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Papers by Alejandro Benítez-Llambay

Research paper thumbnail of Simulations of the reionization of the clumpy intergalactic medium with a novel particle-based two-moment radiative transfer scheme

Proceedings of the International Astronomical Union

The progress of cosmic reionization depends on the presence of over-dense regions that act as pho... more The progress of cosmic reionization depends on the presence of over-dense regions that act as photon sinks. Such sinks may slow down ionization fronts as compared to a uniform intergalactic medium (IGM) by increasing the clumping factor. We present simulations of reionization in a clumpy IGM resolving even the smallest sinks. The simulations use a novel, spatially adaptive and efficient radiative transfer implementation in the SWIFT SPH code, based on the two-moment method. We find that photon sinks can increase the clumping factor by a factor of ∼10 during the first ∼100 Myrs after the passage of an ionization front. After this time, the clumping factor decreases as the smaller sinks photoevaporate. Altogether, photon sinks increase the number of photons required to reionize the Universe by a factor of η ∼2, as compared to the homogeneous case. The value of η also depends on the emissivity of the ionizing sources.

Research paper thumbnail of A thermal-kinetic subgrid model for supernova feedback in simulations of galaxy formation

Cornell University - arXiv, Nov 8, 2022

Research paper thumbnail of Galactic satellite systems in CDM, WDM and SIDM

Monthly Notices of the Royal Astronomical Society

We investigate the population of bright satellites ($M_{*} \ge 10^{5} \, \mathrm{M}_{\odot }$) of... more We investigate the population of bright satellites ($M_{*} \ge 10^{5} \, \mathrm{M}_{\odot }$) of haloes of mass comparable to that of the Milky Way in cosmological simulations in which the dark matter (DM) is either cold, warm, or self-interacting (CDM, WDM, and SIDM, respectively). The nature of the DM gives rise to differences in the abundance and structural properties of field haloes. In WDM, the main feature is a reduction in the total number of galaxies that form, reflecting a suppression of low-mass DM haloes and lower galaxy formation efficiency compared to CDM. For SIDM, the changes are structural, restricted to the central regions of haloes and dependent on the assumed self-interaction cross-section. We also consider different baryonic subgrid physics models for galaxy formation, in which supernova gas blowouts can or cannot induce the formation of a core in dwarf galaxies. Overall, the inclusion of baryons lessen the differences in the halo properties in the different DM ...

Research paper thumbnail of The diversity of rotation curves of simulated galaxies with cusps and cores

Cornell University - arXiv, Mar 30, 2022

Research paper thumbnail of Apparent cores and non-circular motions in the HI discs of simulated galaxies

arXiv: Astrophysics of Galaxies, Jun 22, 2017

Research paper thumbnail of FISA: Fast Integrated Spectra Analyzer

Research paper thumbnail of Differential uptake, kinetics and mechanisms of intracellular trafficking of next-generation antisense oligonucleotides across human cancer cell lines

Research paper thumbnail of py-sphviewer: Py-SPHViewer v1.0.0

This is the first official release of Py-SPHViewer. This is a publicly available Python package t... more This is the first official release of Py-SPHViewer. This is a publicly available Python package to visualize and explore N-Body + Hydrodynamical simulations. In particular, it was developed to visualize cosmological simulations, but it can be applied to render any set of particles. The Smoothed Particle Hydrodynamics interpolation scheme is used to interpolate the underlying density field (or any other property) traced by a finite set of particles, thus producing smooth images of a particle distribution that can be easily interpreted. The computation of the images is made fully in parallel using OpenMP, and its is almost straightforward to extend its use within distribute memory systems using mpi4py. Follow the main repository of the code here For a small hands-on tutorial check the link below: Tutorial

Research paper thumbnail of Cálculo de las alturas del relieve lunar

Research paper thumbnail of The cosmic UV background and the beginning and end of star formation in simulated field dwarf galaxies

