Dust in high-z radio-loud AGN

TL;DR

This study investigates dust presence in high-redshift radio-loud AGN through millimeter and submillimeter observations, revealing thermal dust emission in one galaxy and constraining dust mass in another, with implications for understanding early galaxy evolution.

Contribution

First detection of thermal dust emission in a high-z radio galaxy, MG1019+0535, using millimeter observations, and new constraints on dust mass in radio-loud AGN at high redshift.

Findings

MG1019+0535 shows a 1.25-mm flux excess indicating dust emission.

Dust mass in 1243+036 is constrained to less than 10^8 solar masses.

Radio-loud quasars' spectra steepen from radio to far-infrared at high redshift.

Abstract

We present continuum observations of a small sample of high-redshift, radio-loud AGN (radio galaxies and quasars) aimed at the detection of thermal emission from dust. Seven AGN were observed with IRAM and SEST at 1.25mm; two of them, the radio galaxies 1243+036 ($z \sim 3.6$) and MG1019+0535 ($z \sim 2.8$) were also observed at 0.8mm with the JCMT submillimetre telescope. Additional VLA observations were obtained in order to derive the spectral shape of the synchrotron radiation of MG1019+0535 at high radio frequencies. MG1019+0535 and TX0211$-$122 were expected to contain a large amount of dust based on their depleted Ly$\alpha$ emission. The observations suggest a clear 1.25-mm flux density excess over the synchrotron radiation spectrum of MG1019+0535, suggesting the presence of thermal emission from dust in this radio galaxy, whereas the observations of TX0211$-$122 were not sensitive enough to meaningfully constrain its dust content. On the other hand, our observations of 1243+036 provide a stringent upper limit on the total dust mass of $<10^8$ M$_{\odot}$. Finally, we find that the spectra of the radio-loud quasars in our sample ($2 < z < 4.5$) steepen between rest-frame radio and the far-infrared. We discuss the main implications of our results, concentrating on the dusty radio galaxy, MG1019+0535.