The First Black Holes In The Cosmic Dark Ages
Creators: name: Pacucci, Fabio
Publisher: name: Zenodo
Year: 2016
Subjects: Astronomy
Astrophysics
Cosmology
Black Holes
Direct Collapse Black Holes
Super Massive Black Holes
Accretion Disks
AGN
Quasar
Gravitational Waves

description: The main objective of the original work presented in this Thesis is to develop a theoretical framework to understand the growth, cosmological evolution and observational features of the first black holes, formed when the Universe was younger than \(\sim 1 \, \mathrm{Gyr}\).

In the first part a growth model is assembled, based on the developed radiation hydrodynamic code GEMS (Growth of Early Massive Seeds).

We find that the accretion onto a Direct Collapse Black Hole (DCBH) of initial mass \(M_0=10^5 \, \mathrm{M_{\odot}}\) occurs at an average, super-Eddington, rate \(\dot{M}_{\bullet} \simeq 1.35 \, \dot{M}_{Edd} \simeq 0.1 \, \mathrm{M_{\odot} \, yr^{-1}}\), is intermittent (duty-cycle \(\lesssim 50\%\)) and lasts \(\sim 100 \, \mathrm{Myr}\), during which the black hole can accrete only up to \(\sim 20\%\) of the available mass.

Our model identifies a "feeding-dominated" accretion regime for massive DCBHs (\(\gtrsim 10^{5-6} \, \mathrm{M_{\odot}}\)) and a "feedback-limited" one for light ones (\(\lesssim 10^{3-4} \, \mathrm{M_{\odot}}\)), the latter being characterized by intermittent (duty cycles \(\lesssim 0.5\)) and inefficient growth, with recurring outflow episodes.

We have also explored slim disk models, appropriate for super-Eddington accretion, in which outflows play a negligible role and a black hole can accrete 80%-100% of the gas mass of the host halo in \(\sim 10 \, \mathrm{Myr}\).

We find that the differential growth of light and massive DCBH seeds leads to a bimodal cosmological evolution in mass.

In the second part we investigate the observational properties of these sources.

The time-evolving spectrum emerging from the host halo of a DCBH is analyzed: the emission occurs predominantly in the observed infrared-submm (\(1-1000 \, \mathrm{\mu m}\)) and X-ray (\(0.1 - 100 \, \mathrm{keV}\)) bands.

Such signal should be easily detectable by the JWST at \(\sim 1 \, \mathrm{\mu m}\), and by ATHENA (between \(0.1\) and \(10 \, \mathrm{keV}\)). Deep X-ray surveys like the CDF-S could have already detected these systems. Based on this, we provide upper limits for the \(z \gtrsim 6\) black hole mass density for both accretion models.

A photometric method to identify DCBH candidates in deep multi-wavelength surveys is developed: these sources are characterized by a steep spectrum in the infrared (\(1.6-4.5 \, \mathrm{\mu m}\)), i.e. by very red colors. The method selects the only 2 objects with a robust X-ray detection found in the CANDELS/GOODS-S survey with \(z \gtrsim 6\). To date, the selected objects represent the most promising black hole seed candidates, possibly formed via the DCBH scenario, with predicted mass \(&gt;10^5 \, \mathrm{M_{\odot}}\).

Finally, we note that the abrupt collapse of a massive and rotating object such as a DCBH is a powerful source of gravitational waves emission. We show that the predicted signal lies above the foreseen sensitivity of the DECIGO observatory in the frequency range \((0.8-300) \, \mathrm{mHz}\), with a peak amplitude \(\Omega_{gw} = 1.1 \times 10^{-54}\) at \(\nu_{max} = 0.9 \, \mathrm{mHz}\) and a peak Signal-to-Noise Ratio \(\sim 22\) at \(\nu = 20 \, \mathrm{mHz}\).
description: 196 pages
description: {"references": ["Pacucci F., Ferrara A., 2015, MNRAS, 448, 104", "Pacucci F., Volonteri M., Ferrara A., 2015, MNRAS, 452, 1922", "Pacucci F., Ferrara A., Volonteri M., Dubus G., 2015, MNRAS, 454, 3771", "Pacucci F., Ferrara A., Grazian A., Fiore F., Giallongo E., Puccetti S., 2016, MNRAS, 459, 1432", "Pallottini A., et al., 2015, MNRAS, 453, 2465", "Pacucci F., Ferrara A., Marassi S., 2015, MNRAS, 449, 1076"]}