Claudio Dalla Vecchia

Instituto de Astrofísica de Canarias

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Joop Schaye

Leiden University

Tom Theuns

Durham University

Robert A. Crain

Liverpool John Moores University

R. G. Bower

Durham University

Matthieu Schaller

Leiden University

C. M. Booth

University of Chicago

Carlos S. Frenk

Durham University

Sadegh Khochfar

Royal Observatory

Scott T. Kay

University of Manchester

Ian G. McCarthy

Liverpool John Moores University

Cooperative Institutions

Durham University

Max Planck Society

Universidad de La Laguna

Instituto de Astrofísica de Canarias

Max Planck Institute for Astrophysics

Centre National de la Recherche Scientifique

Leiden University

Max Planck Institute for Extraterrestrial Physics

Consejo Superior de Investigaciones Científicas

Max Planck Institute for Astronomy

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Detection of stellar wakes in the Milky Way: A deep learning approach

Astronomy and Astrophysics (2024)

Sven Põder Joosep Pata María Teresa Rubio Benito Isaac Alonso Asensio Claudio Dalla Vecchia

Due to poor observational constraints on the low-mass end of the subhalo mass function, the detection of dark matter (DM) subhalos on sub-galactic scales would provide valuable information about the nature of DM. Stellar wakes, induced by passing DM subhalos, encode information about the mass (properties) of the inducing perturber and thus serve as an indirect probe for the DM substructure within the Milky Way. Our aim is to assess the viability and performance of deep learning searches for stellar wakes in the Galactic stellar halo caused by DM subhalos of varying mass. We simulated massive objects (subhalos) moving through a homogeneous medium of DM and star particles with phase-space parameters tailored to replicate the conditions of the Galaxy at a specific distance from the Galactic centre. The simulation data was used to train deep neural networks with the purpose of inferring both the presence and mass of the moving perturber. We then investigated the performance of our deep learning models and identified the limitations of our current approach. We present an approach that allows for quantitative assessment of subhalo detectability in varying conditions of the Galactic stellar and DM halos. We find that our binary classifier is able to infer the presence of subhalos in our generated mock datasets, showing non-trivial performance down to a mass of $5 \, M_ In a multiple-hypothesis case, we are also able to discern between samples containing subhalos of different mass. By simulating datasets describing subhalo orbits at different Galactocentric distances, we tested the robustness of our binary classification model and found that it performs well with data generated from different initial physical conditions. Based on the phase-space observables available to us, we conclude that overdensity and velocity divergence are the most important features for subhalo detection performance.

10.1051/0004-6361/202451480

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On the detection of stellar wakes in the Milky Way: a deep learning approach

arXiv (Cornell University) (2024)

Sven Põder Joosep Pata María Teresa Rubio Benito Isaac Alonso Asensio Claudio Dalla Vecchia

Due to poor observational constraints on the low-mass end of the subhalo mass function, the detection of dark matter (DM) subhalos on sub-galactic scales would provide valuable information about the nature of DM. Stellar wakes, induced by passing DM subhalos, encode information about the mass of the inducing perturber and thus serve as an indirect probe for the DM substructure within the Milky Way (MW). Our aim is to assess the viability and performance of deep learning searches for stellar wakes in the Galactic stellar halo caused by DM subhalos of varying mass. We simulate massive objects (subhalos) moving through a homogeneous medium of DM and star particles, with phase-space parameters tailored to replicate the conditions of the Galaxy at a specific distance from the Galactic center. The simulation data is used to train deep neural networks with the purpose of inferring both the presence and mass of the moving perturber, and assess subhalo detectability in varying conditions of the Galactic stellar and DM halos. We find that our binary classifier is able to infer the presence of subhalos, showing non-trivial performance down to a subhalo mass of $5 \times 10^7 \rm \, M_\odot$. We also find that our binary classifier is generalisable to datasets describing subhalo orbits at different Galactocentric distances. In a multiple-hypothesis case, we are able to discern between samples containing subhalos of different masses. Out of the phase-space observables available to us, we conclude that overdensity and velocity divergence are the most important features for subhalo detection performance.

