Astronomy 410 / Physics 410:
Astrophysics

Fall Semester 2009

Astrophysics: Journal Articles

This page of links is assembled automatically via software algorithm. These are links to some current Astrophysics-related Journal Articles (which are peer-reviewed) and preprints (which are NOT peer-reviewed).

USAGE NOTE: The symbol next to each feed item can be clicked in order to bring up a more complete description.

Recent Peer-Reviewed Journal Articles

One of the things that sets science apart from many other fields of human-endeavor is that to prevent personal opinion from being represented as fact, articles that are submitted to scientific journals are "peer-reviewed", which means the paper is sent to a referee (possibly a scientific "competitor") who disects the article and makes sure its conclusions are valid based on the data presented. The process is not perfect, but it tends to drive a high level of scholarly quality in peer-reviewed journals.

Astronomical Journal Latest Articles (10 Most Recent Items)

1. Zhu, L. Y.: WZ Cephei: A Close Binary at the Beginning of Contact Phase
   Photometric photoelectric data of the short-period close binary system, WZ Cephei, are presented. A new photometric analysis with the 2003 version of the Wilson-Devinney method confirmed that it is a shallow contact binary (f ~ 13.3%) with a high level of spot activity on the primary component. Combining new determined times of light minimum with the others published in the literature, the period change of the binary star is investigated. A periodic variation, with a period of 34.2 years and an amplitude of 0fd013, was discovered to be superimposed on a long-term period decrease (dP/dt = --8.8 ?10--8 days year--1). Both the secular period decrease and the shallow contact configuration suggest that this binary system is at the beginning of contact phase. It is on the way to evolving into a normal overcontact phase via secular angular momentum loss and/or mass transfer from the more massive component to the less massive one. The period oscillation can be explained either by the light-time effect due to the presence...
2. Du, Z. L.: The Predictive Power of Ohl's Precursor Method
   Using linear regression techniques and correlation analysis, the predictive power of Ohl's method is shown to satisfy one of the following relationships. Either a successful prediction of cycle amplitude can be obtained if the correlation between the minimum aa geomagnetic index in the declining phase of a solar cycle and the sunspot maximum of the succeeding cycle becomes stronger, or the prediction error exceeds the expected prediction error if the correlation becomes weaker. The correlation coefficient has a declining secular variation, which leads to a weakening trend in predictive power, as well as a 44 year periodicity that may explain why the prediction method did not work well for solar cycle 23. As this finding only emerged twice in the ~100 year period studied, this 44 year periodicity may occur with a degree of uncertainty and may therefore need to be checked in the future. Two quantities, namely a prediction parameter and the prediction index, are proposed to analyze predictive power. Using the above...
3. Capetti, A.: A Very Large Array Radio Survey of Early-Type Galaxies in the Virgo Cluster
   We present the results of an 8.4 GHz Very Large Array radio survey of early-type galaxies extracted from the sample selected by C?and collaborators for the Advanced Camera for Surveys Virgo Cluster Survey. The aim of this survey is to investigate the origin of radio emission in early-type galaxies and its link with the host properties in an unexplored territory toward the lowest levels of both radio and optical luminosities. Radio images, available for all 63 galaxies with B T < 14.4, show the presence of a compact radio source in 12 objects, with fluxes spanning from 0.13 mJy to 2700 mJy. The remaining 51 galaxies, undetected at a flux limit of ~0.1 mJy, have radio luminosities L lsim 4 ?1018 W Hz--1. The fraction of radio-detected galaxies are a strong function of stellar mass, in agreement with previous results: none of the 30 galaxies with M sstarf < 1.7 ?1010 M sun is detected, while 8 of the 11 most massive galaxies have radio cores. There appears to be no simple relation between the presence of a stellar...
4. Rudenko, P.: Intermediate-Age Clusters in a Field Containing M31 and M32 Stars
   Hubble Space Telescope/Advanced Camera for Surveys fields toward M31 and M32 were examined for the presence of possible star clusters. On the basis of stellar photometry, two intermediate-age clusters were found in the field that contains both M31 and M32 stars. One is approximately 200 Myr of age with a mass ~400 M sun, and the other is 1 Gyr old with mass ~8 ?104 M sun. Several other cluster candidates are identified, but their stellar populations are more similar to the field: old and slightly metal-poor.
5. Benedict, G. F.: Astrometry with the Hubble Space Telescope: Trigonometric Parallaxes of Planetary Nebula Nuclei NGC 6853, NGC 7293, Abell 31, and DeHt 5
