Figure 16 - uploaded by Valentina Tamburello
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The evolution of the Q total Toomre parameter in run 16 (i.e. low resolution) on the left and run 22 (i.e. high resolution) on the right. At t 0 the adiabatic relaxation phase ends and, in the case with high resolution, the profile is more stable and smoother than in the case with low resolution. For run 16 the time steps 0.2, 0.5. and 0.8 Gyr correspond to the beginning of the clump formation phase, the middle of the clumpy phase and the end of it, respectively. Horizontal dashed line marks the threshold 1.5 for the stability of a disc. Note that for run 16 at t = 0.2 Gyr the sudden drop around 3.5 kpc corresponds to the radius at which clumps form.
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We study the effect of sub-grid physics, galaxy mass, structural parameters and resolution on the fragmentation of gas-rich
galaxy discs into massive star-forming clumps. The initial conditions are set up with the aid of the ARGO cosmological hydrodynamical
simulation. Blast-wave feedback does not suppress fragmentation, but reduces both the number...
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Citations
... The in situ formation of giant clumps is commonly attributed to Toomre instability (Toomre 1964;Dekel et al. 2009), where small fluctuations collapse to clumps as their self-gravity (Σ) overcomes turbulent pressure ( ) and rotational support ( ), namely once ∝ /Σ < 1. Fragmentation into massive ( c > ∼ 10 8 M ⊙ ) long lived clumps is commonly seen in simulations of isolated galaxy discs, especially when the gas fraction is greater than ∼ 50% (Fensch & Bournaud 2021), though Toomre-like instabilities manifest on multiple scales even when the gas fraction is as low as ∼ 20% (Renaud et al. 2021). Other studies of idealized isolated galaxies suggest that while linear Toomre instability (or a related spiral arm instability, Inoue & Yoshida 2018 is responsible for the initial fragmentation, this occurs on scales smaller than the observed giant clumps which are themselves agglomerations of many small sub-clumps, either physically bound or in projection (e.g Romeo & Agertz 2014;Agertz et al. 2015;Behrendt et al. 2015;Tamburello et al. 2015;Benincasa et al. 2019). However, the Toomre parameter is a linear concept applicable to axisymmetric systems, while the violently unstable discs at high redshift are far from being either linear or axisymmetric. ...
We address the formation of giant clumps in violently unstable gas-rich disc galaxies at cosmic noon. While these are commonly thought to originate from gravitational Toomre instability, cosmological simulations have indicated that clumps form even in regions where the Toomre $Q$ parameter is well above unity, which should be stable according to linear Toomre theory (Inoue et al., 2016). Examining one of these cosmological simulations, we find that it exhibits an excess in compressive modes of turbulence with converging motions. The energy in converging motions within proto-clump regions is $\sim 70\%$ of the total turbulent energy, compared to $\sim 17\%$ expected in equipartition. When averaged over the whole disc, $\sim 32\%$ of the turbulent energy is in converging motions, with a further $\sim 8\%$ in diverging motions. Thus, a total of $\sim 40\%$ of the turbulent energy is in compressive modes, with the rest in solenoidal modes, compared to the $(1/3)-(2/3)$ division expected in equipartition. By contrast, we find that in an isolated-disc simulation with similar properties, resembling high-$z$ star-forming galaxies, the energy in the different turbulence modes are in equipartition, both in proto-clump regions and over the whole disc. We conclude that the origin of the excessive converging motions in proto-clump regions is external to the disc, and propose several mechanisms that can induce them. This is an additional mechanism for clump formation, complementary to and possibly preceding gravitational instability.
... F örster Schreiber et al. 2009 ;Madau & Dickinson 2014 ;Murata et al. 2014 ;Bouwens et al. 2015 ;Zanella et al. 2015 ;Stott et al. 2016 ;Guo et al. 2018 ;Oesch et al. 2018 ;Romano et al. 2021 ;Sommovigo et al. 2021 ;Vanzella et al. 2022 ) and simulated (e.g. Bournaud et al. 2014 ;Tamburello et al. 2015 ;Buck et al. 2017 ;Lo v ell et al. 2021 ;Zanella et al. 2021 ;Calura et al. 2022 ;Pallottini et al. 2022 ;Vizgan et al. 2022 ) galaxies at high redshift represented a key step in the study of galaxy evolution in the early Universe. Recently, thanks to the first data from the James Webb Space Telescope ( JWST ), some studies have reached new and unexplored epochs, discovering E-mail: andrea.bolamperti@phd.unipd.it ...
