Alessio Romeo - Academia.edu (original) (raw)
Papers by Alessio Romeo
"Abstract: The aim of this study is to determine the geochemical and min... more "Abstract: The aim of this study is to determine the geochemical and mineralogical composition of Bima Sandstone deposite of northeastern Nigeria. A total number of sixteen (16) sandstone samples were collected in Yola area inorder to classify the deposit of the Bima Sandstone exposed in this area on the basis of its chemical and mineralogical make-up. All the samples were selected randomly and subjected to both geochemical and petrographic studies. Relative concentration of the major oxide groups such as silica and alumina alkali oxides, iron oxide and magnesia has been used to classify the deposit. The results of the log of ratio of the m ajor oxide groups indicate that Bima Sandstone of the study area can be classified as greywackes, arkoses and lithic arenites including sub-greywackes and protoquartzites. The abundant alkali values as shown by the relatively high log K2O/Na2O ratio in most of the samples indicated immature sandstones whereas low alkali values in sam ples F, H and M revealed mature sandstones. The enrichment of silica (quartz) over Al2O3 (log SiO2/Al2O3<1.5) indicate that Bima Sandstone has undergone long period of transportation and have been subjected to intense weathering resulting in the destruction of other minerals especially plagioclase and potassium feldspars during transportation. Microscopic examination of about sixteen slides (16) of Bima Sandstone under both plane and cross polars revealed the following average mineralogical composition: quartz (65%) feldspars (14%), mica (9%), iron oxide (5%), calcite (3%) further confirms quartz/lithic arenites and greywackes as some of the predominant sedimentary rocks in the study area. Keywords: Bima Sandstone, geochemical, Nigeria, Northeast, petrographic, Yola area"
The Astrophysical Journal, 2005
We use a set of 12 high-resolution N-body/hydrodynamical simulations in the LCDM cosmology to inv... more We use a set of 12 high-resolution N-body/hydrodynamical simulations in the LCDM cosmology to investigate the origin and formation rate of fossil groups (FGs), which are X-ray-bright galaxy groups dominated by a large elliptical galaxy, with the second brightest galaxy being at least 2 mag fainter. The simulations invoke star formation, chemical evolution with noninstantaneous recycling, metal-dependent radiative cooling, strong starburst-driven galactic superwinds, effects of a metagalactic UV field, and full stellar population synthesis. We find an interesting correlation between the magnitude gap between the brightest and second-brightest galaxy and the formation time of the group. It is found that FGs have already assembled half of their final dark matter mass at , and subsequently they typically grow by minor merging only, whereas non-FGs on average form later. z տ 1 The early assembly of FGs leaves sufficient time for galaxies of to merge into the central one by dynamical L ∼ L * friction, resulting in the large magnitude gap at . About of the groups simulated are found to z p 0 33% ע 16% be FGs, whereas the observational estimate is ∼10%-20%. The FGs are found to be overluminous in the X-ray relative to non-FGs of the same optical luminosity, in qualitative agreement with observations. Finally, from a dynamical friction analysis, we find that FGs exist at all only because infall of galaxies happens along L ∼ L * filaments with small impact parameters.
We discuss the problems arising when one tries to create a software interface between a parallel ... more We discuss the problems arising when one tries to create a software interface between a parallel treecode (modelling the collisionless, Dark Matter component) and Adaptive Mesh Refinement (AMR) hydrodynamical schemes (which model the gaseous phases). Such an interface would allow one to perform Nbody/Hydro simulations in those situations where the N-body and hydrodynamical codes are loosely coupled, and the gravitational influence of the dissipative, gaseous component on the DM component can be neglected. We discuss similarities and differences between the tree-and AMR hydrocode data structures, restricting ourselves to two particular examples which are widely used in these days: the oct-tree Barnes-Hut and the cartesian structured grid AMR schemes. Finally, we present a simple scheme for such a software interface which we are beginning to use in cosmological simulations.
