Документ взят из кэша поисковой машины. Адрес оригинального документа : http://hea-www.harvard.edu/AstroStat/astro193/MengGu_PCAofMaGNA.pdf Дата изменения: Wed May 6 18:41:34 2015 Дата индексирования: Sun Apr 10 12:11:52 2016 Кодировка: Поисковые слова: sky

PCA Analysis of MaNGA Sky Spectra
Meng Gu


What is PCA
Set of observations of possibly correlated variables

Set of values of linearly uncorrelated variables (PCs) Straightforward & Has been applied to astro. spectra for many purposes.

QSO-PCA

Bailey 2012


Why PCA in Sky Subtraction
To deal with complex and ever-changing telluric featu L s el One Body ree,vPCA method is promising!

Before

Sky Residual PCA Reconstructed

Body Level Two

Sharp y LarkinsThree Bod& P evel on 2010

After

Body Level Four Body Level Five

Wild & Hewett 2005

PCA has been applied to surveys like SDSS, GAMA, and WiggleZ. Has been proved to be efficient in correcting OH residuals, and recovering weak spectral features


MaGNA: Coma Deep Plate
1. Stellar populations in low surface brightness regions: outskirts of elliptical and ICL 2. Radial dependent star-formation history of BCGs: gradients of stellar population


MaGNA: Coma Deep Plate

Sky subtraction is crucial for all of our scientific goals Especially for the stellar population properties at low surface brightness


Sky Spectra From Coma-Plate
1620 sky spectra from 18 Body Lev exposuresel One Selection criteria:

Sky Spectra

Body Level Two
Residuals from Default Subtraction

1. -0.Body Level Three 2
Body Level Five

1564 sky spectra and their residual from default subtraction are used for PCA


Mean and the First 6 Components from PCA Analysis of Sky and Residual

Empirical PCA-correction using sky-residuals is very efficient

Red: PCA on Sky Spectra Blue: PCA on Sky Residual


Residual of Reconstructed Sky for a Sky Bundle

Red: Default Subtraction Blue: PCA-corrected


One Exposure - 15 mins


One Exposure - 15 mins


Future Work
Applied careful masks or weights to the sky spectra Explore more sophisticated PCA algorithm: e.g. Robust-PCA Use SSP model + Noise + Observed Sky to demonstrate the robustness of this method MaNGA has significantly improved the sky-subtraction method, but the PCA method can still help improve the sky residuals of SDSS/BOSS spectra