10.48550/arxiv.2412.02749

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Star formation and feedback in EAGLE

Claudio Dalla Vecchia

10.14288/1.0340083

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Non-instantaneous gas recycling and chemical evolution in N-body disk galaxies

Astrophysics and Space Science (2004)

B. Jungwiert G. Carraro Claudio Dalla Vecchia

Chemical evolution

10.1023/b:astr.0000014975.42058.90

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The First Billion Years project: Finding infant globular clusters at z = 6

Astronomy and Astrophysics (2020)

Frederika Phipps Sadegh Khochfar Anna Lisa Varri Claudio Dalla Vecchia

We explored a suite of high-resolution cosmological simulations from the First Billion Years Project (FiBY) at $z \geq 6$. All substructures within the simulations have been identified with the SUBFIND algorithm. From our analysis, two distinct groups of objects emerge. We hypothesise that the substructures in the first group, which appear to have a high baryon fraction ($f_{\rm b} \geq 0.95$), are possible infant GC candidates. Objects belonging to the second group have a high stellar fraction ($f_{\rm star} \geq 0.95$) and show a potential resemblance to infant ultra-faint dwarf galaxies. The high baryon fraction objects identified in this study are characterised by a stellar content similar to the one observed in present-day GCs, but they still contain a high gas fraction ($f_{\rm gas} \sim 0.95$) and a relatively low amount of dark matter. They are compact, dense systems. Their sizes are consistent with recent estimates based on the first observations of possible proto-GCs at high redshifts. These types of infant GC candidates appear to be more massive and more abundant in massive host galaxies, indicating that the assembly of galaxies via mergers may play an important role in building several GC-host scaling relations. Specifically, we express the relation between the mass of the most massive infant GC and its host stellar mass as $\log(M_{\rm cl}) = (0.31\pm0.15)\log(M_{\rm *,gal} + (4.17\pm1.06)$. We also report a new relation between the most massive infant GC and the parent specific star formation rate of the form $\log(M_{\rm cl}) = (0.85\pm0.30)\log(sSFR) + \alpha$ that describes the data at both low and high redshift. Finally, we assess the present-day GC mass (GC number) -- halo mass relation offers a satisfactory description of the behaviour of our infant GC candidates at high redshift, suggesting that such a relation may be set at formation.

Stellar mass

10.1051/0004-6361/202037884

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Erratum: Ubiquitous seeding of supermassive black holes by direct collapse

Monthly Notices of the Royal Astronomical Society (2013)

Bhaskar Agarwal Sadegh Khochfar Jarrett L. Johnson Eyal Neistein Claudio Dalla Vecchia

10.1093/mnras/stt2143

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The Aquila comparison project: the effects of feedback and numerical methods on simulations of galaxy formation

Monthly Notices of the Royal Astronomical Society (2012)

Cecilia Scannapieco Markus Wadepuhl Owen H. Parry Julio F. Navarro Adrian Jenkins

We compare the results of thirteen cosmological gasdynamical codes used to simulate the formation of a galaxy in the LCDM structure formation paradigm. The various runs differ in their hydrodynamical treatment (SPH, moving-mesh and AMR) but share the same initial conditions and adopt their latest published model of cooling, star formation and feedback. Despite the common halo assembly history, we find large code-to-code variations in the stellar mass, size, morphology and gas content of the galaxy at z=0, due mainly to the different implementations of feedback. Compared with observation, most codes tend to produce an overly massive galaxy, smaller and less gas-rich than typical spirals, with a massive bulge and a declining rotation curve. A stellar disk is discernible in most simulations, though its prominence varies widely from code to code. There is a well-defined trend between the effects of feedback and the severity of the disagreement with observation. Models that are more effective at limiting the baryonic mass of the galaxy come closer to matching observed galaxy scaling laws, but often to the detriment of the disk component. Our conclusions hold at two different numerical resolutions. Some differences can also be traced to the numerical techniques: more gas seems able to cool and become available for star formation in grid-based codes than in SPH. However, this effect is small compared to the variations induced by different feedback prescriptions. We conclude that state-of-the-art simulations cannot yet uniquely predict the properties of the baryonic component of a galaxy, even when the assembly history of its host halo is fully specified. Developing feedback algorithms that can effectively regulate the mass of a galaxy without hindering the formation of high-angular momentum stellar disks remains a challenge.

