Showing papers by "Tiziana Di Matteo published in 2023"

The CAMELS project: Expanding the galaxy formation model space with new ASTRID and 28-parameter TNG and SIMBA suites

Abstract: We present CAMELS-ASTRID, the third suite of hydrodynamical simulations in the Cosmology and Astrophysics with MachinE Learning (CAMELS) project, along with new simulation sets that extend the model parameter space based on the previous frameworks of CAMELS-TNG and CAMELS-SIMBA, to provide broader training sets and testing grounds for machine-learning algorithms designed for cosmological studies. CAMELS-ASTRID employs the galaxy formation model following the ASTRID simulation and contains 2,124 hydrodynamic simulation runs that vary 3 cosmological parameters ($\Omega_m$, $\sigma_8$, $\Omega_b$) and 4 parameters controlling stellar and AGN feedback. Compared to the existing TNG and SIMBA simulation suites in CAMELS, the fiducial model of ASTRID features the mildest AGN feedback and predicts the least baryonic effect on the matter power spectrum. The training set of ASTRID covers a broader variation in the galaxy populations and the baryonic impact on the matter power spectrum compared to its TNG and SIMBA counterparts, which can make machine-learning models trained on the ASTRID suite exhibit better extrapolation performance when tested on other hydrodynamic simulation sets. We also introduce extension simulation sets in CAMELS that widely explore 28 parameters in the TNG and SIMBA models, demonstrating the enormity of the overall galaxy formation model parameter space and the complex non-linear interplay between cosmology and astrophysical processes. With the new simulation suites, we show that building robust machine-learning models favors training and testing on the largest possible diversity of galaxy formation models. We also demonstrate that it is possible to train accurate neural networks to infer cosmological parameters using the high-dimensional TNG-SB28 simulation set.

Boosting Line Intensity Map Signal-to-Noise with the Ly-α forest cross-correlation

Abstract: We forecast the prospects for cross-correlating future line intensity mapping (LIM) surveys with the current and future Ly-α forest measurements. Using large cosmological hydrodynamic simulations, we model the emission from the CO rotational transition in the COMAP LIM experiment at the 5-year benchmark and the Ly-α forest absorption signal for eBOSS, DESI, and PFS. We show that CO × Ly-α forest significantly enhances the detection signal-to-noise ratio of CO, with up to to $300~{{\%}}$ improvement when correlated with the PFS Ly-α forest survey and a 50–75% enhancement with the available eBOSS or the upcoming DESI observations. This is competitive with even CO × spectroscopic galaxy surveys. Furthermore, our study suggests that the clustering of CO emission is tightly constrained by CO × Ly-α forest due to the increased sensitivity and the simplicity of Ly-α absorption modeling. Foreground contamination or systematics are expected not to be shared between LIM and Ly-α forest observations, providing an unbiased inference. Ly-α forest will aid in detecting the first LIM signals. We also estimate that [C ii] × Ly-α forest measurements from EXCLAIM and DESI/eBOSS should have a larger S/N ratio than planned [C ii] × quasar observations by about an order of magnitude.

High-redshift supermassive black hole mergers in simulations with dynamical friction modelling

Abstract: In the near future, projects like LISA and Pulsar Timing Arrays are expected to detect gravitational waves from mergers between supermassive black holes, and it is crucial to precisely model the underlying merger populations now to maximize what we can learn from this new data. Here we characterize expected high-redshift ( z > 2) black hole mergers using the very large volume Astrid cosmological simulation, which uses a range of seed masses to probe down to low-mass BHs, and directly incorporates dynamical friction so as to accurately model the dynamical processes which bring black holes to the galaxy center where binary formation and coalescence will occur. The black hole populations in Astrid include black holes down to ∼ 10 4 . 5 M (cid:12) , and remain broadly consistent with the TNG simulations at scales > 10 6 M (cid:12) (the seed mass used in TNG). By resolving lower-mass black holes, the overall merger rate is ∼ 5 × higher than in TNG. However, incorporating dynamical friction delays mergers compared to a recentering scheme, reducing the high-z merger rate mass-matched mergers by a factor of ∼ 2 × . We also calculate the expected LISA Signal-to-Noise values, and show that the distribution peaks at