   We present absolute parallaxes and relative proper motions for the central stars of the planetary nebulae NGC 6853 (The Dumbbell), NGC 7293 (The Helix), Abell 31, and DeHt 5. This paper details our reduction and analysis using DeHt 5 as an example. We obtain these planetary nebula nuclei (PNNi) parallaxes with astrometric data from Fine Guidance Sensors FGS 1r and FGS 3, white-light interferometers on the Hubble Space Telescope. Proper motions, spectral classifications and VJHKT2M and DDO51 photometry of the stars comprising the astrometric reference frames provide spectrophotometric estimates of reference star absolute parallaxes. Introducing these into our model as observations with error, we determine absolute parallaxes for each PNN. Weighted averaging with previous independent parallax measurements yields an average parallax precision, sigmapi/pi = 5%. Derived distances are: d NGC 6853 = 405+28 --25 pc, d NGC 7293 = 216+14 --12 pc, d Abell 31 = 621+91 --70 pc, and d DeHt 5 = 345+19 --17 pc. These PNNi distances...
6. Toribio, M. C.: H I Distribution and Tully-Fisher Distances of Gas-Poor Spiral Galaxies in the Virgo Cluster Region
   We present aperture synthesis observations in the 21 cm line of pointings centered on the Virgo Cluster region spirals NGC 4307, NGC 4356, NGC 4411B, and NGC 4492 using the Very Large Array (VLA) radio telescope in its CS configuration. These galaxies were identified in a previous study of the three-dimensional distribution of H I emission in the Virgo region as objects with a substantial dearth of atomic gas and Tully-Fisher (TF) distance estimates that located them well outside the main body of the cluster. We have detected two other galaxies located in two of our fields and observed bands, the spiral NGC 4411A and the dwarf spiral VCC 740. We provide detailed information of the gas morphology and kinematics for all these galaxies. Our new data confirm the strong H I deficiency of all the main targets but NGC 4411B, which is found to have a fairly normal neutral gas content. The VLA observations have also been used to discuss the applicability of TF techniques to the five largest spirals we have observed. We...
7. Courtois, H. M.: The Extragalactic Distance Database: All Digital H I Profile Catalog
   An important component of the Extragalactic Distance Database is a group of catalogs related to the measurement of H I line profile parameters. One of these is the All Digital H I catalog which contains an amalgam of information from new data and old. The new data result from observations with Arecibo and Parkes Telescopes and with the Green Bank Telescope, including continuing input since the award of the NRAO Cosmic Flows Large Program. The old data have been collected from archives, wherever available, particularly the Cornell University Digital H I Archive, the Nan? Telescope extragalactic H I archive, and the Australia Telescope H I archive. The catalog currently contains information on ~15, 000 profiles relating to ~13, 000 galaxies. The channel-flux per channel files, from whatever source, is carried through a common pipeline. The derived parameter of greatest interest is W m50, the profile width at 50% of the mean flux. After appropriate adjustment, the parameter Wmx is derived, the line width that statistically...
8. Mc Greer, I. D.: Radio-Selected Quasars in the Sloan Digital Sky Survey
   We have conducted a pilot survey for z > 3.5 quasars by combining the FIRST radio survey with the Sloan Digital Sky Survey (SDSS). While SDSS already targets FIRST sources for spectroscopy as quasar candidates, our survey includes fainter quasars and greatly improves the discovery rate by using strict astrometric criteria for matching the radio and optical positions. Our method allows for selection of high-redshift quasars with less color bias than with optical selection, as using radio selection essentially eliminates stellar contamination. We report the results of spectroscopy for 45 candidates, including 29 quasars in the range 0.37 < z < 5.2, with 7 having redshifts z > 3.5. We compare quasars selected using radio and optical criteria, and find that radio-selected quasars have a much higher fraction of moderately reddened objects. We derive a radio-loud quasar luminosity function at 3.5 < z < 4.0, and find that it is in good agreement with expectations from prior SDSS results.
9. Manzoori, D.: Cyclic Variations of Orbital Period and Long-Term Luminosity in Close Binary RT Andromedae
   Solutions of standard VR light curves for the eclipsing binary RT And were obtained using the PHOEBE program (ver. 0.3a). Absolute parameters of the stellar components were then determined, enabling them to be positioned on the mass-luminosity diagram. Times of minima data ("O -- C curve") were analyzed using the method of Kalimeris et al. A cyclic variation in the orbital period and brightness, with timescales of about 11.89 and 12.50 yr were found, respectively. This is associated with a magnetic activity cycle modulating the orbital period of RT And via the Applegate mechanism. To check the consistency of the Applegate model, we have estimated some related parameters of the RT And system. The calculated parameters were in accordance with those estimated by Applegate for other similar systems, except B, the subsurface magnetic field of which shows a rather high value for RT And.
10. Sheen, Y.-K.: Tidal Dwarf Galaxies Around a Post-merger Galaxy, NGC 4922
    One possible channel for the formation of dwarf galaxies involves birth in the tidal tails of interacting galaxies. We report the detection of a bright UV tidal tail and several young tidal dwarf galaxy (TDG) candidates in the post-merger galaxy NGC 4922 in the Coma cluster. Based on a two-component population model (combining young and old stellar populations), we find that the light of tidal tail predominantly comes from young stars (a few Myr old). The Galaxy Evolution Explorer ultraviolet data played a critical role in the parameter (age and mass) estimation. Our stellar mass estimates of the TDG candidates are ~106--7 M sun, typical for dwarf galaxies.

