Black holes and Active Galactic Nuclei
Active galactic nuclei (AGN) are believed to be powered by an accretion disk (AD) around a super-massive black hole (SMBH). A broad line region (BLR) surrounds the AD, and farther out there is a molecular dust torus. The BLR responds to the strong and variable UV/Optical continuum at very short time-scales, and thus at small distances (∼ 1 to 250 light days) from the AD. The small distance means that it is very difficult to resolve the central engine of AGN unless several radio telescopes are combined to create an earth-size detector capable to achieve the high-spatial resolution needed. Recent developments in instrumentation allowed to resolve the AD and the BLR system for the particular case of very nearby active galaxies (Gravity collaboration et al. 2018; Event Horizon Telescope collaboration et al. 2019). However, it will be impossible to resolve a large sample of more distant AGN in the foreseeable future. Here is where my work plays an important role. In order to study more distant and larger samples of black holes, we need to resort to methods that do not depend on spacial resolution. I have recently revisited the photometric reverberation mapping method to determine the BLR and AD sizes through the combination of narrow and broad-band imaging data.
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I have planned and carried out optical and near-infrared multi-month observations with multiple telescopes in Chile in order to explore the prospects of inferring the structure of the BLR from photometric monitoring data. Through the use of broad and narrow-band filters I have measured the time delay between variations in the continuum and H-beta/H-alpha emission lines. The time delay was used to infer the size of the broad-line region. These results were placed in the context of the known BLR-size luminosity relationship and discussed its potential application to constrain cosmological parameters.
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From spectroscopic observations I have calculated the velocity dispersion of the emission lines, and in combination with the BLR size I determined the masses of supermassive black holes. I have developed a new method for modeling the geometry of the BLR directly from photometric data which allow the determination of the geometry scaling factor used to constrain the real black hole mass in AGNs. I have found strong evidence for a disk-like BLR geometry, and discussed the deviations of Seyfert-1 galaxies from the SMBH-bulge velocity dispersion relation for quiescent galaxies.
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Results published in:
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Pozo Nunez, F., Ramolla, M., Westhues, C., et al. 2012: Photometric reverberation mapping of 3C 120
Pozo Nunez, F., Westhues, C., Ramolla, M., et al. 2013: Size and disk-like shape of the broad-line region of ESO 399-IG20
Pozo Nunez, F., Haas, M., Ramolla, M., et al. 2014a: Modelling photometric reverberation data: a disk-like broad-line region and a potentially larger black hole mass for 3C120.
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I have performed dust-reverberation studies in order to determine the dust-torus size of Seyfert galaxies. Through the modeling of the optical and near-infrared light curves, I have proposed a new scenario to explain the actual discrepancy between the observed time delay and the dust sublimation radius inferred from the optical-UV luminosity. In this scenario the dust torus is geometrically and optically thick, so that the observer only sees the facing rim of the torus wall, which lies closer to the observer than the torus equatorial plane and therefore leads to an observed foreshortened lag.
I study simultaneous observations for the broad-line region and dust thermal emission in order to test the unified scheme in Seyfert galaxies. I have obtained data with the Spitzer Space telescope/IRAC at 3.6 and 4.5 microns in order to study the echo of cooler dust and of deeply embedded hot dust expected in the optically thick case.
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Results published in:
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- Pozo Nunez et al. 2014b: Dust reverberation-mapping of the Seyfert 1 galaxy WPVS48.
- Pozo Nunez, F., Ramolla, M., Westhues, C., et al. 2015a: The broad-line region and dust torus size of the Seyfert 1 galaxy PGC 50427
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I implemented an automatized photometric monitoring of selected AGNs with the 46 cm and the 1meter telescope of the WISE observatory in Israel. The telescopes was equipped with Sloan r,i,z and five narrow band filters at 4300,5200,5700,6200 and 7000 A in order to perform variability studies of the central engine of AGNs. I have observed a sample of 27 AGNs (V < 17 mag) for which some of them were selected according to tentative continuum time delay measurements obtained in previous works or having previous line RM measurements from the literature indicating good variability.
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First results published in Publications of the Astronomical Society of the Pacific (PASP):
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Pozo Nunez, F., Chelouche, D., Kaspi, S., et al. (2017): Automatized photometric monitoring of active galactic nuclei with the
46 cm telescope of the WISE observatory. Click to Figure 8 of paper.
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Second results published in Nature Astronomy:
- Chelouche, D., Pozo Nunez, F. and Kaspi, S., (2018): Direct Evidence of non-disk optical continuum emission around an active black hole
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