Distribution by Scientific Domains
Distribution within Physics and Astronomy

Selected Abstracts

Growth, etching morphology and spectra of LiAlO2 crystal

Taohua Huang
Abstract ,-LiAlO2 single crystal was successfully grown by Czochralski method. The crystal quality was characterized by X-ray rocking curve and chemical etching. The effects of air-annealing and vapor transport equilibration (VTE) on the crystal quality, etch pits and absorption spectra of LiAlO2 were also investigated in detail. The results show that the as-grown crystal has very high quality with the full width at half maximum (FWHM) of 17.7-22.6 arcsec. Dislocation density in the middle part of the crystal is as low as about 3.0×103 cm,2. The VTE-treated slice has larger FWHM value, etch pits density and absorption coefficient as compared with those of untreated and air-annealed slices, which indicates that the crystal quality became inferior after VTE treatment. (© 2008 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source]

Growth and characterization of magneto-optical YFeO3 crystals

Hui Shen
Abstract The floating zone growth of magneto-optical crystal YFeO3 has been investigated. The polycrystalline feed rod was prepared by a pressure of 250MPa and sintering at about 1500°C. A crack- free YFeO3 single crystal has been successfully grown. The crystal preferred to crystallize along <100> direction with about 10° deviation. The X-ray rocking curve of the crystal has a FWHM of 24 arcsec, confirming the high crystal quality of the sample. The (100) plane was etched by hot phosphoric acid and the dislocation density was about 104/cm2. A thin outer layer with Y2O3 -rich composition was found at the periphery of as-grown crystals, which was attributed to the Fe2O3 evaporation during growth. (© 2007 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source]

Enhancement of crystalline perfection by organic dopants in ZTS, ADP and KHP crystals as investigated by high-resolution XRD and SEM

S. Parthiban
To reveal the influence of complexing agents on crystalline perfection, tristhiourea zinc(II) sulfate (ZTS), ammonium dihydrogen phosphate (ADP) and potassium hydrogen phthalate (KHP) crystals grown by slow-evaporation solution growth technique using low concentrations (5 × 10,3M) of dopants like ethylenediamminetetraacetic acid (EDTA) and 1,10-phenanthroline (phen) were characterized by high-resolution X-ray diffractometry (XRD) and scanning electron microscopy (SEM). High-resolution diffraction curves (DCs) recorded for ZTS and ADP crystals doped with EDTA show that the specimen contains an epilayer, as observed by the additional peak in the DC, whereas undoped specimens do not have such additional peaks. On etching the surface layer, the additional peak due to the epilayer disappears and a very sharp DC is obtained, with full width at half-maximum (FWHM) of less than 10,arcsec, as expected from the plane wave dynamical theory of X-ray diffraction for an ideally perfect crystal. SEM micrographs also confirm the existence of an epilayer in doped specimens. The ZTS specimen has a layer with a rough surface morphology, having randomly oriented needles, whereas the ADP specimen contains a layer with dendric structure. In contrast to ADP and ZTS crystals, the DC of phen-doped KHP shows no additional peak, but it is quite broad (FWHM = 28,arcsec) with a high value of integrated intensity, , (area under the DC). The broadness of the DC and the high value of , indicate the formation of a mosaic layer on the surface of the crystal. However, similar to ADP and ZTS, the DC recorded after etching the surface layer of the KHP specimen shows a very sharp peak with an FWHM of 8 arcsec. An SEM photograph of phen-doped KHP shows deep cracks on the surface, confirming the mosaicity. After removing the surface layer, the SEM pictures reveal a smooth surface. A similar trend is observed with other complexing agents, like oxalic acid, bipy and picolinic acid. However, only typical examples are described in the present article where the effects were observed prominently. The investigations on ZTS, ADP and KHP crystals, employing high-resolution XRD and SEM studies, revealed that some organic dopants added to the solution during the growth lead to the formation of a surface layer, due to complexation of these dopants with the trace metal ion impurities present in the solution, which prevents the entry of impurities, including the solvent, into the crystal, thereby assisting crystal growth with high crystalline perfection. The influence of organic dopants on the second harmonic generation efficiency is also investigated. [source]

Study of micro-channel geometries for internally cooled Si monochromators

P. Oberta
Rocking curves of micro-channel (MC) water-cooled monochromators are broadened by stresses introduced during fabrication and under X-ray thermal load. This is a problem which will be even more serious with the rise of the fourth-generation synchrotron sources, i.e. the free-electron lasers. The X-ray optics group at the Institute of Physics at the ASCR v.v.i. in Prague is designing, testing and, with company Polovodi,e a.s., fabricating novel internally water-cooled Si monochromators. Here three new micro-channel geometries are introduced which reduce rocking-curve enlargement owing to the fabrication to less than 2.5,µrad (,0.5,arcsec). All three MC designs show less rocking-curve enlargement and smoother topographic images. The designs also show better cooling efficiencies than the classical MC design in finite-element analysis calculations. [source]

Plane-wave X-ray topography and its application at SPring-8

Satoshi Iida
Plane-wave X-ray topography experiments were carried out at a 200,m-long beamline, BL20B2, at SPring-8. Relatively high-energy X-rays of 30,keV with an angular divergence of about 0.01,arcsec were produced by using only one collimator crystal. FZ-Si and CZ-Si wafers were characterized in transmission geometry (Laue case). Clear oscillatory profiles in rocking curves of the FZ-Si crystal were observed. Plane-wave topographic images of dislocations, growth striations and grown-in microdefects in the CZ-Si crystals were obtained. The dependence of the topographic images of the lattice defects on the sample,photoplate distance was also studied. [source]

Performance limits of direct cryogenically cooled silicon monochromators , experimental results at the APS

