1,721,062 research outputs found
Investigating Dark Energy Equation of State With High Redshift Hubble Diagram
Full text linkSeveral different data sets revealed the accelerated expansion rate of the Universe, usually assumed to be driven by the so called dark energy, which, according to recent estimates, provides about 70% of the total amount of matter-energy in the Universe. The nature of dark energy is yet unknown. Several models of dark energy have been proposed: a non zero cosmological constant, a potential energy of some self interacting scalar field, effects related to the non homogeneous distribution of matter, or effects due to alternative theories of gravity. A tension between predictions of the flat ΛCDM model and a high-redshift Hubble diagram (HD) of supernovae, and quasars has been discovered in [1, 2], and it has been confirmed in [3] adding a gamma-ray bursts HD. Here we use the same data performing a statistical analysis in order to constraint the dark energy EOS. Our high redshift HD supports indication (at > 3σ level) of an evolving dark energy EOS, thus confirming the previous results
Erratum: “X-Ray Properties of AGN in Brightest Cluster Galaxies. I. A Systematic Study of the Chandra Archive in the 0.2 < z < 0.3 and 0.55 < z < 0.75 Redshift Range” (2018, ApJ, 859, 65)
Full text linkThe SOUX AGN Sample: SDSS-XMM-Newton Optical, Ultraviolet and X-ray selected active galactic nuclei spanning a wide range of parameter space -- Sample definition
Full text linkWe assemble a sample of 696 type 1 active galactic nuclei (AGN) up to a redshift of z = 2.5, all of which have an SDSS spectrum containing at least one broad emission line (H α, H β, or Mg II) and an XMM-Newton X-ray spectrum containing at least 250 counts in addition to simultaneous optical/ultraviolet photometry from the XMM Optical Monitor. Our sample includes quasars and narrow-line Seyfert 1s: thus our AGN span a wide range in luminosity, black hole mass, and accretion rate. We determine single-epoch black hole mass relations for the three emission lines and find that they provide broadly consistent mass estimates whether the continuum or emission line luminosity is used as the proxy for the broad emission line region radius. We explore variations of the UV/X-ray energy index α
ox with the UV continuum luminosity and with black hole mass and accretion rate, and make comparisons to the physical quasar spectral energy distribution model QSOSED. The majority of the AGN in our sample lie in a region of parameter space with 0.02 < L/L
Edd < 2 as defined by this model, with narrow-line type 1 AGN offset to lower masses and higher accretion rates than typical broad-line quasars. We find differences in the dependence of α
ox on UV luminosity between both narrow/broad-line and radio-loud/quiet subsets of AGN: α
ox has a slightly weaker dependence on UV luminosity for broad-line AGN and radio-loud AGN have systematically harder α
ox
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Active galactic nuclei and their panchromatic beauty.
No full textThe rapid development of new observational capabilities provides the ability to detect both the obscured (Type 2) and the unobscured (Type 1) flavours of active galaxies. In particular, the combination of sensitive observations from mid-IR to X-rays allows us to pierce through large columns of gas and dust hiding the Type 2 obscured AGN nuclear region. The study of the relative AGN/host-galaxy contribution over different portions of the broad-band Spectral Energy Distribution (SED) is fundamental to constrain the physical evolution of AGN and how to place them into the context of galaxy evolution.
I will discuss a study of the multi-wavelength properties of an X-ray selected sample of both obscured and unobscured AGN using the XMM-Newton wide field survey in the COSMOS field. I will focus on their SEDs, the morphology of the host-galaxies, the stellar masses, the bolometric luminosities and bolometric corrections. Finally, I will briefly discuss what are the perspectives of AGN in the context of observational cosmology
What we can (still) learn from the non-linear X-ray to UV relation in AGN
Full text linkAGN power engine - SED of QS
AGN as Cosmological Probes
No full textI will review previous methods that have tried to employ active galactic nuclei to measure cosmological parameters. I will introduce a novel technique able to test the cosmological model using quasars as “standard candles” by employing the non- linear relation between their intrinsic UV and X-ray emission as an absolute distance indicator
X-Ray Properties of AGN in Brightest Cluster Galaxies. I. A Systematic Study of the <i>Chandra</i> Archive in the 0.2 < <i>z</i> < 0.3 and 0.55 < <i>z</i> < 0.75 Redshift Range
Full text linkWe present a search for nuclear X-ray emission in the brightest cluster galaxies (BCGs) of a sample of groups and clusters of galaxies extracted from the Chandra archive. The exquisite angular resolution of Chandra allows us to obtain robust photometry at the position of the BCG, and to firmly identify unresolved X-ray emission when present, thanks to an accurate characterization of the extended emission at the BCG position. We consider two redshift bins (0.2 < z < 0.3 and 0.55 < z < 0.75) and analyze all the clusters observed by Chandra with exposure time larger than 20 ks. Our samples have 81 BCGs in 73 clusters and 51 BCGs in 49 clusters in the low- and high-redshift bins, respectively. X-ray emission in the soft (0.5-2 keV) or hard (2-7 keV) band is detected only in 14 and 9 BCGs (∼18% of the total samples), respectively. The X-ray photometry shows that at least half of the BCGs have a high hardness ratio, compatible with significant intrinsic absorption. This is confirmed by the spectral analysis with a power-law model plus intrinsic absorption. We compute the fraction of X-ray bright BCGs above a given hard X-ray luminosity, considering only sources with positive photometry in the hard band (12/5 sources in the low/high-z sample)
The SOUX AGN sample: SDSS–XMM-Newton optical, ultraviolet, and X-ray selected active galactic nuclei spanning a wide range of parameter space – sample definition
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