4,055 research outputs found
Fifty Years of Quasars: Physical Insights and Potential for Cosmology
Last year (2013) was more or less the 50th anniversary of the discovery of
quasars. It is an interesting time to review what we know (and don't know)
about them both empirically and theoretically. These compact sources involving
line emitting plasma show extraordinary luminosities extending to one thousand
times that of our Milky Way in emitting volumes of a few solar system diameters
(bolometric luminosity log L 44-48 [erg s]: D=1-3 light
months - gravitational radii). The advent of 8-10 meter
class telescopes enables us to study them spectroscopically in ever greater
detail.
In 2000 we introduced a 4D Eigenvector 1 parameters space involving optical,
UV and X-Ray measures designed to serve as a 4D equivalent of the 2D
Hertzsprung-Russell diagram so important for depicting the diversity of stellar
types and evolutionary states. This diagram has revealed a principal sequence
of quasars distinguished by Eddington ratio (proportional to the accretion rate
per unit mass). Thus while stellar differences are primarily driven by the mass
of a star, quasar differences are apparently driven by the ratio of
luminosity-to-mass.
Out of this work has emerged the concept of two quasars populations A and B
separated at Eddington ratio around 0.2 which maximizes quasar multispectral
differences. The mysterious 8% of quasars that are radio-loud belong to
population B which are the lowest accretors with the largest black hole masses.
Finally we consider the most extreme population A quasars which are the highest
accretors and in some cases are among the youngest quasars. We describe how
these sources might be exploited as standard candles for cosmology.Comment: Accepted for publication in Journal of Physics Conference Series (10
pages, 4 figures). Invited Lecture at International Symposium on the Physics
of Ionized Gas (SPIG 2014), Belgrade 26-29 August 201
Holographic realization from inflation to reheating in generalized entropic cosmology
The growing cosmological interest of different entropy functions (like the
Tsallis entropy, the R\'{e}nyi entropy, the Barrow entropy, the Sharma-Mittal
entropy, the Kaniadakis entropy and the Loop Quantum gravity entropy) naturally
raises an important question: "Does there exist a generalized entropy that can
bring all the known entropies proposed so far within a single umbrella?" In
spirit of this, recently a four parameter generalized entropy has been
formulated that reduces to different known entropies for suitable limits of the
parameters. Based on such four parameter generalized entropy (symbolized by
), in the present paper, we examine the universe's evolution
during its early phase, particularly from inflation to reheating, in the
context of entropic cosmology where the entropic energy density acts as the
inflaton. It turns out that the entropic energy successfully drives an early
inflationary phase with a graceful exit, and moreover, the theoretical
expectations of the observable indices get consistent with the recent Planck
data for suitable ranges of the entropic parameters. After the inflation ends,
the universe enters to a reheating stage when the entropic energy decays to
relativistic particles with a certain decay rate. Actually the presence of the
entropic parameters in the ensures a continuous evolution of the
Hubble parameter from a quasi de-Sitter phase during the inflation to a power
law phase during the reheating stage dominated by a constant EoS parameter.
Consequently we investigate the reheating phenomenology, and scan the entropic
parameters from both the inflation and reheating requirements. We further
address the possibility of instantaneous reheating in the present context of
generalized entropy.Comment: "Physics of the Dark Universe" Accepte
Attention-deficit/hyperactivity disorder medication and seizures
OBJECTIVE:
Individuals with attention-deficit/hyperactivity disorder (ADHD) are at increased risk of seizures, but there is uncertainty about whether ADHD medication treatment increases risk among patients with and without preexisting seizures.
METHODS:
We followed a sample of 801,838 patients with ADHD who had prescribed drug claims from the Truven Health MarketScan Commercial Claims and Encounters databases to examine whether ADHD medication increases the likelihood of seizures among ADHD patients with and without a history of seizures. First, we assessed overall risk of seizures among patients with ADHD. Second, within-individual concurrent analyses assessed odds of seizure events during months when a patient with ADHD received ADHD medication compared with when the same individual did not, while adjusting for antiepileptic medications. Third, within-individual long-term analyses examined odds of seizure events in relation to the duration of months over the previous 2 years patients received medication.
RESULTS:
Patients with ADHD were at higher odds for any seizure compared with non-ADHD controls (odds ratio [OR] = 2.33, 95% confidence interval [CI] = 2.24-2.42 males; OR = 2.31, 95% CI = 2.22-2.42 females). In adjusted within-individual comparisons, ADHD medication was associated with lower odds of seizures among patients with (OR = 0.71, 95% CI = 0.60-0.85) and without (OR = 0.71, 95% CI = 0.62-0.82) prior seizures. Long-term within-individual comparisons suggested no evidence of an association between medication use and seizures among individuals with (OR = 0.87, 95% CI = 0.59-1.30) and without (OR = 1.01, 95% CI = 0.80-1.28) a seizure history.
