Linewidth Distribution Research Articles

Photoionization of iodine atoms: Rydberg series which converge to the I+(S1)←I(P23/2) threshold

Relative partial photoionization cross sections and angular distribution parameters beta have been measured for the first and fourth (5p)(-1) photoelectron (PE) bands of atomic iodine by performing angle-resolved constant-ionic-state (CIS) measurements on these PE bands between the (1)D(2) and (1)S(0) (5p)(-1) ionic thresholds in the photon energy region of 12.9-14.1 eV. Rydberg series arising from the 5p-->ns and 5p-->nd excitations are observed in both the first PE band, I(+)((3)P(2))<--I((2)P(3/2)), and the fourth PE band, I(+)((1)D(2))<--I((2)P(3/2)), CIS spectra. For each Rydberg state, the resonance energy, quantum defect, linewidth, line shape, and photoelectron angular distribution parameter beta have been determined. For the beta-plots for each PE band, only resonances corresponding to 5p-->nd excitations are observed; no resonances were seen at photon energies corresponding to the 5p-->ns resonances in the CIS spectra. The beta-plots are interpreted in terms of the parity unfavored channel with j(t)=4 being the major contributor at the 5p-->nd resonance positions, where j(t) is the quantum number for angular momentum transferred between the molecule, and the ion and photoelectron. Comparison of the results obtained with those published for bromine shows reasonably good agreement for the CIS spectra but poor agreement for the beta-plots. It appears that parity unfavored channels are playing a greater role in the valence (np)(-1) ionization of atomic iodine than in the corresponding ionization of atomic bromine.

THE EVOLUTION OF THE KINEMATICS OF NEBULAR SHELLS IN PLANETARY NEBULAE IN THE MILKY WAY BULGE

We study the line widths in the [\ion{O}{3}]$\lambda$5007 and H$\alpha$ lines for two groups of planetary nebulae in the Milky Way bulge based upon spectroscopy obtained at the Observatorio Astron\'omico Nacional in the Sierra San Pedro M\'artir (OAN-SPM) using the Manchester Echelle Spectrograph. The first sample includes objects early in their evolution, having high H$\beta$ luminosities, but [\ion{O}{3}]$\lambda 5007/\mathrm H\beta < 3$. The second sample comprises objects late in their evolution, with \ion{He}{2} $\lambda 4686/\mathrm H\beta > 0.5$. These planetary nebulae represent evolutionary phases preceeding and following those of the objects studied by Richer et al. (2008). Our sample of planetary nebulae with weak [\ion{O}{3}]$\lambda$5007 has a line width distribution similar to that of the expansion velocities of the envelopes of AGB stars, and shifted to systematically lower values as compared to the less evolved objects studied by Richer et al. (2008). The sample with strong \ion{He}{2} $\lambda 4686$ has a line width distribution indistinguishable from that of the more evolved objects from Richer et al. (2008), but a distribution in angular size that is systematically larger and so they are clearly more evolved. These data and those of Richer et al. (2008) form a homogeneous sample from a single Galactic population of planetary nebulae, from the earliest evolutionary stages until the cessation of nuclear burning in the central star. They confirm the long-standing predictions of hydrodynamical models of planetary nebulae, where the kinematics of the nebular shell are driven by the evolution of the central star.

MOLECULAR GAS INz∼ 6 QUASAR HOST GALAXIES

We report our new observations of redshifted carbon monoxide emission from six z~6 quasars, using the PdBI. CO (6-5) or (5-4) line emission was detected in all six sources. Together with two other previous CO detections, these observations provide unique constraints on the molecular gas emission properties in these quasar systems close to the end of the cosmic reionization. Complementary results are also presented for low-J CO lines observed at the GBT and the VLA, and dust continuum from five of these sources with the SHARC-II bolometer camera at the CSO. We then present a study of the molecular gas properties in our combined sample of eight CO-detected quasars at z~6. The detections of high-order CO line emission in these objects indicates the presence of highly excited molecular gas, with estimated masses on the order of 10^10 M_sun within the quasar host galaxies. No significant difference is found in the gas mass and CO line width distributions between our z~6 quasars and samples of CO-detected $1.4\leq z\leq5$ quasars and submillimeter galaxies. Most of the CO-detected quasars at z~6 follow the far infrared-CO luminosity relationship defined by actively star-forming galaxies at low and high redshifts. This suggests that ongoing star formation in their hosts contributes significantly to the dust heating at FIR wavelengths. The result is consistent with the picture of galaxy formation co-eval with supermassive black hole (SMBH) accretion in the earliest quasar-host systems. We investigate the black hole--bulge relationships of our quasar sample, using the CO dynamics as a tracer for the dynamical mass of the quasar host. The results place important constraints on the formation and evolution of the most massive SMBH-spheroidal host systems at the highest redshift.