Publications of the Astronomical Society of the Pacific Latest Articles (10 Most Recent Items)

1. Melo, A. M.: Addendum: ``A New Setup for Ground-based Measurements of Solar Activity at 10 mum'' (PASP, 118, 1558 [2006])
   Not Available
2. Bufano, F.: The Ultraviolet View of Supernovae
   Not Available
3. Abt, H. A.: Reviewing and Revision Times for The Astrophysical Journal
   From a study of the editorial log for 251 manuscripts submitted in 2006, we learn that 6% are rejected, 5% are withdrawn, and 88% are eventually accepted for publication. Of the accepted articles, 30% are reviewed once, 58% twice, and 12% are reviewed 3-5 times. The mean time for the first review is 31 days and for the first revision is 44 days. The spread in total reviewing times (dispersion of 16 days) is much shorter than in total revision times (54 days). Important articles, those receiving 31-193 citations in 2 yr, are not reviewed more promptly than others nor revised more promptly. Only in the subfield of high-energy objects do the authors revise their manuscripts marginally more promptly than others.
4. Steiner, J. F.: A Simple Comptonization Model
   We present an empirical model of Comptonization for fitting the spectra of X-ray binaries. This model, named simpl, has been developed as a package implemented in XSPEC. With only two free parameters, simpl is competitive as the simplest model of Compton scattering. Unlike the pervasive standard power-law model, simpl incorporates the basic features of Compton scattering of soft photons by energetic coronal electrons. Using a simulated spectrum, we demonstrate that simpl closely matches the behavior of physical Comptonization models that consider the effects of optical depth, coronal electron temperature, and geometry. We present fits to RXTE spectra of the black hole transient H1743-322 and a BeppoSAX spectrum of LMC X-3 using both simpl and the standard power-law model. A comparison of the results shows that simpl gives equally good fits, while eliminating the troublesome divergence of the standard power-law model at low energies. simpl is completely flexible and can be used self-consistently with any seed...
5. Slater, C. T.: Removing Internal Reflections from Deep Imaging Data Sets
   We present a means of characterizing and removing internal reflections between the CCD and other optical surfaces in an astronomical camera. The stellar reflections appear as out-of-focus images and are not necessarily axisymmetric about the star. Using long exposures of very bright stars as calibration images, we are able to measure the position, size, and intensity of reflections as a function of their position on the field. We also measure the extended stellar point-spread function out to 1°. Together this information can be used to create an empirical model of the excess light from bright stars and reduce systematic artifacts in deep surface photometry. We then reduce a set of deep observations of the Virgo cluster with our method to demonstrate its efficacy and to provide a comparison with other strategies for removing scattered light.
6. Taylor, M.: Tutorial: Exact Solutions for the Populations of the n-level Ion
   This tutorial presents a review of the analytical approach to obtain exact solutions for the populations of n-level ions, and summarizes the ideas behind detailed balance and the statistical physics of collisionally-excited ions. Seaton's analytical solution for the populations of the 3-level ion has been supplanted by matrix methods such as the master equation approach, which are now central to astronomy since there is a need to maintain a parity between improvements in quantum-mechanically calculated values for collision strengths and transition probabilities on the one hand, and three-dimensional (3D) photoionization codes used by astrophysicists for producing nebular diagnostics on the other. We show that the analytical method of solution to the problem using matrices and symbolic mathematics is straightforward, and we illustrate through theoretical, numerical, and empirical checks the validity of its results. First, we recast the equations of thermal statistical equilibrium for the energy level populations...
7. Batcheldor, D.: The Future of Direct Supermassive Black Hole Mass Estimates
   The repeated discovery of supermassive black holes (SMBHs) at the centers of galactic bulges, and the discovery of relations between the SMBH mass (M) and the properties of these bulges, have been fundamental in directing our understanding of both galaxy and SMBH formation and evolution. However, there are still many underlying questions surrounding the SMBH-galaxy relations. For example, are the scaling relations linear and constant throughout cosmic history, and do all SMBHs lie on the scaling relations? These fundamental questions can only be answered by further high quality direct M estimates from a wide range in redshift, before further refinements to galaxy evolution models can be made. In this article we determine the observational requirements necessary to directly determine SMBH masses, across cosmological distances, using current M modeling techniques. We also discuss the SMBH detection abilities of future facilities. We find that if different M modeling techniques, using different spectral features,...
8. Lozi, J.: Phase-Induced Amplitude Apodization on Centrally Obscured Pupils: Design and First Laboratory Demonstration for the Subaru Telescope Pupil
   High-contrast coronagraphic imaging is challenging for telescopes with central obstructions and thick spider vanes, such as the Subaru Telescope. We present in this article the first laboratory demonstration of a high-efficiency PIAA-type coronagraph on such a pupil, using coronagraphic optics which will be part of the Subaru Coronagraphic Extreme-AO (SCExAO) system currently under assembly. Lossless pupil apodization is performed by a set of aspheric PIAA lenses specifically designed to also remove the pupil's central obstruction, coupled with a spider removal plate (SRP) which removes spider vanes by translating four parts of the pupil with tilted plane-parallel plates. An "inverse-PIAA" system, located after the coronagraphic focal plane mask, is used to remove off-axis aberrations and deliver a wide field of view. Our results validate the concept adopted for the SCExAO system, and show that the Subaru Telescope pupil can be properly apodized for high-contrast coronagraphic imaging as close as≈1 lambda/D...
9. Boss, A. P.: The Carnegie Astrometric Planet Search Program
   We are undertaking an astrometric search for gas giant planets and brown dwarfs orbiting nearby low-mass dwarf stars with the 2.5 m du Pont Telescope at the Las Campanas Observatory in Chile. We have built two specialized astrometric cameras, the Carnegie Astrometric Planet Search Cameras (CAPSCam-S and CAPSCam-N), using two Teledyne HAWAII-2RG HyViSI arrays, with the cameras' design having been optimized for high-accuracy astrometry of M dwarf stars. We describe two independent CAPSCam data reduction approaches and present a detailed analysis of the observations to date of one of our target stars, NLTT 48256. Observations of NLTT 48256 taken since 2007 July with CAPSCam-S imply that astrometric accuracies of around 0.3 mas hr are achievable, sufficient to detect a Jupiter-mass companion orbiting 1 AU from a late M dwarf 10 pc away with a signal-to-noise ratio (S/N) of about 4. We plan to follow about 100 nearby (primarily within about 10 pc) low-mass stars, principally late M, L, and T dwarfs, for 10 yr or more,...
10. Gull, T. R.: The Variable 6307 Å Emission Line in the Spectrum of Eta Carinae: Blueshifted [S III] lambda6313 from the Interacting Winds
    The 6307 ?emission line in the spectrum of eta Car, found by Martin et al., is blue-shifted [S iii] lambda6313 emission originating from the outer wind structures of the massive binary system. We realized the identification while analyzing multiple forbidden emission lines not normally seen in the spectra of massive stars. The high spatial and moderate spectral resolutions of HST/STIS resolve forbidden lines of Fe, N, Fe, S, Ne, and Ar into spatially and velocity-resolved ropelike features originating from collisionally-excited ions photoionized by UV photons or collisions. While the [Fe ii] emission extends across a velocity range of ±500 km s out to 0.7", more highly ionized forbidden emissions ([N ii], [Fe iii], [S iii], [Ar iii], and [Ne iii]) range in velocity from -500 to +200 km s, but spatially extend out to only 0.4". The [Fe ii] defines the outer regions of the massive primary wind. The [N ii], [Fe iii] emissions define the the outer wind interaction regions directly photoionized by far-UV radiation....

Astrophysical Journal Latest Issue (10 Most Recent Items)

