Herschel/PACS far-infrared photometry of two z>4 quasars

TL;DR

This study uses Herschel/PACS far-infrared observations to analyze the dust properties and star formation activity in two high-redshift quasars, revealing excess cold dust emission indicative of vigorous star formation.

Contribution

First FIR measurements of two z>4 quasars with Herschel/PACS, constraining their dust temperatures and star formation activity, highlighting differences from low-redshift quasar SEDs.

Findings

Both quasars detected in FIR, showing excess cold dust emission.

FIR SEDs differ from low-redshift quasars, indicating vigorous star formation.

Potential confusion from nearby object affecting FIR luminosity estimates.

Abstract

We present Herschel far-infrared (FIR) observations of two sub-mm bright quasars at high redshift: SDSS J1148+5251 (z=6.42) and BR 1202-0725 (z=4.69) obtained with the PACS instrument. Both objects are detected in the PACS photometric bands. The Herschel measurements provide additional data points that constrain the FIR spectral energy distributions (SEDs) of both sources, and they emphasise a broad range of dust temperatures in these objects. For lambda_rest ~< 20mu, the two SEDs are very similar to the average SEDs of quasars at low redshift. In the FIR, however, both quasars show excess emission compared to low-z QSO templates, most likely from cold dust powered by vigorous star formation in the QSO host galaxies. For SDSS J1148+5251 we detect another object at 160mu with a distance of ~10 arcseconds from the QSO. Although no physical connection between the quasar and this object can be shown with the available data, it could potentially confuse low-resolution measurements, thus resulting in an overestimate of the FIR luminosity of the z=6.42 quasar.