Bimodal gas accretion in the Horizon-MareNostrum galaxy formation simulation

AbstractIn recent years, effects such as the radial migration of stars in disks have been recognized as important drivers of the properties of stellar populations. Radial migration arises due to perturbative effects of disk structures such as bars and spiral arms, and can deposit stars formed in disks to regions far from their birthplaces. Migrant stars can significantly affect the demographics of their new locales, especially in low-density regions such as in the outer disks. However, in the cosmological environment, other effects such as mergers and filamentary gas accretion also influence the disk formation process. Understanding the relative importance of these processes on the detailed evolution of stellar population signatures is crucial for reconstructing the history of the Milky Way and other nearby galaxies. In the Milky Way disk in particular, the formation of the thickened component has recently attracted much attention due to its potential to serve as a diagnostic of the galaxy's early history. Some recent work suggests, however, that the vertical structure of Milky Way stellar populations is consistent with models that build up the thickened component through migration. I discuss these developments in the context of cosmological galaxy formation.

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Are cosmological gas accretion streams multiphase and turbulent?

Astronomy and Astrophysics ◽

10.1051/0004-6361/201629229 ◽

2018 ◽

Vol 610 ◽

pp. A75 ◽

Cited By ~ 9

Author(s):

Nicolas Cornuault ◽

Matthew D. Lehnert ◽

François Boulanger ◽

Pierre Guillard

Keyword(s):

Galaxy Formation ◽

Direct Interaction ◽

Mass Range ◽

Initial Kinetic Energy ◽

Two Phase ◽

Dynamical Time ◽

Order Of Magnitude ◽

Post Shock ◽

Gas Accretion ◽

Halo Gas

Simulations of cosmological filamentary accretion reveal flows (“streams”) of warm gas, T ~ 104 K, which bring gas into galaxies efficiently. We present a phenomenological scenario in which gas in such flows, if it is shocked as it enters the halo as we assume and depending on the post-shock temperature, stream radius, its relative overdensity, and other factors, becomes biphasic and turbulent. We consider a collimated stream of warm gas that flows into a halo from an overdense filament of the cosmic web. The post-shock streaming gas expands because it has a higher pressure than the ambient halo gas and fragments as it cools. The fragmented stream forms a two phase medium: a warm cloudy phase embedded in hot post-shock gas. We argue that the hot phase sustains the accretion shock. During fragmentation, a fraction of the initial kinetic energy of the infalling gas is converted into turbulence among and within the warm clouds. The thermodynamic evolution of the post-shock gas is largely determined by the relative timescales of several processes. These competing timescales characterize the cooling, expansion of the post-shock gas, amount of turbulence in the clouds, and dynamical time of the halo. We expect the gas to become multiphase when the gas cooling and dynamical times are of the same order of magnitude. In this framework, we show that this mainly occurs in the mass range, Mhalo ~ 1011 to 1013 M⊙, where the bulk of stars have formed in galaxies. Because of the expansion of the stream and turbulence, gas accreting along cosmic web filaments may eventually lose coherence and mix with the ambient halo gas. Through both the phase separation and “disruption” of the stream, the accretion efficiency onto a galaxy in a halo dynamical time is lowered. Decollimating flows make the direct interaction between galaxy feedback and accretion streams more likely, thereby further reducing the overall accretion efficiency. As we discuss in this work, moderating the gas accretion efficiency through these mechanisms may help to alleviate a number of significant challenges in theoretical galaxy formation.

