Calibration of semi-analytic models of galaxy formation using Particle Swarm Optimization

We present a fast and accurate method to select an optimal set of parameters in semi-analytic models of galaxy formation and evolution (SAMs). Our approach compares the results of a model against a set of observables applying a stochastic technique called Particle Swarm Optimization (PSO), a self-learning algorithm for localizing regions of maximum likelihood in multidimensional spaces that outperforms traditional sampling methods in terms of computational cost. We apply the PSO technique to the SAG semi-analytic model combined with merger trees extracted from a standard $\Lambda$CDM N-body simulation. The calibration is performed using a combination of observed galaxy properties as constraints, including the local stellar mass function and the black hole to bulge mass relation. We test the ability of the PSO algorithm to find the best set of free parameters of the model by comparing the results with those obtained using a MCMC exploration. Both methods find the same maximum likelihood region, however the PSO method requires one order of magnitude less evaluations. This new approach allows a fast estimation of the best-fitting parameter set in multidimensional spaces, providing a practical tool to test the consequences of including other astrophysical processes in SAMs.Comment: 11 pages, 4 figures, 1 table. Accepted for publication in ApJ. Comments are welcom

High and low Sérsic index bulges in Milky Way- and M31-like galaxies: origin and connection to the bar with TNG50

We study bulge formation in MW/M31-like galaxies in a A-cold dark matter scenario, focusing on the origin of high- and low-Sersic index bulges. For this purpose, we use TNG50, a simulation of the IllustrisTNG project that combines a resolution of similar to 8 x 10(4) M-circle dot in stellar particles with a cosmological volume 52 cMpc in extent. We parametrize bulge surface brightness profiles by the Sersic index and the bulge-to-total (BIT) ratio obtained from two-component photometric decompositions. In our sample of 287 MW/M31-like simulated galaxies, 17.1 per cent of photometric bulges exhibit high-Sersic indices and 82.9 per cent show low-Sersic indices. We study the impact that the environment, mergers and bars have in shaping the surface brightness profiles. We find no correlation between bulge properties and the environment where they reside. Simulated galaxies with higher Sersic indices show, on average, a higher fraction of ex situ stars in their kinematically selected bulges. For this bulge population, the last significant merger (total mass ratio m(sat)/m(host) > 0.1) occurs, on average, at later times. However, a substantial fraction of low-Sersic index bulges also experience a late significant merger. We find that bars play an important role in the development of the different types of photometric bulges. The fraction of simulated galaxies with bars is smaller for the high- than for the low-Sersic index population, reaching differences of 20 per cent at z > 1. Simulated galaxies with high fractions of ex situ stars in the bulge do not develop strong bars. Conversely, simulated galaxies with long-lived strong bars have bulges with ex situ fractions, f(ex situ )< 0.2

Cosmic CARNage II: the evolution of the galaxy stellar mass functionin observations and galaxy formation models

We present a comparison of the observed evolving galaxy stellar mass functions with the predictions of eight semi-analytic models and one halo occupation distribution model. While most models are able to fit the data at low redshift, some of them struggle to simultaneously fit observations at high redshift. We separate the galaxies into ‘passive’ and ‘star-forming’ classes and find that several of the models produce too many low-mass star-forming galaxies at high redshift compared to observations, in some cases by nearly a factor of 10 in the redshift range 2.5 < z < 3.0. We also find important differences in the implied mass of the dark matter haloes the galaxies inhabit, by comparing with halo masses inferred from observations. Galaxies at high redshift in the models are in lower mass haloes than suggested by observations, and the star formation efficiency in low-mass haloes is higher than observed. We conclude that many of the models require a physical prescription that acts to dissociate the growth of low-mass galaxies from the growth of their dark matter haloes at high redshift

Calibration of semi-analytic models of galaxy formation using particle swarm optimization

