Single Line Of Sight Research Articles

Probing the Intergalactic Medium-Galaxy Connection toward PKS 0405-123. II. A Cross-Correlation Study of Lyα Absorbers and Galaxies at z < 0.5

We present a pilot study of the clustering properties of Lyα absorbers with respect to known galaxies based on 112 Lyα absorbers and 482 galaxies identified at z < 0.5 along the sight line toward PKS 0405-123. The principal goal is to determine the origin of Lyα absorbers based on their cross-correlation amplitude with known galaxies and to investigate a possible N(H I) dependence of the cross-correlation function. The main results of our study are as follows: (1) The cross-correlation function ξga measured using only emission-line-dominated galaxies and Lyα absorbers with log N(H I) ≥ 14 shows a comparable strength to the galaxy autocorrelation function ξgg on comoving, projected distance scales of less than 1 h-1 Mpc, while there remains a lack of cross-correlation signal when using only absorption-line-dominated galaxies. This signifies a morphology-dependent ξga and indicates that strong absorbers with log N(H I) ≥ 14 and emission-line galaxies reside in the same halo population. (2) A maximum likelihood analysis shows that Lyα absorbers with log N(H I) < 13.6 are consistent with being more randomly distributed with respect to known galaxies. (3) Finally, we find based on this single sight line that the amplitude of ξga does not depend sensitively on N(H I) for strong absorbers, with log N(H I) ≥ 13.6.

Noise in Strong Lensing Cosmography

Giant arcs in strong lensing galaxy clusters can provide a purely geometric determination of cosmological parameters, such as the dark energy density and equation of state. We investigate sources of noise in cosmography with giant arcs, focusing in particular on errors induced by density fluctuations along the line of sight and errors caused by modeling uncertainties. We estimate parameter errors in two independent ways, first by developing a Fisher matrix formalism for strong lensing parameters and next by directly ray-tracing through N-body simulations using a multiplane lensing code. We show that for reasonable power spectra, density fluctuations from large-scale structures produce >100% errors in cosmological parameters derived from any single sight line, precluding the use of individual clusters or golden lenses to derive accurate cosmological constraints. Modeling uncertainties can similarly lead to large errors, and we show that the use of parameterized mass models in fitting strong lensing clusters can significantly bias the inferred cosmological parameters. We lastly speculate on the means by which these errors may be corrected.

Time resolved radiated power during tokamak disruptions and spectral averaging of AXUV photodiode response in DIII-D

Silicon absolute extreme ultraviolet (AXUV) photodiodes have been employed in a disruption radiometer diagnostic for measurement of radiant power in the DIII-D tokamak with a 170 kHz bandwidth. This is motivated by a need to improve the understanding of radiative processes in tokamak disruptions. The diagnostic described in this article has a single line of sight though the central plasma. Accounting for the photon energy dependence of the AXUV photodiode responsivity is made possible by optical filtering, with the aid of spectra from an extreme ultraviolet survey spectrometer. The appropriate effective responsivity for interpretation of the data is lower than the nominal value typically used for the detector. In the current quench phase of disruptions, it is less than half the nominal value. Comparisons with results from a foil bolometer find good agreement.

Evidence for Extremely High Dust Polarization Efficiency in NGC 3184

Recent studies have found the Type II-plateau supernova (SN) 1999gi to be highly polarized (p_max = 5.8%, where p_max is the highest degree of polarization measured in the optical bandpass; Leonard & Filippenko 2001) and minimally reddened (E[B-V] = 0.21 +/- 0.09 mag; Leonard et al. 2002). From multiple lines of evidence, including the convincing fit of a ``Serkowski'' interstellar polarization (ISP) curve to the continuum polarization shape, we conclude that the bulk of the observed polarization is likely due to dust along the line of sight (l-o-s), and is not intrinsic to SN 1999gi. We present new spectropolarimetric observations of four distant Galactic stars close to the l-o-s to SN 1999gi (two are within 0.02 degrees), and find that all are null to within 0.2%, effectively eliminating Galactic dust as the cause of the high polarization. The high ISP coupled with the low reddening implies an extraordinarily high polarization efficiency for the dust along this l-o-s in NGC 3184: ISP / E(B-V) = 31^{+22}_{-9} % mag^{-1}. This is inconsistent with the empirical Galactic limit (ISP / E[B-V] < 9% mag^{-1}), and represents the highest polarization efficiency yet confirmed for a single sight line in either the Milky Way or an external galaxy.

