arXiv subjects

Andrea Negri

Publications and source records attributed to Andrea Negri.

28 records · Page 2Linked to original sources

arXiv2022

CUSP: a two cubesats constellation for Space Weather and solar flares X-ray polarimetry

The CUbesat Solar Polarimeter (CUSP) project aims to develop a constellation of two CubeSats orbiting the Earth to measure the linear polarisation of solar flares in the hard X-ray band by means of a Compton scattering polarimeter on board of each satellite. CUSP will allow to study the magnetic reconnection and particle acceleration in the flaring magnetic structures. CUSP is a project approved for a Phase A study by the Italian Space Agency in the framework of the Alcor program aimed to develop CubeSat technologies and missions.

astro-ph.SR↗

arXiv2022

The luminosity of cluster galaxies in the Cluster-EAGLE simulations

We computed the luminosity of simulated galaxies of the C-EAGLE project, a suite of 30 high-resolution zoom-in simulations of galaxy clusters based on the EAGLE simulation. The AB magnitudes are derived for different spectral bands, from ultraviolet to infrared, using the simple stellar population modeling based on the E-MILES stellar spectra library. We take into account obscuration due to dust in star forming regions and diffuse interstellar medium. The $g-r$ colour-stellar mass diagram, at z=0.1, presents a defined red sequence, reaching $g-r \simeq 0.8$, 0.05 dex redder than EAGLE at high masses, and a well populated blue cloud, when field galaxies are included. The clusters' inner regions are dominated by red-sequence galaxies at all masses, although a non-negligible amount of blue galaxies are still present. We adopt Bayesian inference to compute the clusters LFs, testing for statistical significance of both single and double Schechter functions. The multicolour LFs at z=0 show a knee luminosity that peaks in the infrared and increases with the cluster's mass. The faint-end is weakly dependent on colour and mass and shows an upturn in the optical, bounded between -1.25 and -1.39, just moderately steeper than the field. The simulations reproduce, within the observational errors, the spectroscopic LFs of the Hercules and Abell 85 clusters, including their faint end upturn. C-EAGLE LFs are in broad agreement with observed LFs taken from SDSS and XXL surveys, up to z=0.67, showing a rather flat faint end when the observational constrains are taken into account.

astro-ph.GA↗

arXiv2022

Observed versus Simulated Halo c-Mvir Relations

The concentration - virial mass relation is a well-defined trend that reflects the formation of structure in an expanding Universe. Numerical simulations reveal a marked correlation that depends on the collapse time of dark matter halos and their subsequent assembly history. However, observational constraints are mostly limited to the massive end via X-ray emission of the hot diffuse gas in clusters. An alternative approach, based on gravitational lensing over galaxy scales, revealed an intriguingly high concentration at Milky Way-sized halos. This letter focuses on the robustness of these results by adopting a bootstrapping approach that combines stellar and lensing mass profiles. We also apply the identical methodology to simulated halos from EAGLE to assess any systematic. We bypass several shortcomings of ensemble type lens reconstruction and conclude that the mismatch between observed and simulated concentration-to-virial-mass relations are robust, and need to be explained either invoking a lensing-related sample selection bias, or a careful investigation of the evolution of concentration with assembly history. For reference, at a halo mass of $10^{12} M_\odot$, the concentration of observed lenses is $c_{12}\sim 40\pm 5$, whereas simulations give $c_{12}\sim 15\pm1$.

astro-ph.GA↗

arXiv2020

Kinematic analysis of EAGLE simulations: Evolution of $λ_{Re}$ and its connection with mergers and gas accretion

