907 research outputs found
Environment of compact extragalactic radio sources
We have studied the interrelation of young AGN with their hosts. The objects
of study are the young and powerful GPS and CSS radio sources. Due to their
small size, GPS and CSS sources are excellent probes of this relation.
Furhthermore, their young age allows us to compare them to the larger, old
radio sources and establish a time-line evolution of this relation. Combining
imaging and spectroscopy at UV, optical and radio wavelengths we find evidence
of strong interaction between the host and the radio source. The presence and
expansion of the radio source clearly affects the properties and evolution of
the host. Furthermore, the radio source and host significantly affect each
other's evolution. We describe our results and how these interactions take
place.Comment: 6 pages. To appear in "Highlights of Spanisg astrophysics IV.
Proceedings of the VII scientific meeting of the Spanish Astronomical
Society". Editors: F. Figueras, J.M. Girart, M.Hernanz, C. Jordi. Springe
The Extreme Ultraviolet Spectra of Low Redshift Radio Loud Quasars
This paper reports on the extreme ultraviolet (EUV) spectrum of three low
redshift () radio loud quasars, 3C 95, 3C 57 and PKS 0405-123. The
spectra were obtained with the Cosmic Origins Spectrograph (COS) of the Hubble
Space Telescope. The bolometric thermal emission, , associated with
the accretion flow is a large fraction of the Eddington limit for all of these
sources. We estimate the long term time averaged jet power, , for
the three sources. , is shown to lie along the
correlation of and found in previous
studies of the EUV continuum of intermediate and high redshift quasars, where
the EUV continuum flux density between 1100 \AA\, and 700 \AA\, is defined by
. The high Eddington ratios of the three
quasars extends the analysis into a wider parameter space. Selecting quasars
with high Eddington ratios has accentuated the statistical significance of the
partial correlation analysis of the data. Namely. the correlation of
and is fundamental and the
correlation of and is spurious at a very high
statistical significance level (99.8\%). This supports the regulating role of
ram pressure of the accretion flow in magnetically arrested accretion models of
jet production. In the process of this study, we use multi-frequency and
multi-resolution Very Large Array radio observations to determine that one of
the bipolar jets in 3C 57 is likely frustrated by galactic gas that keeps the
jet from propagating outside the host galaxy.Comment: To appear in MNRA
The Extreme Ultraviolet Deficit - Jet Connection in the Quasar 1442+101
In previous studies, it has been shown that the long term time average jet
power, , is correlated with the spectral index in the extreme
ultraviolet (EUV), (defined by computed between 700\AA\, and 1100\AA\,). Larger
tends to decrease the EUV emission. This is a curious
relationship because it connects a long term average over years
with an instantaneous measurement of the EUV. The EUV appears to be emitted
adjacent to the central supermassive black hole and the most straightforward
explanation of the correlation is that the EUV emitting region interacts in
real time with the jet launching mechanism. Alternatively stated, the
- correlation is a manifestation of a
contemporaneous (real time) jet power, , correlation with .
In order to explore this possibility, this paper considers the time variability
of the strong radio jet of the quasar 1442+101 that is not aberrated by strong
Doppler enhancement. This high redshift (z = 3.55) quasar is uniquely suited
for this endeavor as the EUV is redshifted into the optical observing window
allowing for convenient monitoring. More importantly, it is bright enough to be
seen through the Lyman forest and its radio flux is strong enough that it has
been monitored frequently. Quasi-simultaneous monitoring (five epochs spanning
years) show that increases in correspond to decreases in the
EUV as expected.Comment: To appear in Ap
The Extreme Ultraviolet Variability of Quasars
We study the extreme ultraviolet (EUV) variability (rest frame wavelengths
500 - 920 ) of high luminosity quasars using HST (low to intermediate
redshift sample) and SDSS (high redshift sample) archives. The combined HST and
SDSS data indicates a much more pronounced variability when the sampling time
between observations in the quasar rest frame is sec
compared to sec. Based on an excess variance analysis, for
time intervals sec in the quasar rest frame, of the
quasars (4/40) show evidence of EUV variability. Similarly, for time intervals
sec in the quasar rest frame, of the quasars (21/38)
show evidence of EUV variability. The propensity for variability does not show
any statistically significant change between sec and
sec (1 yr). The temporal behavior is one of a threshold
time interval for significant variability as opposed to a gradual increase on
these time scales. A threshold time scale can indicate a characteristic spatial
dimension of the EUV region. We explore this concept in the context of the slim
disk models of accretion. We find that for rapidly spinning black holes, the
radial infall time to the plunge region of the optically thin surface layer of
the slim disk that is responsible for the preponderance of the EUV flux
emission (primarily within 0 - 7 black hole radii from the inner edge of the
disk) is consistent with the empirically determined variability time scale.Comment: To appear in Ap
The Properties and Gaseous Environments of Powerful Classical Double Radio Galaxies
The properties of a sample of 31 very powerful classical double radio
galaxies with redshifts between zero and 1.8 are studied. The source
velocities, beam powers, ambient gas densities, total lifetimes, and total
outflow energies are presented and discussed. The rate of growth of each side
of each source were obtained using a spectral aging analysis. The beam power
and ambient gas density were obtained by applying the strong shock jump
conditions to the ends of each side of the source. The total outflow lifetime
was obtained by applying the power-law relationship between the beam power and
the total source lifetime derived elsewhere for sources of this type, and the
total outflow energy was obtained by combining the beam power and the total
source lifetime. Composite profiles were constructed by combining results
obtained from each side of each source. The composite profiles indicate that
the ambient gas density falls with distance from the central engine. The source
velocities, beam powers, total lifetimes, and total energies seem to be
independent of radio source size. This is consistent with the standard model in
which each source grows at a roughly constant rate during which time the
central engine puts out a roughly constant beam power. The fact that the total
source lifetimes and energies are independent of radio source size indicates
that the sources are being sampled at random times during their lifetimes.Comment: 7 pages, 5 figures, to appear in "Extragalactic Jets: Theory and
Observation from Radio to Gamma Ray", eds. T. A. Rector and D. S. De Young,
ASP conference series, Replaced version has minor textual correction
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