Adaptive optics and multi-conjugate adaptive optics with the VTT

We are currently developing adaptive optics (AO) system with a multi-conjugate extension for the German solar vacuum tower telescope (VTT) at the Teide Observatory on Tenerife.Multi-conjugate adaptive optics (MCAO) is a technique for increasing the field of view by compensating atmospheric turbulence along several, adjacent lines of sight. A conventional AO system compensates only a single line of sight in the direction of the lock point of its wavefront sensor. At larger field angles, the light from the source transverses higher layers of turbulence which are not sampled by the conventional system. Measurements at the VTT indicate that full compensation is typically restricted to a field of about 10 arcsec in diameter at visible wavelengths. An MCAO uses (at least) a second deformable mirror close to the focal plane of the telescope to compensate a larger field. The sun is a privileged target for an MCAO because the wavefront errors at larger field angles are easily measured. We intend to extend our existing AO system with a second deformable mirror and a second wavefront sensor which enables us to extend the compensated field by a factor of three in diameter.We present and discuss our concept.

Search and target acquisition: single line of sight versus wide baseline stereo

This study investigates observer performance in visual search and target detection tasks for two different conditions of image viewing: binocular viewing of single line of sight images versus stereoscopic display of wide baseline stereo images. A multiple baseline imagery database was obtained during a field test. The targets were personnel wearing forest camouflage uniforms. They were arrayed at two rural terrain sites. The weather condition at the first site was clear to partly cloudy and at the second site overcast with light rain. The preliminary analysis of the first site database indicated that wide baseline stereo can improve search and target acquisition, but that the baseline used was too wide for many of the closer targets at that site. The database from the second site was then analyzed through observer testing, with single line of sight and wide baseline stereo displays. The results indicate that with training, stereo vision effectively reduces false alarm detection by a factor of 2. Additionally, guidelines are obtained for optimum stereo display that can be used to improve positive target detection by 20%.

Diode-laser absorption sensor for line-of-sight gas temperature distributions

Line-of-sight diode-laser absorption techniques have been extended to enable temperature measurements in nonuniform-property flows. The sensing strategy for such flows exploits the broad wavelength-scanning abilities (>1.7 nm approximately 30 cm(-1)) of a vertical cavity surface-emitting laser (VCSEL) to interrogate multiple absorption transitions along a single line of sight. To demonstrate the strategy, a VCSEL-based sensor for oxygen gas temperature distributions was developed. A VCSEL beam was directed through paths containing atmospheric-pressure air with known (and relatively simple) temperature distributions in the 200-700 K range. The VCSEL was scanned over ten transitions in the R branch of the oxygen A band near 760 nm and optionally over six transitions in the P branch. Temperature distribution information can be inferred from these scans because the line strength of each probed transition has a unique temperature dependence; the measurement accuracy and resolution depend on the details of this temperature dependence and on the total number of lines scanned. The performance of the sensing strategy can be optimized and predicted theoretically. Because the sensor exhibits a fast time response (~30 ms) and can be adapted to probe a variety of species over a range of temperatures and pressures, it shows promise for industrial application.

Neutral atom temperature and flow measurements in the edge region of the Alcator C-mod tokamak

Spectral line shifts have been observed in the Dα transition of neutral deuterium in the Alcator C-mod [I. H. Hutchinson, Proceedings of the IEEE 13th Symposium on Fusion Engineering (IEEE, Piscataway, 1990), Vol. 1, p. 13] tokamak and interpreted as Doppler shifts due to a neutral flow of approximately 5×103 m/s. The emission originates from plasma at the inner wall, as indicated by the Zeeman patterns of the transition. The direction of the flow changes when the plasma transitions from a limited to a diverted configuration. In all cases, the flows are directed toward the point of contact with the wall or divertor plate. Narrow spectral profiles have been observed for the Dα transition near the midplane and within the divertor. Temperatures not higher than 0.86 eV are indicated for the divertor measurements. A difference in plasma conditions for separate locations along a single line of sight has been observed.

Development and characterization of a single-line-of-sight framing camera

We present initial characterization data from a new single-line-of-sight (SLOS) x-ray framing camera. The instrument uses an image-dissecting structure inside an electron optic tube to produce up to four simultaneous dc images from a single image incident on the cathode and a microchannel plate-based device to provide the temporal gating of those images. A series of gated images have been obtained using a short-pulse UV laser source, and the spatial resolution of those images is compared to those obtained using a more traditional-microchannel plate based system.

