The BlueDOG at Cosmic Noon: A Possible Analog to Little Red Dots?

TL;DR

This study reports the discovery and analysis of a hyperluminous BlueDOG at z=2.6, revealing its massive, dust-obscured nature, AGN activity, and potential similarity to JWST's Little Red Dots, while exploring the origin of its blue-excess emission.

Contribution

It presents the first detailed multiwavelength analysis of a BlueDOG, comparing it to Little Red Dots, and investigates the origin of its blue-excess emission using spectroscopic and SED modeling.

Findings

BlueDOG is a highly massive, dust-obscured galaxy with significant old stellar populations.

The galaxy hosts a supermassive black hole with mass ~10^10.2 solar masses.

UV emission lines are powered by an active galactic nucleus, but the blue-excess origin remains ambiguous.

Abstract

We discovered a hyperluminous dust-obscured galaxy with mysterious blue-excess emission (BlueDOG) in rest-frame UV of its spectral energy distribution (SED) from a multi-wavelength survey in the AKARI Deep Field - South (ADF-S). We present the results of SED analysis with multiwavelength photometric data and spectroscopic analysis, observed with Gemini-S/GMOS, FLAMINGOS-2, to explore the origin of blue-excess emission of a hyperluminous BlueDOG, ADFS-KMTDOG-102, at z=2.6. The SED analysis shows that this BlueDOG is a highly massive system (log $M_{*}$/$M_\odot=12.3$) with substantial extinction. Additionally, the proportion of the old stellar population exceeds that of the young stellar population, which suggests stellar evolution cumulated from the early universe. The mass of supermassive black hole (SMBH) estimated using the extinction-corrected broad H$\rm\alpha$ emission line yields log $M_{\rm BH}$/$M_\odot$=10.2. We discuss the similarity between the BlueDOG and 'Little Red Dots' (LRDs), recently discovered with the James Webb Space Telescope, showing SED shapes remarkably similar to those of LRDs. The UV emission line ratios indicate that the emission lines are primarily powered by the central active galactic nuclei (AGN). In contrast, the origin of the blue-excess UV continuum remains ambiguous, since both recent star formation and AGN-induced scattered light are viable explanations, based on the results from the SED fitting and scattered light modeling.