3C 345 - Is the variability of quasars nonlinear?

Vio, R.; Cristiani, S.; Lessi, O.; Salvadori, L.

doi:10.1086/170594

Cited by 24 publications

(24 citation statements)

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“…General reviews of kernel estimators are given by Silverman (1986) and Scott (1992); applications to astronomical data are given by Vio et al (1994), Tremblay & Merritt (1995), and Ryden (1996). Here, we give a brief overview, adopting the notation of Ryden (1996).…”

Section: Methodsmentioning

confidence: 99%

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The Shapes of Galaxies in the Sloan Digital Sky Survey

Alam

Ryden

2002

ApJ

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We estimate the distribution of apparent axis ratios q for galaxies in the Sloan Digital Sky Survey Early Data Release. We divide the galaxies by profile type (de Vaucouleurs vs. exponential) as well as by color (u Ã À r Ã 2:22 vs. u Ã À r Ã > 2:22). The axis ratios found by fitting models to the surface photometry are generally smaller than those found by taking the second moments of the surface brightness distribution. Using the axis ratios found from fitting models, we find that galaxies with de Vaucouleurs profiles have axis ratio distributions that are inconsistent, at the 99% confidence level, with their being a population of randomly oriented oblate spheroids. Red de Vaucouleurs galaxies are slightly rounder, on average, than blue de Vaucouleurs galaxies. By contrast, red galaxies with exponential profiles appear very much flatter, on average, than blue galaxies with exponential profiles. The red exponential galaxies are primarily disk galaxies seen nearly edge-on, with reddening due to the presence of dust, rather than to an intrinsically red stellar population.

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Section: Methodsmentioning

confidence: 99%

“…This formula for h minimizes the expected value of the mean square error for samples that are not strongly skewed (Silverman 1986;Vio et al 1994). We choose a Gaussian kernel to ensure thatf f is smooth and differentiable.…”

Section: Methodsmentioning

confidence: 99%

The Shapes of Galaxies in the Sloan Digital Sky Survey

Alam

Ryden

2002

ApJ

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“…In many papers (e.g. Vio et al 1994;Fadda et al 1998;Ferdosi et al 2011) it has been shown that kernel smoothing is the best and recommended choice for density estimation. It is more robust and reliable than other simpler methods and provides comparable (or better) results than methods with high computational costs (e.g.…”

Section: Appendix A: Kernel Density Estimationmentioning

confidence: 99%

Galaxy filaments as pearl necklaces

Tempel

Kipper

Saar

et al. 2014

A&A

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Context. Galaxies in the Universe form chains (filaments) that connect groups and clusters of galaxies. The filamentary network includes nearly half of the galaxies and is visually the most striking feature in cosmological maps. Aims. We study the distribution of galaxies along the filamentary network, trying to find specific patterns and regularities. Methods. Galaxy filaments are defined by the Bisous model, a marked point process with interactions. We use the two-point correlation function and the Rayleigh Z-squared statistic to study how galaxies and galaxy groups are distributed along the filaments. Results. We show that galaxies and groups are not uniformly distributed along filaments, but tend to form a regular pattern. The characteristic length of the pattern is around 7 h −1 Mpc. A slightly smaller characteristic length 4 h −1 Mpc can also be found, using the Z-squared statistic. Conclusions. We find that galaxy filaments in the Universe are like pearl necklaces, where the pearls are galaxy groups distributed more or less regularly along the filaments. We propose that this well-defined characteristic scale could be used to test various cosmological models and to probe environmental effects on the formation and evolution of galaxies.Key words. methods: numerical -methods: observational -large-scale structure of Universe IntroductionMany cosmological probes have been developed and used to estimate the parameters of the cosmological models describing our Universe. Most of them rely on some aspects of the large-scale structure. The most common probe used to quantify galaxy clustering is the two-point correlation function which was first used decades ago (Davis & Geller 1976;Groth & Peebles 1977;Davis et al. 1988;Hamilton 1988;White et al. 1988;Boerner et al. 1989;Einasto 1991) It is well known that galaxy filaments are visually the most dominant structures in the galaxy distribution, being part of the so-called cosmic network (Jõeveer et al. 1978;Bond et al. 1996). Presumably, nearly half (∼40%) of the galaxies (or mass in simulations) are located in filaments. This number is based on morphological or dynamical classification of the cosmic web (e.g. Jasche et al. 2010;Tempel et al. 2014b;Cautun et al. 2014). Properties of the three-point correlation function also indicate that galaxies tend to populate filamentary structures (Guo et al. 2014a) and, indeed, filaments have been found between galaxy clusters (e.g. Dietrich et al. 2012). Tempel et al. (2014a) show Appendices are available in electronic form at

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“…This cut has been successfully employed in many studies (Girardi et al 1998;Girardi & Mezzetti 2001). To evaluate the optimal smoothing parameter, we minimise the integrated square error (Pisani 1993), fixing the initial value to the estimate proposed by Vio et al (1994). As a second step, we take into account both the position and the velocity information by using the procedure of the shifting gapper (Fadda et al 1996;Girardi et al 1998).…”

Section: Appendix A: Velocity Dispersionmentioning

confidence: 99%

A multiwavelength strong lensing analysis of baryons and dark matter in the dynamically active cluster AC 114

Sereno

Lubini

Jetzer

2010

A&A

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Context. Strong lensing studies can provide detailed mass maps of the inner regions even in dynamically active galaxy clusters. Aims. We illustrate the important role of a proper modelling of the intracluster medium, i.e., the main baryonic component. We demonstrate that the addition of a new contribution accounting for the gas can increase the statistical significance of the lensing model. Methods. We propose a parametric method for strong lensing analyses that exploits multiwavelength observations. The mass model accounts for cluster-sized dark matter halos, galaxies (whose stellar mass can be obtained from optical analyses), and the intracluster medium. The gas distribution is fitted to lensing data exploiting prior knowledge from X-ray observations. This gives an unbiased insight into each matter component and allows us to study the dynamical status of a cluster. The method was applied to AC 114, an irregular X-ray cluster. Results. We find positive evidence of dynamical activity, the dark matter distribution being shifted and rotated with respect to the gas. On the other hand, the dark matter follows the galaxy density in terms of both shape and orientation, illustrating the collisionless nature of dark matter. The inner region ( < ∼ 250 kpc) is underluminous in optical bands, whereas the gas fraction (∼20 ± 5%) slightly exceeds typical values. Evidence of lensing and X-ray suggests that the cluster develops in the plane of the sky and is not affected by the lensing over-concentration bias. Despite the dynamical activity, the matter distribution seems to agree with predictions of N-body simulations. An universal cusped profile provides a good description of either the overall or the dark matter distribution, whereas theoretical scaling relations seem to be accurately fitted.

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3C 345 - Is the variability of quasars nonlinear?

Cited by 24 publications

References 0 publications

The Shapes of Galaxies in the Sloan Digital Sky Survey

The Shapes of Galaxies in the Sloan Digital Sky Survey

Galaxy filaments as pearl necklaces

A multiwavelength strong lensing analysis of baryons and dark matter in the dynamically active cluster AC 114

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