The relationship of word error rate to document ranking

This paper describes two experiments that examine the relationship of Word Error Rate (WER) of retrieved spoken documents returned by a spoken document retrieval system. Previous work has demonstrated that recognition errors do not significantly affect retrieval effectiveness but whether they will adversely affect relevance judgement remains unclear. A user-based experiment measuring ability to judge relevance from the recognised text presented in a retrieved result list was conducted. The results indicated that users were capable of judging relevance accurately despite transcription errors. This lead an examination of the relationship of WER in retrieved audio documents to their rank position when retrieved for a particular query. Here it was shown that WER was somewhat lower for top ranked documents than it was for documents retrieved further down the ranking, thereby indicating a possible explanation for the success of the user experiment

Powerful High Velocity-Dispersion Molecular Hydrogen Associated with an Intergalactic Shock Wave in Stephan's Quintet

We present the discovery of strong mid-infrared emission lines of molecular hydrogen of apparently high velocity dispersion (~870 km/s) originating from a group-wide shock wave in Stephan's Quintet. These Spitzer Space Telescope observations reveal emission lines of molecular hydrogen and little else. this is the first time an almost pure H_2 line spectrum has been seen in an extragalactic object. Along with the absence of PAH features and very low excitation ionized gas tracers, the spectra resemble shocked gas seen in Galactic supernova remnants, but on a vast scale. The molecular emission extends over 24 kpc along the X-ray emitting shock-front, but has ten times the surface luminosity as the soft X-rays, and about one-third the surface luminosity of the IR continuum. We suggest that the powerful H_2 emission is generated by the shock wave caused when a high-velocity intruder galaxy collides with filaments of gas in the galaxy group. Our observations suggest a close connection between galaxy-scale shock-waves and strong broad H_2 emission lines, like those seen in the spectra of Ultraluminous Infrared Galaxies where high-speed collisions between galaxy disks are common.Comment: 4 pages, 4 figures and 1 tabl

Modelling the spectral energy distribution of galaxies. I. Radiation fields and grain heating in the edge-on spiral NGC891

We describe a new tool for the analysis of the UV to the sub-millimeter (sub-mm) spectral energy distribution (SED) of spiral galaxies. We use a consistent treatment of grain heating and emission, solve the radiation transfer problem for a finite disk and bulge, and self-consistently calculate the stochastic heating of grains placed in the resulting radiation field. We use this tool to analyse the well-studied nearby edge- on spiral galaxy NGC 891. First we investigate whether the old stellar population in NGC 891, along with a reasonable assumption about the young stellar population, can account for the heating of the dust and the observed far-infrared and sub- mm emission. The dust distribution is taken from the model of Xilouris et al. (1999), who used only optical and near-infrared observations to determine it. We have found that such a simple model cannot reproduce the SED of NGC 891, especially in the sub-mm range. It underestimates by a factor of 2–4 the observed sub-mm flux. A number of possible explanations exist for the missing sub-mm flux. We investigate a few of them and demonstrate that one can reproduce the observed SED in the far-infrared and the sub-mm quite well, as well as the observed radial profile at 850 µm. For the models calculated we give the relative proportion of the dust radiation powered by the old and young stellar popula- tions as a function of FIR/sub-mm wavelength. In all models we find that the dust is predominantly heated by the young stellar population