1. Gayley, K. G.: Analytic Aperture Calculation and Scaling Laws for Radio Detection of Lunar-target Ultra-high-energy Neutrinos
   We derive analytic expressions and approximate them in closed form, for the effective detection aperture for Cerenkov radio emission from ultra-high-energy neutrinos striking the Moon. The resulting apertures are in good agreement with recent Monte Carlo simulations and support the conclusion of James & Protheroe that neutrino flux upper limits derived from the GLUE search were too low by an order of magnitude. We also use our analytic expressions to derive scaling laws for the aperture as a function of observational and lunar parameters. We find that at low frequencies downward-directed neutrinos always dominate, but at higher frequencies, the contribution from upward-directed neutrinos becomes increasingly important, especially at lower neutrino energies. Detecting neutrinos from Earth near the Greisen-Zatsepin-Kuz'min regime will likely require radio telescope arrays with extremely large collecting area (Ae ~ 106 m2) and hundreds of hours exposure time. Higher-energy neutrinos are most easily detected using...
2. Cao, L.: A Wavelet-Galerkin Algorithm of the E/B Decomposition of Cosmic Microwave Background Polarization Maps
   We develop an algorithm of separating the E and B modes of the cosmic microwave background (CMB) polarization from the noisy and discretized maps of Stokes parameters Q and U in a finite area. A key step of the algorithm is to take a wavelet-Galerkin discretization of the differential relation between the E, B and Q, U fields. This discretization allows derivative operator to be represented by a matrix, which is exactly diagonal in scale space, and narrowly banded in spatial space. We show that the effect of boundary can be eliminated by dropping a few discrete wavelet transform modes, located on or nearby the boundary. This method reveals that the derivative operators will cause large errors in the E and B power spectra on small scales if the Q and U maps contain Gaussian noise. It also reveals that if the Q and U maps are random, these fields lead to the mixing of E and B modes. Consequently, the B mode will be contaminated if the powers of E modes are much larger than that of B modes. Nevertheless, numerical...
3. Boselli, A.: High-mass Star Formation in Normal Late-type Galaxies: Observational Constraints to the Initial Mass Function
   We use Halpha and far-ultraviolet (FUV, 1539 - Galaxy Evolution Explorer (GALEX) data for a large sample of nearby objects to study the high-mass (m>= 2 M sun) star formation activity of normal late-type galaxies. The data are corrected for dust attenuation using the most accurate techniques available at present, namely the Balmer decrement for Halpha data and the total far-infrared to FUV flux ratio for GALEX data. The sample shows a highly dispersed distribution in the Halpha to FUV flux ratio (log f(Halpha)/f(FUV) = 1.10 ± 0.34 - indicating that two of the most commonly used star formation tracers give star formation rates (SFRs) with uncertainties up to a factor of 2-3. The high dispersion is partly due to the presence of active galactic nuclei, where the UV and the Halpha emission can be contaminated by nuclear activity, highly inclined galaxies, for which the applied extinction corrections are probably inaccurate, or starburst galaxies, where the stationarity in the star formation history required for...
4. Honda, M.: Ultra-high Energy Cosmic-ray Acceleration in the Jet of Centaurus A
   We evaluate the achievable maximum energy of nuclei diffusively accelerated by shock wave in the jet of Cen A, based on an updated model involving the stochastic magnetic fields that are responsible for recent synchrotron X-ray measurements. For the maximum energy analysis, conceivable energy constraints from spatiotemporal scales are systematically considered for the jet-wide including discrete X-ray knots. We find that in the inner region within ~1 arcmin from galactic core, which includes knots AX and BX, proton and iron nucleus can be accelerated to 1019-1020 and 1021 eV (10-100 EeV and ZeV) ranges, respectively. The upper cutoff energy of the very energetic neutrinos produced via photopion interaction is also provided. These are essential for identifying the acceleration site of the ultra-high energy cosmic ray detected in the Pierre Auger Observatory, which signifies the arrival from nearby galaxies including Cen A.
5. Houde, M.: Dispersion of Magnetic Fields in Molecular Clouds. II.
   We expand our study on the dispersion of polarization angles in molecular clouds. We show how the effect of signal integration through the thickness of the cloud as well as across the area subtended by the telescope beam inherent to dust continuum measurements can be incorporated in our analysis to correctly account for its effect on the measured angular dispersion and inferred turbulent to large-scale magnetic field strength ratio. We further show how to evaluate the turbulent magnetic field correlation scale from polarization data of sufficient spatial resolution and high enough spatial sampling rate. We apply our results to the molecular cloud OMC-1, where we find a turbulent correlation length of delta ≈ 16 mpc, a turbulent to large-scale magnetic field strength ratio of approximately 0.5, and a plane-of-the-sky large-scale magnetic field strength of approximately 760 muG.
6. Boudreault, S.: A Constraint on Brown Dwarf Formation Via Ejection: Radial Variation of the Stellar and Substellar Mass Function of the Young Open Cluster IC 2391
   We present the stellar and substellar mass function (MF) of the open cluster IC 2391, plus its radial dependence, and use this to put constraints on the formation mechanism of brown dwarfs (BDs). Our multi-band optical and infrared photometric survey with spectroscopic follow-up covers 11 deg2, making it the largest survey of this cluster to date. We observe a radial variation in the MF over the range 0.072-0.3 M sun, but no significant variation in the MF below the substellar boundary at the three cluster radius intervals is analyzed. This lack of radial variation for low masses is what we would expect with the ejection scenario for BD formation, although considering that IC 2391 has an age about three times older than its crossing time, we expect that BDs with a velocity greater than the escape velocity have already escaped the cluster. Alternatively, the variation in the MF of the stellar objects could be an indication that they have undergone mass segregation via dynamical evolution. We also observe a significant...
7. Titarchuk, L.: Discovery of Photon Index Saturation in the Black Hole Binary GRS 1915+105
   We present a study of the correlations between spectral, timing properties, and mass accretion rate observed in X-rays from the Galactic black hole (BH) binary GRS 1915+105 during the transition between hard and soft states. We analyze all transition episodes from this source observed with the Rossi X-ray Timing Explorer, coordinated with Ryle Radio Telescope observations. We show that broadband energy spectra of GRS 1915+105 during all these spectral states can be adequately presented by two bulk motion Comptonization (BMC) components: a hard component (BMC1, photon index Gamma1 = 1.7-3.0) with turnover at high energies and soft thermal component (BMC2, Gamma2 = 2.7-4.2) with characteristic color temperature
8. Mediavilla, E.: Microlensing-based Estimate of the Mass Fraction in Compact Objects in Lens Galaxies
   We estimate the fraction of mass that is composed of compact objects in gravitational lens galaxies. This study is based on microlensing measurements (obtained from the literature) of a sample of 29 quasar image pairs seen through 20 lens galaxies. We determine the baseline for no microlensing magnification between two images from the ratios of emission line fluxes. Relative to this baseline, the ratio between the continua of the two images gives the difference in microlensing magnification. The histogram of observed microlensing events peaks close to no magnification and is concentrated below 0.6 mag, although two events of high magnification, Deltam ~ 1.5, are also present. We study the likelihood of the microlensing measurements using frequency distributions obtained from simulated microlensing magnification maps for different values of the fraction of mass in compact objects, alpha. The concentration of microlensing measurements close to Deltam ~ 0 can be explained only by simulations corresponding to very...
9. Joshi, B.: Magnetic Reconnection During the Two-phase Evolution of a Solar Eruptive Flare
   We present a detailed multi-wavelength analysis and interpretation of the evolution of an M7.6 flare that occurred near the southeast limb on 2003 October 24. Pre-flare images at TRACE 195 'show that the bright and complex system of coronal loops already existed at the flaring site. The X-ray observations of the flare taken from the Reuven Ramaty High Energy Solar Spectroscopic Imager (RHESSI) spacecraft reveal two phases of the flare evolution. The first phase is characterized by the altitude decrease of the X-ray looptop (LT) source for ~11 minutes. Such a long duration of the descending LT source motion is reported for the first time. The EUV loops, located below the X-ray LT source, also undergo contraction with similar speed (~15 km s--1) in this interval. During the second phase the two distinct hard X-ray footpoint (FP) sources are observed which correlate well with UV and Halpha flare ribbons. The X-ray LT source now exhibits upward motion as anticipated from the standard flare model. The RHESSI spectra...
10. Vittorini, V.: Powerful High-energy Emission of the Remarkable BL Lac Object S5 0716+714
    BL Lac objects of the intermediate subclass (IBLs) are known to emit a substantial fraction of their power in the energy range 0.1-10 GeV. Detecting gamma-ray emission from such sources provides therefore a direct probe of the emission mechanisms and of the underlying powerhouse. The gamma-ray satellite, AGILE, detected the remarkable IBL S5 0716+714 (z sime 0.3) during a high state in the period from 2007 September-October, marked by two very intense flares reaching peak fluxes of 200 ?10--8 photons cm--2 s--1 above 100 MeV, with simultaneous optical and X-ray observations. We present here a theoretical model for the two major flares and discuss the overall energetics of the source. We conclude that 0716+714 is among the brightest BL Lac's ever detected at gamma-ray energies. Because of its high power and lack of signs for ongoing accretion or surrounding gas, the source is an ideal candidate to test the maximal power extractable from a rotating supermassive black hole via the pure Blandford-Znajek (BZ) mechanism....