Wah-Keat Lee
The successful use of cryogenically cooled silicon monochromators at third-generation synchrotron facilities is well documented. At the Advanced Photon Source (APS) it has been shown that, at 100,mA operation with the standard APS undulator A, the cryogenically cooled silicon monochromator performs very well with minimal (<2 arcsec) or no observable thermal distortions. However, to date there has not been any systematic experimental study on the performance limits of this approach. This paper presents experimental results on the performance limits of these directly cooled crystals. The results show that if the beam is limited to the size of the radiation central cone then, at the APS, the crystal will still perform well at twice the present 100,mA single 2.4,m-long 3.3,cm-period undulator heat load. However, the performance would degrade rapidly if a much larger incident white-beam size is utilized. [source]

Feedback under the microscope , I. Thermodynamic structure and AGN-driven shocks in M87

E. T. Million
ABSTRACT We present the first in a series of papers discussing the thermodynamic properties of M87 and the central regions of the Virgo Cluster in unprecedented detail. Using a deep Chandra exposure (574 ks), we present high-resolution thermodynamic maps created from the spectra of ,16 000 independent regions, each with ,1000 net counts. The excellent spatial resolution of the thermodynamic maps reveals the dramatic and complex temperature, pressure, entropy and metallicity structure of the system. The ,X-ray arms', driven outwards from M87 by the central active galactic nuclei (AGN), are prominent in the brightness, temperature and entropy maps. Excluding the ,X-ray arms', the diffuse cluster gas at a given radius is strikingly isothermal. This suggests either that the ambient cluster gas, beyond the arms, remains relatively undisturbed by AGN uplift or that conduction in the intracluster medium (ICM) is efficient along azimuthal directions, as expected under action of the heat-flux-driven buoyancy instability (HBI). We confirm the presence of a thick (,40 arcsec or ,3 kpc) ring of high-pressure gas at a radius of ,180 arcsec (,14 kpc) from the central AGN. We verify that this feature is associated with a classical shock front, with an average Mach number M= 1.25. Another, younger shock-like feature is observed at a radius of ,40 arcsec (,3 kpc) surrounding the central AGN, with an estimated Mach number M, 1.2. As shown previously, if repeated shocks occur every ,10 Myr, as suggested by these observations, then AGN-driven weak shocks could produce enough energy to offset radiative cooling of the ICM. A high significance enhancement of Fe abundance is observed at radii 350,400 arcsec (27,31 kpc). This ridge is likely formed in the wake of the rising bubbles filled with radio-emitting plasma that drag cool, metal-rich gas out of the central galaxy. We estimate that at least ,1.0 × 106 solar masses of Fe has been lifted and deposited at a radius of 350,400 arcsec; approximately the same mass of Fe is measured in the X-ray bright arms, suggesting that a single generation of buoyant radio bubbles may be responsible for the observed Fe excess at 350,400 arcsec. [source]

Optical turbulence vertical distribution with standard and high resolution at Mt Graham

E. Masciadri
ABSTRACT A characterization of the optical turbulence vertical distribution (C2N profiles) and all the main integrated astroclimatic parameters derived from the C2N and the wind speed profiles above the site of the Large Binocular Telescope (LBT) (Mt Graham, Arizona, USA) is presented. The statistics include measurements related to 43 nights done with a Generalized SCIDAR (GS) used in standard configuration with a vertical resolution ,H, 1 km on the whole 20 km and with the new technique (High Vertical Resolution GS) in the first kilometre. The latter achieves a resolution ,H, 20,30 m in this region of the atmosphere. Measurements done in different periods of the year permit us to provide a seasonal variation analysis of the C2N. A discretized distribution of C2N, useful for the Ground Layer Adaptive Optics (GLAO) simulations, is provided and a specific analysis for the LBT Laser Guide Star system ARGOS (running in GLAO configuration) case is done including the calculation of the ,grey zones' for J, H and K bands. Mt Graham is confirmed to be an excellent site with median values of the seeing without dome contribution ,= 0.72 arcsec, the isoplanatic angle ,0= 2.5 arcsec and the wavefront coherence time ,0= 4.8 ms. We find that the OT vertical distribution decreases in a much sharper way than what has been believed so far in the proximity of the ground above astronomical sites. We find that 50 per cent of the whole turbulence develops in the first 80 ± 15 m from the ground. We finally prove that the error in the normalization of the scintillation that has been recently demonstrated in the principle of the GS technique affects these measurements by an absolutely negligible quantity (0.04 arcsec). [source]

PG 1258+593 and its common proper motion magnetic white dwarf counterpart

J. Girven
ABSTRACT We confirm SDSS J130033.48+590407.0 as a common proper motion companion to the well-studied hydrogen-atmosphere (DA) white dwarf PG 1258+593 (GD322). The system lies at a distance of 68 ± 3 pc, where the angular separation of 16.1 ± 0.1 arcsec corresponds to a minimum binary separation of 1091 ± 7 au. SDSS J1300+5904 is a cool (Teff= 6300 ± 300 K) magnetic white dwarf (B, 6 mG). PG 1258+593 is a DA white dwarf with Teff= 14790 ± 77 K and log g= 7.87 ± 0.02. Using the white dwarf mass,radius relation implies the masses of SDSS J1300+5904 and PG 1258+593 are 0.54 ± 0.06 and 0.54 ± 0.01 M,, respectively, and therefore a cooling age difference of 1.67 ± 0.05 Gyr. Adopting main-sequence lifetimes from stellar models, we derive an upper limit of 2.2 M, for the mass of the progenitor of PG 1258+593. A plausible range of initial masses is 1.4,1.8 M, for PG 1258+593 and 2,3 M, for SDSS J1300+5904. Our analysis shows that white dwarf common proper motion binaries can potentially constrain the white dwarf initial mass,final mass relation and the formation mechanism for magnetic white dwarfs. The magnetic field of SDSS J1300+5904 is consistent with an Ap progenitor star. A common envelope origin of the system cannot be excluded, but requires a triple system as progenitor. [source]

