Subscribe to the gold package and get unlimited access to Shamra Academy
Register a new userMocking Faint Black Holes during Reionization
494
0
0.0
(
0
)
Ask ChatGPT about the research
No Arabic abstract
To investigate the potential abundance and impact of nuclear black holes (BHs) during reionization, we generate a neural network that estimates their masses and accretion rates by training it on 23 properties of galaxies harbouring them at $z=6$ in the cosmological hydrodynamical simulation Massive-Black II. We then populate all galaxies in the simulation from $z=18$ to $z=5$ with BHs from this network. As the network allows to robustly extrapolate to BH masses below those of the BH seeds, we predict a population of faint BHs with a turnover-free luminosity function, while retaining the bright (and observed) BHs, and together they predict a Universe in which intergalactic hydrogen is $15%$ ionized at $z=6$ for a clumping factor of 5. Faint BHs may play a stronger role in H reionization without violating any observational constraints. This is expected to have an impact also on pre-heating and -ionization, which is relevant to observations of the 21 cm line from neutral H. We also find that BHs grow more efficiently at higher $z$, but mainly follow a redshift-independent galaxy-BH relation. We provide a power law parametrisation of the hydrogen ionizing emissivity of BHs.
rate research
Read More
The feasibility of making highly redshifted HI 21-cm (rest frame) measurements from an early epoch of the Universe between the Dark Ages and Reionization (i.e., z>6 and nu<200 MHz) to probe the effects of feedback from the first stars and quasars is assessed in this paper. It may be possible to determine the distribution of hydrogen through the Universe and to constrain the birth of the first stars and black holes via HI tomography. Such observations may also place limits on the properties of Inflation and any exotic heating mechanisms before the first star formation begins (e.g., dark matter decay). The global (all-sky) HI signal after Recombination has distinct features at different frequencies between 30 and 200 MHz that changes as the relative balance between the CMB and spin temperatures changes due to the expansion of the Universe and the ignition of stars and/or black holes. A technology roadmap to approach these observations beginning with ground-based arrays and ending with a low frequency radio array on the lunar farside is described.
The EUV provides most of the ionization that creates the high equivalent width (EW) broad and narrow emission lines (BELs, NELs) of quasars. Spectra of Hypermassive Schwarzschild black holes (HMBHs, $M_{BH} geq 10^{10} M_{odot}$) with $alpha$-discs, decline rapidly in the EUV suggesting much lower EWs. Model spectra for black holes of mass $10^{6}-10^{12} M_{odot}$ and accretion rates $0.03 leq L_{bol}/L_{edd} leq 1.0$ were input to the CLOUDY photoionization code. BELs become $sim$100 times weaker in EW from $M_{BH} sim 10^8 M_{odot}$ to $M_{BH} sim 10^{10} M_{odot}$. The high ionization BELs (O VI 1034 $overset{circ}{mathrm {A}}$, C IV 1549 $overset{circ}{mathrm {A}}$, He II 1640 $overset{circ}{mathrm {A}}$) decline in EW from ($M_{BH} geq 10^6 M_{odot}$, reproducing the Baldwin effect, but regain EW for $M_{BH} geq 10^{10} M_{odot}$). The low ionization lines (MgII 2798 $overset{circ}{mathrm {A}}$, H$beta$ 4861 $overset{circ}{mathrm {A}}$ and H$alpha$ 6563 $overset{circ}{mathrm {A}}$) remain weak. Lines for maximally spinning HMBHs behave similarly. Line ratio diagrams for the BELs show that high OVI/H$beta$ and low CIV/H$alpha$ may pick out HMBH, although OVI is often hard to observe. In NEL BPT diagrams HMBHs lie among star-forming regions, except for highly spinning, high accretion rate HMBHs. In summary, the BELs expected from HMBHs would be hard to detect using the current optical facilities. From 100 to $10^{12} M_{odot}$, the emission lines used to detect AGN only have high EW in the $10^6 - 10^9 M_{odot}$ window, where most AGN are found. This selection effect may be distorting reported distributions of $M_{BH}$.
