Cooler Dust Research Articles

Arsenic removal using steel manufacturing byproducts as permeable reactive materials in mine tailing containment systems

Steel manufacturing byproducts were tested as a means of treating mine tailing leachate with a high As concentration. Byproduct materials can be placed in situ as permeable reactive barriers to control the subsurface release of leachate from tailing containment systems. The tested materials had various compositions of elemental Fe, Fe oxides, Ca–Fe oxides and Ca hydroxides typical of different steel manufacturing processes. Among these materials, evaporation cooler dust (ECD), oxygen gas sludge (OGS), basic oxygen furnace slag (BOFS) and to a lesser degree, electrostatic precipitator dust (EPD) effectively removed both As(V) and As(III) during batch experiments. ECD, OGS and BOFS reduced As concentrations to <0.5 mg/l from 25 mg/l As(V) or As(III) solution in 72 h, exhibiting higher removal capacities than zero-valent iron. High Ca concentrations and alkaline conditions (pH ca. 12) provided by the dissolution of Ca hydroxides may promote the formation of stable, sparingly soluble Ca–As compounds. When initial pH conditions were adjusted to 4, As reduction was enhanced, probably by adsorption onto iron oxides. The elution rate of retained As from OGS and ECD decreased with treatment time, and increasing the residence time in a permeable barrier strategy would be beneficial for the immobilization of As. When applied to real tailing leachate, ECD was found to be the most efficient barrier material to increase pH and to remove As and dissolved metals.

The origin of the UV excess in powerful radio galaxies: spectroscopy and polarimetry of a complete sample of intermediate-redshift radio galaxies

We present spectroscopic and polarimetric observations of a complete, optically unbiased sample of 2-Jy radio galaxies at intermediate redshifts (0.15 10 per cent level. Careful measurement and modelling of our spectra have allowed us to quantify the contributions of other components to the UV excess. We show that nebular continuum (present in all objects at the 3-40 per cent level), direct active galactic nucleus (AGN) light (significant in 40 per cent of objects) and young stellar populations (significant in 15 - 50 per cent of objects) all make important contributions to the UV continuum in the population of powerful radio galaxies. These results serve to emphasize the multicomponent nature of the UV continuum in radio galaxies. The results also point to an interesting link between the optical/UV and far-IR properties of our sample objects, in the sense that the objects with the clearest evidence for optical/UV starburst activity are also the most luminous at far-IR wavelengths. This supports the idea that the cooler dust components in radio galaxies are heated by starbursts rather than by AGN.

The clustering of hot and cold IRAS galaxies: the redshift-space correlation function

We measure the autocorrelation function of galaxies in the IRAS Point Source Catalogue galaxy redshift (PSCz) survey and investigate its dependence on the far-infrared colour and absolute luminosity of the galaxies. We find that the PSCz survey correlation function can be modelled out to a scale of 10 h^{-1}Mpc as a power law of slope 1.30 +/- 0.04 and correlation length 4.77 +/- 0.20. At a scale of 75 h^{-1}Mpc we find the value of J_3 to be 1500 +/- 400. We also find that galaxies with cooler dust temperatures, are more strongly clustered than warmer galaxies. Splitting the survey into three colour subsamples, we find that, between 1 and 10 h^{-1}Mpc, the ratio of the correlation function is factor of 1.5 higher for the cooler galaxies compared to the hotter galaxies. This is consistent with the suggestion that hotter galaxies have higher star-formation rates, and correspond to later-type galaxies which are less clustered than earlier types. Using volume limited sub-samples, we find a weak variation of the correlation function as a function of absolute luminosity, in the sense that more luminous galaxies are less clustered than fainter galaxies. The trend is consistent with the colour dependence of the correlation function and the observed colour-luminosity correlation, but the large uncertainties mean that it has a low statistical significance.

