The impact of baryonic physics on the subhalo mass function and implications for gravitational lensing

We investigate the impact of baryonic physics on the subhalo population by analyzing the results of two recent hydrodynamical simulations (EAGLE and Illustris), which have very similar configuration, but a different model of baryonic physics. We concentrate on haloes with a mass between $10^{12.5}$ and $10^{14}M_{\odot}h^{-1}$ and redshift between 0.2 and 0.5, comparing with observational results and subhalo detections in early-type galaxy lenses. We compare the number and the spatial distribution of subhaloes in the fully hydro runs and in their dark matter only counterparts, focusing on the differences between the two simulations. We find that the presence of baryons reduces the number of subhaloes, especially at the low mass end ($\leq 10^{10}M_{\odot}h^{-1}$), by different amounts depending on the model. The variations in the subhalo mass function are strongly dependent on those in the halo mass function, which is shifted by the effect of stellar and AGN feedback. Finally, we search for analogues of the observed lenses (SLACS) in the simulations, selecting them in velocity dispersion and dynamical properties. We use the selected galaxies to quantify detection expectations based on the subhalo populations in the different simulations, calculating the detection probability and the predicted values for the projected dark matter fraction in subhaloes $f_{DM}$ and the slope of the mass function $\alpha$. We compare these values with those derived from subhalo detections in observations and conclude that the dark-matter-only and hydro EAGLE runs are both compatible with observational results, while results from the hydro Illustris run do not lie within the errors.Comment: 15 pages, 11 figures, accepted for publication in MNRA

Statistics of mass substructure from strong gravitational lensing: quantifying the mass fraction and mass function

A Bayesian statistical formalism is developed to quantify the level at which the mass function slope (alpha) and the projected cumulative mass fraction (f) of (CDM) substructure in strong gravitational-lens galaxies, with arcs or Einstein rings, can be recovered as function of the lens-survey parameters and the detection threshold of the substructure mass. The method is applied to different sets of mock data to explore a range of observational limits: (i) the number of lens galaxies in the survey, (ii) the mass threshold, Mlow, for the detection of substructures and (iii) the uncertainty of the measured substructure masses. We explore two different priors on the mass function slope: a uniform prior and a Gaussian prior with alpha = 1.90+-0.1. With a substructure detection threshold Mlow=3x10^8 Msun, the number of lenses available now (n_l=30), a true dark-matter mass fraction in (CDM) substructure <=1.0% and a prior of alpha = 1.90+-0.1, we find that the upper limit of f can be constrained down to a level <=1.0% (95% CL). In the case of a Gaussian prior on alpha, it is always possible to set stringent constraints on both parameters. We also find that lowering the detection threshold has the largest impact on the ability to recover alpha, because of the (expected) steep mass-function slope. In the future, thanks to new surveys with telescopes, such as SKA, LSST and JDEM and follow-up telescopes with high-fidelity data, a significant increase in the number of known lenses will allow us to recover the satellite population in its completeness. For example, a sample of 200 lenses, equivalent in data-quality to the Sloan Lens ACS Survey and a detection threshold of 10^8 Msun, allows one to determine f=0.5+-0.1% (68% CL) and alpha=1.90+-0.2 (68% CL).Comment: MNRAS (in press

Quantifying dwarf satellites through gravitational imaging: the case of SDSS J120602.09+514229.5

SDSS J120602.09+514229.5 is a gravitational lens system formed by a group of galaxies at redshift z=0.422 lensing a bright background galaxy at redshift z=2.001. The main peculiarity of this system is the presence of a luminous satellite near the Einstein radius, that slightly deforms the giant arc. This makes SDSS J120602.09+514229.5 the ideal system to test our grid-based Bayesian lens modelling method, designed to detect galactic satellites independently from their mass-to-light ratio, and to measure the mass of this dwarf galaxy despite its high redshift. Thanks to the pixelized source and potential reconstruction technique of Vegetti and Koopmans 2009a we are able to detect the luminous satellite as a local positive surface density correction to the overall smooth potential. Assuming a truncated Pseudo-Jaffe density profile, the satellite has a mass M=(2.75+-0.04)10^10 M_sun inside its tidal radius of r_t=0.68". We determine for the satellite a luminosity of L_B=(1.6+-0.8)10^9 L_sun, leading to a total mass-to-light ratio within the tidal radius of (M/L)_B=(17.2+-8.5) M_sun/L_sun. The central galaxy has a sub-isothermal density profile as in general is expected for group members. From the SDSS spectrum we derive for the central galaxy a velocity dispersion of sigma_kinem=380+-60 km/s within the SDSS aperture of diameter 3". The logarithmic density slope of gamma=1.7+0.25-0.30 (68% CL), derived from this measurement, is consistent within 1-sigma with the density slope of the dominant lens galaxy gamma~1.6, determined from the lens model. This paper shows how powerful pixelized lensing techniques are in detecting and constraining the properties of dwarf satellites at high redshift.Comment: Submitted to MNRAS; Abstract abridge

