Banca de DEFESA: ASNAKEW BEWKETU BELETE

Uma banca de DEFESA de DOUTORADO foi cadastrada pelo programa.
STUDENT : ASNAKEW BEWKETU BELETE
DATE: 29/01/2022
TIME: 15:00
LOCAL: Plataforma Zoom
TITLE:

The variability properties of active galactic nuclei and their intractions with the host galaxies

KEY WORDS:

métodos: estatísticos; modelagem cinemática de gás; galáxias: galáxias-ativas: individuais:  3C 273; 

                        3C 279; 3C 345; 3C 454,3; Q0957 + 561; NGC 4151; NGC 7469; Arp 102B; E1821 + 643; 3C 

                        390,3; NGC 5548; Mrk 509; NGC 5548; NGC 4151;  NGC 4593 ; NGC 4968, NGC 4845, MCG-

                        06-30-15

PAGES: 186
BIG AREA: Ciências Exatas e da Terra
AREA: Física
SUMMARY:

Active galactic nuclei (AGNs), a compact regions that consist of a super-massive
black hole surrounded by an accretion disk in the center of massive galaxies, have
long been known in their unique observational properties. Strong variability has
been identified as one of those properties that can be used to probe the interior of
the system. Also, most astrophysical objects, like AGNs, are possibly associated
with continuous nonlinear stochastic systems due to their complexity in nature. It
has been indicated that quasars, a sub-class of AGN, are among complex systems
that have nonlinear time series characterized by fractal behavior and also by sudden
bursts of very large amplitude, implying that the dynamical evolution of quasars
is nonlinear (i.e., described by nonlinear stochastic differential equations). Addi-
tionally, there is a suggestion that extragalactic radio sources are intermittent on
timescales of ∼ 10 4 - 10 5 yr. Despite the complex nature of AGNs, astronomers
have been trying to investigate the variability properties of AGNs using linear tech-
niques, such as structure function, periodogram, Fourier analysis, etc. However,
most valuable information in a complex system signal is contained by its irregu-
lar structures and transient phenomena called singularities. Thus, particularly in
physics, it is important to analyze irregular structures in a signal to deduce proper-
ties about the underlying physical phenomena. Moreover, among other evidences,
the recently discovered tight correlation between super-massive black hole mass and
the host galaxy bulge properties revealed the fact that AGNs are not isolated objects
-they interact and co-evolve with their host galaxies. The interaction mechanisms
are thought to be through AGN feedback and feeding, and have been known to af-
fect both the observational properties of AGNs, and the properties and kinematics
of the gas in the surrounding environment, thereby regulating AGN- host galaxy
co-evolution. Thus, understanding the types of variabilities along with their driv-
ing physical mechanisms and the physics behind the AGN-host galaxy interaction
mechanisms(AGNfeedbackandfeeding)providesapotentiallysignificantinforma-
tion to constrain the nature of AGNs and get a full picture to construct a universal
model to study the co-evolution of the two physically connected systems. The AGN-
host galaxy interaction can easily be studied by modelling the kinematics of gas (in
all form) in the nuclear/circumnuclear regions of the host galaxy.
In this thesis I studied the nonlinear (multifractal) signature printed in the long-
term light curves of different classes of AGNs and its correlation with different AGN
and other observational parameters, and whether multifractality is an intrinsic be-
haviour of AGNs and it can be affected by extrinsic variations (e.g., gravitational
lensing). I applied the one-dimensional multifractal detrended moving average and
the wavelet transform modulus maxima approachs to characterize the nonlinearity
presented in the light curves. In addition, I also present the analysis of the kinemat-
ics of CO molecular gas in the nuclear and circumnuclear regions of three nearby
Seyfert galaxies, NGC 4968, NGC 4845, and MCG-06-30-15, by using their bright
CO(2-1) emission line as a tracer. I used two different softwares, the 3D-Based Anal-
ysis of Rotating Object via Line Observations (3 D BAROLO) and DiskFit, to model
the kinematics of cold CO molecular gas in these three galaxies.
I found that AGNs are strongly nonlinear and intermitent systems, and nonlinearity
is an intrinsic behaviour of AGNs (i.e., the degree of nonlinearity does not change
with cosmological redshift), indicating that AGNs are really complex systems, and
the information contained in their light curves cannot be fully captured by linear
analysis techniques. The nonlinear behaviour of AGNs is found to be affected by
extrinsic variation (gravitational lensing). Moreover, the degree of nonlinearity is
found to be inversly correlated with wavelength, the shorter the wavelength the
vii
stronger the nonlinearity, and strongly correlated with fractaional variability ampli-
tude. I did not find any significant correlation between the degree of nonlinearity
and AGN parameters such as black hole mass, the size of the Broad-Line Region
(BLR), and continuum luminostiy. However, an important correlation is observed
between the degree of nonlinearity and the Eddington ratio. I also found that re-
processing in the BLR introduces additional nonlinearity, i.e., the reprocessing in the
BLR increases the nonlinearity of the ionizing continuum.
Circular motion is found to be the dominant kinematics of the CO molecular gas
in the inner molecular disk of the three nearby Seyfert galaxies, NGC 4968, NGC
4845 and MCG-06-30-15, mainly in NGC 4845 and MCG-06-30-15. However, there
is a clear evidence for the presence of non-circular motions in the central regions of
NGC 4968 and NGC 4845. The strongest non-circular motion is detected in the nu-
clear region of NGC 4968, mainly in the minor kinematic axis, with velocity ∼ 115
km s
− 1 . For NGC 4968, the Ω b
pattern speed for the bar put corotation at 3.5 kpc
and inner Lindblad resonance (ILR) ring at R = 300pc, which corresponds to the CO
ring. Moreover, of all DiskFit models, bisymmetric model is found to be the best-
fit model, indicating that the observed non-circular motions, mainly in NGC 4968,
could be due the molecular gas in the disk of the galaxy being perturbed by the nu-
clear barred structure. Considering the CO-to-H 2 conversion factor α in the interval
[0.8, 3.2], the molecular mass in the molecular disk of each galaxy is estimated to be
∼ 2.8 × 10 9 (α= 0.8) and ∼ 11 × 10 9 (α=3.2) for NGC 4968, ∼ 4 × 10 9 (α= 0.8) and ∼ 16
× 10 9 (α= 3.2) for NGC 4845, and ∼ 0.3 × 10 9 (α= 0.8) and ∼ 1.2 × 10 9 (α= 3.2) for
MCG-06-30-15. For the galaxy NGC 4968, the computation of the torques exerted by
the stellar bar on the gas are positive inside the molecular ring, and negative inside,
revealing that the gas is accumulating in the inner Lindblad resonance.

BANKING MEMBERS:
Interno - 1675216 - BRUNO LEONARDO CANTO MARTINS
Interno - 3060853 - IZAN DE CASTRO LEÃO
Externo à Instituição - JAILSON SOUZA DE ALCANIZ - ON/MCT
Presidente - 346785 - JOSE RENAN DE MEDEIROS
Externa à Instituição - ZULEMA ABRAHAM - USP