arXiv subjects

Laura V. Sales

Publications and source records attributed to Laura V. Sales.

At least 19 recordsLinked to original sources

arXiv2026

SMUGGLE-Ring: Evolutionary link between nuclear star cluster and nuclear disk

We present a high-resolution hydrodynamical simulation of the formation and evolution of nuclear structures in a Milky Way-mass galaxy using the SMUGGLE model. The system naturally develops a bar in isolation of $\approx5$ kpc in length, driving sustained gas inflows toward the center that lead to the formation of a nuclear stellar disk (NSD) and a nuclear star cluster (NSC). By only considering stars born after bar formation, we can cleanly isolate the nuclear structures and recover a clear inside-out growth of the NSD. In line with observations, we find that stellar feedback induces repeated shocks that regulate the size of the nuclear gas disk and drive gas from its outer edge toward the NSC region. Over time, the NSD and NSC share similar mass growth and star formation histories, except during the accretion of a massive star cluster. Our results suggest that both the evolutionary timescale of the bar (and thus of the NSD) and the accretion history of star clusters are essential for obtaining tighter scaling relations for nuclear structures and their host galaxies. Finally, our results favor a lower bulge mass for the Milky Way than that of our model ($B/D\approx 0.045$) to explain the compact size of its nuclear disk.

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arXiv2026

AGN-driven outflows in dwarf galaxies from cosmological simulations: Internal properties and observational signatures

While AGN feedback is a key driver of massive galaxy evolution, its physical properties and observational signatures in the dwarf regime remain poorly understood. We investigate the impact of AGN-driven outflows on the ISM of dwarf galaxies and assess whether these events can be robustly identified through emission-line diagnostics. We analysed a high-resolution cosmological magneto-hydrodynamical zoom-in simulation from the AURIGA project. We focused on a dwarf galaxy with 1e9.7 M*/Msun hosting a BH of 1e7 Msun. We identified individual outflow episodes via pressure peaks in the gas surrounding the central BH, tracked the thermodynamic and kinematic history of such gas, and computed synthetic, spatially resolved nebular emission using photoionisation models to construct BPT diagnostic diagrams. We show that AGN activity in this regime produces compact, over-pressurised central bubbles reaching >1e6 K temperatures. These structures accelerate the ISM up to 600km/s, exceeding those driven by stellar feedback: the outflowing material does not escape the halo, but instead decelerates and redistributes within 10kpc from the galaxy center. Synthetic emission-line modelling reveals clear, time-dependent signatures of such AGN-driven feedback. Over its life cycle, the simulated AGN-hosting galaxy traces the locus of observed dwarf AGNs and migrates from the SF sequence in the BPT diagrams through the composite region into the AGN regime, highlighting a self-regulation mechanism in which the BH accretes its fuel supply, progressively moving towards the low-ionisation nuclear region. Our results suggest that AGN-driven outflows in dwarfs primarily regulate the central ISM through episodic heating and rapid gas recycling, rather than large-scale gas ejection. These processes generate observable spectroscopic signatures, offering a promising avenue for identifying AGN feedback in low-mass galaxies.

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arXiv2026

The Entangling of Supernova Feedback Impacts with Coarsening Simulation Resolution

It is often understood that supernova (SN) feedback in galaxies is responsible for regulating star formation (SF) and generating gaseous outflows. However, a detailed look at their small-scale effects on the interstellar medium (ISM) in simulations shows that these processes proceed in distinct and separate channels. We demonstrate this finding in two independent simulations of isolated dwarf galaxies with very high ($m_{\rm gas}$ $\sim \msun$) numerical resolution, {\small LYRA} and {\small RIGEL}. Focusing on the immediate environment surrounding SNe, our findings suggest that the macroscopic effect of a given SN on the galaxy is best predicted by its local density. Outflows are driven by SNe in diffuse regions expanding to their cooling radii on large ($\sim$ kpc) scales, while dense SF regions are disrupted in a localized ($\sim$ pc) manner. However, these separate feedback channels are only distinguishable at very high resolutions capable of following mass scales $\lesssim 10^2 \,\msun$. When averaging on coarser scales, ISM densities are greatly mis-estimated, and variations between different SF and SNe-affected regions are severely washed out. It therefore cannot be self-consistently determined, from coarse-resolution information \textit{alone}, (1) whether a SN tends to contribute to outflows or direct SF suppression, and (2) the rate of SF in a given region. In particular, commonly used parameters in coarse-resolution (subgrid) models, such as the SN cooling radius and SF density threshold, may require more detailed treatments informed by high-resolution studies.

