scholarly journals Angular Momentum Accretion onto Disc Galaxies

2018 ◽  
Vol 14 (A30) ◽  
pp. 228-232
Author(s):  
Filippo Fraternali ◽  
Gabriele Pezzulli
Keyword(s):  
Angular Momentum ◽  
Star Formation ◽  
Momentum Distribution ◽  
Intergalactic Medium ◽  
Star Forming ◽  
Gas Accretion ◽  
Hot Corona ◽  
Inside Out ◽  
Disc Galaxies ◽  
Hubble Time

AbstractThroughout the Hubble time, gas makes its way from the intergalactic medium into galaxies fuelling their star formation and promoting their growth. One of the key properties of the accreting gas is its angular momentum, which has profound implications for the evolution of, in particular, disc galaxies. Here, we discuss how to infer the angular momentum of the accreting gas using observations of present-day galaxy discs. We first summarize evidence for ongoing inside-out growth of star forming discs. We then focus on the chemistry of the discs and show how the observed metallicity gradients can be explained if gas accretes onto a disc rotating with a velocity 20 – 30% lower than the local circular speed. We also show that these gradients are incompatible with accretion occurring at the edge of the discs and flowing radially inward. Finally, we investigate gas accretion from a hot corona with a cosmological angular momentum distribution and describe how simple models of rotating coronae guarantee the inside-out growth of disc galaxies.

scholarly journals Different modes of star formation – II. Gas accretion phase of initially subcritical star-forming clouds

2020 ◽  
Vol 494 (1) ◽  
pp. 827-845 ◽  
Author(s):  
Masahiro N Machida ◽  
Shantanu Basu
Keyword(s):  
Angular Momentum ◽  
Star Formation ◽  
Magnetic Flux ◽  
Flux Ratio ◽  
Ohmic Dissipation ◽  
Star Forming ◽  
Rotation Direction ◽  
Magnetic Braking ◽  
Magnetohydrodynamic Simulations ◽  
Gas Accretion

ABSTRACT The accretion phase of star formation is investigated in magnetically dominated clouds that have an initial subcritical mass-to-flux ratio. We employ non-ideal magnetohydrodynamic simulations that include ambipolar diffusion and ohmic dissipation. During the early prestellar phase, the mass-to-flux ratio rises towards the critical value for collapse, and during this time the angular momentum of the cloud core is reduced significantly by magnetic braking. Once a protostar is formed in the core, the accretion phase is characterized by the presence of a small amount of angular momentum but a large amount of magnetic flux in the near-protostellar environment. The low angular momentum leads to a very small (or even non-existent) disc and weak outflow, while the large magnetic flux can lead to an interchange instability that rapidly removes flux from the central region. The effective magnetic braking in the early collapse phase can even lead to a counterrotating disc and outflow, in which the rotation direction of the disc and outflow is opposite to that of the infalling envelope. The solutions with a counterrotating disc, tiny disc, or non-existent disc (direct collapse) are unique outcomes that are realized in collapse from magnetically dominated clouds with an initial subcritical mass-to-flux ratio.

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

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.

scholarly journals Planck’s dusty GEMS

2018 ◽  
Vol 620 ◽  
pp. A60 ◽  
Author(s):  
R. Cañameras ◽  
N. P. H. Nesvadba ◽  
M. Limousin ◽  
H. Dole ◽  
R. Kneissl ◽  
...  
Keyword(s):  
Star Formation ◽  
Near Infrared ◽  
Infrared Imaging ◽  
High Redshift ◽  
Dust Emission ◽  
Galaxy Cluster ◽  
Star Forming ◽  
The Galaxy ◽  
Mass Outflow ◽  
Gas Accretion

We report the discovery of a molecular wind signature from a massive intensely star-forming clump of a few 109 M⊙, in the strongly gravitationally lensed submillimeter galaxy “the Emerald” (PLCK_G165.7+49.0) at z = 2.236. The Emerald is amongst the brightest high-redshift galaxies on the submillimeter sky, and was initially discovered with the Planck satellite. The system contains two magnificient structures with projected lengths of 28.5″ and 21″ formed by multiple, near-infrared arcs, falling behind a massive galaxy cluster at z = 0.35, as well as an adjacent filament that has so far escaped discovery in other wavebands. We used HST/WFC3 and CFHT optical and near-infrared imaging together with IRAM and SMA interferometry of the CO(4–3) line and 850 μm dust emission to characterize the foreground lensing mass distribution, construct a lens model with LENSTOOL, and calculate gravitational magnification factors between 20 and 50 in most of the source. The majority of the star formation takes place within two massive star-forming clumps which are marginally gravitationally bound and embedded in a 9 × 1010 M⊙, fragmented disk with 20% gas fraction. The stellar continuum morphology is much smoother and also well resolved perpendicular to the magnification axis. One of the clumps shows a pronounced blue wing in the CO(4–3) line profile, which we interpret as a wind signature. The mass outflow rates are high enough for us to suspect that the clump might become unbound within a few tens of Myr, unless the outflowing gas can be replenished by gas accretion from the surrounding disk. The velocity offset of –200 km s−1 is above the escape velocity of the clump, but not that of the galaxy overall, suggesting that much of this material might ultimately rain back onto the galaxy and contribute to fueling subsequent star formation.

