| 1. |
- Chen, C. T.J., et al.
(författare)
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The XMM-SERVS survey : New XMM-Newton point-source catalogue for the XMM-LSS field
- 2018
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Ingår i: Monthly Notices of the Royal Astronomical Society. - : Oxford University Press (OUP). - 0035-8711 .- 1365-2966. ; 478:2, s. 2132-2163
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Tidskriftsartikel (refereegranskat)abstract
- We present an X-ray point-source catalogue from the XMM-Large Scale Structure (XMMLSS) survey region, one of the XMM-Spitzer Extragalactic Representative Volume Survey (XMM-SERVS) fields. We target the XMM-LSS region with 1.3 Ms of new XMM-Newton AO-15 observations, transforming the archival X-ray coverage in this region into a 5.3 deg2 contiguous field with uniform X-ray coverage totaling 2.7 Ms of flare-filtered exposure, with a 46 ks median PN exposure time. We provide an X-ray catalogue of 5242 sources detected in the soft (0.5-2 keV), hard (2-10 keV), and/or full (0.5-10 keV) bands with a 1 per cent expected spurious fraction determined from simulations. A total of 2381 new X-ray sources are detected compared to previous source catalogues in the same area. Our survey has flux limits of 1.7 × 10-15, 1.3 × 10-14, and 6.5 × 10-15 erg cm-2 s-1 over 90 per cent of its area in the soft, hard, and full bands, respectively, which is comparable to those of the XMM-COSMOS survey. We identify multiwavelength counterpart candidates for 99.9 per cent of the X-ray sources, of which 93 per cent are considered as reliable based on their matching likelihood ratios. The reliabilities of these high-likelihood-ratio counterparts are further confirmed to be ≈97 per cent reliable based on deep Chandra coverage over ≈5 per cent of the XMM-LSS region. Results of multiwavelength identifications are also included in the source catalogue, along with basic optical-to-infrared photometry and spectroscopic redshifts from publicly available surveys. We compute photometric redshifts for X-ray sources in 4.5 deg2 of our field where forced-aperture multiband photometry is available; > 70 per cent of the X-ray sources in this subfield have either spectroscopic or high-quality photometric redshifts.
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| 2. |
- Vito, F., et al.
(författare)
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High-redshift AGN in the Chandra Deep Fields : The obscured fraction and space density of the sub-L* population
- 2018
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Ingår i: Monthly Notices of the Royal Astronomical Society. - : Oxford University Press (OUP). - 0035-8711 .- 1365-2966. ; 473:2, s. 2378-2406
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Tidskriftsartikel (refereegranskat)abstract
- We investigate the population of high-redshift (3≤z < 6) active galactic nuclei (AGN) selected in the two deepest X-ray surveys, the 7 Ms Chandra Deep Field-South and 2 Ms Chandra Deep Field-North. Their outstanding sensitivity and spectral characterization of faint sources allow us to focus on the sub-L* regime (logLX ≲ 44), poorly sampled by previous works using shallower data, and the obscured population. Taking fully into account the individual photometric-redshift probability distribution functions, the final sample consists of ≈102 X-ray-selected AGN at 3 ≤ z < 6. The fraction of AGN obscured by column densities logNH > 23 is ~0.6-0.8, once incompleteness effects are taken into account, with no strong dependence on redshift or luminosity. We derived the high-redshift AGN number counts down to F0.5-2 keV = 7 × 10-18 erg cm-2 s-1, extending previous results to fainter fluxes, especially at z > 4. We put the tightest constraints to date on the low-luminosity end of AGN luminosity function at high redshift. The space density, in particular, declines at z > 3 at all luminosities, with only a marginally steeper slope for low-luminosity AGN. By comparing the evolution of the AGN and galaxy densities, we suggest that such a decline at high luminosities is mainly driven by the underlying galaxy population, while at low luminosities there are hints of an intrinsic evolution of the parameters driving nuclear activity. Also, the black hole accretion rate density and star formation rate density, which are usually found to evolve similarly at z ≲ 3, appear to diverge at higher redshifts.