The Massive End of the Stellar Mass Function

We derive average flux corrections to the \texttt{Model} magnitudes of the Sloan Digital Sky Survey (SDSS) galaxies by stacking together mosaics of similar galaxies in bins of stellar mass and concentration. Extra flux is detected in the outer low surface brightness part of the galaxies, leading to corrections ranging from 0.05 to 0.32 mag for the highest stellar mass galaxies. We apply these corrections to the MPA-JHU (Max-Planck Institute for Astrophysics - John Hopkins University) stellar masses for a complete sample of half a million galaxies from the SDSS survey to derive a corrected galaxy stellar mass function at $z=0.1$ in the stellar mass range $9.5<\log(M_\ast/M_\odot)<12.0$. We find that the flux corrections and the use of the MPA-JHU stellar masses have a significant impact on the massive end of the stellar mass function, making the slope significantly shallower than that estimated by Li \& White (2009), but steeper than derived by Bernardi et al. (2013). This corresponds to a mean comoving stellar mass density of galaxies with stellar masses $\log(M_\ast/M_\odot) \ge 11.0$ that is a factor of 3.36 larger than the estimate by Li \& White (2009), but is 43\% smaller than reported by Bernardi et al. (2013).Comment: 11 pages, 8 figures, Accepted to MNRA

Integrated management of hierarchical levels: towards a CAPE tool

The integration of decision-making procedures usually assigned to different hierarchical production systems requires the use of complex mathematical models and high computational efforts, in addition to the need of an extensive management of data and knowledge within the production systems. This work addresses this integration problem and proposes a comprehensive solution approach, as well as guidelines for Computer Aided Process Engineering (CAPE) tools managing the corresponding cyberinfrastructure. This study presents a methodology based on a domain ontology which is used as the connector between the introduced data, the different available formulations developed to solve the decision-making problem, and the necessary information to build the finally required problem instance. The methodology has demonstrated its capability to help exploiting different available decision-making problem formulations in complex cases, leading to new applications and/or extensions of these available formulations in a robust and flexible way.Peer ReviewedPostprint (author's final draft

Galeno e la rifondazione della medicina

Gli scritti di Galeno discussi in questo articolo presentano un profilo del progetto cui egli dedico la sua vita. Primo, la ricostruzione di un modello alto del sapere medico, sia nella sua legittimazione epistemologica, sia nel suo ruolo culturale e sociale. La rifondazione galenica dello statuto epistemológico della medicina passerà per un sovraccarico di assiomatizzazione, non disgiunto da un controllo finale con i dati di esperienza. Moltre, la costruzione di una morale laica, indipendente dai vincoli del potere e dalle costrizioni religiose. Si tratta della comprensione, tramite l'anatomo-fisiologia, del piano provvidenziale che governa la natura: una ideologia potente che si contrappone alle incertezze dei filosofi e al dilagare delle religioni irrazionalistiche. Il medico galenico rivendica alla medicina non solo un compito generale di orientamento ideologico e culturale, bensi un vero e proprio potere di controllo sulle condotte morali e sulle devianze sociali

Parametrizing the Stellar Haloes of Galaxies

We study the stellar haloes of galaxies out to 70-100 kpc as a function of stellar mass and galaxy type by stacking aligned $r$ and $g$ band images from a sample of 45508 galaxies from SDSS DR9 in the redshift range $0.06\,\le\,z\,\le\,0.1$ and in the mass range $10^{10.0} M_{\odot} < M_{*} < 10^{11.4} M_{\odot}$r. We derive surface brightness profiles to a depth of almost $\mu_r \sim 32 \,\mathrm{mag\,arcsec}^{-2}$. We find that the ellipticity of the stellar halo is a function of galaxy stellar mass and that the haloes of high concentration ($C > 2.6$) galaxies are more elliptical than those of low concentration ($C < 2.6$) galaxies. The $g$-$r$ colour profile of high concentration galaxies reveals that the $g$-$r$ colour of the stellar population in the stellar halo is bluer than in the main galaxy, and the colour of the stellar halo is redder for higher mass galaxies. We further demonstrate that the full two-dimensional surface intensity distribution of our galaxy stacks can only be fit through multi-component S\'{e}rsic models. Using the fraction of light in the outer component of the models as a proxy for the fraction of accreted stellar light, we show that this fraction is a function of stellar mass and galaxy type. For high concentration galaxies, the fraction of accreted stellar light rises from $30\%$ to $70\%$ for galaxies in the stellar mass range from $10^{10.0} M_{\odot}$ to $10^{11.4} M_{\odot}$. The fraction of accreted light is much smaller in low concentration systems, increasing from $2\%$ to $25\%$ over the same mass range. This work provides important constraints for the theoretical understanding of the formation of stellar haloes of galaxies.Comment: Submitted to MNRAS, 18 pages, 19 figure