Ultrasonic mapping of the microvasculature: signal alignment

The ultimate goal of this work was the development of a system capable of estimating the low flow velocities in the microvasculature. Estimation of low velocity flow within these vessels is challenging due to the small signal levels and the effect of cardiac and respiratory motion. Realignment of the signal from a single line-of–sight to remove physiological tissue motion is a critical part of the process of small-vessel flow mapping, and our methods for this alignment are considered in this paper. Each method involves the correlation of pulses acquired from the same line-of–sight. The first method involves the correlation of adjacent pulses (nearest-neighbor), the second involves a single reference line and the third involves averaging the correlation over a set of reference lines. We find that a nearest-neighbor strategy is suboptimal, and that strategies involving a global reference line are superior. A bound on the variance of estimates of the location of the correlation peak is presented. This bound allows us to consider our results in comparison with an absolute limit. Finally, a new algorithm allowing for alignment between lines-of–sight is described, and initial results are presented. Such an algorithm does, in fact, reduce jitter, correct for tissue motion and enables us to better visualize vessel continuity. We find that vessels as small as 40 μm can be mapped in two dimensions using a 50-MHz transducer.

Reobservation of Close QSO Groups: The Size Evolution and Shape of Lyα Forest Absorbers

In order to study the size and shape of the absorbers that lie in front of the QSOs, in particular the Ly? forest, we present an analysis of 785 absorption lines in the spectra of five QSOs in close groupings: a pair (LB 9605: 1517+2357 at z = 1.834 and LB 9612: 1517+2356 at z = 1.903, with a separation of 102'' between them) and a triplet (KP 76: 1623+2651A at z = 2.467, KP 77: 1623+2653 at z = 2.526, and KP 78: 1623+2651B at z = 2.605, with separations of 127'', 147'', and 177'' between pairs 76:78, 76:77, and 77:78, respectively). Both of these QSO groups have been observed before, but these data represent a drastic increase in signal-to-noise ratio and/or wavelength coverage over earlier data and provide a qualitatively different view of the nature of the absorbers. The pair samples a scale critical in determining the size upper bound of Ly? absorbers, with significant leverage in redshift compared to previous studies. In the case of the triplet, this represents the spatially densest sample of Ly? forest absorbers ever studied and an almost ideally suited probe of the shape of absorbers. We observe a significant number of Ly? lines in common between the triplet sight lines, for lines stronger than rest equivalent width W0 > 0.4 ? (and no detected metal lines) and velocity differences up to 200 km s-1, corresponding to a two-point correlation function ?=1.88 -->+ 0.78?0.50 on scales of 0.5-0.8 h-1 Mpc with z = 2.14 and inconsistent at the 99.999% level with the absence of any clustering. These data also show that a significant fraction of the W0 > 0.4 ? Ly? forest absorbers spans all three sight lines to the KP triplet, indicating that the strong-lined absorbers are consistent with nearly round shapes, chosen from a range of possible cylinders of different elongations. This may be inconsistent with results from hydrodynamic/gravitational simulations of H I in the early Universe, indicating that the theoretical counterparts of Ly? forest clouds are long and filamentary. Furthermore, there is a probable correlation of W0 with ?v suggestive of the clouds being flattened and expanding with the Hubble flow in their long dimension, as would be indicative of sheets or filaments. This is supported by the uniformity of line strengths between the three sight lines for W0 > 0.4 ?. We conclude, tentatively, that the W0 > 0.4 ? Ly? forest objects are sheetlike. In contrast, the weaker lines, 0.2 ? > W0 > 0.4 ?, show no evidence of spanning the sight lines of these groups but have sizes significantly larger than the luminous portions of galaxies and C IV absorbers as revealed by closer separation QSO pairs. When the LB sight-line pair is included with other pairs at different redshifts and sight-line separations, one finds no strong evidence for evolution of Ly? absorber size with redshift. We also show that there is no evidence of large-scale structure in the Ly? forest consistent with ionization of H II by foreground QSOs as seen in the spectrum of background QSOs (the foreground proximity effect). Finally, we see a marginal detection of the sight-line two-point cross-correlation function for C IV lines ?=2.05 -->+ 1.82?1.21 over scales of 0.5-1 h-1 Mpc. This is significantly weaker than ? measured by autocorrelation along single sight lines for 200 km s-1 < ?v < 600 km s-1, suggesting that most of the latter signal may be due to the internal motions within absorbers that are smaller than 0.5 h-1 Mpc.

