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Search Results: 1 - 10 of 550006 matches for " S. J. Lilly "
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The Metallicity of 0.5
C. M. Carollo,S. J. Lilly
Physics , 2000, DOI: 10.1086/319104
Abstract: We have measured the emission line ratios in a sample of 34 CFRS star-forming galaxies with redshifts between 0.5 < z < 1.0, and computed their metallicities by means of the empirically-calibrated R_23 metallicity estimator introduced by Pagel et al. (1979). The current analysis concentrates on the 15 galaxies with L_Hbeta > 1.2x10^41 erg s-1. Although our results can only be regarded as preliminary until near-IR spectroscopy of Halpha and [NII]6583 are available, the metallicities of these galaxies appear to be remarkably similar to those of local galaxies selected in the same way, and there appears to have been little change in the relationship between metallicity and line- and continuum-luminosity from z~1 to today. At this stage our results do not support the idea that these galaxies, known to be generally small and with late-type morphologies, are dwarf galaxies brightened by large bursts of star-formation, as had been suggested from previous studies. Rather, our findings are more consistent with a picture in which these systems are the progenitors of today's massive metal-rich galaxies.
Environmental effects in the interaction and merging of galaxies in zCOSMOS survey
P. Kampczyk,S. J. Lilly,the zCOSMOS Collaboration
Physics , 2012,
Abstract: The zCOSMOS-bright 10k spectroscopic sample reveals a strong environmental dependence of close kinematic galaxy pair fractions in the redshift range 0.2 < z < 1. The fraction of close pairs is three times higher in the top density quartile than in the lowest one. This environmental variation in pair fractions will translate into merger fractions since merger timescales are shown, based on Millennium simulation catalogs, to be largely independent of environment. While galactic properties of close kinematic pairs (morphologies and star formation rates) may seem to be non-representative of an underlying galaxy population, they can be explained by taking into account well-known effects of environment, and changes caused by interactions. The latter is responsible for an increase of irregular galaxies in pairs by a factor of 50-75%, with a disproportionate increase in the number of irregular-irregular pairs (4-8 times), due to disturbance of about 15% of the disk galaxies in pairs. Another sign of interaction is an observed boost in specific star formation rate (factor 2-4) for the closest pairs. While significant for paired galaxies, this triggered star-formation due to interactions represents only about 5% of the integrated star-formation activity in our volume-limited sample. Although majority of close kinematic pairs are in dense environments, the effects of interactions appear to be strongest in the lower density environments. This may introduce strong biases into observational studies of mergers, especially those based on morphological criteria. Relative excess of post-starburst galaxies observed in paired galaxies (factor \sim2) as well as excess of AGNs (factor of over 2), linked with environmental dependence of the pair fractions could indicate that early phases of interactions and merging are plausible candidates for environmental quenching, observed in the global galaxy populations.
Higher-Order Properties of Analytic Wavelets
J. M. Lilly,S. C. Olhede
Mathematics , 2008, DOI: 10.1109/TSP.2008.2007607
Abstract: The influence of higher-order wavelet properties on the analytic wavelet transform behavior is investigated, and wavelet functions offering advantageous performance are identified. This is accomplished through detailed investigation of the generalized Morse wavelets, a two-parameter family of exactly analytic continuous wavelets. The degree of time/frequency localization, the existence of a mapping between scale and frequency, and the bias involved in estimating properties of modulated oscillatory signals, are proposed as important considerations. Wavelet behavior is found to be strongly impacted by the degree of asymmetry of the wavelet in both the frequency and the time domain, as quantified by the third central moments. A particular subset of the generalized Morse wavelets, recognized as deriving from an inhomogeneous Airy function, emerge as having particularly desirable properties. These "Airy wavelets" substantially outperform the only approximately analytic Morlet wavelets for high time localization. Special cases of the generalized Morse wavelets are examined, revealing a broad range of behaviors which can be matched to the characteristics of a signal.
