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Column Density (column + density)
Kinds of Column Density Selected AbstractsUpper limits on X-ray emission from two rotating radio transientsMONTHLY NOTICES OF THE ROYAL ASTRONOMICAL SOCIETY, Issue 3 2009D. L. Kaplan ABSTRACT X-ray emission from the enigmatic rotating radio transients (RRATs) offers a vital clue to understanding these objects and how they relate to the greater neutron star population. An X-ray counterpart to RRAT J1819,1458 is known, and its properties are similar to those of other middle-aged (0.1 Myr) neutron stars. We have searched for X-ray emission with Chandra/Advanced CCD Imaging Spectrometer at the positions of two RRATs with arcsecond (or better) localization, J0847,4316 and J1846,0257. Despite deep searches (especially for RRAT J1846,0257) we did not detect any emission with 0.3,8 keV count-rate limits of 1 and 0.068 counts ks,1, respectively, at 3, confidence. Assuming thermal emission similar to that seen from RRAT J1819,1458 (a blackbody with radius ,20 km), we derive effective temperature limits of 77 and 91 eV for the nominal values of the distances and column densities to both sources, although both of those quantities are highly uncertain and correlated. If we instead fix the temperature of the emission (a blackbody with kT= 0.14 keV), we derive unabsorbed luminosity limits in the 0.3,8 keV range of 1 × 1032 and 3 × 1032 erg s,1. These limits are considerably below the luminosity of RRAT J1819,1458(4 × 1033 erg s,1), suggesting that RRATs J0847,4316 and J1846,0257 have cooled beyond the point of visibility (plausible given the differences in characteristic age). However, as we have not detected X-ray emission, it may also be that the emission from RRATs J0847,4316 and J1846,0257 has a different character from that of RRAT J1819,1458. The two non-detections may prove a counterpoint to RRAT J1819,1458, but more detections are certainly needed before we can begin to derive general X-ray emission properties for the RRAT populations. [source] Probing feedback in protogalaxies: multiphase gas in a DLA at z, 2.4MONTHLY NOTICES OF THE ROYAL ASTRONOMICAL SOCIETY, Issue 1 2008N. Lehner ABSTRACT We investigate the physical processes occurring in the multiphase gas of a damped Ly, absorber (DLA). We base our analysis on a high-quality Keck High-Resolution Echelle Spectrometer (HIRES) spectrum of the QSO J1211+0422 in which a DLA is detected at z, 2.377. There is little contamination of the high-ion (O vi, N v, C iv, Si iv) absorption, allowing us to explore the properties of the highly ionized gas and its connection to other gas phases. The metallicity ([Z/H]=,1.41 ± 0.08), H i column density [], full-width velocity (,vneut, 70 km s,1) and relative abundances ([Si/Fe]=+0.23 ± 0.05 and [N/Si]=,0.88 ± 0.07) of this DLA are not unusual. However, we derive the lowest C ii* cooling rate in a DLA, lc < 10,27.8 erg s,1 per H atom (3,). Using this stringent limit, we show that the neutral gas (confined at |v| < +39 km s,1) must be warm and the star formation rate is <7.1 × 10,3 M, yr,1 kpc,2. Surprisingly, the gas shows strong, complex absorption profiles from highly ionized gas whose kinematics appear connected to each other and the low ions. The total amount of highly and weakly ionized gas is very large with ,1.5. At |v| ,+39 km s,1, the gas is fully and highly ionized []. Based on ionization models, O vi and N v are generally difficult to produce by hard photons, while Si iv and C iv can be photoionized to a large extent. There is, however, no evidence of O vi -bearing gas at T, 106 K associated with this DLA. In contrast, there is some evidence for narrow O vi, N v and C iv components (unexplained by photoionization), implying too low temperatures (T < 105 K) for simple collisional ionization models to produce their observed column densities. Stellar feedback is a possible source for producing the high ions, but we cannot rule out accretion of non-pristine material on to the protogalaxy. [source] Coincident, 100 kpc scale damped Ly, absorption towards a binary QSO: how large are galaxies at z, 3?MONTHLY NOTICES OF THE ROYAL ASTRONOMICAL SOCIETY, Issue 3 2007Sara L. Ellison ABSTRACT We report coincident damped Ly, (DLA) and sub-DLA absorption at zabs= 2.66 and zabs= 2.94 towards the z, 3, 13.8 arcsec separation binary quasar SDSS 1116+4118 AB. At the redshifts of the absorbers, this angular separation corresponds