579 research outputs found
On the Exotic Hard X-ray Source Populations in the Hellas2XMM survey
Recent hard X-ray surveys have proven to be effective in discovering large
numbers of X-ray sources that, despite the likely association with active
nuclei, appear to be characterized by "peculiar" properties. Among these
"exotic" source populations, we will focus on the nature of two classes of hard
X-ray sources: those characterized by high X-ray-to-optical flux ratios -- a
fraction of these are associated with the rather elusive Type 2 quasars -- and
the X-ray bright optically normal galaxies, also known as XBONGs.Comment: On behalf of the HELLAS2XMM Collaboration, 6 pages, 4 figures,
contribution to the Proceedings of the COSPAR Scientific Assembly, E1.3
"High-Energy Radiation from Black Holes: from Supermassive Black Holes to
Galactic Solar Mass Black Holes", Paris (France), July 18-25, 2004, accepted
for publication in Advances in Space Researc
Il difficile cammino della democrazia paritaria: gli interventi normativi tra quote e preferenza di genere
Il presente lavoro ha come obiettivo quello di analizzare il difficile cammino della democrazia paritaria in Italia procedendo con un’esposizione ragionata della giurisprudenza costituzionale sul tema, che ha tanto influenzato tutta la materia: a partire dalla bocciatura delle “quote rosa” con la sent. n. 422 del 1995, modificata però dalla successiva sent. n. 49 del 2003 che traccia le linee della legittimità di futuri provvedimenti; sino alla riforma dell’art. 51 Cost., avvenuta con l. cost. n. 1 del 2003. che ha costituito un nodo cruciale negli interventi in materia di pari opportunità che sono state, così, “costituzionalizzate”.La ricerca, espressa nel secondo capitolo della trattazione, è nata dall'esigenza di approfondire il quadro teorico normativo e di disporre di un’analisi dettagliata elle principali esperienze vigenti in Italia in tema di pari opportunità tra donne e uomini alle cariche elettive. Soffermandosi sulla riforma costituzionale del titolo V della Costituzione si è ampiamente sottolineato proprio come le modifiche costituzionali hanno affidato alle Regioni un importante ruolo, spesso propulsore, in materia. Si sono prese in considerazioni eventuali scelte del legislatore regionale che ammettono clausole antidiscriminatorie, seguendo modelli diversi. Oltre al consueto strumento delle quote, con la presente analisi ci si è soffermati su uno strumento peculiare ed innovativo in tema di pari opportunità ossia la “preferenza di genere” introdotta dalla regione Campania e ottenuto l’avallo dei giudici costituzionali diventa una soluzione alla questione della rappresentanza di genere intrapresa non solo da diversi legislatori regionali ma, con la nuova legge elettorale, diventa strumento che vedremo utilizzare anche nelle prossime elezioni politiche. La ricerca, infine, ha voluto dedicarsi anche all’analisi della tematica negli enti locali, in particolare nei comuni, attraverso il richiamo alle principali modifiche normative e alla giurisprudenza amministrativa, che insieme a quella costituzionale, hanno dato man forte bocciando giunte “monogenere” e, soprattutto, riconoscendo diretta applicabilità all’art. 51 Cost. La trattazione procede nel capitolo terzo analizzando le disposizioni a tutela della rappresentanza di genere incluse nella normativa elettorale nazionale dalla legge Calderoli all'italicum con cui si introduce la "doppia preferenza di genere".Inoltre, non si è voluto tralasciare il ruolo fondamentale che i partiti politici hanno nella promozione della rappresentata di genere ma, allo stesso tempo, si sono evidenziate le carenze di quest’ultimi. Nel quarto e ultimo capitolo della trattazione per completezza d indagine si è analizzato il principio delle pari opportunità nell'ordinamento europeo, della tripla preferenza di genere introdotta per l'elezione dei nostri eurodeputati ed infine si è fornita un'analisi comparatistica disegnando una mappa della diffusione delle quote riservate alle donne in Europa e elenca i molti e diversi tipi di quote utilizzate dagli stati membri che si muovono, sostanzialmente, nell'ambito di due modelli di riferimento: il modello francese che prevede quote imposte per legge e quote liberamente scelte dai partiti politici previste, invece, nel modello scandinavo
An X-ray/SDSS sample (II): outflowing gas plasma properties
Galaxy-scale outflows are nowadays observed in many active galactic nuclei
(AGNs); however, their characterisation in terms of (multi-) phase nature,
amount of flowing material, effects on the host galaxy, is still unsettled. In
particular, ionized gas mass outflow rate and related energetics are still
affected by many sources of uncertainties. In this respect, outflowing gas
plasma conditions, being largely unknown, play a crucial role.
