Starbursts driven by central gas compaction

Starburst (SB) galaxies are a rare population of galaxies with star formation rates (SFRs) greatly exceeding those of the majority of star-forming galaxies with similar stellar mass. It is unclear whether these bursts are the result of either especially large gas reservoirs or enhanced efficiencies in converting gas into stars. Tidal torques resulting from gas-rich galaxy mergers are known to enhance the SFR by funneling gas towards the centre. However, recent theoretical works show that mergers do not always trigger a SB and not all SB galaxies are interacting systems, raising the question of what drives a SB. We analyse a large sample of SB galaxies and a mass- and redshift-matched sample of control galaxies, drawn from the FIREbox cosmological volume at z=0-1. We find that SB galaxies have both larger molecular gas fractions and shorter molecular depletion times than control galaxies, but similar total gas masses. Control galaxies evolve towards the SB regime by gas compaction in their central regions, over timescales of about 70 Myr, accompanied by an increase in the fraction of ultra-dense and molecular gas. The driving mechanism behind the SB varies depending on the mass of the galaxy. Massive (Mstar > 1e10 Msun) galaxies undergoing intense, long-lasting SBs are mostly driven by galaxy interactions. Conversely, SBs in non-interacting galaxies are often triggered by a global gravitational instability, that can result in a breathing mode in low-mass galaxies.Comment: 21 pages, 18 figures, submitted to MNRA

Galaxies in the central regions of simulated galaxy clusters

In this paper, we assess the impact of numerical resolution and of the implementation of energy input from AGN feedback models on the inner structure of cluster sub-haloes in hydrodynamic simulations. We compare several zoom-in re-simulations of a sub-sample of the cluster-sized haloes studied in Meneghetti et al. (2020), obtained by varying mass resolution, softening length and AGN energy feedback scheme. We study the impact of these different setups on the subhalo abundances, their radial distribution, their density and mass profiles and the relation between the maximum circular velocity, which is a proxy for subhalo compactness. Regardless of the adopted numerical resolution and feedback model, subhaloes with masses Msub < 1e11Msun/h, the most relevant mass-range for galaxy-galaxy strong lensing, have maximum circular velocities ~30% smaller than those measured from strong lensing observations of Bergamini et al. (2019). We also find that simulations with less effective AGN energy feedback produce massive subhaloes (Msub> 1e11 Msun/h ) with higher maximum circular velocity and that their Vmax - Msub relation approaches the observed one. However the stellar-mass number count of these objects exceeds the one found in observations and we find that the compactness of these simulated subhaloes is the result of an extremely over-efficient star formation in their cores, also leading to larger-than-observed subhalo stellar mass. We conclude that simulations are unable to simultaneously reproduce the observed stellar masses and compactness (or maximum circular velocities) of cluster galaxies. Thus, the discrepancy between theory and observations that emerged from the analysis of Meneghetti et al. (2020) persists. It remains an open question as to whether such a discrepancy reflects limitations of the current implementation of galaxy formation models or the LCDM paradigm.Comment: 11 pages, 10 figures, abstract is redacted to fit arXiv character count limi

158 μm emission as an indicator of galaxy star formation rate

Observations of local star-forming galaxies (SFGs) show a tight correlation between their singly ionized carbon line luminosity () and star formation rate (SFR), suggesting that may be a useful SFR tracer for galaxies. Some other galaxy populations, however, are found to have lower than local SFGs, including the infrared (IR)-luminous, starburst galaxies at low and high redshifts as well as some moderately SFGs at the epoch of re-ionization (EoR). The origins of this ' deficit' is unclear. In this work, we study the -SFR relation of galaxies using a sample of z = 0-8 galaxies with extracted from cosmological volume and zoom-in simulations from the Feedback in Realistic Environments (fire) project. We find a simple analytic expression for /SFR of galaxies in terms of the following parameters: mass fraction of -emitting gas (Zgas), gas metallicity (Zgas), gas density (ngas), and gas depletion time (). We find two distinct physical regimes: -rich galaxies, where tdep is the main driver of the deficit and -poor galaxies where Zgas is the main driver. The observed deficit of IR-luminous galaxies and early EoR galaxies, corresponding to the two different regimes, is due to short gas depletion time and low gas metallicity, respectively. Our result indicates that the deficit is a common phenomenon of galaxies, and caution needs to be taken when applying a constant -to-SFR conversion factor derived from local SFGs to estimate cosmic SFR density at high redshifts and interpret data from upcoming line intensity mapping experiments

