1,720,977 research outputs found
Growth of Supermassive Black Hole Seeds in ETG Star-forming Progenitors: Multiple Merging of Stellar Compact Remnants via Gaseous Dynamical Friction and Gravitational-wave Emission
No full textWe propose a new mechanism for the growth of supermassive black hole (BH) seeds in the star-forming
progenitors of local early-type galaxies (ETGs) at z1. This envisages the migration and merging of stellar
compact remnants (neutron stars and stellar-mass BHs) via gaseous dynamical friction toward the central highdensity
regions of such galaxies. We show that, under reasonable assumptions and initial conditions, the process
can build up central BH masses of the order of 104–106Me within some 107 yr, so effectively providing heavy
seeds before standard disk (Eddington-like) accretion takes over to become the dominant process for further BH
growth. Remarkably, such a mechanism may provide an explanation, alternative to super-Eddington accretion
rates, for the buildup of billion-solar-massed BHs in quasar hosts at z7, when the age of the universe 0.8 Gyr
constitutes a demanding constraint; moreover, in more common ETG progenitors at redshift z∼2–6, it can concur
with disk accretion to build such large BH masses even at moderate Eddington ratios 0.3 within the short star
formation duration Gyr of these systems. Finally, we investigate the perspectives to detect the merger events
between the migrating stellar remnants and the accumulating central supermassive BH via gravitational-wave
emission with future ground- and space-based detectors such as the Einstein Telescope and the Laser
Interferometer Space Antenna
Searching for Anisotropic Stochastic Gravitational-wave Backgrounds with Constellations of Space-based Interferometers
Full text linkMany recent works have shown that the angular resolution of ground-based detectors is too poor to characterize the
anisotropies of the stochastic gravitational-wave background (SGWB). For this reason, we asked ourselves if a
constellation of space-based instruments could be more suitable. We consider the Laser Interferometer Space
Antenna (LISA), a constellation of multiple LISA-like clusters, and the Deci-hertz Interferometer Gravitationalwave
Observatory (DECIGO). Specifically, we test whether these detector constellations can probe the anisotropies
of the SGWB. For this scope, we considered the SGWB produced by two astrophysical sources: merging compact
binaries, and a recently proposed scenario for massive black hole seed formation through multiple mergers of
stellar remnants. We find that measuring the angular power spectrum of the SGWB anisotropies is almost
unattainable. However, it turns out that it could be possible to probe the SGWB anisotropies through crosscorrelation
with the cosmic microwave background (CMB) fluctuations. In particular, we find that a constellation
of two LISA-like detectors and CMB-S4 can marginally constrain the cross-correlation between the CMB lensing
convergence and the SGWB produced by the black hole seed formation process. Moreover, we find that DECIGO
can probe the cross-correlation between the CMB lensing and the SGWB from merging compact binaries
Time-dependent ground movements induced by shield tunneling in soft clay: a parametric study
No full textIn this work, the effects of coupled hydromechanical (consolidation) processes associated with shield tunneling excavation in soft clays are investigated with particular attention to the prediction of ground movements at the ground surface. A series of 2d FE analyses have been carried out in parametric form in order to investigate the effects of tunnel excavation velocity relative to the soil consolidation rate and the hydraulic boundary conditions at the tunnel boundary. The shield advancement process has
been simulated with a simplified procedure incorporating both volume loss and ovalization of the tunnel section. In order to investigate the relative importance of soil consolidation during the excavation process, different characteristic times for the tunnel face advancement and for the consolidation process around the tunnel have been considered, for the two limiting conditions of fully permeable liner and impervious liner. The potential damage induced by the tunnel excavation on existing structures, based on computed ground surface distortions and horizontal deformations, has been found to vary significantly with time during the consolidation process. The results of the simulations allowed to obtain useful information on the minimum tunnel face advancement speed for which the assumption of fully undrained conditions for the soil during the excavations is acceptable, as well as on the speed rang
Exploring galaxies-gravitational waves cross-correlations as an astrophysical probe
No full textGravitational waves astronomy has opened a new opportunity to study the Universe. Full exploitation of this window can especially be provided by combining data coming from gravitational waves experiments with luminous tracers of the Large Scale Structure, like galaxies. In this work we investigate the cross-correlation signal between gravitational waves resolved events, as detected by the Einstein Telescope, and actively star-forming galaxies. The galaxies distribution is computed through their UV and IR luminosity functions and the gravitational waves events, assumed to be of stellar origin, are self-consistently computed from the aforementioned galaxies distribution. We provide a state-of-the-art treatment both on the astrophysical side, {taking} into account the impact of the star formation and chemical evolution histories of galaxies, and in computing the cross-correlation signal, for which we include lensing and relativistic effects. {We find that the measured cross-correlation signal can be sufficiently strong to overcome the noise and provide a clear signal. As a possible application of this methodology, we consider a proof-of-concept case in which we aim at discriminating a metallicity dependence on the compact objects merger efficiency against a reference case with no metallicity dependence.} When considering galaxies with a Star Formation Rate ψ > 10 Mo ̇/yr, a Signal-to-Noise ratio around a value of 2-4 is gained after a decade of observation time, depending on the observed fraction of the sky. This formalism can be exploited as an astrophysical probe and could potentially allow to test and compare different astrophysical scenarios
