ABSTRACT
The properties of quasar-host galaxies might be determined by the growth and feedback of their supermassive black holes (SMBHs, 108−10 M⊙). We investigate such connection with a suite of ...cosmological simulations of massive (halo mass ≈1012 M⊙) galaxies at z ≃ 6 that include a detailed subgrid multiphase gas and accretion model. BH seeds of initial mass 105 M⊙ grow mostly by gas accretion, and become SMBH by z = 6 setting on the observed MBH−M⋆ relation without the need for a boost factor. Although quasar feedback crucially controls the SMBH growth, its impact on the properties of the host galaxy at z = 6 is negligible. In our model, quasar activity can both quench (via gas heating) or enhance (by interstellar medium overpressurization) star formation. However, we find that the star formation history is insensitive to such modulation as it is largely dominated, at least at z > 6, by cold gas accretion from the environment that cannot be hindered by the quasar energy deposition. Although quasar-driven outflows can achieve velocities $\gt 1000~\rm km~s^{-1}$, only ≈4 per cent of the outflowing gas mass can actually escape from the host galaxy. These findings are only loosely constrained by available data, but can guide observational campaigns searching for signatures of quasar feedback in early galaxies.
The growth efficiency of high-redshift black holes Pacucci, Fabio; Volonteri, Marta; Ferrara, Andrea
Monthly notices of the Royal Astronomical Society,
09/2015, Letnik:
452, Številka:
2
Journal Article
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The observational evidence that Super-Massive Black Holes (M
• ∼ 109–10 M⊙) are already in place less than 1 Gyr after the big bang poses stringent time constraints on the growth efficiency of their ...seeds. Among proposed possibilities, the formation of massive (∼103–6 M⊙) seeds and/or the occurrence of super-Eddington (
$\dot{M}>\dot{M}_{{\rm Edd}}$
) accretion episodes may contribute to the solution of this problem. In this work, using a set of astrophysically motivated initial conditions, we analytically and numerically investigate the accretion flow on to high-redshift (z ∼ 10) black holes to understand the physical requirements favouring rapid and efficient growth. Our model identifies a ‘feeding-dominated’ accretion regime and a ‘feedback-limited’ one, the latter being characterized by intermittent (duty cycles
${\cal D} \lesssim 0.5$
) and inefficient growth, with recurring outflow episodes. We find that low-mass seeds (≲103–4 M⊙) evolve in the feedback-limited regime, while more massive seeds (≳105–6 M⊙) grow very rapidly as they are found in the feeding-dominated regime. In addition to the standard accretion model with a fixed matter–energy conversion factor (ϵ = 0.1), we have also explored slim disc models, appropriate for super-Eddington accretion, where radiation is trapped in the disc and the radiative efficiency is reduced (ϵ ≲ 0.04), which may ensure a continuous growth with
$\dot{M} \gg \dot{M}_{{\rm Edd}}$
(up to
${\sim } 300\,\dot{M}_{{\rm Edd}}$
in our simulations). Under these conditions, outflows play a negligible role and a black hole can accrete 80–100 per cent of the gas mass of the host halo (∼107 M⊙) in ∼10 Myr, while in feedback-limited systems we predict that black holes can accrete only up to ∼15 per cent of the available mass.
Recent data indicate that the cosmic ultraviolet emissivity decreased with decreasing redshift z near the end of reionization. Lacking evidence for very massive early stars, this could signal a ...decline with time in the mass-averaged escape fraction of ionizing radiation from galaxies 〈f
esc〉 at z 6. We calculate the evolution of ionization fronts in dark matter haloes which host gas in hydrostatic equilibrium at its cooling temperature floor (T 104 K for atomic hydrogen). We find a high escape fraction only for the lowest mass haloes with M < 108.7 M at (1 + z) = 10, provided their star formation efficiency f
10−3. Since the low-mass galaxy population is depleted by radiative feedback, we find that indeed 〈f
esc〉 decreases with time during reionization.
The cosmological 21 cm signal is a physics-rich probe of the early Universe, encoding information about both the ionization and the thermal history of the intergalactic medium (IGM). The latter is ...likely governed by X-rays from star formation processes inside very high redshift (z ≳ 15) galaxies. Due to the strong dependence of the mean free path on the photon energy, the X-ray spectral energy distribution (SED) can have a significant impact on the interferometric signal from the cosmic dawn. Recent Chandra observations of nearby, star-forming galaxies show that their SEDs are more complicated than is usually assumed in 21 cm studies. In particular, these galaxies have ubiquitous, sub-keV thermal emission from the hot interstellar medium (ISM), which generally dominates the soft X-ray luminosity (with energies ≲1 keV, sufficiently low to significantly interact with the IGM). Using illustrative soft and hard SEDs, we show that the IGM temperature fluctuations in the early Universe would be substantially increased if the X-ray spectra of the first galaxies were dominated by the hot ISM, compared with X-ray binaries with harder spectra. The associated large-scale power of the 21 cm signal would be higher by a factor of ∼3. More generally, we show that the peak in the redshift evolution of the large-scale (k ∼ 0.2 Mpc−1) 21 cm power is a robust probe of the soft-band SED of the first galaxies, and importantly, is not degenerate with their bolometric luminosities. On the other hand, the redshift of the peak constrains the X-ray luminosity and halo masses which host the first galaxies.