We study the ultraviolet (UV) continuum β slope of a sample of 166 clumps, individual star-forming regions observed in high redshift galaxies. They are hosted by 67 galaxies with redshift between 2 and 6.2, strongly lensed by the Hubble Frontier Fields cluster of galaxies MACS J0416.1−2403. The β slope is sensitive to a variety of physical properties, such as the metallicity, the age of the stellar population, the dust attenuation throughout the galaxy, the stellar initial mass function (IMF), and the star-formation history (SFH). The aim of this study is to compare the β values of individual clumps with those measured on the entire galaxy, to investigate possible physical differences between these regions and their hosts. We found a median value of β ∼ −2.4, lower than that of integrated galaxies. This result confirms that clumps are sites of intense star formation, populated by young, massive stars, whose spectrum strongly emits in the UV. This is also consistent with the assumption that the dust extinction at the location of the clumps is lower than the average extinction of the galaxy, or that clumps have a different IMF or SFH. We made use of the correlations, discovered for high-redshift galaxies, of the β value with those of redshift and UV magnitude, MUV, finding that clumps follow the same relations, extended to much fainter magnitudes (MUV < −13). We also find evidence of eight clumps with extremely blue (β ≲ −2.7) slopes, which could be the signpost of low-metallicity stars and constrain the emissivity of ionizing photons at high redshift.
... The giant star-forming clumps do not necessarily require mergers and, in simulations, can be produced as a result of secular processes such as cold stream accretion ) with subsequent clump mergers (Tamburello et al. 2015). All of these processes can be at play in J1652, but in addition, its tidal tail indicates the possibility of a recent major merger. ...
Massive galaxies formed most actively at redshifts z = 1–3 during the period known as “cosmic noon.” Here we present an emission-line study of the extremely red quasar SDSSJ165202.64+172852.3’s host galaxy at z = 2.94, based on observations with the Near Infrared Spectrograph integral field unit on board JWST. We use standard emission-line diagnostic ratios to map the sources of gas ionization across the host and a swarm of companion galaxies. The quasar dominates the photoionization, but we also discover shock-excited regions orthogonal to the ionization cone and the quasar-driven outflow. These shocks could be merger-induced or—more likely, given the presence of a powerful galactic-scale quasar outflow—these are signatures of wide-angle outflows that can reach parts of the galaxy that are not directly illuminated by the quasar. Finally, the kinematically narrow emission associated with the host galaxy presents as a collection of 1 kpc–scale clumps forming stars at a rate of at least 200 M ⊙ yr ⁻¹ . The interstellar medium within these clumps shows high electron densities, reaching up to 3000 cm ⁻³ , with metallicities ranging from half to a third solar with a positive metallicity gradient, and V -band extinctions up to 3 mag. The star formation conditions are far more extreme in these regions than in local star-forming galaxies but consistent with those of massive galaxies at cosmic noon. The JWST observations simultaneously reveal an archetypal rapidly forming massive galaxy undergoing a merger, a clumpy starburst, an episode of obscured near-Eddington quasar activity, and an extremely powerful quasar outflow.
... But in early simulations, inefficient thermal feedback of supernovae resulted in overcooling, which then enhanced disc instability and star formation and led to an overproduction of giant clumps (Ceverino & Klypin 2009;Agertz et al. 2009b). More recently, various works within cosmological simulations and simulations of isolated disc galaxies were again focusing on disc fragmentation at high-, but including novel feedback recipes which systematically led to less fragmentation even in massive gas-rich discs and generally lower clump masses in the range 10 7 -10 8 M ⊙ (Tamburello et al. 2015;Behrendt et al. 2015;Moody et al. 2014;Mandelker et al. 2017;Oklopčić et al. 2017). It was further proposed that some of the most massive observed star forming clumps might not be the result of "in-situ" disc fragmentation, but rather they could be accreted cores of massive satellite galaxies (Mandelker et al. 2017;Oklopčić et al. 2017). ...