Cosmological LambdaCDM TreeSPH simulations of the formation and evolution of galaxy groups and cl... more Cosmological LambdaCDM TreeSPH simulations of the formation and evolution of galaxy groups and clusters have been performed. The simulations include: star formation, chemical evolution with non-instantaneous recycling, metal dependent radiative cooling, strong star burst and (optionally) AGN driven galactic super winds, effects of a meta-galactic UV field and thermal conduction. The properties of the galaxy populations in the two richest
Proceedings of The International Astronomical Union, 2004
We present fully cosmological, hydrodynamical simulations of clusters of galaxies, including star... more We present fully cosmological, hydrodynamical simulations of clusters of galaxies, including star formation, supernova feedback, chemical enrichment and metal-dependent cooling. We investigate the relation between feedback, metal enrichment of the intra-cluster medium (ICM) and the distribution of baryons in the various phases (cold gas+stars and hot ICM) at varying Initial Mass Function and wind efficiency.
Arxiv preprint astro-ph/ …, 2005
Abstract: Cosmological LambdaCDM TreeSPH simulations of the formation and evolution of galaxy gro... more Abstract: Cosmological LambdaCDM TreeSPH simulations of the formation and evolution of galaxy groups and clusters have been performed. The simulations include: star formation, chemical evolution with non-instantaneous recycling, metal dependent radiative cooling, ...
The Astrophysical Journal, 2013
ABSTRACT We present results from SPH-cosmological simulations, including self-consistent modellin... more ABSTRACT We present results from SPH-cosmological simulations, including self-consistent modelling of SN feedback and chemical evolution, of galaxies belonging to two clusters and twelve groups. We reproduce the mass-metallicity (ZM) relation of galaxies classified in two samples according to their star-forming activity, as parametrized by their sSFR, across a redshift range up to z=2. Its slope shows irrelevant evolution in the passive sample, being steeper in groups than in clusters. However, the sub-sample of high-mass passive galaxies only is characterized by a steep increase of the slope with redshift, from which it can be inferred that the bulk of the slope evolution of the ZM relation is driven by the more massive passive objects. (...ABRIDGED...) The ZM relation for the star-forming sample reveals an increasing scatter with redshift, indicating that it is still being built at early epochs. The star-forming galaxies make up a tight sequence in the SFR-M_* plane at high redshift, whose scatter increases with time alongside with the consolidation of the passive sequence. We also confirm the anti-correlation between sSFR and stellar mass, pointing at a key role of the former in determining the galaxy downsizing, as the most significant means of diagnostics of the star formation efficiency. Likewise, an anti-correlation between sSFR and metallicity can be established for the star-forming galaxies, while on the contrary more active galaxies in terms of simple SFR are also metal-richer. We discuss these results in terms of the mechanisms driving the evolution within the high- and low-mass regimes at different epochs: mergers, feedback-driven outflows and the intrinsic variation of the star formation efficiency.
Monthly Notices of the Royal Astronomical Society, 2014
We investigate the interplay between jets from active galactic nuclei (AGNs) and the surrounding ... more We investigate the interplay between jets from active galactic nuclei (AGNs) and the surrounding interstellar medium (ISM) through full 3D, high-resolution, adaptive mesh refinement simulations performed with the FLASH code. We follow the jet-ISM system for several Myr in its transition from an early, compact source to an extended one including a large cocoon. During the jet evolution, we identify three major evolutionary stages and we find that, contrary to the prediction of popular theoretical models, none of the simulations shows a self-similar behaviour. We also follow the evolution of the energy budget, and find that the fraction of input power deposited into the ISM (the AGN coupling constant) is of the order of a few per cent during the first few Myr. This is in broad agreement with galaxy formation models employing AGN feedback. However, we find that in these early stages, this energy is deposited only in a small fraction (<1 per cent) of the total ISM volume. Finally, we demonstrate the relevance of backflows arising within the extended cocoon generated by a relativistic AGN jet within the ISM of its host galaxy, previously proposed as a mechanism for self-regulating the gas accretion on to the central object. These backflows tend later to be destabilized by the 3D dynamics, rather than by hydrodynamic (Kelvin-Helmholtz) instabilities. Yet, in the first few hundred thousand years, backflows may create a central accretion region of significant extent, and convey there as much as a few millions of solar masses.