A QSO host galaxy and its Ly, emission at z= 6.43,

Tomotsugu Goto
ABSTRACT Host galaxies of highest redshift quasi-stellar objects (QSOs) are of interest; they provide us with a valuable opportunity to investigate physics relevant to the starburst,active galactic nuclei (AGN) connection at the earliest epoch of the Universe, with the most luminous black holes. Here, we report an optical detection of an extended structure around a QSO at z= 6.43 in deep z,- and zr -band images of the Subaru/Suprime-Cam. Our target is CFHQS J2329-0301 (z= 6.43), the highest redshift QSO currently known. We have carefully subtracted a point spread function (PSF) constructed using nearby stars from the images. After the PSF (QSO) subtraction, a structure in the z, band extends more than 4 arcsec on the sky (Re= 11 kpc), and, thus, is well resolved (16, detection). The PSF-subtracted zr -band structure is in a similar shape to that in the z, band, but less significant with a 3, detection. In the z, band, a radial profile of the QSO+host shows a clear excess over that of the averaged PSF in 0.8,3 arcsec radius. Since the z, band includes a Ly, emission at z= 6.43, we suggest the z, flux is a mixture of the host (continuum light) and its Ly, emission, whereas the zr -band flux is from the host. Through a SED modelling, we estimate 40 per cent of the PSF-subtracted z,-band light is from the host (continuum) and 60 per cent is from Ly, emission. The absolute magnitude of the host is M1450=,23.9 (cf. M1450=,26.4 for the QSO). A lower limit of the SFR(Ly,) is 1.6 M, yr,1 with stellar mass ranging from 6.2 × 108 to 1.1 × 1010 M, when 100 Myr of age is assumed. The detection shows that a luminous QSO is already harboured by a large, star-forming galaxy in the early Universe only after ,840 Myr after the big bang. The host may be a forming giant galaxy, co-evolving with a super-massive black hole. [source]

New multiply-lensed galaxies identified in ACS/NIC3 observations of Cl0024+1654 using an improved mass model

Adi Zitrin
ABSTRACT We present an improved strong-lensing analysis of Cl0024+1654 (z= 0.39) using deep Hubble Space Telescope (HST)/Advanced Camera for Surveys (ACS)/NIC3 images, based on 33 multiply-lensed images of 11 background galaxies. These are found with a model that assumes mass approximately traces light, with a low-order expansion to allow for flexibility on large scales. The model is constrained initially by the well-known five-image system (z= 1.675) and refined as new multiply-lensed systems are identified using the model. Photometric redshifts of these new systems are then used to constrain better the mass profile by adopting the standard cosmological relation between redshift and lensing distance. Our model requires only six free parameters to describe well all positional and redshift data. The resulting inner mass profile has a slope of d log M/d log r,,0.55, consistent with new weak-lensing measurements where the data overlap, at r, 200 kpc/h70. The combined profile is well fitted by a high-concentration Navarro, Frenk & White (NFW) mass profile, Cvir, 8.6 ± 1.6, similar to other well-studied clusters, but larger than predicted with standard , cold dark matter (,CDM). A well-defined radial critical curve is generated by the model and is clearly observed at r, 12 arcsec, outlined by elongated images pointing towards the centre of mass. The relative fluxes of the multiply-lensed images are found to agree well with the modelled magnifications, providing an independent consistency check. [source]

GEMINI 3D spectroscopy of BAL + IR + Fe ii QSOs , I. Decoupling the BAL, QSO, starburst, NLR, supergiant bubbles and galactic wind in Mrk 231

S. Lipari
ABSTRACT In this paper we present the first results of a study of BAL QSOs (at low and high redshift), based on very deep Gemini GMOS integral field spectroscopy. In particular, the results obtained for the nearest BAL IR,QSO Mrk 231 are presented. For the nuclear region of Mrk 231, the QSO and host galaxy components were modelled, using a new technique of decoupling 3D spectra. From this study, the following main results were found: (i) in the pure host galaxy spectrum an extreme nuclear starburst component was clearly observed, as a very strong increase in the flux, at the blue wavelengths; (ii) the BAL system I is observed in the spectrum of the host galaxy; (iii) in the clean/pure QSO emission spectrum, only broad lines were detected. 3D GMOS individual spectra (specially in the near-infrared Ca ii triplet) and maps confirm the presence of an extreme and young nuclear starburst (8 < age < 15 Myr), which was detected in a ring or toroid with a radius r= 0.3 arcsec , 200 pc, around the core of the nucleus. The extreme continuum blue component was detected only to the south of the core of the nucleus. This area is coincident with the region where we previously suggested that the galactic wind is cleaning the nuclear dust. Very deep 3D spectra and maps clearly show that the BAL systems I and II , in the strong ,absorption lines' Na iD,5889,95 and Ca ii K,3933 , are extended (reaching ,1.4,1.6 arcsec , 1.2,1.3 kpc, from the nucleus) and clearly elongated at the position angle (PA) close to the radio jet PA, which suggest that the BAL systems I and II are ,both' associated with the radio jet. The physical properties of the four expanding nuclear bubbles were analysed, using the GMOS 3D spectra and maps. In particular, we found strong multiple LINER/OF emission-line systems and Wolf,Rayet features in the main knots of the more external super bubble S1 (r= 3.0 kpc). The kinematics of these knots , and the internal bubbles , suggest that they are associated with an area of rupture of the shell S1 (at the south-west). In addition, in the more internal superbubble S4 and close to the core of the nucleus (for r < 0.7 arcsec , 0.6 kpc), two similar narrow emission-line systems were detected, with strong [S ii] and [O i] emission and ,V,,200 km s,1. These results suggest that an important part of the nuclear NLR is generated by the OF process and the associated low-velocity ionizing shocks. Finally, the nature of the composite BAL systems and very extended OF process , of 50 kpc , in Mrk 231 (and similar QSOs) are discussed. In addition, the ,composite hyperwind scenario' (already proposed for BALs) is suggested for the origin of giant Ly, blobs. The importance of study the end phases of Mrk 231, and similar evolving elliptical galaxies and QSOs (i.e. galaxy remnants) is discussed. [source]

What is the largest Einstein radius in the universe?