Monthly Notices of the Royal Astronomical Society

We use the APOSTLE cosmological simulations to examine the role of the cosmic UV background in re... more We use the APOSTLE cosmological simulations to examine the role of the cosmic UV background in regulating star formation (SF) in low-mass Lambda cold dark matter (ΛCDM) haloes. In agreement with earlier work, we find that after reionization SF proceeds mainly in haloes whose mass exceeds a redshift-dependent ‘critical’ mass, Mcrit, set by the structure of the haloes and by the thermal pressure of UV-heated gas. Mcrit increases from sim108,mathrmModot\sim 10^{8}\, \mathrm{M}_\odotsim108,mathrmModot at z ∼ 10 to Mrmcritsim109.7,mathrmModotM_{\rm crit}\sim 10^{9.7}\, \mathrm{M}_\odotMrmcritsim109.7,mathrmModot at z = 0, roughly following the average mass growth of haloes in that mass range. This implies that haloes well above or below critical at present have remained so since early times. Haloes of luminous dwarfs today were already above-critical and star forming at high redshift, explaining naturally the ubiquitous presence of ancient stellar populations in dwarfs, regardless of luminosity. The SF history of systems close to the critical boundary is more complex. SF ...

Research paper thumbnail of The detailed structure and the onset of galaxy formation in low-mass gaseous dark matter haloes

Monthly Notices of the Royal Astronomical Society, 2020

We present a model for the formation of the first galaxies before and after the reionization of h... more We present a model for the formation of the first galaxies before and after the reionization of hydrogen in the early universe. In this model, galaxy formation can only take place in dark matter haloes whose mass exceeds a redshift-dependent critical value, which, before reionization, is equal (in the simplest case) to the mass at which atomic hydrogen cooling becomes effective and, after reionization, is equal to the mass above which gas cannot remain in hydrostatic equilibrium. We define the Halo Occupation Fraction (HOF) as the fraction of haloes that host a luminous galaxy as a function of halo mass. The HOF is established by the interplay between the evolution of the critical mass and the assembly history of haloes and depends on three factors: the minimum halo mass for galaxy formation before reionization, the redshift of reionization, and the intensity of the (evolving) external photoheating rate. Our fiducial model predicts a cutoff in the galaxy mass function at a present-d...

Research paper thumbnail of The properties of "dark" ΛCDM halos in the Local Group

We examine the baryon content of low-mass ΛCDM halos (10^8<M_200/ M_<5× 10^9) using the APO... more We examine the baryon content of low-mass ΛCDM halos (10^8<M_200/ M_<5× 10^9) using the APOSTLE cosmological hydrodynamical simulations. Most of these systems are free of stars and have a gaseous content set by the combined effects of cosmic reionization, which imposes a mass-dependent upper limit, and of ram pressure stripping, which reduces it further in high-density regions. Halos mainly affected by reionization (RELHICs; REionization-Limited HI Clouds) inhabit preferentially low-density regions and make up a population where the gas is in hydrostatic equilibrium with the dark matter potential and in thermal equilibrium with the ionizing UV background. Their thermodynamic properties are well specified, and their gas density and temperature profiles may be predicted in detail. Gas in RELHICs is nearly fully ionized but with neutral cores that span a large range of HI masses and column densities and have negligible non-thermal broadening. We present predictions for their char...

Research paper thumbnail of OUP accepted manuscript

Monthly Notices of the Royal Astronomical Society, 2022

We select a sample of Milky Way (MW) mass haloes from a high-resolution version of the EAGLE simu... more We select a sample of Milky Way (MW) mass haloes from a high-resolution version of the EAGLE simulation to study their inner dark matter (DM) content and how baryons alter it. As in previous studies, we find that all haloes are more massive at the centre compared to their DM-only (DMO) counterparts at the present day as a result of the dissipational collapse of baryons during the assembly of the galaxy. However, we identify two processes that can reduce the central halo mass during the evolution of the galaxy. Firstly, gas blowouts induced by AGN feedback can lead to a substantial decrease of the central DM mass. Secondly, the formation of a stellar bar and its interaction with the DM can induce a secular expansion of the halo; the rate at which DM is evacuated from the central region by this process is related to the average bar strength and the timescale on which it acts determines how much the halo has decontracted. Although the inner regions of the haloes we have investigated ar...