Inferring the impact of feedback on the matter distribution using the Sunyaev Zel'dovich effect: Insights from CAMELS simulations and ACT+DES data

Abstract: Feedback from active galactic nuclei and stellar processes changes the matter distribution on small scales, leading to significant systematic uncertainty in weak lensing constraints on cosmology. We investigate how the observable properties of group-scale halos can constrain feedback’s impact on the matter distribution using Cosmology and Astrophysics with MachinE Learning Simulations (CAMELS). Extending the results of previous work to smaller halo masses and higher wavenumber, k , we find that the baryon fraction in halos contains significant information about the impact of feedback on the matter power spectrum. We explore how the thermal Sunyaev Zel’dovich (tSZ) signal from group-scale halos contains similar information. Using recent Dark Energy Survey (DES) weak lensing and Atacama Cosmology Telescope (ACT) tSZ cross-correlation measurements and models trained on CAMELS, we obtain 10% constraints on feedback effects on the power spectrum at k ∼ 5 h/ Mpc. We show that with future surveys, it will be possible to constrain baryonic effects on the power spectrum to O ( < 1%) at k = 1 h/ Mpc and O (3%) at k = 5 h/ Mpc using the methods that we introduce here. Finally, we investigate the impact of feedback on the matter bispectrum, finding that tSZ observables are highly informative in this case.

A look at financial dependencies by means of econophysics and financial economics

Abstract: Abstract This is a review about financial dependencies which merges efforts in econophysics and financial economics during the last few years. We focus on the most relevant contributions to the analysis of asset markets’ dependencies, especially correlational studies, which in our opinion are beneficial for researchers in both fields. In econophysics, these dependencies can be modeled to describe financial markets as evolving complex networks. In particular, we show that a useful way to describe dependencies is by means of information filtering networks that are able to retrieve relevant and meaningful information in complex financial datasets. In financial economics these dependencies can describe asset comovement and spill-overs. In particular, several models are presented that show how network and factor model approaches are related to modeling of multivariate volatility and asset returns, respectively. Finally, we sketch out how these studies can inspire future research and how they contribute to support researchers in both fields to find a better and a stronger common language.

AI-assisted super-resolution cosmological simulations III: Time evolution

Abstract: In this work, we extend our recently developed super-resolution (SR) model for cosmological simulations to produce fully time consistent evolving representations of the particle phase-space distribution. We employ a style-based constrained generative adversarial network (Style-GAN) where the changing cosmic time is an input style parameter to the network. The matter power spectrum and halo mass function agree well with results from high-resolution N-body simulations over the full trained redshift range ($10 \le z \le 0$). Furthermore, we assess the temporal consistency of our SR model by constructing halo merger trees. We examine progenitors, descendants and mass growth along the tree branches. All statistical indicators demonstrate the ability of our SR model to generate satisfactory high-resolution simulations based on low-resolution inputs.

