Planned intervention: On Wednesday April 3rd 05:30 UTC Zenodo will be unavailable for up to 2-10 minutes to perform a storage cluster upgrade.
Published August 22, 2016 | Version v1
Thesis Open

The First Black Holes in the Cosmic Dark Ages

Creators

  • 1. Scuola Normale Superiore

Contributors

Supervisor:

  • 1. Scuola Normale Superiore

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 \(>10^5 \, \mathrm{M_{\odot}}\).

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 \(\nu = 20 \, \mathrm{mHz}\).

Notes

196 pages

Files

Pacucci_Fabio.pdf

Files (7.5 MB)

Name Size Download all
md5:d6b16b71a5c348a4c8dcbb2028a134fe
7.5 MB Preview Download

Additional details

Related works

Is identical to
2016PhDT........61P (Bibcode)

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