A Sustainability-based Approach for Geotechnical Infrastructure

Urban growth needs large cities, and the current emphasis on landscape preservation makes using underground spaces both an opportunity and a significant necessity. However, underground construction techniques significantly impact the sustainability of the built environment, including infrastructure systems and their entire supply chains. Nowadays, there is a shortage of quantitative methodologies to assess and measure the sustainability of underground building processes that effectively integrate the three pillars of sustainability (environmental, social, and economic). Thus, this study aims to solve the abovementioned issues by explaining how to incorporate sustainability goals into geotechnical projects to address measure-driven strategies and eco-design-based solutions appropriately. This study illustrates a novel methodology based on the Life Cycle Thinking approach, with a particular emphasis on geotechnical ground improvement techniques. Specifically, the suggested method incorporates the concept of the EU Taxonomy, following the EU Green Deal, with the Envision framework to guide decision-makers toward a more sustainable, resilient, and equitable infrastructure design. In addition, incorporating a cradleto-grave Life Cycle Assessment (LCA) into the suggested methodological approach will improve the quantitative estimation of the performance of construction processes. The definition of the proposed method will provide the guidelines to systematically assess the sustainability of geotechnical infrastructures to allow further the selection of an optimal solution to reduce their impact from an environmental, social, and economic point of view

Jet-regulated cooling catastrophe

We present the first implementation of Active Galactic Nuclei (AGN) feedback in the form of momentum driven jets in an Adaptive Mesh Refinement (AMR) cosmological resimulation of a galaxy cluster. The jets are powered by gas accretion onto Super Massive Black Holes (SMBHs) which also grow by mergers. Throughout its formation, the cluster experiences different dynamical states: both a morphologically perturbed epoch at early times and a relaxed state at late times allowing us to study the different modes of BH growth and associated AGN jet feedback. BHs accrete gas efficiently at high redshift (z>2), significantly pre-heating proto-cluster halos. Gas-rich mergers at high redshift also fuel strong, episodic jet activity, which transports gas from the proto-cluster core to its outer regions. At later times, while the cluster relaxes, the supply of cold gas onto the BHs is reduced leading to lower jet activity. Although the cluster is still heated by this activity as sound waves propagate from the core to the virial radius, the jets inefficiently redistribute gas outwards and a small cooling flow develops, along with low-pressure cavities similar to those detected in X-ray observations. Overall, our jet implementation of AGN feedback quenches star formation quite efficiently, reducing the stellar content of the central cluster galaxy by a factor 3 compared to the no AGN case. It also dramatically alters the shape of the gas density profile, bringing it in close agreement with the beta model favoured by observations, producing quite an isothermal galaxy cluster for gigayears in the process. However, it still falls short in matching the lower than Universal baryon fractions which seem to be commonplace in observed galaxy clusters.Comment: 18 pages, 17 figures, 1 table, Accepted for publication in MNRA

Blowing cold flows away: the impact of early AGN activity on the formation of a brightest cluster galaxy progenitor

Supermassive black holes (BH) are powerful sources of energy that are already in place at very early epochs of the Universe (by z=6). Using hydrodynamical simulations of the formation of a massive M_vir=5 10^11 M_sun halo by z=6 (the most massive progenitor of a cluster of M_vir=2 10^15 M_sun at z=0), we evaluate the impact of Active Galactic Nuclei (AGN) on galaxy mass content, BH self-regulation, and gas distribution inside this massive halo. We find that SN feedback has a marginal influence on the stellar structure, and no influence on the mass distribution on large scales. In contrast, AGN feedback alone is able to significantly alter the stellar-bulge mass content by quenching star formation when the BH is self-regulating, and by depleting the cold gas reservoir in the centre of the galaxy. The growth of the BH proceeds first by a rapid Eddington-limited period fed by direct cold filamentary infall. When the energy delivered by the AGN is sufficiently large to unbind the cold gas of the bulge, the accretion of gas onto the BH is maintained both by smooth gas inflow and clump migration through the galactic disc triggered by merger-induced torques. The feedback from the AGN has also a severe consequence on the baryon mass content within the halo, producing large-scale hot superwinds, able to blow away some of the cold filamentary material from the centre and reduce the baryon fraction by more than 30 per cent within the halo's virial radius. Thus in the very young universe, AGN feedback is likely to be a key process, shaping the properties of the most massive galaxies.Comment: 18 pages, 16 figures, MNRAS accepte

Evolution of the baryon fraction in the Local Group: accretion versus feedback at low and high z