We present a fast and accurate method to select an optimal set of parameters in semi-analytic models of galaxy formation and evolution (SAMs). Our approach compares the results of a model against a set of observables applying a stochastic technique called Particle Swarm Optimization (PSO), a self-learning algorithm for localizing regions of maximum likelihood in multidimensional spaces that outperforms traditional sampling methods in terms of computational cost. We apply the PSO technique to the SAG semi-analytic model combined with merger trees extracted from a standard Lambda Cold Dark Matter N-body simulation. The calibration is performed using a combination of observed galaxy properties as constraints, including the local stellar mass function and the black hole to bulge mass relation. We test the ability of the PSO algorithm to find the best set of free parameters of the model by comparing the results with those obtained using a MCMC exploration. Both methods find the same maximum likelihood region, however, the PSO method requires one order of magnitude fewer evaluations. This new approach allows a fast estimation of the best-fitting parameter set in multidimensional spaces, providing a practical tool to test the consequences of including other astrophysical processes in SAMs.Facultad de Ciencias Astronómicas y GeofísicasInstituto de Astrofísica de La Plat

Cosmic CARNage II: the evolution of the galaxy stellar mass function in observations and galaxy formation models

We present a comparison of the observed evolving galaxy stellar mass functions with the predictions of eight semi-analytic models and one halo occupation distribution model. While most models are able to fit the data at low redshift, some of them struggle to simultaneously fit observations at high redshift. We separate the galaxies into 'passive' and 'star-forming' classes and find that several of the models produce too many low-mass star-forming galaxies at high redshift compared to observations, in some cases by nearly a factor of 10 in the redshift range 2.5 < z < 3.0. We also find important differences in the implied mass of the dark matter haloes the galaxies inhabit, by comparing with halo masses inferred from observations. Galaxies at high redshift in the models are in lower mass haloes than suggested by observations, and the star formation efficiency in low-mass haloes is higher than observed. We conclude that many of the models require a physical prescription that acts to dissociate the growth of low-mass galaxies from the growth of their dark matter haloes at high redshift.Facultad de Ciencias Astronómicas y GeofísicasInstituto de Astrofísica de La Plat

Cosmic CARNage II: the evolution of the galaxy stellar mass function in observations and galaxy formation models

We present a comparison of the observed evolving galaxy stellar mass functions with the predictions of eight semi-analytic models and one halo occupation distribution model. While most models are able to fit the data at low redshift, some of them struggle to simultaneously fit observations at high redshift. We separate the galaxies into 'passive' and 'star-forming' classes and find that several of the models produce too many low-mass star-forming galaxies at high redshift compared to observations, in some cases by nearly a factor of 10 in the redshift range 2.5 < z < 3.0. We also find important differences in the implied mass of the dark matter haloes the galaxies inhabit, by comparing with halo masses inferred from observations. Galaxies at high redshift in the models are in lower mass haloes than suggested by observations, and the star formation efficiency in low-mass haloes is higher than observed. We conclude that many of the models require a physical prescription that acts to dissociate the growth of low-mass galaxies from the growth of their dark matter haloes at high redshift.Facultad de Ciencias Astronómicas y GeofísicasInstituto de Astrofísica de La Plat

Cosmic CARNage I: on the calibration of galaxy formation models

We present a comparison of nine galaxy formation models, eight semi-analytical, and one halo occupation distribution model, run on the same underlying cold dark matter simulation (cosmological box of comoving width 125h−1 Mpc, with a dark-matter particle mass of 1.24 × 109h−1M) and the same merger trees. While their free parameters have been calibrated to the same observational data sets using two approaches, they nevertheless retain some ‘memory’ of any previous calibration that served as the starting point (especially for the manually tuned models). For the first calibration, models reproduce the observed z = 0 galaxy stellar mass function (SMF) within 3σ. The second calibration extended the observational data to include the z = 2 SMF alongside the z ∼ 0 star formation rate function, cold gas mass, and the black hole–bulge mass relation. Encapsulating the observed evolution of the SMF from z = 2 to 0 is found to be very hard within the context of the physics currently included in the models. We finally use our calibrated models to study the evolution of the stellar-to-halo mass (SHM) ratio. For all models, we find that the peak value of the SHM relation decreases with redshift. However, the trends seen for the evolution of the peak position as well as the mean scatter in the SHM relation are rather weak and strongly model dependent. Both the calibration data sets and model results are publicly available