New Analytic Solutions for Galaxy Evolution. II. Wind Recycling, Galactic Fountains, and Late-type Galaxies
No full textWe generalize the analytic solutions presented in Pantoni et al. by including a simple yet effective description of
wind recycling and galactic fountains, with the aim of self-consistently investigating the spatially averaged time
evolution of the gas, stellar, metal, and dust content in disk-dominated late-type galaxies (LTGs). Our analytic
solutions, when supplemented with specific prescriptions for parameter setting and with halo accretion rates from
N-body simulations, can be exploited to reproduce the main statistical relationships followed by local LTGs; these
involve, as a function of the stellar mass, the star formation efficiency, the gas mass fraction, the gas/stellar
metallicity, the dust mass, the star formation rate, the specific angular momentum, and the overall mass/metal
budget. Our analytic solutions allow us to easily disentangle the diverse role of the main physical processes ruling
galaxy formation in LTGs; in particular, we highlight the crucial relevance of wind recycling and galactic fountains
in efficiently refurnishing the gas mass, extending the star formation timescale, and boosting the metal enrichment
in gas and stars. All in all, our analytic solutions constitute a transparent, handy, and fast tool that can provide a
basis for improving the (sub-grid) physical recipes presently implemented in more sophisticated semi-analytic
models and numerical simulations, and can serve as a benchmark for interpreting and forecasting current and future
spatially averaged observations of local and higher redshift LTGs
The impact of the FMR and starburst galaxies on the (low metallicity) cosmic star formation history
Full text linksponsorship: We thank Karina Caputi and Jarle Brinchmann for helpful discussions. We thank the anonymous referee for their thoughtful comments that helped to improve this paper. MC and GN acknowledge support from the Netherlands Organisation for Scientific Research (NWO). ALandLBare supported by PRINMIUR 2017 prot. 20173ML3WW, `Opening the ALMA window on the cosmic evolution of gas, stars and supermassive black holes', and by the EU H2020-MSCA-ITN2019 Project 860744 'BiD4BESt: Big Data applications for black hole Evolution STudies.' (Netherlands Organisation for Scientific Research (NWO), PRINMIUR|20173ML3WW, EU H2020-MSCA-ITN2019|860744)status: Publishe
Growth of massive black hole seeds by migration of stellar and primordial black holes: Gravitational waves and stochastic background
No full textWe investigate the formation and growth of massive black hole (BH) seeds in dusty star-forming galaxies, relying and extending the framework proposed by [1]. Specifically, the latter envisages the migration of stellar compact remnants (neutron stars and stellar-mass black holes) via gaseous dynamical friction towards the galaxy nuclear region, and their subsequent merging to grow a massive central BH seed. In this paper we add two relevant ingredients: (i) we include primordial BHs, that could constitute a fraction f pBH of the dark matter, as an additional component participating in the seed growth; (ii) we predict the stochastic gravitational wave background originated during the seed growth, both from stellar compact remnant and from primordial BH mergers. We find that the latter events contribute most to the initial growth of the central seed during a timescale of 106-107 yr, before stellar compact remnant mergers and gas accretion take over. In addition, if the fraction of primordial BHs f pBH is large enough, gravitational waves emitted by their mergers in the nuclear galactic regions could be detected by future interferometers like Einsten Telescope, DECIGO and LISA. As for the associated stochastic gravitational wave background, we predict that it extends over the wide frequency band 10-6 ≲ f[Hz] ≲ 10, which is very different from the typical range originated by mergers of isolated binary compact objects. On the one hand, the detection of such a background could be a smoking gun to test the proposed seed growth mechanism; on the other hand, it constitutes a relevant contaminant from astrophysical sources to be characterized and subtracted, in the challenging search for a primordial background of cosmological origin
Evolution of Galaxy Star Formation and Metallicity: Impact on Double Compact Object Mergers
Full text linkContains fulltext :
230768.pdf (Publisher’s version ) (Closed access)
Contains fulltext :
230768pre.pdf (Author’s version preprint ) (Open Access
Going Beyond Counting First Authors in Author Co-citation Analysis
Full text linkThe present study examines one of the fundamental aspects of author co-citation analysis (ACA) - the way co-citation
counts are defined. Co-citation counting provides the data on which all subsequent statistical analyses and mappings
are based, and we compare ACA results based on two different types of co-citation counting - the traditional type that
only counts the first one among a cited work's authors on the one hand and a non-traditional type that takes into
account the first 5 authors of a cited work on the other hand. Results indicate that the picture produced through this non-traditional author co-citation counting contains more coherent author groups and is therefore considerably clearer. However, this picture represents fewer specialties in the research field being studied than that produced through the traditional first-author co-citation counting when the same number of top-ranked authors is selected and analyzed. Reasons for these effects are discussed
- …
