Rapid early gas accretion for the inner Galactic disc. A case for a short accretion timescale

Numerical calculations of spiral shocks in the gas discs of galaxies (1,2,3) usually assume that the disc is flat, i.e. the gas motion is purely horizontal. However there is abundant evidence that the discs of galaxies are warped and corrugated (4,5,6) and it is therefore of interest to consider the effect of the consequent vertical motion on the structure of spiral shocks. If one uses the tightly wound spiral approximation to calculate the gas flow in a vertical cut around a circular orbit (i.e the ⊝ -z plane, see Nelson & Matsuda (7) for details), then for a gas disc with Gaussian density profile in the z-direction and initially zero vertical velocity a doubly periodic spiral potential modulation produces the steady shock structure shown in Fig. 1. The shock structure is independent of z, and only a very small vertical motion appears with anti-symmetry about the mid-plane.

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Effects of initial density profiles on massive star cluster formation in giant molecular clouds

Monthly Notices of the Royal Astronomical Society ◽

10.1093/mnras/stab491 ◽

2021 ◽

Author(s):

Yingtian Chen ◽

Hui Li ◽

Mark Vogelsberger

Keyword(s):

Angular Momentum ◽

Star Formation ◽

Molecular Clouds ◽

Globular Clusters ◽

Cluster Formation ◽

Initial Density ◽

Giant Molecular Clouds ◽

Density Profiles ◽

Stellar Feedback ◽

Gas Accretion

Abstract We perform a suite of hydrodynamic simulations to investigate how initial density profiles of giant molecular clouds (GMCs) affect their subsequent evolution. We find that the star formation duration and integrated star formation efficiency of the whole clouds are not sensitive to the choice of different profiles but are mainly controlled by the interplay between gravitational collapse and stellar feedback. Despite this similarity, GMCs with different profiles show dramatically different modes of star formation. For shallower profiles, GMCs first fragment into many self-gravitation cores and form sub-clusters that distributed throughout the entire clouds. These sub-clusters are later assembled ‘hierarchically’ to central clusters. In contrast, for steeper profiles, a massive cluster is quickly formed at the center of the cloud and then gradually grows its mass via gas accretion. Consequently, central clusters that emerged from clouds with shallower profiles are less massive and show less rotation than those with the steeper profiles. This is because 1) a significant fraction of mass and angular momentum in shallower profiles is stored in the orbital motion of the sub-clusters that are not able to merge into the central clusters 2) frequent hierarchical mergers in the shallower profiles lead to further losses of mass and angular momentum via violent relaxation and tidal disruption. Encouragingly, the degree of cluster rotations in steeper profiles is consistent with recent observations of young and intermediate-age clusters. We speculate that rotating globular clusters are likely formed via an ‘accretion’ mode from centrally-concentrated clouds in the early Universe.

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Formation of supermassive black hole seeds in nuclear star clusters via gas accretion and runaway collisions

Monthly Notices of the Royal Astronomical Society ◽

10.1093/mnras/stab402 ◽

2021 ◽

Author(s):

Arpan Das ◽

Dominik R G Schleicher ◽

Nathan W C Leigh ◽

Tjarda C N Boekholt

Keyword(s):

Black Holes ◽

Initial Conditions ◽

High Redshift ◽

Star Clusters ◽

Gas Reservoir ◽

Highly Sensitive ◽

Stellar Collisions ◽

Key Variables ◽

Chaotic Nature ◽

Gas Accretion

Abstract More than two hundred supermassive black holes (SMBHs) of masses ≳ 109 M⊙ have been discovered at z ≳ 6. One promising pathway for the formation of SMBHs is through the collapse of supermassive stars (SMSs) with masses ∼103 − 5 M⊙ into seed black holes which could grow upto few times 109 M⊙ SMBHs observed at z ∼ 7. In this paper, we explore how SMSs with masses ∼103 − 5 M⊙ could be formed via gas accretion and runaway stellar collisions in high-redshift, metal-poor nuclear star clusters (NSCs) using idealised N-body simulations. We explore physically motivated accretion scenarios, e.g. Bondi-Hoyle-Lyttleton accretion and Eddington accretion, as well as simplified scenarios such as constant accretions. While gas is present, the accretion timescale remains considerably shorter than the timescale for collisions with the most massive object (MMO). However, overall the timescale for collisions between any two stars in the cluster can become comparable or shorter than the accretion timescale, hence collisions still play a crucial role in determining the final mass of the SMSs. We find that the problem is highly sensitive to the initial conditions and our assumed recipe for the accretion, due to the highly chaotic nature of the problem. The key variables that determine the mass growth mechanism are the mass of the MMO and the gas reservoir that is available for the accretion. Depending on different conditions, SMSs of masses ∼103 − 5 M⊙ can form for all three accretion scenarios considered in this work.