PRIYA: A New Suite of Lyman-alpha Forest Simulations for Cosmology

Abstract: We present the PRIYA suite of cosmological simulations, based on the code and hydrodynamic model of the ASTRID simulation, and designed for cosmological analyses of the Lyman-$\alpha$ forest. Our simulation suite spans a $9$-dimensional parameter space, including $4$ cosmological parameters and $5$ astrophysical/thermal parameters. We have run $48$ low fidelity simulations with $1536^3$ particles in a $120$ Mpc/h box and $3$ high fidelity simulations with $3072^3$ particles in a $120$ Mpc/h box. All our simulations include a full physics model for galaxy formation, including supernova and AGN feedback, and thus also contain a realistic population of DLAs. We advance on earlier simulations suites by larger particle loads, by incorporating new physical models for patchy hydrogen and helium reionization, and by self-consistently incorporating a model for AGN feedback. We show that patchy helium reionization imprints an excess in the 1D flux power spectrum on large scales, which may allow future measurements of helium reionization bubble sizes. Simulation parameters are chosen based on a Latin hypercube design and a Gaussian process is used to interpolate to arbitrary parameter combinations. We build a multi-fidelity emulator for the 1D flux power spectrum and the mean IGM temperature. We show that our final interpolation error is $<1\%$ and that our simulations produce a flux power spectrum converged at the percent level for $z=5.4$ - $2.2$. Our simulation suite will be used to interpret Lyman-$\alpha$ forest 1D flux power spectra from SDSS and future DESI data releases.

Efficient Reionization in a Large Hydrodynamic Galaxy Formation Simulation

Abstract: Accuracy in the topology and statistics of a simulated Epoch of Reionization (EoR) are vital to draw connections between observations and physical processes. While full radiative transfer models produce the most accurate reionization models, they are highly computationally expensive, and are infeasible for the largest cosmological simulations. Instead, large simulations often include EoR models that are pre-computed via the initial density field, or post-processed where feedback effects are ignored. We introduce Astrid-ES, a resimulation of the Astrid epoch of reionisation $20>z>5.5$ which includes an excursion-set reionization algorithm. Astrid-ES produces more accurate reionization histories without significantly impacting the computational time. This model directly utilises the star particles produced in the simulation to calculate the EoR history and includes a UV background which heats the gas particles after their reionization. We contrast the reionization topology and statistics in Astrid-ES with the previously employed parametric reionisation model, finding that in Astrid-ES, ionised regions are more correlated with galaxies, and the 21cm power-spectrum shows an increase in large scale power. We calculate the relation between the size of HII regions and the UV luminosity of the brightest galaxy within them. Prior to the overlap phase, we find a power-law fit of $\mathrm{log} (R) = -0.314 M_\mathrm{UV} - 2.550 \mathrm{log}(1+z) + 7.408$ with a standard deviation $\sigma_R<0.15 \mathrm{dex}$ across all mass bins. We also examine the properties of halos throughout reionization, finding that while the properties of halos in the simulation are correlated with the redshift of reionisation, they are not greatly affected by reionisation itself.

Direct formation of massive black holes via dynamical collapse in metal-enriched merging galaxies at $z \sim 10$: fully cosmological simulations

Abstract: We present the results of the first fully cosmological hydrodynamical simulations studying the merger-driven model for massive black hole (BH) seed formation via direct collapse. Using the zoom-in technique as well as particle splitting, we achieve a final spatial resolution of $2$ pc. We show that the major merger of two massive galaxies at redshift $z \sim 8$ results in the formation of a nuclear supermassive disk (SMD) of only $4$ pc in radius, owing to a prodigious gas inflow sustained at $100$-$1000$ $M_{\odot}$ yr$^{-1}$. The core of the merger remnant is metal-rich, well above solar abundance, and the SMD reaches a gaseous mass of $3 \times 10^8$ $M_{\odot}$ in less than a million years after the merger, despite a concurrent prominent nuclear starburst. Dynamical heating as gas falls into the deepest part of the potential well, and heating and stirring by supernova blastwaves, generate a turbulent multi-phase interstellar medium, with a gas velocity dispersion exceeding 100 km s$^{-1}$. As a result, only moderate fragmentation occurs in the inner $10$-$20$ pc despite the temperature falls below $1000$ K. The SMD is Jeans-unstable as well as bar-unstable and will collapse further adiabatically, becoming warm and ionized. We show that the SMD, following inevitable contraction, will become general relativistic unstable and directly form a supermassive BH of mass in the range $10^6$-$10^8$ $M_{\odot}$, essentially skipping the stage of BH seed formation. These results confirm that mergers between the most massive galaxies at $z \sim 8$-$10$ can naturally explain the rapid emergence of bright high-redshift quasars.