Masamune Oguri
ABSTRACT The Einstein radius plays a central role in lens studies as it characterizes the strength of gravitational lensing. In particular, the distribution of Einstein radii near the upper cut-off should probe the probability distribution of the largest mass concentrations in the universe. Adopting a triaxial halo model, we compute expected distributions of large Einstein radii. To assess the cosmic variance, we generate a number of Monte Carlo realizations of all-sky catalogues of massive clusters. We find that the expected largest Einstein radius in the universe is sensitive to parameters characterizing the cosmological model, especially ,8: for a source redshift of unity, they are 42+9,7, 35+8,6 and 54+12,7 arcsec (errors denote 1, cosmic variance), assuming best-fitting cosmological parameters of the Wilkinson Microwave Anisotropy Probe five-year (WMAP5), three-year (WMAP3) and one-year (WMAP1) data, respectively. These values are broadly consistent with current observations given their incompleteness. The mass of the largest lens cluster can be as small as , 1015 M,. For the same source redshift, we expect in all sky ,35 (WMAP5), ,15 (WMAP3) and ,150 (WMAP1) clusters that have Einstein radii larger than 20 arcsec. For a larger source redshift of 7, the largest Einstein radii grow approximately twice as large. Whilst the values of the largest Einstein radii are almost unaffected by the level of the primordial non-Gaussianity currently of interest, the measurement of the abundance of moderately large lens clusters should probe non-Gaussianity competitively with cosmic microwave background experiments, but only if other cosmological parameters are well measured. These semi-analytic predictions are based on a rather simple representation of clusters, and hence calibrating them with N -body simulations will help to improve the accuracy. We also find that these ,superlens' clusters constitute a highly biased population. For instance, a substantial fraction of these superlens clusters have major axes preferentially aligned with the line-of-sight. As a consequence, the projected mass distributions of the clusters are rounder by an ellipticity of ,0.2 and have , 40,60 per cent larger concentrations compared with typical clusters with similar redshifts and masses. We argue that the large concentration measured in A1689 is consistent with our model prediction at the 1.2, level. A combined analysis of several clusters will be needed to see whether or not the observed concentrations conflict with predictions of the flat ,-dominated cold dark matter model. [source]

Effects of galaxy-halo alignment and adiabatic contraction on gravitational lens statistics

Quinn E. Minor
ABSTRACT We study the strong gravitational lens statistics of triaxial cold dark matter haloes occupied by central early-type galaxies. We calculate the image separation distribution for double, cusp and quad configurations. The ratios of image multiplicities at large separations are consistent with the triaxial NFW model, and at small separations are consistent with the singular isothermal ellipsoid model. At all the separations, the total lensing probability is enhanced by adiabatic contraction. If no adiabatic contraction is assumed, naked cusp configurations become dominant at ,2.5 arcsec, which is inconsistent with the data. We also show that at small-to-moderate separations (,5 arcsec) the image multiplicities depend sensitively on the alignment of the shapes of the luminous and dark matter projected density profiles. In contrast to other properties that affect these ratios, the degree of alignment does not have a significant effect on the total lensing probability. These correlations may therefore be constrained by comparing the theoretical image separation distribution to a sufficiently large lens sample from future wide and deep sky surveys such as Pan-Stars, LSST and JDEM. Understanding the correlations in the shapes of galaxies and their dark matter halo is important for future weak lensing surveys. [source]

Structure and dynamics of galaxies with a low surface-brightness disc , I. The stellar and ionized-gas kinematics

A. Pizzella
ABSTRACT Photometry and long-slit spectroscopy are presented for a sample of six galaxies with a low surface-brightness stellar disc and a bulge. The characterizing parameters of the bulge and disc components were derived by means of a two-dimensional photometric decomposition of the images of the sample galaxies. Their surface-brightness distribution was assumed to be the sum of the contribution of a Sérsic bulge and an exponential disc, with each component being described by elliptical and concentric isophotes of constant ellipticity and position angle. The stellar and ionized-gas kinematics were measured along the major and minor axes in half of the sample galaxies, whereas the other half was observed only along two diagonal axes. Spectra along two diagonal axes were obtained also for one of the objects with major and minor axis spectra. The kinematic measurements extend in the disc region out to a surface-brightness level ,R, 24 mag arcsec,2, reaching in all cases the flat part of the rotation curve. The stellar kinematics turns out to be more regular and symmetric than the ionized-gas kinematics, which often shows the presence of non-circular, off-plane and non-ordered motions. This raises the question about the reliability of the use of the ionized gas as the tracer of the circular velocity in the modelling of the mass distribution, in particular in the central regions of low surface-brightness galaxies. [source]

Photometric properties and scaling relations of early-type Brightest Cluster Galaxies