to a proper transverse separation of ,110 h,170 kpc. A third absorber, a sub-DLA at zabs= 2.47, is detected towards SDSS 1116+4118 B, but no corresponding high column density absorber is present towards SDSS 1116+4118 A. We use high-resolution galaxy simulations and a clustering analysis to interpret the coincident absorption and its implications for galaxy structure at z, 3. We conclude that the common absorption in the two lines of sight is unlikely to arise from a single galaxy, or a galaxy plus satellite system, and is more feasibly explained by a group of two or more galaxies with separations ,100 kpc. The impact of these findings on single line-of-sight observations is also discussed; we show that abundances of DLAs may be affected by up to a few tenths of a dex by line-of-sight DLA blending. From a Keck Echellette Spectrograph and Imager spectrum of the two quasars, we measure metal column densities for all five absorbers and determine abundances for the three absorbers with log N(H i) > 20. For the two highest N(H i) absorbers, we determine high levels of metal enrichment, corresponding to 1/3 and 1/5 Z,. These metallicities are amongst the highest measured for DLAs at any redshift and are consistent with values measured in Lyman-break galaxies at 2 < z < 3. For the DLA at zabs= 2.94 we also infer an approximately solar ratio of ,-to-Fe peak elements from [S/Zn]=+0.05, and measure an upper limit for the molecular fraction in this particular line of sight of log f (H 2) < ,5.5. [source] The sources of intergalactic metalsMONTHLY NOTICES OF THE ROYAL ASTRONOMICAL SOCIETY, Issue 2 2006E. Scannapieco ABSTRACT We study the clustering properties of metals in the intergalactic medium (IGM) as traced by 619 C iv and 81 Si iv absorption components with N, 1012 cm,2 and 316 Mg ii and 82 Fe ii absorption components with N, 1011.5 cm,2 in 19 high signal-to-noise ratio (60,100 pixel,1), high-resolution (R= 45 000) quasar spectra. C iv and Si iv trace each other closely and their line-of-sight correlation functions ,(v) exhibit a steep decline at large separations and a flatter profile below ,150 km s,1, with a large overall bias. These features do not depend on absorber column densities, although there are hints that the overall amplitude of ,C iv (v) increases with time over the redshift range detected (1.5,3). Carrying out a detailed smoothed particle hydrodynamic simulation (2 × 3203, 57 Mpc3 comoving), we show that the C iv correlation function cannot be reproduced by models in which the IGM metallicity is constant or a local function of overdensity (Z,,2/3). However, the properties of ,C iv(v) are generally consistent with a model in which metals are confined within bubbles with a typical radius Rs about sources of mass ,Ms. We derive best-fitting values of Rs, 2 comoving Mpc and Ms, 1012 M, at z= 3. Our lower-redshift (0.5,2) measurements of the Mg ii and Fe ii correlation functions also uncover a steep decline at large separations and a flatter profile at small separations, but the clustering is even higher than in the z= 1.5,3 measurements, and the turnover is shifted to somewhat smaller distances, ,75 km s,1. Again, these features do not change with column density, but there are hints that the amplitudes of ,Mg ii(v) and ,Fe ii(v) increase with time. We describe an analytic ,bubble' model for these species, which come from regions that are too compact to be accurately simulated numerically, deriving best-fitting values of Rs, 2.4 Mpc and Ms, 1012 M,. Equally good analytic fits to all four species are found in a similarly biased high-redshift enrichment model in which metals are placed within 2.4 comoving Mpc of Ms, 3 × 109 sources at z= 7.5. [source] Galaxies as fluctuations in the ionizing background radiation at low redshiftMONTHLY NOTICES OF THE ROYAL ASTRONOMICAL SOCIETY, Issue 4 2003Suzanne M. Linder ABSTRACT Some Lyman continuum photons are likely to escape from most galaxies, and these can play an important role in ionizing gas around and between galaxies, including gas that gives rise to Lyman-alpha absorption. Thus the gas surrounding galaxies and in the intergalactic medium will be exposed to varying amounts of ionizing radiation depending upon the distances, orientations and luminosities of any nearby galaxies. The ionizing background can be recalculated at any point within a simulation by adding the flux from the galaxies to a uniform quasar contribution. Normal