Bright Blobs Research Articles

STRONG FIELD-TO-FIELD VARIATION OF Lyα NEBULAE POPULATIONS ATz≃ 2.3

Understanding the nature of distant Ly-alpha nebulae ("blobs") and connecting them to their present-day descendants requires constraining their number density, clustering, and large-scale environment. To measure these basic quantities, we conduct a deep narrowband imaging survey in four different fields, Chandra Deep Field South (CDFS), Chandra Deep Field North, and two COSMOS subfields, for a total survey area of 1.2deg^2. We discover 25 blobs at z=2.3 with Ly-alpha luminosities of 0.7-8x10^43 erg/s and isophotal areas of Aiso = 10-60 arcsec^2. The transition from compact Ly-alpha emitters (Aiso ~ a few arcsec^2) to extended blobs (Aiso > 10 arcsec^2) is continuous, suggesting a single family perhaps governed by similar emission mechanisms. Surprisingly, most blobs (16/25) are in one survey field, the CDFS. The six brightest, largest blobs with L > 1.5x10^43 erg/s and Aiso > 16 arcsec^2 lie only in the CDFS. These large, bright blobs have a field-to-field variance of sigma_v >~ 1.5 (150%) about their number density n ~ 1.0x10^-5 Mpc^-3. This variance is large, significantly higher than that of unresolved LAEs (sigma_v ~ 0.3 or 30%), and can adversely affect comparisons of blob number densities and luminosity functions among different surveys. We compare the statistics of our blobs with dark matter halos in a 1 Gpc/h cosmological N-body simulation. At z=2.3, the number density (n) implies that each bright, large blob could occupy a halo of M_halo > 10^13 Msun if most halos have detectable blobs. The predicted variance in n is consistent with that observed and corresponds to a bias of ~7. Blob halos lie at the high end of the halo mass distribution at z=2.3 and are likely to evolve into the ~10^14 Msun halos typical of galaxy clusters today. On larger scales of ~10 co-moving Mpc, blobs cluster where compact LAEs do, indicating that blobs lie in coherent, highly overdense structures.

Signature of slow acoustic oscillations in a non-flaring loop observed by EIS/Hinode

We study intensity oscillations near the apex of a coronal loop to find the signature of MHD oscillations. We analyse the time series of the strongest Fe XII 195.12Å image data, observed by 40″ SLOT of the EUV Imaging Spectrometer (EIS) onboard the Hinode spacecraft. Using a standard wavelet tool, we produce power spectra of intensity oscillations at location ‘L3’ near the apex of a clearly visible coronal loop. We detect intensity oscillations of a period of ≈322s with a probability of 96%. This oscillation period of ≈322s is found to be in good agreement with theory of the (second) harmonics of standing slow acoustic oscillations of P2ndslow≈313±31s. We detect, for the first time, the observational signature of multiple (first and second) harmonics of slow acoustic oscillations in the non-flaring coronal loop. Such oscillations have been observed in the past in hot and flaring coronal loops only, but have been predicted recently to exist in comparatively cooler and non-flaring coronal loops as well. We find the periodicities ∼497s and ∼592s with the probability 99–100% at the ‘L1’ and ‘L2’ locations, respectively, near the clearly visible western footpoint of the loop. We interpret these oscillations to be likely associated with the first harmonics (fundamental mode) of slow acoustic oscillations. Using the period ratios P1/P2=1.54and1.84, we estimate the density scale heights in the EUV loop as ∼10Mm and 21Mm, respectively, in which the latter value (∼21Mm) is compared well with the loop half length. We also find an evidence of propagating bright blob at its lower bound sub-sonic speed of ≈6.4km/s, suggesting that they are caused by the mass flow from one end to the other in the coronal loop. We also suggest that standing oscillations, and propagating bright blobs caused probably by the pulse of plasma flow, co-exist in comparatively cooler and non-flaring coronal loop.