scholarly journals A new method to derive star formation histories in dwarf galaxies

2018 ◽  
Vol 14 (S344) ◽  
pp. 267-270
Author(s):  
Marius Čeponis ◽  
Rima Stonkutė ◽  
Vladas Vansevičius
Keyword(s):  
Star Formation ◽  
New Method ◽  
Star Forming ◽  
Stellar Photometry ◽  
Star Forming Regions ◽  
Density Maps ◽  
Irregular Galaxies ◽  
Star Formation Histories ◽  
Dwarf Irregular Galaxies ◽  
Inside Out

AbstractWe present a new method to derive 2D star formation histories in dwarf irregular galaxies. Based on multicolor stellar photometry data we have found that in the Leo A galaxy during the last ∽400 Myr star formation was propagating according to the inside-out scenario. Star-forming regions have spread strongly asymmetrically from the center and their present day distribution correlates well with the Hi surface density maps.

scholarly journals The lifecycle of molecular clouds in nearby star-forming disc galaxies

2019 ◽  
Vol 493 (2) ◽  
pp. 2872-2909 ◽  
Author(s):  
Mélanie Chevance ◽  
J M Diederik Kruijssen ◽  
Alexander P S Hygate ◽  
Andreas Schruba ◽  
Steven N Longmore ◽  
...  
Keyword(s):  
Star Formation ◽  
Flux Ratio ◽  
Molecular Gas ◽  
H Ii Regions ◽  
Dynamical Processes ◽  
Nearby Star ◽  
Star Forming ◽  
Spatially Resolved ◽  
Stellar Feedback ◽  
Disc Galaxies

ABSTRACT It remains a major challenge to derive a theory of cloud-scale ($\lesssim100$ pc) star formation and feedback, describing how galaxies convert gas into stars as a function of the galactic environment. Progress has been hampered by a lack of robust empirical constraints on the giant molecular cloud (GMC) lifecycle. We address this problem by systematically applying a new statistical method for measuring the evolutionary timeline of the GMC lifecycle, star formation, and feedback to a sample of nine nearby disc galaxies, observed as part of the PHANGS-ALMA survey. We measure the spatially resolved (∼100 pc) CO-to-H α flux ratio and find a universal de-correlation between molecular gas and young stars on GMC scales, allowing us to quantify the underlying evolutionary timeline. GMC lifetimes are short, typically $10\!-\!30\,{\rm Myr}$, and exhibit environmental variation, between and within galaxies. At kpc-scale molecular gas surface densities $\Sigma _{\rm H_2}\ge 8\,\rm {M_\odot}\,{{\rm pc}}^{-2}$, the GMC lifetime correlates with time-scales for galactic dynamical processes, whereas at $\Sigma _{\rm H_2}\le 8\,\rm {M_\odot}\,{{\rm pc}}^{-2}$ GMCs decouple from galactic dynamics and live for an internal dynamical time-scale. After a long inert phase without massive star formation traced by H α (75–90 per cent of the cloud lifetime), GMCs disperse within just $1\!-\!5\,{\rm Myr}$ once massive stars emerge. The dispersal is most likely due to early stellar feedback, causing GMCs to achieve integrated star formation efficiencies of 4–10 per cent. These results show that galactic star formation is governed by cloud-scale, environmentally dependent, dynamical processes driving rapid evolutionary cycling. GMCs and H ii regions are the fundamental units undergoing these lifecycles, with mean separations of $100\!-\!300\,{{\rm pc}}$ in star-forming discs. Future work should characterize the multiscale physics and mass flows driving these lifecycles.

scholarly journals The role of external gas accretion on galaxy transformations, and evidence of such accretion

2012 ◽  
Vol 10 (H16) ◽  
pp. 366-366
Author(s):  
Françoise Combes
Keyword(s):  
Star Formation ◽  
Mass Relation ◽  
Galaxy Interactions ◽  
Radial Migration ◽  
Secular Evolution ◽  
Gas Accretion ◽  
Bulge Formation ◽  
Inside Out