Energy Resolution Performance of the CMS Electromagnetic Calorimeter

The energy resolution performance of the CMS lead tungstate crystal electromagnetic calorimeter is presented. Measurements were made with an electron beam using a fully equipped supermodule of the calorimeter barrel. Results are given both for electrons incident on the centre of crystals and for electrons distributed uniformly over the calorimeter surface. The electron energy is reconstructed in matrices of 3 times 3 or 5 times 5 crystals centred on the crystal containing the maximum energy. Corrections for variations in the shower containment are applied in the case of uniform incidence. The resolution measured is consistent with the design goals

Tracking the orbit of unresolved subhalos for semi-analytic models

We present a model to track the orbital evolution of "unresolved subhaloes" (USHs) in cosmological simulations. USHs are subhaloes that are no longer distinguished by halo finders as self-bound overdensities within their larger host system due to limited mass resolution. These subhaloes would host "orphan galaxies" in semi-analytic models of galaxy formation and evolution (SAMs). Predicting the evolution of the phase-space components of USHs is crucial for the adequate modelling of environmental processes, interactions and mergers implemented in SAMs that affect the baryonic properties of orphan satellites. Our model takes into account dynamical friction drag, mass loss by tidal stripping and merger with the host halo, involving three free parameters. To calibrate this model, we consider two DM-only simulations of different mass resolution (MultiDark simulations). The simulation with higher-mass resolution ({\sc smdpl}; $m_{\rm DM} = 9.6 \times 10^7 ~ h^{-1}\,\mathrm{M_{\odot}}$) provides information about subhaloes that are not resolved in the lower-mass resolution one ({\sc mdpl2}; $m_{\rm DM} = 1.5 \times 10^9 ~ h^{-1}\,\mathrm{M_{\odot}}$); the orbit of those USHs is tracked by our model. We use as constraining functions the subhalo mass function (SHMF) and the two-point correlation function (2PCF) obtained from {\sc smdpl}, being the latter a novel aspect of our approach. While the SHMF fails to put tight constraints on the efficiency of dynamical friction and the merger condition, the addition of clustering information helps to specify the parameters of the model related to the spatial distribution of subhaloes. Our model allows to achieve good convergence between the results of simulations of different mass resolution, with a precision better than 10 per cent for both SHMF and 2PCF.Comment: 21 pages, 9 figures. Replaced to match the version accepted by MNRA

Alpha-element enhancement in a LCDM Universe

Abstract. We study the chemical enrichment of elliptical galaxies using a semi-analytic model of galaxy formation combined with a cosmological Nbody simulation of dark matter particles. In particular, we study the α-element abundances with respect to the iron content of galaxies. The main modification to the previous models (Cora 2006; Lagos et al. 2008; Tecce et al. 2010) was the implementation of a top heavy variable initial mass function with a theoretical basis (Weidner & Kroupa 2004, 2005, 2006; Weidner et al. 2011). We find that with a single initial mass function at all epochs the observed trend of [Alpha/Fe] with the stellar mass of elliptical galaxies can be hardly reproduced. We propound that a top heavy integrated galactic mass function can be a plausible solution for this problem.Fil: Gargiulo, Ignacio Daniel. Universidad Nacional de La Plata. Facultad de Ciencias Astronómicas y Geofísicas; Argentina. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - La Plata. Instituto de Astrofísica La Plata. Universidad Nacional de La Plata. Facultad de Ciencias Astronómicas y Geofísicas. Instituto de Astrofísica La Plata; ArgentinaFil: Muñoz Arancibia, Alejandra. Pontificia Universidad Católica de Chile; ChileFil: Cora, Sofia Alejandra. Universidad Nacional de La Plata. Facultad de Ciencias Astronómicas y Geofísicas; Argentina. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - La Plata. Instituto de Astrofísica La Plata. Universidad Nacional de La Plata. Facultad de Ciencias Astronómicas y Geofísicas. Instituto de Astrofísica La Plata; ArgentinaFil: Padilla, Nelson D.. Pontificia Universidad Católica de Chile; Chile54a Reunión Anual de la Asociación Argentina de AstronomíaSan JuanArgentinaAsociación Argentina de AstronomíaSociedad Chilena de Astronomí