Most Recent Astrophysical Journal Letters (10 Most Recent Items)

1. Giroletti, M.: The Faintest Seyfert Radio Cores Revealed by VLBI
   In this Letter, we report on dual-frequency European VLBI Network observations of the faintest and least luminous radio cores in Seyfert nuclei, going to sub-millijansky flux densities and radio luminosities around 1019 W Hz--1. We detect radio emission from the nuclear region of four galaxies (NGC 4051, NGC 4388, NGC 4501, and NGC 5033), while one (NGC 5273) is undetected at the level of ~100 muJy. The detected compact nuclei have rather different radio properties: spectral indices range from steep (alpha>0.7) to slightly inverted (alpha = --0.1), brightness temperatures vary from TB = 105 K to larger than 107 K, and cores are either extended or unresolved, in one case accompanied by lobe-like features (NGC 4051). In this sense, diverse underlying physical mechanisms can be at work in these objects: jet-base or outflow solutions are the most natural explanations in several cases; in the case of the undetected NGC 5273 nucleus, the presence of an advection-dominated accretion flow is consistent with the radio...
2. Comerón, S.: On the Curvature of Dust Lanes in Galactic Bars
   We test the theoretical prediction that the straightest dust lanes in bars are found in strongly barred galaxies, or more specifically, that the degree of curvature of the dust lanes is inversely proportional to the strength of the bar. The test uses archival images of barred galaxies for which a reliable nonaxisymmetric torque parameter (Q b) and the radius at which Q b has been measured (r(Q b)) have been published in the literature. Our results confirm the theoretical prediction but show a large spread that cannot be accounted for by measurement errors. We simulate 238 galaxies with different bar and bulge parameters in order to investigate the origin of the spread in the dust lane curvature versus Q b relation. From these simulations, we conclude that the spread is greatly reduced when describing the bar strength as a linear combination of the bar parameters Q b and the quotient of the major and minor axes of the bar, a/b. Thus, we conclude that the dust lane curvature is predominantly determined by the parameters...
3. La Cognata, M.: Solving the Large Discrepancy Between Inclusive and Exclusive Measurements of the 8Li + 4He --> 11B + n Reaction Cross Section at Astrophysical Energies
   A solution of the large discrepancy existing between inclusive and exclusive measurements of the 8Li + 4He --> 11B + n reaction cross section at E cm < 3 MeV is evaluated. This problem has profound astrophysical relevance for this reaction is of great interest in big bang and r-process nucleosynthesis. By means of a novel technique, a comprehensive study of all existing 8Li + 4He --> 11B + n cross section data is carried out, setting up a consistent picture in which all the inclusive measurements provide the reliable value of the cross section. New unambiguous signatures of the strong branch pattern non-uniformities, near the threshold of higher 11B excited levels, are presented and their possible origin, in terms of the cluster structure of the involved excited states of 11B and 12Bnuclei, is discussed.
4. Fragile, P. C.: Effective Inner Radius of Tilted Black Hole Accretion Disks
   One of the primary means of determining the spin a of an astrophysical black hole is by actually measuring the inner radius r in of a surrounding accretion disk and using that to infer a. By comparing a number of different estimates of r in from simulations of tilted accretion disks with differing black hole spins, we show that such a procedure can give quite wrong answers. Over the range 0
5. Gosain, S.: HINODE Observations of Coherent Lateral Motion of Penumbral Filaments During a X-Class Flare
   The X-3.4 class flare of 2006 December 13 was observed with a high cadence of 2 minutes at 0.2 arcsec resolution by HINODE/SOT FG instrument. The flare ribbons could be seen in G-band images also. A careful analysis of these observations after proper registration of images shows flare-related changes in penumbral filaments of the associated sunspot for the first time. The observations of sunspot deformation, decay of penumbral area, and changes in magnetic flux during large flares have been reported earlier in the literature. In this Letter, we report lateral motion of the penumbral filaments in a sheared region of the delta-sunspot during the X-class flare. Such shifts have not been seen earlier. The lateral motion occurs in two phases: (1) motion before the flare ribbons move across the penumbral filaments and (2) motion afterward. The former motion is directed away from expanding flare ribbons and lasts for about 4 minutes. The latter motion is directed in the opposite direction and lasts for more than 40...
6. Maurya, R. A.: Variations in p-Mode Parameters with Changing Onset Time of a Large Flare
   It is expected that energetic solar flares releasing a large amount of energy at the photosphere may be able to excite the acoustic (p-) modes of oscillations. We have determined the characteristic properties of mode parameters by applying the ring diagram technique to three-dimensional power spectra obtained for solar active region NOAA 10486 during the long-duration energetic X17.2/4B flare of 2003 October 28. Strong evidence of substantial increase in mode amplitude and systematic variations in sub-surface flows, i.e., meridional and zonal components of velocity, kinetic helicity, and vorticity, is found from comparison of the pre- to the post-flare phases.
7. Miller-Jones, J. C. A.: The First Accurate Parallax Distance to a Black Hole
   Using astrometric VLBI observations, we have determined the parallax of the black hole X-ray binary V404 Cyg to be 0.418 ± 0.024 mas, corresponding to a distance of 2.39 ± 0.14 kpc, significantly lower than the previously accepted value. This model-independent estimate is the most accurate distance to a Galactic stellar-mass black hole measured to date. With this new distance, we confirm that the source was not super-Eddington during its 1989 outburst. The fitted distance and proper motion imply that the black hole in this system likely formed in a supernova, with the peculiar velocity being consistent with a recoil (Blaauw) kick. The size of the quiescent jets inferred to exist in this system is
8. Shinnaga, H.: Warm Extended Dense Gas at the Heart of a Cold Collapsing Dense Core
   In order to investigate when and how the birth of a protostellar core occurs, we made survey observations of four well-studied dense cores in the Taurus molecular cloud using CO transitions in submillimeter bands. We report here the detection of unexpectedly warm (~30-70 K), extended (radius of ~2400 AU), dense (a few times 105 cm--3) gas at the heart of one of the dense cores, L1521F (MC27), within the cold dynamically collapsing components. We argue that the detected warm, extended, dense gas may originate from shock regions caused by collisions between the dynamically collapsing components and outflowing/rotating components within the dense core. We propose a new stage of star formation, "warm-in-cold core stage (WICCS)," i.e., the cold collapsing envelope encases the warm extended dense gas at the center due to the formation of a protostellar core. WICCS would constitute a missing link in evolution between a cold quiescent starless core and a young protostar in class 0 stage that has a large-scale bipolar...
9. Yu, Y.-W.: The Newly Born Magnetars Powering Gamma-Ray Burst Internal-Plateau Emission: Are There Strange Stars?
   The internal-plateau X-ray emission of gamma-ray bursts (GRBs) indicates that a newly born magnetar could be the central object of some GRBs. The observed luminosity and duration of the plateaus suggest that, for such a magnetar, a rapid spin with a sub- or millisecond period is sometimes able to last thousands of seconds. In this case, the conventional neutron star (NS) model for the magnetar may be challenged, since the rapid spin of nascent NSs would be remarkably decelerated within hundreds of seconds due to r-mode instability. In contrast, the r-modes can be effectively suppressed in nascent strange stars (SSs). In other words, to a certain extent, only SSs can keep nearly constant extremely rapid spin for a long period of time during the early ages of the stars. We thus propose that the sample of the GRB rapidly spinning magnetars can be used to test the SS hypothesis based on the distinct spin limits of NSs and SSs.
10. Jahnke, K.: Massive Galaxies in COSMOS: Evolution of Black Hole Versus Bulge Mass but not Versus Total Stellar Mass Over the Last 9 Gyr?
    We constrain the ratio of black hole (BH) mass to total stellar mass of type-1 active galactic nuclei (AGNs) in the COSMOS survey at 1 < z < 2. For 10 AGNs at mean redshift z ~ 1.4 with both Hubble Space Telescope (HST)/ACS and HST/NICMOS imaging data, we are able to compute the total stellar mass M *,total, based on rest-frame UV-to-optical host galaxy colors which constrain mass-to-light ratios. All objects have virial M BH estimates available from the COSMOS Magellan/IMACS and zCOSMOS surveys. We find within errors zero difference between the M BH-M *,total relation at z ~ 1.4 and the M BH-M *,bulge relation in the local universe. Our interpretation is (1) if our objects were purely bulge-dominated, the M BH-M *,bulge relation has not evolved since z ~ 1.4. However, (2) since we have evidence for substantial disk components, the bulges of massive galaxies (M *,total = 11.1 ± 0.3 or log M BH ~ 8.3 ± 0.2) must have grown over the last 9 Gyr predominantly by redistribution of the disk into the bulge mass. Since...

