Interstellar Mg II and C IV absorption by 1 1/2 galaxies along the sightline to MrK 205

The first results of our HST survey designed to search for Mg 2 and C 4 absorption lines from the disks and halos of low-redshift galaxies using background QSO's and supernovae as probes are presented. Our survey utilizes the high resolution of the Goddard High Resolution Spectrograph enabling us to calculate the column densities and doppler parameters of individual components within an absorption complex, and hence determine the physical conditions of the absorbing gas. Observing the complexity of the absorption line profiles i.e., the velocity distribution and total velocity extent of the constituent components, offers an important description of the kinematics of the absorbing gas, and hence an understanding of its origin. Focus is on one sight line in particular, that towards Mrk 205, which passes 3-5 kpc from the intervening galaxy NGC 4319. Mg 2 and C 4 absorption from both local Milky Way halo gas and from NGC 4319 is detected

The Detection of Lyman-alpha Absorption from Nine Nearby Galaxies

We have used STIS aboard HST to search for Lyman-alpha (Lya) absorption in the outer regions of nine nearby (cz<6000 km/s) galaxies using background QSOs and AGN as probes. The foreground galaxies are intercepted between 26 and 199 h-1 kpc from their centers, and in all cases we detect Lya within +/-500 km/s of the galaxies' systemic velocities. The intervening galaxies have a wide range of luminosities, from M_B = -17.1 to -20.0, and reside in various environments: half the galaxies are relatively isolated, the remainder form parts of groups or clusters of varying richness. The equivalent widths of the Lya lines range from 0.08 - 0.68 A and, with the notable exception of absorption from one pair, crudely correlate with sightline separation in a way consistent with previously published data, though the column densities derived from the lines do not. The lack of correlation between line strength and galaxy luminosity or, in particular, the environment of the galaxy, suggests that the absorption is not related to any individual galaxy, but arises in gas which follows the same dark-matter structures that the galaxies inhabit.Comment: 8 pages, invited review to appear in the proceedings of the Yale Cosmology Workshop on `The Shapes of Galaxies & their Halos", P. Natarajan, ed. Best figures found in (17Mb) PS file at http://astro.princeton.edu/~dvb/yale.p

Redshifts of galaxies close to bright QSO lines of sight

To expand the known number of low-redshift galaxies which lie close to bright ($V < 17.2$) QSO lines of sight, we have identified 24 galaxies within 11 arcmins of nine QSOs which have been observed with the Hubble Space Telescope (HST). Galaxies are found between redshifts of $0.0114-0.145$ and lie between $39-749$ $h^{-1}$ kpc from QSO sightlines. Knowing the redshifts of these galaxies has already proved important in understanding results from HST programmes designed to search for UV absorption lines from low-redshift galaxies, and will enable future observations to probe the halos of these galaxies in detail.Comment: MNRAS in press. 9 pages LaTeX using MNRAS sty. Postscript figures are excluded due to large size. Paper with figures can be obtained from http://www.roe.ac.uk/research/bowen1.ps.

The Detection of Lyman-alpha Absorption from Nine Nearby Galaxies

We have used STIS aboard HST to search for Lyman-alpha (Lya) absorption in the outer regions of nine nearby (cz<6000 km/s) galaxies using background QSOs and AGN as probes. The foreground galaxies are intercepted between 26 and 199 h-1 kpc from their centers, and in all cases we detect Lya within +/-500 km/s of the galaxies' systemic velocities. The intervening galaxies have a wide range of luminosities, from M_B = -17.1 to -20.0, and reside in various environments: half the galaxies are relatively isolated, the remainder form parts of groups or clusters of varying richness. The equivalent widths of the Lya lines range from 0.08 - 0.68 A and, with the notable exception of absorption from one pair, crudely correlate with sightline separation in a way consistent with previously published data, though the column densities derived from the lines do not. The lack of correlation between line strength and galaxy luminosity or, in particular, the environment of the galaxy, suggests that the absorption is not related to any individual galaxy, but arises in gas which follows the same dark-matter structures that the galaxies inhabit.Comment: 8 pages, invited review to appear in the proceedings of the Yale Cosmology Workshop on `The Shapes of Galaxies & their Halos", P. Natarajan, ed. Best figures found in (17Mb) PS file at http://astro.princeton.edu/~dvb/yale.p

Lyman-alpha absorption around nearby galaxies

We have used STIS aboard HST to search for Lyman-alpha (Lya) absorption lines in the outer regions of eight nearby galaxies using background QSOs and AGN as probes. Lya lines are detected within a few hundred km/s of the systemic velocity of the galaxy in all cases. We conclude that a background line-of-sight which passes within 26-200 h-1 kpc of a foreground galaxy is likely to intercept low column density neutral hydrogen with log N(HI) >~ 13.0. The ubiquity of detections implies a covering factor of ~ 100% for low N(HI) gas around galaxies within 200 h-1 kpc. We discuss the difficulty in trying to associate individual absorption components with the selected galaxies and their neighbors, but show that by degrading our STIS data to lower resolutions, we are able to reproduce the anti-correlation of Lya equivalent width and impact parameter found at higher redshift. We also show that the equivalent width and column density of Lya complexes (when individual components are summed over ~ 1000 km/s) correlate well with a simple estimate of the volume density of galaxies brighter than M(B) = -17.5 at the same redshift as a Lya complex. We do not reject the hypothesis that the selected galaxies are directly responsible for the observed Lya lines, but our analysis indicates that absorption by clumpy intragroup gas is an equally likely explanation. (Abriged)Comment: Accepted for publication in Nov 20, 2002 issue of ApJ. Paper with all figures can be found at http://www.astro.princeton.edu/~dvb/lyapaper.ps (preferable). Minor typos fixe