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Efficiency of thermal conduction in a magnetized circumgalactic medium

Monthly Notices of the Royal Astronomical Society ◽

10.1093/mnras/stab110 ◽

2021 ◽

Vol 502 (1) ◽

pp. 1263-1278

Author(s):

Richard Kooij ◽

Asger Grønnow ◽

Filippo Fraternali

Keyword(s):

Magnetic Field ◽

Thermal Conduction ◽

Large Temperature ◽

Gas Condensation ◽

Circumgalactic Medium ◽

Field Lines ◽

Gas Accretion ◽

Cloud Evolution ◽

The Magnetic Field ◽

Cold Gas

ABSTRACT The large temperature difference between cold gas clouds around galaxies and the hot haloes that they are moving through suggests that thermal conduction could play an important role in the circumgalactic medium. However, thermal conduction in the presence of a magnetic field is highly anisotropic, being strongly suppressed in the direction perpendicular to the magnetic field lines. This is commonly modelled by using a simple prescription that assumes that thermal conduction is isotropic at a certain efficiency f < 1, but its precise value is largely unconstrained. We investigate the efficiency of thermal conduction by comparing the evolution of 3D hydrodynamical (HD) simulations of cold clouds moving through a hot medium, using artificially suppressed isotropic thermal conduction (with f), against 3D magnetohydrodynamical (MHD) simulations with (true) anisotropic thermal conduction. Our main diagnostic is the time evolution of the amount of cold gas in conditions representative of the lower (close to the disc) circumgalactic medium of a Milky-Way-like galaxy. We find that in almost every HD and MHD run, the amount of cold gas increases with time, indicating that hot gas condensation is an important phenomenon that can contribute to gas accretion on to galaxies. For the most realistic orientations of the magnetic field with respect to the cloud motion we find that f is in the range 0.03–0.15. Thermal conduction is thus always highly suppressed, but its effect on the cloud evolution is generally not negligible.

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Radial metallicity gradients with Galactic nebular probes

Proceedings of the International Astronomical Union ◽

10.1017/s1743921319004150 ◽

2018 ◽

Vol 14 (A30) ◽

pp. 240-241 ◽

Cited By ~ 1

Author(s):

Jorge García-Rojas

Keyword(s):

Milky Way ◽

Galactic Disc ◽

Formation And Evolution

AbstractThe study of radial metallicity gradients in the disc of the Milky Way is a powerful tool to understand the mechamisms that have been acting in the formation and evolution of the Galactic disc. In this proceeding, I will put the eye on some problems that should be carefully addressed to obtain precise determinations of the metallicity gradients.

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Detecting the halo heating from AGN feedback with ALMA

Monthly Notices of the Royal Astronomical Society ◽

10.1093/mnras/stz2945 ◽

2019 ◽

Vol 490 (4) ◽

pp. 5134-5146 ◽

Cited By ~ 2

Author(s):

S Brownson ◽

R Maiolino ◽

M Tazzari ◽

S Carniani ◽

N Henden

Keyword(s):

