arXiv subjects

Sijing Shen

Publications and source records attributed to Sijing Shen.

At least 19 recordsLinked to original sources

arXiv2026

The Simulated Oxygen Shortage (SOS): Mapping the Missing OVI in Simulated Dwarf Galaxies to Subgrid Physics

Observations reveal extended \OVI\, reservoirs in the circumgalactic medium (CGM) of dwarf galaxies, yet current simulations systematically underpredict \OVI\, column densities. Utilizing two suites run with different simulation codes, the \MM\, simulations (Marvelous Massive Dwarfs and Marvel-ous Dwarfs) and the publicly available FIRE-2 simulations, we explore the role of subgrid models and the resulting CGM phase in shaping \OVI\, production. By comparing observationally derived \OVI\, masses to the mass of oxygen produced over the galaxies' star formation history, we find evidence for an underproduction of oxygen for low-mass simulated galaxies. Despite clear differences in feedback implementation, CGM structure, and metal mixing, we find that \OVI\, in both suites generally self-selects cool/warm ($\rm log\, T\,/K \sim 4.5$), diffuse ($\rm log\,n_{gas}\,/cm^{-3} \sim -5.0 $), and moderately metal-enriched ($\rm log\, Z/Z_{\odot} \sim -1 $) material at large radii from the galaxy. We show that neither the choice of ultraviolet background nor plausible variations in CGM thermal structure can close the gap with observations. Taken together, our results point to a possible underproduction of oxygen in low-mass galaxies. Feedback prescriptions contribute via insufficient metal transport to large radii. Hence, the \OVI\, deficit may motivate an investigation of current modeling choices for supernova yields, star formation, and feedback in low-metallicity environments.

astro-ph.GA↗

arXiv2025

In-Situ High Performance Visualization for Astronomy & Cosmology

The Astronomy & Cosmology (A&C) community is presently witnessing an unprecedented growth in the quality and quantity of data coming from simulations and observations. Writing results of numerical simulations to disk files has long been a bottleneck in high-performance computing. To access effectively and extract the scientific content of such large-scale data sets appropriate tools and techniques are needed. This is especially true for visualization tools, where petascale data size problems cannot be visualized without some data filtering, which reduces either the resolution or the amount of data volume managed by the visualization tool. A solution to this problem is to run the analysis and visualization concurrently (in-situ) with the simulation and bypass the storage of the full results. In particular we use Hecuba, a framework offering a highly distributed database to stream A\&C simulation data for on-line visualization. We will demonstrate the Hecuba platform integration with the Changa high performant cosmological simulator and the in-situ visualization of its N-body results with the ParaView and VisIVO tools.

astro-ph.IM↗

arXiv2025

The Seven Dwarfs illuminated. The impact of radiation on dwarf galaxies and their circumgalactic medium

We present a high-resolution cosmological zoom-in simulation of a group of field dwarf galaxies which includes on-the-fly radiative transfer (RT) and is evolved to $z=0$. Emission from stars is included according to age-dependent spectra, and a redshift-dependent UV background. The inclusion of RT results in the formation of eight additional faint dwarf galaxies with stellar masses of $10^{4}$ M$_{\odot}$ to several $10^{5}$ M$_{\odot}$ and only old stellar populations, similar to the observed Ultra-Faint Dwarf galaxies. They formed before and during cosmic reionisation and were mostly quenched by $z \sim 3-4$. The simulated galaxies follow many observed scaling relations such as the stellar mass-halo mass relation, the mass-size relation, and the luminosity-velocity dispersion relation. For the more massive dwarf galaxies, radiative feedback suppresses star formation, making it less bursty and reducing explosive outflows. This consequently reduces the dark matter core sizes by a factor of 2-3, rendering the core sizes ($\sim$ 1 kpc) more consistent with observations. The distribution of HI in the circumgalactic medium (CGM) is ubiquitous with a covering fraction of unity within $R_{vir}$, in good agreement with observations. It is rather insensitive to radiative or SN feedback at $z=0$, but at $z>5$ it is much higher in the RT simulation. In contrast, the distribution of low ions like SiII is very compact and declines sharply beyond the ISM scale. CIV and OVI have a more extended distribution, but their column densities are generally below the detection limit. Radiative feedback leads to smaller column densities of the metal ions, partly due to the reduction of total metal production, and partly because hard photons from the stellar radiation escape the ISM and further ionise the CGM. The abundance of CIV is particularly sensitive to the latter effect.

