80 research outputs found
Matter content in AGN jets: constraint from cocoon dynamics?
The matter content of jets in active galactic nuclei is examined in a new
way. We model the dynamical expansion of its cocoon embedded in the
intra-cluster medium (ICM). By comparing the observed shape of the cocoon with
that expected from the theoretical model, we estimate the total pressure
() and electron temperature () of the cocoon. The number
density of the total electrons () is constrained by using the
non-thermal spectrum of the hot spot and the analysis of the momentum balance
between the jet thrust and the rum pressure of ICM. Together with the obtained
, and , we constrain the matter content in the
jets. We find that, in the case of Cygnus A, the ratio of number density of
protons to that of electrons is of order of . This implies the
existence of a large number of positron in the jet.Comment: 4 pages, to appear in the proceedings of "Astrophysical Sources of
High Energy Particles and Radiation", Torun, 20-24 June 200
Evolution of non-thermal emission from shell associated with AGN jets
We explore the evolution of the emissions by accelerated electrons in shocked
shells driven by jets in active galactic nuclei (AGNs). Focusing on powerful
sources which host luminous quasars, we evaluated the broadband emission
spectra by properly taking into account adiabatic and radiative cooling effects
on the electron distribution. The synchrotron radiation and inverse Compton
(IC) scattering of various photons that are mainly produced in the accretion
disc and dusty torus are considered as radiation processes. We show that the
resultant radiation is dominated by the IC emission for compact sources (<
10kpc), whereas the synchrotron radiation is more important for larger sources.
We also compare the shell emissions with those expected from the lobe under the
assumption that a fractions of the energy deposited in the shell and lobe
carried by the non-thermal electrons are and
, respectively. Then, we find that the shell
emissions are brighter than the lobe ones at infra-red and optical bands when
the source size is > 10kpc, and the IC emissions from the shell at > 10 GeV can
be observed with the absence of contamination from the lobe irrespective of the
source size. In particular, it is predicted that, for most powerful nearby
sources (), TeV gamma-rays produced via the IC
emissions can be detected by the modern Cherenkov telescopes such as MAGIC,
HESS and VERITAS.Comment: 13 pages, 5 figures, accepted for publication in Ap
Supermassive Black Hole Mass Regulated by Host Galaxy Morphology
We investigated the relationship between supermassive black hole (SMBH) mass
and host starburst luminosity in Seyfert galaxies and Palomar-Green QSOs,
focusing on the host galaxy morphology. Host starburst luminosity was derived
from the 11.3 micron polycyclic aromatic hydrocarbon luminosity. We found that
the SMBH masses of elliptical-dominated host galaxies are more massive than
those of disk-dominated host galaxies statistically. We also found that the
SMBH masses of disk-dominated host galaxies seem to be suppressed even under
increasing starburst luminosity. These findings imply that final SMBH mass is
strongly regulated by host galaxy morphology. This can be understood by
considering the radiation drag model as the SMBH growth mechanism, taking into
account the radiation efficiency of the host galaxy.Comment: 6 pages, 1 figure; accepted for publication in MNRA
Accretion Properties of High- and Low-Excitation Young Radio Galaxies
Young radio galaxies (YRGs) provide an ideal laboratory to explore the
connection between accretion disk and radio jet thanks to their recent jet
formation. We investigate the relationship between the emission-line
properties, the black hole accretion rate, and the radio properties using a
sample of 34 low-redshift (z < 0.4) YRGs. We classify YRGs as high-excitation
galaxies (HEGs) and low-excitation galaxies (LEGs) based on the flux ratio of
high-ionization to low-ionization emission lines. Using the H{\alpha}
luminosities as a proxy of accretion rate, we find that HEGs in YRGs have \sim1
dex higher Eddington ratios than LEGs in YRGs, suggesting that HEGs have higher
mass accretion rate or higher radiative efficiency than LEGs. In agreement with
previous studies, we find that the luminosities of emission lines, in
particular H{\alpha}, are correlated with radio core luminosity, suggesting
that accretion and young radio activities are fundamentally connected.Comment: 14 pages, 12 figures, 5 tables. Accepted for publication in Ap
New prediction of extragalactic GeV gamma-ray emission from radio lobes of young AGN jets
We present a new prediction of GeV -ray emission from radio lobes of
young AGN jets. In the previous work of Kino et al. (2007), MeV -ray