Smoothed Particle Hydrodynamics

Structure formation

10.1111/j.1365-2966.2012.20993.x

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Citations (415)

The eagle simulations of galaxy formation: the importance of the hydrodynamics scheme

Monthly Notices of the Royal Astronomical Society (2015)

Matthieu Schaller Claudio Dalla Vecchia Joop Schaye R. G. Bower Tom Theuns

We present results from a subset of simulations from the "Evolution and Assembly of GaLaxies and their Environments" (EAGLE) suite in which the formulation of the hydrodynamics scheme is varied. We compare simulations that use the same subgrid models without re-calibration of the parameters but employing the standard GADGET flavour of smoothed particle hydrodynamics (SPH) instead of the more recent state-of-the-art ANARCHY formulation of SPH that was used in the fiducial EAGLE runs. We find that the properties of most galaxies, including their masses and sizes, are not significantly affected by the details of the hydrodynamics solver. However, the star formation rates of the most massive objects are affected by the lack of phase mixing due to spurious surface tension in the simulation using standard SPH. This affects the efficiency with which AGN activity can quench star formation in these galaxies and it also leads to differences in the intragroup medium that affect the X-ray emission from these objects. The differences that can be attributed to the hydrodynamics solver are, however, likely to be less important at lower resolution. We also find that the use of a time step limiter is important for achieving the feedback efficiency required to match observations of the low-mass end of the galaxy stellar mass function.

Smoothed Particle Hydrodynamics

Spurious relationship

10.1093/mnras/stv2169

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Citations (209)

One simulation to have them all: performance of the Bias Assignment Method against N-body simulations

Monthly Notices of the Royal Astronomical Society (2019)

A. Balaguera-Antolínez Francisco-Shu Kitaura Marcos Pellejero-Ibáñez Martha Lippich Cheng Zhao

In this paper we demonstrate that the information encoded in \emph{one} single (sufficiently large) $N$-body simulation can be used to reproduce arbitrary numbers of halo catalogues, using approximated realisations of dark matter density fields with different initial conditions. To this end we use as a reference one realisation (from an ensemble of $300$) of the Minerva $N$-body simulations and the recently published Bias Assignment Method to extract the local and non-local bias linking the halo to the dark matter distribution. We use an approximate (and fast) gravity solver to generate $300$ dark matter density fields from the down-sampled initial conditions of the reference simulation and sample each of these fields using the halo-bias and a kernel, both calibrated from the arbitrarily chosen realisation of the reference simulation. We show that the power spectrum, its variance and the three-point statistics are reproduced within $\sim 2\%$ (up to $k\sim1.0\,h\,{\rm Mpc}^{-1}$), $\sim 5-10\%$ and $\sim 10\%$, respectively. Using a model for the real space power spectrum (with three free bias parameters), we show that the covariance matrices obtained from our procedure lead to parameter uncertainties that are compatible within $\sim 10\%$ with respect to those derived from the reference covariance matrix, and motivate approaches that can help to reduce these differences to $\sim 1\%$. Our method has the potential to learn from one simulation with moderate volumes and high-mass resolution and extrapolate the information of the bias and the kernel to larger volumes, making it ideal for the construction of mock catalogues for present and forthcoming observational campaigns such as Euclid or DESI.

Kernel (algebra)

Solver

10.1093/mnras/stz3206

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Citations (19)

The origin of discs and spheroids in simulated galaxies

Monthly Notices of the Royal Astronomical Society (2012)

Laura V. Sales Julio F. Navarro Tom Theuns Joop Schaye Simon D. M. White

In the simplest scenario, disk galaxies form predominantly in halos with high angular momentum and quiet recent assembly history, whereas spheroids are the slowly-rotating remnants of repeated merging events. We explore these assumptions using one hundred systems with halo masses similar to that of the Milky Way, identified in a series of cosmological gasdynamical simulations GIMIC. At z=0, the simulated galaxies exhibit a wide variety of morphologies, from dispersion-dominated spheroids to pure disk galaxies. Surprisingly, these morphological features are very poorly correlated with their halo properties: disks form in halos with high and low net spin, and mergers play a negligible role in the formation of spheroid stars, most of which form in-situ. More important to morphology is the coherent alignment of the angular momentum of baryons that accrete over time to form a galaxy. Spheroids tend to form when the spin of newly-accreted gas is misaligned with that of the extant galaxy, leading to the episodic formation of stars with different kinematics that cancel out the net rotation of the system. Disks, on the other hand, form out of gas that flows in with similar angular momentum to that of earlier-accreted material. Gas accretion from a hot corona thus favours disk formation, whereas gas that flows "cold", often along separate, misaligned filaments, favours the formation of spheroids. In this scenario, most spheroids consist of superpositions of stellar components with distinct kinematics, age, and metallicity, an arrangement that might survive to the present day given the paucity of major mergers. Since angular momentum is acquired largely at turnaround, morphology is imprinted early by the interplay of the tidal field and the shape of the material destined to form the galaxy.

10.1111/j.1365-2966.2012.20975.x

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Citations (238)