The Ly�� forest at redshifts 0.1���1.6: good agreement between a large hydrodynamic simulation andHSTspectra

We give a comprehensive statistical description of the Lyman-alpha absorption from the intergalactic medium in a hydrodynamic simulation at redshifts 0.1-1.6, the range of redshifts covered by HST spectra of QSOs. We use the ENZO code to make a 76 comoving Mpc cube simulation using 75 kpc cells, for a Hubble constant of 71 km/s/Mpc. The best prior work, by \citet{dave99},used an SPH simulation in a 15.6 Mpc box with an effective resolution of 245 kpc and slightly different cosmological parameters. At redshifts z=2 this simulation is different from data. \citet{tytler07b} found that the simulated spectra at z=2 have too little power on large scales, Lyman-alpha lines are too wide, there is a lack high column density lines, and there is a lack of pixels with low flux. Here we present statistics at z<1.6, including the flux distribution, the mean flux, the effective opacity, and the power and correlation of the flux. We also give statistics of the lyman alpha lines including the line width distribution, the column density distribution, the number of lines per unit equivalent width and redshift, and the correlation between the line width and column density. We find that the mean amount of absorption in the simulated spectra changes smoothly with redshift with DA(z)=0.01(1+z)^{2.25}. Both the trend and absolute values are close to measurements of HST spectra by \citet{kirkman07a}. The column density and line width distributions are also close to those measured from HST spectra by \citet{janknecht06a}, except for the mode of the line width distribution which is smaller in the HST spectra. Although some differences that we saw at z=2 are too subtle to be seen in existing HST spectra, overall, the simulation gives an good description of HST spectra at 0.1<z<1.6.

Spectral dynamics and spatial localization of single molecules in a polymer

We report on the high-resolution spectroscopy of single dibenzanthanthrene molecules embedded in polymethyl methacrylate (PMMA). We employed three methods for the characterization of spectral line shapes based on fitting a Lorentzian function, determining full widths at half-maxima, and calculation of the second-order spectral cumulant. The three approaches provide comparable histograms of linewidth distributions, displaying slowly decaying tails that are indicative of the Lévy stable law. In addition, we introduce an alternative method for the analysis of spectral dynamics, in which ensemble spectra are reconstructed by adding single molecule spectral autocorrelations. Furthermore, we examine the spectral width and distributions of single molecules on the PMMA chain length over three orders of magnitude and find a very small dependence. Lastly, we demonstrate that, despite the strong spectral dynamics, it is possible to collect enough photons from single molecules to localize their positions to better than 10 nm.

Resonance Widths in Open Microwave Cavities Studied by Harmonic Inversion

From the measurement of a reflection spectrum of an open microwave cavity, the poles of the scattering matrix in the complex plane have been determined. The resonances have been extracted by means of the harmonic inversion method. By this, it became possible to resolve the resonances in a regime where the linewidths exceed the mean level spacing up to a factor of 10, a value inaccessible in experiments up to now. The obtained experimental distributions of linewidths were found to be in perfect agreement with predictions from random matrix theory when wall absorption and fluctuations caused by couplings to additional channels are considered.

Biases in Virial Black Hole Masses: An SDSS Perspective

We compile black hole (BH) masses for ~60,000 quasars in the redshift range 0.1 z 4.5 included in the Fifth Data Release of the Sloan Digital Sky Survey, using virial BH mass estimators based on the Hβ, Mg II, and C IV emission lines. Within our sample, the widths of the three lines follow lognormal distributions, with means and dispersions that do not depend strongly on luminosity or redshift. The Mg II- and Hβ-estimated BH masses are consistent with one another, but there is a positive bias between the C IV- and Mg II-estimated BH masses correlated with the C IV-Mg II blueshift, suggesting that the C IV estimator is more severely affected by a disk wind. If the underlying BH mass distribution decreases with mass and the Eddington ratio distribution at fixed true BH mass has nonzero width, we show that the measured virial BH mass and Eddington ratio distributions within finite luminosity bins are subject to Malmquist bias. We present a model that reproduces the observed virial mass distribution, quasar luminosity function, and line width distribution of our sample; it has an underlying BH mass distribution dN/dlog M ∝ M−2.6 and a lognormal true Eddington ratio distribution at fixed true mass with dispersion 0.4 dex and mean dependent on BH mass. In this model, the observed virial mass (Eddington ratio) distribution for the SDSS sample is biased high (low) by ~0.6 dex within finite luminosity bins. Finally, we compare virial BH masses of radio and broad absorption line quasars with ordinary quasars matched in redshift and luminosity.