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arXiv2025

Chemical enrichment of metal-poor stars orbiting massive black hole companions

There are millions of undetected black holes wandering through our galaxy. Observatories like {\it Chandra}, LIGO, and more recently, {\it Gaia}, have provided valuable insights into the configurations of these elusive objects when residing in binary systems. Motivated by these advances, we study, for the first time, the enhanced accretion of metals from the interstellar medium (ISM) onto low-mass companions in binary systems with highly unequal mass ratios, utilizing a series of hydrodynamical simulations. Our study demonstrates that a stellar companion's metal accretion history from the ISM alone, from its formation to the present, can significantly influence its surface abundances, especially when enhanced by a massive black hole companion. However, this effect is likely only measurable in stars that are still in the main sequence. Once a stellar companion evolves off the main sequence, similar to what has been observed with the {\it Gaia} BH3 companion, the initial dredge-up process are likely to erase any excess surface abundance resulting from the metals that were accreted. As we discover more unequal mass ratio binary systems, it is crucial to understand how the observed metallicity of sun-like companions may differ from their birth metallicity, especially if they are not yet evolved.

astro-ph.SR↗

arXiv2025

Optimized smoothing kernels for SPH

We present a set of new smoothing kernels for smoothed particle hydrodynamics (SPH) that improve the convergence of the method without any additional computational cost. These kernels are generated through a linear combination of other SPH kernels, combined with an optimization strategy to minimize the error in the Gresho-Chan vortex test case. To facilitate the different choices in gradient operators for SPH in the literature, we perform this optimization for both geometric density average force SPH (GDSPH) and linear-corrected gradient SPH (ISPH). In addition to the Gresho-Chan vortex, we also perform simulations of the hydrostatic glass, Kelvin-Helmholtz instability, and the Sod shocktube case. At low neighbour numbers (< 128), there is a significant improvement across the different tests, with the greatest impact shown for GDSPH. Apart from the popular Wendland kernels, we also explore other positive-definite kernels in this paper, which include the "missing" Wendland kernels, Wu kernels, and Buhmann kernels. In addition, we also present a method for producing arbitrary non-biased initial conditions in SPH. This method uses the SPH momentum equation together with an artificial pressure, combined with a global and local relaxation stage to minimize local and global errors.

astro-ph.IM↗

arXiv2025

Marvelous Metals: Surveying the Circumgalactic Medium of Simulated Dwarf Galaxies

Dwarf galaxies are uniquely sensitive to energetic feedback processes and are known to experience substantial mass and metal loss from their disk. Here, we investigate the circumgalactic medium (CGM) of 64 isolated dwarf galaxies ($6.0<$log(M$_*/M_{\odot}$)$<9.5$) at $z=0$ from the Marvel-ous Dwarfs and Marvelous Massive Dwarfs hydrodynamic simulations. Our galaxies produce column densities broadly consistent with current observations. We investigate these column densities in the context of mass and metal retention rates and the physical properties of the CGM. We find $48\pm11\%$ of all baryons within $R_{200c}$ reside in the CGM, with $\sim70\%$ of CGM mass existing in a warm gas phase, $10^{4.5} 40\%$ towards lower masses. Our findings highlight the CGM (primarily its warm component) as a key reservoir of mass and metals for dwarf galaxies across stellar masses and underscore its importance in understanding the baryon cycle in the low-mass regime. Finally, we provide individual galaxy properties of our full sample and quantify the fraction of ultraviolet observable mass to support future observational programs, particularly those aimed at performing a metal budget around dwarf galaxies.

