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Robert J. J. Grand

Publications and source records attributed to Robert J. J. Grand.

At least 55 records · Page 3Linked to original sources
arXiv2023

A high fidelity Milky Way simulation with Kraken, Gaia-Enceladus, and Sequoia analogues: clues to their accretion histories

Within a simulated Milky Way-like galaxy, we identify and analyse analogues of the Gaia-Enceladus (GE), Kraken and Sequoia mergers that each matches remarkably well observational results, including in velocity and chemical abundance space, and their distributions in the $j_{z}$-Energy plane. The Kraken analogue is the earliest merger and has the highest total mass ratio. Consistent with previous studies, it is chemically indistinguishable from old in-situ stars at the time of its accretion. The GE and Sequoia analogue events accrete at similar times in our simulation, both along filaments but from opposite sides of the main galaxy. The mean stellar ages of the GE and Sequoia analogues are both similar and, from our simulation results, we see that they can be separate entities and still naturally reproduce the observed properties of their stellar remnants at the present day, including the significant retrograde velocities of the Sequoia analogue remnant stars and the difference in the tracks of the two galaxies through chemical abundance space. Our results provide supporting information about the properties of these three merger events, and show for the first time that they can all be reproduced with a fully cosmological simulation, providing a possible self consistent evolutionary pathway for the Milky Way's formation.

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arXiv2023

The stellar halo in Local Group Hestia simulations I. The in-situ component and the effect of mergers

Theory suggests that mergers play an important role in shaping galactic discs and stellar haloes, which was observationally confirmed in the MW thanks to Gaia data. In this work, aiming to probe the contribution of mergers to the in situ stellar halo formation, we analyse six M31/MW analogues from the HESTIA suite of cosmological hydrodynamical zoom-in simulations of the LG. We found that all the HESTIA galaxies experience between one to four mergers with stellar mass ratios between 0.2 and 1 relative to the host at the time of the merger. These significant mergers, with a single exception, happened 7-11Gyr ago. The overall impact of the most massive mergers in HESTIA is clearly seen as a sharp increase in the orbital eccentricity (and a corresponding decrease in the rotational velocity Vphi of pre-existing disc stars of the main progenitor, thus nicely reproducing the Splash-, Plume-like feature that was discovered in the MW. We do find a correlation between mergers and close pericentric passages of massive satellites and bursts of star formation in the in situ component. Massive mergers sharply increase the disc velocity dispersion of the in situ stars; however, the latest significant merger often heats up the disc up to the numbers when the contribution of the previous ones is less prominent in the age-velocity dispersion relation. In HESTIA galaxies, the in situ halo is an important component of the inner stellar halo where its fraction is about 30-40%, while in the outer parts it typically does not exceed ~5% beyond 15 kpc. The simulations suggest that this component of the stellar haloes continues to grow well after mergers conclude; however, the most significant contribution comes from stars that formed recently before the merger. The orbital analysis of the HESTIA galaxies suggests that wedges in Rmax-Zmax space are mainly populated by the stars born between significant mergers.

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arXiv2023

The stellar halo in Local Group Hestia simulations II. The accreted component

In the Milky Way, recent progress in the exploration of its assembly history is driven by the tremendous amount of high-quality data delivered by Gaia, which has revealed a number of substructures potentially linked to several ancient accretion events. In this work, aiming to explore the phase-space structure of accreted stars, we analyze six M31/MW analogues from the HESTIA suite of cosmological hydrodynamics zoom-in simulations of the Local Group. We found that all the HESTIA galaxies experience a few dozen mergers but only 1-4 mergers have the stellar mass ratio >0.2 where, depending on the halo definition, the most massive merger contributes from 20% to 70% of the total stellar halo. Individual merger remnants show diverse density distributions at z=0, significantly overlapping with each other and with the in-situ stars in the ELz, UV and RVphi coordinates. The mergers debris often change their position in the ELz with time due to the galactic mass growth and the non-axisymmetry of the potential. In agreement with previous works, we show that even individual merger debris exhibit a number of distinct ELz features. In the UV plane, all HESTIA galaxies reveal radially hot, non-rotating or weakly counter-rotating, Gaia-Sausage-like features. We found an age gradient in Elz space for the individual debris, where the youngest stars, formed in the inner regions of accreting systems, deposit to the innermost regions of the host. The bulk of these stars is being formed during the last stages of accretion, making it possible to date the merger. In actions space (Jr, Jz, Jϕ), the mergers debris do not appear as isolated substructures but are instead scattered over a large parameters area and overlapping with the in-situ stars. We also introduce a purely kinematic space (Jz/Jr-eccentricity), where different merger debris can be disentangled better from each other and from the in-situ stars.