We have developed a new tool to analyse galaxies in the EAGLE simulations as close as possible to observations.We investigated the evolution of their kinematic properties by means of the angular momentum proxy parameter,$ λ_{Re} $for galaxies with $M_{*} \ge 5 \times 10^{9} M_{\odot}$ in the RefL0100N1504 simulation up to redshift two (z = 2). Galaxies in the simulation show a wide variety of kinematic features, similiar to those found in integral-field spectroscopic studies. At z=0 the distribution of galaxies in the $λ_{Re}-ε$ plane is also in good agreement with results from observations. Scaling relations at z = 0 indicate that there is critical mass, $M_{crit} = 10^{10.3} M_{\odot}$, that divides two different regimes when we include the $λ_{Re}$ parameter. The simulation shows that the distribution of galaxies in the $λ_{Re}-ε$ plane evolves with time until z = 2 when galaxies are equally distributed both in $λ_{Re}$ and $ε$. We studied the evolution of $λ_{Re}$ with time and found that there is no connection between the angular momentum at z = 2 and z = 0. All systems reach their maximum $λ_{Re}$ at z = 1 and then steadily lose angular momentum regardless of their merger history, except for the high star-forming systems that sustain that maximum value over time. The evolution of the Re in galaxies that have not experienced any merger in the last 10 Gyr can be explained by their level of gas accretion.

astro-ph.GA↗

arXiv2019

Sub one percent mass fractions of young stars in red massive galaxies

Early-type galaxies are considered to be the end-products of massive galaxy formation. Optical spectroscopic studies reveal that massive early-type galaxies formed the bulk of their stars over short timescales (1 2), followed by passive evolution to the present. However, their optical spectra are insensitive to constrain small episodes of recent star formation, since they are dominated by old stars. Fortunately, this problem can be tackled in the ultraviolet range. While recent studies that make use of ultraviolet absorption lines have suggested the presence of young stars in a few early-type galaxies, the age and mass fractions of young stars and their dependence on galaxy mass, is unknown. Here we report a detailed study of these young stellar populations, from high-quality stacked spectra of 28,663 galaxies from the BOSS survey, analysing optical and ultraviolet absorption lines simultaneously. We find that residual star formation is ubiquitous in massive early-type galaxies, measuring average mass fractions of ~0.5% in young stars in the last 2 Gyr of their evolution. This fraction shows a decreasing trend with galaxy stellar mass, consistent with a down-sizing scenario. We also find that synthetic galaxies from state-of-the-art cosmological numerical simulations significantly overproduce both intermediate and young stellar populations. Therefore, our results pose stringent constraints on numerical simulations of galaxy formation.

astro-ph.GA↗

arXiv2017

Black hole feeding and feedback: the physics inside the "subgrid"

Black holes (BHs) are believed to be a key ingredient of galaxy formation. However, the galaxy-BH interplay is challenging to study due to the large dynamical range and complex physics involved. As a consequence, hydrodynamical cosmological simulations normally adopt sub-grid models to track the unresolved physical processes, in particular BH accretion; usually the spatial scale where the BH dominates the hydrodynamical processes (the Bondi radius) is unresolved, and an approximate Bondi-Hoyle accretion rate is used to estimate the growth of the BH. By comparing hydrodynamical simulations at different resolutions (300, 30, 3 pc) using a Bondi-Hoyle approximation to sub-parsec runs with non-parameterized accretion, our aim is to probe how well an approximated Bondi accretion is able to capture the BH accretion physics and the subsequent feedback on the galaxy. We analyse an isolated galaxy simulation that includes cooling, star formation, Type Ia and Type II supernovae, BH accretion and AGN feedback (radiation pressure, Compton heating/cooling) where mass, momentum, and energy are deposited in the interstellar medium through conical winds. We find that on average the approximated Bondi formalism can lead to both over- and under-estimations of the BH growth, depending on resolution and on how the variables entering into the Bondi-Hoyle formalism are calculated.

astro-ph.GA↗

arXiv2015

X-ray haloes and star formation in early-type galaxies

High resolution 2D hydrodynamical simulations describing the evolution of the hot ISM in axisymmetric two-component models of early-type galaxies well reproduced the observed trends of the X-ray luminosity ($L_\mathrm{x}$) and temperature ($T_\mathrm{x}$) with galaxy shape and rotation, however they also revealed the formation of an exceedingly massive cooled gas disc in rotating systems. In a follow-up of this study, here we investigate the effects of star formation in the disc, including the consequent injection of mass, momentum and energy in the pre-existing interstellar medium. It is found that subsequent generations of stars originate one after the other in the equatorial region; the mean age of the new stars is $> 5$ Gyr, and the adopted recipe for star formation can reproduce the empirical Kennicutt-Schmidt relation. The results of the previous investigation without star formation, concerning $L_\mathrm{x}$ and $T_\mathrm{x}$ of the hot gas, and their trends with galactic shape and rotation, are confirmed. At the same time, the consumption of most of the cold gas disc into new stars leads to more realistic final systems, whose cold gas mass and star formation rate agree well with those observed in the local universe. In particular, our models could explain the observation of kinematically aligned gas in massive, fast-rotating early-type galaxies.