galaxies are found to almost always make some contribution to the ionizing background radiation at a redshift of zero, as seen by absorbers and at random points in space. Assuming that ,2 per cent of ionizing photons escape from a galaxy such as the Milky Way, we find that normal galaxies make a contribution of at least 30,40 per cent of the assumed quasar background. Lyman-alpha absorbers with a wide range of neutral column densities are found to be exposed to a wide range of ionization rates, although the distribution of photoionization rates for absorbers is found to be strongly peaked. On average, fewer highly ionized absorbers are found to arise further from luminous galaxies, while local fluctuations in the ionization rate are seen around galaxies having a wide range of properties. [source] The K, complex of He-like iron with dielectronic satellitesMONTHLY NOTICES OF THE ROYAL ASTRONOMICAL SOCIETY, Issue 4 2001Justin Oelgoetz It is shown that the dielectronic satellites (DES) dominate X-ray spectral formation in the 6.7-keV K, complex of Fe xxv at temperatures below that of maximum abundance in collisional ionization equilibrium Tm. Owing to their extreme temperature sensitivity, the DES are excellent spectral diagnostics for in photoionized, collisional or hybrid plasmas; whereas the forbidden, intercombination and resonance lines of Fe xxv are not. A diagnostic line ratio GD(T) is defined including the DES and the lines, with parameters from new relativistic atomic calculations. The DES absorption resonance strengths may be obtained from differential oscillator strengths, possibly to yield the column densities. The DES contribution to highly ionized Fe should be of interest for models of redward broadening of K, features, ionized accretion discs, accretion flows and K, temporal-temperature variability in AGN. [source] , Velorum: another variable interstellar sightline?MONTHLY NOTICES OF THE ROYAL ASTRONOMICAL SOCIETY, Issue 2 2000I. A. Crawford We present ultra-high-resolution (R = 900 000) observations of interstellar Na i and K i absorption lines towards , Vel (HD 81188) which show clear evidence for temporal variation between 1994 and 2000. Specifically, the column densities of K0 and Na0 in the main velocity component have increased by 40 and 16 per cent, respectively, over this period. Earlier work had suggested that this component actually consists of two unresolved sub-components; this result is confirmed here, and the overall line profile is found to be consistent with only one of these sub-components having increased in strength since 1994. We argue that this variation is consistent with the line of sight gradually probing a cold, dense interstellar filament of the kind recently proposed by Heiles to explain other observations of small-scale structure in the interstellar medium. [source] The X-ray spectra of Compton-thick Seyfert 2 galaxies as seen by BeppoSAXMONTHLY NOTICES OF THE ROYAL ASTRONOMICAL SOCIETY, Issue 1 2000G. Matt Results from BeppoSAX observations of Compton-thick Seyfert 2 galaxies are summarized and reviewed, and their general properties derived and discussed. In five out of the seven observed sources, the nucleus is directly visible at high X-ray energies, where the photons penetrate absorbers with column densities in the range 1.1,4.3×1024 cm,2 (in the other two sources, NGC 1068 and NGC 7674, the nucleus is instead totally obscured at all energies, implying even larger column densities). In most sources there is unambiguous evidence of a reflection component from optically thick, cold matter, while in two (or maybe four) cases there is also evidence of reflection from ionized matter. For the sources with a measured X-ray luminosity, a comparison with the infrared luminosity is made; while in two cases (the Circinus galaxy and NGC 4945) the IR emission appears to be dominated by starburst activity, in the other three sources (NGC 6240, Mrk 3 and TOL 0109-383) it is likely to be dominated by reprocessing of the UV and X-ray photons emitted by an active galactic nucleus. [source] Modelling the broad-band spectra of X-ray emitting GPS galaxiesASTRONOMISCHE NACHRICHTEN, Issue 2-3 2009L. Ostorero Abstract The study of the broad-band emission of GHz-Peaked-Spectrum (GPS) radio galaxies is a powerful tool to investigate the physical processes taking place in the central, kpc-sized region of their active hosts, where the jets propagate and the lobes