Using hydrodynamical zoom simulations in the standard LCDM cosmology, we investigate the evolution of the distribution of baryons (gas and stars) in a local group-type universe. First, with standard star formation and supernova feedback prescriptions, we find that the mean baryonic fraction value estimated at the virial radius of the two main central objects (i.e. the Milky Way and Andromeda) is decreasing over time, and is 10-15% lower than the universal value, 0.166, at z=0. This decrease is mainly due to the fact that the amount of accretion of dissipative gas onto the halo, especially at low redshift, is in general much lower than that of the dissipationless dark matter. Indeed, a significant part of the baryons does not collapse onto the haloes and remains in their outskirts, mainly in the form of warm-hot intergalactic medium (WHIM). Moreover, during the formation of each object, some dark matter and baryons are also expelled through merger events via tidal disruption. In contrast to baryons, expelled dark matter can be more efficiently re-accreted onto the halo, enhancing both the reduction of fb inside Rv, and the increase of the mass of WHIM outside Rv. Varying the efficiency of supernovae feedback at low redshift does not seem to significantly affect these trends. Alternatively, when a significant fraction of the initial gas in the main objects is released at high redshifts by more powerful sources of feedback, such as AGN from intermediate mass black holes in lower mass galaxies, the baryonic fraction at the virial radius can have a lower value (fb~0.12) at low redshift. Hence physical mechanisms able to drive the gas out of the virial radius at high redshifts will have a stronger impact on the deficit of baryons in the mass budget of Milky Way type-galaxies at present times than those that expel the gas in the longer, late phases of galaxy formation.Comment: Accepted for publication in MNRAS. Major changes from the previous versio

The role of mergers in driving morphological transformation over cosmic time

Accepted for publication in MNRASUnderstanding the processes that trigger morphological transformation is central to understanding how and why the Universe transitions from being disc-dominated at early epochs to having the morphological mix that is observed today. We use Horizon-AGN, a cosmological hydrodynamical simulation, to perform a comprehensive study of the processes that drive morphological change in massive (M*/M ⊙ > 10 10) galaxies over cosmic time. We show that (1) essentially all the morphological evolution in galaxies that are spheroids at z = 0 is driven by mergers with mass ratios greater than 1: 10; (2) major mergers alone cannot produce today's spheroid population - minor mergers are responsible for a third of all morphological transformation over cosmic time and are its dominant driver after z ~ 1; (3) prograde mergers trigger milder morphological transformation than retrograde mergers - while both types of event produce similar morphological changes at z > 2, the average change due to retrograde mergers is around twice that due to their prograde counterparts at z ~ 0; (4) remnant morphology depends strongly on the gas fraction of a merger, with gas-rich mergers routinely re-growing discs; and (5) at a given stellar mass, discs do not exhibit drastically different merger histories from spheroids - disc survival in mergers is driven by acquisition of cold gas (via cosmological accretion and gas-rich interactions) and a preponderance of prograde mergers in their merger histories.Peer reviewedFinal Accepted Versio

From galaxy-scale fueling to nuclear-scale feedback- The merger-state of radio galaxies 3C 293, 3C 305, and 4C 12.50

Powerful radio galaxies are often associated with gas-rich galaxy mergers. These mergers may provide the fuel to trigger starburst and active galactic nuclear (AGN) activity. In this Research Note, we study the host galaxies of three seemingly young or re-started radio sources that drive fast outflows of cool neutral hydrogen (H i) gas, namely 3C 293, 3C 305 and 4C 12.50 (PKS 1345+12). Our aim is to link the feedback processes in the central kpc-scale region with new information on the distribution of stars and gas at scales of the galaxy. For this, we use deep optical V-band imaging of the host galaxies, complemented with H i emission-line observations to study their gaseous environments. We find prominent optical tidal features in all three radio galaxies, which confirm previous claims that 3C 293, 3C 305, and 4C 12.50 have been involved in a recent galaxy merger or interaction. Our data show the complex morphology of the host galaxies and identify the companion galaxies that are likely involved in the merger or interaction. The radio sources appear to be (re-)triggered at a different stage of the merger; 4C 12.50 is a pre-coalescent and possibly multiple merger, 3C 293 is a post-coalescent merger that is undergoing a minor interaction with a close satellite galaxy, while 3C 305 appears to be shaped by an interaction with a gas-rich companion. For 3C 293 and 3C 305, we do not detect H i beyond the inner ~30−45 kpc region, which shows that the bulk of the cold gas is concentrated within the host galaxy, rather than along the widespread tidal features

The impact of the connectivity of the cosmic web on the physical properties of galaxies at its nodes

