Letter to the Editor

Absence of nuclear polycyclic aromatic hydrocarbon emission from a compact starburst: The case of the type-2 quasar Mrk 477

¹ Instituto de Astrofísica de Canarias, Calle Vía Láctea, s/n, 38205 La Laguna, Tenerife, Spain
e-mail: cra@iac.es
² Departamento de Astrofísica, Universidad de La Laguna, 38206 La Laguna, Tenerife, Spain
³ Instituto de Radioastronomía and Astrofísica (IRyA-UNAM), 3-72 (Xangari), 8701 Morelia, Mexico
⁴ Department of Physics, University of Oxford, Oxford OX1 3RH, UK
⁵ Centro de Astrobiología (CSIC-INTA), Ctra. de Ajalvir, Km 4, 28850 Torrejón de Ardoz, Madrid, Spain
⁶ Observatorio Astronómico Nacional (OAN-IGN)-Observatorio de Madrid, Alfonso XII, 3, 28014 Madrid, Spain
⁷ Centro de Astrobiología (CAB), CSIC-INTA, Camino Bajo del Castillo s/n, 28692 Villanueva de la Cañada, Madrid, Spain
⁸ Space Telescope Science Institute, Baltimore, MD 21218, USA
⁹ Department of Physics & Astronomy, University of Sheffield, S3 7RH Sheffield, UK
¹⁰ Korea Astronomy and Space Science Institute 776, Daedeokdae-ro, Yuseong-gu, 34055 Daejeon, Republic of Korea
¹¹ Instituto de Astrofísica de Andalucía – CSIC, Glorieta de la Astronomía s/n, 18008 Granada, Spain

Received: 8 November 2022
Accepted: 1 December 2022

Abstract

Mrk 477 is the closest type-2 quasar, at a distance of 163 Mpc. This makes it an ideal laboratory for studying the interplay between nuclear activity and star formation with a great level of detail and signal-to-noise. In this Letter we present new mid-infrared (mid-IR) imaging and spectroscopic data with an angular resolution of 0.4″ (∼300 pc) obtained with the Gran Telescopio Canarias instrument CanariCam. The N-band (8–13 μm) spectrum of the central ∼400 pc of the galaxy reveals [S IV]λ10.51 μm emission, but no 8.6 or 11.3 μm polycyclic aromatic hydrocarbon (PAH) features, which are commonly used as tracers of recent star formation. This is in stark contrast with the presence of a nuclear starburst of ∼300 pc in size, an age of 6 Myr, and a mass of 1.1×10⁸ M_⊙, as constrained from ultraviolet Hubble Space Telescope observations. Considering this, we argue that even the more resilient, neutral molecules that mainly produce the 11.3 μm PAH band are most likely being destroyed in the vicinity of the active nucleus despite the relatively large X-ray column density, log N_H = 23.5 cm⁻², and modest X-ray luminosity, 1.5×10⁴³ erg s⁻¹. This highlights the importance of being cautious when using PAH features as star formation tracers in the central region of galaxies to evaluate the impact of feedback from active galactic nuclei.