Monthly Notices of the Royal Astronomical Society, 2009
We study the feedback from an AGN on stellar formation within its host galaxy, mainly using one h... more We study the feedback from an AGN on stellar formation within its host galaxy, mainly using one high resolution numerical simulation of the jet propagation within the interstellar medium of an early-type galaxy. In particular, we show that in a realistic simulation where the jet propagates into a two-phase ISM, star formation can initially be slightly enhanced and then, on timescales of few million years, rapidly quenched, as a consequence both of the high temperatures attained and of the reduction of cloud mass (mainly due to Kelvin-Helmholtz instabilities). We then introduce a model of (prevalently) negative AGN feedback, where an exponentially declining star formation is quenched, on a very short time scale, at a time t AGN , due to AGN feedback. Using the Bruzual & Charlot (2003) population synthesis model and our star formation history, we predict galaxy colours from this model and match them to a sample of nearby early-type galaxies showing signs of recent episodes of star formation . We find that the quantity t gal − t AGN , where t gal is the galaxy age, is an excellent indicator of the presence of feedback processes, and peaks significantly around t gal − t AGN ≈ 0.85 Gyr for our sample, consistent with feedback from recent energy injection by AGNs in relatively bright (M B ∼ < −19) and massive nearby early-type galaxies. Galaxies that have experienced this recent feedback show an enhancement of 3 magnitudes in N U V (GALEX) − g, with respect to the unperturbed, no-feedback evolution. Hence they can be easily identified in large combined near UV-optical surveys.
Monthly Notices of the Royal Astronomical Society, 2006
We have performed a series of N-body/hydrodynamical (TREESPH) simulations of clusters and groups ... more We have performed a series of N-body/hydrodynamical (TREESPH) simulations of clusters and groups of galaxies, selected from a cosmological volume within a Lambda cold dark matter ( CDM) framework: these objects have been resimulated at higher resolution to z = 0, in order to follow also the dynamical, thermal and chemical input on to the intracluster medium (ICM) from stellar populations within galaxies. The simulations include metallicitydependent radiative cooling, star formation according to different initial mass functions (IMFs), energy feedback as strong starburst-driven galactic superwinds, chemical evolution with noninstantaneous recycling of gas and heavy elements, effects of a metagalactic ultraviolet (UV) field and thermal conduction in the ICM.
Monthly Notices of the Royal Astronomical Society, 2011
The age and metallicity gradients for a sample of group and cluster galaxies from N-body+hydrodyn... more The age and metallicity gradients for a sample of group and cluster galaxies from N-body+hydrodynamical simulation are analyzed in terms of galaxy stellar mass. Dwarf galaxies show null age gradient with a tail of high and positive values for systems in groups and cluster outskirts. Massive systems have generally zero age gradients which turn to positive for the most massive ones. Metallicity gradients are distributed around zero in dwarf galaxies and become more negative with mass; massive galaxies have steeper negative metallicity gradients, but the trend flatten with mass. In particular, fossil groups are characterized by a tighter distribution of both age and metallicity gradients. We find a good agreement with both local observations and independent simulations. The results are also discussed in terms of the central age and metallicity, as well as the total colour, specific star formation and velocity dispersion.
Monthly Notices of The Royal Astronomical Society, 2008
Differently from the DS, the operatively defined RS evolves more evidently with z, the epoch when... more Differently from the DS, the operatively defined RS evolves more evidently with z, the epoch when it changes its slope being closely corresponding to that at which the passive galaxies population takes over the star forming one: this goes from z~1 in clusters down to 0.4 in normal groups.
Monthly Notices of the Royal Astronomical Society, 2005
We performed N-body + hydrodynamical simulations of the formation and evolution of galaxy groups ... more We performed N-body + hydrodynamical simulations of the formation and evolution of galaxy groups and clusters in a cold dark matter cosmology. The simulations invoke star formation, chemical evolution with non-instantaneous recycling, metal-dependent radiative cooling, strong starbursts and (optionally) active galactic nucleus (AGN) driven galactic superwinds, effects of a meta-galactic ultraviolet field and thermal conduction. The properties of the galaxy populations in two clusters, one Virgo-like (T ∼ 3 keV) and one (sub)Coma-like (T ∼ 6 keV), are discussed. The global star formation rates of the cluster galaxies are found to decrease very significantly from redshift z = 2 to 0, in agreement with observations. The total K-band luminosity of the cluster galaxies correlates tightly with total cluster mass, and for models without additional AGN feedback, the zero-point of the relation matches the observed one fairly well. Compared to the observed galaxy luminosity function (LF), the simulations nicely match the number of intermediate-mass galaxies (−20 M B −17, smaller galaxies being affected by resolution limits) but they show a deficiency of bright galaxies in favour of an overgrown central dominant (cD) galaxy. High-resolution tests indicate that this deficiency is not simply due to numerical 'overmerging'.
