69 research outputs found
Quasar Host Orientation and Polarization: Insights into the Type 1/Type 2 Dichotomy
We investigate correlations between the optical linear polarization position
angle and the orientation of the host galaxy/extended emission of Type 1 and
Type 2 Radio-Loud (RL) and Radio-Quiet (RQ) quasars. We have used high
resolution Hubble Space Telescope (HST) data and deconvolution process to
obtain a good determination of the host galaxy orientation. With these new
measurements and a compilation of data from the literature, we find a
significant correlation between the polarization position angle and the
position angle of the major axis of the host galaxy/extended emission. The
correlation appears different for Type 1 and Type 2 objects and depends on the
redshift of the source. Interpretations in the framework of the unification
model are discussed.Comment: 3 pages, 1 figure, to appear in "The Nuclear Region, Host Galaxy and
Environment of Active Galaxies", eds. E. Benitez, I. Cruz-Gonzalez and Y.
Krongold, RevMexAA (Serie de Conferencias
The Sloan Digital Sky Survey Reverberation Mapping Project: Rapid CIV Broad Absorption Line Variability
We report the discovery of rapid variations of a high-velocity CIV broad
absorption line trough in the quasar SDSS J141007.74+541203.3. This object was
intensively observed in 2014 as a part of the Sloan Digital Sky Survey
Reverberation Mapping Project, during which 32 epochs of spectroscopy were
obtained with the Baryon Oscillation Spectroscopic Survey spectrograph. We
observe significant (>4sigma) variability in the equivalent width of the broad
(~4000 km/s wide) CIV trough on rest-frame timescales as short as 1.20 days
(~29 hours), the shortest broad absorption line variability timescale yet
reported. The equivalent width varied by ~10% on these short timescales, and by
about a factor of two over the duration of the campaign. We evaluate several
potential causes of the variability, concluding that the most likely cause is a
rapid response to changes in the incident ionizing continuum. If the outflow is
at a radius where the recombination rate is higher than the ionization rate,
the timescale of variability places a lower limit on the density of the
absorbing gas of n_e > 3.9 x 10^5 cm^-3. The broad absorption line variability
characteristics of this quasar are consistent with those observed in previous
studies of quasars, indicating that such short-term variability may in fact be
common and thus can be used to learn about outflow characteristics and
contributions to quasar/host-galaxy feedback scenarios.Comment: 15 pages, 14 figures. Accepted for publication in the Astrophysical
Journa
On the co-evolution of supermassive black holes and their host galaxies since z = 3
[Abridged] To investigate the evolution in the relation between galaxy
stellar and central black hole mass we construct a volume limited complete
sample of 85 AGN with host galaxy stellar masses M_{*} > 10^{10.5} M_{sol}, and
specific X-ray luminosities L_{X} > 2.35 x 10^{43} erg s^{-1} at 0.4 < z < 3.
We calculate the Eddington limiting masses of the supermassive black holes
residing at the centre of these galaxies, and observe an increase in the
average Eddington limiting black hole mass with redshift. By assuming that
there is no evolution in the Eddington ratio (\mu) and then that there is
maximum possible evolution to the Eddington limit, we quantify the maximum
possible evolution in the M_{*} / M_{BH} ratio as lying in the range 700 <
M_{*}/M_{BH} < 10000, compared with the local value of M_{*}/M_{BH} ~ 1000. We
furthermore find that the fraction of galaxies which are AGN (with L_{X} > 2.35
x 10^{43} erg s^{-1}) rises with redshift from 1.2 +/- 0.2 % at z = 0.7 to 7.4
+/- 2.0 % at z = 2.5. We use our results to calculate the maximum timescales
for which our sample of AGN can continue to accrete at their observed rates
before surpassing the local galaxy-black hole mass relation. We use these
timescales to calculate the total fraction of massive galaxies which will be
active (with L_{X} > 2.35 x 10^{43} erg s^{-1}) since z = 3, finding that at
least ~ 40% of all massive galaxies will be Seyfert luminosity AGN or brighter
during this epoch. Further, we calculate the energy density due to AGN activity
in the Universe as 1.0 (+/- 0.3) x 10^{57} erg Mpc^{-3} Gyr^{-1}, potentially
providing a significant source of energy for AGN feedback on star formation. We
also use this method to compute the evolution in the X-ray luminosity density
of AGN with redshift, finding that massive galaxy Seyfert luminosity AGN are
the dominant source of X-ray emission in the Universe at z < 3.Comment: 25 pages, 10 figures, accepted for publication in MNRA
Catalytic Transformations of Alkynes via Ruthenium Vinylidene and Allenylidene Intermediates
NOTICE: This is the peer reviewed version of the following book chapter: Varela J. A., González-RodrĂguez C., Saá C. (2014). Catalytic Transformations of Alkynes via Ruthenium Vinylidene and Allenylidene Intermediates. In: Dixneuf P., Bruneau C. (eds) Ruthenium in Catalysis. Topics in Organometallic Chemistry, vol 48, pp. 237-287. Springer, Cham. [doi: 10.1007/3418_2014_81]. This article may be used for non-commercial purposes in accordance with Springer Verlag Terms and Conditions for self-archiving.Vinylidenes are high-energy tautomers of terminal alkynes and they can be stabilized by coordination with transition metals. The resulting metal-vinylidene species have interesting chemical properties that make their reactivity different to that of the free and metal Ď€-coordinated alkynes: the carbon α to the metal is electrophilic whereas the β carbon is nucleophilic. Ruthenium is one of the most commonly used transition metals to stabilize vinylidenes and the resulting species can undergo a range of useful transformations. The most remarkable transformations are the regioselective anti-Markovnikov addition of different nucleophiles to catalytic ruthenium vinylidenes and the participation of the Ď€ system of catalytic ruthenium vinylidenes in pericyclic reactions. Ruthenium vinylidenes have also been employed as precatalysts in ring closing metathesis (RCM) or ring opening metathesis polymerization (ROMP).
Allenylidenes could be considered as divalent radicals derived from allenes. In a similar way to vinylidenes, allenylidenes can be stabilized by coordination with transition metals and again ruthenium is one of the most widely used metals. Metalallenylidene complexes can be easily obtained from terminal propargylic alcohols by dehydration of the initially formed metal-hydroxyvinylidenes, in which the reactivity of these metal complexes is based on the electrophilic nature of Cα and Cγ, while Cβ is nucleophilic. Catalytic processes based on nucleophilic additions and pericyclic reactions involving the π system of ruthenium allenylidenes afford interesting new structures with high selectivity and atom economy
QSO Type1/Type2 dichotomy (Borguet+, 2008)
This table contains the measurements/compilation of host galaxy/ extended emission position angle in the visible and near-IR domain, polarimetric data, and radio axis orientation for the 135 quasars of our sample. The angles are given in degrees east of north. The table gives the spectral and the radio-loud/radio-quiet classification of each object according to the references. (2 data files)
- …