Feedback through multiple outbursts in the cluster 2A 0335+096

We examine the core of the X-ray bright galaxy cluster 2A 0335+096 using deep Chandra X-ray imaging and spatially-resolved spectroscopy, and include new radio observations. The set of around eight X-ray bright blobs in the core of the cluster, appearing like eggs in a bird's nest, contains multiphase gas from ~0.5 to 2 keV. The morphology of the coolest X-ray emitting gas at 0.5 keV temperature is similar to the Halpha emitting nebula known in this cluster, which surrounds the central galaxy. XMM-Newton grating spectra confirm the presence of material at these temperatures, showing excellent agreement with Chandra emission measures. On scales of 80 to 250 kpc there is a low temperature, high metallicity, swirl of intracluster medium as seen in other clusters. In the core we find evidence for a further three X-ray cavities, in addition to the two previously discovered. Enhancements in 1.5 GHz radio emission are correlated with the X-ray cavities. The total 4PV enthalpy associated with the cavities is around 5x10^59 erg. This energy would be enough to heat the cooling region for ~5x10^7 yr. We find a maximum pressure discontinuity of 26 per cent (2 sigma) across the surface brightness edge to the south-west of the cluster core. This corresponds to an upper limit on the Mach number of the cool core with respect to its surroundings of 0.55.

EXTENDED Lyα NEBULAE ATz≃ 2.3: AN EXTREMELY RARE AND STRONGLY CLUSTERED POPULATION?

To obtain an unbiased sample of bright LyA blobs [L(LyA) > 10^43 ergs/s], we have undertaken a blind, wide-field, narrow-band imaging survey in the NOAO Deep Wide Field Survey Bootes field with the Steward Bok-2.3m telescope. After searching over 4.82 sq. degrees at z=2.3, we discover four LyA blobs with L(LyA) = 1.6-5.3 x 10^43 ergs/s, isophotal areas of 28-57 sq. arcsec, and broad LyA line profiles (FWHM = 900-1250 km/s). In contrast with the extended Lyman alpha halos associated with high-z radio galaxies, none of our four blobs are radio-loud. The X-ray luminosities and optical spectra of these blobs are diverse. Two blobs (3 and 4) are X-ray-detected with L_X(2-7 keV) = 2-4 x 10^44 ergs/s and have broad optical emission lines (C IV) characteristic of AGN, implying that 50% of our sample blobs are associated with strong AGN. The other 50% of blobs (1 and 2) are not X-ray or optically-detected as AGN down to similar limits. The number density of the four blobs is ~3 x 10^{-6} Mpc^{-3}, comparable to that of galaxy clusters at similar redshifts and 3x lower than that found in the SSA22 proto-cluster at z=3.1, even after accounting for the over-density of that region. The two X-ray undetected blobs are separated by only 70" (550 kpc) and have almost identical redshifts (< 360 kpc along the line-of-sight), suggesting that they are part of the same system. Given the rarity of the blobs and our discovery of a close pair, we speculate that blobs occupy the highest density regions and thus may be precursors of today's rich cluster galaxies.

A z = 3 Lyα BLOB ASSOCIATED WITH A DAMPED Lyα SYSTEM PROXIMATE TO ITS BACKGROUND QUASAR

We report on the discovery of a bright Lyα blob associated with the z = 3 quasar SDSS J124020.91+145535.6 which is also coincident with strong damped Lyα absorption from a foreground galaxy (a so-called proximate damped Lyα (PDLA) system). The one-dimensional spectrum acquired by the Sloan Digital Sky Survey (SDSS) shows a broad Lyα emission line with a FWHM 500 km s-1 and a luminosity of L Lyα = 3.9 × 1043 erg s-1 superposed on the trough of the PDLA. Follow-up observations using the Keck/LRIS spectrometer confirm that this source has a Lyα nebula with spatial extent exceeding 5'', corresponding to a proper size >39 kpc. Mechanisms for powering the large Lyα luminosity in this nebula are discussed. We use a Monte Carlo radiative transfer simulation to investigate the possibility that the line emission is fluorescent recombination radiation from a kpc-scale PDLA galaxy powered by the ionizing flux of the quasar, but find that the predicted Lyα flux is several orders of magnitude lower than observed. We conclude that the Lyα emission is not associated with the PDLA galaxy at all, but instead is intrinsic to the quasar's host and similar to the extended Lyα fuzz which is detected around many active galactic nuclei. PDLAs are natural coronagraphs that block their background quasar at Lyα and we discuss how systems similar to SDSS J124020.91+145535.6 might be used to image the neutral hydrogen in the PDLA galaxy in silhouette against the screen of extended Lyα emission from the background quasar.