F. S. Liu
ABSTRACT We investigate the photometric properties of the early-type Brightest Cluster Galaxies (BCGs) using a carefully selected sample of 85 BCGs from the C4 cluster catalogue with a redshift of less than 0.1. We perform accurate background subtractions and surface photometry for these BCGs to 25 mag arcsec,2 in the Sloan r band. By quantitatively analysing the gradient of the Petrosian profiles of BCGs, we find that a large fraction of BCGs have extended stellar envelopes in their outskirts; more luminous BCGs tend to have more extended stellar haloes that are likely to be connected with mergers. A comparison sample of elliptical galaxies was chosen with similar apparent magnitude and redshift ranges, for which the same photometric analysis procedure is applied. We find that BCGs have steeper size,luminosity (R,L,) and Faber,Jackson (L,,,) relations than the bulk of early-type galaxies. Furthermore, the power-law indices (, and ,) in these relations increase as the isophotal limits become deeper. For isophotal limits from 22 to 25 mag arcsec,2, BCGs are usually larger than the bulk of early-type galaxies, and a large fraction (,49 per cent) of BCGs have discy isophotal shapes. The differences in the scaling relations are consistent with a scenario where the dynamical structure and formation route of BCGs may be different from the bulk of early-type galaxies; in particular dry (dissipationless) mergers may play a more important role in their formation. We highlight several possible dry merger candidates in our sample. [source]

Australia Telescope Compact Array 1.2-cm observations of the massive star-forming region G305.2+0.2

Andrew J. Walsh
ABSTRACT We report on Australia Telescope Compact Array observations of the massive star-forming region G305.2+0.2 at 1.2 cm. We detected emission in five molecules towards G305A, confirming its hot core nature. We determined a rotational temperature of 26 K for methanol. A non-local thermodynamic equilibrium excitation calculation suggests a kinematic temperature of the order of 200 K. A time-dependent chemical model is also used to model the gas-phase chemistry of the hot core associated with G305A. A comparison with the observations suggest an age of between 2 × 104 and 1.5 × 105 yr. We also report on a feature to the south-east of G305A which may show weak Class I methanol maser emission in the line at 24.933 GHz. The more evolved source G305B does not show emission in any of the line tracers, but strong Class I methanol maser emission at 24.933 GHz is found 3 arcsec to the east. Radio continuum emission at 18.496 GHz is detected towards two H ii regions. The implications of the non-detection of radio continuum emission towards G305A and G305B are also discussed. [source]

Very high contrast integral field spectroscopy of AB Doradus C: 9-mag contrast at 0.2 arcsec without a coronagraph using spectral deconvolution,

Niranjan Thatte
ABSTRACT We present an extension of the spectral deconvolution (SD) method to achieve very high contrast at small inner working radii. We apply the method to the specific case of ground-based adaptive optics fed integral field spectroscopy (without a coronagraph). Utilizing the wavelength dependence of the Airy and speckle patterns, we make an accurate estimate of the point spread function that can be scaled and subtracted from the data cube. The residual noise in the resulting spectra is very close to the photon noise from the starlight halo. We utilize the technique to extract a very high signal-to-noise ratio H - and K -band spectrum of AB Doradus (AB Dor) C, the low-mass companion to AB Dor A. By effectively eliminating all contamination from AB Dor A, the extracted spectrum retains both continuum and spectral features. The achieved 1, contrast is 9 mag at 0.2 arcsec, 11 mag at 0.5 arcsec, in 20 min exposure time, at an effective spectral bandwidth of 5.5 nm, proving that the method is applicable even in low-Strehl regimes. The SD method clearly demonstrates the efficacy of image slicer based integral field units in achieving very high contrast imaging spectroscopy at small angular separations, validating their use as high-contrast spectrographs/imagers for extreme adaptive optics systems. [source]

A case of mistaken identity?

GRB 060912A, short GRB divide, the nature of the long
ABSTRACT We investigate the origin of the GRB 060912A, which has observational properties that make its classification as either a long or short burst ambiguous. Short-duration gamma-ray bursts (SGRBs) are thought to have typically lower energies than long-duration bursts, can be found in galaxies with populations of all ages and are likely to originate from different progenitors to the long-duration bursts. However, it has become clear that duration alone is insufficient to make a distinction between the two populations in many cases, leading to a desire to find additional discriminators of burst type. GRB 060912A had a duration of 6 s and occurred only ,10 arcsec from a bright, low-redshift (z= 0.0936) elliptical galaxy, suggesting that this may have been the host, which would favour it being a short burst. However, our deep optical imaging and spectroscopy of the location of GRB 060912A using the Very Large Telescope (VLT) shows that GRB 060912A more likely originates in a distant star-forming galaxy at z= 0.937, and is most likely a long burst. This demonstrates the risk in identifying bright, nearby galaxies as the hosts of given gamma-ray bursts (GRBs) without further supporting evidence. Further, it implies that, in the absence of secure identifications, ,host' type, or more broadly discriminators that rely on galaxy redshifts, may not be good indicators of the true nature of any given GRB. [source]

Intracluster light and the extended stellar envelopes of cD galaxies: an analytical description

Marc S. Seigar
ABSTRACT We have analysed deep R -band images, down to a limiting surface brightness of 26.5 R-mag arcsec,2 (equivalent to ,28 B-mag arcsec,2), of five cD galaxies to determine the shape of the surface brightness profiles of their extended stellar envelopes. Both de Vaucouleurs R1/4 and Sérsic R1/n models, on their own, provide a poor description of the surface brightness profiles of cD galaxies. This is due to the presence of outer stellar envelopes, thought to have accumulated over the merger history of the central cluster galaxy and also from the tidal stripping of galaxies at larger cluster radii. We therefore simultaneously fit two Sérsic functions to measure the shape of the inner and outer components of the cD galaxies. We show that, for three out of our five galaxies, the surface brightness profiles are best fitted by an inner Sérsic model, with indices n, 1 ,6, and an outer exponential component. For these systems, the galaxy-to-envelope size ratio is 0.1,0.4 and the contribution of the stellar envelope to the total R -band light (i.e. galaxy + envelope) is around 60,80 per cent (based on extrapolation to a 300 kpc radius). The exceptions are NGC 6173, for which our surface brightness profile modelling is consistent with just a single component (i.e. no envelope) and NGC 4874 which appears to have an envelope with a de Vaucouleurs, rather than exponential, profile. [source]

