The VIRMOS deep imaging survey: I. overview and survey strategy

This paper presents the CFH12K-VIRMOS survey: a deep B, V, R and I imaging survey in four fields totalling more than 17 deg^2, conducted with the 30x40 arcmin^2 field CFH-12K camera. The survey is intended to be a multi-purpose survey used for a variety of science goals, including surveys of very high redshift galaxies and weak lensing studies. Four high galactic latitude fields, each 2x2 deg^2, have been selected along the celestial equator: 0226-04, 1003+01, 1400+05, and 2217+00. The 16 deg^2 of the "wide" survey are covered with exposure times of 2h, 1.5h, 1h, 1h, while the 1.3x1 deg^2 area of the "deep" survey at the center of the 0226-04 field is covered with exposure times of 7h, 4.5h, 3h, 3h, in B,V,R and I respectively. The data is pipeline processed at the Terapix facility at the Institut d'Astrophysique de Paris to produce large mosaic images. The catalogs produced contain the positions, shape, total and aperture magnitudes for the 2.175 million objects. The depth measured (3sigma in a 3 arc-second aperture) is I_{AB}=24.8 in the ``Wide'' areas, and I_{AB}=25.3 in the deep area. Careful quality control has been applied on the data as described in joint papers. These catalogs are used to select targets for the VIRMOS-VLT Deep Survey, a large spectroscopic survey of the distant universe (Le F\`evre et al., 2003). First results from the CFH12K-VIRMOS survey have been published on weak lensing (e.g. van Waerbeke & Mellier 2003). Catalogs and images are available through the VIRMOS database environment under Oracle ({\tt http://www.oamp.fr/virmos}). They will be open for general use on July 1st, 2003.Comment: 17 pages including 9 figures, submitted to A&

Mining the SDSS archive. I. Photometric redshifts in the nearby universe

We present a supervised neural network approach to the determination of photometric redshifts. The method was tuned to match the characteristics of the Sloan Digital Sky Survey and it exploits the spectroscopic redshifts provided by this unique survey. In order to train, validate and test the networks we used two galaxy samples drawn from the SDSS spectroscopic dataset: the general galaxy sample (GG) and the luminous red galaxies subsample (LRG). The method consists of a two steps approach. In the first step, objects are classified in nearby (z<0.25) and distant (0.25<z<0.50). In the second step two different networks are separately trained on objects belonging to the two redshift ranges. Using a standard MLP operated in a Bayesian framework, the optimal architectures were found to require 1 hidden layer of 24 (24) and 24 (25) neurons for the GG (LRG) sample. The presence of systematic deviations was then corrected by interpolating the resulting redshifts. The final results on the GG dataset give a robust sigma_z = 0.0208 over the redshift range [0.01, 0.48] and sigma_z = 0.0197 and sigma_z = 0.0238 for the nearby and distant samples respectively. For the LRG subsample we find a robust sigma_z = 0.0164 over the whole range, and sigma_z = 0.0160, sigma_z = 0.0183 for the nearby and distant samples respectively. After training, the networks have been applied to all objects in the SDSS Table GALAXY matching the same selection criteria adopted to build the base of knowledge, and photometric redshifts for ca. 30 million galaxies having z<0.5 were derived. A catalogue containing photometric redshifts for the LRG subsample was also produced.Comment: 45 pages, 14 figures, accepted for publication is the Astrophysical Journa

Error analysis of the photometric redshift tecnique

We present a calculation of the systematic component of the error budget in the photometric redshift technique. We make use of it to describe a simple technique that allows for the assignation of confidence limits to redshift measurements obtained through photometric methods. We show that our technique, through the calculation of a redshift probability function, gives complete information on the probable redshift of an object and its associated confidence intervals. This information can and must be used in the calculation of any observable quantity which makes use of the redshift.Comment: 6 pages, 5 figures, MNRAS style. Accepted for publication in MNRA

The COMBO-17 survey: Evolution of the galaxy luminosity function from 25 000 galaxies with 0.2<0.2< z