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arXiv2023

The stellar halo in Local Group Hestia simulations III. Chemical abundance relations for accreted and in-situ stars

Since the chemical abundances of stars are the fossil records of the physical conditions in galaxies, they provide the key information for recovering the assembly history of galaxies. In this work, we explore the chemo-chrono-kinematics of accreted and in-situ stars, by analyzing six M31/MW analogues from the HESTIA suite of cosmological hydrodynamics zoom-in simulations of the Local Group. We found that the merger debris are chemically distinct from the survived dwarf galaxies. The mergers debris have abundances expected for stars originating from dwarfs that had their star formation activity quenched at early times. Accreted stellar haloes, including individual debris, reveal abundance gradients in the ELz, where the most metal-rich stars have formed in the inner parts of the disrupted systems before the merger and mainly contribute to the central regions of the hosts. Therefore, we suggest that abundance measurements in the inner MW will allow constraining better the parameters of building blocks of the MW stellar halo. The MDFs of the individual debris show several peaks and the majority of debris have lower metallicity than the in-situ stars for Lz>0, while non-rotating and retrograde accreted stars are similar to the in-situ. Prograde accreted stars show a prominent knee in the [Fe/H]-[Mg/Fe] plane while the retrograde stars typically deposit to a high-[Mg/Fe] sequence. We found that the metal-poor stars ([Fe/H]<-1) of the HESTIA galaxies exhibit between zero to 80 km/s net rotation which is consistent with the Aurora population. At higher metallicities, we detect a sharp transition (spin-up) from the turbulent phase to a disk-like rotation. Mergers debris are similar in the [Fe/H]-[Mg/Fe] plane. However, combining a set of abundances allows to capture chemical patterns corresponding to different debris, which are the most prominent as a function of stellar age.

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arXiv2023

Exploring the diversity and similarity of radially anisotropic Milky Way-like stellar haloes: implications for disrupted dwarf galaxy searches

We investigate the properties of mergers comparable to the Gaia-Sausage-Enceladus (GSE) using cosmological hydrodynamical simulations of Milky Way-like galaxies. The merger progenitors span an order of magnitude in their peak stellar mass ($3\times10^8 10^6\,\rm{M}_{\odot}$), but most of these do not follow the merger to low orbital energies. Between $0-1$ of these satellites may survive to $z=0$, but with no clear signatures of their past association. We show that the fraction of stars originating from GSE-like mergers is reduced for lower metallicities (reaching a minimum around $\text{[Fe/H]} = -2$), and also within $5\,$kpc of the galactic centre. Whilst these central regions are dominated by in-situ stars, the ex-situ fraction trends towards a 100 per cent asymptote when considering the most metal-poor stars ($\text{[Fe/H]}\ll-2.5$). Considering this, its near proximity, and its small volume on the sky, the Galactic centre lends itself as a prime environment in the search for the stars from the earliest galaxies, whilst avoiding contamination from GSE stars.

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arXiv2023

Unraveling the Complexity of Dwarf Galaxy Dynamics: A study of Binary Orbital Motions

We investigate the impact of binary orbital motions on the dynamical modeling of dwarf galaxies with intrinsic line-of-sight velocity dispersions ($σ_{v_r}$) of 1 to 9 km/s. Using dwarf galaxies from the Auriga level-2 and level-3 simulations, we apply the Jeans Anisotropic Multi-Gaussian Expansion modelling to tracer stars before and after including binaries to recover the dynamical masses. The recovered total masses within the half-mass radius of tracers, $M(<r_\mathrm{half})$, are always inflated due to binary motions, with greater inflations occurring for smaller $σ_{v_r}$. However, many dwarf galaxies experience central density deflated due to binary motions, with little dependences on $σ_{v_r}$. This is due to the negative radial gradients in the velocity dispersion profiles, with the fractional inflation in $σ_{v_r}$ due to binaries more significant in outskirts. An extreme binary fraction of 70% can lead to central density deflation of up to 10-20% at 3 km/s$<σ_{v_r}<$8 km/s, with $M(<r_\mathrm{half})$ inflated by 4% at 9 km/s and up to 15% at 3 km/s. A lower binary fraction of 36% leads to similar deflations, with the inflations decreasing to approximately 10% at 3 km/s and becoming statistically insignificant. The choice of binary orbit distribution models does not result in significant differences, and observational errors tend to slightly weaken the deflations in the recovered central density. Two observations separated by one year to exclude binaries lead to almost zero inflations/deflations for a binary fraction of 36% over 3 km/s$<σ_{v_r}<$9 km/s. For $σ_{v_r}\sim$1 km/s to 3 km/s, a binary fraction of 70% (36%) still results in 60% (30%) to 10% (1%) of inflations in $M(<r_\mathrm{half})$, even with two-epoch observation.