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arXiv2026

The SMUGGLE-Ring project: Bar and bulge effects on nuclear disk and ring formation

We present the first results from the SMUGGLE-Ring project, a suite of simulations employing the SMUGGLE ISM and stellar feedback model to explore nuclear structures in Milky Way-mass galaxies. We discuss results from three simulations evolved for 5 Gyr in isolation, in which we vary the classical bulge mass, while keeping the disk and halo structures identical. Nuclear stellar disks and rings emerge exclusively in our bulge models, with more massive bulges associated with earlier formation and more extended initial gas reservoirs shortly after bar formation. After gas depletion via active star formation, the nuclear stellar disks bifurcate into pressure-supported nuclear star clusters (NSCs, $v_ϕ/σ_R < 0.7$) and rotationally supported nuclear stellar rings (NSRs, $v_ϕ/σ_R = 1.2$--1.7, radii 0.64--0.76 kpc). The bulgeless model fails to build up and sustain stable nuclear gas disks against feedback disruptions. The enclosed stellar mass of NSCs ($\sim10^{9}\Msun$) dominates over that of NSRs ($\sim10^{8}\Msun$). The star formation rates decline over time due to gas depletion (NSCs 0.1--1 $\Msun$/yr, NSRs 0.01--$0.1 \Msun$/yr). Kinematics reveal outward-shifting rotation peaks with $σ$-drops in NSRs, while a fraction of stars in NSCs exhibits radial shift after 3 Gyr. These findings support inside-out NSD formation via secular bar evolution, with NSRs tracing the star-forming outer edge of the nuclear gas disk and NSCs forming the kinematically hotter inner component. The range of nuclear stellar disk sizes (0.25--0.76 kpc) falls within the observationally inferred ranges, but the existence of larger rings would require external gas flow and/or a longer period of evolution. Future SMUGGLE-Ring extensions will incorporate varying gas fractions, tidal/merger effects, and the circumgalactic medium to further elucidate nuclear diversity and outliers.

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arXiv2026

The abundance of thin dwarf galaxies: a challenge for cosmological simulations

We study the prevalence of thin galaxies as a function of stellar mass in the range $10^7 < M_{\star} / \rm{M_\odot} < 10^{11}$ using data from the GAMA, DESI, ALFALFA, and Nearby Galaxy catalogs. We use the distribution of projected axis ratios, $q$, to infer the abundance of intrinsically flat galaxies needed to reproduce the observed abundance of highly elongated systems in projection. We find that as many as $40\%$ of galaxies in the mass range $10^9<M_{\star}/\rm{M_\odot}<10^{10}$ are intrinsically flatter than $1$:$5$ (i.e., $c/a<0.2$), a fraction that rises to $\sim 80\%$ for $c/a<0.3$. Although the incidence of thin galaxies decreases towards lower and higher $M_{\star}$, they are still quite common in dwarfs: $\sim 30\%$ and $\sim 65\%$ of $\sim 10^8 ~ \rm{M_\odot}$ galaxies are inferred to be intrinsically flatter than $c/a=0.2$ and $0.3$, respectively. A comparison of these results with several state-of-the-art cosmological hydrodynamical simulations (TNG50, FIREbox, Romulus25) reveals a distinctive lack of thin simulated dwarfs. In particular, there are no $M_{\star} < 10^9 ~ \rm{M_{\odot}}$ simulated galaxies flatter than $c/a=0.2$, in clear contrast with observational samples. This discrepancy likely reflects limitations in resolution and in the treatment of baryonic physics, suggesting that our understanding of the mechanisms regulating the formation of disk galaxies less massive than the Milky Way is still quite incomplete. Our results present a clear challenge to current numerical models of dwarf galaxy formation, which future models should attempt to meet.