Imaging and spectroscopy of ultrasteep spectrum radio sources,

Carlos G. Bornancini
ABSTRACT We present a sample of 40 ultrasteep spectrum (USS; ,,, 1.3, S,,,,) radio sources selected from the Westerbork in the Southern Hemisphere (WISH) catalogue. The USS sources have been imaged in K band at the Cerro Tololo Inter-American Observatory (CTIO) and with the Very Large Telescope (VLT) at Cerro Paranal. We also present VLT, Keck and William Herschel Telescope (WHT) optical spectroscopy of 14 targets selection from four different USS samples. For 12 sources, we have been able to determine the redshifts, including four new radio galaxies at z > 3. We find that most of our USS sources have predominantly small (<6 arcsec) radio sizes and faint magnitudes (K, 18). The mean K -band counterpart magnitude is . The expected redshift distribution estimated using the Hubble K,z diagram has a mean of , which is higher than the predicted redshift obtained for the Sydney University Molonglo Sky Survey,NRAO VLA Sky Survey (SUMSS,NVSS) sample and the expected redshift obtained in the 6C** survey. The compact USS sample analysed here may contain a higher fraction of galaxies which are high redshift and/or are heavily obscured by dust. Using the 74, 352 and 1400 MHz flux densities of a subsample, we construct a radio colour,colour diagram. We find that all but one of our USS sources have a strong tendency to flatten below 352 MHz. We also find that the highest redshift source from this paper (at z= 3.84) does not show evidence for spectral flattening down to 151 MHz. This suggests that very low frequency selected USS samples will likely be more efficient to find high redshift galaxies. [source]

Structural parameters of Mayall II = G1 in M31

J. Ma
ABSTRACT Mayall II = G1 is one of the most luminous globular clusters (GCs) known in M31. New deep, high-resolution observations with the Advanced Camera for Surveys on the Hubble Space Telescope are used to provide accurate photometric data to the smallest radii yet. In particular, we present the precise variation of ellipticity and position angle, and of surface brightness for the core of the object. Based on these accurate photometric data, we redetermine the structural parameters of G1 by fitting a single-mass isotropic King model. We derive a core radius, rc= 0.21 ± 0.01 arcsec (= 0.78 ± 0.04 pc), a tidal radius, rt= 21.8 ± 1.1 arcsec (= 80.7 ± 3.9 pc), and a concentration index c= log (rt/rc) = 2.01 ± 0.02. The central surface brightness is 13.510 mag arcsec,2. We also calculate the half-light radius, at rh= 1.73 ± 0.07 arcsec (= 6.5 ± 0.3 pc). The results show that, within 10 core radii, a King model fits the surface brightness distribution well. We find that this object falls in the same region of the MV versus log Rh diagram as , Centauri, M54 and NGC 2419 in the Milky Way. All three of these objects have been claimed to be the stripped cores of now defunct dwarf galaxies. We discuss in detail whether GCs, stripped cores of dwarf spheroidals and normal dwarf galaxies form a continuous distribution in the MV versus log Rh plane, or if GCs and dwarf spheroidals constitute distinct classes of objects; we present arguments in favour of this latter view. [source]

Space very long baseline interferometry observations of polarization in the jet of 3C 380

A. Papageorgiou
ABSTRACT A comparison between low-frequency space very long baseline interferometry (VLBI) and high-frequency ground-based VLBI images can, in principle, be used to detect small variations in rotation measure (RM) on fine angular scales inaccessible to ground arrays alone. This paper reports an attempt to perform such a comparison using the jet in the quasar 3C 380. Observations made with the VSOP antenna HALCA together with a ground array at wavelength 1.6 GHz provide total intensity and polarization images of comparable resolution to those from the ground array alone at 5 GHz. The results provide an image showing derotated magnetic vector position angle of somewhat higher resolution than that available earlier. The results show variations in an RM around component A of the order of 10 rad m,2 that could not have been detected with the ground array alone. It is concluded that satellite VLBI observations provide a promising means to study the distribution of matter and magnetic fields around parsec-scale jets. The ground observations used here follow the steady outward drift of component A, which has approximately doubled its distance from the core since the first observations in 1982. They also reveal total intensity and polarization structure associated with a bright knot 0.7 arcsec from the core which is reminiscent of that expected for a conical shock wave. [source]

Infrared mergers and infrared quasi-stellar objects with galactic winds , III.