astro-ph.GA↗

arXiv2024

Interference in Fuzzy Dark Matter Filaments: Idealised Models and Statistics

Fuzzy (wave) dark matter (FDM), the dynamical model underlying an ultralight bosonic dark matter species, produces a rich set of non-gravitational signatures that distinguishes it markedly from the phenomenologically related warm (particle) dark matter (WDM) scenario. The emergence of extended interference fringes hosted by cosmic filaments is one such phenomenon reported by cosmological simulations, and a detailed understanding of such may strengthen existing limits on the boson mass but also break the degeneracy with WDM, and provide a unique fingerprint of interference in cosmology. In this paper, we provide initial steps towards this goal. In particular, we show in a bottom-up approach, how the presence of interference in an idealised filament population can lead to a non-suppressive feature in the matter power spectrum -- an observation supported by fully-cosmological FDM simulations. To this end, we build on a theoretically motivated and numerically observed steady-state approximation for filaments and express the equilibrium dynamics of such in an expansion of FDM eigenstates. We optimise the size of the expansion by incorporating classical phase-space information. Ellipsoidal collapse considerations are used to construct a fuzzy filament mass function which, together with the reconstructed FDM wave function, allow us to efficiently compute the one-filament power spectrum. We showcase our non-perturbative interference model for a selection of boson masses and confirm our approach is able to produce the matter power boost observed in fully-cosmological FDM simulations. More precisely, we find an excess in correlation between the spatial scale associated with the FDM ground state and the quantum pressure scale. We speculate about applications of this effect in data analysis.

astro-ph.CO↗

arXiv2024

A theoretical investigation of far-infrared fine structure lines at $z>6$ and of the origin of the [OIII]88/[CII]158 enhancement

[Abridged] The [OIII]$_{88\mu m}$/[CII]$_{158\mu m}$ and [OIII]$_{88\mu m}$/[NII]$_{122\mu m}$ luminosity ratios have shown to be promising tracers of the ionisation state and gas-phase metallicity of the ISM. Observations of galaxies at redshift $z > 6$ show peculiarly higher [OIII]$_{88\mu m}$/[CII]$_{158\mu m}$ luminosity ratios compared to local sources. No model has so far successfully managed to match the observed emission from both [OIII]$_{88\mu m}$ and [CII]$_{158\mu m}$ as well as their ratio. We use Cloudy to model the [CII]$_{158\mu m}$, [OIII]$_{88\mu m}$, [NII]$_{122\mu m}$ and [NIII]$_{57\mu m}$ emission lines of Ponos: a high-resolution ($m_{\mathrm{gas}} = 883.4\, M_{\odot}$) cosmological zoom-in simulation of a galaxy at redshift $z = 6.5$, which is post-processed using kramses-rt. We modify Carbon, Nitrogen and Oxygen abundances in our Cloudy models to obtain C/O and N/O abundance ratios respectively lower and higher than Solar, more in line with recent high-z observational constraints. We find [OIII]$_{88\mu m}$/[CII]$_{158\mu m}$ luminosity ratios that are a factor of $\sim 5$ higher compared to models assuming solar abundances. Additionally, we find an overall better agreement of the simulation with high-z observational constraints of the [CII]$_{158\mu m}$-SFR and [OIII]$_{88\mu m}$-SFR relations. This shows that a lower C/O abundance ratio is essential to reproduce the enhanced [OIII]$_{88\mu m}$/[CII]$_{158\mu m}$ luminosity ratios observed at $z > 6$. By assuming a super-solar N/O ratio, motivated by recent $z > 6$ JWST observations, our models yield an [OIII]$_{88\mu m}$/[NII]$_{122\mu m}$ ratio of $1.3$, which, according to current theoretical models, would be more appropriate for a galaxy with a lower ionisation parameter than the one we estimated for Ponos.