Experimental Studies on Surface Roughness in Drilling MDF Composite Panels using Taguchi and Regression Analysis Method
S. Prakash,J. Lilly Mercy,K. Palanikumar,S. Ramesh
Journal of Applied Sciences , 2012,
Abstract: Medium Density Fiber board (MDF) panels are appropriate for many exterior and interior industrial applications. The degree of surface roughness of MDF plays an important role since, any surface irregularities will affect the final quality of the product. In the present study, regression model were developed to predict surface roughness in drilling MDF panels with carbide step drills. In the development of predictive models, drilling parameters of spindle speed, feed rate and drill diameter were considered as model variables. For this purpose, Taguchi’s design of experiments was carried out in order to collect surface roughness value. The Orthogonal Array (OA) and Analysis of Variance (ANOVA) are employed to study the surface roughness characteristics in drilling operation of MDF panels. The objective is to establish a correlation between spindle speed, feed rate and drill diameter with surface roughness in a MDF panel. The experiments are conducted as per Taguchi L27 orthogonal array with different cutting conditions. ANOVA and F-test were used to check the validity of regression model and to determine the significant parameter affecting the surface roughness. The statistical analysis showed that the feed rate was an utmost parameter on surface roughness. The microstructure of drilled surfaces were also studied by scanning electron microscopy (SEM).The SEM investigations reveled that drilling MDF panels with step drill produce surface striations and waviness which were increased significantly with feed rate.
The CANADA-FRANCE REDSHIFT SURVEY XIII: The luminosity density and star-formation history of the Universe to z ~ 1
S. J. Lilly,O. Le Fevre,F. Hammer,David Crampton
Physics , 1996, DOI: 10.1086/309975
Abstract: The comoving luminosity density of the Universe is estimated from the CFRS faint galaxy sample in three wavebands (2800A, 4400A and 1 micron) over the redshift range 0 < z < 1. In all three wavebands, the comoving luminosity density increases markedly with redshift. For a (q_0 = 0.5, Omega = 1.0) cosmological model, the comoving luminosity density increases as $(1+z)^{2.1 \pm 0.5}$ at 1 micron, as $(1+z)^{2.7 \pm 0.5}$ at 4400A and as $(1+z)^{3.9 \pm 0.75}$ at 2800A, these exponents being reduced by 0.43 and 1.12 for (0.05,0.1) and (-0.85,0.1) cosmological models respectively. The variation of the luminosity density with epoch can be reasonably well modelled by an actively evolving stellar population with a Salpeter initial mass function (IMF) extending to 125 M_sun, a star-formation rate declining with a power 2.5, and a turn-on of star-formation at early epochs. A Scalo (1986) IMF extending to the same mass limit produces too many long-lived low mass stars. This rapid evolution of the star-formation rate and comoving luminosity density of the Universe is in good agreement with the conclusions of Pei and Fall (1995) from their analysis of the evolving metallicity of the Universe. One consequence of this evolution is that the physical luminosity density at short wavelengths has probably declined by two orders of magnitude since z ~ 1.
MgII absorption systems with W_0 > 0.1 ?for a radio selected sample of 77 QSOs and their associated magnetic fields at high redshifts
M. L. Bernet,F. Miniati,S. J. Lilly
Physics , 2010, DOI: 10.1088/0004-637X/711/1/380
Abstract: We present a catalogue of MgII absorption systems obtained from high resolution UVES/VLT data of 77 QSOs in the redshift range 0.6 < z < 2.0, and down to an equivalent width W_0 > 0.1 \AA. The statistical properties of our sample are found to be in agreement with those from previous work in the literature. However, we point out that the previously observed increase with redshift of dN/dz for weak absorbers, pertains exclusively to very weak absorbers with W_0 < 0.1 \AA. Instead, dN/dz for absorbers with W_0 in the range 0.1-0.3 \AA actually decreases with redshift, similarly to the case of strong absorbers. We then use this catalogue to extend our earlier analysis of the links between the Faraday Rotation Measure of the quasars and the presence of intervening MgII absorbing systems in their spectra. In contrast to the case with strong MgII absorption systems W_0 > 0.3 \AA, the weaker systems do not contribute significantly to the observed Rotation Measure of the background quasars. This is possibly due to the higher impact parameters of the weak systems compared to strong ones, suggesting that the high column density magnetized material that is responsible for the Faraday Rotation is located within about 50 kpc of the galaxies. Finally, we show that this result also rules out the possibility that some unexpected secondary correlation between the quasar redshift and its intrinsic Rotation Measure is responsible for the association of high Rotation Measure and strong intervening MgII absorption that we have presented elsewhere, since this would have produced an equal effect for the weak absorption line systems, which exhibit a very similar distribution of quasar redshifts.