Using new high-resolution data of CO (2–1), Hα and Hβ obtained with the Northern Extended Millimeter Array (NOEMA) and the Multi-Unit Spectroscopic Explorer (MUSE) at the Very Large Telescope, we have performed a Toomre Q disc stability analysis and studied star formation, gas depletion times and other environmental parameters on sub-kpc scales within the z ∼ 0 galaxy SDSS J125013.84+073444.5 (LARS 8). The galaxy hosts a massive, clumpy disc and is a proto-typical analogue of main-sequence galaxies at z ∼ 1 − 2. We show that the massive (molecular) clumps in LARS 8 are the result of an extremely gravitationally unstable gas disc, with large scale instabilities found across the whole extent of the rotating disc, with only the innermost 500 pc being stabilized by its bulgelike structure. The radial profiles further reveal that – contrary to typical disc galaxies – the molecular gas depletion time decreases from more than 1 Gyr in the center to less than ∼100 Myr in the outskirts of the disc, supporting the findings of a Toomre-unstable disc. We further identified and analysed 12 individual massive molecular clumps. They are virialized and follow the mass-size relation, indicating that on local (cloud/clump) scales the stars form with efficiencies comparable to those in Milky Way clouds. The observed high star formation rate must thus be the result of triggering of cloud/clump formation over large scales due to disc instability. Our study provides evidence that ‘in-situ’ massive clump formation (as also observed at high redshifts) is very efficiently induced by large-scale instabilities.
... However other studies have questioned the importance of clumps for the evolution of galaxies. Efficient coupling of feedback energy to gas destroys clumps (Elmegreen et al. 2008;Hopkins et al. 2012) and many simulations that employ high feedback prescriptions have failed to find significant clumps or have found ones that do not contribute much to bulges (e.g., Tamburello et al. 2015). The short-lived clumps in the FIRE simulations do not manage to migrate to the bulge (Oklopčić et al. 2017), and may not even have been bound. ...
In Paper I, we showed that clumps in high-redshift galaxies, having a high star formation rate density (Σ SFR ), produce disks with two tracks in the [Fe/H]–[ α /Fe] chemical space, similar to that of the Milky Way’s (MW’s) thin+thick disks. Here we investigate the effect of clumps on the bulge’s chemistry. The chemistry of the MW’s bulge is comprised of a single track with two density peaks separated by a trough. We show that the bulge chemistry of an N -body + smoothed particle hydrodynamics clumpy simulation also has a single track. Star formation within the bulge is itself in the high-Σ SFR clumpy mode, which ensures that the bulge’s chemical track follows that of the thick disk at low [Fe/H] and then extends to high [Fe/H], where it peaks. The peak at low metallicity instead is comprised of a mixture of in situ stars and stars accreted via clumps. As a result, the trough between the peaks occurs at the end of the thick disk track. We find that the high-metallicity peak dominates near the mid-plane and declines in relative importance with height, as in the MW. The bulge is already rapidly rotating by the end of the clump epoch, with higher rotation at low [ α /Fe]. Thus clumpy star formation is able to simultaneously explain the chemodynamic trends of the MW’s bulge, thin+thick disks, and the splash.
... But in early simulations, inefficient thermal feedback of supernovae resulted in overcooling, which then enhanced disc instability and star formation and led to an overproduction of giant clumps (Ceverino & Klypin 2009;Agertz et al. 2009b). More recently, various works within cosmological simulations and simulations of isolated disc galaxies were again focusing on disc fragmentation at high-, but including novel feedback recipes which systematically led to less fragmentation even in massive gas-rich discs and generally lower clump masses in the range 10 7 -10 8 M (Tamburello et al. 2015;Behrendt et al. 2015;Moody et al. 2014;Mandelker et al. 2017;Oklopčić et al. 2017). It was further proposed that some of the most massive observed star forming clumps might not be the result of "in-situ" disc fragmentation, but rather they could be accreted cores of massive satellite galaxies (Mandelker et al. 2017;Oklopčić et al. 2017). ...