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arXiv2024

Constraining the physical properties of gas in high-z galaxies with far-infrared and submillimetre line ratios

Optical emission line diagnostics, which are a common tool to constrain the properties of the interstellar medium (ISM) of galaxies, become progressively inaccessible at higher redshifts for ground-based facilities. Far-infrared (FIR) emission lines, which are redshifted into atmospheric windows accessible by ground-based sub-millimeter facilities, could provide alternative ISM diagnostics to optical emission lines. We investigate FIR line ratios involving [CII]$λ158 μ$m, [OIII]$λ88 μ$m, [OIII]$λ52 μ$m, [NII]$λ122 μ$m and [NIII$λ57 μ$m, using synthetic emission lines applied to a high-resolution (m$_{\rm gas}$= 883.4 M$_{\odot}$) cosmological zoom-in simulation, including radiative-transfer post processing with KramsesRT at z = 6.5. We find that the [CII]/[NII]122 ratio is sensitive to the temperature and density of photo-dissociation regions, and thus could be a useful tool to trace the properties of this gas phase in galaxies. We also find that [NII]/[NIII] is a good tracer of the temperature and [OIII]52/[OIII]88 a good tracer of the gas density of HII regions. Emission line ratios containing the [OIII]$λ88 μ$m line are sensitive to high velocity outflowing gas.

astro-ph.GA↗

arXiv2024

Atacama Large Aperture Submillimeter Telescope (AtLAST) Science: The hidden circumgalactic medium

Our knowledge of galaxy formation and evolution has incredibly progressed through multi-wavelength observational constraints of the interstellar medium (ISM) of galaxies at all cosmic epochs. However, little is known about the physical properties of the more diffuse and lower surface brightness reservoir of gas and dust that extends beyond ISM scales and fills dark matter haloes of galaxies up to their virial radii, the circumgalactic medium (CGM). New theoretical studies increasingly stress the relevance of the latter for understanding the feedback and feeding mechanisms that shape galaxies across cosmic times, whose cumulative effects leave clear imprints into the CGM. Recent studies are showing that a -- so far unconstrained -- fraction of the CGM mass may reside in the cold (T < 1e4 K) molecular and atomic phase, especially in high-redshift dense environments. These gas phases, together with the warmer ionised phase, can be studied in galaxies from z ~ 0 to z ~ 10 through bright far-infrared and sub-millimeter emission lines such as [C II] 158$μ$m, [O III] 88 $μ$m, [C I] 609$μ$m, [C I] 370$μ$m, and the rotational transitions of CO. Imaging such hidden cold CGM can lead to a breakthrough in galaxy evolution studies but requires a new facility with the specifications of the proposed Atacama Large Aperture Submillimeter Telescope (AtLAST). In this paper, we use theoretical and empirical arguments to motivate future ambitious CGM observations with AtLAST and describe the technical requirements needed for the telescope and its instrumentation to perform such science.

astro-ph.GA↗

arXiv2024

The origin of cold gas in the Circumgalactic Medium

The presence of cold ($T \lesssim 10^4$ K) gas in the circumgalactic medium (CGM) of galaxies has been confirmed both in observations and high-resolution simulations, but its origin still represents a puzzle. Possible mechanisms are cold accretion from the intergalactic medium (IGM), clumps embedded in outflows and transported from the disk, gas detaching from the hot CGM phase via thermal instabilities. In this work, we aim at characterizing the history of cold CGM gas, in order to identify the dominant origin channels at different evolutionary stages of the main galaxy. To this goal, we track gas particles in different snapshots of the SPH cosmological zoom-in simulation Eris2k. We perform a backward tracking of cold gas, starting from different redshifts, until we identify one of the followings origins for the particle: cold inflow, ejected from the disk, cooling down in-situ or stripped from a satellite. We also perform a forward tracking of gas in different components of the galaxy (such as the disk and outflows). We find a clear transition between two epochs. For $z>2$, most cold gas (up to 80%) in the CGM comes from cold accretion streams as the galaxy is accreting in the "cold mode" from the IGM. At lower $z$, gas either cools down in-situ after several recycles (with 10-20% of the gas cooling in outflow), or it is ejected directly from the disk (up to 30%). Outflows have a major contribution to the cold CGM gas budget at $z<1$, with almost 50% of hot gas cooling in outflow. Finally, we discuss possible mechanisms for CGM cooling, showing that the thermally unstable gas with $t_{\rm cool}/t_{\rm ff}<1$ (precipitation-regulated feedback) is abundant up to $r\sim 100$ kpc and cooling times are shorter than 50 Myr for densities $n>10^{-2}\,{\rm cm}^{-3}$.

