Resolving the Host Galaxy of a Distant Blazar with LBT/LUCI1 + ARGOS

TL;DR

This study uses advanced adaptive optics at the Large Binocular Telescope to resolve the host galaxy of a distant VHE blazar, enabling redshift estimation and insights into the EBL's effects on gamma-ray spectra.

Contribution

First direct imaging of the host galaxy of HESS J1943+213 using adaptive optics, providing a new redshift estimate for this VHE blazar.

Findings

Host galaxy well fitted by a Sersic profile with n~2

Estimated redshift of z~0.21 consistent with EBL models

Demonstrates the effectiveness of adaptive optics in resolving faint host galaxies

Abstract

BL Lac objects emitting in the Very High Energy (VHE) regime are unique tools to peer into the properties of the Extragalactic Background Light (EBL). However, due to the typical absence of features in their spectra, the determination of their redshifts has proven challenging. In this work we exploit the superb spatial resolution delivered by the new Advanced Rayleigh guided Ground layer adaptive Optics System (ARGOS) at the Large Binocular Telescope to detect the host galaxy of HESS J1943+213, a VHE emitting BL Lac shining through the Galaxy. Deep H-band imaging collected during the ARGOS commissioning allowed us to separate the contribution of the nuclear emission and to unveil the properties of the host galaxy with unprecedented detail. The host galaxy is well fitted by a S\'ersic profile with index of n~2 and total magnitude of H~16.15 mag. Under the assumption that BL Lac host galaxies are standard candles, we infer a redshift of z~0.21. In the framework of the current model for the EBL, this value is in agreement with the observed dimming of the VHE spectrum due to the scatter of energetic photons on the EBL.