Interference between two coherently driven monochromatic terahertz sources

We report the interference between two phase-locked, continuous-wave, and coherent terahertz (Thz) photomixers. Both spatial and temporal coherence are observed with a narrow linewidth of less than 10MHz. Phase locking is achieved by using one pair of lasers for both sources. The concept of optical narrow linewidth (fiber) distribution of the mixing signal opens various applications. We outline the necessary steps to extend this scheme for very long base line interferometric THz detection in the tens of kilometer range and for the improvement of spatial resolution for active stand-off THz imaging.

New active galactic nuclei detected in ROSAT All Sky Survey galaxies

Aims. The ROSAT ALL Sky Survey Bright Source Catalogue (RASS-BSC) has been correlated with the Catalogue of Principal Galaxies (PGC) to identify new extragalactic counterparts. 550 reliable optical counterparts have been detected. However there existed no optical spectra for about 200 Active Galactic Nuclei (AGN) candidates before the ROSAT ALL Sky Survey (RASS) was completed. Methods. We took optical spectra of 176 X-ray candidates and companions at ESO, Calar Alto observatory and McDonald observatory. When necessary we used a line profile decomposition to measure line fluxes, widths and centers to classify their type of activity. Results. We discuss the redshift-, linewidth-, as well as optical and X-ray luminosity distribution of our ROSAT selected sample. 139 galaxies of our 166 X-ray counterparts have been identified as AGN with 93 being Seyfert 1 galaxies (61%). Eighteen of them (20%) are Narrow Line Seyfert 1 galaxies. 34 X-ray candidates (21%) are LINERs and only eight candidates (5%) are Seyfert 2. The ratio of the number of Seyfert 1 galaxies to Seyfert 2 galaxies is about 11/1. Optical surveys result in ratios of 1/1.4. The high fraction of detected Seyfert 1 galaxies is explained by the sensitivity of the ROSAT to soft X-rays which are heavily absorbed in type 2 AGN. Two X-ray candidates are HII-galaxies and 25 candidates (15%) show no signs of spectral activity. The AGN in our RASS selected sample exhibit slightly higher optical luminosities ( M B = (-20.71 ± 1.75) mag) and similar X-ray luminosities (log($L_{\mathrm{X}}$ [ erg s -1 ] ) = 42.9 ± 1.7) compared to other AGN surveys. The H α line width distribution ( FWHM ) of our newly identified ROSAT AGN sample is similar to the line widths distribution based on SDSS AGN. However, our newly identified RASS AGN have rather reddish colors explaining why they have not been detected before in ultraviolet or blue excess surveys.

Single dot spectroscopy of site-controlled InAs quantum dots nucleated on GaAs nanopyramids

Single InAs quantum dots, site-selectively grown by a patterning and regrowth technique, were probed using high-resolution low-temperature microphotoluminescence spectroscopy. Systematic measurements on many individual dots show a statistical distribution of homogeneous linewidths with a peak value of ∼120μeV, exceeding that of unpatterned dots but comparing well with previously reported patterning approaches. The linewidths do not appear to depend upon the specific facet on which the dots grow and often can reach the spectrometer resolution limit (&amp;lt;100μeV). These measurements show that the site-selective growth approach can controllably position the dots with good optical quality, suitable for constrained structures such as microcavities.

How Many Stages in the Coil-to-Globule Transition of Linear Homopolymer Chains in a Dilute Solution?

How Many Stages in the Coil-to-Globule Transition of Linear Homopolymer Chains in a Dilute Solution?

Does the Standard Model of Low-Temperature Glass Dynamics Describe a Real Glass?

We present the first experimental single-molecule (SM) spectroscopy study of the local dynamics in molecular glasses (frozen toluene and deuterated toluene weakly doped with a substituted terrylene) at T=2-30 K. Surprisingly, the dynamics does not follow the standard model of low-temperature glasses. An extra contribution to the dynamics was detected causing drifts and irreproducible jumps of the SM spectra. The isotope effects in the SM linewidth distribution and the density of states (boson peak) show that the fast dynamics at T=2 K is due to excitations of tunneling nature, whereas at T>7 K it is related to vibrations; H/D atoms are directly involved in both types of excitations.