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| 3. |
- Dall` Olio, Daria, 1981, et al.
(författare)
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Costellazione Manga: explaining astronomy using Japanese comics and animation
- 2018
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Ingår i: Communicating Astronomy with the Public Journal. - 1996-563X .- 1996-5621. ; :24, s. 7-16
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Tidskriftsartikel (refereegranskat)abstract
- Comics and animation are intensely engaging and can be successfully used to communicate science to the public. They appear to stimulate many aspects of the learning process and can help with the development of links between ideas. Given these pedagogical premises, we conducted a project called Costellazione Manga, in which we considered astronomical concepts present in several manga and anime (Japanese comics and animations) and highlighted the physics behind them. These references to astronomy allowed us to introduce interesting topics of modern astrophysics and communicate astronomy-related concepts to a large spectrum of people. In this paper, we describe the methodology and techniques that we developed and discuss the results of our project. Depending on the comic or anime considered, we can introducegeneral topics such as the difference between stars, planets and galaxies or ideas such as the possibility of nding life onother planets, the latest discoveries of Earth-like planets orbiting other stars or the detection of complex organic molecules in the interstellar space. When presenting the night sky and the shapes of constellations, we can also describe how the same stars are perceived and grouped by different cultures. The project outcomes indicate that Costellazione Manga is a powerful tool to popularise astronomy and stimulate important aspects of learning development, such as curiosity and critical thinking. We show through our experience that Costellazione Manga has attracted a broader and more diverse public than traditional planetarium activities and astronomy lectures.
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| 4. |
- Ranalli, P., et al.
(författare)
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Astrometry and exoplanets in the Gaia era : A Bayesian approach to detection and parameter recovery
- 2018
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Ingår i: Astronomy and Astrophysics. - : EDP Sciences. - 0004-6361 .- 1432-0746. ; 614
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Tidskriftsartikel (refereegranskat)abstract
- The Gaia mission is expected to make a significant contribution to the knowledge of exoplanet systems, both in terms of their number and of their physical properties. We develop Bayesian methods and detection criteria for orbital fitting, and revise the detectability of exoplanets in light of the in-flight properties of Gaia. Limiting ourselves to one-planet systems as a first step of the development, we simulate Gaia data for exoplanet systems over a grid of S/N, orbital period, and eccentricity. The simulations are then fit using Markov chain Monte Carlo methods. We investigate the detection rate according to three information criteria and the Δχ2. For the Δχ2, the effective number of degrees of freedom depends on the mission length. We find that the choice of the Markov chain starting point can affect the quality of the results; we therefore consider two limit possibilities: an ideal case, and a very simple method that finds the starting point assuming circular orbits. We use 6644 and 4402 simulations to assess the fraction of false positive detections in a 5 yr and in a 10 yr mission, respectively; and 4968 and 4706 simulations to assess the detection rate and how the parameters are recovered. Using Jeffreys' scale of evidence, the fraction of false positives passing a strong evidence criterion is ≤ 0.2% (0.6%) when considering a 5 yr (10 yr) mission and using the Akaike information criterion or the Watanabe-Akaike information criterion, and <0.02% (<0.06%) when using the Bayesian information criterion. We find that there is a 50% chance of detecting a planet with a minimum S/N = 2.3 (1.7). This sets the maximum distance to which a planet is detectable to ∼70 pc and ∼3.5 pc for a Jupiter-mass and Neptune-mass planets, respectively, assuming a 10 yr mission, a 4 au semi-major axis, and a 1 M⊙ star. We show the distribution of the accuracy and precision with which orbital parameters are recovered. The period is the orbital parameter that can be determined with the best accuracy, with a median relative difference between input and output periods of 4.2% (2.9%) assuming a 5 yr (10 yr) mission. The median accuracy of the semi-major axis of the orbit can be recovered with a median relative error of 7% (6%). The eccentricity can also be recovered with a median absolute accuracy of 0.07 (0.06).
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