redshifts in the interval 0.8<z<1.2, 4 of which are new. A further 11 candidate cluaters have between 8 and 10 band photometric redshifts in the interval 0.8<z<2.2, while the remaining 2 candidates do not have information in sufficient wavebands to generate a reliable photometric redshift. All candidate clusters are new. These clusters with NIR photometry display evidence for a RS galaxy population, determined either individually or via stacking, whose color is consistent with the expectation of an old, coeval stellar population observed at the cluster redshift. Note that the sample displays a large range of red fraction values indicating that the clusters may be at different stages of red sequence assembly. Compare the observed X-ray emission to the flux expected from a suite of model clusters and find that the sample displays an effective mass limit M200~1e14 Msun with all clusters displaying masses consistent with M200<5e14 Msun. This XMM distant cluster study represents a complete sample of X-ray selected z>0.8 clusters. [really? complete?]
[*]1212.4359
Purring the precision in precision cosmology: how accurate should your data covariance matrix be?
Taylor, Joachimi, Kitching
Parameter estimation in cosmology requires that the likelihood function of the data is accurately known. Assuming that cosmological large-scale structure power spectra data are multivariate Gaussian-distributed, we show the accuracy of parameter estimation is limited by the accuracy of the inverse data covariance matrix - the precision matrix. If the data covariance and precision matrices are estimated by sampling independent realizations of the data, their statistical properties are described by the Wishart and Inverse-Wishart distributions, respectively. Independent of any details of the survey, show that the fractional error on a parameter variance, or FoM, is equal to the fractional variance of the parameter error depends only on the difference between the number of independent realisations and the number of data points, and so can easily diverge. For a 5% error on a parameter error and N_D << 100 data points, a minimum of 200 realisations of the survey are needed, with 10% accuracy for the data covariance. If the number of data-points N_D>>100, need N_S > N_D realizations and a fractional accuracy of <sqrt(2/N_D) in the data covariance. As the number of power spectra data points grows to N_D>1e4-6 this approach will be problematic. We discuss possible ways to relax these conditions: improved theoretical modeling; shrinkage methods; data-compression; simulation and data resampling methods.
[*]1212.4433
Influence of baryonic physics in galaxy simulations: the molecular component
Halle, Combes
Role of baryon physics to solve the main problems encountered by the standard theory at the galactic scale, such as the galaxy stellar mass functions, or the missing satellites problem. The present work aims at investigating in particular the role of the cold and dense molecular phase, which could play a role of gas reservoir in the outer galaxy discs, with low star formation efficiency. Through TreeSPH simulations, implementing the cooling to low temperatures, and the inclusion of the molecular hydrogen component, several feedback efficiencies are studied, and results on the gas morphology and SF are obtained. It is shown that molecular hydrogen allows some slow SF to occur in the outer parts of the discs. This dense and quiescent phase might be a way to store a significant fraction of dark baryons, in a relatively long time-scale, in the complete baryonic cycle, connecting the galaxy discs to host gaseous haloes and to the cosmic filaments.
1212.4452
The escape fraction of ionizing radiation from primordial galaxies
Benson, Venkatesan, Shull
Escape of ionizing radiation from galaxies plays a critical role in the evolution of gas in galaxies, and the heating and ionization history of the IGM. Present semi-analytic calculations of the escape fraction of ionizing radiation for both H and He from primordial galaxies, as well as analytic derivations of these quantities. Consider variations in the galaxy density profile, source type, location, and spectrum, and gas clumping/distribution factors. For sufficiently hard first-light sources, the He ionization fronts closely track or even advance beyond that of hydrogen. Key new results in this work include calculations of the escape fractions for He I and He II ionizing radiation, and the impact of partial ionization from X-rays from early AGN or stellar clusters on the escape fractions from primordial haloes. When factoring in frequency-dependent effects, find that X-rays play an important role in boosting the escape fractions for both H and He, but especially for He II. Briefly discuss the implications of these results for recent observations of the He II reionization epoch at low redshifts, as well as the UV data and emission line signatures from early galaxies anticipated from future satellite missions.
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