astro-ph.GA↗

arXiv2024

TREVR2: Illuminating fast $N\log_2\,N$ radiative transfer

We present TREVR2 (Tree-based REVerse Ray Tracing 2), a fast, general algorithm for computing the radiation field, suitable for both particle and mesh codes. It is designed to self-consistently evolve chemistry for zoomed-in astrophysical simulations, such as cosmological galaxies with both internal sources and prescribed background radiation, rather than large periodic volumes. Light is propagated until absorbed, with no imposed speed limit other than those due to opacity changes (e.g. ionization fronts). TREVR2 searches outward from receiving gas in discrete directions set by the HEALPIX algorithm (unlike its slower predecessor TREVR), accumulating optical depth and adding the flux due to sources combined into progressively larger tree cells with distance. We demonstrate $N_\textrm{active}\log_2 N$ execution time with absorption and many sources. This allows multi-band RT costs comparable to tree-based gravity and hydrodynamics, and the usual speed-up when active particles evolve on individual timesteps. Sources embedded in non-homogeneous absorbing material introduce systematic errors. We introduce transmission averaging instead of absorption averaging which dramatically reduces these systematic effects. We outline other ways to address systematics including an explicit complex source model. We demonstrate the overall performance of the method via a set of astrophysical test problems.

astro-ph.IM↗

arXiv2023

High resolution modeling of [CII], [CI], [OIII] and CO line emission from the ISM and CGM of a star forming galaxy at z ~ 6.5

The circumgalactic medium (CGM) is a crucial component of galaxy evolution, but thus far its physical properties are highly unconstrained. As of yet, no cosmological simulation has reached convergence when it comes to constraining the cold and dense gas fraction of the CGM. Such components are also challenging to observe, and require sub-millimeter instruments with a high sensitivity to extended, diffuse emission, like the proposed Atacama Large Aperture Sub-millimetre telescope (AtLAST). We present a state-of-the-art theoretical effort at modeling the [CII], [CI](1-0), [CI](2-1), CO(3-2), and [OIII] line emissions of galaxies. We use the high-resolution cosmological zoom-in simulation Ponos, representing a star forming galaxy system at z = 6.5 ($M_*=2\times10^9~M_{\odot}$), undergoing a major merger. We adopt different modeling approaches based on the photoionisation code Cloudy. Our fiducial model uses radiative transfer post-processing with RamsesRT and Krome to create realistic FUV radiation fields, which we compare to sub-grid modeling approaches adopted in the literature. We find significant differences in the luminosity and in the contribution of different gas phases and galaxy components between the different modeling approaches. [CII] is the least model-dependant gas tracer, while [CI](1-0) and CO(3-2) are very model-sensitive. In all models, we find a significant contribution to the emission of [CII] (up to $\sim$10%) and [OIII] (up to $\sim$20%) from the CGM. [CII] and [OIII] trace different regions of the CGM: [CII] arises from an accreting filament and from tidal tails, while [OIII] traces a puffy halo surrounding the main disc, probably linked to SN feedback. We discuss our results in the context of current and future sub-mm observations with ALMA and AtLAST.

astro-ph.GA↗

arXiv2023

Spectral reconstruction for radiation hydrodynamic simulations of galaxy evolution