Star Formation ◽

Correction Factor ◽

Spatial Scales ◽

Complex Structure ◽

Host Galaxy ◽

Cosmological Simulations ◽

Beam Attenuation ◽

Gas Accretion ◽

Marginal Detection ◽

Compact Sources

ABSTRACT The Sunyaev–Zel’dovich (SZ) effect can potentially be used to investigate the heating of the circumgalactic medium and subsequent suppression of cold gas accretion on to the host galaxy caused by quasar feedback. We use a deep ALMA observation of HE0515-4414 in band 4, the most luminous quasar known at the peak of cosmic star formation (z = 1.7), to search for the SZ signal tracing the heating of the galaxy’s halo. ALMA’s sensitivity to a broad range of spatial scales enables us to disentangle emitting compact sources from the negative, extended SZ signal. We obtain a marginal SZ detection (∼3.3σ) on scales of about 300 kpc (30–40 arcsec), at the 0.2 mJy level, 0.5 mJy after applying a correction factor for primary beam attenuation and flux that is resolved out by the array. We show that our result is consistent with a simulated ALMA observation of a similar quasar in the fable cosmological simulations. We emphasize that detecting an SZ signal is more easily achieved in the visibility plane than in the (inferred) images. We also confirm a marginal detection (3.2σ) of a potential SZ dip on smaller scales (<100 kpc) already claimed by other authors, possibly highlighting the complex structure of the halo heating. Finally, we use SZ maps from the fable cosmological simulations, convolved with ALMA simulations, to illustrate that band 3 observations are much more effective in detecting the SZ signal with higher significance, and discuss the optimal observing strategy.

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Modelling the Galactic disc: perturbed distribution functions in the presence of spiral arms

Monthly Notices of the Royal Astronomical Society ◽

10.1093/mnras/stw171 ◽

2016 ◽

Vol 457 (3) ◽

pp. 2569-2582 ◽

Cited By ~ 51

Author(s):

Giacomo Monari ◽

Benoit Famaey ◽

Arnaud Siebert

Keyword(s):

Distribution Functions ◽

Galactic Disc ◽

Spiral Arms

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Formation of supermassive black holes in galactic nuclei – I. Delivering seed intermediate-mass black holes in massive stellar clusters

Monthly Notices of the Royal Astronomical Society ◽

10.1093/mnras/stab113 ◽

2021 ◽

Vol 502 (2) ◽

pp. 2682-2700

Author(s):

Abbas Askar ◽

Melvyn B Davies ◽

Ross P Church

Keyword(s):

Black Holes ◽

Galactic Nuclei ◽

Supermassive Black Holes ◽

Stellar Clusters ◽

Orbital Eccentricity ◽

Intermediate Mass ◽

Stellar Cluster ◽

Wave Emission ◽

Gas Accretion ◽

Intermediate Mass Black Holes

ABSTRACT Supermassive black holes (SMBHs) are found in most galactic nuclei. A significant fraction of these nuclei also contains a nuclear stellar cluster (NSC) surrounding the SMBH. In this paper, we consider the idea that the NSC forms first, from the merger of several stellar clusters that may contain intermediate-mass black holes (IMBHs). These IMBHs can subsequently grow in the NSC and form an SMBH. We carry out N-body simulations of the simultaneous merger of three stellar clusters to form an NSC, and investigate the outcome of simulated runs containing zero, one, two, and three IMBHs. We find that IMBHs can efficiently sink to the centre of the merged cluster. If multiple merging clusters contain an IMBH, we find that an IMBH binary is likely to form and subsequently merge by gravitational wave emission. We show that these mergers are catalyzed by dynamical interactions with surrounding stars, which systematically harden the binary and increase its orbital eccentricity. The seed SMBH will be ejected from the NSC by the recoil kick produced when two IMBHs merge, if their mass ratio q ≳ 0.15. If the seed is ejected then no SMBH will form in the NSC. This is a natural pathway to explain those galactic nuclei that contain an NSC but apparently lack an SMBH, such as M33. However, if an IMBH is retained then it can seed the growth of an SMBH through gas accretion and tidal disruption of stars.

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Galaxy Dynamics: Secular Evolution and Accretion

Proceedings of the International Astronomical Union ◽

10.1017/s1743921311017522 ◽

2010 ◽

Vol 6 (S271) ◽

pp. 119-126 ◽

Cited By ~ 1

Author(s):

Francoise Combes

Keyword(s):

Angular Momentum ◽

Galaxy Evolution ◽

Resonant Scattering ◽

Relative Role ◽

Radial Migration ◽

Galaxy Dynamics ◽

Secular Evolution ◽

Minor Mergers ◽

Gas Accretion

AbstractRecent results are reviewed on galaxy dynamics, bar evolution, destruction and re-formation, cold gas accretion, gas radial flows and AGN fueling, minor mergers. Some problems of galaxy evolution are discussed in particular, exchange of angular momentum, radial migration through resonant scattering, and consequences on abundance gradients, the frequency of bulgeless galaxies, and the relative role of secular evolution and hierarchical formation.

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