Characterising the extended morphologies of BL Lacs at 144 MHz with LOFAR

Abstract

We present a morphological and spectral study of a sample of 99 BL Lacs using the LOFAR Two-Metre Sky Survey Second Data Release (LDR2). Extended emission has been identified at gigahertz frequencies around BL Lacs, but with LDR2 it is now possible to systematically study their morphologies at 144 MHz, where more diffuse emission is expected. LDR2 reveals the presence of extended radio structures around 66/99 of the BL Lac nuclei, with angular extents ranging up to 115 arcseconds, corresponding to spatial extents of 410 kpc. The extended emission is likely to be both unbeamed diffuse emission and beamed emission associated with relativistic bulk motion in jets. The spatial extents and luminosities of the extended emission are consistent with the AGN unification scheme where BL Lacs correspond to low-excitation radio galaxies with the jet axis aligned along the line-of-sight. While extended emission is detected around the majority of BL Lacs, the median 144-1400 MHz spectral index and core dominance at 144 MHz indicate that the core component contributes ~42% on average to the total low-frequency flux density. A stronger correlation was found between the 144 MHz core flux density and the gamma-ray photon flux (r = 0.69) compared to the 144 MHz extended flux density and the gamma-ray photon flux (r = 0.42). This suggests that the radio-to-gamma-ray connection weakens at low radio frequencies because the population of particles that give rise to the gamma-ray flux are distinct from the electrons producing the diffuse synchrotron emission associated with spatially-extended features.

arXiv comment15 pages, 9 figures, accepted for publication in the Astrophysical Journal Supplement Series

References in corpus (46)

• Astropy: A Community Python Package for Astronomy
• The NumPy array: a structure for efficient numerical computation
• Unified Schemes for Radio-Loud Active Galactic Nuclei
• The Large Area Telescope on the Fermi Gamma-ray Space Telescope Mission
• LOFAR: The LOw-Frequency ARray
• Fermi Large Area Telescope Fourth Source Catalog
• A gravitational-wave standard siren measurement of the Hubble constant
• A Cosmology Calculator for the World Wide Web
• On the fundamental dichotomy in the local radio-AGN population: accretion, evolution, and host galaxy properties
• The LOFAR Two-metre Sky Survey - I. Survey Description and Preliminary Data Release
• The LOFAR Two-metre Sky Survey - II. First data release
• CRATES: An All-Sky Survey of Flat-Spectrum Radio Sources
• The Fourth Catalog of Active Galactic Nuclei Detected by the Fermi Large Area Telescope
• The 5th edition of the Roma-BZCAT. A short presentation
• The Last of FIRST: The Final Catalog and Source Identifications
• The LOFAR Two Meter Sky Survey: Deep Fields, I -- Direction-dependent calibration and imaging
• Faceting for direction-dependent spectral deconvolution
• Radio interferometric gain calibration as a complex optimization problem
• From the Blazar Sequence to the Blazar Envelope: Revisiting the Relativistic Jet Dichotomy in Radio-loud AGN
• A pilot study of the radio-emitting AGN population: the emerging new class of FR0 radio-galaxies
• The radio/gamma-ray connection in Active Galactic Nuclei in the era of the Fermi Large Area Telescope
• Non-linear Kalman filters for calibration in radio interferometry
• A radio spectral index map and catalogue at 147-1400 MHz covering 80 per cent of the sky
• Numerical modelling of the lobes of radio galaxies in cluster environments II: Magnetic field configuration and observability
• The Deep X-ray Radio Blazar Survey (DXRBS). II. New Identifications
• The LOFAR LBA Sky Survey I. survey description and preliminary data release
• Optical spectroscopic observations of $\gamma$-ray blazar candidates VI. Further observations from TNG, WHT, OAN, SOAR and Magellan telescopes
• Making Fanaroff-Riley I radio sources. Numerical Hydrodynamic 3D Simulations of Low Power Jets
• Unveiling the nature of the unidentified gamma-ray sources III: gamma-ray blazar-like counterparts at low radio frequencies
• Optical spectroscopic observations of gamma-ray blazar candidates III. The 2013/2014 campaign in the Southern Hemisphere
• Intermittent jet activity in the radio galaxy 4C29.30?
• The Gamma-ray Blazar Quest: new optical spectra, state of art and future perspectives
• Optical spectroscopic observations of gamma-ray blazar candidates IV. Results of the 2014 follow-up campaign
• High-energy sources at low radio frequency: the Murchison Widefield Array view of Fermi blazars
• The low-frequency radio catalog of flat spectrum sources
• Optical spectroscopic survey of a sample of Unidentified Fermi objects: II
• Blazars spectral properties at 74 MHz
• Optical spectroscopic observations of gamma-ray blazar candidates. IX. Optical archival spectra and further observations from SOAR and OAGH
• Optical characterization of WISE selected blazar candidates
• The Radio/Gamma Connection of Blazars from High to Low Radio Frequencies
• The large-scale environment of FR 0 radio galaxies
• Deciphering the Large-Scale Environment of Radio Galaxies in the Local Universe II. A Statistical Analysis of Environmental Properties
• Blazars in the LOFAR Two-Metre Sky Survey First Data Release
• The Extreme Ultraviolet Deficit - Jet Connection in the Quasar 1442+101
• Radio spectral properties of cores and extended regions in blazars in the MHz regime
• From Nearby Low Luminosity AGN to High Redshift Radio Galaxies: Science Interests with SKA

Cited by in corpus (6)

• Searching for nascent planetary nebulae: OHPNe candidates in the SPLASH survey
• A Multiwavelength Machine-learning Approach to Classifying X-ray Sources in the Fields of Unidentified 4FGL-DR4 sources
• Detecting intermediate mass black holes in midiquasars with current and future surveys
• The Accretion Properties and Jet Mechanisms for the Low-Excitation Radio Galaxies
• Linking {\it Fermi} blazars and radio galaxies through accretion and jet radiation mechanisms
• Modelling observable signatures of jet-ISM interaction: thermal emission and gas kinematics