Very Red and Extremely Red Galaxies in the Fields of z ~ 1.5 Radio-Loud Quasars

TL;DR

This study investigates the environment of z~1.5 radio-loud quasars, revealing an excess of red galaxies and candidate high-redshift, dusty, and passively evolving galaxies through multi-wavelength observations and photometric analysis.

Contribution

It provides new observational evidence of galaxy overdensities and dusty high-redshift galaxy populations around radio-loud quasars using diverse techniques.

Findings

Detected an excess of red galaxies near quasars.

Identified candidate dusty high-redshift galaxies.

Found some galaxies at the quasar redshift with evidence of dust reddening.

Abstract

We previously identified an excess of mostly red galaxies around 31 RLQs at z=1-2. These fields have an ERO (extremely red object, R-K>6) density 2.7 times higher than the field. Assuming the EROs are passively evolved galaxies at the quasar redshifts, they have characteristic luminosities of only ~L^*. We also present new observations of four z~1.54 RLQ fields: (1) Wide-field J & Ks data confirm an Abell richness ~2 excess within 140" of Q0835+580 but an excess only within 50" of Q1126+101. (2) In 3 fields we present deep narrow-band redshifted H-alpha observations. We detect five candidate galaxies at the quasar redshifts, a surface density 2.5x higher than the field. (3) SCUBA sub-mm observations of 3 fields detect 2 quasars and 2 galaxies with SEDs best fit as highly reddened galaxies at the quasar z. (4) H-band adaptive optics (AO) imaging is used to estimate redshifts for 2 red, bulge-dominated galaxies using the Kormendy relation. Both have structural redshifts foreground to the quasar, but these are not confirmed by photometric redshifts, possibly because their optical photometry is corrupted by scattered light from the AO guidestar. (5) We use quantitative SED fits to constrain the photometric redshifts z_ph for some galaxies. Most galaxies near Q0835+580 are consistent with being at its redshift, including a candidate very old passively evolving galaxy. Many very & extremely red objects have z_ph z_q, and dust reddening is required to fit most of them, including many objects whose fits also require relatively old stellar populations. Large reddenings of E(B-V)~0.6 are required to fit four J-K selected EROs, though all but one of them have best-fit z_ph>z_q. These objects may represent a population of dusty high-z galaxies underrepresented in optically selected samples. (Abridged)