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arXiv2026

The abundance and radial distribution of faint and ultra-faint dwarfs in galaxy clusters

Cosmological simulations of galaxy clusters are unable to resolve dwarf galaxies due to limited numerical resolution which drives the artificial disruption of dark matter substructures. We address these limitations by combining the results of the cosmological hydrodynamical simulation TNG50 in $Λ$CDM with an empirical model of tidal evolution of cluster galaxies calibrated using high-resolution idealized N-body simulations. Applied to the three most massive clusters in TNG50, our model allows us to study the stellar mass and radial distribution of dwarfs well below the formal resolution limit of the parent simulation. We find that, at $z=0$, clusters with virial mass $M_{200} \sim 10^{14}~\mathrm{M_\odot}$ host a vast population of dwarf galaxies within the virial radius, amounting to $2000$-$7000$ systems with $M_* > 100~\mathrm{M_\odot}$. Taken together, these satellites follow a radial distribution that matches the underlying dark matter profile of the host. However, applying a minimum mass or luminosity threshold for detection, as expected in observational studies, tends to exclude the most heavily-stripped objects, which tend to populate the inner regions. Future surveys targeting ultra-faint galaxies in group and cluster environments, such as those made possible by the Euclid, Rubin, or Roman telescopes, will be fundamental to refute or confirm this prediction.

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arXiv2025

AGN feedback in merging galaxies with a SMUGGLE multiphase ISM

We study fast nuclear winds driven by Active Galactic Nucleus (AGN) feedback in merging galaxies using high-resolution hydrodynamics simulations. We use Stars and MUltiphase Gas in GaLaxiEs (SMUGGLE) to explicitly model the multiphase interstellar medium (ISM) and employ sub-grid dynamical friction for massive black holes (BHs). Furthermore, we use a super-Lagrangian refinement scheme to resolve AGN feedback coupling to the ISM at $\sim10-100\,$pc scales. By comparison between merging and isolated galaxies, with and without AGN feedback, we identify trends in the complex interplay between dynamics, BH fueling and feedback, and star formation and feedback. We consider three galaxy types: Milky Way analogs, Sbc-type galaxies, and Small Magellanic Cloud (SMC) analogs. The synergy between AGN feedback and merger dynamics is strongest in the Milky Way-like mergers, where the AGN winds are energetically dominant and entrain more gas when the initially thin disks become thick and amorphous during the merger. In contrast, the merger of thicker, vigorously star-forming Sbc galaxies is not strongly impacted by AGN feedback until star formation declines in the post-merger phase. Finally, while the sub-grid dynamical friction prescription effectively retains BHs in galactic nuclei during more massive mergers, the clumpy multiphase ISM induces significant wandering of low-mass BHs $\mathrm{(<10^5M_\odot)}$ in the shallow potentials of the SMC-like galaxies. These low-mass BHs wander at distances $\gtrsim 2$ kpc from the galactic center, yielding negligible BH accretion and feedback. This has implications for LISA event rates and present a further challenge to understanding the rapid growth of $z\sim7-10$ quasars discovered by JWST.