Research paper thumbnail of Espectros integrados EFOSC2/NTT de 10 cúmulos estelares pertenecientes a las Nubes de Magallanes

Fil: Ahumada, Andrea Veronica. Universidad Nacional de Cordoba. Observatorio Astronomico de Cordo... more Fil: Ahumada, Andrea Veronica. Universidad Nacional de Cordoba. Observatorio Astronomico de Cordoba; Argentina

Research paper thumbnail of OUP accepted manuscript

Monthly Notices of the Royal Astronomical Society, 2019

A number of Local Group dwarf galaxies are known to have two spatially segregated stellar metalli... more A number of Local Group dwarf galaxies are known to have two spatially segregated stellar metallicity populations, a centrally concentrated metal-rich population and a more extended metal-poor population. In this work we discuss mechanisms that lead to the formation of two spatially segregated metallicity populations. Using a set of high-resolution hydrodynamical simulations of Local Group-like environments, we select a sample of satellite and field galaxies, spanning the stellar mass range 106 − 109M⊙, that exhibit bimodality in their metallicity distributions. Among those, we identify a subsample with a strong spatial segregation in the two populations. We find three distinct mechanisms for their formation. In field dwarfs and in a small fraction of satellites, a merger causes the metal-poor stars to migrate to larger radii and encourages the available gas to sink to the centre of the dwarf. Most of the gas is subsequently blown out of the halo through star formation feedback, but...

Research paper thumbnail of HBT+: An Improved Code for Finding Subhaloes and Building Merger Trees in Cosmological Simulations

Monthly Notices of the Royal Astronomical Society, 2017

Research paper thumbnail of OUP accepted manuscript

Monthly Notices of the Royal Astronomical Society, 2017

Research paper thumbnail of Mergers and the outside-in formation of dwarf spheroidals

Monthly Notices of the Royal Astronomical Society, 2015

Research paper thumbnail of Determinación espectroscópica de parámetros fundamentales de 18 cúmulos abiertos de pequeño diámetro angular

Following specific criteria, we have carefully selected objects catalogued as galactic open clust... more Following specific criteria, we have carefully selected objects catalogued as galactic open cluster candidates. Out of a total of 58 small angular diameter selected objects without previous studies, we obtained integrated spectra of 18 of them at CASLEO (San Juan, Argentina). Using a computational tool specially developed for the analysis of integrated spectra, reddenings and ages of the observed clusters were determined for the first time. FULL TEXT IN SPANISH

Research paper thumbnail of Reddening and age of six poorly studied star clusters of the Large Magellanic Cloud derived from integrated spectra

Astronomy & Astrophysics, 2014

Research paper thumbnail of Simulations of the reionization of the clumpy intergalactic medium with a novel particle-based two-moment radiative transfer scheme

Proceedings of the International Astronomical Union

The progress of cosmic reionization depends on the presence of over-dense regions that act as pho... more The progress of cosmic reionization depends on the presence of over-dense regions that act as photon sinks. Such sinks may slow down ionization fronts as compared to a uniform intergalactic medium (IGM) by increasing the clumping factor. We present simulations of reionization in a clumpy IGM resolving even the smallest sinks. The simulations use a novel, spatially adaptive and efficient radiative transfer implementation in the SWIFT SPH code, based on the two-moment method. We find that photon sinks can increase the clumping factor by a factor of ∼10 during the first ∼100 Myrs after the passage of an ionization front. After this time, the clumping factor decreases as the smaller sinks photoevaporate. Altogether, photon sinks increase the number of photons required to reionize the Universe by a factor of η ∼2, as compared to the homogeneous case. The value of η also depends on the emissivity of the ionizing sources.

Research paper thumbnail of A thermal-kinetic subgrid model for supernova feedback in simulations of galaxy formation

Cornell University - arXiv, Nov 8, 2022

Research paper thumbnail of Galactic satellite systems in CDM, WDM and SIDM

Monthly Notices of the Royal Astronomical Society

We investigate the population of bright satellites ($M_{*} \ge 10^{5} \, \mathrm{M}_{\odot }$) of... more We investigate the population of bright satellites ($M_{*} \ge 10^{5} \, \mathrm{M}_{\odot }$) of haloes of mass comparable to that of the Milky Way in cosmological simulations in which the dark matter (DM) is either cold, warm, or self-interacting (CDM, WDM, and SIDM, respectively). The nature of the DM gives rise to differences in the abundance and structural properties of field haloes. In WDM, the main feature is a reduction in the total number of galaxies that form, reflecting a suppression of low-mass DM haloes and lower galaxy formation efficiency compared to CDM. For SIDM, the changes are structural, restricted to the central regions of haloes and dependent on the assumed self-interaction cross-section. We also consider different baryonic subgrid physics models for galaxy formation, in which supernova gas blowouts can or cannot induce the formation of a core in dwarf galaxies. Overall, the inclusion of baryons lessen the differences in the halo properties in the different DM ...