Monthly Notices of The Royal Astronomical Society, 2004
Cosmological (LambdaCDM) TreeSPH simulations of the formation and evolution of galaxy groups and ... more Cosmological (LambdaCDM) TreeSPH simulations of the formation and evolution of galaxy groups and clusters have been performed. The simulations invoke star formation, chemical evolution with non-instantaneous recycling, metal dependent radiative cooling, strong star burst and (optionally) AGN driven galactic super winds, effects of a meta-galactic UV field and thermal conduction. The properties of the galaxy populations in two clusters, one Virgo-like (T~3 keV) and one (sub) Coma-like (T~6 keV), are discussed. The global star formation rates of the cluster galaxies are found to decrease very significantly with time from redshift z=2 to 0, in agreement with observations. The total K-band luminosity of the cluster galaxies correlates tightly with total cluster mass, and for models without additional AGN feedback, the zero point of the relation matches the observed one fairly well. The match to observed galaxy luminosity functions is reasonable, except for a deficiency of bright galaxies (M_B < -20), which becomes increasingly significant with super-wind strength. Results of a high resolution test indicate that this deficiency is not due to ``over--merging''. The redshift evolution of the luminosity functions from z=1 to 0 is mainly driven by luminosity evolution, but also by merging of bright galaxies with the cD. The colour--magnitude relation of the cluster galaxies matches the observed "red sequence" very well and, on average, galaxy metallicity increases with luminosity. As the brighter galaxies are essentially coeval, the colour--magnitude relation results from metallicity rather than age effects, as observed.
Monthly Notices of The Royal Astronomical Society, 2004
Cosmological (LCDM) TreeSPH simulations of galaxy clusters have been performed, invoking star-for... more Cosmological (LCDM) TreeSPH simulations of galaxy clusters have been performed, invoking star-formation, chemical evolution with non-instantaneous recycling, metal dependent radiative cooling, strong star-burst and/or AGN driven super-winds, effects of a meta-galactic UV field and thermal conduction. Results for two clusters, one Virgo-like (T~3 keV) and one (sub) Coma-like (T~6 keV), are presented. At z=0, the stellar contents of both clusters consist of a central dominant (cD) galaxy surrounded by galaxies and intracluster (IC) stars. The IC stars are found to contribute 20-40% of the total cluster B-band light and to form at a mean redshift z_f~3, on average about 0.5 Gyr prior to the stars in galaxies. UBVRIJHK surface brightness profiles of the IC star populations are presented; the profile of the larger cluster matches the observed V-band profile of the cD in Abell 1413 (T~8 keV). The IC stellar populations have B-R=1.4-1.5, comparable to larger E galaxies. The mean [Fe/H]~0.0 in the central part of the cluster (r~100 kpc) decreasing to about -0.3 at r_vir. The IC stars are alpha-element enhanced, with a weak trend of [O/Fe] increasing with r, and an overall [O/Fe]~0.4 dex. The IC stars are kinematically colder than the galaxies: The velocity dispersions of the IC stars are at r~100-500 kpc only about half of those of the galaxies increasing to about 70% at r=1-2 Mpc. The projected velocity dispersion in the Virgo-like cluster at R>~50 kpc is 300-600 km/s depending on orientation and R. Rotation is dynamically insignificant for the IC stars. The velocity distributions of IC stars and galaxies are in one cluster highly radially anisotropic, in the other close to isotropic.
Monthly Notices of the Royal Astronomical Society, Jul 24, 2008
N-body + hydrodynamical simulations of the formation and evolution of galaxy groups and clusters ... more N-body + hydrodynamical simulations of the formation and evolution of galaxy groups and clusters in a ΛCDM cosmology are used in order to follow the building-up of the colour-magnitude relation in two clusters and in 12 groups. We have found that galaxies, starting from the more massive, move to the Red Sequence (RS) as they get aged over times and eventually set upon a "dead sequence" (DS) once they have stopped their bulk star formation activity. Fainter galaxies keep having significant star formation out to very recent epochs and lie broader around the RS. Environment plays a role as galaxies in groups and cluster outskirts hold star formation activity longer than the central cluster regions. However galaxies experiencing infall from the outskirts to the central parts keep star formation on until they settle on to the DS of the core galaxies. Merging contributes to mass assembly until z ∼ 1, after which major events only involve the brightest cluster galaxies.