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Simulations at the Dwarf Scale: From Violent Dwarfs at Cosmic Dawn and Cosmic Noon to Quiet Discs today

Proceedings of the International Astronomical Union ◽

10.1017/s1743921318006476 ◽

2018 ◽

Vol 14 (S344) ◽

pp. 468-472

Author(s):

Daniel Ceverino

Keyword(s):

Galaxy Formation ◽

Mass Scale ◽

Local Scaling ◽

James Webb Space Telescope ◽

Accretion Rates ◽

Hydrodynamical Simulations ◽

First Galaxies ◽

Fisher Relation ◽

Gas Accretion ◽

Stellar Masses

AbstractDwarf galaxies with stellar masses around 109M⊙ can be explored at high and low redshifts and they give a glimpse of the different conditions of galaxy formation at different epochs. Using a large sample of about 300 zoom-in cosmological hydrodynamical simulations of galaxy formation I will briefly describe the formation of dwarfs at this mass scale at 3 different epochs: cosmic dawn (Ceverino, Klessen, Glover 2018), cosmic noon (Ceverino, Primack, Dekel 2015), and today (Ceverino et al. 2017). I will describe the FirstLight simulations of first galaxies at redshifts 5-15. These first dwarfs have extremely high star formation efficiencies due to high gas fractions and high gas accretion rates. These simulations will make predictions that will be tested for the first time with the James Webb Space Telescope (JWST). At cosmic noon, z = 2, galaxy formation is still a very violent and dynamic process. The VELA simulations have generated a set of dispersion-dominated dwarfs that show an elongated morphology due to their prolate dark-matter halos. Between z = 1 and 0, the AGORA simulation shows the formation of a low-mass disc due to slow gas accretion. The disc agrees with many local scaling relations, such as the stellar-mass-halo-mass and the baryonic Tully-Fisher relation.

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Effects of reionization on dwarf galaxy formation

Proceedings of the International Astronomical Union ◽

10.1017/s174392130802471x ◽

2008 ◽

Vol 4 (S255) ◽

pp. 142-146

Author(s):

Massimo Ricotti

Keyword(s):

Star Formation ◽

Galaxy Formation ◽

High Velocity ◽

Dwarf Galaxy ◽

Late Phase ◽

Star Formation History ◽

Formation History ◽

High Velocity Clouds ◽

Gas Accretion ◽

In Virtue Of

AbstractIn this talk I revisit the problem of gas accretion onto minihalos after reionization. I show that primordial minihalos with vcir < 20 km s−1 stop accreting gas after reionization, as is usually assumed, but in virtue of their increasing concentration and the decreasing temperature of the intergalactic medium as redshift decreases, they have a late phase (at redshift z<2) of gas accretion and possibly star formation. As a result we expect that pre-reionization fossils have a more complex star formation history than previously envisioned. A signature of this model is a bimodal star formation history. The dwarf spheroidal galaxy Leo T, that inspired the present work, fits with this scenario. Another prediction of the model is the existence of a population of gas rich minihalos that never formed stars. A subset of compact high-velocity clouds may be identified as such objects but the bulk of them may still be undiscovered.

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Gas Accretion and Mergers in Massive Galaxies at z ~ 2

Proceedings of the International Astronomical Union ◽

10.1017/s1743921313004225 ◽

2012 ◽

Vol 8 (S295) ◽

pp. 45-48

Author(s):

C. J. Conselice ◽

Jamie Ownsworth ◽

Alice Mortlock ◽

Asa F. L. Bluck ◽

Keyword(s):

Galaxy Formation ◽

Theoretical Models ◽

Massive Galaxies ◽

A Value ◽

The Galaxy ◽

Hydrodynamical Simulations ◽

Minor Mergers ◽

Galaxy Assembly ◽

Gas Accretion

AbstractGalaxy assembly is an unsolved problem, with ΛCDM theoretical models unable to easily account for among other things, the abundances of massive galaxies, and the observed merger history. We show here how the problem of galaxy formation can be addressed in an empirical way without recourse to models. We discuss how galaxy assembly occurs at 1.5 < z < 3 examining the role of major and minor mergers, and gas accretion from the intergalactic medium in forming massive galaxies with log M* > 11 found within the GOODS NICMOS Survey (GNS). We find that major mergers, minor mergers and gas accretion are roughly equally important in the galaxy formation process during this epoch, with 64% of the mass assembled through merging and 36% through accreted gas which is later converted to stars, while 58% of all new star formation during this epoch arises from gas accretion. We also discuss how the total gas accretion rate is measured as Ṁ = 90±40 M⊙ yr−1 at this epoch, a value close to those found in some hydrodynamical simulations.