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arXiv2023

Action-based dynamical models of M31-like galaxies

In this work, we present an action-based dynamical equilibrium model to constrain the phase-space distribution of stars in the stellar halo, present-day dark matter distribution, and the total mass distribution in M31-like galaxies. The model comprises a three-component gravitational potential (stellar bulge, stellar disk, and a dark matter halo), and a double-power law distribution function (DF), $f(\mathbf{J})$, which is a function of actions. A Bayesian model-fitting algorithm was implemented that enabled both parameters of the potential and DF to be explored. After testing the model-fitting algorithm on mock data drawn from the model itself, it was applied to a set of three M31-like haloes from the Auriga simulations (Auriga 21, Auriga 23, Auriga 24). Furthermore, we tested the equilibrium assumption and the ability of a double-power law distribution function to represent the stellar halo stars. The model incurs an error in the total enclosed mass of around 10 percent out to 100 kpc, thus justifying the equilibrium assumption. Furthermore, the double-power law DF used proves to be an appropriate description of the investigated M31-like halos. The anisotropy profiles of the halos were also investigated and discussed from a merger history point of view.

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arXiv2023

An ever-present $Gaia$ snail shell triggered by a dark matter wake

We utilize a novel numerical technique to model star formation in cosmological simulations of galaxy formation - called Superstars - to simulate a Milky Way-like galaxy with $\gtrsim10^8$ star particles to study the formation and evolution of out-of-equilibrium stellar disc structures in a full cosmological setting. In the plane defined by the coordinate and velocity perpendicular to the mid-plane (vertical phase space, $\{Z,V_Z\}$), stars in Solar-like volumes at late times exhibit clear spirals qualitatively similar in shape and amplitude to the $Gaia$ ``Snail shell'' phase spiral. We show that the phase spiral forms at a look back time of $\sim 6$ Gyr during the pericentric passage of a $\sim10^{10}$ $\rm M_{\odot}$ satellite on a polar orbit. This satellite stimulates the formation of a resonant wake in the dark matter halo while losing mass at a rate of $\sim0.5$-$1$ dex per orbit loop. The peak magnitude of the wake-induced gravitational torque at the Solar radius is $\sim 8$ times that from the satellite, and triggers the formation of a disc warp that wraps up into a vertical phase spiral over time. As the wake decays, the phase spiral propagates several Gigayears to present-day and can be described as ``ever-present'' once stable disc evolution is established. These results suggest an alternative scenario to explain the $Gaia$ phase spiral which does not rely on a perturbation from bar buckling or a recent direct hit from a satellite.

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arXiv2023

Can we really pick and choose? Benchmarking various selections of Gaia Enceladus/Sausage stars in observations with simulations

Large spectroscopic surveys plus Gaia astrometry have shown us that the inner stellar halo of the Galaxy is dominated by the debris of Gaia Enceladus/Sausage (GES). With the richness of data at hand, there are a myriad of ways these accreted stars have been selected. We investigate these GES selections and their effects on the inferred progenitor properties using data constructed from APOGEE and Gaia. We explore selections made in eccentricity, energy-angular momentum (E-Lz), radial action-angular momentum (Jr-Lz), action diamond, and [Mg/Mn]-[Al/Fe] in the observations, selecting between 144 and 1,279 GES stars with varying contamination from in-situ and other accreted stars. We also use the Auriga cosmological hydrodynamic simulations to benchmark the different GES dynamical selections. Applying the same observational GES cuts to nine Auriga galaxies with a GES, we find that the Jr-Lz method is best for sample purity and the eccentricity method for completeness. Given the average metallicity of GES (-1.28 < [Fe/H] < -1.18), we use the $z=0$ mass-metallicity relationship to find an average $\rm M_{\star}$ of $\sim 4 \times 10^{8}$ $\rm M_{\odot}$. We adopt a similar procedure and derive $\rm M_{\star}$ for the GES-like systems in Auriga and find that the eccentricity method overestimates the true $\rm M_{\star}$ by $\sim2.6\times$ while E-Lz underestimates by $\sim0.7\times$. Lastly, we estimate the total mass of GES to be $\rm 10^{10.5 - 11.1}~M_{\odot}$ using the relationship between the metallicity gradient and the GES-to-in-situ energy ratio. In the end, we cannot just `pick and choose' how we select GES stars, and instead should be motivated by the science question.