Spitzer Observations of Cold Dust Galaxies

We combine new Spitzer Space Telescope observations in the mid- and far-infrared with SCUBA 850 micron observations to improve the measurement of dust temperatures, masses and luminosities for 11 galaxies of the SCUBA Local Universe Galaxy Survey (SLUGS). By fitting dust models we measure typical dust masses of 10E7.9 M_sol and dust luminosities of ~ 10E10 L_sol, for galaxies with modest star formation rates. The data presented in this paper combined with previous observations show that cold dust is present in all types of spiral galaxies and is a major contributor to their total luminosity. Because of the lower dust temperature of the SCUBA sources measured in this paper, they have flatter Far-IR nu F_nu(160um)/nu F_nu(850um) slopes than the larger Spitzer Nearby Galaxies Survey (SINGS), the sample that provides the best measurements of the dust properties of galaxies in the nearby universe. The new data presented here added to SINGS extend the parameter space that is well covered by local galaxies, providing a comprehensive set of templates that can be used to interpret the observations of nearby and distant galaxies.Comment: Accepted by A.J. 16 pages, 10 figures, 7 tables. High resolution version at http://mips.as.arizona.edu/~cnaw/slugs_hires.pd

Radioactivity and Electron Acceleration in Supernova Remnants

We argue that the decays of radioactive nuclei related to $^{44}$Ti and $^{56}$Ni ejected during supernova explosions can provide a vast pool of mildly relativistic positrons and electrons which are further accelerated to ultrarelativistic energies by reverse and forward shocks. This interesting link between two independent processes - the radioactivity and the particle acceleration - can be a clue for solution of the well known theoretical problem of electron injection in supernova remnants. In the case of the brightest radio source Cas A, we demonstrate that the radioactivity can supply adequate number of energetic electrons and positrons for interpretation of observational data provided that they are stochastically pre-accelerated in the upstream regions of the forward and reverse shocks.Comment: 6 pages, 1 figure, revised version accepted to Phys.Rev.

Powerful H2_2 Line-cooling in Stephan's Quintet : I - Mapping the Significant Cooling Pathways in Group-wide Shocks

We present results from the mid-infrared spectral mapping of Stephan's Quintet using the Spitzer Space Telescope. A 1000 km/s collision has produced a group-wide shock and for the first time the large-scale distribution of warm molecular hydrogen emission is revealed, as well as its close association with known shock structures. In the main shock region alone we find 5.0 $\times10^{8}$ M$_{\odot}$ of warm H$_2$ spread over $\sim$ 480 kpc$^2$ and additionally report the discovery of a second major shock-excited H$_2$ feature. This brings the total H$_2$ line luminosity of the group in excess of 10$^42$ erg/s. In the main shock, the H$_2$ line luminosity exceeds, by a factor of three, the X-ray luminosity from the hot shocked gas, confirming that the H$_2$-cooling pathway dominates over the X-ray. [Si II]34.82$\mu$m emission, detected at a luminosity of 1/10th of that of the H$_2$, appears to trace the group-wide shock closely and in addition, we detect weak [FeII]25.99$\mu$m emission from the most X-ray luminous part of the shock. Comparison with shock models reveals that this emission is consistent with regions of fast shocks (100 < $V_{s}$ < 300 km/s) experiencing depletion of iron and silicon onto dust grains. Star formation in the shock (as traced via ionic lines, PAH and dust emission) appears in the intruder galaxy, but most strikingly at either end of the radio shock. The shock ridge itself shows little star formation, consistent with a model in which the tremendous H$_{2}$ power is driven by turbulent energy transfer from motions in a post-shocked layer. The significance of the molecular hydrogen lines over other measured sources of cooling in fast galaxy-scale shocks may have crucial implications for the cooling of gas in the assembly of the first galaxies.Comment: 23 pages, 15 figures, Accepted to Ap

The dust emission SED of X-ray emitting regions in Stephan's Quintet

We analysed the Spitzer maps of Stephan's Quintet in order to investigate the nature of the dust emission associated with the X-ray emitting regions of the large scale intergalactic shock and of the group halo. This emission can in principle be powered by dust-gas particle collisions, thus providing efficient cooling of the hot gas. However the results of our analysis suggest that the dust emission from those regions is mostly powered by photons. Nonetheless dust collisional heating could be important in determining the cooling of the IGM gas and the large scale star formation morphology observed in SQ.Comment: Conference proceedings IAU Symposium 284 "The Spectral energy distribution of galaxies", 5-9 September 2011, Preston, U