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arXiv2025

Tracing the Origins of Hot Halo Gas in Milky Way-Type Galaxies with SMUGGLE

Current galaxy formation models predict the existence of X-ray-emitting gaseous halos around Milky Way (MW)-type galaxies. To investigate properties of this coronal gas in MW-like galaxies, we analyze a suite of high-resolution simulations based on the SMUGGLE framework and compare the results with X-ray observations of both the MW and external galaxies. We find that for subgrid models incorporating any form of stellar feedback, e.g., early feedback (including stellar winds and radiation) and/or supernova (SN) explosions, the total 0.5-2 keV luminosity is consistent within uncertainties with X-ray observations of the MW and with scaling relations derived for external disk galaxies. However, all models exhibit an X-ray surface brightness profile that declines too steeply beyond $\sim5$ kpc, underpredicting the extended emission seen in recent eROSITA stacking results. Across all subgrid prescriptions, the simulated surface brightness and emission measure fall below MW observations by at least 1-2 orders of magnitude, with the most severe discrepancy occurring in the no-feedback model. Our results suggest that (i) stellar feedback primarily shapes the innermost hot atmosphere (central $\sim5$ kpc), with comparable contributions from early feedback and SNe to the resulting X-ray luminosity; (ii) additional mechanisms such as gravitational heating, active galactic nuclei feedback, and/or Compton effects of GeV cosmic ray are necessary to generate the extended, volume-filling hot gaseous halo of MW-mass galaxies; (iii) the origins of hot corona in MW-like galaxies are partially distinct from those of the warm ($\sim10^5$ K) gas, by combining our previous finding that the SMUGGLE model successfully reproduces the kinematics and spatial distribution of MW O VI absorbers.

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arXiv2025

Disks no more: the morphology of low-mass simulated galaxies in FIREbox

We study the morphology of hundreds of simulated central galaxies in the stellar mass range $M_\star=10^{7.5} \rm - 10^{11}~$\msun\, from the FIREbox cosmological volume. We demonstrate that FIREbox is able to predict a wide variety of morphologies, spanning from disk-dominated objects to spheroidal galaxies supported by stellar velocity dispersion. However, the simulations predict a strong relation between morphology (degree of rotational support) and stellar mass: galaxies comparable to the Milky Way are often disk-dominated while the presence of stellar disks mostly vanishes for dwarfs with $M_\star <10^9 ~$\msun. This defines a ``morphology transition'' regime for galaxies with $10^9 <M_\star/\rm{M_\odot}< 10^{10}$ in which disks become increasingly common, but below which disks are rare. We show that burstiness in the star formation history and the deepening of the gravitational potential strongly correlate in our simulations with this transition regime, with disks forming in objects with lower levels of burstiness in the last $\sim 6$ Gyr and halos with mass $\sim 10^{11} ~ \rm{M_{\odot}}$ and above. While observations support a transition towards thicker disks in the regime of dwarfs, our results are in partial disagreement with observations of at least some largely rotationally supported gas disks in dwarfs with $M_\star < 10^9$\msun. This study highlights dwarf morphology as a fundamental benchmark for testing future galaxy formation models.

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arXiv2025

The life cycle of giant molecular clouds in simulated Milky Way-mass galaxies

In this work, we trace the complete life cycle of individual GMCs in high-resolution Milky Way-mass galaxy simulations to determine how different stellar feedback mechanisms and galactic-scale processes govern cloud lifetimes, mass evolution, and local star formation efficiency (SFE). We identify GMCs in simulated galaxies and track their evolution using cloud evolution trees. Via cloud evolution trees, we quantify the lifetimes and SFE of GMCs. We further apply our diagnostics on a suite of simulations with varying star formation and stellar feedback subgrid models and explore their impact together with galactic environments to the GMC life cycles. Our analysis reveals that GMCs undergo dynamic evolution, characterized by continuous gas accretion, gravitational collapse, and star formation, followed by disruption due to stellar feedback. The accretion process sustains the gas content throughout most of the GMC life cycles, resulting in a positive correlation between GMC lifetimes and their maximum masses. The GMC lifetimes range from a few to several tens of Myr, with two distinct dynamical modes: (1) GMCs near the galactic center experience strong tidal disturbances, prolonging their lifetimes when they remain marginally unbound; (2) those in the outer regions are less affected by tides, remain gravitationally bound, and evolve more rapidly. In all model variations, we observe that GMC-scale SFE correlates with the baryonic surface density of GMCs, consistent with previous studies of isolated GMCs. Additionally, we emphasize the critical role of galactic shear in regulating GMC-scale star formation and refine the correlation between local SFE and surface density by including its effects. These findings demonstrate how stellar feedback and galactic-scale dynamics jointly shape GMC-scale star formation in realistic galactic environments.