The gravitational lens CFRS14.1311 = HST 14176+5226
David Crampton,O. Le Fevre,F. Hammer,S. J. Lilly
Physics , 1996,
Abstract: Ratnatunga et al. (1995) have recently proposed that an object, HST 14176+5226, in the "Groth-Westphal" HST survey strip is an "Einstein cross" gravitational lens. By chance, this object has been previously observed in the Canada-France Redshift Survey. The candidate lens, catalogued as CFRS14.1311, is an elliptical galaxy at z = 0.81. In addition, the spectrum shows a strong, spatially-extended, emission feature at 5342A that almost certainly originates from two of the four "lensed" images. We tentatively identify this emission line as Ly alpha at z =3.4. A less prominent emission feature at 6822A may be C IV 1549. Our data thus support the identification of this system as a new quadruple-image lens.
THE CANADA-FRANCE REDSHIFT SURVEY IV: Spectroscopic Selection Effects and 0300+00 Field Spectroscopic Data
F. Hammer,David Crampton,O. Le Fevre,S. J. Lilly
Physics , 1995, DOI: 10.1086/176558
Abstract: Possible surface brightness selection effects in the redshift catalogs of the Canada-France Redshift Survey are investigated through comparisons of subsamples of the data. Our analyses demonstrate that the securing of redshifts is independent of possible biases arising from surface brightness effects and/or differing galaxy morphologies and orientations. The unusual geometry of the mask designs for our spectroscopic observations also do not produce any significant bias. There is however a bias at the highest and lowest redshifts, especially for absorption-line galaxies at z > 1 and z < 0.2, due to the adopted spectral range (4250A to 8500A). Apart from the latter, we conclude that our sample of identified galaxies is an unbiased subsample of the original photometric catalogue and is essentially limited by I-band flux density ($17.5 \leq I_{AB} \leq 22.5$). Finally, spectroscopic data for 273 objects in the 0300+00 CFRS field are presented.
THE CANADA-FRANCE REDSHIFT SURVEY III: "Single Emission Line" Objects, Analysis of Repeat Observations, and Spectroscopic Identifications in the 1415+52 and 2215+00 Fields
S. J. lilly,F. Hammer,O. Le Fevre,David Crampton
Physics , 1995, DOI: 10.1086/176557
Abstract: This paper is one of a series describing the Canada-France Redshift Survey (CFRS). It is shown how the shape of the continuum around the emission line can be used to distinguish between [OII] 3727 at z > 0.76 and H$\alpha$ at low redshift in spectra for which only a single isolated emission line is visible. Based on this, [OII] 3727 is most likely to be the emission line in most of the single emission line galaxies in the CFRS. The statistics of the repeated observations are analyzed to derive an empirical calibration of the reliability of the spectroscopic identifications in the CFRS, to determine how often additional observations could lead to the identification of an initially unidentified object and to provide an estimate of the internal velocity accuracy. Finally, the results of spectroscopic observations of 413 objects in the 1415+52 and 2215+00 CFRS survey fields are presented.
THE CANADA-FRANCE REDSHIFT SURVEY V: Global Properties of the Sample
David Crampton,O. Le Fevre,S. J. Lilly,F. Hammer
Physics , 1995, DOI: 10.1086/176559
Abstract: The photometric and spectroscopic data of the CFRS survey of objects with 17.5 < I_{AB} < 22.5 are combined and analysed. The overall completeness is 85%. The redshift histogram of the sample is presented for 591 field galaxies with secure redshifts. The median redshift is z = 0.56, and the highest redshift observed is z = 1.3; 25 galaxies have z > 1 The distributions of magnitudes and colors demonstrate that galaxies at these high redshifts have very similar colors to those observed locally. The survey thus represents a major improvement in our knowledge of field galaxies at large look-back times. Only ~1% of the galaxies are as compact as stars (on images with FWHM ~ 0.9") and comparisons of the photometric and spectroscopic data show that only one galaxy was initially incorrectly classified spectroscopically as a star, and only two stars were misclassified as galaxies. It is demonstrated that the redshift distributions in the five fields are statistically consistent with each other, once the reduction in the effective number of independent galaxies due to small-scale clustering in redshift is taken into account. The photometric properties of the spectroscopically-unidentified objects indicate that most are likely to be galaxies rather than stars. At least half of these must have the same redshift distribution as the identified galaxies, and a combination of magnitudes, colors and compactness of the remaining unidentified galaxies is used to predict their redshifts. The majority are probably ordinary galaxies at the high redshift end of our sample, including some quiescent galaxies at z > 1.0, rather than some new or unusual population.
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