Star formation rate in simulated clusters

The star formation rate (SFR) of simulated galaxy clusters is compared to recent observational studies at z=0 and z∼2. In particular, we analyze a set of zoom-in cosmological hydrodynamical simulations centered on twelve clusters and carried out with the GADGET-3 TreePM/SPH code. We find that simulated central galaxies produce an excess of stars at z=0, however at z∼2 simulations under-predict the normalization of the relation SFR-stellar mass of star forming galaxies by a factor of about 3 and are unable to reproduce the observed starburst population. We conclude that the adopted sub-grid model for star formation (Springel & Hernquist 2003), introduced to reproduce the self-regulated evolution of quiescent galaxies, is not suitable to describe violent events like high-redshift starbursts, independently of the choice of the parameters for the star formation and active-galactic-nuclei models. A more extensive analysis is present in Bassini et al. (2020)

The probability of galaxy-galaxy strong lensing events in hydrodynamical simulations of galaxy clusters

Meneghetti et al. (2020) recently reported an excess of galaxy-galaxy strong lensing (GGSL) in galaxy clusters compared to expectations from the LCDM cosmological model. Theoretical estimates of the GGSL probability are based on the analysis of numerical hydrodynamical simulations in the LCDM cosmology. We quantify the impact of the numerical resolution and AGN feedback scheme adopted in cosmological simulations on the predicted GGSL probability and determine if varying these simulation properties can alleviate the gap with observations. We repeat the analysis of Meneghetti et al. (2020) on cluster-size halos simulated with different mass and force resolutions and implementing several independent AGN feedback schemes. We find that improving the mass resolution by a factor of ten and twenty-five, while using the same galaxy formation model that includes AGN feedback, does not affect the GGSL probability. We find similar results regarding the choice of gravitational softening. On the contrary, adopting an AGN feedback scheme that is less efficient at suppressing gas cooling and star formation leads to an increase in the GGSL probability by a factor between three and six. However, we notice that such simulations form overly massive subhalos whose contribution to the lensing cross-section would be significant while their Einstein radii are too large to be consistent with the observations. The primary contributors to the observed GGSL cross-sections are subhalos with smaller masses, that are compact enough to become critical for lensing. The population with these required characteristics appears to be absent in simulations.Comment: 13 pages, 11 figures. Submitted for publication on Astronomy and Astrophysic

Buchi neri e formazione stellare negli ammassi di galassie: una vista dalle simulazioni