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arXiv2025

Understanding the Baryon Cycle: Fueling Star Formation via Inflows in Milky Way-like Galaxies

Galaxies are not isolated systems; they continuously interact with their surroundings by ejecting gas via stellar feedback and accreting gas from the environment. Understanding the interplay between outflows from the disc and the surrounding circumgalactic medium (CGM) is key to learning how star-forming galaxies evolve. Our goal is to understand how gas in the CGM is accreted onto the inner regions of the disc, making it available for the formation of stars, exploring the connection between stellar feedback and gas accretion from the CGM in Milky Way-like galaxies. We focus on the distribution of vertical and radial gas flows to and from the disc as a function of galactocentric radius, and examine the implications of these processes for the evolution of such galaxies. We use the Arepo code coupled with the SMUGGLE sub-grid model to perform hydrodynamic N-body simulations of 9 different galaxies surrounded by a hot CGM. Each simulation features a gaseous disc with different mass and scale length, allowing us to examine how disc structure impacts gas dynamics. We find evidence of a crucial link between stellar feedback and gas accretion from the CGM, which together play an essential role in sustaining ongoing star formation in the disc. In particular, the ejection of gas from the disc plane by stellar feedback leads to the generation of a baryon cycle in which the CGM gas is mainly accreted onto the external regions of the disc ($ \approx 3-10$ M$_{\odot}$ yr$^{-1}$ of gas is accreted into the whole disc). From these regions it is then transported to the centre with radial mass rates $\approx 1-4$ M$_{\odot}$ yr$^{-1}$ on average, owing to angular momentum conservation, forming new stars and starting the whole cycle again. We find that both vertical accretion onto the inner regions of the disc and the radial transport of gas from the disc outskirts are necessary to sustain star formation.

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arXiv2025

The Environmental Quenching Mechanisms of Field Dwarf Galaxies

Field dwarf galaxies not actively forming stars are relatively rare in the local Universe, but are present in cosmological hydrodynamical simulations. We use the TNG50 simulation to investigate their origin and find that they all result from environmental effects that have removed or reduced their gas content. Quenched field dwarfs consist of either backsplash objects ejected from a massive host or of systems that have lost their gas after crossing overdense regions such as filaments or sheets (``cosmic web stripping''). Quenched fractions rise steeply with decreasing stellar mass, with quenched systems making up roughly $\sim 15\%$ of all field dwarfs (i.e., excluding satellites) with stellar masses $10^{7} 10^9\, M_{\odot}$ within {$1.5$} Mpc is applied. Of these isolated dwarfs, $\sim 6\%$ are backsplash, while the other $\sim 94\%$ have been affected by the cosmic web. Backsplash systems are more deficient in dark matter, have retained less or no gas, and have stopped forming stars earlier than cosmic web-stripped systems. The discovery of deeply isolated dwarf galaxies which were quenched relatively recently would lend observational support to the prediction that the cosmic web is capable of inducing the cessation of star formation in dwarfs.

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arXiv2025

Large dark matter content and steep metallicity profile predicted for Ultra-Diffuse Galaxies formed in high-spin halos

