142 research outputs found
Tracing dark energy with quasars
The nature of dark energy, driving the accelerated expansion of the Universe,
is one of the most important issues in modern astrophysics. In order to
understand this phenomenon, we need precise astrophysical probes of the
universal expansion spanning wide redshift ranges. Quasars have recently
emerged as such a probe, thanks to their high intrinsic luminosities and, most
importantly, our ability to measure their luminosity distances independently of
redshifts. Here we report our ongoing work on observational reverberation
mapping using the time delay of the Mg II line, performed with the South
African Large Telescope (SALT).Comment: 3 pages, 2 figures, submitted as PTA proceeding
Emission Line Galaxies and Active Galactic Nuclei in WINGS clusters
We present the analysis of the emission line galaxies members of 46 low
redshift (0.04 < z < 0.07) clusters observed by WINGS (WIde-field Nearby Galaxy
cluster Survey, Fasano et al. 2006). Emission line galaxies were identified
following criteria that are meant to minimize biases against non-star forming
galaxies and classified employing diagnostic diagrams. We have examined the
emission line properties and frequencies of star forming galaxies, transition
objects and active galactic nuclei (AGNs: LINERs and Seyferts), unclassified
galaxies with emission lines, and quiescent galaxies with no detectable line
emission. A deficit of emission line galaxies in the cluster environment is
indicated by both a lower frequency with respect to control samples, and by a
systematically lower Balmer emission line equivalent width and luminosity (up
to one order of magnitude in equivalent width with respect to control samples
for transition objects) that implies a lower amount of ionised gas per unit
mass and a lower star formation rate if the source is classified as Hii region.
A sizable population of transition objects and of low-luminosity LINERs
(approx. 10 - 20% of all emission line galaxies) is detected among WINGS
cluster galaxies. With respect to Hii sources they are a factor of approx. 1.5
more frequent than (or at least as frequent as) in control samples. Transition
objects and LINERs in cluster are most affected in terms of line equivalent
width by the environment and appear predominantly consistent with "retired"
galaxies. Shock heating can be a possible gas excitation mechanism able to
account for observed line ratios. Specific to the cluster environment, we
suggest interaction between atomic and molecular gas and the intracluster
medium as a possible physical cause of line-emitting shocks.Comment: Astronomy and Astrophysics, accepte
Radio Loud AGN in the Context of the Eigenvector 1 Parameter Space
We consider the properties of radio-loud (RL) AGN in the context of the
Eigenvector 1 (E1) parameter space. RL sources show a restricted E1 parameter
space occupation relative to the radio-quiet (RQ) majority. The Fanaroff-Riley
II ``parent population'' of relatively un-boosted RL sources (median
radio/optical flux ratio ~490) shows the most restricted occupation. RL sources
have different broad line properties (and inferred black hole masses and
Eddington ratios). FWHM H_beta for the broad line component in RL sources are
at least twice as large as the RQ majority. The average broad FeII emission
line strength is also about half that for RQ sources. Our sample suggests that
the RL cutoff occurs near R_k=70 or logP(6cm)=32.0 ergs/s/Hz. Sources below
this cutoff are RQ although we cannot rule out the existence of a distinct
intermediate population. We show that the Doppler boosted core-dominated RL
sources (median flux ratio ~1000) lie towards smaller FWHM(H_beta_bc) and
stronger FeII in E1 as expected if the lines arise in an accretion disk. Our
subsample of superluminal sources, with orientation inferred from the
synchrotron self Compton model, reinforce this general E1 trend and allow us to
estimate the role of source orientation in driving E1 domain occupation.Comment: 9 pages, 3 figures, accepted for publication in ApJ
The role of black hole mass in quasar radio activity
We use a homogeneous sample of about 300, 0.3 <~ z <~ 3, radio-loud quasars
drawn from the FIRST and 2dF QSO surveys to investigate a possible dependence
of radio activity on black-hole mass. By analyzing composite spectra for the
populations of radio-quiet and radio-loud QSOs -- chosen to have the same
redshift and luminosity distribution -- we find with high statistical
significance that radio-loud quasars are on average associated with black holes
of masses ~10^{8.6} M_sun, about twice as large as those measured for
radio-quiet quasars (~10^{8.3} M_sun). We also find a clear dependence of black
hole mass on optical luminosity of the form log (M_BH/M_sun)_{RL}= 8.57(\pm
0.06) - 0.27(\pm 0.06) (M_B + 24.5) and log (M_BH/M_sun)_{RQ}= 8.43(\pm 0.05)
-0.32(\pm 0.06) (M_B + 24.5), respectively for the case of radio-loud and
radio-quiet quasars. It is intriguing to note that these two trends run roughly
parallel to each other, implying that radio-loud quasars are associated to
black holes more massive than those producing the radio-quiet case at all
sampled luminosities. On the other hand, in the case of radio-loud quasars, we
find evidence for only a weak (if any) dependence of the black hole mass on
radio power. The above findings seem to support the belief that there exists --
at a given optical luminosity -- a threshold black hole mass associated with
the onset of significant radio activity such as that of radio-loud QSOs;
however, once the activity is triggered, there appears to be very little
connection between black hole mass and level of radio output.Comment: 10 pages, 10 figures, minor changes to match the accepted versio
The hybrid solution for the Fundamental Plane
By exploiting the database of early-type galaxies (ETGs) members of the WINGS
survey of nearby clusters, we address here the long debated question of the
origin and shape of the Fundamental Plane (FP). Our data suggest that different
physical mechanisms concur in shaping and tilting the FP with respect to the
virial plane (VP) expectation. In particular, an hybrid solution in which the
structure of galaxies and their stellar population are the main contributors to
the FP tilt seems to be favoured. We find that the bulk of the tilt should be
attributed to structural non-homology, while stellar population effects play an
important but less crucial role. Our data indicate that the differential FP
tilt between the V and K-band is due to a sort of entanglement between
structural and stellar population effects, for which the inward steepening of
color profiles (V-K) tends to increase at increasing the stellar mass of ETGs.