International audienceWe investigate the impact of the number of filaments connected to the nodes of the cosmic web on the physical properties of their galaxies using the Sloan Digital Sky Survey. We compare these measurements to the cosmological hydrodynamical simulations H orizon-(no)AGN and Simba. We find that more massive galaxies are more connected, in qualitative agreement with theoretical predictions and measurements in dark-matter-only simulations. The star formation activity and morphology of observed galaxies both display some dependence on the connectivity of the cosmic web at a fixed stellar mass: Less star forming and less rotation supported galaxies also tend to have higher connectivity. These results qualitatively hold both for observed and for virtual galaxies, and can be understood given that the cosmic web is the main source of fuel for galaxy growth. The simulations show the same trends at a fixed halo mass, suggesting that the geometry of filamentary infall impacts galaxy properties beyond the depth of the local potential well. Based on simulations, it is also found that active galactic nucleus feedback is key to reversing the relationship between stellar mass and connectivity at a fixed halo mass. Technically, connectivity is a practical observational proxy for past and present accretion (minor mergers or diffuse infall)

The importance of minor-merger-driven star formation and black-hole growth in disk galaxies

This article has been accepted for publication in Monthly Notices of the Royal Astronomical Society. © 2014 The Authors. Published by Oxford University Press on behalf of the Royal Astronomical Society.We use the SDSS Stripe 82 to empirically quantify the stellar-mass and black-hole growth triggered by minor mergers in local spiral (disk) galaxies. Since major mergers destroy disks and create spheroids, morphologically disturbed spirals are likely remnants of minor mergers. Disturbed spirals exhibit enhanced specific star formation rates (SSFRs), the enhancement increasing in galaxies of 'later' morphological type (which have more gas and smaller bulges). By combining the SSFR enhancements with the fraction of time spirals spend in this 'enhanced' mode, we estimate that ~40% of the star formation in local spirals is directly triggered by minor mergers. The disturbed spirals also exhibit higher nuclear-accretion rates, implying that minor mergers enhance the growth rate of the central black hole. However, the specific accretion rate shows a lower enhancement than that in the SSFR, suggesting that the coupling between stellar-mass and black-hole growth is weak in minor-merger-driven episodes. Given the significant fraction of star formation that is triggered by minor mergers, this weaker coupling may contribute to the large intrinsic scatter observed in the stellar vs. black-hole mass relation in spirals. Combining our results with the star formation in early-type galaxies -- which is minor-merger-driven and accounts for ~14% of the star formation budget -- suggests that around half of the star formation activity in the local Universe is triggered by the minor-merger process.Peer reviewedFinal Published versio

The Current Status of Galaxy Formation

Understanding galaxy formation is one of the most pressing issues in cosmology. We review the current status of galaxy formation from both an observational and a theoretical perspective, and summarise the prospects for future advances.Comment: Minor change in Sect. 6 (resolution of ERIS simulation). Note that the figures of the arXiv version are typically sharper than on the published versio

Quantifying the impact of mergers on the angular momentum of simulated galaxies.

We use EAGLE to quantify the effect galaxy mergers have on the stellar specific angular momentum of galaxies, jstars. We split mergers into dry (gas-poor)/wet (gas-rich), major/minor and different spin alignments and orbital parameters. Wet (dry) mergers have an average neutral gas-to-stellar mass ratio of 1.1 (0.02), while major (minor) mergers are those with stellar mass ratios ≥0.3 (0.1–0.3). We correlate the positions of galaxies in the jstars–stellar mass plane at z = 0 with their merger history, and find that galaxies of low spins suffered dry mergers, while galaxies of normal/high spins suffered predominantly wet mergers, if any. The radial jstars profiles of galaxies that went through dry mergers are deficient by ≈0.3 dex at r ≲ 10 r50 (with r50 being the half-stellar mass radius), compared to galaxies that went through wet mergers. Studying the merger remnants reveals that dry mergers reduce jstars by ≈30 per cent, while wet mergers increase it by ≈10 per cent, on average. The latter is connected to the build-up of the bulge by newly formed stars of high rotational speed. Moving from minor to major mergers accentuates these effects. When the spin vectors of the galaxies prior to the dry merger are misaligned, jstars decreases by a greater magnitude, while in wet mergers corotation and high orbital angular momentum efficiently spun-up galaxies. We predict what would be the observational signatures in the jstars profiles driven by dry mergers: (i) shallow radial profiles and (ii) profiles that rise beyond ≈10 r50, both of which are significantly different from spiral galaxies