We study the stellar properties of a sample of simulated ultra-diffuse galaxies (UDGs) with stellar mass $\rm{M_\star=10^{7.5} - 10^{9} ~ M_{\odot}}$, selected from the TNG50 simulation, where UDGs form mainly in high-spin dwarf-mass halos. We divide our sample into star-forming and quenched UDGs, finding good agreement with the stellar assembly history measured in observations. Star-forming UDGs and quenched UDGs with $\rm{M_\star \geq 10^8 ~ M_\odot}$ in our sample are particularly inefficient at forming stars, having $2$ - $10$ times less stellar mass than non-UDGs for the same virial mass halo. These results are consistent with recent mass inferences in UDG samples and suggest that the most inefficient UDGs arise from a late assembly of the dark matter mass followed by a stellar growth that is comparatively slower (for star-forming UDGs) or that was interrupted due to environmental removal of the gas (for quenched UDGs). Regardless of efficiency, UDGs are $60\%$ poorer in [Fe/H] than the population of non-UDGs at a fixed stellar mass, with the most extreme objects having metal content consistent with the simulated mass-metallicity relation at $z \sim 2$. Quenched UDGs stop their star formation in shorter timescales than non-UDGs of similar mass and are, as a consequence, alpha-enhanced with respect to non-UDGs. We identify metallicity profiles in UDGs as a potential avenue to distinguish between different formation paths for these galaxies, where gentle formation as a result of high-spin halos would present well-defined declining metallicity radial profiles while powerful-outflows or tidal stripping formation models would lead to flatter or constant metallicity as a function of radius due to the inherent mixing of stellar orbits.

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arXiv2024

Star formation beyond galaxies: widespread in-situ formation of intra-cluster stars

We study the fraction of the intra-cluster light (ICL) formed in-situ in the three most massive clusters of the TNG50 simulation, with virial masses $\sim 10^{14}$ M$_{\odot}$. We find that a significant fraction of ICL stars ($8\%$-$28\%$) are born in-situ. This amounts to a total stellar mass comparable to the central galaxy itself. Contrary to simple expectations, only a sub-dominant fraction of these in-situ ICL stars are born in the central regions and later re-distributed to more energetic orbits during mergers. Instead, many in-situ ICL stars form directly hundreds of kiloparsecs away from the central galaxy, in clouds condensing out of the circum-cluster medium. The simulations predict a present-date diffuse star formation rate of $\sim$1 $\mathrm{M}_{\odot}$/yr, with higher rates at higher redshifts. The diffuse star forming component of the ICL is filamentary in nature, extends for hundreds of kiloparsecs and traces the distribution of neutral gas in the cluster host halo. We discuss briefly how numerical details of the baryonic treatment in the simulation, in particular the density threshold for star formation and the equation of state, may play a role in this result. We conclude that a sensitivity of $1.6 \times 10^{-19} - 2.6 \times 10^{-18}$ erg s$^{-1}$ cm$^{-2}$ arcsec$^{-2}$ in H$_α$ flux (beyond current observational capabilities) would be necessary to detect this diffuse star-forming component in galaxy clusters.

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arXiv2024

The Spatial Distribution of Globular Cluster Systems in Early Type Galaxies: Estimation Procedure and Catalog of Properties for Globular Cluster Systems Observed with Deep Imaging Surveys

We present an analysis of the spatial distribution of globular cluster (GC) systems of 118 nearby early-type galaxies in the Next Generation Virgo Cluster Survey (NGVS) and Mass Assembly of early-Type GaLAxies with their fine Structures (MATLAS) survey programs, which both used MegaCam on the Canada-France-Hawaii Telescope. We describe the procedure used to select GC candidates and fit the spatial distributions of GCs to a two-dimensional Sérsic function, which provides effective radii (half number radii) and Sérsic indices, and estimate background contamination by adding a constant term to the S'ersic function. In cases where a neighboring galaxy affects the estimation of the GC spatial distribution in the target galaxy, we fit two 2D Sérsic functions, simultaneously. We also investigate the color distributions of GCs in our sample by using Gaussian Mixture Modeling. For GC systems with bimodal color distributions, we divide the GCs into blue and red subgroups and fit their respective spatial distributions with Sérsic functions. Finally, we measure the total number of GCs based on our fitted Sérsic function, and calculate the GC specific frequency.