Gli ammassi di galassie sono gli oggetti pi\uf9 massicci dell'universo; si trovano ai nodi della rete cosmica da cui accrescono continuamente materia e altre galassie. Le galassie all'interno degli ammassi sono principalmente ellittiche massicce, con poca formazione stellare in corso. Tra queste, un ruolo rilevante \ue8 svolto dalla galassia pi\uf9 luminosa tipicamente situata al centro dell'ammasso (BCG). Nelle BCG, i bassi valori dei tassi di formazione stellare sono correlati all'energia liberata dai nuclei galattici attivi (AGN), come evidenziato dalla frequente presenza di AGN ad alta emissione nelle onde radio. Poich\ue9 questo processo \ue8 generato dall'accrescimento del gas attorno al buco nero (SMBH) centrale, non \ue8 del tutto sorprendente che varie osservazioni abbiano trovato strette correlazioni tra la massa dei SMBH e la massa stellare delle BCG. Due anni fa, sono state trovate altre correlazioni che coinvolgono le masse dei SMBH e le propriet\ue0 globali degli ammasi. Motivato da questi lavori osservativi, nella prima parte della mia tesi ho utilizzato una serie di simulazioni cosmologiche per studiare la crescita simbiotica degli ammassi di galassie e dei SMBH al loro centro, con l'obiettivo di indagare le correlazioni tra la massa dei SMBH e la massa degli ammassi che li ospitano. Anche se il feedback degli AGN \ue8 fondamentale nella regolazione della formazione stellare negli ammassi di galassie a basso redsfhit, quando inizia ad essere efficace gli ammassi di galassie sono gi\ue0 popolati dalle galassie pi\uf9 massicce dell'universo. Data la loro grande massa e la loro bassa velocit\ue0 di formazione stellare, si pensa che la maggior parte delle stelle siano prodotte ad alto redshift durante una breve ed intensa fase di formazione stellare. Questo punto di vista ha numerose prove indirette, sia teoriche che osservative. Per esempio, l'analisi astroarcheologica di enormi ellittiche mostra una proporzionalit\ue0 diretta tra la massa di una galassia e la sua et\ue0. Inoltre, simulazioni cosmologiche e modelli semi-analitici prevedono che la maggior parte delle stelle all'interno delle BCG (> 50%) siano gi\ue0 formate a z ~ 3 durante la fase di protoammasso, e vengono successivamente assemblate attraverso fusioni di galassie. Tuttavia, \ue8 ancora difficile tracciare un quadro completo dell'evoluzione degli ammassi di galassie utilizzando i dati disponibili. Infatti, anche se il numero di protocluster rilevati \ue8 in rapido aumento, il campione risultante \ue8 ancora abbastanza eterogeneo essendo basato su diversi metodi di rilevamento, ciascuno con i propri limiti e bias. In questo contesto, le simulazioni cosmologiche rappresentano lo strumento pi\uf9 avanzato per fornire un quadro interpretativo coerente di tutte queste osservazioni su proto-ammassi. Tuttavia, prima di ottenere un'interpretazione significativa dei dati osservativi sull'evoluzione degli ammassi, \ue8 importante studiare se i modelli teorici riproducono le osservazioni disponibili ad alto z. Pertanto, nella seconda parte del mio progetto di dottorato ho studiato il tasso di formazione stellare all'interno di ammassi di galassie e protoammassi a 0<z<4. Questa analisi suggerisce fortemente che simulazioni cosmologiche allo stato dell'arte hanno difficolt\ue0 a riprodurre i tassi di formazione stellare molto elevati misurati nelle recenti osservazioni. Per comprendere meglio le ragioni fisiche della differenza tra teoria e osservazioni, ho anche studiato le propriet\ue0 della galassia nell'ambiente di protoammasso con un approccio pi\uf9 statistico, studiando le correlazioni e le distribuzioni delle propriet\ue0 delle galassie. Questa analisi evidenzia la necessit\ue0 di una migliore comprensione e modellizzazione dei processi fisici coinvolti nella formazione stellare, necessaria per raggiungere un accordo con le osservazioni disponibili ad alto redshift.Galaxy clusters are the most massive objects in the universe; they are located at the nodes of the cosmic web from which they continuously accrete matter and other galaxies. The galaxies within clusters are mainly red massive ellipticals or bulge dominated, with little ongoing star formation. Among them, a relevant role is played by the brightest cluster galaxy (BCG), the most luminous and massive cluster galaxy typically located at the cluster center. In the BCGs, the low values of star formation rates are related to a hampering of the cooling rate by the feedback from the active galactic nuclei (AGN), as highlighted by the frequent presence of radio-loud AGNs. Since this feedback is generated by the gas accretion around the central SMBH, it is not completely surprising that observational works found tight correlations between SMBH mass and BCG stellar mass and stellar velocity dispersion. Two years ago, other correlations involving SMBHs masses and global cluster properties (like cluster mass and temperature) was found. Motivated by these observational works, in the first part of my thesis I used a set of cosmological simulations to study the symbiotic growth of galaxy clusters and the SMBHs at their center, with the aim of investigating the correlations between SMBH mass and cluster mass and temperature, their establishment and evolution. Moreover, I studied how gas accretion and BH-BH mergers contribute to SMBH growth across cosmic time. Even though AGN feedback is fundamental in regulating the star formation in low-redshift galaxy clusters, by the time it starts to be effective galaxy clusters are already populated by the most massive galaxies in the universe. Given their large mass and their low star formation rates, it is thought that most of the stars are produced at high redshift during a brief and intense burst of star formation. This view has numerous indirect pieces of evidence, both observational and theoretical. For example, astroarchaeology analysis of massive ellipticals shows a direct proportionality between the mass of a galaxy and its age. Moreover, numerical simulations and semi-analytical models predict that most of the stars within the BCGs (> 50%) are already formed by z~3 during the proto-cluster stage, i.e. the infancy stage of clusters of galaxies, and are later assembled through galaxy mergers. However, it is still difficult to draw a complete picture of galaxy cluster evolution using available data. Indeed, even though the number of detected protoclusters is rapidly increasing, the resulting sample is still fairly heterogenous being based on different detection methods, each having its own limitations and bias. In this context, cosmological hydrodynamical simulations represent the most advanced tool to provide a coherent interpretative framework of all such observations on proto-clusters. However, before obtaining a meaningful interpretation of observational data on cluster evolution, it is important to study whether theoretical models match the already available high redshift observational constraints. Therefore, in the second part of my PhD project I studied the star formation rate within galaxy clusters and proto-clusters over the redshift range 0<z<4. This analysis strongly suggests that state-of-the-art cosmological simulations have difficulties in reproducing the very high star formation rates measured from recent observations. To better understand the physical reasons for the difference between theory and observations, I also studied galaxy properties in protocluster environment in a more statistical approach, e.g. studying galaxy properties correlations and distributions. This analysis highlights the need for a better understanding and modeling of the physical processes involved in star formation, needed to reach an agreement with the available observations at high redshift

Powder spreading and spreadability in the additive manufacturing of metallic materials: a critical review

3noreservedembargoed_20240701Capozzi, Luigi C.; Sivo, Antonio; Bassini, EmilioCapozzi, Luigi C.; Sivo, Antonio; Bassini, Emili

The inefficiency of stellar feedback in driving galactic outflows in massive galaxies at high redshift

