119060696
Distributions of Galaxy Spectral Types in the Sloan Digital Sky Survey
We perform an objective classification of 170,000 galaxy spectra in the Sloan Digital Sky Survey (SDSS) using the Karhunen-Loeve (KL) transform. With about one-sixth of the total set of galaxy spectra that will be obtained by the survey, we are able to carry out the most extensive analysis of its kind to date. The formalism proposed by Connolly and Szalay is adopted to correct for gappy regions in the spectra and to derive eigenspectra and eigencoefficients. From this analysis, we show that this gap-correction formalism leads to a converging set of eigenspectra and KL-repaired spectra. Furthermore, KL eigenspectra of galaxies are found to be convergent not only as a function of iteration, but also as a function of the number of randomly selected galaxy spectra used in the analysis. From these data a set of 10 eigenspectra of galaxy spectra are constructed, with rest-wavelength coverage 3450–8350 A. The eigencoefficients describing these galaxies naturally place the spectra into several classes defined by the plane formed by the first three eigencoefficients of each spectrum. Spectral types corresponding to different Hubble types and galaxies with extreme emission lines are identified for the 170,000 spectra and are shown to be complementary to existing spectral classifications. From a nonparametric classification technique, we find that the population of galaxies can be divided into three classes that correspond to early late-type through intermediate late-type galaxies. This finding is believed to be related to the color separation of SDSS galaxies discussed in earlier works. Bias in the spectral classifications due to the aperture spectroscopy in the SDSS is small and within the signal-to-noise limit for a majority of galaxies, except for the reddest nearby galaxies and large galaxies (>30 kpc) with prominent emissions. The mean spectra and eigenspectra derived from this work can be downloaded from the SDSS Web site.
16921302
Toward a resolution of the discrepancy between different estimators of star formation rate
Different wavelength regimes and methods for estimating the space density of the star formation rate (SFR) result in discrepant values. While it is recognized that ultraviolet (UV) and Hα emission-line data must be corrected for the effects of extinction, the magnitude of the required correction is uncertain. Even when these corrections are made there remains a significant discrepancy between SFRs derived from UV and Hα measurements compared with those derived from far-infrared (FIR) and radio luminosities. Since the FIR-radio–derived SFRs are not affected by extinction and simple corrections to reconcile the UV and Hα measurement with these do not fully account for the discrepancies, a more sophisticated correction may be required. Recent results suggest that at least part of the solution may be a form of extinction that increases with increasing SFR (or luminosity, given the common assumption that SFR is proportional to luminosity). We present an analysis of the effects of a dust reddening dependent on star formation rate applied to estimators of SFR. We show (1) that the discrepancies between Hα and FIR-radio SFR estimates may be explained by such an effect and we present an iterative method for applying the correction and (2) that UV-based estimates of SFR are harder to reconcile with FIR-radio estimates using this method, although the extent of the remaining discrepancy is less than for a non-SFR–dependent correction. Particularly at high redshift, our understanding of extinction at UV wavelengths may require a still more complex explanation.
119214510
INTERPOLATING MASKED WEAK-LENSING SIGNAL WITH KARHUNEN-LOÈVE ANALYSIS
We explore the utility of Karhunen-Lo?ve (KL) analysis in solving practical problems in the analysis of gravitational shear surveys. Shear catalogs from large-field weak-lensing surveys will be subject to many systematic limitations, notably incomplete coverage and pixel-level masking due to foreground sources. We develop a method to use two-dimensional KL eigenmodes of shear to interpolate noisy shear measurements across masked regions. We explore the results of this method with simulated shear catalogs, using statistics of high-convergence regions in the resulting map. We find that the KL procedure not only minimizes the bias due to masked regions in the field, it also reduces spurious peak counts from shape noise by a factor of ~3 in the cosmologically sensitive regime. This indicates that KL reconstructions of masked shear are not only useful for creating robust convergence maps from masked shear catalogs, but also offer promise of improved parameter constraints within studies of shear peak statistics.
119191264
Classification of Stellar Spectra with LLE
We investigate the use of dimensionality reduction techniques for the classification of stellar spectra selected from the SDSS. Using local linear embedding (LLE), a technique that preserves the local (and possibly non-linear) structure within high dimensional data sets, we show that the majority of stellar spectra can be represented as a one dimensional sequence within a three dimensional space. The position along this sequence is highly correlated with spectral temperature. Deviations from this “stellar locus” are indicative of spectra with strong emission lines (including misclassified galaxies) or broad absorption lines (e.g. Carbon stars). Based on this analysis, we propose a hierarchical classification scheme using LLE that progressively identifies and classifies stellar spectra in a manner that requires no feature extraction and that can reproduce the classic MK classifications to an accuracy of one type.
118985428
Three-Point Correlation Functions of SDSS Galaxies in Redshift Space: Morphology, Color, and Luminosity Dependence
We present measurements of the redshift-space three-point correlation function of galaxies in the Sloan Digital Sky Survey (SDSS). For the first time, we analyze the dependence of this statistic on galaxy morphology, color, and luminosity. In order to control systematics due to selection effects, we used r-band, volume-limited samples of galaxies, constructed from magnitude-limited SDSS data (14.5 <r< 17.5), and further divided the samples into two morphological types (early and late) or two color populations (red and blue). The three-point correlation function of SDSS galaxies follows the hierarchical relation well, and the reduced three-point amplitudes in redshift-space are almost scale-independent (Qz =0 .5 ∼ 1.0). In addition, their dependence on the morphology, color, and luminosity is not statistically significant. Given the robust morphological, color, and luminosity dependences of the two-point correlation function, this implies that galaxy biasing is complex on weakly non-linear to non-linear scales. We show that a simple deterministic linear relation with the underlying mass could not explain our measurements on these scales.