&amp;amp;amp;quot;Abstract: The aim of this study is to determine the geochemical and min... more &amp;amp;amp;quot;Abstract: The aim of this study is to determine the geochemical and mineralogical composition of Bima Sandstone deposite of northeastern Nigeria. A total number of sixteen (16) sandstone samples were collected in Yola area inorder to classify the deposit of the Bima Sandstone exposed in this area on the basis of its chemical and mineralogical make-up. All the samples were selected randomly and subjected to both geochemical and petrographic studies. Relative concentration of the major oxide groups such as silica and alumina alkali oxides, iron oxide and magnesia has been used to classify the deposit. The results of the log of ratio of the m ajor oxide groups indicate that Bima Sandstone of the study area can be classified as greywackes, arkoses and lithic arenites including sub-greywackes and protoquartzites. The abundant alkali values as shown by the relatively high log K2O/Na2O ratio in most of the samples indicated immature sandstones whereas low alkali values in sam ples F, H and M revealed mature sandstones. The enrichment of silica (quartz) over Al2O3 (log SiO2/Al2O3&amp;amp;amp;lt;1.5) indicate that Bima Sandstone has undergone long period of transportation and have been subjected to intense weathering resulting in the destruction of other minerals especially plagioclase and potassium feldspars during transportation. Microscopic examination of about sixteen slides (16) of Bima Sandstone under both plane and cross polars revealed the following average mineralogical composition: quartz (65%) feldspars (14%), mica (9%), iron oxide (5%), calcite (3%) further confirms quartz/lithic arenites and greywackes as some of the predominant sedimentary rocks in the study area. Keywords: Bima Sandstone, geochemical, Nigeria, Northeast, petrographic, Yola area&amp;amp;amp;quot;
The Astrophysical Journal, 2005
We use a set of 12 high-resolution N-body/hydrodynamical simulations in the LCDM cosmology to inv... more We use a set of 12 high-resolution N-body/hydrodynamical simulations in the LCDM cosmology to investigate the origin and formation rate of fossil groups (FGs), which are X-ray-bright galaxy groups dominated by a large elliptical galaxy, with the second brightest galaxy being at least 2 mag fainter. The simulations invoke star formation, chemical evolution with noninstantaneous recycling, metal-dependent radiative cooling, strong starburst-driven galactic superwinds, effects of a metagalactic UV field, and full stellar population synthesis. We find an interesting correlation between the magnitude gap between the brightest and second-brightest galaxy and the formation time of the group. It is found that FGs have already assembled half of their final dark matter mass at , and subsequently they typically grow by minor merging only, whereas non-FGs on average form later. z տ 1 The early assembly of FGs leaves sufficient time for galaxies of to merge into the central one by dynamical L ∼ L * friction, resulting in the large magnitude gap at . About of the groups simulated are found to z p 0 33% ע 16% be FGs, whereas the observational estimate is ∼10%-20%. The FGs are found to be overluminous in the X-ray relative to non-FGs of the same optical luminosity, in qualitative agreement with observations. Finally, from a dynamical friction analysis, we find that FGs exist at all only because infall of galaxies happens along L ∼ L * filaments with small impact parameters.
We discuss the problems arising when one tries to create a software interface between a parallel ... more We discuss the problems arising when one tries to create a software interface between a parallel treecode (modelling the collisionless, Dark Matter component) and Adaptive Mesh Refinement (AMR) hydrodynamical schemes (which model the gaseous phases). Such an interface would allow one to perform Nbody/Hydro simulations in those situations where the N-body and hydrodynamical codes are loosely coupled, and the gravitational influence of the dissipative, gaseous component on the DM component can be neglected. We discuss similarities and differences between the tree-and AMR hydrocode data structures, restricting ourselves to two particular examples which are widely used in these days: the oct-tree Barnes-Hut and the cartesian structured grid AMR schemes. Finally, we present a simple scheme for such a software interface which we are beginning to use in cosmological simulations.