Persistent Horizontal Flows and Magnetic Support of Vertical Threads in a Quiescent Prominence

There has been some controversy as to whether the magnetic fields of vertical threads seen in quiescent prominences are predominantly vertical or horizontal. We report finding special patterns of flow in a quiescent prominence observed by the Solar Optical Telescope aboard Hinode. This prominence is a small hedgerow prominence composed of many vertical threads. To one side of it, we found a pattern of persistent horizontal flows of Hα-emitting plasma. These flows originated from a region in the chromosphere, rose to coronal heights, and then extended horizontally for a long distance until they reached the main body of the prominence. In the higher altitudes the flows either moved across vertical threads or lifted them up, while in the lower altitudes they often formed bright blobs of plasma and shed them, resulting in a sudden change of flow direction from horizontal to vertical. The observed persistent horizontal flows support a configuration of initially horizontal magnetic fields, and our results appear to be consistent with the traditional theory that vertical threads in quiescent prominences are stacks of plasma supported against gravity by the sagging of initially horizontal magnetic field lines.

Individual classification of buried transistors in live microprocessors by functional infrared emission spectral microscopy

The authors classify good, leaky, and broken field effect transistors (FET’s) in a live 90nm flip-chip microprocessor using functional infrared emission spectral microscopy. The FET’s are in the active layer that is sandwiched between a thick heat-absorbing silicon material and a highly reflecting grid of metal interconnects. Together they are optically imaged only as a single bright blob. They classify FET’s individually from their distinct electroluminescence spectra that are recovered efficiently by spectral decomposition of the detected composite spectrum. Leaky FET’s have no apparent structural damage and are detectable only in live microprocessors.

Visual-acoustic mapping in posterior cortical atrophy: Evidence from a single case study

