Photometric Selection of Emission Line Galaxies, Clustering Analysis and a Search for the ISW effect

TL;DR

This paper develops a method to select emission line galaxies using SDSS photometry, measures their clustering properties, and searches for the ISW effect, finding a weak positive correlation in WMAP data.

Contribution

It introduces a simple colour-cut technique for photometric selection of emission line galaxies up to z<1 and calibrates it with spectroscopic data, enabling clustering and ISW analyses.

Findings

Photometric redshifts of selected galaxies range from 0.32 to 0.65.

Measured clustering lengths increase with redshift, from 2.64 to 5.88 h^{-1} Mpc.

Detected a weak positive ISW signal with 1.7 sigma significance.

Abstract

We investigate the use of simple colour cuts applied to the SDSS optical imaging to perform photometric selections of emission line galaxies out to z<1. From colour-cuts using the SDSS g, r and i bands, we obtain mean photometric redshifts of z=0.32+-0.08, z=0.44+-0.12 and z=0.65+-0.21. We further calibrate our high redshift selection using spectroscopic observations with the AAOmega spectrograph on the 4m Anglo-Australian Telescope (AAT), observing ~50-200 galaxy candidates in 4 separate fields. With just 1-hour of integration time and with seeing of ~1.6", we successfully determined redshifts for ~65% of the targeted candidates. We calculate the angular correlation functions of the samples and find correlation lengths of r0=2.64 h-1 Mpc, r0=3.62 h-1 Mpc and r0=5.88 h-1 Mpc for the low, mid and high redshift samples respectively. Comparing these results with predicted dark matter clustering, we estimate the bias parameter for each sample to be b=0.70, b=0.92 and b=1.46. We calculate the 2-point redshift-space correlation function at z~0.6 and find a clustering amplitude of s0=6.4 h-1 Mpc. Finally, we use our photometric sample to search for the Integrated Sachs-Wolfe signal in the WMAP 5yr data. We cross-correlate our three redshift samples with the WMAP W, V, Q and K bands and find an overall trend for a positive signal similar to that expected from models. However, the signal in each is relatively weak. Combining all three galaxy samples we find a signal of wTg(<100')=0.20+-0.12 microK in the WMAP W-band, a significance of 1.7sigma.