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SDSS-IV MaNGA: environmental dependence of gas metallicity gradients in local star-forming galaxies

Monthly Notices of the Royal Astronomical Society ◽

10.1093/mnras/stz2218 ◽

2019 ◽

Vol 489 (1) ◽

pp. 1436-1450 ◽

Cited By ~ 4

Author(s):

Jianhui Lian ◽

Daniel Thomas ◽

Cheng Li ◽

Zheng Zheng ◽

Claudia Maraston ◽

...

Keyword(s):

Star Formation ◽

Galaxy Formation ◽

Cold Dark Matter ◽

Star Forming ◽

Spatially Resolved ◽

The Galaxy ◽

Low Mass ◽

Satellite Galaxies ◽

Galaxy Environment ◽

Gas Accretion

ABSTRACT Within the standard model of hierarchical galaxy formation in a Λ cold dark matter universe, the environment of galaxies is expected to play a key role in driving galaxy formation and evolution. In this paper, we investigate whether and how the gas metallicity and the star formation surface density (ΣSFR) depend on galaxy environment. To this end, we analyse a sample of 1162 local, star-forming galaxies from the galaxy survey Mapping Nearby Galaxies at APO (MaNGA). Generally, both parameters do not show any significant dependence on environment. However, in agreement with previous studies, we find that low-mass satellite galaxies are an exception to this rule. The gas metallicity in these objects increases while their ΣSFR decreases slightly with environmental density. The present analysis of MaNGA data allows us to extend this to spatially resolved properties. Our study reveals that the gas metallicity gradients of low-mass satellites flatten and their ΣSFR gradients steepen with increasing environmental density. By extensively exploring a chemical evolution model, we identify two scenarios that are able to explain this pattern: metal-enriched gas accretion or pristine gas inflow with varying accretion time-scales. The latter scenario better matches the observed ΣSFR gradients, and is therefore our preferred solution. In this model, a shorter gas accretion time-scale at larger radii is required. This suggests that ‘outside–in quenching’ governs the star formation processes of low-mass satellite galaxies in dense environments.

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How do Galaxies get their Baryons?

Proceedings of the International Astronomical Union ◽

10.1017/s1743921311022927 ◽

2010 ◽

Vol 6 (S277) ◽

pp. 267-272

Author(s):

Christopher J. Conselice

Keyword(s):

Star Formation ◽

Galaxy Formation ◽

Cosmic Time ◽

Third Way ◽

History Of ◽

Galaxy Assembly ◽

Gas Accretion ◽

Effects Of Feedback ◽

Stellar Masses ◽

Baryonic Mass

AbstractUnderstanding how galaxies obtain baryons, their stars and gas, over cosmic time is traditionally approached in two different ways - theoretically and observationally. In general, observational approaches to galaxy formation include measuring basic galaxy properties, such as luminosities, stellar masses, rotation speeds, star formation rates and how these features evolve through time. Theoretically, cosmologically based models collate the physical effects driving galaxy assembly - mergers of galaxies, accretion of gas, star formation, and feedback, amongst others, to form predictions which are matched to galaxy observables. An alternative approach is to examine directly, in an observational way, the processes driving galaxy assembly, including the effects of feedback. This is a new ‘third way’ towards understanding how galaxies are forming from gas accretion and mergers, and directly probes these effects instead of relying on simulations designed to reproduce observations. This empirical approach towards understanding galaxy formation, including the acquisition history of baryons, displays some significant differences with the latest galaxy formation models, in addition to directly demonstrating the mechanisms by which galaxies form most of their baryonic mass.