University of Pennsylvania School of Medicine, Department of Neurology, Philadelphia, Pennsylvania, USAAccepted 6 July 2006IntroductionAnomiacanresultfromarangeofperceptualdeficits(e.g.,agnosia);cen-tral semantic degradation (e.g., dementia); impaired linguistic access (e.g.,aphasia);oracombinationofthesefactors(HodgesPMar-tin & Saffran, 1990). One unexplored possibility, however, is that anomiamayalsostemfromimpairedmappingofarbitraryphonologicalformsontoconcepts. Here, we investigated integrity of the phonology-semantics map-pingprocessinapatientwithposteriorcorticalatrophyassociatedwithAlz-heimer’s disease. We predicted that visual deficits should interfere with theability to link phonetic attributes to a novel object. We introduce anapproach, known as phonetic symbolism, to test this hypothesis.Some phonemic combinations have been found to be associated withideas such as magnitude of physical size, brightness, affection, and propernounsacrossmanyunrelatedlanguages(Nuckolls,1999;Ohala,1994;Sapir,1949). This effect, phonetic symbolism, is tested with a novel object and achoiceofpossiblenonwordnames.The‘‘best’’nameisselectedbymappingacoustic-phoneticpropertiesofaworddirectlyontophysicalfeaturesoftheobject (Ohala, 1994). For example, if one is forced to choose between twonames (pleek or ploke) for a tiny, bright yellow animal, they choose Pleekwithagreementfargreaterthanchance.Thischoiceismadethroughnon-ar-bitrary mapping of phonology directly onto an object’s visual attributes.Phonetic symbolism taps many crucial elements of word learning thatarenotdirectlyaccessiblethroughassessmentofknownobjectsandwords.Inordertocorrectlychoosethename,Pleek,apersonmustperceivesalientvisual attributes (e.g., brightness), process acoustic-phonetic features (e.g.,vowel height), and then complete a mapping of these characteristics. Theuse of novel stimuli (both words and objects), therefore, provides a uniqueway of examining potential deficits in word to object mapping.MethodCase descriptionAtrophy in the occipital and temporal visual areas and posterior por-tions of the parietal lobes causes patients with the visual-variant of Alzhei-mer’s disease (vAD) to have object recognition deficits and visuospatialproblems including optic apraxia and simultanagnosia. As vAD evolves,memory and language difficulties also become prevalent (Levine, Lee, F Ross, Graham, Stuart-Green, & Prins, 1996). CP is a 61-year-old, right-handed female diagnosed with vAD through examinationby a behavioral neurologist and consensus review using NINCDS-ADRDA criteria (McKhann et al., 1984).CP initially presented to the University of Pennsylvania (12/03) withsignificant visual-perceptual difficulties (profound difficulty copying thesimplest visual geometric designs) and also demonstrates mild semanticimpairment (Pyramids & Palm Trees Words 46/52). CP shows impairedconfrontation naming of pictures (Boston Naming Test: 3/15) and speechproduction significant for frequent circumlocutions, word-finding pausesand anomia. She was able to read and could appreciate the color butnot the form of visual stimuli. Structural MRI obtained in 2003 revealedleft ventral-occipital and parietal-occipital atrophy as well as mild rightparietal and inferior frontal atrophy Fig. 1.Experiment 1—Phonetic symbolismCP viewed 25 randomized images of novel objects (i.e., blobs, n = 10)and pseudoanimals (n = 15) presented via E-prime software on a laptopcomputer. Stimuli were manipulated by salience of visual features, includ-ing: brightness, physical size, angularity, roundness, motion, and loudness.Two monosyllabic (CVC or CVCC) nonwords appeared below eachimage. Nonwords varied by medial vowel, which maximally differed byplace and height (e.g., pleek–ploke). CP was instructed to ‘‘choose the bestname’’ for each image by signaling with a key-press. 13 healthy controlsdemonstrated high agreement on the target nonword selected as a namefor each item. Small, bright pseudoanimals were associated with high fre-quency/narrow vocal tract vowels; large, dark pseudoanimals with low fre-quency/wide vocal tract vowels; dull, dark blobs with back vowelsproduced with lip rounding; and sharp, bright blobs with high frequen-cy/narrow vocal tract vowels.ResultsCP did show a strong effect of phonetic symbolism for the manipula-tion of ‘‘roundness’’ collapsed across conditions. That is, CP reliably asso-ciated back, rounded vowels (e.g., ‘‘mome’’) with rounded objects andpseudoanimals (8/8) p < .004. Otherwise she did not associate phoneticfeatures with visual-perceptual attributes of novel objects andpseudoanimals.doi:10.1016/j.bandl.2006.06.075* Corresponding author. Fax: +1 215 349 8464.www.elsevier.com/locate/b&lBrain and Language 99 (2006) 8–219

Salience and target selection in visual search

Why is it easy to find strawberries and difficult to collect gooseberries or green tomatoes? Why don't we see the tree in the forest but do see the single tree in the garden? Various explanations have been given to account for these phenomena. The present paper is concentrating on salience, a property apparently important for search but not frequently discussed in this context. Salience lets targets stand out and thus controls the selection of items that need to be investigated when a certain target is to be searched for. This proposal was tested in two series of experiments. It was found that salience detection and target identification followed different time courses; even typical “pop-out” targets (bright or dark blobs, gaps) were faster located than identified. The importance of salience in visual search was further investigated by manipulating target salience without affecting stimulus properties that are assumed to be relevant for search. When the salience of individual items was increased, the effective set size was reduced and search performance improved. This suggests an interactive and complementary function of salience and attention which is further discussed.