The same analysis applied to the ATLAS3D and SDSS data in common with WINGS
(WSDSS throughout the paper) confirms our results, the only remarkable
difference being the less important role of the stellar mass-to-light-ratio in
determining the FP tilt. The ATLAS3D data also suggest that the tilt depends as
well on the dark matter (DM) fraction and on the rotational contribution to the
kinetic energy (Vrot/sigma). We show that the global properties of the FP can
be understood in terms of the underlying correlation among mass, structure and
stellar population of ETGs, for which, at increasing the stellar mass, ETGs
become (on average) older and more centrally concentrated. Finally, we show
that a Malmquist-like selection effect may mimic a differential evolution of
the mass-to-light ratio for galaxies of different masses. This should be taken
into account in the studies investigating the amount of the so called
downsizing phenomenon.Comment: 22 pages, 17 figure
The Case for Optically-Thick High Velocity Broad Line Region Gas in Active Galactic Nuclei
A combined analysis of the profiles of the main broad quasar emission lines
in both Hubble Space Telescope and optical spectra shows that while the
profiles of the strong UV lines are quite similar, there is frequently a strong
increase in the Ly-alpha/H-alpha ratio in the high-velocity gas. We show that
the suggestion that the high velocity gas is optically-thin presents many
problems. We show that the relative strengths of the high velocity wings arise
naturally in an optically-thick BLR component. An optically-thick model
successfully explains the equivalent widths of the lines, the Ly-alpha/H-alpha
ratios and flatter Balmer decrements in the line wings, the strengths of CIII]
and the lambda 1400 blend, and the strong variability of high-velocity,
high-ionization lines (especially HeII and HeI).Comment: 34 pages in AASTeX, including 10 pages of figures. Submitted to
Astrophysical Journa
Immunotherapy as a turning point in the treatment of acute myeloid leukemia
Acute myeloid leukemia (AML) is a malignant disease of hematopoietic precursors at
the earliest stage of maturation, resulting in a clonalproliferation of myoblasts replacing normal
hematopoiesis. AML represents one of the most common types of leukemia, mostly affecting elderly
patients. To date, standard chemotherapy protocols are only effective in patients at low risk of relapse
and therapy-related mortality. The average 5-year overall survival (OS) is approximately 28%. Allogeneic hematopoietic stem cell transplantation (HSCT) improves prognosis but is limited by donor
availability, a relatively young age of patients, and absence of significant comorbidities. Moreover, it
is associated with significant morbidity and mortality. However, increasing understanding of AML
immunobiology is leading to the development of innovative therapeutic strategies. Immunotherapy
is considered an attractive strategy for controlling and eliminating the disease. It can be a real
breakthrough in the treatment of leukemia, especially in patients who are not eligible forintensive
chemotherapy. In this review, we focused on the progress of immunotherapy in the field of AML by
discussing monoclonal antibodies (mAbs), immune checkpoint inhibitors, chimeric antigen receptor
T cells (CAR-T cells), and vaccine therapeutic choices
Black hole mass estimation from X-ray variability measurements in AGN
We propose a new method of estimation of the black hole masses in AGN based
on the normalized excess variance, sigma_{nxs}^2. We derive a relation between
sigma_{nxs}^2, the length of the observation, T, the light curve bin size,
Delta t, and the black hole mass, assuming that (i) the power spectrum above
the high frequency break, f_{bf}, has a slope of -2, (ii) the high frequency
break scales with black hole mass, (iii) the power spectrum amplitude (in
'frequency x power' space) is universal and (iv) sigma_{nxs}^2 is calculated
from observations of length T < 1/f_{bf}. Values of black hole masses in AGN
obtained with this method are consistent with estimates based on other
techniques such as reverberation mapping or the Mbh-stellar velocity dispersion
relation. The method is formally equivalent to methods based on power spectrum
scaling with mass but the use of the normalized excess variance has the big
advantage of being applicable to relatively low quality data.Comment: 5 pages, 1 figure, 1 table, accepted for publication in MNRAS Letter.
Added minor change on page 5 - corrected mistake (1/T 1/T > nu
PG 1211+143: probing high frequency lags in a high mass AGN
We present the timing analysis of the four archived XMM-Newton observations
of PG 1211+143. The source is well-known for its spectral complexity,
comprising a strong soft-excess and different absorption systems. Soft energy
band (0.3-0.7 keV) lags are detected over all the four observations, in the
frequency range \nu \lsim 6 \times 10^{-4} Hz, where hard lags, similar to
those observed in black hole X-ray binaries, are usually detected in smaller
mass AGN. The lag magnitude is energy-dependent, showing two distinct trends
apparently connectable to the two flux levels at which the source is observed.
The results are discussed in the context of disk- and/or corona-reprocessing
scenarios, and of disk wind models. Similarities with the high-frequency
negative lag of 1H 0707-495 are highlighted, and, if confirmed, they would
support the hypothesis that the lag in PG 1211+143 represents the signature of
the same underlying mechanism, whose temporal characteristics scale with the
mass of the central object.Comment: 6 pages, 6 figures, accepted for publication in MNRAS Letter
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