The Weakness of C [CSC]iv[/CSC] Absorber Clustering in Keck HIRES Spectraof Adjacent Quasar Sight Lines

We observe with Keck/HIRES the z ≈ 2.5 QSO triplet 1623+27 in order to explore on the scale of 1 Mpc the spatial clustering of C IV absorbers between adjacent sight lines. We find this signal to be significantly weaker than the clustering in velocity on corresponding scales along single sight lines, assuming that the relative velocity of absorbers is dominated by the Hubble flow. This indicates that small-scale clustering (200 km s-1 < Δv < 600 km s-1) of the C IV absorbers cannot be interpreted in terms of the positions of the absorbers in space but must be considered as internal motions within individual absorbers or within clusters of absorbers whose internal velocities dominate over Hubble expansion across the cluster scale. If the single sight line signal is due to spatial clustering, it is caused by absorber clusters smaller than would be implied by their velocities if a Hubble flow is assumed. The spatial clustering of C IV absorbers at z ≈ 2 is consistent with data on Lyα forest clustering measured in the same way at the same redshifts. However, present-day galaxy clustering, evolved back to z ≈ 2, is consistent with C IV spatial clustering but perhaps not with that of the Lyα forest. Even so, one cannot as yet distinguish the two absorber populations on the basis of spatial clustering on these small scales.

Quasar Absorbing Galaxies atz≲ 1: Deep Imaging and Spectroscopy in the Field of 3C 336

We present very deep WFPC2 images and FOS spectroscopy from the Hubble Space Telescope (HST) together with numerous supporting ground-based observations of the field of the quasar 3C 336 ($z_{em}=0.927$). The observations are designed to investigate the nature of galaxies producing metal line absorption systems in the spectrum of the QSO. Along a single line of sight, we find at least 6 metal line absorption systems (of which 3 are newly discovered) ranging in redshift from 0.317 to 0.892. Through an extensive program of optical and IR imaging, QSO spectroscopy, and faint galaxy spectroscopy, we have identified 5 of the 6 metal line absorption systems with luminous (L_K > 0.1 L*_K) galaxies. These have morphologies ranging from very late-type spiral to S0, and exhibit a wide range of inclination and position angles with respect to the QSO sightline. The only unidentified absorber, despite our intensive search, is a damped Lyman $\alpha$ system at $z_{abs}=0.656$. Analysis of the absorption spectrum suggests that the metal abundances ([Fe/H]$=-1.2$) in this system are similar to those in damped systems at $z \sim 2$, and to the two other damped systems for which abundances have been determined at $z <1$. We have found no examples of intrinsically faint galaxies ($L < 0.1 L^{\ast}$) at small impact parameters that might have been missed as absorber candidates in our previous ground-based imaging and spectroscopic programs on MgII absorbing galaxies. There are no bright galaxies (L > 0.1 L_K) within 50h^{-1} kpc which do not produce detectable metal lines (of Mg II 2796, 2803 and/or C IV 1548, 1550) in the QSO spectrum. All of these results generally support the inferences which we have previously reached from a larger survey for absorption-selected galaxies at $z\simlt 1$.

Ultrasonic mapping of blood flow through the microvasculature

An overview of the use of high-frequency ultrasound to map blood flow through the microvasculature will be presented. The correlation of scattered echoes from blood at frequencies from 20 to 100 MHz are shown to demonstrate a smaller probability of error than the correlation at a lower transducer frequency. Experimental three-dimensional (3-D) maps of the velocity profile within vessels with a diameter of 100 μm or less will be presented. Blood velocity within vessels as small as 40 μm can be mapped using a transducer with a nominal center frequency of 50 MHz. Estimation of flow within these small vessels at the appropriate low velocities is challenging due to the small signal levels, the effect of cardiac and respiratory motion, and the unknown rate of fluctuation of the received signal from the small number of red blood cells contained within these sample volumes. Reliable in vivo estimation of the velocity within the microvasculature requires realignment of the signal from a single line of sight, and this method is presented. Recognition of 3-D continuity of a vessel tree is required to eliminate spurious noise. The rate of fluctuation in the received signal from small blood vessels is evaluated as a function of the sample volume and vessel size. A minimum time window for reliable detection of flow through a small vessel is determined. Finally, the use of acoustic contrast agents to improve the visualization of flow within small vessels will be introduced.