Using new high-resolution data of CO (2-1), H-alpha and H-beta obtained with the Northern Extended Millimeter Array (NOEMA) and the Multi-Unit Spectroscopic Explorer (MUSE) at the Very Large Telescope, we have performed a Toomre-Q disc stability analysis and studied star formation, gas depletion times and other environmental parameters on sub-kpc scales within the z~0 galaxy SDSS J125013.84+073444.5 (LARS 8). The galaxy hosts a massive, clumpy disc and is a proto-typical analogue of main-sequence galaxies at z~1-2. We show that the massive (molecular) clumps in LARS 8 are the result of an extremely gravitationally unstable gas disc, with large scale instabilities found across the whole extent of the rotating disc, with only the innermost 500 pc being stabilized by its bulgelike structure. The radial profiles further reveal that - contrary to typical disc galaxies - the molecular gas depletion time decreases from more than 1 Gyr in the center to less than ~100 Myr in the outskirts of the disc, supporting the findings of a Toomre-unstable disc. We further identified and analysed 12 individual massive molecular clumps. They are virialized and follow the mass-size relation, indicating that on local (cloud/clump) scales the stars form with efficiencies comparable to those in Milky Way clouds. The observed high star formation rate must thus be the result of triggering of cloud/clump formation over large scales due to disc instability. Our study provides evidence that "in-situ" massive clump formation (as also observed at high redshifts) is very efficiently induced by large-scale instabilities.
... In particular, fragmentation is almost invariably seen to occur along spiral arms generated in the initial phase of a gravitational instability in realistic discs on a variety of scales, hence clumps form in a gas flow having inherently a non-axisymmetric character (see, e.g. Boley et al. 2010 for protoplanetary disc scales or Tamburello et al. 2015 for galaxy-scale fragmentation). In addition, soon after fragmentation ensues, other effects matter in the nonlinear stage, which, by construction, cannot be captured by perturbation theory, such as the rotational support in clumps (Galvagni et al. 2012), and their vulnerability by local shear and stellar tidal forces (Galvagni & Mayer 2014;Müller et al. 2018). ...
We investigate the properties of stars born via gravitational instability in accretion discs around supermassive black holes (SMBHs) in active galactic nuclei (AGN), and how this varies with the SMBH mass, accretion rate, or viscosity. We show with geometrically thin, steady-state disc solutions that fragmentation results in different populations of stars when one considers the initial conditions (e.g. density and temperature of the gravitationally unstable regions). We find that opacity gaps in discs around 106 M⊙ SMBHs can trigger fragmentation at radii ≲ 10−2 pc, although the conditions lead to the formation of initially low stellar masses primarily at 0.1–0.5 M⊙. Discs around more massive SMBHs (MBH = 107 − 8 M⊙) form moderately massive or supermassive stars (the majority at 100 − 2 M⊙). Using linear migration estimates, we discuss three outcomes: stars migrate till they are tidally destroyed, accreted as extreme mass ratio inspirals (EMRIs), or leftover after disc dispersal. For a single AGN activity cycle, we find a lower-limit for the EMRI rate $R_{\rm emri}\sim 0\hbox{-}10^{-4} \, \rm yr^{-1}$ per AGN assuming a SF efficiency $\epsilon =1\hbox{-}30{{\ \rm per\ cent}}$. In cases where EMRIs occur, this implies a volumetric rate up to $0.5\hbox{-}10 \, \rm yr^{-1}\, Gpc^{-3}$ in the local Universe. The rates are particularly sensitive to model parameters for MBH = 106 M⊙, for which EMRIs only occur if stars can accrete to 10s of solar masses. Our results provide further evidence that gas-embedded EMRIs can contribute a substantial fraction of events detectable by milliHz gravitational wave detectors such as LISA. Our disc solutions suggest the presence of migration traps, as has been found for more massive SMBH discs. Finally, the surviving population of stars after the disc lifetime leaves implications for stellar discs in galactic nuclei.
... Efficient coupling of feedback energy to gas destroys clumps (Elmegreen et al. 2008;Hopkins et al. 2012) and many simulations that employ high feedback prescriptions have failed to find significant clumps or have found ones that do not contribute much to bulges (e.g. Tamburello et al. 2015). The short-lived clumps in the FIRE simulations do not manage to migrate to the bulge (Oklopčić et al. 2017), and may not even have been bound. ...