The jets of the Vela pulsar

Chandra observations of the Vela pulsar-wind nebula (PWN) have revealed a jet in the direction of the pulsar’s proper motion, and a counter-jet in the opposite direction, embedded in diffuse nebular emission. The jet consists of a bright, 8″-long inner jet, between the pulsar and the outer arc, and a dim, curved outer jet that extends up to ∼100″ in approximately the same direction. From the analysis of thirteen Chandra observations spread over ≈2.5 years we found that this outer jet shows particularly strong variability, changing its shape and brightness. We observed bright blobs in the outer jet moving away from the pulsar with apparent speeds (0.3– 0.6) c and fading on time-scales of days to weeks. The spectrum of the outer jet fits a power-law model with a photon index Γ=1.3±0.1. For a distance of 300 pc, the apparent average luminosity of the outer jet in the 1–8 keV band is about 3×10 30 erg s −1, compared to 6×10 32 from the whole PWN within 42″ from the pulsar. The X-ray emission of the outer jet can be interpreted as synchrotron radiation of ultrarelativistic electrons/positrons. This interpretation allows one to estimate the magnetic field, ∼100 μG, maximum energy of X-ray emitting electrons, ∼2×10 14 eV, and energy injection rate, ∼8×10 33 erg s −1, for the outer jet. In the summed PWN image we see a dim, ∼2′-long outer counter-jet, which also shows a power-law spectrum with Γ≈1.2–1.5. Southwest of the jet/counter-jet (i.e., approximately perpendicular to the direction of pulsar’s proper motion), an extended region of diffuse emission is seen. Relativistic particles responsible for this radiation are apparently supplied by the outer jet.

The Variable Jet of the Vela Pulsar

Observations of the Vela pulsar-wind nebula (PWN) with the Chandra X-ray Observatory have revealed a complex, variable PWN structure, including inner and outer arcs, a jet in the direction of the pulsar's proper motion, and a counter-jet in the opposite direction, embedded in diffuse nebular emission. From the analysis of thirteen Chandra observations spread over about 2.5 years we found that this outer jet shows particularly strong variability, changing its shape and brightness. We observed bright blobs in the outer jet moving away from the pulsar with apparent speeds (0.3-0.6)c and fading on time-scales of days to weeks. The spectrum of the outer jet fits a power-law model with a photon index of 1.3. The X-ray emission of the outer jet can be interpreted as synchrotron radiation of ultrarelativistic electrons/positrons. This interpretation allows one to estimate the magnetic field, ~100 microGauss, maximum energy of X-ray emitting electrons, $2 \times 10^{14}$ eV, and energy injection rate, $8\times 10^{33}$ erg/s, for the outer jet. In the summed PWN image, we see a faint, strongly bent, extension of the outer jet. The more extreme bends closer to the pulsar, as well as the apparent side motions of the outer jet, can be associated with kink instabilities of a magnetically confined, pinched jet flow. Another feature found in the summed image is a dim, 2'-long outer counter-jet, which also shows a power-law spectrum with photon index of 1.2-1.5. Southwest of the jet/counter-jet (i.e., approximately perpendicular to the direction of pulsar's proper motion), an extended region of diffuse emission is seen. Relativistic particles responsible for this radiation are apparently supplied by the outer jet.

Imaging and Spatially Resolved Spectroscopy of AFGL 2688 in the Thermal Infrared Region

We present ground-based high-resolution (~03) imaging of AFGL 2688 at L' (3.8 μm) and M' (4.7 μm). A wealth of structure in the central region is revealed as a consequence of less extinction in the thermal infrared. A clear border in the southern lobe at L' corresponds to the edge of the heavily obscured region in visible, indicating that there is a dense material surrounding the central region. The images also show a narrow dark lane oriented to 140° east of north with the normal at 50°. The normal position angle is inconsistent with the optical polar axis (P.A. = 15°) but is aligned to the high-velocity CO components found in the radio wavelength observations. The central star remains invisible at L' and M'. Several clumpy regions in the north lobe dominate in L' and M' luminosity. In particular, a pointlike source (peak A) at 05 northeast of the center of the nebula exhibits the highest surface brightness with a very red spectral energy distribution (SED). Based on the almost identical SED at adjacent regions, we suggest that the pointlike source is not self-luminous, as was proposed, but is a dense dusty blob reflecting thermal emission from the central star. We also present spatially resolved slit spectroscopy of the bright dusty blobs. An emission feature at 3.4 μm as well as at 3.3 μm is detected everywhere within our field of view. There is no spatial variation in the infrared emission feature throughout the observed area (02-15, or 240-1800 AU from the central source). The constant flux ratio of the emission feature relative to the continuum is consistent with the view that the blobs are mostly reflecting the light from the central star in the 3 μm region.