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The role of cold and hot gas flows in feeding early-type galaxy formation

Proceedings of the International Astronomical Union ◽

10.1017/s1743921316010243 ◽

2014 ◽

Vol 11 (S308) ◽

pp. 394-397

Author(s):

Peter H. Johansson

Keyword(s):

Galaxy Formation ◽

Gas Flows ◽

Early Type ◽

Gas Streams ◽

Hot Gas ◽

Stellar Component ◽

The Galaxy ◽

History Of ◽

Gas Accretion ◽

Low Entropy

AbstractWe study the evolution of the gaseous components in massive simulated galaxies and show that their early formation is fuelled by cold, low entropy gas streams. At lower redshifts of z ≲ 3 the simulated galaxies are massive enough to support stable virial shocks resulting in a transition from cold to hot gas accretion. The gas accretion history of early-type galaxies is directly linked to the formation of their stellar component in the two phased formation scenario, in which the central parts of the galaxy assemble rapidly through in situ star formation and the later assembly is dominated primarily by minor stellar mergers.

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Faint features in the isolated galaxy CIG96

Proceedings of the International Astronomical Union ◽

10.1017/s1743921316008826 ◽

2016 ◽

Vol 11 (S321) ◽

pp. 292-292

Author(s):

P. Ramírez-Moreta ◽

L. Verdes-Montenegro ◽

S. Leon ◽

J. Blasco-Herrera ◽

M. Fernández-Lorenzo ◽

...

Keyword(s):

Galaxy Formation ◽

Optical Observations ◽

Local Universe ◽

Isolated Galaxies ◽

Galaxy Formation And Evolution ◽

Formation And Evolution ◽

Minor Mergers ◽

Gas Accretion ◽

Shed Light

The AMIGA project carries out a multiwavelength study of the largest catalogue of isolated galaxies from the Local Universe (CIG, Karachentseva 1973). Compared to any other sample —field galaxies included— and using highly strict isolation criteria (unperturbed for at least ~3 Gyr, Verdes-Montenegro et al. 2005), all the results show that these galaxies have the lowest values of the physical magnitudes expected to be enhanced by interactions. This strongly supports isolated galaxies as ideal laboratories for the study of galaxy formation and evolution. Despite CIG galaxies show the lowest HI integrated profile asymmetry level when compared to any other sample, some cases present up to 50% HI asymmetry (Espada et al. 2011b). We aim to shed light over the causes and sources of such asymmetries with our deep radiointerferometric and optical observations of CIG targets. Since major mergers are ruled out by the isolation criteria, in this work we are addressing whether minor mergers, internal processes or primordial gas accretion are responsible for such asymmetries.

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The atomic gas in outer disks in semi-analytic models of galaxy formation

Proceedings of the International Astronomical Union ◽

10.1017/s1743921316011017 ◽

2016 ◽

Vol 11 (S321) ◽

pp. 131-131

Author(s):

Jian Fu ◽

Yu Luo

Keyword(s):

Galaxy Formation ◽

Surface Density ◽

Mass Relation ◽

Gas Stripping ◽

Density Region ◽

Radial Profiles ◽

Gas Accretion ◽

Analytic Models ◽

Gas Component ◽

Cold Gas

AbstractWe use semi-analytic models of galaxy formation L-Galaxies based on ΛCDM cosmology to study the HI gas component in galaxy outskirts. We adopt the radially-resolved version of the models by Fu et al. (2013), which includes both atomic and molecular gas component in interstellar medium. This model has been recently updated by Luo et al. (2016) to include cold gas stripping in the outer disk regions of the satellite galaxies by ram pressure. In our models, we can perfectly reproduce the HI size-mass relation, which is discovered by Broeils & Rhee (1997) and confirmed by many subsequent observations. In our model, the reason for such tight correlation between HI size and mass is atomic-molecular phase conversion in high gas surface density regions while HI ionization in low gas surface density region, which leads to very narrow distribution of HI mean surface density. The models also reproduce the universal exponential HI radial profiles in galaxy outskirts found by Bluedisk (Wang et al. 2013), which arises from cold gas accretion onto the galaxy disks in exponentially profiles.

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