Research paper thumbnail of The diversity of rotation curves of simulated galaxies with cusps and cores

Cornell University - arXiv, Mar 30, 2022

Research paper thumbnail of Apparent cores and non-circular motions in the HI discs of simulated galaxies

arXiv: Astrophysics of Galaxies, Jun 22, 2017

Research paper thumbnail of FISA: Fast Integrated Spectra Analyzer

Research paper thumbnail of Differential uptake, kinetics and mechanisms of intracellular trafficking of next-generation antisense oligonucleotides across human cancer cell lines

Research paper thumbnail of py-sphviewer: Py-SPHViewer v1.0.0

This is the first official release of Py-SPHViewer. This is a publicly available Python package t... more This is the first official release of Py-SPHViewer. This is a publicly available Python package to visualize and explore N-Body + Hydrodynamical simulations. In particular, it was developed to visualize cosmological simulations, but it can be applied to render any set of particles. The Smoothed Particle Hydrodynamics interpolation scheme is used to interpolate the underlying density field (or any other property) traced by a finite set of particles, thus producing smooth images of a particle distribution that can be easily interpreted. The computation of the images is made fully in parallel using OpenMP, and its is almost straightforward to extend its use within distribute memory systems using mpi4py. Follow the main repository of the code here For a small hands-on tutorial check the link below: Tutorial

Research paper thumbnail of Cálculo de las alturas del relieve lunar

Research paper thumbnail of The cosmic UV background and the beginning and end of star formation in simulated field dwarf galaxies

Monthly Notices of the Royal Astronomical Society

We use the APOSTLE cosmological simulations to examine the role of the cosmic UV background in re... more We use the APOSTLE cosmological simulations to examine the role of the cosmic UV background in regulating star formation (SF) in low-mass Lambda cold dark matter (ΛCDM) haloes. In agreement with earlier work, we find that after reionization SF proceeds mainly in haloes whose mass exceeds a redshift-dependent ‘critical’ mass, Mcrit, set by the structure of the haloes and by the thermal pressure of UV-heated gas. Mcrit increases from sim108,mathrmModot\sim 10^{8}\, \mathrm{M}_\odotsim108,mathrmModot at z ∼ 10 to Mrmcritsim109.7,mathrmModotM_{\rm crit}\sim 10^{9.7}\, \mathrm{M}_\odotMrmcritsim109.7,mathrmModot at z = 0, roughly following the average mass growth of haloes in that mass range. This implies that haloes well above or below critical at present have remained so since early times. Haloes of luminous dwarfs today were already above-critical and star forming at high redshift, explaining naturally the ubiquitous presence of ancient stellar populations in dwarfs, regardless of luminosity. The SF history of systems close to the critical boundary is more complex. SF ...

Research paper thumbnail of The detailed structure and the onset of galaxy formation in low-mass gaseous dark matter haloes

Monthly Notices of the Royal Astronomical Society, 2020

We present a model for the formation of the first galaxies before and after the reionization of h... more We present a model for the formation of the first galaxies before and after the reionization of hydrogen in the early universe. In this model, galaxy formation can only take place in dark matter haloes whose mass exceeds a redshift-dependent critical value, which, before reionization, is equal (in the simplest case) to the mass at which atomic hydrogen cooling becomes effective and, after reionization, is equal to the mass above which gas cannot remain in hydrostatic equilibrium. We define the Halo Occupation Fraction (HOF) as the fraction of haloes that host a luminous galaxy as a function of halo mass. The HOF is established by the interplay between the evolution of the critical mass and the assembly history of haloes and depends on three factors: the minimum halo mass for galaxy formation before reionization, the redshift of reionization, and the intensity of the (evolving) external photoheating rate. Our fiducial model predicts a cutoff in the galaxy mass function at a present-d...