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arXiv2024

Bursty Star Formation in Dwarfs is Sensitive to Numerical Choices in Supernova Feedback Models

Simulations of galaxy formation are mostly unable to resolve the energy-conserving phase of individual supernova events, having to resort to subgrid models to distribute the energy and momentum resulting from stellar feedback. However, the properties of these simulated galaxies, including the morphology, stellar mass formed and the burstiness of the star formation history, are highly sensitive to numerical choices adopted in these subgrid models. Using the {\small SMUGGLE} stellar feedback model, we compute idealized simulations of a $M_{\rm vir} \sim 10^{10} \, \msun$ dwarf galaxy, a regime where most simulation codes predict significant burstiness in star formation, resulting in strong gas flows that lead to the formation of dark matter cores. We find that by varying only the directional distribution of momentum imparted from supernovae to the surrounding gas, while holding the total momentum per supernova constant, bursty star formation may be amplified or completely suppressed, and the total stellar mass formed can vary by as much as a factor of $\sim 3$. In particular, when momentum is primarily directed perpendicular to the gas disk, less bursty and lower overall star formation rates result, yielding less gas turbulence, more disky morphologies and a retention of cuspy dark matter density profiles. An improved understanding of the non-linear coupling of stellar feedback into inhomogeneous gaseous media is thus needed to make robust predictions for stellar morphologies and dark matter core formation in dwarfs independent of uncertain numerical choices in the baryonic treatment.

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arXiv2024

Measures of luminous and dark matter in galaxies across time

Dark matter is one of the pillars of the current standard model of structure formation: it is assumed to constitute most of the matter in the Universe. However, it can so far only be probed indirectly through its gravitational effects, and its nature remains elusive. In this focus meeting, we discussed different methods used to estimate galaxies' visible and dark matter masses in the nearby and distant Universe. We reviewed successes of the standard model relying on cold dark matter, confronted observations with simulations, and highlighted inconsistencies between the two. We discussed how robust mass measurements can help plan, perform, and refine particle dark matter searches. We further exchanged about alternatives to cold dark matter, such as warm, self-interacting, and fuzzy dark matter, as well as modified gravity. Finally, we discussed prospects and strategies that could be implemented to reveal the nature of this crucial component of the Universe.

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arXiv2024

The assembly of the most rotationally supported disc galaxies in the TNG100 simulations

Disc dominated galaxies can be difficult to accommodate in a hierarchical formation scenario like $Λ$CDM, where mergers are an important growth mechanism. However, observational evidence indicates that these galaxies are common. We seek to characterise the conditions that lead to the formation of disc dominated galaxies within $Λ$CDM. We use dynamical decomposition in all galaxies with stellar mass $M_*=[10^{10} \rm - 10^{11}]\; \rm M_\odot$ within the simulation Illustris TNG100. We select a sample of 43 mostly-disc galaxies having less than $\sim 10\%$ of their mass into a bulge component. For comparison, we also study two additional stellar-mass matched samples: 43 intermediate galaxies having $\sim 30\%$ of their mass in the bulge and 43 with purely spheroidal-like morphology. We find that the selection based on stellar dynamics is able to reproduce the expected stellar population trends of different morphologies, with higher star-formation rates and younger stars in disc-dominated galaxies. Halo spin seems to play no role in the morphology of the galaxies. At fixed $M_*$, our mostly-disc and intermediate samples form in dark matter haloes that are $2$-$10$ times less massive than the spheroidal sample, highlighting a higher efficiency in disc galaxies to retain and condensate their baryons. On average, mergers are less prevalent in the build up of discs than in spheroidal galaxies, but there is a large scatter, including the existence of mostly-disc galaxies with $15\%$-$30\%$ of their stars from accreted origin. Discs start forming early on, settling their low vertical velocity dispersion as early as $9$-$10$ Gyr ago, although the dominance of the disc over the spheroid gets established more recently ($3$-$4$ Gyr ago). The most rotationally supported discs form in haloes with the lowest mass in the sample and best aligned distribution of angular momentum in the gas.

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