Wednesday. Most hilarious flat visit yesterday. Frank, I'm really not going to take your flat. I'm not coming to visit just for the heck of it either. And you're seriously overpricing your apartment.
MPIfR Lunch Colloquium
Shining a light on the galactic magnetic field with pulsars
Aris Noutsos (MPIfR Bonn)
* read it yesterday. Probing MW's magnetic field with pulsars.
1110.0005
Unsupervised self-organized mapping: a versatile empirical tool for object selection, classification and redshift estimation in large surveys
Geach
Self-organized map (SOM): unsupervised machine learning. Apply for visualizing, exploring and mining the catalogues of large astronomical surveys. SOM culminates in a low-resolution representation of the 'topology' of a parameter volume; exploit for astronomy. Using COSMOS, demonstrate: (i) object classification and selection (ex.: galaxies with AGN) (ii) photometric redshift estimation (SOM as totally empirical predictive tools). Training set of 3800 galaxies with z_spec<1, photo-z accuracy of sigma(Dz)=0.03 with ~2% outlier rate when using u*-band to 8um photometry. Test SOM as a photo-z tool using the PHAT synthetic catalogue of Hildebrandt+ (2010). Find SOM can deliver accuracies that are competitive with many of the sstablished template-fitting and empirical methods. Some clear limitation discussed; but possibly an efficient tool in extremely large databases.
1110.0345
Precision cosmography with stacked voids
Lavaux, Wandelt
Present purely geometrical method for probing the expansion history of the Universe form the observation of the shape of stacked voids in spectroscopic redshift surveys. It's and Alcock-Pasczinsky test based on the average sphericity of voids, posited on the local isotropy of the Universe; compares temporal extent of cosmic voids along the LoS with their angular, spatial extent. Describe algorithm used to detect and stack voids in redshfit shells on the light cone and test it on N-body sim. Establish robust statistical model for estimating average stretching of voids in z-space and quantify the contamination by peculiar velocities. Assess the capability of this approach to constrain DE params in terms of De FoM for the proposed Euclid mission, a spectroscopic survey. FoM due to stacked voids from the Euclid wide survey is double that of all other DE probes derived from Euclid data alone, combined with Planck priors. Voids outperform BAO by an order of magnitude. Result is consistent with simple estimates based on mode-counting. The AP test based on stacked voids is therefore a potentially significant addition to the portfolio of DE probes, and the systematics should be studied in detail.
1109.0282
A simple harmonic universe
Graham, Horn, Kachru, Rajendran, Torroba
Simple but novel bouncing solutions of GR that avoid singularities. Solutions require curvature k=+1; supported by a negative cosmological term and matter with -1<w<-1/3 [?]. Moderate bounces where a_max/a_min ~ O(1), the solutions are classically stable and cycle through an infinite set of bounces. For more extreme cases, the solution can still oscillate many times before classical instabilities take them out of the regime of validity of approximations; quantum particle production also leads eventually to a depature from the realm of validity of semiclassical GR, likely yielding a singular crunch. Briefly discuss possible applications of these models to realistic cosmology.
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