Effect of the beam-vessel angle on the received acoustic signal from blood

In order to explore the feasibility of algorithms to determine the three dimensional (3D) velocity magnitude from the received ultrasonic blood echo from a single line of sight, the signal from small sample volumes is studied as a function of beam-vessel angle. As opposed to previous treatments of the effect of the beam-vessel angle on the received acoustic signal, a wideband signal is transmitted and the returned signal in each sample volume is analyzed. High-resolution experimental M-mode images of radio-frequency (rf) echo signals are used to visualize the flow in individual regions of interest. These experiments confirm the predictions of a theoretical model for the signal and its second moment. It is shown that the two major effects limiting the correlated signal interval are the spread of axial velocities within the sample volume and the transit time across the lateral beam width. Particularly for small beam-vessel angles, the spread of velocities limits the correlated signal interval. In addition, the experimental results demonstrate that accurate velocity estimation for low volume flow rates and particularly for large beam-vessel angles may involve detection of changes in the correlation magnitude. For low volume flow rates, the shape of the correlation surface can be affected by small regions of blood with a strong scattering intensity located near the initial region of interest. >

Experimental velocity profiles and volumetric flow via two-dimensional speckle tracking

The performance of a two-dimensional speckle tracking system in measuring in vitro laminar flow is evaluated. The system uses a pattern matching algorithm to track subresolution-sized speckle regions between successive ultrasonic 2D pulse-echo acquisitions in order to determine both the axial and the lateral components of velocity. In this study, multiple 2D vector velocity maps were acquired in real time using a calibrated laminar flow phantom, and then statistically analyzed off-line. At a 90° transducer angle, volumetric flow rates computed from measured velocity profiles exhibited excellent linearity ( R 2 > 0.99), with a mean error of −6.1%, over the range 5–30 mL/s. At 105° and 120°, experimental volume flow rates also agreed well with actual rates, although measured velocity profiles appeared more irregular with decreasing Doppler angles. Velocity profiles estimated using sampled radio-frequency data rather than envelope-detected data were inconsistent due to an insufficient sampling rate and the quantization of the velocity grid. Results indicate that excellent flow velocity and volume rate estimates can be obtained from vector velocity measurements along a single line of sight, without a priori knowledge of the flow direction, at transducer angles near 90° where Doppler instruments are prone to large errors.

Accommodation without pupillary constriction

In this paper it will be shown that the association of pupillary contraction with even substantial accommodation breaks down under rigorous control of alignment. Conditions exclude other than “accommodative” (blur induced) pupillary responses by eliminating light reflexes due to temporal and spatial luminance differences, colour and polarization differences. The visual solid angles of the targets were also precisely equalized. A subtle procedure is described to obtain accurate alignment along a single line of sight of the stimulated eye. The pupillary system appears to be quite sensitive to alignment errors, but the “accommodative pupillary reflex” is totally absent under rigorous alignment. Pupillometry used an infrared television camera to monitor the non-stimulated eye in total darkness and silence. Occurrence of correct accommodation for every stimulus event was confirmed by observing accommodative vergence. Judging by the size of the accommodative vergence response and, occasionally, the size of Purkinje-Sanson images, the accommodative response was found to be essentially equal to the stimulation.

Goings on between the stars

Goings on between the stars

V. TOPOLOGY OF LARGE-SCALE STRUCTURE IN THE EARLY UNIVERSE (OR SEARCHING FOR VOIDS IN THE LYMAN-ALPHA FOREST)

ABSTRACT The objects causing Lyman-α forest absorption in quasar spectra are the only population both detectable at high redshift and with a large-enough number density for detailed studies of structure like that found in the large-scale distribution of galaxies. Various limits can be placed on void-like structure in the Lα distribution by observing that the two-point correlation function of Lα redshifts along a single line of sight to a quasar is close to zero at scales larger than a few megaparsecs; certainly the distribution of galaxies now and Lα clouds in the early universe are very different. A similar statement can be made by looking for a nonrandom distribution of gaps between sequential Lα redshifts. These data do not rule out the possibility that either a population of voids exist that have a filling factor much smaller than that for galaxy voids or that large underdensities can be found in the Lα forest that are only partially evacuated of Lα clouds. To study either possibility a higher space density of Lα systems needs to be detected; this can be accomplished by studying quasars close to each other in the sky and considering the combined sample from Lα forests of several quasars. Data from the first such sample are presented, indicating at least one strong example of a significant underdensity in the Lα forest distribution. This feature is probably not caused by ionization of the neutral hydrogen by local quasars and, therefore, may be a sign of void-like structure created in the early universe by the same processes which produced the voids seen in the galaxy distribution today.

An atlas of interstellar CA II and NA I profiles in the Carina Nebula

Optical interstellar absorption line profiles in the spectra of 22 stars within the Carina Nebula, observed with the 4 m echelle spectrograph at resolving powers of 3--6 x 10/sup 4/, are presented. Radial velocities, equivalent widths, and representative column densities are given for resolved velocity components. As many as 12 distinct components spanning several hundred km s/sup -1/ are seen in a single line of sight. Large Ca II/Na I ratios are found for components with velocities >40 km s/sup -1/; one extreme case may correspond to a high-ionization feature associated with a WN-A star.