Cosmological LambdaCDM TreeSPH simulations of the formation and evolution of galaxy groups and cl... more Cosmological LambdaCDM TreeSPH simulations of the formation and evolution of galaxy groups and clusters have been performed. The simulations include: star formation, chemical evolution with non-instantaneous recycling, metal dependent radiative cooling, strong star burst and (optionally) AGN driven galactic super winds, effects of a meta-galactic UV field and thermal conduction. The properties of the galaxy populations in the two richest
Proceedings of The International Astronomical Union, 2004
We present fully cosmological, hydrodynamical simulations of clusters of galaxies, including star... more We present fully cosmological, hydrodynamical simulations of clusters of galaxies, including star formation, supernova feedback, chemical enrichment and metal-dependent cooling. We investigate the relation between feedback, metal enrichment of the intra-cluster medium (ICM) and the distribution of baryons in the various phases (cold gas+stars and hot ICM) at varying Initial Mass Function and wind efficiency.
Arxiv preprint astro-ph/ …, 2005
Abstract: Cosmological LambdaCDM TreeSPH simulations of the formation and evolution of galaxy gro... more Abstract: Cosmological LambdaCDM TreeSPH simulations of the formation and evolution of galaxy groups and clusters have been performed. The simulations include: star formation, chemical evolution with non-instantaneous recycling, metal dependent radiative cooling, ...
The Astrophysical Journal, 2013
ABSTRACT We present results from SPH-cosmological simulations, including self-consistent modellin... more ABSTRACT We present results from SPH-cosmological simulations, including self-consistent modelling of SN feedback and chemical evolution, of galaxies belonging to two clusters and twelve groups. We reproduce the mass-metallicity (ZM) relation of galaxies classified in two samples according to their star-forming activity, as parametrized by their sSFR, across a redshift range up to z=2. Its slope shows irrelevant evolution in the passive sample, being steeper in groups than in clusters. However, the sub-sample of high-mass passive galaxies only is characterized by a steep increase of the slope with redshift, from which it can be inferred that the bulk of the slope evolution of the ZM relation is driven by the more massive passive objects. (...ABRIDGED...) The ZM relation for the star-forming sample reveals an increasing scatter with redshift, indicating that it is still being built at early epochs. The star-forming galaxies make up a tight sequence in the SFR-M_* plane at high redshift, whose scatter increases with time alongside with the consolidation of the passive sequence. We also confirm the anti-correlation between sSFR and stellar mass, pointing at a key role of the former in determining the galaxy downsizing, as the most significant means of diagnostics of the star formation efficiency. Likewise, an anti-correlation between sSFR and metallicity can be established for the star-forming galaxies, while on the contrary more active galaxies in terms of simple SFR are also metal-richer. We discuss these results in terms of the mechanisms driving the evolution within the high- and low-mass regimes at different epochs: mergers, feedback-driven outflows and the intrinsic variation of the star formation efficiency.
Monthly Notices of the Royal Astronomical Society, 2014
We investigate the interplay between jets from active galactic nuclei (AGNs) and the surrounding ... more We investigate the interplay between jets from active galactic nuclei (AGNs) and the surrounding interstellar medium (ISM) through full 3D, high-resolution, adaptive mesh refinement simulations performed with the FLASH code. We follow the jet-ISM system for several Myr in its transition from an early, compact source to an extended one including a large cocoon. During the jet evolution, we identify three major evolutionary stages and we find that, contrary to the prediction of popular theoretical models, none of the simulations shows a self-similar behaviour. We also follow the evolution of the energy budget, and find that the fraction of input power deposited into the ISM (the AGN coupling constant) is of the order of a few per cent during the first few Myr. This is in broad agreement with galaxy formation models employing AGN feedback. However, we find that in these early stages, this energy is deposited only in a small fraction (<1 per cent) of the total ISM volume. Finally, we demonstrate the relevance of backflows arising within the extended cocoon generated by a relativistic AGN jet within the ISM of its host galaxy, previously proposed as a mechanism for self-regulating the gas accretion on to the central object. These backflows tend later to be destabilized by the 3D dynamics, rather than by hydrodynamic (Kelvin-Helmholtz) instabilities. Yet, in the first few hundred thousand years, backflows may create a central accretion region of significant extent, and convey there as much as a few millions of solar masses.
