1,355,377 research outputs found
The evolution of obscured accretion
No full textOur current understanding of the evolution of obscured accretion onto supermassive black holes is reviewed. We consider the literature results on the relation between the fraction of moderately obscured, Compton-thin AGN and redshift, and discuss the biases which possibly affect the various measurements. Then, we discuss a number of methods - from ultradeep X-ray observations to the detection of high-ionization optical emission lines - to select the population of the most heavily obscured, Compton-thick AGN, whose cosmological evolution is basically unknown. The space density of heavily obscured AGN measured through different techniques is discussed and compared with the predictions by current synthesis models of the X-ray background. Preliminary results from the first half of the 3 Ms XMM observation of the Chandra Deep Field South (CDFS) are also presented. The prospects for population studies of heavily obscured AGN with future planned or proposed X-ray missions are finally discussed
The puzzling case of XBONGs: will 3D-spectroscopy explain their true nature?
No full textThe discovery of luminous hard X-ray sources hosted by "normal" galaxies
with optical spectra typical of early-type systems (XBONG; Comastri et al.
2002) represents one of the most surprising results of Chandra and XMM-Newton
surveys.
Why the relatively bright X-ray emission, typical of moderately luminous
Active Galactic Nuclei (AGN), does not leave any optical signature of the
presence of a nuclear source is still subject of debate. Although several
possibilities have been discussed in the recent years, the main concern about
the nature of these sources is that the AGN emission lines may be "hidden"
by the host galaxy starlight. The already granted VIMOS-IFU observations will
provide us with a unique opportunity to understand these enigmatic sources.
High spatial resolution, integral field spectroscopy in the optical,
isolating the nuclei of the XBONGs, would help to settle the AGN line absence
vs. starlight dilution controversy. The 3D-spectroscopy will also provide
a clear insight into the optical properties of these X-ray emitting galaxies
and, therefore, into the nature of the obscured super-massive black holes
(SMBH) they host
Extragalactic X-ray surveys: AGN physics and evolution
No full textWe review the most important findings on AGN physics and cosmological
evolution as obtained by extragalactic X-ray surveys and associated
multiwavelength observations. We briefly discuss the perspectives for
future enterprises and in particular the scientific case for an
extremely deep (2-3 Ms) XMM surve
Reseña del libro : La construcción del carisma peronista. Cartas a Juan y Eva Perón de Donna J. Guy
No full textFil: Comastri, Hernán. Consejo Nacional de Investigaciones Científicas y Técnicas (CONICET). Universidad de Buenos Aires; Argentina
Commento agli artt. 361 c.p.c. (riserva facoltativa di ricorso contro sentenze non definitive) e 133 disp. att. c.p.c. (riserva di ricorso. estinzione del processo)
No full textX-ray spectral analysis of optically faint sources in the Chandra deep fields
No full textWe present the results of a detailed spectral analysis of optically
faint hard X-ray sources in the Chandra deep fields selected on the
basis of their high X-ray to optical flux ratio (X/O). The stacked
spectra of high X/O sources in both Chandra deep fields, fitted with a
single power-law model, are much harder than the spectrum of the X-ray
background (XRB). The average slope is also insensitive to the 2-8 keV
flux, being approximately constant around Γ~= 1 over more than two
decades, strongly indicating that high X/O sources represent the most
obscured component of the XRB. For about half of the sample, a redshift
estimate (in most of the cases a photometric redshift) is available from
the literature. Individual fits of a few of the brightest objects and of
stacked spectra in different redshift bins imply column densities in the
range 1022-1023.5 cm-2. A trend of
increasing absorption towards higher redshifts is suggested
Natalia Milanesio, Cuando los trabajadores salieron de compras. Nuevos consumidores, publicidad y cambio cultural durante el primer peronismo, Buenos Aires, Siglo XXI, 2014, 262 páginas.
No full textFil: Comastri, Hernán. Universidad de Buenos Aires; Argentina.Fil: Comastri, Hernán. Consejo Nacional de Investigaciones Científicas y Técnicas; Argentina.El libro de Natalia Milanesio presenta al consumidor obrero no solo como una novedad histórica para la Argentina de mediados del siglo XX, sino también como “una fuerza social modernizadora” que ayudaría a modelar una nueva cultura comercial, así como una transformación de las relaciones sociales, de las identidades colectivas y del rol del Estado como mediador entre empresas y consumidores. Es en este sentido que su investigación, si bien ha llenado un vacío historiográfico en los estudios sobre el primer peronismo, busca explícitamente insertarse en una historia de más largo plazo sobre el consumo en la Argentina, objeto de estudio que ha tenido un desarrollo tardío en relación a otros casos nacionales
Ensino e avaliação na formação de professores: aprendendo após a pandemia
No full textEquipo del proyecto: Marcela Comastri, Élida Hodar, Eugenia de la Rosa, Néstor Olivera, María de los Ángeles Barrionuevo (IES 9-028 “Prof. Estela S. Quiroga”), Paula González Ardizzone
- …