expand, interacting with the surrounding interstellar medium (ISM). We recently developed a new dynamical-radiative model to describe the evolution of the GPS phenomenon (Stawarz et al. 2008): as the relativistic jets propagate through the ISM, gradually engulfing narrow-line emitting gas clouds along their way, the electron population of the expanding lobes evolves, emitting synchrotron light, as well as inverse-Compton radiation via up-scattering of the photon fields from the host galaxy and its active nucleus. The model, which successfully reproduces the key features of the GPS radio sources as a class, provides a description of the evolution of their spectral energy distribution (SED) with the lobes' expansion, predicting significant and complex X-ray to , -ray emission. We apply here the model to the broad-band SED's of a sample of known, X-ray emitting GPS galaxies, and show that (i) the free-free absorption mechanism enables us to reproduce the radio continuum at frequencies below the turnover; (ii) the lobes' non-thermal, inverse-Compton emission can account for the observed X-ray spectra, providing a viable alternative to the thermal, accretion-dominated scenario. We also show that, in our sample, the relationship between the X-ray and radio hydrogen column densities, NH and NHI, is suggestive of a positive correlation, which, if confirmed, would support the scenario of high-energy emitting lobes (© 2009 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source] Investigation of ion beam techniques for the analysis and exposure of particles encapsulated by silica aerogel: Applicability for StardustMETEORITICS & PLANETARY SCIENCE, Issue 9 2004G. A. GRAHAM These particles will be the first sample return from a solid planetary body since the Apollo missions. In preparation for the return, analogue particles were implanted into a keystone of silica aerogel that had been extracted from bulk silica aerogel using the optical technique described in Westphal et al. (2004). These particles were subsequently analyzed using analytical techniques associated with the use of a nuclear microprobe. The particles have been analyzed using: a) scanning transmission ion microscopy (STIM) that enables quantitative density imaging; b) proton elastic scattering analysis (PESA) and proton backscattering (PBS) for the detection of light elements including hydrogen; and c) proton-induced X-ray emission (PIXE) for elements with Z > 11. These analytical techniques have enabled us to quantify the composition of the encapsulated particles. A significant observation from the study is the variable column density of the silica aerogel. We also observed organic contamination within the silica aerogel. The implanted particles were then subjected to focused ion beam (FIB) milling using a 30 keV gallium ion beam to ablate silica aerogel in site-specific areas to expose embedded particles. An ion polished flat surface of one of the particles was also prepared using the FIB. Here, we show that ion beam techniques have great potential in assisting with the analysis and exposure of Stardust particles. [source] Probing feedback in protogalaxies: multiphase gas in a DLA at z, 2.4MONTHLY NOTICES OF THE ROYAL ASTRONOMICAL SOCIETY, Issue 1 2008N. Lehner ABSTRACT We investigate the physical processes occurring in the multiphase gas of a damped Ly, absorber (DLA). We base our analysis on a high-quality Keck High-Resolution Echelle Spectrometer (HIRES) spectrum of the QSO J1211+0422 in which a DLA is detected at z, 2.377. There is little contamination of the high-ion (O vi, N v, C iv, Si iv) absorption, allowing us to explore the properties of the highly ionized gas and its connection to other gas phases. The metallicity ([Z/H]=,1.41 ± 0.08), H i column density [], full-width velocity (,vneut, 70 km s,1) and relative abundances ([Si/Fe]=+0.23 ± 0.05 and [N/Si]=,0.88 ± 0.07) of this DLA are not unusual. However, we derive the lowest C ii* cooling rate in a DLA, lc < 10,27.8 erg s,1 per H atom (3,). Using this stringent limit, we show that the neutral gas (confined at |v| < +39 km s,1) must be warm and the star formation rate is <7.1 × 10,3 M, yr,1 kpc,2. Surprisingly, the gas shows strong, complex absorption profiles from highly ionized gas whose kinematics appear connected to each other and the low ions. The total amount of highly and weakly ionized gas is very large with ,1.5. At |v| ,+39 km s,1, the gas is fully