We present a detailed empirical assessment of how the galaxy luminosity function and stellar luminosity density evolves over the last half of the universe's age ($0.2<z<1.2$) for galaxies of different spectral energy distributions (SED). The results are based on ~$25\,000$ galaxies (R\la24) with redshift measurements ($\sigma_z\approx 0.03$) and SEDs across $\lambda_{{\rm obs}}\approx 350\ldots 930$ nm. The redshifts and SEDs were derived from medium-band photometry in 17 filters, observed as part of the COMBO-17 survey (“Classifying Objects by Medium-Band Observations in 17 Filters”) over three disjoint fields with a total area of 0.78 square degrees. Luminosity functions (LF), binned in redshift and SED-type, are presented in the restframe passbands of the SDSS r-band, the Johnson B-band and a synthetic UV continuum band at 280 nm. We find that the luminosity function depends strongly on SED-type at all redshifts covered. The shape of the LF, i.e. the faint-end power-law slope, does depend on SED type, but not on redshift. However, the redshift evolution of the characteristic luminosity M* and density $\phi^*$ depends strongly on SED-type: (1) Early-type galaxies, defined as redder than a present-day reference Sa spectrum, become drastically more abundant towards low redshift, by a factor of 10 in the number density $\phi^*$ from $z=1.1$ to now, and by a factor of 4 in their contribution to the co-moving r-band luminosity density, jr. (2) Galaxies resembling present-day Sa- to Sbc-colours show a co-moving number density and contribution to jr that does not vary much with redshift. (3) Galaxies with blue spectra reflecting strong star formation decrease towards low redshift both in luminosity and density, and by a factor of 4 in their jr contribution. Summed over all SED types and galaxy luminosities, the comoving luminosity density decreases towards low redshift, between $z=1.1$ and now, by a small amount in restframe r and B, but by a factor of ~6 in restframe 280 nm. At $z=1.1$, galaxies redder than Sbc's, contribute 40% to the total jr, which increases to 75% by $z=0$. For $\lambda_{{\rm rest}}=$280 nm, this increase is from 12% to 25% over the same redshift interval. Comparison of the three independent sight-lines shows that our results are not significantly affected by large-scale structure. Our lowest redshift bin at $z= [0.2,0.4]$ largely agrees with the recent assessment of the present-day galaxy population by SDSS and 2dFGRS and deviates only by an excess of “faint blue galaxies” at $z\sim 0.3$ compared to very local samples. Overall our findings provide a set of new and much more precise constraints to model the waning of overall star formation activity, the demise of star-bursts and the strong emergence of “old” galaxies, with hardly any young population, over the last 6-8 Gigayears

An extension of the granophyric quartz-dolerite intrusion of Centre 2, Ardnamurchan, Argyllshire

SummarySheet-like bodies of dolerite with granophyre within the Hypersthene-gabbro on the NE shore of Sanna Bay are shown to be akin to the granophyric quartz-dolerite, and suggest that the latter originally extended for a considerable distance N of its previously mapped limits.</jats:p

Who's story is it anyway? Some considerations on disability from an aesthetic and narrative perspective of lived experience

This PaR aims to use film-making and theoretical materials to explore the persistent practical problems of social injustices and inequalities disabled people face in society today. In accounting for prejudices against those with atypical bodies and/or minds, disability is taken up as a core concept in society, that treats it as a symbol for how being human inevitably means embracing debility, dependency and pain. I examine how this projection upon disabled people is predominantly denied. How, in the failure to acknowledge the symbolic charge they carry on behalf of the whole of society, disabled people are rendered marginal. Their words carry less credibility than those of more powerful agents, and their knowledge is not integrated into shared epistemological resources, which exclusion perpetuates the prejudices they face. Two of the films submitted are exposés of injustices disabled people experience. One tackles the system of mental health; the other, government benefits provision. These injustices are explicitly intertwined with epistemic oppression. The impaired body (taken to include the mind), lies at the heart of the disabled lived experience, but is displaced in critical disability studies. This shortcoming is traced to a social constructivism that prioritises language and representation over the lived reality of bodily impairment. This exclusion, within theory, risks denying disabled people's agency, leaving their representation to be undertaken by the non-disabled, with a consequent neglect to combat the negative aesthetic judgements that inform prejudices against disabled people, and lead them to be targeted for unfair treatment and, sometimes, hate crimes and violence, a subject another of the films investigates. The idea of disability as central to social practices generally is examined in a film about art and impaired vision, where the manifestly extensive contribution of disability and disabled artists is recorded. Disabled people, by claiming agency and owning their own narratives, are able to show different representations of disability (and of humanity), that are not derogatory or dehumanising. The work specifically made for this PaR - the 'Untitled' film - seeks to reclaim the silence surrounding disability, and exemplifies the recommendations made in the text: that disabled people's perspectives be made room for. These narratives are inevitably also critiques of unacknowledged ableism, which makes them subversive

Some aspects of extragalactic astrophysics

Available from British Library Document Supply Centre- DSC:D52423/84 / BLDSC - British Library Document Supply CentreSIGLEGBUnited Kingdo