Radiation from stars and AGN plays an important role in galaxy formation and evolution, and profoundly transforms the IGM, CGM & ISM. On-the-fly RT has started being incorporated in cosmological simulations, but the complex, evolving radiation spectra are often crudely approximated with a small number of broad bands with piece-wise constant intensity and a fixed photo-ionisation cross-section. Such a treatment is unable to capture the changes to the spectrum as light is absorbed while it propagates through a medium with non-zero opacity. This can lead to large errors in photo-ionisation and heating rates. We present a novel approach of discretising the radiation field in narrow bands, located at the edges of the typically used bands, in order to capture the power-law slope of the radiation field. In combination with power-law approximations for the photo-ionisation cross-sections, this model allows us to self-consistently combine radiation from sources with different spectra and accurately follow the ionisation states of primordial and metal species through time. The method is implemented in Gasoline2 in connection with Trevr2. We compare our new piece-wise power-law reconstruction to the piece-wise constant method in calculating the primordial chemistry photo-ionisation and heating rates under an evolving UVB and stellar spectrum, and find that our method reduces errors significantly, up to two orders of magnitude in the case of HeII ionisation. We apply our new spectral reconstruction method in RT post-processing of a cosmological zoom-in simulation, including radiation from stars and a live UVB, and find a significant increase in total neutral hydrogen mass in the ISM and the CGM due to shielding of the UVB and a low escape fraction of the stellar radiation. This demonstrates the importance of RT and an accurate spectral approximation in simulating the CGM-galaxy ecosystem.

astro-ph.GA↗

arXiv2022

Numerical dependencies of the galactic dynamo in isolated galaxies with SPH

Understanding the numerical dependencies that act on the galactic dynamo is a crucial step in determining what resolution and what conditions are required to properly capture the magnetic fields observed in galaxies. Here, we present an extensive study on the numerical dependencies of the galactic dynamo in isolated spiral galaxies using smoothed particle magnetohydrodynamics (SPMHD). We performed 53 isolated spiral galaxy simulations with different initial setups, feedback, resolution, Jeans floor and dissipation parameters. The results show a strong mean-field dynamo occurring in the spiral-arm region of the disk, likely produced by the classical alpha-omega dynamo or the recently described gravitational instability dynamo. The inclusion of feedback is seen to work in both a destructive and positive fashion for the amplification process. Destructive interference for the amplification occurs due to break down of filament structure in the disk, increase of turbulent diffusion and the ejection of magnetic flux from the central plane to the circumgalactic medium. The positive effect of feedback is the increase in vertical motions and the turbulent fountain flows that develop, showing a high dependence on the small-scale vertical structure and the numerical dissipation within the galaxy. Galaxies with an effective dynamo saturate their magnetic energy density at levels between 10-30% of the thermal energy density. The density averaged numerical Prandtl number is found to be below unity throughout the galaxy for all our simulations, with an increasing value with radius. Assuming a turbulent injection length of 1 kpc, the numerical magnetic Reynolds number are within the range of $Re_{mag}=10-400$, indicating that some regions are below the levels required for the small-scale dynamo ($Re_{mag,crit}=30-2700$) to be active.

astro-ph.GA↗

arXiv2022

The Dawn of Disk Formation in a Milky Way-sized Galaxy Halo: Thin Stellar Disks at $z > 4$

We present results from \textsc{GigaEris}, a cosmological, $N$-body hydrodynamical "zoom-in" simulation of the formation of a Milky Way-sized galaxy halo with unprecedented resolution, encompassing of order a billion particles within the refined region. The simulation employs a modern implementation of smoothed-particle hydrodynamics, including metal-line cooling and metal and thermal diffusion. We focus on the early assembly of the galaxy, down to redshift $z=4.4$. The simulated galaxy has properties consistent with extrapolations of the main sequence of star-forming galaxies to higher redshifts and levels off to a star formation rate of $\sim$60$\, M_{\odot}$~yr$^{-1}$ at $z=4.4$. A compact, thin rotating stellar disk with properties analogous to those of low-redshift systems arises already at $z \sim 8$. The galaxy rapidly develops a multi-component structure, and the disk, at least at these early stages, does not grow "upside-down" as often reported in the literature. Rather, at any given time, newly born stars contribute to sustain a thin disk. The kinematics reflect the early, ubiquitous presence of a thin disk, as a stellar disk component with $v_ϕ/σ_R$ larger than unity is already present at $z \sim 9$--10. Our results suggest that high-resolution spectro-photometric observations of very high-redshift galaxies should find thin rotating disks, consistent with the recent discovery of cold rotating gas disks by ALMA. Finally, we present synthetic images for the JWST NIRCam camera, showing how the early disk would be easily detectable already at those early times.