Recent observations indicate that galactic outflows are ubiquitous in high-redshift (high-z) galaxies, including normal star-forming galaxies, quasar hosts, and dusty star-forming galaxies (DSFGs). However, the impact of outflows on the evolution of their hosts is still an open question. Here, we analyse the star-formation histories and galactic outflow properties of galaxies in massive haloes ($10^{12}\, {\rm M}_{\odot }\ \lt\ M_{\rm vir}\ \lt\ 5\times 10^{12}\, {\rm M}_{\odot }$) at z ≳ 5.5 in three zoom-in cosmological simulations from the MassiveFIRE suite, as part of the Feedback In Realistic Environments (FIRE) project. The simulations were run with the FIRE-2 model, which does not include feedback from active galactic nuclei. The simulated galaxies resemble z &gt; 4 DSFGs, with star-formation rates of $\sim\!{1000}\ {\rm M}_{\odot }\, \rm yr^{-1}$ and molecular gas masses of Mmol ∼ 1010 M⊙. However, the simulated galaxies are characterized by higher circular velocities than those observed in high-z DSFGs. The mass loading factors from stellar feedback are of the order of ∼0.1, implying that stellar feedback is inefficient in driving galactic outflows and gas is consumed by star formation on much shorter time-scales than it is expelled from the interstellar medium. We also find that stellar feedback is highly inefficient in self-regulating star formation in this regime, with an average integrated star formation efficiency (SFE) per dynamical time of 30 per cent. Finally, compared with FIRE-2 galaxies hosted in similarly massive haloes at lower redshift, we find lower mass loading factors and higher SFEs in the high-z sample. We argue that both effects originate from the higher total and gas surface densities that characterize high-z massive systems

HyPer-QuarCh II: a laboratory-scale device for hydrogen isotopes permeation experiments

In a D-T fusion reactor, the correct estimation of the tritium inventory and permeation fluxes towards the coolant and to the external environment is a crucial issue for the reactor licensing. Within this frame, a fast and reliable sensor for the online measurement of hydrogen isotopes concentration in the breeder is therefore necessary. At ENEA Brasimone research centre, Italy, the development, qualification and characterization of hydrogen isotopes permeation sensors (HPS) were carried out since the early 2000s. A new experimental laboratory-scale device, named Hyper-Quarch II (Hydrogen Permeation Quartz Chamber), was developed on the basis of the experience gained in the past experimental campaigns. This device is characterised by an upgraded test section in quartz and new instrumentation equipment, and will be used to test advanced hydrogen permeation sensor in both gas phase and in stagnant LiPb eutectic alloy (15.7 at.% Li). Hydrogen or deuterium will be adopted instead of tritium to simulate the operative conditions of the Water-Cooled Lithium-Lead (WCLL) Test Blanket Module of ITER and the WCLL Breeding Blanket of the European DEMO reactor. Moreover, the upgrade was performed to also allow the measurement of the Sieverts’ constant of hydrogen or deuterium solubilised in the LiPb with absorption or desorption techniques in a temperature range from 300 to 550∘C and pressure range 0.1 to 100 hPa

FIREbox: simulating galaxies at high dynamic range in a cosmological volume

We introduce a suite of cosmological volume simulations to study the evolution of galaxies as part of the Feedback in Realistic Environments project. FIREbox, the principal simulation of the present suite, provides a representative sample of galaxies (∼1000 galaxies with $M_{\rm star}\gt 10^8\, M_\odot$ at z  = 0) at a resolution ($\Delta {}x\sim {}20\, {\rm pc}$ , $m_{\rm b}\sim {}6\times {}10^4\, M_\odot$ ) comparable to state-of-the-art galaxy zoom-in simulations. FIREbox captures the multiphase nature of the interstellar medium in a fully cosmological setting (L = 22.1 Mpc) thanks to its exceptionally high dynamic range (≳106) and the inclusion of multichannel stellar feedback. Here, we focus on validating the simulation predictions by comparing to observational data. We find that star formation rates, gas masses, and metallicities of simulated galaxies with $M_{\rm star}\lt 10^{10.5-11}\, M_\odot$ broadly agree with observations. These galaxy scaling relations extend to low masses ($M_{\rm star}\sim {}10^7\, M_\odot$ ) and follow a (broken) power-law relationship. Also reproduced are the evolution of the cosmic HI density and the HI column density distribution at z ∼ 0–5. At low z , FIREbox predicts a peak in the stellar-mass–halo-mass relation but also a higher abundance of massive galaxies and a higher cosmic star formation rate density than observed, showing that stellar feedback alone is insufficient to reproduce the properties of massive galaxies at late times. Given its high resolution and sample size, FIREbox offers a baseline prediction of galaxy formation theory in a ΛCDM Universe while also highlighting modelling challenges to be addressed in next-generation galaxy simulations