Non Peer-Reviewed Preprints

Preprints are a time-honored way for scientists to pass on their cutting-edge work to their colleagues. Preprints have not generally been peer-reviewed, so any conclusions in the article may be considered tenttive. Furthermore, in the modern preprint process, authors upload their preprints to a publically accessible server, so in practice, a few completely non-scientific papers that would never survive the peer-review process do sneak onto the preprint servers. So Caveat Emptor.

Astro-Ph Preprint Server (20 Most Recent Items)

1. Revealing an Energetic Galaxy-Wide Outflow in a z~2 Ultraluminous Infrared Galaxy.
   Leading models of galaxy formation require large-scale energetic outflows to regulate the growth of distant galaxies and their central black holes. However, current observational support for this hypothesis at high redshift is mostly limited to rare z>2 radio galaxies. Here we present Gemini-North NIFS Intregral Field Unit (IFU) observations of the [O III]5007 emission from a z~2 ultraluminous infrared galaxy (ULIRG; L_IR>10^12 L_sol) with an optically identified Active Galactic Nucleus (AGN). The spatial extent (~4-8 kpc) of the high velocity and broad [O III] emission are consistent with that found in z>2 radio galaxies, indicating the presence of a large-scale energetic outflow in a galaxy population potentially orders of magnitude more common than distant radio galaxies. The low radio luminosity of this system indicates that radio-bright jets are unlikely to be responsible for driving the outflow. However, the estimated energy input required to produce the large-scale outflow signatures (of order...
2. Temporal properties of GX 301-2 over a year-long observation with SuperAGILE.
   We present the long-term monitoring of the High Mass X-ray Binary GX 301-2 performed with the SuperAGILE instrument on-board the AGILE mission. The source was monitored in the 20-60 keV energy band during the first year of the mission from 2007 July 17 to 2008 August 31, covering about one whole orbital period and three more pre-periastron passages for a total net observation time of about 3.7 Ms. The SuperAGILE dataset represents one of the most continuous and complete monitoring at hard X-ray energies of the 41.5 day long binary period available to date. The source behaviour was characterized at all orbital phases in terms of hard X-ray flux, spectral hardness, spin period history, pulsed fraction and pulse shape profile. We also complemented the SuperAGILE observations with the soft X-ray data of the RossiXTE/ASM. Our analysis shows a clear orbital modulation of the spectral hardness, with peaks in correspondence of the pre-periastron flare and near phase 0.25. The hardness peaks we found could be related...
3. Catalog of Radio Galaxies with z>0.3. II: Photometric Data.
   We describe the procedure of the construction of a sample of distant ($z>0.3$) radio galaxies using the NED, SDSS, and CATS databases. We believe the sample to be free of objects with quasar properties. This paper is the second part of the description of the radio galaxies catalog we plan to use for cosmological tests. We report the photometric parameters for the objects of the list, and perform its preliminary statistical analysis including the construction of the Hubble diagrams.
4. Catalog of Radio Galaxies with z>0.3. III: Angular Sizes and Flux Density According to the NVSS Data.
   We describe the procedure of the construction of a sample of distant ($z>0.3$) radio galaxies using the NED, CATS and SDSS databases for further use in various statistical tests. We believe the sample to be free of objects with quasar properties. This paper is the third part of the description of the radio galaxies catalog that we plan to use for cosmological tests. We report the results of the sample of angular sizes for the NVSS survey list objects, and its preliminary statistical analysis. Three-parameter diagrams "angular size-redshift-flux density" and "angular size-redshift-spectral index", and their two-parameter projections are constructed. Three subsamples of radio galaxies are separated in the "source size--flux density" diagram.
5. Metallicity gradients in the Milky Way.
   Radial metallicity gradients are observed in the disks of the Milky Way and in several other spiral galaxies. In the case of the Milky Way, many objects can be used to determine the gradients, such as HII regions, B stars, Cepheids, open clusters and planetary nebulae. Several elements can be studied, such as oxygen, sulphur, neon, and argon in photoionized nebulae, and iron and other elements in cepheids, open clusters and stars. As a consequence, the number of observational characteristics inferred from the study of abundance gradients is very large, so that in the past few years they have become one of the main observational constraints of chemical evolution models. In this paper, we present some recent observational evidences of abundance gradients based on several classes of objects. We will focus on (i) the magnitude of the gradients, (ii) the space variations, and (iii) the evidences of a time variation of the abundance gradients. Some comments on recent theoretical models are also given, in an effort...
6. Molecular Gas in NUclei of GAlaxies (NUGA) XIII. The interacting Seyfert 2/LINER galaxy NGC 5953.
   We present $^{12}$CO(1--0) and $^{12}$CO(2--1) maps of the interacting Seyfert 2/LINER galaxy NGC 5953 obtained with the IRAM interferometer at resolutions of 2\farcs1 $\times$ 1\farcs4 and 1\farcs1 $\times$ 0\farcs7, respectively. The CO emission is distributed over a disk of diameter $\sim$16\arcsec ($\sim$2.2 kpc), within which are several, randomly distributed peaks. The strongest peak does not coincide with the nucleus, but is instead offset from the center, $\sim2-3^{\prime\prime}$ ($\sim$340 pc) toward the west/southwest. The kinematics of the molecular component are quite regular, as is typical of a rotating disk. We also compared the $^{12}$CO distribution of NGC 5953 with observations at other wavelengths in order to study correlations between different tracers of the interstellar medium. Using NIR images, we computed the gravity torques exerted by the stellar potential on the gas. The torques are predominantly positive in both $^{12}$CO(1--0) and $^{12}$CO(2--1), suggesting that gas is not flowing...
7. Characteristic velocities of stripped-envelope core-collapse supernova cores.