Mrk 231: an exploding young quasi-stellar object with composite outflow/broad absorption lines (and multiple expanding superbubbles)
ABSTRACT We present a study of outflow (OF) and broad absorption line (BAL) systems in Mrk 231, and in similar infrared (IR) quasi-stellar objects (QSOs). This study is based mainly on one-dimensional and two-dimensional spectroscopy (obtained at La Palma/William Herschel Telescope, Hubble Space Telescope, International Ultraviolet Explorer, European Southern Observatory/New Technology Telescope, Kitt Peak National Observatory, Apache Point Observatory and Complejo Astronomico El Leoncito observatories) plus Hubble Space Telescope images. For Mrk 231, we report evidence that the extreme nuclear OF process has at least three main components on different scales, which are probably associated with: (i) the radio jet, at parsec scale; (ii) the extreme starburst at parsec and kiloparsec scale. This OF has generated at least four concentric expanding superbubbles and the BAL systems. Specifically, inside and very close to the nucleus the two-dimensional spectra show the presence of an OF emission bump in the blend H,+[N ii], with a peak at the same velocity of the main BAL-I system (VEjection BAL-I,,4700 km s,1). This bump was more clearly detected in the area located at 0.6,1.5 arcsec (490,1220 pc), to the south-west of the nucleus core, showing a strong and broad peak. In addition, in the same direction [at position angle (PA) ,,120°, i.e. close to the PA of the small-scale radio jet] at 1.7,2.5 arcsec, we also detected multiple narrow emission-line components, with ,greatly' enhanced [N ii]/H, ratio (very similar to the spectra of jets bow shocks). These results suggest that the BAL-I system is generated in OF clouds associated with the parsec-scale jet. The Hubble Space Telescope images show four (or possibly five) nuclear superbubbles or shells with radii r, 2.9, 1.5, 1.0, 0.6 and 0.2 kpc. For these bubbles, the two-dimensional H, velocity field map and two-dimensional spectra show the following. (i) At the border of the more extended bubble (S1), a clear expansion of the shell with blueshifted velocities (with circular shape and at a radius r, 5.0 arcsec). This bubble shows a rupture arc , to the south , suggesting that the bubble is in the blowout phase. The axis of this rupture or ejection (at PA , 00°) is coincident with the axis of the intermediate and large-scale structures detected at radio wavelengths. (ii) In addition, in the three more external bubbles (S1, S2, S3), the two-dimensional William Herschel Telescope spectra show multiple emission-line components with OF velocities, of ,VOF Bubble, S1, S2 and S3 =[,(650 , 420) ± 30], [,500 ± 30] and [,230 ± 30] km s,1. (iii) In the whole circumnuclear region (1.8 < r < 5 arcsec), the [N ii]/H, and [S ii]/H, narrow emission-line ratios show high values (>0.8), which are consistent with low-ionization nuclear emission-line region/OF processes associated with fast velocity shocks. Therefore, we suggest that these giant bubbles are associated with the large-scale nuclear OF component, which is generated , at least in part , by the extreme nuclear starburst: giant supernova/hypernova explosions. The variability of the short-lived BAL-III Na i D system was studied, covering almost all the period in which this system appeared (between ,1984 and 2004). We have found that the BAL-III light curve is clearly asymmetric with a steep increase, a clear maximum and an exponential fall (similar to the shape of a supernova light curve). The origin of this BAL-III system is discussed, mainly in the framework of an extreme explosive event, probably associated with giant supernova/hypernova explosions. Finally, the IR colour diagram and the ultraviolet BAL systems of IR + GW/OF + Fe ii QSOs are analysed. This study shows two new BAL IR QSOs and suggests/confirms that these objects could be nearby young BAL QSOs, similar to those detected recently at z, 6.0. We propose that the phase of young QSOs is associated with accretion of a large amount of gas (by the supermassive black hole) + extreme starbursts + extreme composite OFs/BALs. [source]

Non-thermal X-rays, a high-abundance ridge and fossil bubbles in the core of the Perseus cluster of galaxies

J. S. Sanders
ABSTRACT Using a deep Chandra observation of the Perseus cluster of galaxies, we find a high-abundance shell 250 arcsec (93 kpc) from the central nucleus. This ridge lies at the edge of the Perseus radio mini-halo. In addition we identify two H, filaments pointing towards this shell. We hypothesize that this ridge is the edge of a fossil radio bubble, formed by entrained enriched material lifted from the core of the cluster. There is a temperature jump outside the shell, but the pressure is continuous indicating a cold front. A non-thermal component is mapped over the core of the cluster with a morphology similar to the mini-halo. Its total luminosity is 4.8 × 1043 erg s,1, extending in radius to ,75 kpc. Assuming the non-thermal emission to be the result of inverse Compton scattering of the cosmic microwave background and infrared emission from NGC 1275, we map the magnetic field over the core of the cluster. [source]

Haloes around edge-on disc galaxies in the Sloan Digital Sky Survey

Stefano Zibetti
ABSTRACT We present a statistical analysis of halo emission for a sample of 1047 edge-on disc galaxies imaged in five bands by the Sloan Digital Sky Survey (SDSS). Stacking the homogeneously rescaled images of the galaxies, we can measure surface brightnesses as deep as ,r, 31 mag arcsec,2. The results strongly support the almost ubiquitous presence of stellar haloes around disc galaxies, whose spatial distribution is well described by a power law ,,r,3, in a moderately flattened spheroid (c/a, 0.6). The colour estimates in g,r and r,i, although uncertain, give a clear indication for extremely red stellar populations, hinting at old ages and/or non-negligible metal enrichment. These results support the idea of haloes being assembled via early merging of satellite galaxies. [source]

The nature, evolution, clustering and X-ray properties of extremely red galaxies in the Chandra Deep Field South/Great Observatories Origins Deep Survey field