Monthly Notices of the Royal Astronomical Society, 2009
We study the feedback from an AGN on stellar formation within its host galaxy, mainly using one h... more We study the feedback from an AGN on stellar formation within its host galaxy, mainly using one high resolution numerical simulation of the jet propagation within the interstellar medium of an early-type galaxy. In particular, we show that in a realistic simulation where the jet propagates into a two-phase ISM, star formation can initially be slightly enhanced and then, on timescales of few million years, rapidly quenched, as a consequence both of the high temperatures attained and of the reduction of cloud mass (mainly due to Kelvin-Helmholtz instabilities). We then introduce a model of (prevalently) negative AGN feedback, where an exponentially declining star formation is quenched, on a very short time scale, at a time t AGN , due to AGN feedback. Using the Bruzual & Charlot (2003) population synthesis model and our star formation history, we predict galaxy colours from this model and match them to a sample of nearby early-type galaxies showing signs of recent episodes of star formation . We find that the quantity t gal − t AGN , where t gal is the galaxy age, is an excellent indicator of the presence of feedback processes, and peaks significantly around t gal − t AGN ≈ 0.85 Gyr for our sample, consistent with feedback from recent energy injection by AGNs in relatively bright (M B ∼ < −19) and massive nearby early-type galaxies. Galaxies that have experienced this recent feedback show an enhancement of 3 magnitudes in N U V (GALEX) − g, with respect to the unperturbed, no-feedback evolution. Hence they can be easily identified in large combined near UV-optical surveys.
Monthly Notices of the Royal Astronomical Society, 2006
We have performed a series of N-body/hydrodynamical (TREESPH) simulations of clusters and groups ... more We have performed a series of N-body/hydrodynamical (TREESPH) simulations of clusters and groups of galaxies, selected from a cosmological volume within a Lambda cold dark matter ( CDM) framework: these objects have been resimulated at higher resolution to z = 0, in order to follow also the dynamical, thermal and chemical input on to the intracluster medium (ICM) from stellar populations within galaxies. The simulations include metallicitydependent radiative cooling, star formation according to different initial mass functions (IMFs), energy feedback as strong starburst-driven galactic superwinds, chemical evolution with noninstantaneous recycling of gas and heavy elements, effects of a metagalactic ultraviolet (UV) field and thermal conduction in the ICM.
Monthly Notices of the Royal Astronomical Society, 2011
The age and metallicity gradients for a sample of group and cluster galaxies from N-body+hydrodyn... more The age and metallicity gradients for a sample of group and cluster galaxies from N-body+hydrodynamical simulation are analyzed in terms of galaxy stellar mass. Dwarf galaxies show null age gradient with a tail of high and positive values for systems in groups and cluster outskirts. Massive systems have generally zero age gradients which turn to positive for the most massive ones. Metallicity gradients are distributed around zero in dwarf galaxies and become more negative with mass; massive galaxies have steeper negative metallicity gradients, but the trend flatten with mass. In particular, fossil groups are characterized by a tighter distribution of both age and metallicity gradients. We find a good agreement with both local observations and independent simulations. The results are also discussed in terms of the central age and metallicity, as well as the total colour, specific star formation and velocity dispersion.
Monthly Notices of The Royal Astronomical Society, 2008
Differently from the DS, the operatively defined RS evolves more evidently with z, the epoch when... more Differently from the DS, the operatively defined RS evolves more evidently with z, the epoch when it changes its slope being closely corresponding to that at which the passive galaxies population takes over the star forming one: this goes from z~1 in clusters down to 0.4 in normal groups.
Monthly Notices of the Royal Astronomical Society, 2005
We performed N-body + hydrodynamical simulations of the formation and evolution of galaxy groups ... more We performed N-body + hydrodynamical simulations of the formation and evolution of galaxy groups and clusters in a cold dark matter cosmology. The simulations invoke star formation, chemical evolution with non-instantaneous recycling, metal-dependent radiative cooling, strong starbursts and (optionally) active galactic nucleus (AGN) driven galactic superwinds, effects of a meta-galactic ultraviolet field and thermal conduction. The properties of the galaxy populations in two clusters, one Virgo-like (T ∼ 3 keV) and one (sub)Coma-like (T ∼ 6 keV), are discussed. The global star formation rates of the cluster galaxies are found to decrease very significantly from redshift z = 2 to 0, in agreement with observations. The total K-band luminosity of the cluster galaxies correlates tightly with total cluster mass, and for models without additional AGN feedback, the zero-point of the relation matches the observed one fairly well. Compared to the observed galaxy luminosity function (LF), the simulations nicely match the number of intermediate-mass galaxies (−20 M B −17, smaller galaxies being affected by resolution limits) but they show a deficiency of bright galaxies in favour of an overgrown central dominant (cD) galaxy. High-resolution tests indicate that this deficiency is not simply due to numerical 'overmerging'.