Isotope effect in the linewidth distribution of single-molecule spectra in doped toluene at 2 K

The low-temperature dynamics of two different varieties of a low-molecular glass—protonated toluene (C 6H 5CH 3) and perdeuterated toluene (C 6D 5CD 3)—weakly doped with tetra -tert-butylterrylene (TBT) molecules was investigated with single-molecule spectroscopy. In both glassy matrices the distributions of the spectral widths were measured for a large number of single TBT molecules at T=2 K. The marked shift of the distribution upon deuteration of matrix was observed and attributed to an isotope effect which is qualitatively analyzed. It was found that at this temperature the tunneling dynamics of the matrix dominates the broadening behavior and hydrogen/deuterium atoms are involved in the tunneling motions.

When Does the Intergalactic Medium Become Enriched?

We use cosmological hydrodynamic simulations including galactic feedback based on observations of local starbursts to find a self-consistent evolutionary model capable of fitting the observations of the intergalactic metallicity history as traced by C IV between z=6.0->1.5. Our main finding is that despite the relative invariance in the measurement of Omega(C IV) as well as the column density and linewidth distributions over this range, continual feedback from star formation-driven winds are able to reproduce the observations, while an early enrichment scenario where a majority of the metals are injected into the IGM at z>6 is disfavored. The constancy of the C IV observations results from a rising IGM metallicity content balanced by a declining C IV ionization fraction due to a 1) decreasing physical densities, 2) increasing ionization background strength, and 3) metals becoming more shock-heated at lower redshift. Our models predict that ~20x more metals are injected into the IGM between z=6->2 than at z>6. We show that the median C IV absorber at z=2 traces metals injected 1 Gyr earlier indicating that the typical metals traced by C IV are neither from very early times nor from very recent feedback.

Cosmological simulations of intergalactic medium enrichment from galactic outflows

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 Civ 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 ∼ x 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.

Consistent simulation of X- and Q-band EPR spectra of an unsymmetric dinuclear [formula omitted] complex

Simulation of X- and Q-band electron paramagnetic resonance (EPR) spectra of an unsymmetric dinuclear [ Mn 2 II , III L ( μ - OAc ) 2 ] ClO 4 complex ( 1), (L is the dianion of 2-{[ N, N-bis(2-pyridylmethyl)amino]methyl}-6-{[ N-(3,5-di- tert-butyl-2-hydroxybenzyl)- N-(2-pyridylmethyl)amino]methyl}-4-methylphenol) was performed using one consistent set of simulation parameters. Rhombic g-tensors and hyperfine tensors were necessary to obtain satisfactory simulation of the EPR spectra. The anisotropy of the effective hyperfine tensors of each individual 55Mn ion was further analyzed in terms of intrinsic hyperfine tensors. Detailed analysis shows that the hyperfine anisotropy of the Mn III ion is a result of the Jahn-Teller effect and thus an inherent character. In contrast, the anomalous hyperfine anisotropy of the Mn II ion is attributed as being transferred from the Mn III ion through the spin exchange interaction. The anisotropy parameter for the Mn II is deduced as D II = −1.26 ± 0.2 cm −1. This is the first reported D II value for a Mn II ion in a weakly exchange coupled mixed-valence Mn 2 II , III complex with a bis-μ-acetato-bridge. The d xy 1 d yz 1 d zx 1 d x 2 - y 2 1 electronic configuration of the Mn III ion in 1 is revealed by the negative sign of its intrinsic hyperfine tensor anisotropy, Δ a III = a z − a x, y = −46 cm −1. Lower spectral resolution of the Q-band EPR spectrum as compared to the X-band EPR spectrum is associated to large line width broadening of the x- and y-components in contrast to the z-component. The origins of the unequal distribution of line width between the z- and x-, y-components are discussed.

Low-Luminosity Active Galaxies and Their Central Black Holes

Central black hole masses for 117 spiral galaxies representing morphological stages S0/a through Sc and taken from the large spectroscopic survey of Ho et al. are derived using Ks-band data from the Two Micron All Sky Survey. Black hole masses are found using a calibrated black hole-Ks bulge luminosity relation, while bulge luminosities are measured by means of a two-dimensional bulge-disk decomposition routine. The black hole masses are correlated against a variety of parameters representing properties of the nucleus and host galaxy. Nuclear properties such as line width (FWHM [N II]), as well as emission-line ratios (e.g., [O III]/Hβ, [O I]/Hα, [N II]/Hα, and [S II]/Hα), show a very high degree of correlation with black hole mass. The excellent correlation with line width supports the view that the emission-line gas is in virial equilibrium with either the black hole or bulge potential. The very good emission-line ratio correlations may indicate a change in ionizing continuum shape with black hole mass in the sense that more massive black holes generate harder spectra. Apart from the inclination-corrected rotational velocity, no excellent correlations are found between black hole mass and host galaxy properties. Significant differences are found between the distributions of black hole masses in early-, mid-, and late-type spiral galaxies (subsamples A, B, and C) in the sense that early-type galaxies have preferentially larger central black holes, consistent with observations that Seyfert galaxies are found preferentially in early-type systems. The line width distributions show a marked difference among subsamples A, B, and C in the sense that earlier type galaxies have larger line widths. There are also clear differences in line ratios between subsamples A+B and C that likely are related to the level of ionization in the gas. Finally, a Ks-band Simien & de Vaucouleurs diagram shows excellent agreement with the original B-band relation, although there is a large dispersion at a given morphological stage.