AbstractContinuously accreting matter from cosmic filaments is one of the main way to assemble mass for galaxies (Keres et al.2005, Dekel et al.2009). This external accretion accelerates secular processes, and maintain star formation, but also bar and spiral formation (Bournaud & Combes 2002), and consequent radial migration. Secular evolution may alleviate the problem of too massive bulge formation in the standard LCDM hierarchical scenario. Inside out formation of galaxies may account for the evolution of the size-mass relation and evolution with redshift. I will show how gas accretion from the inter galactic medium can mimick perturbations due to galaxy interactions (cf Figure 1), and I will describe evidence of such accretion, through warps, polar rings or damped Lyman-α systems.

scholarly journals Warps and Accretion

2010 ◽  
Vol 6 (S277) ◽  
pp. 71-74 ◽  
Author(s):  
Gyula I. G. Józsa
Keyword(s):  
Star Formation ◽  
Intergalactic Medium ◽  
Ambient Medium ◽  
Basic Feature ◽  
Optical Disk ◽  
Disk Galaxies ◽  
Galactic Disks ◽  
Star Forming ◽  
Show Evidence ◽  
Excitation Mechanisms

AbstractWarps are a basic feature of disk galaxies. Usually they occur at radii where the optical disk fades and become most pronounced in the outermost gaseous disks.As such, warps present a massive reservoir to replenish star forming material in the inner, star forming disks. Furthermore, some possible excitation mechanisms for warps connect their formation to the accretion of extragalctic material. Interactions or mergers with gas-rich companions or the direct accretion of the ambient intergalactic medium might lead to the formation of warps, at the same time supplementing fuel to maintain star formation in galactic disks.Employing a number of H i studies of warped galaxies, including ultra-deep observations of the prototype warped galaxies NGC 5907 and NGC 4013, I discuss whether the observed kinematics may show evidence for a connection of warps and accretion from the ambient medium.

Super-rotating protostellar jets

2020 ◽  
Author(s):  
Yuko Matsushita ◽  
Satoko Takahashi ◽  
Shun Ishii ◽  
Kohji Tomisaka ◽  
Paul Ho ◽  
...  
Keyword(s):  
Angular Momentum ◽  
Star Formation ◽  
Formation Process ◽  
Rotation Velocity ◽  
Solar Mass ◽  
Large Rotation ◽  
Star Forming ◽  
Disk Wind ◽  
Star Forming Regions ◽  
Protostellar Jets

Abstract Protostellar jets are most striking phenomena in star-forming regions and considered to be an essential ingredient in the star formation process. Stars form in gravitationally collapsing clouds. The mass of protostar at its birth is equivalent to Jovian mass or 0.1 percent of the solar mass. After the birth, the protostar acquires its mass by accreting material from a surrounding rotation disk embedded in an infalling envelope that is a remnant of the natal cloud of the star. Protostellar jets are believed to expel the excess angular momentum from the circumstellar region that allows accretion on to the star. Here, we report the detection of super-rotating jets driven from a protostar FIR 6b (HOPS 60) in Orion Molecular Cloud-2. The jet rotation velocity exceeds 20kms-1 and the specific angular momentum of the jet is as large as ∼ 1022cm2s-1, which hitherto are the largest that have been observed in protostellar jets. The extraordinary large rotation velocity and specific angular momentum can be explained by a magnetohydrodynamic disk wind. This is clear evidence that magnetic fields play a crucial role for protostellar evolution and that angular momentum is removed by protostellar jets.

scholarly journals The build-up of the outskirts of distant star-forming galaxies at z ~ 2

2016 ◽  
Vol 11 (S321) ◽  
pp. 327-329 ◽  
Author(s):  
Sandro Tacchella ◽  
C. Marcella Carollo ◽  
Avishai Dekel ◽  
Natascha Förster Schreiber ◽  
Alvio Renzini ◽  
...  
Keyword(s):  
Star Formation ◽  
Formation Rate ◽  
Stellar Mass ◽  
Mass Star ◽  
Intermediate Mass ◽  
Massive Galaxies ◽  
Star Forming ◽  
Star Formation Activity ◽  
Dust Attenuation ◽  
Inside Out

AbstractIn order to constrain – and understand – the growth of galaxies, we present a sample of ~ 30 galaxies at z ~ 2 with resolved distribution of stellar mass, star-formation rate, and dust attenuation on scales of ~ 1 kpc. We find that low- and intermediate-mass galaxies grow self-similarly, doubling their stellar mass in the centers and outskirts with the same pace. More massive galaxies (~ 1011 M⊙) have a reduced star-formation activity in their center: they grow mostly in the outskirts (inside-out quenching / formation). Similar trends are find in cosmological zoom-in simulations, highlighting that high stellar mass densities are formed in a gas-rich compaction phase. This nuclear ‘starburst’ phase is followed by a suppressed star-formation activity in the center, resulting in growth of the outskirts. All in all, we put forward that we witness at z ~ 2 the dissipative formation of z = 0 M* early-type galaxies.

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

2019 ◽  
Vol 489 (1) ◽  
pp. 1436-1450 ◽  
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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