Extended gas in Seyfert galaxies: near-infrared observations of 15 active nuclei

ABSTRA C T Results from an analysis of low-resolution OR , 250U near-infrared long-slit spectra covering simultaneously the I, J, H and K bands, for a sample of 15 Seyfert galaxies and the NGC 5253 starburst nucleus, are presented. The Seyfert galaxies were selected as presenting ‘linear’ or cone-like high-excitation emission lines in the optical, most probably arising from the collimation of the radiation of the central source by a dusty molecular torus. Our goal was to look for signatures of this torus, and to investigate the gaseous distribution, excitation and reddening. The strongest emission lines detected are usually He i 1.083mm and [S iii]l 9532, followed by Pab. In some cases, [Fe ii] 1.26 and 1.64mm are also seen. [Fe ii] 1.26mm and H2 va 1 2 0 S(1) are detected in some of the higher resolution spectra obtained for five galaxies. The emission lines are spatially extended in most cases, and we have used the [Fe ii]/Pab ratio as a measure of the gaseous excitation in Mrk 573, NGC 1386 and NGC 7582. Values for this ratio between 1.5 and 6 are found, suggesting excitation of [Fe ii] by X-rays or shock waves in some regions. Broad permitted lines are observed in three Seyfert 1 galaxies. Nuclear Pab in NGC 1365 and possibly nuclear Brg in Mrk 573 are also broad. From analysis of the spatial distribution of the continuumOJ 2 HU andOH 2 KU colours derived from our spectra, we find redder colours for the nucleus than for the nearby bulge in most of the Seyfert 2s observed. Comparison with models including emission from dust and stars shows that hot OT , 1000 KU dust emission dominates the nuclear continuum in NGC 1365, NGC 2110, NGC 3281, NGC 7582 and ESO 362-G18. In NGC 1386, 5643 and 5728 the main contributor is the underlying stellar population, combined with some foreground reddening and/or cooler dust emission. In a few cases, theOJ 2 HU colours on opposite sides of the nucleus differ by 0.3‐0.8 mag, an effect that we interpret as partly resulting from differences in the local stellar population, and possibly extinction gradients.

Mid‐Infrared (8–21 micron) Imaging of Proto–Planetary Nebulae

We present mid-infrared (8-21 μm) images of thermal dust emission from two proto-planetary nebulae (PPNs), IRAS 07134+1005 and IRAS 22272+5435, which show a strong 21 μm emission feature. Both of the sources are well resolved and show evidence for axial symmetry. From our images, we calculate temperature and optical depth maps and estimate the abundance of the 11 μm and 21 μm feature carriers. In both sources, the dust temperatures range from ~160-200 K. The optical depths in IRAS 07134 are about a factor of 3 lower than those in IRAS 22272, but the emission is optically thin in both sources. Our analyses of the feature-to-continuum ratios suggests that 0.5%-5% of the carbon in these objects may be in the form of large PAH molecules. We construct optically thin, axially symmetric cylindrical shell models to simulate the observed mid-IR morphologies and spectra, and calculate nebular masses of 0.26 M☉ for IRAS 07134 and 0.42 M☉ for IRAS 22272. Although the mid-IR emission primarily comes from warm (T ≈ 190 K) dust, our models require a significant cooler dust (T ≈ 80 K) component to fit the observed mid- and far-IR spectral energy distributions.

Infrared mapping of the Galactic plane. IV - The Galactic center

Mid-infrared observations of the galactic center region were obtained at 4, 11, 29, and 27 micrometers on three rocket-borne experiments. The diffuse emission around the galactic center can be separated into three components: (a) a foreground emission from the galactic disk and the 4-5 kpc ring, (b) a spheroidal component surrounding the center, due to unresolved stellar sources of T > 2000 K, and (c) a diffuse elliptical component immediately surrounding the galactic center. The color temperatures of (a) and (c) are consistent with an interpretation of a two-component source of emission from warm dust (about 400 K) characteristic of circumstellar dust shells and cooler dust from extended low-density H II regions. Current models for the infrared emission from interstellar grains cannot reproduce our spectral distribution in the mid-infrared.