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arXiv2023

The galaxy size to halo spin relation of disk galaxies in cosmological hydrodynamical simulations

In the standard disk galaxy formation model, the sizes of galactic disks are tightly related to the spin parameters $λ$ of their dark matter haloes. The model has been wildly adopted by various semi-analytic galaxy formation models which have been extremely successful to interpret a large body of observational data. However, the size-$λ$ correlation was rarely seen in most modern hydrodynamical simulations of galaxy formation. In this short paper, we make use of 4 sets of large hydrodynamical simulations to explore the size-spin parameter relation with a large sample of simulated disk galaxies, and compare it with a popular disk galaxy formation model of Mo et al. (1998). Intriguingly, galactic sizes correlate strongly with spin parameters of their dark matter haloes in the simulations developed by the IllustrisTNG collaborations, albeit the relation does not always agree with prediction of MMW98 model over all stellar mass range we examined. There is also a size-spin correlation for the Milky way analogies in the EAGLE simulations, while it is relatively weaker than that of the IllustrisTNG counterparts. For the dwarfs in the simulations from the EAGLE collaboration, there is NULL correlation. We conclude that either the detailed subgrid physics or hydrodynamics solvers account for the size-spin relation, which will be explored in our future work.

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arXiv2023

Chasing the impact of the Gaia-Sausage-Enceladus merger on the formation of the Milky Way thick disc

We employ our Bayesian Machine Learning framework BINGO (Bayesian INference for Galactic archaeOlogy) to obtain high-quality stellar age estimates for 68,360 red giant and red clump stars present in the 17th data release of the Sloan Digital Sky Survey, the APOGEE-2 high-resolution spectroscopic survey. By examining the denoised age-metallicity relationship of the Galactic disc stars, we identify a drop in metallicity with an increase in [Mg/Fe] at an early epoch, followed by a chemical enrichment episode with increasing [Fe/H] and decreasing [Mg/Fe]. This result is congruent with the chemical evolution induced by an early-epoch gas-rich merger identified in the Milky Way-like zoom-in cosmological simulation Auriga. In the initial phase of the merger of Auriga 18 there is a drop in metallicity due to the merger diluting the metal content and an increase in the [Mg/Fe] of the primary galaxy. Our findings suggest that the last massive merger of our Galaxy, the Gaia-Sausage-Enceladus, was likely a significant gas-rich merger and induced a starburst, contributing to the chemical enrichment and building of the metal-rich part of the thick disc at an early epoch.

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arXiv2023

Unravelling the mass spectrum of destroyed dwarf galaxies with the metallicity distribution function

Accreted stellar populations are comprised of the remnants of destroyed galaxies, and often dominate the `stellar haloes' of galaxies such as the Milky Way (MW). This ensemble of external contributors is a key indicator of the past assembly history of a galaxy. We introduce a novel statistical method that uses the unbinned metallicity distribution function (MDF) of a stellar population to estimate the mass spectrum of its progenitors. Our model makes use of the well-known mass-metallicity relation of galaxies and assumes Gaussian MDF distributions for individual progenitors: the overall MDF is thus a mixture of MDFs from smaller galaxies. We apply the method to the stellar halo of the MW, as well as the classical MW satellite galaxies. The stellar components of the satellite galaxies have relatively small sample sizes, but we do not find any evidence for accreted populations with L > L_host/100. We find that the MW stellar halo has N~1-3 massive progenitors (L > 10^8 L_Sun) within 10 kpc, and likely several hundred progenitors in total. We also test our method on simulations of MW-mass haloes, and find that our method is able to recover the true accreted population within a factor of two. Future datasets will provide MDFs with orders of magnitude more stars, and this method could be a powerful technique to quantify the accreted populations down to the ultra-faint dwarf mass-scale for both the MW and its satellites.