Nathan D. Roche
ABSTRACT We identify a very deep sample of 198 extremely red objects (EROs) in the Chandra Deep Field South, selected on the basis of I775,Ks > 3.92, to a limit Ks, 22 using the public European Southern Observatory (ESO)/Great Observatories Origins Deep Survey (GOODS) survey. The ERO number counts flatten from a slope of ,, 0.59 to 0.16 at K > 19.5, where they remain below the predictions for pure luminosity evolution, and fall below even a non-evolving model. This suggests there is a significant decrease with redshift in the comoving number density of passive/very red galaxies. We investigate the angular correlation function, ,(,), of these EROs and detect positive clustering for Ks= 20.5,22.0 sources. The EROs show stronger clustering than other galaxies at the same magnitudes. The ,(,) amplitudes are best-fitted by models in which the EROs have a comoving correlation radius r0, 12.5 ± 1.2 h,1 Mpc, or r0, 21.4 ± 2.0 h,1 Mpc in a stable clustering model. We find a 40-arcsec diameter overdensity of 10 EROs, centred on the Chandra X-ray source (and ERO) XID:58. On the basis of colours we estimate that about seven, including XID:58, belong to a cluster of EROs at z, 1.5. The 942-ks Chandra survey detected 73 X-ray sources in the area of our ERO sample, 17 of which coincide with EROs. Of these sources, 13 have X-ray properties indicative of obscured active galactic nuclei (AGN), while the faintest four may be starbursts. In addition, we find evidence that Chandra sources and EROs are positively cross-correlated at non-zero (,2,20 arcsec) separations, implying that they tend to trace the same large-scale structures. In conclusion, these findings appear consistent with a scenario where EROs are the z > 1 progenitors of elliptical/S0 galaxies, some forming very early as massive spheroids, which are strongly clustered and may evolve via an AGN phase, others more recently from mergers of disc galaxies. [source]

Extended X-ray emission in the high-redshift quasar GB 1508+5714 at z= 4.3

W. Yuan
ABSTRACT We report the discovery of extended X-ray emission around the powerful high-redshift quasar GB 1508+5714 at z= 4.3, revealed in a long Chandra ACIS observation. The emission feature is 3,4 arcsec away from the quasar core, which corresponds to a projected distance of about 25 kpc. The X-ray spectrum is best fitted with a power law of photon index 1.92 ± 0.35 (90 per cent confidence limit). The X-ray flux and luminosity reach 9.2 × 10,15 erg cm,2 s,1 (0.5,8 keV) and 1.6 × 1045 erg s,1 (2.7,42.4 keV rest frame, ,,= 0.73, ,m= 0.27, H0= 71 km s,1 Mpc,1), which is about 2 per cent of the total X-ray emission of the quasar. We interpret the X-ray emission as inverse Compton scattering of cosmic microwave background photons. The scattering relativistic electron population could either be a quasi-static diffuse cloud fed by the jet, or an outer extension of the jet with a high bulk Lorentz factor. We argue that the lack of an obvious detection of radio emission from the extended component could be a consequence of Compton losses on the electron population, or of a low magnetic field. Extended X-ray emission produced by inverse Compton scattering may be common around high-redshift radio galaxies and quasars, demonstrating that significant power is injected into their surroundings by powerful jets. [source]

A star-forming galaxy at z= 5.78 in the Chandra Deep Field South

Andrew J. Bunker
ABSTRACT We report the discovery of a luminous z= 5.78 star-forming galaxy in the Chandra Deep Field South. This galaxy was selected as an ,i -drop' from the GOODS public survey imaging with the Hubble Space Telescope/Advanced Camera for Surveys (object 3 in the work of Stanway, Bunker & McMahon 2003). The large colour of (i,,z,)AB= 1.6 indicated a spectral break consistent with the Lyman , forest absorption shortward of Lyman , at z, 6. The galaxy is very compact (marginally resolved with ACS with a half-light radius of 0.08 arcsec, so rhl < 0.5 h,170 kpc). We have obtained a deep (5.5 h) spectrum of this z,AB= 24.7 galaxy with the DEIMOS optical spectrograph on the Keck Telescope, and here we report the discovery of a single emission line centred on 8245 Ĺ detected at 20, with a flux of f, 2 × 10,17 erg cm,2 s,1. The line is clearly resolved with detectable structure at our resolution of better than 55 km s,1, and the only plausible interpretation consistent with the ACS photometry is that we are seeing Lyman , emission from a z= 5.78 galaxy. This is the highest redshift galaxy to be discovered and studied using HST data. The velocity width (,vFWHM= 260 km s,1) and rest-frame equivalent width (WLy,rest= 20 Ĺ) indicate that this line is most probably powered by star formation, as an AGN would typically have larger values. The starburst interpretation is supported by our non-detection of the high-ionization N v,1240- Ĺ emission line, and the absence of this source from the deep Chandra X-ray images. The star formation rate inferred from the rest-frame UV continuum is 34 h,270 M, yr,1 (,M= 0.3, ,,= 0.7). This is the most luminous starburst known at z > 5. Our spectroscopic redshift for this object confirms the validity of the i,-drop technique of Stanway et al. to select star-forming galaxies atz, 6. [source]

First stars contribution to the near-infrared background fluctuations

M. Magliocchetti
ABSTRACT We show that the emission from the first, metal-free stars inside Population III objects (Pop IIIs) is needed to explain the level of fluctuations in the near-infrared background (NIRB) recently discovered by Kashlinsky et al., at least at the shortest wavelengths. Clustering of (unresolved) Pop IIIs can in fact account for the entire signal at almost all the ,1,30 arcsec scales probed by observations in the J band. Their contribution fades away at shorter frequencies and becomes negligible in the K band. ,Normal', highly clustered, ,z,, 3 galaxies undergoing intense star formation such as those found in the Hubble Deep Fields can ,fill in' this gap and provide for the missing signal. It is in fact found that their contribution to the intensity fluctuations is the dominant one at ,= 2.17 ,m, while it gradually loses importance in the H andJ bands. The joint contribution from these two populations of cosmic objects is able, within the errors, to reproduce the observed power spectrum in the whole near-infrared range on small angular scales (,, 200 arcsec for Pop III protogalaxies). Signals on larger scales detected by other experiments instead require the presence of more local sources. [source]