astro-ph.GA↗

arXiv2014

The effects of galaxy shape and rotation on the X-ray haloes of early-type galaxies - II. Numerical simulations

By means of high resolution 2D hydrodynamical simulations, we study the evolution of the hot ISM for a large set of early-type galaxy models, characterized by various degrees of flattening and internal rotation. The galaxies are described by state-of-the-art axisymmetric two-component models, tailored to reproduce real systems; the dark matter haloes follow the Navarro-Frenk-White or the Einasto profile. The gas is produced by the evolving stars, and heated by Type Ia SNe. We find that, in general, the rotation field of the ISM in rotating galaxies is very similar to that of the stars, with a consequent negligible heating contribution from thermalization of the ordered motions. The relative importance of flattening and rotation in determining the final X-ray luminosity $L_x$ and temperature $T_x$ of the hot haloes is a function of the galactic mass. Flattening and rotation in low mass galaxies favour the establishment of global winds, with the consequent reduction of $L_x$. In medium-to-high mass galaxies, flattening and rotation are not sufficient to induce global winds, however, in the rotating models the nature of the gas flows is deeply affected by conservation of angular momentum, resulting in a reduction of both $L_x$ and $T_x$.

astro-ph.GA↗

arXiv2014

The effects of stellar dynamics on the X-ray emission of flat early-type galaxies

Observational and numerical studies gave hints that the hot gaseous haloes of ETGs may be sensitive to the galaxy internal kinematics. By using high resolution 2D hydro simulations, and realistic two-component (stars plus dark matter) axisymmetric galaxy models, we study the evolution of the hot haloes in a suite of flat ETGs of fixed mass distribution, but with variable amounts of azimuthal velocity dispersion and rotational support, including the possibility of a counter-rotating inner stellar disc. The hot halo is fed by stellar mass losses and heated by SNIa explosions and thermalization of stellar motions. We measure the value of the thermalization parameter gamma (the ratio between the heating due to the relative velocity between the stellar streaming and the ISM bulk flow, and the heating attainable by complete thermalization of the stellar streaming motions). We find that 1) the X-ray emission and the average temperature are larger in fully velocity dispersion supported systems; 2) 0.1<gamma<0.2 for isotropic rotators (with a trend for being larger for lower dark mass models); 3) systems that are isotropic rotators at large radii with an inner counter-rotating disc, or fully velocity dispersion supported systems with an inner rotating disc, have gamma=1, again with a trend to increase for lower dark mass contents. We also find that the lower X-ray luminosities of isotropic rotators cannot be explained just by their low gamma, but are due to the complicated flow structure, consequence of the angular momentum stored at large radii. X-ray emission weighted temperatures and luminosities nicely match observed values; the X-ray isophotes are boxy in case of significant galaxy rotation. Overall, it is found that rotation has an important role to explain the observational result that more rotationally supported ETGs on average show a lower X-ray emission [abridged].

astro-ph.CO↗

arXiv2013

Disk dynamics and the X-ray emission of S0 and flat early-type galaxies

With 2D hydrodynamical simulations, we study the evolution of the hot gas flows in early-type galaxies, focussing on the effects of galaxy rotation on the thermal and dynamical status of the ISM. The galaxy is modelled as a two-component axisymmetric system (stars and dark matter), with a variable amount of azimuthal velocity dispersion and rotational support; the presence of a counter rotating stellar disk is also considered. It is found that the ISM of the rotationally supported (isotropic) model is more prone to thermal instabilities than the fully velocity dispersion counterpart, while its ISM temperature and X-ray luminosity are lower. The model with counter rotation shows an intermediate behaviour.

astro-ph.CO↗