   The velocity of the inner ejecta of stripped-envelope core-collapse supernovae (CC-SNe) is studied by means of an analysis of their nebular spectra. Stripped-envelope CC-SNe are the result of the explosion of bare cores of massive stars ($\geq 8$ M$_{\odot}$), and their late-time spectra are typically dominated by a strong [O {\sc i}] $\lambda\lambda$6300, 6363 emission line produced by the innermost, slow-moving ejecta which are not visible at earlier times as they are located below the photosphere. A characteristic velocity of the inner ejecta is obtained for a sample of 56 stripped-envelope CC-SNe of different spectral types (IIb, Ib, Ic) using direct measurements of the line width as well as spectral fitting. For most SNe, this value shows a small scatter around 4500 km s$^{-1}$. Observations ($< 100$ days) of stripped-envelope CC-SNe have revealed a subclass of very energetic SNe, termed broad-lined SNe (BL-SNe) or hypernovae, which are characterised by broad absorption lines in the early-time spectra,...
8. The circumnuclear environment of the peculiar galaxy NGC 3310.
   Gas and star velocity dispersions have been derived for eight circumnuclear star-forming regions (CNSFRs) and the nucleus of the spiral galaxy NGC3310 using high resolution spectroscopy in the blue and far red. Stellar velocity dispersions have been obtained from the CaII triplet in the near-IR, using cross-correlation techniques, while gas velocity dispersions have been measured by Gaussian fits to the Hb 4861A and [OIII]5007A emission lines. The CNSFRs stellar velocity dispersions range from 31 to 73 km/s. These values, together with the sizes measured on archival HST images, yield upper limits to the dynamical masses for the individual star clusters between 1.8 and 7.1 x 10$^6$ M$_\odot$, for the whole CNSFR between 2 x 10$^7$ and 1.4 x 10$^8$ M$_\odot$, and 5.3 x 10$^7$ M$_\odot$ for the nucleus inside the inner 14.2 pc. The masses of the ionizing stellar population responsible for the HII region gaseous emission have been derived from their published Ha luminosities and are found to be between 8.7 x 10$^5$...
9. Catalog of Radio Galaxies with z>0.3. I:Construction of the Sample.
   The procedure of the construction of a sample of distant ($z>0.3$) radio galaxies using NED, SDSS, and CATS databases for further application in statistical tests is described. The sample is assumed to be cleaned from objects with quasar properties. Primary statistical analysis of the list is performed and the regression dependence of the spectral index on redshift is found.
10. Dissecting the Lyman Alpha Emission Halo of LAB1.
    We report observations of Lyman Alpha Blob 1 (LAB1) in the SSA 22 protocluster region (z=3.09) with the integral-field spectrograph SAURON. We increased the signal-to-noise in the spectra by more than a factor three compared to our previous observations. This allows us to probe the structure of the LAB system in detail, examining its structure in the spatial and wavelength dimensions. We find that the emission from the system comes largely from five distinct blobs. Two of the emission regions are associated with Lyman Break Galaxies, while a third appears to be associated with a heavily obscured submillimeter galaxy. The fourth and fifth components do not appear to be associated with any galaxy despite the deep imaging that is available in this field. If we interpret wavelength shifts in the line centroid as velocity structure in the underlying gas, many of these emission systems show evidence of velocity shear. It remains difficult to distinguish between an underlying rotation of the gas and an outflow driven...
11. An Evaluation of the Excitation Class Parameter for the Central Stars of Planetary Nebulae.
    The three main methods currently in use for estimating the excitation class of planetary nebulae (PNe) central stars are compared and evaluated using 586 newly discovered and previously known PNe in the Large Magellanic Cloud (LMC). In order to achieve this we ran a series of evaluation tests using line ratios derived from de-reddened, flux calibrated spectra. Pronounced differences between the methods are exposed. Diagrams were created by comparing excitation classes with H-beta line fluxes. The best methods are then compared to published temperatures using the Zanstra method and assessed for their ability to reflect central star effective temperatures and evolution. As a result we call for a clarification of the term `excitation class' according to the different input parameters used. The first method, which we refer to as Exneb relies purely on the ratios of certain key emission lines. The second method, which we refer to as Ex* includes modeling to create a continuous variable and, for optically thick...
12. Planetary Formation and Evolution Revealed with a Saturn Entry Probe: The Importance of Noble Gases.
    The determination of Saturn's atmospheric noble gas abundances are critical to understanding the formation and evolution of Saturn, and giant planets in general. These measurements can only be performed with an entry probe. A Saturn probe will address whether enhancement in heavy noble gases, as was found in Jupiter, are a general feature of giant planets, and their ratios will be a powerful constraint on how they form. The helium abundance will show the extent to which helium has phase separated from hydrogen in the planet's deep interior. Jupiter's striking neon depletion may also be tied to its helium depletion, and must be confirmed or refuted in Saturn. Together with Jupiter's measured atmospheric helium abundance, a consistent evolutionary theory for both planets, including "helium rain" will be possible. We will then be able to calibrate the theory of the evolution of all giant planets, including exoplanets. In addition, high pressure H/He mixtures under giant planet conditions are...
13. Simulating X-ray Supercavities and Their Impact on Galaxy Clusters.
    Recent X-ray observations of hot gas in the galaxy cluster MS 0735.6+7421 reveal huge radio-bright, quasi-bipolar X-ray cavities having a total energy ~10^{62} ergs, the most energetic AGN outburst currently known. We investigate the evolution of this outburst with two-dimensional axisymmetric gasdynamical calculations in which the cavities are inflated by relativistic cosmic rays. Many key observational features of the cavities and associated shocks are successfully reproduced. The radial elongation of the cavities indicates that cosmic rays were injected into the cluster gas by a (jet) source moving out from the central AGN. AGN jets of this magnitude must be almost perfectly identically bipolar. The relativistic momentum of a single jet would cause a central AGN black hole of mass 10^9 M_{sun} to recoil at ~6000 km s^{-1}, exceeding kick velocities during black hole mergers, and be ejected from the cluster-center galaxy. When the cavity inflation is complete, 4PV underestimates the total energy received by...
14. The Role of Starburst-AGN composites in Luminous Infrared Galaxy Mergers: Insights from the New Optical Classification Scheme.
