We study the initial mass function (IMF) and hosting halo properties of intermediate-mass black holes (IMBHs, 104−6 M⊙) formed inside metal-free, UV-illuminated atomic-cooling haloes (virial ...temperature T
vir ≥ 104 K) either via the direct collapse of the gas or via an intermediate supermassive star (SMS) stage. These IMBHs have been recently advocated as the seeds of the supermassive black holes observed at z ≈ 6. We achieve this goal in three steps: (a) we derive the gas accretion rate for a proto-SMS to undergo General Relativity instability and produce a direct collapse black hole (DCBH) or to enter the zero-age main sequence and later collapse into an IMBH; (b) we use merger-tree simulations to select atomic-cooling haloes in which either a DCBH or SMS can form and grow, accounting for metal enrichment and major mergers that halt the growth of the proto-SMS by gas fragmentation. We derive the properties of the hosting haloes and the mass distribution of black holes at this stage, and dub it the ‘birth mass function’; (c) we follow the further growth of the DCBH by accreting the leftover gas in the parent halo and compute the final IMBH mass. We consider two extreme cases in which minihaloes (T
vir < 104 K) can (fertile) or cannot (sterile) form stars and pollute their gas leading to a different IMBH IMF. In the (fiducial) fertile case, the IMF is bimodal extending over a broad range of masses, M ≈ (0.5–20) × 105 M⊙, and the DCBH accretion phase lasts from 10 to 100 Myr. If minihaloes are sterile, the IMF spans the narrower mass range M ≈ (1–2.8) × 106 M⊙, and the DCBH accretion phase is more extended (70–120 Myr). We conclude that a good seeding prescription is to populate haloes (a) of mass 7.5 < log (M
h/ M⊙) < 8, (b) in the redshift range 8 < z < 17, (c) with IMBH in the mass range 4.75 < (log M
•/ M⊙) < 6.25.
We present zoom-in, adaptive mesh refinement, high-resolution (...30 pc) simulations of high-redshift (z ... 6) galaxies with the aim of characterizing their internal properties and interstellar ...medium. Among other features, we adopt a star formation model based on a physically sound molecular hydrogen prescription, and introduce a novel scheme for supernova feedback, stellar winds and dust-mediated radiation pressure. In the zoom-in simulation, the target halo hosts 'Dahlia', a galaxy with a stellar mass M... = 1.6 x 10 super( 10) M..., representative of a typical z ~ 6 Lyman-break galaxy. Dahlia has a total H2 mass of 108.5 M... that is mainly concentrated in a disc-like structure of effective radius ...0.6 kpc and scale height ...200 pc. Frequent mergers drive fresh gas towards the centre of the disc, sustaining a star formation rate per unit area of ...15 M...yr super( -1) kpc super( -2). The disc is composed of dense (n ... 25 cm super( -3)), metal-rich (Z ... 0.5 Z...) gas that is pressure supported by radiation. We compute the 158 ...m Cii emission arising from Dahlia, and find that ...95 per cent of the total Cii luminosity ($$L_...\rm C\,\small ...II......\simeq 10 greater than or equal to ..7.5...\,...\rm L..._...\odot ...$$) arises from the H2 disc. Although 30 per cent of the Cii mass is transported out of the disc by outflows, such gas negligibly contributes to Cii emission, due to its low density (n ... 10 cm super( -3)) and metallicity (Z ... 10 super( -1) Z...). Dahlia is underluminous with respect to the local Cii-SFR relation; however, its luminosity is consistent with upper limits derived for most z ~ 6 galaxies. (ProQuest: ... denotes formulae/symbols omitted.)
A survey of high-z galaxies: serra simulations Pallottini, A; Ferrara, A; Gallerani, S ...
Monthly notices of the Royal Astronomical Society,
05/2022, Letnik:
513, Številka:
4
Journal Article
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ABSTRACT
We introduce serra, a suite of zoom-in high-resolution ($1.2\times 10^4 \, {\rm M}_{\odot }$, $\simeq 25\, {\rm {pc}}$ at z = 7.7) cosmological simulations including non-equilibrium ...chemistry and on-the-fly radiative transfer. The outputs are post-processed to derive galaxy ultraviolet (UV) + far-infrared (FIR) continuum and emission line properties. Results are compared with available multiwavelength data to constrain the physical properties e.g. star formation rates (SFRs), stellar/gas/dust mass, metallicity of high-redshift 6 ≲ z ≲ 15 galaxies. This flagship paper focuses on the z = 7.7 sub-sample, including 202 galaxies with stellar mass $10^7 \, {\rm M}_{\odot }\lesssim M_\star \lesssim 5\times 10^{10}\, {\rm M}_{\odot }$, and specific star formation rate ranging from ${\rm sSFR} \sim 100\, {\rm Gyr}^{-1}$ in young, low-mass galaxies to $\sim 10\, {\rm Gyr}^{-1}$ for older, massive ones. At this redshift, serra galaxies are typically bursty, i.e. they are located above the Schmidt–Kennicutt relation by a factor $\kappa _s = 3.03^{+4.9}_{-1.8}$, consistent with recent findings for O iii and C ii emitters at high z. They also show relatively large InfraRed eXcess (IRX = LFIR/LUV) values as a result of their compact/clumpy morphology effectively blocking the stellar UV luminosity. Note that this conclusion might be affected by insufficient spatial resolution at the molecular cloud level. We confirm that early galaxies lie on the standard C ii$\!-\!\rm SFR$ relation; their observed LOIII/LCII ≃ 1–10 ratios can be reproduced by a part of the serra galaxies without the need of a top-heavy initial mass function and/or anomalous C/O abundances. O i line intensities are similar to local ones, making ALMA high-z detections challenging but feasible ($\sim 6\, \rm h$ for an SFR of $50\, \, {\rm M}_{\odot }\, {\rm yr}^{-1}$).