Triple and quadruple black holes in the ASTRID simulation at z ∼ 2

Abstract: We use the ASTRID cosmological hydrodynamic simulation to investigate the properties and evolution of triple and quadruple Massive Black Hole (MBH) systems at z = 2 − 3. Only a handful of MBH tuple systems have been detected to date. In ASTRID, we find 4% of the MBH > 107 M⊙ are in tuples with Δrmax < 200 kpc. The tuple systems span a range of separations with the majority of the observable AGN systems at Δr ∼ 50 − 100 kpc. They include some of the most massive BHs (up to 1010 M⊙) but with at least one of the components of MBH ∼ 107 M⊙. Tuples’ host galaxies are typically massive with M* ∼ 1010 − 11 M⊙. We find that $>10~{{\%}}$ massive halos with Mhalo > 1013M⊙ host MBH tuples. Following the subsequent interactions between MBHs in tuples, we found that in $\sim 5~{{\%}}$ of the triplets all three MBHs merge within a Gyr, and 15% go through one merger. As a by-product of the complex multi-galaxy interaction of these systems, we also find that up to $\sim 5~{{\%}}$ of tuples lead to runaway MBHs. In ASTRID, virtually all of the ultramassive black holes (>1010 M⊙) have undergone a triple quasar phase while for BHs with MBH ∼ 109 M⊙ this fraction drops to 50%.

Over-massive Central Black Holes in the cosmological simulations ASTRID and Illustris TNG50

Abstract: Recent dynamical measurements indicate the presence of a central SMBH with mass ∼3 × 106 M⊙ in the dwarf galaxy Leo I, placing the system ∼50 times above the standard, local MBH − M⋆ relation. While a few over-massive central SMBHs are reported in nearby isolated galaxies, this is the first detected in a Milky Way satellite. We used the ASTRID and Illustris TNG50 LCDM cosmological simulations to investigate the assembly history of galaxies hosting over-massive SMBHs. We estimate that, at the stellar mass of Leo I, $\sim 15~{{\ \rm per\ cent}}$ of galaxies above the MBH − M⋆ relation lie >10 times above it. Leo I-like systems are rare but exist in LCDM simulations: they occur in $\sim 0.005~{{\ \rm per\ cent}}$ of all over-massive systems. Examining the properties of simulated galaxies harboring over-massive central SMBHs, we find that: (i) stars assemble more slowly in galaxies above the MBH − M⋆ relation; (ii) the gas fraction in these galaxies experiences a significantly steeper decline over time; and (iii) $>95~{{\ \rm per\ cent}}$ of satellite host galaxies in over-dense regions are located above the MBH − M⋆ relation. This suggests that massive satellite infall and consequent tidal stripping in a group/dense environment can drive systems away from the MBH − M⋆ relation, causing them to become over-massive. As the merging histories of over-massive and under-massive systems do not differ, we conclude that additional environmental effects, such as being in overdense regions, must play a crucial role. In the high-z Universe, central over-massive SMBHs are a signature of heavy black hole seeds; we demonstrate, in contrast, that low-z over-massive systems result from complex environmental interactions.

Massive black holes in galactic nuclei: Theory and Simulations

Abstract: Massive black holes are fundamental constituents of our cosmos, from the Big Bang to today. Understanding their formation from cosmic dawn, their growth, and the emergence of the first, rare quasars in the early Universe remains one of our greatest theoretical and observational challenges. Hydrodynamic cosmological simulations self-consistently combine the processes of structure formation at cosmological scales with the physics of smaller, galaxy scales. They capture our most realistic understanding of massive black holes and their connection to galaxy formation and have become the primary avenue for theoretical research in this field. The space-based gravitational wave interferometer, LISA, will open up new investigations into the dynamical processes involving massive black holes. Multi-messenger astrophysics brings new exciting prospects for tracing the origin, growth and merger history of massive black holes across cosmic ages.