In Paper I we showed that clumps in high-redshift galaxies, having a high star formation rate density (\Sigma_SFR), produce disks with two tracks in the [Fe/H]-[\alpha/Fe] chemical space, similar to that of the Milky Way's (MW's) thin + thick disks. Here we investigate the effect of clumps on the bulge's chemistry. The chemistry of the MW's bulge is comprised of a single track with two density peaks separated by a trough. We show that the bulge chemistry of an N-body + smoothed particle hydrodynamics clumpy simulation also has a single track. Star formation within the bulge is itself in the high-\Sigma_SFR clumpy mode, which ensures that the bulge's chemical track follows that of the thick disk at low [Fe/H] and then extends to high [Fe/H], where it peaks. The peak at low metallicity instead is comprised of a mixture of in-situ stars and stars accreted via clumps. As a result, the trough between the peaks occurs at the end of the thick disk track. We find that the high-metallicity peak dominates near the mid-plane and declines in relative importance with height, as in the MW. The bulge is already rapidly rotating by the end of the clump epoch, with higher rotation at low [\alpha/Fe]. Thus clumpy star formation is able to simultaneously explain the chemodynamic trends of the MW's bulge, thin + thick disks and the Splash.
... The giant star-forming clumps do not necessarily require mergers and, in simulations, can be produced as a result of secular processes such as cold stream accretion ) with subsequent clump mergers (Tamburello et al. 2015). All of these processes can be in play in J1652, but in addition, its tidal tail indicates a possibility of a recent major merger. ...
Massive galaxies formed most actively at redshifts $z=1-3$ during the period known as `cosmic noon.' Here we present an emission-line study of an extremely red quasar SDSSJ165202.64+172852.3 host galaxy at $z=2.94$, based on observations with the Near Infrared Spectrograph (NIRSpec) integral field unit (IFU) on board JWST. We use standard emission-line diagnostic ratios to map the sources of gas ionization across the host and a swarm of companion galaxies. The quasar dominates the photoionization, but we also discover shock-excited regions orthogonal to the ionization cone and the quasar-driven outflow. These shocks could be merger-induced or -- more likely, given the presence of a powerful galactic-scale quasar outflow -- these are signatures of wide-angle outflows that can reach parts of the galaxy that are not directly illuminated by the quasar. Finally, the kinematically narrow emission associated with the host galaxy presents as a collection of 1 kpc-scale clumps forming stars at a rate of at least 200 $M_{\odot}$ yr$^{-1}$. The ISM within these clumps shows high electron densities, reaching up to 3,000 cm$^{-3}$ with metallicities ranging from half to a third solar with a positive metallicity gradient and V band extinctions up to 3 magnitudes. The star formation conditions are far more extreme in these regions than in local star-forming galaxies but consistent with that of massive galaxies at cosmic noon. JWST observations reveal an archetypical rapidly forming massive galaxy undergoing a merger, a clumpy starburst, an episode of obscured near-Eddington quasar activity, and an extremely powerful quasar outflow simultaneously.
... Recent studies have found evidence of bias toward larger clump radii and masses at low spatial resolution (Dessauges-Zavadsky et al. 2017;Cava et al. 2018). Furthermore, while lower-resolution simulations tended to favor larger, more massive (∼10 9 M e ) clumps (Mandelker et al. 2014), more recent higher-resolution simulations have found broader mass ranges spanning ∼10 7 -10 9 M e , with a greater number of smaller (∼10 7 M e ) clumps (Tamburello et al. 2015;Mandelker et al. 2017;Oklopčić et al. 2017). Lower-mass clump radii in these higher-resolution simulations are typically ∼100 pc, still notably larger than many clumps revealed in some high-redshift lensed galaxies. ...
Detailed observations of star-forming galaxies at high redshift are critical to understanding the formation and evolution of the earliest galaxies. Gravitational lensing provides an important boost, allowing observations at physical scales unreachable in unlensed galaxies. We present three lensed galaxies from the RELICS survey at z phot = 6–10, including the most highly magnified galaxy at z phot ∼ 6 (WHL 0137–zD1, dubbed the Sunrise Arc), the brightest known lensed galaxy at z phot ∼ 6 (MACS 0308–zD1), and the only spatially resolved galaxy currently known at z phot ∼ 10 (SPT 0615–JD). The Sunrise Arc contains seven star-forming clumps with delensed radii as small as 3 pc, the smallest spatial scales yet observed in a z > 6 galaxy, while SPT 0615–JD contains features measuring a few tens of parsecs. MACS 0308–zD1 contains an r ∼ 30 pc clump with a star formation rate (SFR) of ∼3 M ⊙ yr ⁻¹ , giving it an SFR surface density of Σ SFR ∼ 10 ³ M ⊙ yr ⁻¹ kpc ⁻² . These galaxies provide a unique window into small-scale star formation during the epoch of reionization. They will be excellent targets for future observations with JWST, including one approved program targeting the Sunrise Arc.