Laser-light-scattering study of structure and dynamics of waxy corn amylopectin in dilute aqueous solution

The average molecular weight ( M ¯ w ) , gyration radius (< R g>), second virial coefficient ( A 2) and fractal dimension ( d f) of waxy corn amylopectin in aqueous solution were characterized by static light scattering. The results indicated that the single waxy corn amylopectin molecule had a compact structure compared with the linear polymer and was like a swollen branched cluster. The associated waxy corn amylopectin molecule was like a non-swollen branched cluster. The dynamics of waxy corn amylopectin in dilute aqueous solution were investigated by dynamic light scattering. When qR g≤2 (where q is the scattering vector and R g is the gyration radius of amylopectin), the single line-width distribution was found, which was caused by the translational diffusion of waxy corn amylopectin in dilute aqueous solution. The average hydrodynamic radius < R h> could be obtained through Stokes-Einstein equation. When qR g>2, the dynamics of waxy corn amylopectin were dominated by the internal motion of waxy corn amylopectin branching sections, and the first cumulant line-width (< Γ>) could be scaled to the scattering vector ( q) as < Γ>∼ q n ( n=2.73±0.06). It was found that some internal motions were not found at certain observation length by dynamic laser light scattering and some internal motions were suppressed due to the hyperbranched structure of amylopectin. The reduced cumulant Γ*=< Γ>/( q 3 k B T/η 0) could not approach a plateau value with increase of the qR g, and the < Γ>/( q 3 k B T/η 0) value of waxy corn amylopectin was much lower than the value of the linear polymer due to the branched structure and rigid chain of waxy corn amylopectin.

Ferroelastic phase transitions and domain structures in powders

Abstract Powder patterns of samples resulting from ferroelastic phase transitions generally show typical line profiles: asymmetry into the direction of the position of the corresponding hypothetical high symmetry reflection and strongly anisotropic line broadening. An approximate model is presented that describes the characteristic distribution of individual line widths based on the variation of lattice spacings within the domain walls. The variation with temperature is governed by the competition of decreasing spontaneous strain and increasing wall widths and/or wall densities. It is argued that conventional Rietveld refinements can easily lead to erroneous results and a simplified method is proposed to approximate the actual line profiles via the introduction of a second phase with anisotropic strain broadening to take into account the scattering fom the domain walls.

Joint modelling of the probability distribution function and power spectrum of the Ly forest: comparison with observations at z= 3

We present results of joint modelling of the probability distribution function (PDF) and the one-dimensional power spectrum (PS) of the Lya forest flux decrement. The sensitivity of these statistical measures to the shape and amplitude of the linear matter power spectrum is investigated using N-body simulations of two variants of the ACDM cosmology. In the first model, the linear power spectrum has a scale-invariant spectral index n s = 1, whereas in the second, it has a negative running spectral index (RSI), dn/d lnk < 0. We generate mock catalogues of quasi-stellar object (QSO) spectra, and compare their statistical properties to those of the observations at z = 3. We perform a joint fit of the PS and the PDF. A scale-invariant model with σ 8 = 0.9 matches the data well if the mean temperature of the intergalactic medium is T ≤ 1.5 x 10 4 K. For higher temperature, it tends to overestimate the flux PS over scales k ≤ 0.01 s km -1 . The discrepancy is less severe when the PS alone is fitted. However, models matching the PS alone do not yield a good fit to the PDF. A joint analysis of the flux PS and PDF tightens the constraints on the model parameters and reduces systematic biases. The RSI model is consistent with the observed PDF and PS only if the temperature is T ≥ 2 x 10 4 K. The best-fitting models reproduce the slope and normalization of the column density distribution, irrespective of the shape and amplitude of the linear power spectrum. They are also consistent with the observed linewidth distribution, given the large uncertainties. Our joint analysis suggests that σ 8 is likely to be in the range 0.7-0.9 for a temperature 1 x 10 4 ≤ T ≤ 2 x 10 4 K and a reasonable reionization history.