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arXiv2023

Colour and infall time distributions of satellite galaxies in simulated Milky-Way analogs

We use the Auriga simulations to probe different satellite quenching mechanisms operating at different mass scales ($10^5 M_\odot \lesssim M_\star \lesssim 10^{11} M_\odot$) in Milky Way-like hosts. Our goal is to understand the origin of the satellite colour distribution and star-forming properties in both observations and simulations. We find that the satellite populations in the Auriga simulations, which was originally designed to model Milky Way-like host galaxies, resemble the populations in the Exploration of Local VolumE Satellites (ELVES) Survey and the Satellites Around Galactic Analogs (SAGA) survey in their luminosity function in the luminosity range $-12 \lesssim M_V \lesssim -15$ and resemble ELVES in their quenched fraction and colour--magnitude distribution in the luminosity range $-12 \lesssim M_g \lesssim -15$. We find that satellites transition from blue colours to red colours at the luminosity range $-15 \lesssim M_g \lesssim -12$ in both the simulations and observations and we show that this shift is driven by environmental effects in the simulations. We demonstrate also that the colour distribution in both simulations and observations can be decomposed into two statistically distinct populations based on their morphological type or star-forming status that are statistically distinct. In the simulations, these two populations also have statistically distinct infall time distributions. The comparison presented here seems to indicate that the tension between the quenched fraction in SAGA and simulations is resolved by the improved target selection of ELVES, but there are still tensions in understanding the colours of faint galaxies, of which ELVES appears to have a significant population of faint blue satellites not recovered in Auriga.

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arXiv2023

The interplay of internal and external processes in the buildup of disk galaxies: thick-disk star formation histories in AURIGA simulations

Recent integral-field spectroscopy observations have revealed that thick- and thin-disk star-formation histories are regulated by the interplay of internal and external processes. We analyze stellar-population properties of 24 spiral galaxies from the AURIGA zoom-in cosmological simulations, to offer a more in-depth interpretation of observable properties. We present edge-on maps of stellar age, metallicity and [Mg/Fe] abundance, and we extract the star-formation and chemical-evolution histories of thin and thick disks. Both show signs of the interplay between internal chemical enrichment and gas and star accretion. Thick disks show particularly complex stellar populations, including an in-situ component, formed from both slowly enriched and accreted more pristine gas, and an additional significant fraction of ex-situ stars.

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arXiv2022

Is the core-cusp problem a matter of perspective: Jeans Anisotropic Modeling against numerical simulations

Mock member stars for 28 dwarf galaxies are constructed from the cosmological Auriga simulation, which reflect the dynamical status of realistic stellar tracers. The axis-symmetric Jeans Anisotropic Multi-Gaussian Expansion (JAM) modeling is applied to 6,000 star particles for each system, to recover the underlying matter distribution. The stellar or dark matter component individually is poorly recovered, but the total profile is constrained more reasonably. The mass within the half-mass radius of tracers is recovered the tightest, and the mass between 200 and 300 pc, $M(200-300\mathrm{pc})$, is constrained ensemble unbiasedly, with a scatter of 0.167 dex. If using 2,000 particles and only line-of-sight velocities with typical errors, the scatter in $M(200-300\mathrm{pc})$ is increased by $\sim$50%. Quiescent Sagittarius dSph-like systems and star-forming systems with strong outflows show distinct features, with $M(200-300\mathrm{pc})$ mostly under-estimated for the former, and likely over-estimated for the latter. The biases correlate with the dynamical status, which is a result of contraction motions due to tidal effects in quiescent systems or galactic winds in star-forming systems, driving them out of equilibrium. After including Gaia DR3 proper motion errors, we find proper motions can be as useful as line-of-sight velocities for nearby systems at $<\sim$60 kpc. By extrapolating the actual density profiles and the dynamical constraints down to scales below the resolution, we find the mass within 150 pc can be constrained ensemble unbiasedly, with a scatter of $\sim$0.255 dex. In the end, we show that the contraction of member stars in nearby systems is detectable based on Gaia DR3 proper motion errors.