The recent discovery of the gravitational wave source GW150914 has revealed a coalescing binary black hole (BBH) with masses of $sim 30~M_odot$. Previous proposals for the origin of such a massive binary include Population III (PopIII) stars. PopIII stars are efficient producers of BBHs and of a gravitational wave background (GWB) in the $10-100$ Hz band, and also of ionizing radiation in the early Universe. We quantify the relation between the amplitude of the GWB ($Omega_{rm gw}$) and the electron scattering optical depth ($tau_{rm e}$), produced by PopIII stars, assuming that $f_{rm esc}approx 10%$ of their ionizing radiation escapes into the intergalactic medium. We find that PopIII stars would produce a GWB that is detectable by the future O5 LIGO/Virgo if $tau_{rm e} gtrsim 0.07$, consistent with the recent Planck measurement of $tau_e=0.055 pm 0.09$. Moreover, the spectral index of the background from PopIII BBHs becomes as small as ${rm d}ln Omega_{rm gw}/{rm d}ln flesssim 0.3$ at $f gtrsim 30$ Hz, which is significantly flatter than the value $sim 2/3$ generically produced by lower-redshift and less-massive BBHs. A detection of the unique flattening at such low frequencies by the O5 LIGO/Virgo will indicate the existence of a high-chirp mass, high-redshift BBH population, which is consistent with the PopIII origin. A precise characterization of the spectral shape near $30-50$ Hz by the Einstein Telescope could also constrain the PopIII initial mass function and star formation rate.
Motivated by the stellar fossil record of Local Group (LG) dwarf galaxies, we show that the star-forming ancestors of the faintest ultra-faint dwarf galaxies (UFDs; ${rm M}_{rm V}$ $sim -2$ or ${rm M}_{star}$ $sim 10^{2}$ at $z=0$) had ultra-violet (UV) luminosities of ${rm M}_{rm UV}$ $sim -3$ to $-6$ during reionization ($zsim6-10$). The existence of such faint galaxies has substantial implications for early epochs of galaxy formation and reionization. If the faint-end slopes of the UV luminosity functions (UVLFs) during reionization are steep ($alphalesssim-2$) to ${rm M}_{rm UV}$ $sim -3$, then: (i) the ancestors of UFDs produced $>50$% of UV flux from galaxies; (ii) galaxies can maintain reionization with escape fractions that are $>$2 times lower than currently-adopted values; (iii) direct HST and JWST observations may detect only $sim10-50$% of the UV light from galaxies; (iv) the cosmic star formation history increases by $gtrsim4-6$ at $zgtrsim6$. Significant flux from UFDs, and resultant tensions with LG dwarf galaxy counts, are reduced if the high-redshift UVLF turns over. Independent of the UVLF shape, the existence of a large population of UFDs requires a non-zero luminosity function to ${rm M}_{rm UV}$ $sim -3$ during reionization.
Nebular emission lines associated with galactic HII regions carry information about both physical properties of the ionised gas and the source of ionising photons as well as providing the opportunity of measuring accurate redshifts and thus distances once a cosmological model is assumed. While nebular line emission has been extensively studied at lower redshift there are currently only few constraints within the epoch of reionisation (EoR, $z>6$), chiefly due to the lack of sensitive near-IR spectrographs. However, this will soon change with the arrival of the Webb Telescope providing sensitive near-IR spectroscopy covering the rest-frame UV and optical emission of galaxies in the EoR. In anticipation of Webb we combine the large cosmological hydrodynamical simulation Bluetides with photoionisation modelling to predict the nebular emission line properties of galaxies at $z=8to 13$. We find good agreement with the, albeit limited, existing direct and indirect observational constraints on equivalent widths though poorer agreement with luminosity function constraints.
Log in to be able to interact and post comments
comments
Fetching comments
Sign in to be able to follow your search criteria