Taking advantage of the spectroscopic analysis results we obtained studying
the X-ray/SDSS sample of 563 AGNs at z presented in our companion paper,
we analyse stacked spectra and sub-samples of sources with high signal-to-noise
temperature- and density-sensitive emission lines to derive the plasma
properties of the outflowing ionized gas component. For these sources, we also
study in detail various diagnostic diagrams to infer information about
outflowing gas ionization mechanisms. We derive, for the first time, median
values for electron temperature and density of outflowing gas from medium-size
samples ( targets) and stacked spectra of AGNs. Evidences of shock
excitation are found for outflowing gas.
We measure electron temperatures of the order of K and
densities of cm for faint and moderately luminous AGNs
(intrinsic X-ray luminosity in the 2-10 keV band). We
caution that the usually assumed electron density ( cm) in
ejected material might result in relevant overestimates of flow mass rates and
energetics and, as a consequence, of the effects of AGN-driven outflows on the
host galaxy.Comment: 16 pages, 10 figures. Accepted for publication in A&
Decomposition of variance in terms of conditional means
We test against two different sets of data an apparently new approach to the
analysis of the variance of a numerical variable which depends on qualitative
characters. We suggest that this approach be used to complement other existing
techniques to study the interdependence of the variables involved. According to
our method the variance is expressed as a sum of orthogonal components,
obtained as differences of conditional means, with respect to the qualitative
characters. The resulting expression for the variance depends on the ordering
in which the characters are considered. We suggest an algorithm which leads to
an ordering which is deemed natural. The first set of data concerns the score
achieved by a population of students, on an entrance examination, based on a
multiple choice test with 30 questions. In this case the qualitative characters
are dyadic and correspond to correct or incorrect answer to each question. The
second set of data concerns the delay in obtaining the degree for a population
of graduates of Italian universities. The variance in this case is analyzed
with respect to a set of seven specific qualitative characters of the
population studied (gender, previous education, working condition, parent's
educational level, field of study, etc.)Comment: 3 figure
Chemical abundances and properties of the ionized gas in NGC 1705
We obtained [O III] narrow-band imaging and multi-slit MXU spectroscopy of
the blue compact dwarf (BCD) galaxy NGC 1705 with FORS2@VLT to derive chemical
abundances of PNe and H II regions and, more in general, to characterize the
properties of the ionized gas. The auroral [O III]\lambda4363 line was detected
in all but one of the eleven analyzed regions, allowing for a direct estimate
of their electron temperature. The only object for which the [O III]\lambda4363
line was not detected is a possible low-ionization PN, the only one detected in
our data. For all the other regions, we derived the abundances of Nitrogen,
Oxygen, Neon, Sulfur and Argon out to ~ 1 kpc from the galaxy center. We detect
for the first time in NGC 1705 a negative radial gradient in the oxygen
metallicity of -0.24 \pm 0.08 dex kpc^{-1}. The element abundances are all
consistent with values reported in the literature for other samples of dwarf
irregular and blue compact dwarf galaxies. However, the average (central)
oxygen abundance, 12 + log(O/H)=7.96 \pm 0.04, is ~0.26 dex lower than previous
literature estimates for NGC 1705 based on the [O III]\lambda4363 line. From
classical emission-line diagnostic diagrams, we exclude a major contribution
from shock excitation. On the other hand, the radial behavior of the emission
line ratios is consistent with the progressive dilution of radiation with
increasing distance from the center of NGC 1705. This suggests that the
strongest starburst located within the central 150 pc is responsible for
the ionization of the gas out to at least 1 kpc. The gradual dilution of
the radiation with increasing distance from the center reflects the gradual and
continuous transition from the highly ionized H II regions in the proximity of
the major starburst into the diffuse ionized gas.Comment: Accepted for publication on A
Listening to galaxies tuning at z ~ 2.5 - 3.0: The first strikes of the Hubble fork
We investigate the morphological properties of 494 galaxies selected from the
GMASS survey at z>1, primarily in their optical rest frame, using HST images,
from the CANDELS survey. We propose that the Hubble sequence of galaxy
morphologies takes shape at redshift 2.5<z<3. The fractions of both ellipticals
and disks decrease with increasing lookback time at z>1, such that at redshifts
z=2.5-2.7 and above, the Hubble types cannot be identified, and most galaxies
are classified as irregular. The quantitative morphological analysis shows
that, at 1<z<3, morphological parameters are not as effective in distinguishing
the different morphological Hubble types as they are at low redshift. No
significant morphological k-correction was found to be required for the Hubble