and highly ionized []. Based on ionization models, O vi and N v are generally difficult to produce by hard photons, while Si iv and C iv can be photoionized to a large extent. There is, however, no evidence of O vi -bearing gas at T, 106 K associated with this DLA. In contrast, there is some evidence for narrow O vi, N v and C iv components (unexplained by photoionization), implying too low temperatures (T < 105 K) for simple collisional ionization models to produce their observed column densities. Stellar feedback is a possible source for producing the high ions, but we cannot rule out accretion of non-pristine material on to the protogalaxy. [source] A homogeneous sample of sub-damped Lyman systems , IV.MONTHLY NOTICES OF THE ROYAL ASTRONOMICAL SOCIETY, Issue 1 2007Global metallicity evolution ABSTRACT An accurate method to measure the abundance of high-redshift galaxies involves the observation of absorbers along the line of sight towards a background quasar. Here, we present abundance measurements of 13 z, 3 sub-damped Lyman , (sub-DLA) systems (quasar absorbers with H i column density in the range 19 < log N(H i) < 20.3 cm,2) based on high-resolution observations with the VLT UVES spectrograph. These observations more than double the amount of metallicity information for sub-DLAs available at z > 3. These new data, combined with other sub-DLA measurements from the literature, confirm the stronger evolution of metallicity with redshift for sub-DLAs than for the classical damped Lyman , absorbers. In addition, these observations are used to compute for the first time, using photoionization modelling in a sample of sub-DLAs, the fraction of gas that is ionized. Based on these results, we calculate that sub-DLAs contribute no more than 6 per cent of the expected amount of metals at z, 2.5. We therefore conclude that, even if sub-DLAs are found to be more metal-rich than classical DLAs, their contribution is insufficient to solve the so-called ,missing-metals' problem. [source] Observations towards early-type stars in the ESO-POP Survey , II.MONTHLY NOTICES OF THE ROYAL ASTRONOMICAL SOCIETY, Issue 3 2007Searches for intermediate-, high-velocity clouds ABSTRACT We present Ca ii K and Ti ii optical spectra of early-type stars taken mainly from the ultraviolet and visual echelle spectrograph (UVES) Paranal Observatory Project, plus H i 21-cm spectra, from the Vila-Elisa and Leiden-Dwingeloo Surveys, which are employed to obtain distances to intermediate- and high-velocity clouds (IHVCs). H i emission at a velocity of ,117 km s,1 towards the sightline HD 30677 () with column density ,1.7 × 1019 cm,2 has no corresponding Ca ii K absorption in the UVES spectrum, which has a signal-to-noise ratio (S/N) of 610 per resolution element. The star has a spectroscopically determined distance of 2.7 kpc, and hence sets this as a firm lower distance limit towards Anti-Centre cloud ACII. Towards another sightline (HD 46185 with ), H i at a velocity of +122 km s,1 and column density of 1.2 × 1019 cm,2 is seen. The corresponding Ca ii K spectrum has a S/N of 780, although no absorption is observed at the cloud velocity. This similarly places a firm lower distance limit of 2.9 kpc towards this parcel of gas that may be an intermediate-velocity (IV) cloud. The lack of IV Ca ii absorption towards HD 196426 () at a S/N of 500 reinforces a lower distance limit of ,700 pc towards this part of complex gp, where the H i column density is 1.1 × 1019 cm,2 and velocity is +78 km s,1. Additionally, no IV Ca ii is seen in absorption in the spectrum of HD 19445, which is strong in H i with a column density of 8 × 1019 cm,2 at a velocity of ,,42 km s,1, placing a firm although uninteresting lower distance limit of 39 pc to this part of IV South. Finally, no high-velocity Ca ii K absorption is seen towards HD 115363 () at a S/N of 410, placing a lower distance of ,3.2 kpc towards the HVC gas at velocity of ,+224 km s,1 and H i column density of 5.2 × 1019 cm,2. This gas is in the same region of the sky as complex WE (Wakker 2001), but at higher velocities. The non-detection of Ca ii K absorption sets a lower distance of ,3.2 kpc towards the HVC, which is unsurprising if this feature is indeed related to the Magellanic System. [source] Cosmological simulations of intergalactic medium enrichment from galactic outflowsMONTHLY NOTICES OF THE ROYAL ASTRONOMICAL SOCIETY, Issue 4 2006Benjamin D. Oppenheimer ABSTRACT We