The nucleosynthetic site of the rapid (
r
) neutron-capture process is currently being debated. The direct detection of the neutron star merger GW170817, through gravitational waves and ...electromagnetic radiation, has confirmed such events as important sources of the
r
-process elements. However, chemical evolution models are not able to reproduce the observed chemical abundances in the Milky Way when neutron star mergers are assumed to be the only
r
-process site and realistic time distributions of such events are taken into account. Now for the first time, we combine all the available observational evidence of the Milky Way and its dwarf galaxy satellites to show that the data can only be explained if there are (at least) two distinct
r
-process sites: a quick source with timescales comparable to core-collapse supernovae,
t
quick
≲ 10
8
yr, and a delayed source with characteristic timescales
t
delayed
≳ 4 Gyr. The delayed
r
-process source most probably originates in neutron star mergers, as the timescale fits well with that estimated for GW170817. Given the short timescales of the quick source, it is likely associated with massive stars, though a specific fast-track channel for compact object mergers cannot be excluded at this point. Our approach demonstrates that only by looking at all the available data will we be able to solve the puzzle that is the
r
-process.
Abstract
To improve our understanding of high-z galaxies, we study the impact of H2 chemistry on their evolution, morphology and observed properties. We compare two zoom-in high-resolution (30 pc) ...simulations of prototypical M
⋆ ∼ 1010 M⊙ galaxies at z = 6. The first, ‘Dahlia’, adopts an equilibrium model for H2 formation, while the second, ‘Althæa’, features an improved non-equilibrium chemistry network. The star formation rate (SFR) of the two galaxies is similar (within 50 per cent), and increases with time reaching values close to 100 M⊙ yr−1 at z = 6. They both have SFR–stellar mass relation consistent with observations, and a specific SFR of ≃5 Gyr−1. The main differences arise in the gas properties. The non-equilibrium chemistry determines the H → H2 transition to occur at densities >300 cm−3, i.e. about 10 times larger than predicted by the equilibrium model used for Dahlia. As a result, Althæa features a more clumpy and fragmented morphology, in turn making SN feedback more effective. Also, because of the lower density and weaker feedback, Dahlia sits 3σ away from the Schmidt–Kennicutt relation; Althæa, instead nicely agrees with observations. The different gas properties result in widely different observables. Althæa outshines Dahlia by a factor of 7 (15) in C
$\scriptstyle \rm II$
157.74 μm (H217.03 μm) line emission. Yet, Althæa is underluminous with respect to the locally observed C
$\scriptstyle \rm II$
–SFR relation. Whether this relation does not apply at high-z or the line luminosity is reduced by cosmic microwave background and metallicity effects remain as an open question.
We study the formation and evolution of a sample of Lyman break galaxies in the epoch of reionization by using high-resolution (similar to 10 pc), cosmological zoom-in simulations part of the SERRA ...suite. In SERRA, we follow the interstellar medium thermochemical non-equilibrium evolution and perform on-the-fly radiative transfer of the interstellar radiation field (ISRF). The simulation outputs are post-processed to compute the emission of far infrared lines (C II, N II, and O III). At z = 8, the most massive galaxy, 'Freesia', has an age t(star) similar or equal to 409 Myr, stellar mass M-star similar or equal to 4.2 x 10(9)M(circle dot), and a star formation rate (SFR), SFR similar or equal to 11.5M(circle dot) yr(-1), due to a recent burst. Freesia has two stellar components (A and B) separated by similar or equal to 2.5 kpc; other 11 galaxies are found within 56.9 +/- 21.6 kpc. The mean ISRF in the Habing band is G = 7.9G(0) and is spatially uniform; in contrast, the ionization parameter is U = 2(-2)(+20) x 10(-3), and has a patchy distribution peaked at the location of star-forming sites. The resulting ionizing escape fraction from Freesia is f(esc) similar or equal to 2 per cent. While C II emission is extended (radius 1.54 kpc), O III is concentrated in Freesia-Lambda (0.85 kpc), where the ratio Sigma(O III)/Sigma(C II) similar or equal to 10. As many high-z galaxies, Freesia lies below the local C II-SFR relation. We show that this is the general consequence of a starburst phase (pushing the galaxy above the Kennicutt-Schmidt relation) that disrupts/photodissociates the emitting molecular clouds around star-forming sites. Metallicity has a sub-dominant impact on the amplitude of C II-SFR deviations.