8278022
First Results from the SPICES Survey
We present first results from SPICES, the Spectroscopic, Photometric, Infrared-Chosen Extragalactic Survey. SPICES is comprised of four ~30 square arcminute high Galactic latitude fields with deep BRIzJK imaging reaching depths of ~25th magnitude (AB) in the optical and ~23rd magnitude (AB) in the near-infrared. To date we have 626 spectroscopic redshifts for infrared-selected SPICES sources with K 1. One of the SPICES fields has been the target of a deep 190 ksec Chandra exposure; we discuss initial results from analysis of that data set. Finally, we briefly discuss a successful campaign to identify high-redshift sources in the SPICES fields.
122312631
Design and initial performance of the Askaryan Radio Array prototype EeV neutrino detector at the South Pole
Abstract We report on studies of the viability and sensitivity of the Askaryan Radio Array (ARA), a new initiative to develop a Teraton-scale ultra-high energy neutrino detector in deep, radio-transparent ice near Amundsen-Scott station at the South Pole. An initial prototype ARA detector system was installed in January 2011, and has been operating continuously since then. We describe measurements of the background radio noise levels, the radio clarity of the ice, and the estimated sensitivity of the planned ARA array given these results, based on the first five months of operation. Anthropogenic radio interference in the vicinity of the South Pole currently leads to a few-percent loss of data, but no overall effect on the background noise levels, which are dominated by the thermal noise floor of the cold polar ice, and galactic noise at lower frequencies. We have also successfully detected signals originating from a 2.5 km deep impulse generator at a distance of over 3 km from our prototype detector, confirming prior estimates of kilometer-scale attenuation lengths for cold polar ice. These are also the first such measurements for propagation over such large slant distances in ice. Based on these data, ARA-37, the ∼200 km 2 array now in its initial construction phase, will achieve the highest sensitivity of any planned or existing neutrino detector in the 10 16 –10 19  eV energy range.
124352899
MEASURING THE NEUTRINO-NUCLEON CROSS SECTION WITH SALSA
These proceedings describe a study of the expected sensitivity of the SalSA experiment to the neutrino-nucleon cross section. We expect the measurement to be statistics limited for the events rates expected from SalSA. With 100 measured events, we expect to measure a standard model cross section with a 38% uncertainty that is dominantly statistical.
16975620
The radio Cherenkov technique for ultra-high energy neutrino detection
I review the status of the radio Cherenkov detection technique in searches for ultra-high energy (UHE) neutrinos of cosmic origin. After outlining the physics motivations for UHE neutrino searches, I give an overview of the status of current and proposed experiments in the field.
119288671
The Effective Number Density of Galaxies for Weak Lensing Measurements in the LSST Project
Future weak lensing surveys potentially hold the highest statistical power for constraining cosmological parameters compared to other cosmological probes. The statistical power of a weak lensing survey is determined by the sky coverage, the inverse of the noise in shear measurements, and the galaxy number density. The combination of the latter two factors is often expressed in terms of $n_{\rm eff}$ -- the "effective number density of galaxies used for weak lensing measurements". In this work, we estimate $n_{\rm eff}$ for the Large Synoptic Survey Telescope (LSST) project, the most powerful ground-based lensing survey planned for the next two decades. We investigate how the following factors affect the resulting $n_{\rm eff}$ of the survey with detailed simulations: (1) survey time, (2) shear measurement algorithm, (3) algorithm for combining multiple exposures, (4) inclusion of data from multiple filter bands, (5) redshift distribution of the galaxies, and (6) masking and blending. For the first time, we quantify in a general weak lensing analysis pipeline the sensitivity of $n_{\rm eff}$ to the above factors. 
We find that with current weak lensing algorithms, expected distributions of observing parameters, and all lensing data ($r$- and $i$-band, covering 18,000 degree$^{2}$ of sky) for LSST, $n_{\rm eff} \approx37$ arcmin$^{-2}$ before considering blending and masking, $n_{\rm eff} \approx31$ arcmin$^{-2}$ when rejecting seriously blended galaxies and $n_{\rm eff} \approx26$ arcmin$^{-2}$ when considering an additional 15% loss of galaxies due to masking. With future improvements in weak lensing algorithms, these values could be expected to increase by up to 20%. Throughout the paper, we also stress the ways in which $n_{\rm eff}$ depends on our ability to understand and control systematic effects in the measurements.
119123041
Observational constraints on the ultrahigh energy cosmic neutrino flux from the second flight of the ANITA experiment
The Antarctic Impulsive Transient Antenna (ANITA) completed its second Long Duration Balloon flight in January 2009, with 31 days aloft (28.5 live days) over Antarctica. ANITA searches for impulsive coherent radio Cherenkov emission from 200 to 1200 MHz, arising from the Askaryan charge excess in ultrahigh energy neutrino-induced cascades within Antarctic ice. This flight included significant improvements over the first flight in payload sensitivity, efficiency, and flight trajectory. Analysis of in-flight calibration pulses from surface and subsurface locations verifies the expected sensitivity. In a blind analysis, we find 2 surviving events on a background, mostly anthropogenic, of 0.97{+-}0.42 events. We set the strongest limit to date for 10{sup 18}-10{sup 21} eV cosmic neutrinos, excluding several current cosmogenic neutrino models.