investigate models of self-consistent chemical enrichment of the intergalactic medium (IGM) from z= 6.0 , 1.5, based on hydrodynamic simulations of structure formation that explicitly incorporate outflows from star-forming galaxies. Our main result is that outflow parametrizations derived from observations of local starburst galaxies, in particular momentum-driven wind scenarios, provide the best agreement with observations of C iv absorption at z, 2,5. Such models sufficiently enrich the high- z IGM to produce a global mass density of C iv absorbers that is relatively invariant from z= 5.5 , 1.5, in agreement with observations. This occurs despite continual IGM enrichment causing an increase in volume-averaged metallicity by ,× 5,10 over this redshift range, because energy input accompanying the enriching outflows causes a drop in the global ionization fraction of C iv. Comparisons to observed C iv column density and linewidth distributions and C iv -based pixel optical depth ratios provide significant constraints on wind models. Our best-fitting outflow models show mean IGM temperatures only slightly above our no-outflow case, metal filling factors of just a few per cent with volume-weighted metallicities around 10,3 at z, 3, significant amounts of collisionally ionized C iv absorption and a metallicity,density relationship that rises rapidly at low overdensities and flattens at higher ones. In general, we find that outflow speeds must be high enough to enrich the low-density IGM at early times but low enough not to overheat it, and concurrently must significantly suppress early star formation while still producing enough early metals. It is therefore non-trivial that locally calibrated momentum-driven wind scenarios naturally yield the desired strength and evolution of outflows, and suggest that such models represent a significant step towards understanding the impact of galactic outflows on galaxies and the IGM across cosmic time. [source] Evidence of a change in the long-term spin-down rate of the X-ray pulsar 4U 1907+09MONTHLY NOTICES OF THE ROYAL ASTRONOMICAL SOCIETY, Issue 4 2006A. Baykal ABSTRACT We analysed RXTE archival observations of 4U 1907+09 between 1996 February 17 and 2002 March 6. The pulse timing analysis showed that the source stayed at almost constant period around 1998 August and then started to spin-down at a rate of (,1.887 , 0.042) × 10,14 Hz s,1 which is ,0.60 times lower than the long-term (,15 yr) spin-down rate. Our pulse-frequency measurements for the first time resolved significant spin-down rate variations since the discovery of the source. We also presented orbital phase resolved X-ray spectra during two stable spin-down episodes during 1996 November,1997 December and 2001 March,2002 March. The source has been known to have two orbitally locked flares. We found that X-ray flux and spectral parameters except hydrogen column density agreed with each other during the flares. We interpreted the similar values of X-ray fluxes as an indication of the fact that the source accretes not only via transient retrograde accretion disc but also via the stellar wind of the companion, so that the variation of the accretion rate from the disc does not cause significant variation in the observed X-ray flux. Lack of significant change in spectral parameters except hydrogen column density was interpreted as a sign of the fact that the change in the spin-down rate of the source was not accompanied by a significant variation in the accretion geometry. [source] Early-type stars observed in the ESO UVES Paranal Observatory Project , I. Interstellar Na i UV, Ti ii and Ca ii K observations,MONTHLY NOTICES OF THE ROYAL ASTRONOMICAL SOCIETY, Issue 4 2006I. Hunter ABSTRACT We present an analysis of interstellar Na i (,air= 3302.37 and 3302.98 Å), Ti ii(,air= 3383.76 Å) and Ca ii K (,air= 3933.66 Å) absorption features for 74 sightlines towards O- and B-type stars in the Galactic disc. The data were obtained from the Ultraviolet and Visual Echelle Spectrograph Paranal Observatory Project, at a spectral resolution of 3.75 km s,1 and with mean signal-to-noise ratios per pixel of 260, 300 and 430 for the Na i, Ti ii and Ca ii observations, respectively. Interstellar features were detected in all but one of the Ti ii sightlines and all of the Ca ii sightlines. The dependence of the column density of these three species with distance, height relative to the Galactic plane, H i column