    We investigate the fraction of starbursts, starburst-AGN composites, Seyferts, and LINERs as a function of infrared luminosity (L_IR) and merger progress for ~500 infrared-selected galaxies. Using the new optical classifications afforded by the extremely large data set of the Sloan Digital Sky Survey, we find that the fraction of LINERs in IR-selected samples is rare (< 5%) compared with other spectral types. The lack of strong infrared emission in LINERs is consistent with recent optical studies suggesting that LINERs contain AGN with lower accretion rates than in Seyfert galaxies. Most previously classified infrared-luminous LINERs are classified as starburst-AGN composite galaxies in the new scheme. Starburst-AGN composites appear to "bridge" the spectral evolution from starburst to AGN in ULIRGs. The relative strength of the AGN versus starburst activity shows a significant increase at high infrared luminosity. In ULIRGs (L_IR >10^12 L_odot), starburst-AGN composite galaxies dominate at early--intermediate...
15. Search for chameleon-like scalar fields with the ammonia method.
    (Abridged) The ammonia method, recently proposed to explore the electron-to-proton mass ratio, mu = m_e/m_p, is applied to nearby dark clouds in the Milky Way. This ratio, being measured in essentially different physical environments of high (terrestrial) and low (interstellar) densities of baryonic matter is supposed to vary in chameleon-like scalar field models which predict strong dependence of masses and coupling constants on the local matter density. High resolution spectral observations of molecular cores in lines of NH3 (J,K) = (1,1), HC3N J = 2-1, and N2H+ J = 1-0 have been carried out at three radio telescopes in order to measure the radial velocity offsets, DeltaV = V_rot - V_inv, between the inversion transition of NH3 (1,1) and rotational transitions of other molecules having different sensitivities to the parameter dmm = (mu_obs - mu_lab)/mu_lab. The measured values of DeltaV show a statistically significant velocity offset of 23 +/- 4_stat +/- 3_sys m/s. Being interpreted in terms of mu-variation,...
16. Dust tori in radio galaxies.
    We investigate the validity of the quasar - radio galaxy unification scenario and determine the presence of dust tori among radio galaxies of various types. Actively accreting supermassive black holes in the centres of radio galaxies may be uncovered through their dust tori reradiating the optical and ultraviolet continuum in mid-infrared bands. Using VISIR on the VLT, we have obtained sub-arcsecond (~0.40") resolution N-band images, at a wavelength of 11.85 micron, of the nuclei of a sample of 27 radio galaxies of four types in the redshift range z=0.006-0.156. The sample consists of 8 edge-darkened, low-power Fanaroff-Riley class I (FR-I) radio galaxies, 6 edge-brightened, class II (FR-II) radio galaxies displaying low-excitation optical emission, 7 FR-IIs displaying high-excitation optical emission, and 6 FR-II broad emission line radio galaxies. Out of the sample of 27 objects, 10 nuclei are detected and several have constraining non-detections at 10 sigma sensitivities of 7 mJy. On the basis of the core...
17. The VIMOS VLT Deep Survey: the group catalogue.
    [Abridged] We used the purely flux limited (17.5<=I<=24.0) VIMOS-VLT Deep Survey (VVDS) sample to produce a homogeneous and complete optically-selected group catalogue, with reliable group properties. Using mock catalogues extracted from the MILLENNIUM simulations, we first studied how many groups can potentially be found in a survey with the same sampling rate as the VVDS, and then we tested how well the virial line of sight velocity dispersion (s_los) of such groups can be measured using galaxy velocities. We verified that, given VVDS observational strategy, we are able to recover s_los when s_los >= 350 km/s. We then optimized our group-finding algorithm, based on the Voronoi-Delaunay method, training it on mocks mimicking all the VVDS survey strategies: we required the redshift and s_los distributions of the output groups (n(z) and n(s_los)) to be in agreement with those given by the group halos defined in the simulations. We also maximized the completeness (C) and purity (P) of the output group...
18. The Skeleton: Connecting Large Scale Structures to Galaxy Formation.
    We report on two quantitative, morphological estimators of the filamentary structure of the Cosmic Web, the so-called global and local skeletons. The first, based on a global study of the matter density gradient flow, allows us to study the connectivity between a density peak and its surroundings, with direct relevance to the anisotropic accretion via cold flows on galactic halos. From the second, based on a local constraint equation involving the derivatives of the field, we can derive predictions for powerful statistics, such as the differential length and the relative saddle to extrema counts of the Cosmic web as a function of density threshold (with application to percolation of structures and connectivity), as well as a theoretical framework to study their cosmic evolution through the onset of gravity-induced non-linearities.
19. Spiral-like structure in nearby clusters of galaxies.
    X-ray data analysis have recently revealed fairly complex structures in cluster centres to be more common than expected. Besides, great part of these structures resemble in morphology, presenting a spiral-like substructure. It is not yet well known how this specific pattern is formed or maintained. In particular, understanding the nature of these spiral-like feature at the centre of some clusters is the major motivation of this work. We analyse Chandra deep observation data of 15 nearby galaxy clusters (0.01 < z < 0.06). We used X-ray temperature and substructure maps to detect small features in the core of the clusters. We detect a spiral-like feature in the centre of 7 clusters: A85, A426, A496, Hydra A cluster, Centaurus, Ophiuchus and A4059. This particular pattern is similar to those found in numerical hydrodynamic simulations of cluster merger with non-zero impact parameter. In some clusters of our sample a strong radio source also occupies the inner region of the cluster, suggesting a possible connection...
20. Extent radiation in different types of radio sources.
    The contribution of an extent component of source radio emission is estimated for quasars and galaxies. The consideration of source radio structures at kiloparsec scales is used at the decameter and the higher frequency bands. The determination of the contribution of an extent component to source radio emission as well as main physical parameters of sample sources is carried out. We found that especially extent sources, giant radio galaxies, have smaller luminosity of core region, weaker magnetic field and greater characteristic age in comparison with compact radio galaxies and quasars. As it follows from our examination, the extent component contribution to source emission may be the indicator of the radio source age.