Nir Mandelker

Compaction and quenching of high-z galaxies in cosmological simulations: blue and red nuggets

We use cosmological simulations to study a characteristic evolution pattern of high redshift galaxies. Early, stream-fed, highly perturbed, gas-rich discs undergo phases of dissipative contraction into compact, star-forming systems (blue nuggets) at z~4-2. The peak of gas compaction marks the onset of central gas depletion and inside-out quenching into compact ellipticals (red nuggets) by z~2. These are sometimes surrounded by gas rings or grow extended dry stellar envelopes. The compaction occurs at a roughly constant specific star-formation rate (SFR), and the quenching occurs at a constant stellar surface density within the inner kpc (

Rotational support of giant clumps in high-z disc galaxies

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Clumpy Galaxies in Candels: I. The Definition of UV Clumps and the Fraction of Clumpy Galaxies at 0.5 < Z < 3

). Massive galaxies quench earlier, faster, and at a higher

The population of giant clumps in simulated high-z galaxies: in situ and ex situ migration and survival

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Evolution of density profiles in high-z galaxies: compaction and quenching inside-out

than lower-mass galaxies, which compactify and attempt to quench more than once. This evolution pattern is consistent with the way galaxies populate the SFR-radius-mass space, and with gradients and scatter across the main sequence. The compaction is triggered by an intense inflow episode, involving (mostly minor) mergers, counter-rotating streams or recycled gas, and is commonly associated with violent disc instability. The contraction is dissipative, with the inflow rate >SFR, and the maximum

Star formation and clumps in cosmological galaxy simulations with radiation pressure feedback

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Giant clumps in simulated high-z Galaxies: properties, evolution and dependence on feedback

anti-correlated with the initial spin parameter, as predicted by Dekel & Burkert (2014). The central quenching is triggered by the high SFR and stellar/supernova feedback (possibly also AGN feedback) due to the high central gas density, while the central inflow weakens as the disc vanishes. Suppression of fresh gas supply by a hot halo allows the long-term maintenance of quenching once above a threshold halo mass, inducing the quenching downsizing.

The AGORA High-resolution Galaxy Simulations Comparison Project II: Isolated disk test

We address the internal support against total free-fall col lapse of the giant clumps that form by violent gravitational instability in high-z disc galaxies. Guidance is provided by an analytic model, where the proto-clumps are cut from a rotating disc and collapse to equilibrium while preserving angular momentum. This model predicts prograde clump rotation, which dominates the support if the clump has contracted to a surface-density contrast > ∼10. This is confirmed in hydro-AMR zoom-in simulations of galaxies in a cosmological context. In most high-z clumps, the centrifugal force dominates the support, R ≡ V 2 rot/V 2 circ > 0.5, where Vrot is the rotation velocity and the circular velocity Vcirc measures the potential well. The clump spin indeed tends to be in the sense of the global disc angular momentum, but substantial tilts are frequent, reflecting the highly wa rped nature of the high-z discs. Most clumps are in Jeans equilibrium, with the rest of the support provided by turbulence, partly driven by the gravitational instability itself. The general agreement between model and simulations indicates that angular-momentum loss or gain in most clumps is limited to a factor of two. Simulations of isolated gas-rich discs that resolve the clump substructure reveal that the cosmological simulations may overestimate R by ∼30%, but the dominance of rotational support at high z is not a resolution artifact. In turn, isolated gas-poor dis c simulations produce at z = 0 smaller gaseous non-rotating transient clouds, indicatin g that the difference in rotational support is associated with the fra ction of cold baryons in the disc. In our current cosmological simulations, the clump rotation velocity is typically more than twice the disc dispersion, Vrot ∼100kms −1 , but when beam smearing of >0.1 arcsec is imposed, the rotation signal is reduced to a small gradient of 6 30kms −1 kpc −1 across the clump. The velocity dispersion in the simulated clumps is comparable to the disc dispersion so it is expected to leave only a marginal signal for any beam smearing. Retrograde minor-merging galaxies could lead to massive clumps that do not show rotation even when marginally resolved. Testable predictions of the scenario as simulate d are that the mean stellar age of the clumps, and the stellar fraction, are declining linearl y with distance from the disc center.

Non-linear violent disc instability with high Toomre's Q in high-redshift clumpy disc galaxies

Although giant clumps of stars are crucial to galaxy formation and evolution, the most basic demographics of clumps are still uncertain, mainly because the definition of clumps has not been thoroughly discussed. In this paper, we study the basic demographics of clumps in star-forming galaxies (SFGs) at 0.5 0.5. The redshift evolution of Fclumpy changes with the stellar mass (M*) of the galaxies. Low-mass (log(M*/Msun)<9.8) galaxies keep an almost constant Fclumpy of about 60% from z~3.0 to z~0.5. Intermediate-mass and massive galaxies drop their Fclumpy from 55% at z~3.0 to 40% and 15%, respectively, at z~0.5. We find that (1) the trend of disk stabilization predicted by violent disk instability matches the Fclumpy trend of massive galaxies; (2) minor mergers are a viable explanation of the Fclumpy trend of intermediate-mass galaxies at z<1.5, given a realistic observability timescale; and (3) major mergers are unlikely responsible for the Fclumpy trend in all masses at z<1.5. The clump contribution to the rest-frame UV light of SFGs shows a broad peak around galaxies with log(M*/Msun)~10.5 at all redshifts, possibly linked to the molecular gas fraction of the galaxies. (Abridged)

Evolution of galaxy shapes from prolate to oblate through compaction events

We study the properties of giant clumps and their radial gradients in high-