Monthly Notices of The Royal Astronomical Society, 2004
Cosmological (LambdaCDM) TreeSPH simulations of the formation and evolution of galaxy groups and ... more Cosmological (LambdaCDM) TreeSPH simulations of the formation and evolution of galaxy groups and clusters have been performed. The simulations invoke star formation, chemical evolution with non-instantaneous recycling, metal dependent radiative cooling, strong star burst and (optionally) AGN driven galactic super winds, effects of a meta-galactic UV field and thermal conduction. The properties of the galaxy populations in two clusters, one Virgo-like (T~3 keV) and one (sub) Coma-like (T~6 keV), are discussed. The global star formation rates of the cluster galaxies are found to decrease very significantly with time from redshift z=2 to 0, in agreement with observations. The total K-band luminosity of the cluster galaxies correlates tightly with total cluster mass, and for models without additional AGN feedback, the zero point of the relation matches the observed one fairly well. The match to observed galaxy luminosity functions is reasonable, except for a deficiency of bright galaxies (M_B < -20), which becomes increasingly significant with super-wind strength. Results of a high resolution test indicate that this deficiency is not due to ``over--merging''. The redshift evolution of the luminosity functions from z=1 to 0 is mainly driven by luminosity evolution, but also by merging of bright galaxies with the cD. The colour--magnitude relation of the cluster galaxies matches the observed "red sequence" very well and, on average, galaxy metallicity increases with luminosity. As the brighter galaxies are essentially coeval, the colour--magnitude relation results from metallicity rather than age effects, as observed.
Monthly Notices of The Royal Astronomical Society, 2004
Cosmological (LCDM) TreeSPH simulations of galaxy clusters have been performed, invoking star-for... more Cosmological (LCDM) TreeSPH simulations of galaxy clusters have been performed, invoking star-formation, chemical evolution with non-instantaneous recycling, metal dependent radiative cooling, strong star-burst and/or AGN driven super-winds, effects of a meta-galactic UV field and thermal conduction. Results for two clusters, one Virgo-like (T~3 keV) and one (sub) Coma-like (T~6 keV), are presented. At z=0, the stellar contents of both clusters consist of a central dominant (cD) galaxy surrounded by galaxies and intracluster (IC) stars. The IC stars are found to contribute 20-40% of the total cluster B-band light and to form at a mean redshift z_f~3, on average about 0.5 Gyr prior to the stars in galaxies. UBVRIJHK surface brightness profiles of the IC star populations are presented; the profile of the larger cluster matches the observed V-band profile of the cD in Abell 1413 (T~8 keV). The IC stellar populations have B-R=1.4-1.5, comparable to larger E galaxies. The mean [Fe/H]~0.0 in the central part of the cluster (r~100 kpc) decreasing to about -0.3 at r_vir. The IC stars are alpha-element enhanced, with a weak trend of [O/Fe] increasing with r, and an overall [O/Fe]~0.4 dex. The IC stars are kinematically colder than the galaxies: The velocity dispersions of the IC stars are at r~100-500 kpc only about half of those of the galaxies increasing to about 70% at r=1-2 Mpc. The projected velocity dispersion in the Virgo-like cluster at R>~50 kpc is 300-600 km/s depending on orientation and R. Rotation is dynamically insignificant for the IC stars. The velocity distributions of IC stars and galaxies are in one cluster highly radially anisotropic, in the other close to isotropic.
Monthly Notices of the Royal Astronomical Society, Jul 24, 2008
N-body + hydrodynamical simulations of the formation and evolution of galaxy groups and clusters ... more N-body + hydrodynamical simulations of the formation and evolution of galaxy groups and clusters in a ΛCDM cosmology are used in order to follow the building-up of the colour-magnitude relation in two clusters and in 12 groups. We have found that galaxies, starting from the more massive, move to the Red Sequence (RS) as they get aged over times and eventually set upon a "dead sequence" (DS) once they have stopped their bulk star formation activity. Fainter galaxies keep having significant star formation out to very recent epochs and lie broader around the RS. Environment plays a role as galaxies in groups and cluster outskirts hold star formation activity longer than the central cluster regions. However galaxies experiencing infall from the outskirts to the central parts keep star formation on until they settle on to the DS of the core galaxies. Merging contributes to mass assembly until z ∼ 1, after which major events only involve the brightest cluster galaxies.