density, reddening and depletion relative to the solar abundance has been investigated. We also examine the accuracy of using the Na i column density as an indicator of that for H i. In general, we find similar strong correlations for both Ti and Ca, and weaker correlations for Na. Our results confirm the general belief that Ti and Ca occur in the same regions of the interstellar medium (ISM) and also that the Ti ii/Ca ii ratio is constant over all parameters. We hence conclude that the absorption properties of Ti and Ca are essentially constant under the general ISM conditions of the Galactic disc. [source] The sources of intergalactic metalsMONTHLY NOTICES OF THE ROYAL ASTRONOMICAL SOCIETY, Issue 2 2006E. Scannapieco ABSTRACT We study the clustering properties of metals in the intergalactic medium (IGM) as traced by 619 C iv and 81 Si iv absorption components with N, 1012 cm,2 and 316 Mg ii and 82 Fe ii absorption components with N, 1011.5 cm,2 in 19 high signal-to-noise ratio (60,100 pixel,1), high-resolution (R= 45 000) quasar spectra. C iv and Si iv trace each other closely and their line-of-sight correlation functions ,(v) exhibit a steep decline at large separations and a flatter profile below ,150 km s,1, with a large overall bias. These features do not depend on absorber column densities, although there are hints that the overall amplitude of ,C iv (v) increases with time over the redshift range detected (1.5,3). Carrying out a detailed smoothed particle hydrodynamic simulation (2 × 3203, 57 Mpc3 comoving), we show that the C iv correlation function cannot be reproduced by models in which the IGM metallicity is constant or a local function of overdensity (Z,,2/3). However, the properties of ,C iv(v) are generally consistent with a model in which metals are confined within bubbles with a typical radius Rs about sources of mass ,Ms. We derive best-fitting values of Rs, 2 comoving Mpc and Ms, 1012 M, at z= 3. Our lower-redshift (0.5,2) measurements of the Mg ii and Fe ii correlation functions also uncover a steep decline at large separations and a flatter profile at small separations, but the clustering is even higher than in the z= 1.5,3 measurements, and the turnover is shifted to somewhat smaller distances, ,75 km s,1. Again, these features do not change with column density, but there are hints that the amplitudes of ,Mg ii(v) and ,Fe ii(v) increase with time. We describe an analytic ,bubble' model for these species, which come from regions that are too compact to be accurately simulated numerically, deriving best-fitting values of Rs, 2.4 Mpc and Ms, 1012 M,. Equally good analytic fits to all four species are found in a similarly biased high-redshift enrichment model in which metals are placed within 2.4 comoving Mpc of Ms, 3 × 109 sources at z= 7.5. [source] Near-infrared identification of the counterpart to X1908+075: a new OB-supergiant X-ray binaryMONTHLY NOTICES OF THE ROYAL ASTRONOMICAL SOCIETY, Issue 2 2005T. Morel ABSTRACT We report the near-infrared (near-IR) identification of the likely counterpart to X1908+075, a highly absorbed Galactic X-ray source recently suspected to belong to the rare class of OB supergiant,neutron star binary systems. Our JHKs -band imaging of the field reveals the existence within the X-ray error boxes of a near-IR source consistent with an early-type star lying at d, 7 kpc and suffering AV, 16 mag of extinction, the latter value being in good agreement with the hydrogen column density derived from modelling of the X-ray spectrum. Our follow-up, near-IR spectroscopic observations confirm the nature of this candidate and lead to a late O-type supergiant classification, thereby supporting the identification of a new Galactic OB-supergiant X-ray binary. [source] XMM,Newton observations of GB B1428+4217: confirmation of intrinsic soft X-ray absorptionMONTHLY NOTICES OF THE ROYAL ASTRONOMICAL SOCIETY, Issue 4 2004M. A. Worsley ABSTRACT We report the results of XMM,Newton observations of the X-ray bright, radio-loud blazar GB B1428+4217 at a redshift of z= 4.72. We confirm the presence of soft X-ray spectral flattening at energies ,0.7 keV as reported in previous ROSAT and BeppoSAX observations. At hard X-ray energies, the spectrum is consistent with a power law, although we find that the spectral slope varied between both XMM,Newton observations and it is also significantly different from that reported previously. Whilst we cannot rule