CONCLUSIONS:
Results reaffirm that patients with ADHD are at higher risk of seizures. However, ADHD medication was associated with lower risk of seizures within individuals while they were dispensed medication, which is not consistent with the hypothesis that ADHD medication increases risk of seizures
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
Arp 194: Evidence of Tidal Stripping of Gas and Cross-Fueling
We present new imaging and spectroscopic observations of the interacting system Arp 194 (= UGC 06945 = VV 126). The northern component (A194N) is a distorted spiral or ring galaxy likely disrupted by a collision or close encounter with a southern galaxy (A194S). There is evidence that a third galaxy with similar recession velocity is projected on A194N but its role is likely secondary. A194S is connected to A194N by a string of emission knots which motivates our interpretation that the former was the intruder. Three of the knots are easily discernible in B,R, and H-alpha images and are assumed to trace the path of the intruder following the encounter, which we estimate occurred a few 10^8 yr ago. Both A194S and N are experiencing strong bursts of star formation: the H-alpha luminosity indicates a total star formation rate ~ 10 solar masses per year. The lack of detectable J and K emission from the blobs, along with strong H-alpha emission, indicates that an evolved stellar population is not likely to be present. The brightest knot (closest to A194S) shows a star formation rate of ~1.2 solar masses per year which, if sustained over a time ~ 7 10^7 yr, could explain the spectral energy distribution. This suggests that the stripped matter was originally predominantly gaseous. The brightest knot is detected as a FIRST radio source and this is likely the signature of supernova remnants related to enhanced star formation. Motions in the gas between the brightest knot and A194S, traced by an emission line link of increasing radial velocity, suggests infall toward the center of the intruder. Arp 194 is therefore one of the few galaxies where evidence of ``cross-fueling'' is observed [LaTeX removed]
Quasars: from the Physics of Line Formation to Cosmology
Quasars accreting matter at very high rates (known as extreme Population A
[xA] or super-Eddington accreting massive black holes) provide a new class of
distance indicators covering cosmic epochs from the present-day Universe up to
less than 1 Gyr from the Big Bang. The very high accretion rate makes it
possible that massive black holes hosted in xA quasars radiate at a stable,
extreme luminosity-to-mass ratio. This in turns translates into stable physical
and dynamical conditions of the mildly ionized gas in the quasar low-ionization
line emitting region. In this contribution, we analyze the main optical and UV
spectral properties of extreme Population A quasars that make them easily
identifiable in large spectroscopic surveys at low-z (z < 1) and intermediate-z
(2 < z < 2.6), and the physical conditions that are derived for the formation
of their emission lines. Ultimately, the analysis supports the possibility of
identifying a virial broadening estimator from low-ionization line widths, and
the conceptual validity of the redshift-independent luminosity estimates based
on virial broadening for a known luminosity-to-mass ratio.Comment: 13 pages, 5 figures. Invited lecture at SPIG 2018, Belgrade. To
appear in Ato
The concentration-mass relation of clusters of galaxies from the OmegaWINGS survey
The relation between a cosmological halo concentration and its mass (cMr) is
a powerful tool to constrain cosmological models of halo formation and
evolution. On the scale of galaxy clusters the cMr has so far been determined
mostly with X-ray and gravitational lensing data. The use of independent
techniques is helpful in assessing possible systematics. Here we provide one of
the few determinations of the cMr by the dynamical analysis of the
projected-phase-space distribution of cluster members. Based on the WINGS and
OmegaWINGS data sets, we used the Jeans analysis with the MAMPOSSt technique to
determine masses and concentrations for 49 nearby clusters, each of which has
~60 spectroscopic members or more within the virial region, after removal of
substructures. Our cMr is in statistical agreement with theoretical predictions
based on LambdaCDM cosmological simulations. Our cMr is different from most
previous observational determinations because of its flatter slope and lower
normalization. It is however in agreement with two recent cMr obtained using
the lensing technique on the CLASH and LoCuSS cluster data sets. In the future
we will extend our analysis to galaxy systems of lower mass and at higher
redshifts.Comment: Astronomy & Astrophysics in press. 11 pages, 6 figure
A New Approach to the Study of Stellar Populations in Early-Type Galaxies: K-band Spectral Indices and an Application to the Fornax Cluster
New measurements of K-band spectral features are presented for eleven
early-type galaxies in the nearby Fornax galaxy cluster. Based on these
measurements, the following conclusions have been reached: (1) in galaxies with
no signatures of a young stellar component, the K-band Na I index is highly
correlated with both the optical metallicity indicator [MgFe]' and central
velocity dispersion; (2) in the same galaxies, the K-band Fe features saturate
in galaxies with sigma > 150 km/s while Na I (and [MgFe]') continues to
increase; (3) [Si/Fe] (and possibly [Na/Fe]) is larger in all observed Fornax
galaxies than in Galactic open clusters with near-solar metallicity; (4) in
various near-IR diagnostic diagrams, galaxies with signatures of a young
stellar component (strong Hbeta, weak [MgFe]') are clearly separated from
galaxies with purely old stellar populations; furthermore, this separation is
consistent with the presence of an increased number of M-giant stars (most
likely to be thermally pulsating AGB stars); (5) the near-IR diagrams discussed
here seem as efficient for detecting putatively young stellar components in
early-type galaxies as the more commonly used age/metallicity diagnostic plots
using optical indices (e.g Hbeta vs. [MgFe]').Comment: 47 pages, 16 figures, ApJ accepte
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