Understanding the AC conductivity and permittivity of trapdoor chabazites for future development of next-generation gas sensors

Synthetic K+ chabazite (KCHA), Cs+ chabazite (CsCHA) and Zn2+ chabazite (ZnCHA) have been synthesized and investigated in order to relate the differences in their crystalline structures to their thermal stability, moisture content and frequency dependent alternating current (AC) conductivity, permittivity and phase angle at a range of temperatures. The materials are shown to exhibit the universal dielectric response, which is typical of materials consisting of both conductive and insulating regions. Due to the presence of porosity, the three chabazites were hydrated significantly at room temperature and so the dehydrated state was achieved by heating the chabazites to high temperatures to ensure that all different energetic types of water were removed. Cation migration activation energies for KCHA (0.66 ± 0.10) eV, CsCHA (0.88 ± 0.01) eV and ZnCHA (0.90 ± 0.01) eV were determined during the cooling cycle from the fully dehydrated state to provide an accurate measurement of the activation energies. Good thermal stability of the materials was observed up to 710 °C and below 200 °C the electrical properties can be strongly influenced by hydration level. Overall, it was determined that when either hydrated or dehydrated, KCHA had the highest conductivity and lowest cation migration activation energy of the three studied chabazites and thus has the most promising electrical properties for potential use as a gas sensing material in next-generation electrical-based gas sensors.</p

Diagnosis of carbonation induced corrosion initiation and progression in reinforced concrete structures using piezo-impedance transducers

In addition to chloride induced corrosion, the other commonly occurring type of rebar corrosion in reinforced concrete structures is that induced by the ingress of atmospheric carbon dioxide into concrete, commonly referred to as ‘carbonation induced corrosion’. This paper presents a new approach for detecting the onset and quantifying the level of carbonation induced rebar corrosion. The approach is based on the changes in the mechanical impedance parameters acquired using the electro-mechanical coupling of a piezoelectric lead zirconate titanate (PZT) ceramic patch bonded to the surface of the rebar. The approach is non-destructive and is demonstrated though accelerated tests on reinforced concrete specimens subjected to controlled carbon dioxide exposure for a period spanning over 230 days. The equivalent stiffness parameter, extracted from the frequency response of the admittance signatures of the PZT patch, is found to increase with penetration of carbon dioxide inside the surface and the consequent carbonation, an observation that is correlated with phenolphthalein staining. After the onset of rebar corrosion, the equivalent stiffness parameter exhibited a reduction in magnitude over time, providing a clear indication of the occurrence of corrosion and the results are correlated with scanning electron microscope images and Raman spectroscopy measurements. The average rate of corrosion is determined using the equivalent mass parameter. The use of PZT ceramic transducers, therefore, provides an alternate and effective technique for diagnosis of carbonation induced rebar corrosion initiation and progression in reinforced concrete structures non-destructively

Interstellar and Circumstellar Optical & Ultraviolet Lines Towards SN1998S

We have observed SN1998S which exploded in NGC3877, with the UES at the WHT and with the E230M echelle of STIS aboard HST. Both data sets were obtained at two seperate epochs. From our own Galaxy we detect interstellar absorption lines of CaII, FeII, MgI, and probably MnII from the edge of the HVC Complex M. We derive gas-phase abundances which are very similar to warm disk clouds in the local ISM, which we believe argues against the HVC material having an extragalactic origin. At the velocity of NGC3877 we detect interstellar MgI, MgII, MnII, CaII, & NaI. Surprisingly, one component is seen to increase by a factor of ~1 dex in N(NaI) and N(MgI) between the two epochs over which the data were taken. Unusually, our data also show narrow Balmer, HeI, and metastable FeII P-Cygni profiles, with a narrow absorption component superimposed on the bottom of the profile's absorption trough. Both the broad and narrow components of the optical lines are seen to increase substantially in strength between the two epochs. Most of the low-ionization absorption can be understood in terms of gas co-rotating with the disk of NGC 3877, providing the SN is at the back of an HI disk with a similar thickness to that of our own Galaxy. However, the variable absorption components, and the classic P-Cygni emission profiles, most likely arise in slow-moving circumstellar outflows originating from the red supergiant progenitor of SN1998S. [Abridged.]Comment: Accepted by ApJ, 26 pages including 9 figure

Complex Mg II absorption in the outer disk of M61

The increasing availability of high quality spectra of QSO absorption line systems at resolutions of only a few km/s is expected to facilitate the translation of the kinematics of components comprising the lines into the spatial distribution of gas around an absorbing galaxy. In this Letter, we present Hubble Space Telescope (HST) spectra of Q1219+047, a QSO whose sightline passes 21 h-1 kpc from the center of M61, through the outer regions of an extended H I disk. We detect complex Mg II absorption, spanning a velocity range of approximately 300 km/s, and strong C IV absorption; these are the first UV observations of a QSO absorption line system arising in the outskirts of a disk of a nearby galaxy at low inclination. Our observations are at odds with models of galaxies in which absorbing clouds co-rotate with a galaxy's disk, because M61's low inclination should give rise to only a few Mg II components spread over a small velocity range in such a model. Hence our results throw doubt on whether absorption line profiles can be used to infer the spatial distribution of gas around absorbing galaxies.Comment: Accepted by Astrophysical Journal Letters. AASTeX style, includes two Postscript figures. Paper can also be obtained from http://www.roe.ac.uk/#researc