Noise reveals visual mechanisms of detection and discrimination

When performance is limited by stochastically defined masks, (psychophysical) reverse correlation has proven to be an especially efficient tool for estimating the templates used by detection and discrimination mechanisms. Here I describe a maximum-likelihood approach to quantifying the significance of differences between estimates of template. Four methodologically related experiments illustrate the versatility of reverse correlation. Experiment 1 shows significant differences between the templates used by different observers when detecting a bright Gaussian blob. The results of Experiment 2 are consistent with observers not using information about the phase of a parafoveal wavelet when detecting it. Experiments 3 and 4 reveal not only the templates used by detection mechanisms but also aspects of their response functions. Both results are consistent with a sensory threshold. Experiment 3 shows that 2-alternative forced-choice detection errors are caused when the target's effective contrast is reduced, not when the mask looks more like the expected target+mask than the actual target+mask. Experiment 4 suggests that observers use optimally tuned detection templates for orientation discrimination.

Nature of expertise in searching mammograms for breast masses

The authors investigated how training and experience affect the performance of observers searching mammograms for breast masses. Eye positions of mammographers, mammography technologists, mammography residents, and laypersons were compared to scan paths generated by a simulated scanner as each searched nine two-view digital mammogram pairs for breast masses. Analysis of time-to-hit data revealed that mammographers and mammography technologists with the most extensive training and experience had the fastest search times in the detection and confirmation of a breast mass on two views. Scanning patterns of less-experienced mammography residents were less efficient due to wider dispersion of visual attention between potential breast masses and perturbations in breast parenchyma. Because laypersons lacked both training and experience in mammography, bright blobs in the breast image were considered to be intuitively valid target candidates and these features distracted the search by capturing visual attention. Experience reading normal and abnormal mammograms plays a critical role in training radiologists. Experience combined with training provides the basis for generating efficient visual search strategies and developing distinctive conceptual criteria for perceptual differentiation and interpretation of true breast masses from image artifacts and structured noise that mimics breast abnormalities.

Optical Images and Spectra of the Galactic Supernova Remnant G109.1-1.0

view Abstract Citations (27) References (25) Co-Reads Similar Papers Volume Content Graphics Metrics Export Citation NASA/ADS Optical Images and Spectra of the Galactic Supernova Remnant G109.1-1.0 Fesen, Robert A. ; Hurford, Alan P. Abstract Hα and [O III] images of the galactic SNR G109. 1-1.0 plus optical spectra of five associated emission filaments and two neighboring H II regions are presented. These data show the remnant's optical filaments are more extensive and have a larger diffuse component than previously realized. New filamentary emission is also detected near U109. 1-1.0's projected center, along the SW edge of the remnant's bright x-ray blob. Balmer decrements for five filaments indicate significant variations in optical reddening, E(B - V) =0.79- 1.2 mag, on both large and small spatial scales. [S II] λ6716/λ6731 line ratios indicate filament electron densities of ≤100-800 cm-3, with the high end of this range implying preshock densities ≃20. These relatively high densities, together with the tendency of the remnant's optical emission to lie along the boundaries of faint H II regions to the north and southeast, suggest that much of G109.1-1.0's optical emission may be the result of its interaction with these H II regions. Publication: The Astronomical Journal Pub Date: August 1995 DOI: 10.1086/117559 Bibcode: 1995AJ....110..747F Keywords: SUPERNOVA REMNANTS; ISM STRUCTURE full text sources ADS | data products SIMBAD (7)

Compact Array Mapping of the Nuclear Starburst in NGC 7552

We discuss new observations of the starburst galaxy NGC 7552. From optical and near–infrared colour maps we find a red, dusty circumnuclear ring. High-resolution radio mapping from the ATCA reveals the same ring, and a number of bright blobs (probably SNRs). The ring is probably associated with gas and dust which have lost angular momenta due to torques in the bar potential and settled at the inner Lindblad resonance. These circumnuclear starburst rings may be relatively common (when mapped without the obscuring affects of dust) and may play a role in collimating material of a nuclear outflow.