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arXiv2022

The impact of two massive early accretion events in a Milky Way-like galaxy: repercussions for the buildup of the stellar disc and halo

We identify and characterise a Milky Way-like realisation from the Auriga simulations with two consecutive massive mergers $\sim2\,$Gyr apart at high redshift, comparable to the reported Kraken and Gaia-Sausage-Enceladus. The Kraken-like merger ($z=1.6$, $M_{\rm Tot} = 8\times10^{10}\,$M$_{\odot}$) is gas-rich, deposits most of its mass in the inner $10\,$kpc, and is largely isotropic. The Sausage-like merger ($z=1.14$, $M_{\rm Tot} = 1\times10^{11}\,$M$_{\odot}$) leaves a more extended mass distribution at higher energies, and has a radially anisotropic distribution. For the higher redshift merger, the stellar mass ratio of the satellite to host galaxy is 1:3. As a result, the chemistry of the remnant is indistinguishable from contemporaneous in-situ populations, making it challenging to identify this component through chemical abundances. This naturally explains why all abundance patterns attributed so far to Kraken are in fact fully consistent with the metal-poor in-situ so-called Aurora population and thick disc. However, our model makes a falsifiable prediction: if the Milky Way underwent a gas-rich double merger at high redshift, then this should be imprinted on its star formation history with bursts about $\sim2\,$Gyrs apart. This may offer constraining power on the highest-redshift major mergers.

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arXiv2022

Kinematics of the Local Group gas and galaxies in the Hestia simulations

We investigate the kinematic properties of gas and galaxies in the Local Group (LG) using high-resolution simulations performed by the {\sc Hestia} (High-resolution Environmental Simulations of The Immediate Area) collaboration. Our simulations include the correct cosmography surrounding LG-like regions consisting of two main spiral galaxies of $\sim 10^{12}$~M$_\odot$, their satellites and minor isolated galaxies, all sharing the same large-scale motion within a volume of a few Mpc. We characterise the gas and galaxy kinematics within the simulated LGs, from the perspective of the Sun, to compare with observed trends from recent HST/COS absorption-line observations and LG galaxy data. To analyse the velocity pattern of LG gas and galaxies seen in the observational data, we build sky maps from the local standard of rest, and the galactic and local group barycentre frames. Our findings show that the establishment of a radial velocity dipole at low/high latitudes, near the preferred barycentre direction, is a natural outcome of simulation kinematics for material {\it outside} the Milky Way virial radius after removing galaxy rotation when the two main LG galaxies are approaching. Our results favour a scenario where gas and galaxies stream towards the LG barycentre producing a velocity dipole resembling observations. While our study shows in a qualitative way the global matter kinematics in the LG as part of its on-going assembly, quantitative estimates of gas-flow rates and physical conditions of the LG gas have to await a more detailed modeling of the ionization conditions, which will be presented in a follow-up paper.

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arXiv2022

Cosmological gas accretion history onto the stellar discs of Milky Way-like galaxies in the Auriga simulations -- (I) Temporal dependency

We use the 30 simulations of the Auriga Project to estimate the temporal dependency of the inflow, outflow and net accretion rates onto the discs of Milky Way-like galaxies. The net accretion rates are found to be similar for all galaxies at early times, increasing rapidly up to $\sim 10~\mathrm{M}_\odot \, \mathrm{yr}^{-1}$. After $\sim 6~\mathrm{Gyr}$ of evolution, however, the net accretion rates are diverse: in most galaxies, these exhibit an exponential-like decay, but some systems instead present increasing or approximately constant levels up to the present time. An exponential fit to the net accretion rates averaged over the MW analogues yields typical decay time-scale of $7.2~\mathrm{Gyr}$. The analysis of the time-evolution of the inflow and outflow rates, and their relation to the star formation rate (SFR) in the discs, confirms the close connection between these quantities. First, the inflow$/$outflow ratio stays approximately constant, with typical values of $\dot{M}_\mathrm{out}/ \dot{M}_\mathrm{in} \sim 0.75$, indicating that the gas mass involved in outflows is of the order of 25% lower compared to that involved in inflows. A similar behaviour is found for the SFR$/$inflow rate ratio, with typical values between 0.1 and 0.3, and for the outflow rate$/$SFR which varies in the range $3.5$--$5.5$. Our results show that continuous inflow is key to the SFR levels in disc galaxies, and that the star formation activity and the subsequent feedback in the discs is able to produce mass-loaded galaxy winds in the disc-halo interface.

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