Research paper thumbnail of The properties of "dark" ΛCDM halos in the Local Group

We examine the baryon content of low-mass ΛCDM halos (10^8<M_200/ M_<5× 10^9) using the APO... more We examine the baryon content of low-mass ΛCDM halos (10^8<M_200/ M_<5× 10^9) using the APOSTLE cosmological hydrodynamical simulations. Most of these systems are free of stars and have a gaseous content set by the combined effects of cosmic reionization, which imposes a mass-dependent upper limit, and of ram pressure stripping, which reduces it further in high-density regions. Halos mainly affected by reionization (RELHICs; REionization-Limited HI Clouds) inhabit preferentially low-density regions and make up a population where the gas is in hydrostatic equilibrium with the dark matter potential and in thermal equilibrium with the ionizing UV background. Their thermodynamic properties are well specified, and their gas density and temperature profiles may be predicted in detail. Gas in RELHICs is nearly fully ionized but with neutral cores that span a large range of HI masses and column densities and have negligible non-thermal broadening. We present predictions for their char...

Research paper thumbnail of OUP accepted manuscript

Monthly Notices of the Royal Astronomical Society, 2022

We select a sample of Milky Way (MW) mass haloes from a high-resolution version of the EAGLE simu... more We select a sample of Milky Way (MW) mass haloes from a high-resolution version of the EAGLE simulation to study their inner dark matter (DM) content and how baryons alter it. As in previous studies, we find that all haloes are more massive at the centre compared to their DM-only (DMO) counterparts at the present day as a result of the dissipational collapse of baryons during the assembly of the galaxy. However, we identify two processes that can reduce the central halo mass during the evolution of the galaxy. Firstly, gas blowouts induced by AGN feedback can lead to a substantial decrease of the central DM mass. Secondly, the formation of a stellar bar and its interaction with the DM can induce a secular expansion of the halo; the rate at which DM is evacuated from the central region by this process is related to the average bar strength and the timescale on which it acts determines how much the halo has decontracted. Although the inner regions of the haloes we have investigated ar...

Research paper thumbnail of Espectros integrados EFOSC2/NTT de 10 cúmulos estelares pertenecientes a las Nubes de Magallanes

Fil: Ahumada, Andrea Veronica. Universidad Nacional de Cordoba. Observatorio Astronomico de Cordo... more Fil: Ahumada, Andrea Veronica. Universidad Nacional de Cordoba. Observatorio Astronomico de Cordoba; Argentina

Research paper thumbnail of OUP accepted manuscript

Monthly Notices of the Royal Astronomical Society, 2019

A number of Local Group dwarf galaxies are known to have two spatially segregated stellar metalli... more A number of Local Group dwarf galaxies are known to have two spatially segregated stellar metallicity populations, a centrally concentrated metal-rich population and a more extended metal-poor population. In this work we discuss mechanisms that lead to the formation of two spatially segregated metallicity populations. Using a set of high-resolution hydrodynamical simulations of Local Group-like environments, we select a sample of satellite and field galaxies, spanning the stellar mass range 106 − 109M⊙, that exhibit bimodality in their metallicity distributions. Among those, we identify a subsample with a strong spatial segregation in the two populations. We find three distinct mechanisms for their formation. In field dwarfs and in a small fraction of satellites, a merger causes the metal-poor stars to migrate to larger radii and encourages the available gas to sink to the centre of the dwarf. Most of the gas is subsequently blown out of the halo through star formation feedback, but...

Research paper thumbnail of HBT+: An Improved Code for Finding Subhaloes and Building Merger Trees in Cosmological Simulations

Monthly Notices of the Royal Astronomical Society, 2017

Research paper thumbnail of OUP accepted manuscript

Monthly Notices of the Royal Astronomical Society, 2017

Research paper thumbnail of Mergers and the outside-in formation of dwarf spheroidals

Monthly Notices of the Royal Astronomical Society, 2015

Research paper thumbnail of Determinación espectroscópica de parámetros fundamentales de 18 cúmulos abiertos de pequeño diámetro angular

Following specific criteria, we have carefully selected objects catalogued as galactic open clust... more Following specific criteria, we have carefully selected objects catalogued as galactic open cluster candidates. Out of a total of 58 small angular diameter selected objects without previous studies, we obtained integrated spectra of 18 of them at CASLEO (San Juan, Argentina). Using a computational tool specially developed for the analysis of integrated spectra, reddenings and ages of the observed clusters were determined for the first time. FULL TEXT IN SPANISH

Research paper thumbnail of Reddening and age of six poorly studied star clusters of the Large Magellanic Cloud derived from integrated spectra

Astronomy & Astrophysics, 2014