Massive black hole (MBH) seeds at redshift z ≳ 10 are now thought to be key ingredients to explain the presence of the supermassive (109–10 M⊙) black holes in place <1 Gyr after the big bang. Once ...formed, massive seeds grow and emit copious amounts of radiation by accreting the left-over halo gas; their spectrum can then provide crucial information on their evolution. By combining radiation-hydrodynamic and spectral synthesis codes, we simulate the time-evolving spectrum emerging from the host halo of a MBH seed with initial mass 105 M⊙, assuming both standard Eddington-limited accretion, or slim accretion discs, appropriate for super-Eddington flows. The emission occurs predominantly in the observed infrared-submm (1-1000 μm) and X-ray (0.1–100 keV) bands. Such signal should be easily detectable by JWSTaround ∼ 1 μm up to z ∼ 25, and by ATHENA (between 0.1 and 10 keV, up to z ∼ 15). Ultra-deep X-ray surveys like the Chandra Deep Field South could have already detected these systems up to z ∼ 15. Based on this, we provide an upper limit for the z ≳ 6 MBH mass density of ρ• ≲ 2.5 × 102 M⊙ Mpc−3 assuming standard Eddington-limited accretion. If accretion occurs in the slim disc mode the limits are much weaker, ρ• ≲ 7.6 × 103 M⊙ Mpc−3 in the most constraining case.
Abstract
We interpret the peculiar supersolar nitrogen abundance recently reported by the James Webb Space Telescope observations for GN-z11 (
z
= 10.6) using our state-of-the-art chemical evolution ...models. The observed CNO ratios can be successfully reproduced—independently of the adopted initial mass function, nucleosynthesis yields, and presence of supermassive (>1000
M
⊙
) stars—if the galaxy has undergone an intermittent star formation history with a quiescent phase lasting ∼100 Myr, separating two strong starbursts. Immediately after the second burst, Wolf–Rayet stars (up to 120
M
⊙
) become the dominant enrichment source, also temporarily (<1 Myr) enhancing particular elements (N, F, Na, and Al) and isotopes (
13
C and
18
O). Alternative explanations involving (i) single burst models, also including very massive stars and/or pair-instability supernovae, or (ii) pre-enrichment scenarios fail to match the data. Feedback-regulated, intermittent star formation might be common in early systems. Elemental abundances can be used to test this hypothesis and to get new insights on nuclear and stellar astrophysics.
Abstract JWST is providing a unique opportunity to directly study the feedback processes regulating star formation (SF) in early galaxies. The two z > 5 quiescent systems (JADES-GS-z7-01-QU and ...MACS0417-z5BBG) detected so far show a recent starburst after which SF is suppressed. To clarify whether such quenching is due to supernova (SN) feedback, we have developed a minimal physical model. We derive a condition on the minimum star formation rate, SFR min , lasting for a time interval Δ t b , required to quench SF in a galaxy at redshift z , with gas metallicity Z , and hosted by a halo of mass M h . We find that lower ( z , Z , M h ) systems are more easily quenched. We then apply the condition to JADES-GS-z7-01-QU ( z = 7.3, M ⋆ = 10 8.6 M ⊙ ) and MACS0417-z5BBG ( z = 5.2, M ⋆ = 10 7.6 M ⊙ ) and find that SN feedback largely fails to reproduce the observed quenched SF history. Alternatively, we suggest that SF is rapidly suppressed by radiation-driven dusty outflows sustained by the high specific star formation rates (43 and 25 Gyr −1 , respectively) of the two galaxies. Our model provides a simple tool to interpret the SF histories of post-starburst galaxies and unravel quenching mechanisms from incoming JWST data.
ABSTRACT
Dust is an essential ingredient of galaxies, determining the physical and chemical conditions in the interstellar medium. Several complementary observational evidences indicate that the ...cosmic dust mass density significantly drops from redshift z = 1 to z = 0. Clearly, and for the first time during cosmic evolution, dust must be destroyed more rapidly than it is formed. By considering the dust production/destruction processes acting in this cosmic time lapse, we find that the drop can be explained if dust is mainly destroyed by astration (49 per cent contribution in the fiducial case) and supernova (SN) shocks within galaxies (42 per cent). Our results further imply that on average each SN destroys only $M_{\mathrm{ d},\mathrm{ sn}} =0.45\, \mathrm{ M}_\odot$ of dust, i.e. 5–10 times less than usually assumed, with a hard upper limit of Md,sn < 3.0 M⊙ set by the available metal budget and maximal grain growth. The lower efficiency might be explained by effective shielding of dust against shock processing in pre-SN wind shells.
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