type classification, with some exceptions. In general, different morphological
types occupy the two peaks of the rest-frame (U-B) colour bimodality of
galaxies: most irregulars occupy the blue peak, while ellipticals are mainly
found in the red peak, though with some level of contamination. Disks are more
evenly distributed than either irregulars and ellipticals. We find that the
position of a galaxy in a UVJ diagram is related to its morphological type: the
"quiescent" region of the plot is mainly occupied by ellipticals and, to a
lesser extent, by disks. We find that only ~33% of all morphological
ellipticals in our sample are red and passively evolving galaxies. Blue
galaxies morphologically classified as ellipticals show a remarkable structural
similarity to red ones. Almost all irregulars have a star-forming galaxy
spectrum. In addition, the majority of disks show some sign of star-formation
activity in their spectra, though in some cases their red continuum is
indicative of old stellar populations. Finally, an elliptical morphology may be
associated with either passively evolving or strongly star-forming galaxies.Comment: 27 pages, 16 figures, 5 tables. "Morphological atlas" in the
appendix. Revised version accepted for publication in A&
A new photometric technique for the joint selection of star-forming and passive galaxies at 1.4<z<2.5
A simple two color selection based on B-, z-, and K- band photometry is
proposed for culling galaxies at 1.4<z<2.5 in K-selected samples and
classifying them as star-forming or passive systems. The method is calibrated
on the highly complete spectroscopic redshift database of the K20 survey,
verified with simulations and tested on other datasets. Requiring
BzK=(z-K)-(B-z)>-0.2 (AB) allows to select actively star-forming galaxies at
z>1.4, independently on their dust reddening. Instead, objects with BzK<-0.2
and (z-K)>2.5 (AB) colors include passively evolving galaxies at z>1.4, often
with spheroidal morphologies. Simple recipes to estimate the reddening, SFRs
and masses of BzK-selected galaxies are derived, and calibrated on K<20
galaxies. Based on their UV (reddening-corrected), X-ray and radio
luminosities, the BzK-selected star-forming galaxies with K<20 turn out to have
average SFR ~ 200 Msun yr^-1, and median reddening E(B-V)~0.4. Besides missing
the passively evolving galaxies, the UV selection appears to miss some relevant
fraction of the z~2 star-forming galaxies with K<20, and hence of the
(obscured) star-formation rate density at this redshift. The high SFRs and
masses add to other existing evidence that these z=2 star-forming galaxies may
be among the precursors of z=0 early-type galaxies. Theoretical models cannot
reproduce simultaneously the space density of both passively evolving and
highly star-forming galaxies at z=2. In view of Spitzer Space Telescope
observations, an analogous technique based on the RJL photometry is proposed to
complement the BzK selection and to identify massive galaxies at 2.5<z<4.0.
These color criteria should help in completing the census of the stellar mass
and of the star-formation rate density at high redshift (abridged).Comment: 19 pages, 17 figures, to appear on ApJ (20 December 2004 issue
The space density of Compton-thick AGN at z~0.8 in the zCOSMOS-Bright Survey
The obscured accretion phase in BH growth is a key ingredient in many models
linking the AGN activity with the evolution of their host galaxy. At present, a
complete census of obscured AGN is still missing. The purpose of this work is
to assess the reliability of the [NeV] emission line at 3426 A to pick up
obscured AGN up to z~1 by assuming that [NeV] is a reliable proxy of the
intrinsic AGN luminosity and using moderately deep X-ray data to characterize
the amount of obscuration. A sample of 69 narrow-line (Type 2) AGN at
z=0.65-1.20 were selected from the 20k-zCOSMOS Bright galaxy sample on the
basis of the presence of the [NeV] emission. The X-ray properties of these
galaxies were then derived using the Chandra-COSMOS coverage of the field; the
X-ray-to-[NeV] flux ratio, coupled with X-ray spectral and stacking analyses,
was then used to infer whether Compton-thin or Compton-thick absorption were
present in these sources. Then the [NeV] luminosity function was computed to
estimate the space density of Compton-thick (CT) AGN at z~0.8. Twenty-three
sources were detected by Chandra, and their properties are consistent with
moderate obscuration (on average, ~a few 10^{22} cm^-2). The X-ray properties
of the remaining 46 X-ray undetected Type 2 AGN were derived using X-ray
stacking analysis. Current data indicate that a fraction as high as ~40% of the
present sample is likely to be CT. The space density of CT AGN with
logL_2-10keV>43.5 at z=0.83 is (9.1+/-2.1) 10^{-6} Mpc^{-3}, in good agreement
with both XRB model expectations and the previously measured space density for
objects in a similar redshift and luminosity range. We regard our selection
technique for CT AGN as clean but not complete, since even a mild extinction in
the NLR can suppress [NeV] emission. Therefore, our estimate of their space
density should be considered as a lower limit.Comment: 10 pages, 7 figures, 2 tables, A&A, in pres
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