We study the impact of star-forming minihaloes, and the initial mass function (IMF) of Population III (Pop III) stars, on the Galactic halo metallicity distribution function (MDF) and on the ...properties of C-enhanced and C-normal stars at Fe/H < -3. For our investigation we use a data-constrained merger tree model for the Milky Way formation, which has been improved to self-consistently describe the physical processes regulating star formation in minihaloes, including the poor sampling of the Pop III IMF. We find that only when star-forming minihaloes are included the low-Fe tail of the MDF is correctly reproduced, showing a plateau that is built up by C-enhanced metal-poor stars imprinted by primordial faint supernovae. The incomplete sampling of the Pop III IMF in inefficiently star-forming minihaloes (<10 super( -3) M... yr super( -1)) strongly limits the formation of pair-instability supernovae (PISNe), with progenitor masses mPopIII = 140-260 M..., even when a flat Pop III IMF is assumed. Second-generation stars formed in environments polluted at >50 per cent level by PISNe are thus extremely rare, corresponding to ...0.25 per cent of the total stellar population at Fe/H < -2, which is consistent with recent observations. The low-Fe tail of the MDF strongly depends on the Pop III IMF shape and mass range. Given the current statistics, we find that a flat Pop III IMF model with mPopIII = 10-300 M... is disfavoured by observations. We present testable predictions for Pop III stars extending down to lower masses, with mPopIII = 0.1-300 M... (ProQuest: ... denotes formulae/symbols omitted.)
From ESO VLT/FLAMES/GIRAFFE spectra, abundance measurements of Zn have been made in ≈100 individual red giant branch (RGB) stars in the Sculptor dwarf spheroidal galaxy. This is the largest sample of ...individual Zn abundance measurements within a stellar system beyond the Milky Way. In the observed metallicity range, −2.7 ≤ Fe/H ≤ −0.9, the general trend of Zn abundances in Sculptor is similar to that of α-elements. That is, super-solar abundance ratios of Zn/Fe at low metallicities, which decrease with increasing Fe/H, eventually reaching subsolar values. However, at the higher metallicities in Sculptor, Fe/H ≳ −1.8, we find a significant scatter, −0.8 ≲ Zn/Fe ≲ +0.4, which is not seen in any α-element. Our results are consistent with previous observations of a limited number of stars in Sculptor and in other dwarf galaxies. These results suggest that zinc has a complex nucleosynthetic origin, behaving neither completely like an α- nor an iron-peak element.
We study cosmic metal enrichment via adaptive mesh refinement hydrodynamical simulations in a (10 Mpc h...)3 volume following the Population III (PopIII)-PopII transition and for different PopIII ...initial mass function (IMFs). We have analysed the joint evolution of metal enrichment on galactic and intergalactic scales at z = 6 and z = 4. Galaxies account for ...9 per cent of the baryonic mass; the remaining gas resides in the diffuse phases: (a) voids, i.e. regions with extremely low density (... ≤ 1), (b) the true intergalactic medium (IGM, 1 < ... ≤ 10) and (c) the circumgalactic medium (CGM, 10 < ... ≤ 10...), the interface between the IGM and galaxies. At z = 6, a galactic mass-metallicity relation is established. At z = 4, galaxies with a stellar mass M* ... 10... M... show log(O/H)+12=8.19, consistent with observations. The total amount of heavy elements rises from ...=1.52x10... at z = 6 to 8.05 x 10... at z = 4. Metals in galaxies make up to ...0.89 of such budget at z = 6; this fraction increases to ...0.95 at z = 4. At z = 6 (z = 4), the remaining metals are distributed in CGM/IGM/voids with the following mass fractions: 0.06/0.04/0.01 (0.03/0.02/0.01). Analogously to galaxies, at z = 4 a density-metallicity (...-Z) relation is in place for the diffuse phases: the IGM/voids have a spatially uniform metallicity, Z ... 10... Z...; in the CGM, Z steeply rises with density up to ...10... Z... In all diffuse phases, a considerable fraction of metals is in a warm/hot (T...>10...K) state. Due to these physical conditions, Civ absorption line experiments can probe only ...2 per cent of the total carbon present in the IGM/CGM; however, metal absorption line spectra are very effective tools to study reionization. Finally, the PopIII star formation history is almost insensitive to the chosen PopIII IMF. PopIII stars are preferentially formed in truly pristine (Z = 0) gas pockets, well outside polluted regions created by previous star formation episodes. (ProQuest: ... denotes formulae/symbols omitted.)
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