astro-ph.GA↗

arXiv2020

Ultra-faint dwarfs in a Milky Way context: Introducing the Mint Condition DC Justice League Simulations

We present results from the "Mint" resolution DC Justice League suite of Milky Way-like zoom-in cosmological simulations, which extend our study of nearby galaxies down into the ultra-faint dwarf (UFD) regime for the first time. The mass resolution of these simulations is the highest ever published for cosmological Milky Way zoom-in simulations run to $z=0$, with initial star (dark matter) particle masses of 994 (17900) M$_\odot$, and a force resolution of 87 pc. We study the surrounding dwarfs and UFDs, and find the simulations match the observed dynamical properties of galaxies with $-3 < M_V < -19$, and reproduce the scatter seen in the size-luminosity plane for $r_h\gtrsim200$ pc. We predict the vast majority of nearby galaxies will be observable by the Vera Rubin Observatory's co-added Legacy Survey of Space and Time (LSST). We additionally show that faint dwarfs with velocity dispersions $\lesssim5$ km/s result from severe tidal stripping of the host halo. We investigate the quenching of UFDs in a hydrodynamical Milky Way context, and find that the majority of UFDs are quenched prior to interactions with the Milky Way, though some of the quenched UFDs retain their gas until infall. Additionally these simulations yield some unique dwarfs that are the first of their kind to be simulated, e.g., an HI-rich field UFD, a late-forming UFD that has structural properties similar to Crater 2, as well as a compact dwarf satellite that has no dark matter at $z=0$.

astro-ph.GA↗

arXiv2020

The baryon cycle of Seven Dwarfs with superbubble feedback

We present results from a high-resolution, cosmological, $Λ$CDM simulation of a group of field dwarf galaxies with the "superbubble" model for clustered SN feedback, accounting for thermal conduction and cold gas evaporation. The initial conditions and the galaxy formation physics, other than SN feedback, are the same as in Shen et al. (2014). The simulated luminous galaxies have blue colors, low star formation efficiencies and metallicities, and high cold gas content, reproducing the observed scaling relations of dwarfs in the Local Volume. Bursty star formation histories and superbubble-driven outflows lead to the formation of kpc-size DM cores when stellar masses reaches $M_{*} > 10^6$ $M_{\odot}$, similar to previous findings. However, the superbubble model appears more effective in destroying DM cusps than the previously adopted "blastwave" model, reflecting a higher coupling efficiency of SN energy with the ISM. On larger scale, superbubble-driven outflows have a more moderate impact: galaxies have higher gas content, more extended stellar disks, and a smaller metal-enriched region in the CGM. The two halos with $M_{vir} \sim 10^9$ $M_{\odot}$, which formed ultra-faint dwarf galaxies in Shen et al. (2014), remain dark due to the different impact of metal-enriched galactic winds from two nearby luminous galaxies. The column density distributions of H I, Si II, C IV and O VI are in agreement with recent observations of CGM around isolated dwarfs. While H I is ubiquitous with a covering fraction of unity within the CGM, Si II and C IV are less extended. O VI is more extended, but its mass is only 11% of the total CGM oxygen budget, as the diffuse CGM is highly ionised by the UVB. Superbubble feedback produces C IV and O VI an order of magnitude higher column densities than those with blastwave feedback. The CGM and DM cores are most sensitive probes of feedback mechanisms.

astro-ph.GA↗