bremsstrahlung emission was predicted from young cocoons/radio-lobes in the
regime of no coolings. In this study, we include cooling effects of
bremsstrahlung emission and adiabatic loss. With the initial conditions
determined by observed young radio lobes, we solve a set of equations
describing the expanding lobe evolution. Then we find that the lobes initially
have electron temperature of GeV, and they cool down to MeV by the
adiabatic loss. Correspondingly, the lobes initially yield bright
bremsstrahlung luminosity in GeV range and they fade out. We estimate
these -ray emissions and show that nearby young radio lobes could be
detected with Fermi Gamma-ray Space Telescope.Comment: 5 pages, 3 figures, MNRAS Letters, accepte
Coevolution of Supermassive Black Holes and Circumnuclear Disks
We propose a new evolutionary model of a supermassive black hole (SMBH) and a
circumnuclear disk (CND), taking into account the mass-supply from a host
galaxy and the physical states of CND. In the model, two distinct accretion
modes depending on gravitational stability of the CND play a key role on
accreting gas to a SMBH. (i) If the CMD is gravitationally unstable, energy
feedback from supernovae (SNe) supports a geometrically thick, turbulent gas
disk. The accretion in this mode is dominated by turbulent viscosity, and it is
significantly larger than that in the mode (ii), i.e., the CMD is supported by
gas pressure. Once the gas supply from the host is stopped, the high accretion
phase () changes to the low one (mode
(ii), ), but there is a delay with yr. Through this evolution, the gas-rich CND turns into the gas poor
stellar disk. We found that not all the gas supplied from the host galaxy
accrete onto the SMBH even in the high accretion phase (mode (i)), because the
part of gas is used to form stars. As a result, the final SMBH mass () is not proportional to the total gas mass supplied from the host
galaxy (); decreases with .This would indicate that it is difficult to form a SMBH with observed at high- QSOs. The evolution of the SMBH and CND would
be related to the evolutionary tracks of different type of AGNs.Comment: 11 pages, 11 figures, accepted for publication in Ap
Extragalactic MeV gamma-ray emission from cocoons of young radio galaxies
Strong -ray emission from cocoons of young radio galaxies is newly
predicted. Considering the process of adiabatic injection of the shock
dissipation energy and mass of the relativistic jet in active nuclei (AGNs)
into the cocoon, while assuming thermalizing electron plasma interactions, we
find that the thermal electron temperature of the cocoon is typically predicted
in MeV, which is determined only by the bulk Lorentz factor of the
relativistic jet. Together with the time-dependent dynamics of the cocoon
expansion, we find that young cocoons can yield thermal bremsstrahlung
emissions at energies MeV.Comment: 5pages, 1figure, MNRAS accepte
Long Gamma-Ray Bursts and Their Host Galaxies at High Redshift
Motivated by the recent observational and theoretical evidence that long
Gamma-Ray Bursts (GRBs) are likely associated with low metallicity, rapidly
rotating massive stars, we examine the cosmological star formation rate (SFR)
below a critical metallicity Z_crit Z_sun/10 - Z_sun/5, to estimate the event
rate of high-redshift long GRB progenitors. To this purpose, we exploit a
galaxy formation scenario already successfully tested on a wealth of
observational data on (proto)spheroids, Lyman break galaxies, Lyman alpha
emitters, submm galaxies, quasars, and local early-type galaxies. We find that
the predicted rate of long GRBs amounts to about 300 events/yr/sr, of which
about 30 per cent occur at z>~6. Correspondingly, the GRB number counts well
agree with the bright SWIFT data, without the need for an intrinsic luminosity
evolution. Moreover, the above framework enables us to predict properties of
the GRB host galaxies. Most GRBs are associated with low mass galaxy halos
M_H<~10^11 M_sun, and effectively trace the formation of small galaxies in such
halos. The hosts are young, with age smaller than 5*10^7 yr, gas rich, but
poorly extincted (A_V<~0.1) because of their chemical immaturity; this also
implies high specific SFR and quite extreme alpha-enhancement. Only the
minority of hosts residing in large halos with M_H>~10^12 M_sun have larger
extinction (A_V~0.7-1), SFRs exceeding 100 M_sun/yr and can be detected at
submm wavelengths. Most of the hosts have UV magnitudes in the range -20
<~M_1350<~ -16, and Lyman alpha luminosity in the range 2*10^40
<~L_Lya<~2*10^42 erg/s. GRB hosts are thus tracing the faint end of the
luminosity function of Lyman break galaxies and Lyman alpha emitters.Comment: 11 pages, 8 figures, uses mn2e.cls. Minor changes. In press on MNRA
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