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Register a new userSNLS: Overview and High-z Spectroscopy
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Authors
D. Andrew Howell
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The Supernova Legacy Survey (SNLS; http://cfht.hawaii.edu/SNLS) will discover and obtain griz lightcurves for more than 700 spectroscopically confirmed SNe Ia (0.3<z<0.9) to differentiate between competing models for Dark Energy. We fit the multicolor lightcurves of the candidates to determine which are likely SNe Ia and send them for follow-up spectroscopy to the Keck, VLT, and Gemini telescopes. Here we show the results from Gemini, where we send most of our highest redshift (0.6<z<0.9) targets.
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We present new techiques for improving the efficiency of supernova (SN) classification at high redshift using 64 candidates observed at Gemini North and South during the first year of the Supernova Legacy Survey (SNLS). The SNLS is an ongoing five year project with the goal of measuring the equation of state of Dark Energy by discovering and following over 700 high-redshift SNe Ia using data from the Canada-France-Hawaii Telescope Legacy Survey. We achieve an improvement in the SN Ia spectroscopic confirmation rate: at Gemini 71% of candidates are now confirmed as SNe Ia, compared to 54% using the methods of previous surveys. This is despite the comparatively high redshift of this sample, where the median SN Ia redshift is z=0.81 (0.155 <= z <= 1.01). These improvements were realized because we use the unprecedented color coverage and lightcurve sampling of the SNLS to predict whether a candidate is an SN Ia and estimate its redshift, before obtaining a spectrum, using a new technique called the SN photo-z. In addition, we have improved techniques for galaxy subtraction and SN template chi^2 fitting, allowing us to identify candidates even when they are only 15% as bright as the host galaxy. The largest impediment to SN identification is found to be host galaxy contamination of the spectrum -- when the SN was at least as bright as the underlying host galaxy the target was identified more than 90% of the time. However, even SNe on bright host galaxies can be easily identified in good seeing conditions. When the image quality was better than 0.55 arcsec the candidate was identified 88% of the time. Over the five-year course of the survey, using the selection techniques presented here we will be able to add approximately 170 more confirmed SNe Ia than would be possible using previous methods.
Aims: We present a quantitative study of a new data set of high redshift Type Ia supernovae spectra, observed at the Gemini telescopes during the first 34 months of the Supernova Legacy Survey. During this time 123 supernovae candidates were observed, of which 87 have been identified as SNe Ia at a median redshift of z=0.720. Spectra from the entire second year of the survey and part of the third year (59 total SNe candidates with 46 confirmed SNe Ia) are published here for the first time. The spectroscopic measurements made on this data set are used determine if these distant SNe comprise a population similar to those observed locally. Methods: Rest-frame equivalent width and ejection velocity measurements are made on four spectroscopic features. Corresponding measurements are presented for a set of 167 spectra from 24 low-z SNe Ia from the literature. Results: We show that there exists a sample at high redshift with properties similar to nearby SNe. No significant difference was found between the distributions of measurements at low and high redsift for three of the features. The fourth feature displays a possible difference that should be investigated further. Correlations between Type Ia SNe properties and host galaxy morphology were also found to be similar at low and high z, and within each host galaxy class we see no evidence for redshift-evolution in SN properties. A new correlation between SNe Ia peak magnitude and the equivalent width of SiII absorption is presented. We demonstrate that this correlation reduces the scatter in SNe Ia luminosity distances in a manner consistent with the lightcurve shape-luminosity corrections that are used for Type Ia SNe cosmology. Conclusions: We show that this new sample of SNLS SNe Ia has spectroscopic properties similar to nearby objects. (Abridged)
The High Contrast spectroscopy testbed for Segmented Telescopes (HCST) is being developed at Caltech. It aims at addressing the technology gap for future exoplanet imagers and providing the U.S. community with an academic facility to test components and techniques for high contrast imaging, focusing on segmented apertures proposed for future ground-based (TMT, ELT) and space-based telescopes (HabEx, LUVOIR). We present an overview of the design of the instrument and a detailed look at the testbed build and initial alignment. We offer insights into stumbling blocks encountered along the path and show that the testbed is now operational and open for business. We aim to use the testbed in the future for testing of high contrast imaging techniques and technologies with amongst with thing, a TMT-like pupil.
This proceeding broadly overviews the current landscape of heavy exotic spectroscopy. Such work includes the composition of certain X, Y , and Z states, and proceeds to discuss tetraquarks made exclusively of four quarks.
We present spectra taken with the Low Resolution Imaging Spectrograph on the Keck 10m telescope of spatially-resolved structures (fuzz) around the high-redshift radio-loud quasars PKS 0445+097 (z=2.108) and PKS 2338+042 (z=2.589). For PKS 0445+097 we find that there is faint extended HeII1640 and CIII]1909 from the quasar host galaxy. Both of the lines are broad (FWHM(HeII)=1000+-200 km/s and FWHM=2200+-600 km/s). The limits on the fluxes, the large line widths, and the line ratio HeII/CIII] are similar to that observed for high redshift radio galaxies. From the spectrum of PKS 2338+042, we find extended Ly-alpha emission on scales about 10 which is strongly one sided (on the side of the stronger, closer to the nucleus, more distorted radio lobe). The extended Ly-alpha line is broad with widths of over 1000 km/s. We also find weak extended CIV and HeII emission which has similar characteristics (line widths, line fluxes, and line ratios) to that of high redshift radio galaxies. In addition, we serendipitously discovered what appears to be a Ly-alpha emitting galaxy about 29 to the southeast of the quasar at z=2.665.
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