out intrinsic cold absorption to explain the spectral depression, we favour a dust-free warm absorber. Cold absorption requires a column density ,1.4,1.6 × 1022 cm,2, whilst a warm absorber could have up to ,1023 cm,2 and an ionization parameter ,102. The spectrum of GB B1428+4217 shows remarkable parallels with that of the z= 4.4 blazar PMN J0525,3343, in which the available evidence is also most consistent with a warm absorber model. [source] Gigamasers: the key to the dust-obscured star formation history of the Universe?MONTHLY NOTICES OF THE ROYAL ASTRONOMICAL SOCIETY, Issue 2 2001R.H.D. Townsend We discuss the possibility of using OH and H2O gigamasers to trace the redshift distribution of luminous, dust-obscured, star-forming galaxies. It has long been thought that ultraluminous, interacting galaxies should host gigamasers, owing to their vast pumping infrared (IR) luminosity, the large column density of molecules available to populate the maser states and the turbulent motion of the gas in these dynamically complex systems, which allows unsaturated maser emission. OH masers may thus be well suited to the redshift-blind detection of ultraluminous and hyperluminous infrared galaxies such as those uncovered by the SCUBA submillimetre camera. The bandwidth requirement is low, <1 GHz for (lower still if additional redshift constraints are available) and the dual-line 1665-/1667-MHz OH spectral signature can act as a check on the reality of detections. [source] Spectropolarimetry of a complete infrared-selected sample of Seyfert 2 galaxiesMONTHLY NOTICES OF THE ROYAL ASTRONOMICAL SOCIETY, Issue 2 2001S.L. Lumsden We report the results of a spectropolarimetric survey of a complete far-infrared-selected sample of Seyfert 2 galaxies. We have found polarized broad H, emission in one new source, NGC 5995. In the sample as a whole, there is a clear tendency for galaxies in which we have detected broad H, in polarized light to have warm mid,far-infrared colours in agreement with our previous results. However, a comparison of the optical, radio and hard X-ray properties of these systems leads us to conclude that this is a secondary consequence of the true mechanism governing our ability to see scattered light from the broad-line region. We find a strong trend for galaxies showing such emission to lie above a critical value of the relative luminosity of the active core to the host galaxy (as measured from the [O iii] 5007-Å equivalent width) which varies as a function of the obscuring column density as measured from hard X-ray observations. The warmth of the infrared colours is then largely due to a combination of the luminosity of the active core, the obscuring column and the relative importance of the host galaxy in powering the far-infrared emission, and not solely orientation as we inferred in our previous paper. Our data may also provide an explanation as to why the most highly polarized galaxies, which appear to have tori that are largely edge-on, are also the most luminous and have the most easily detectable scattered broad H,. [source] Beginning of the super-soft phase of the classical nova V2491 CygniASTRONOMISCHE NACHRICHTEN, Issue 2 2010D. Takei Abstract We present the results of soft X-ray studies of the classical nova V2491 Cygni using the Suzaku observatory. On day 29 after outburst, a soft X-ray component with a peak at ,0.5 keV has appeared, which is tantalising evidence for the beginning of the super-soft X-ray emission phase. We show that an absorbed blackbody model can describe the observed spectra, yielding a temperature of 57 eV, neutral hydrogen column density of 2 × 1021 cm,2, and a bolometric luminosity of ,1036 erg s,1. However, at the same time, we also found a good fit with an absorbed thin-thermal plasma model, yielding a temperature of 0.1 keV, neutral hydrogen column density of 4 × 1021 cm,2, and a volume emission measure of ,1058 cm,3. Owing to low spectral resolution and low signal-to-noise ratio below 0.6 keV, the statistical parameter uncertainties are large, but the ambiguity of the two very different models demonstrates that the systematic errors are the main point of concern. The thin-thermal plasma model implies that the soft emission originates from optically thin ejecta, while the blackbody model suggests that we are seeing optically thick emission from the white dwarf (© 2010 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source] | ||||||||||