The Spitzer view of FR-I radio galaxies: on the origin of the nuclear mid-infrared continuum

Abstract

We present Spitzer MIR spectra of 25 FR-I radio galaxies and investigate the nature of their MIR continuum emission. MIR spectra of star-forming galaxies and quiescent elliptical galaxies are used to identify host galaxy contributions while radio/optical core data are used to isolate the nuclear non-thermal emission. Out of the 15 sources with detected optical compact cores, four sources are dominated by emission related to the host galaxy. Another four sources show signs of warm, nuclear dust emission: 3C15, 3C84, 3C270, and NGC 6251. It is likley that these warm dust sources result from hidden AGN of optical spectral type 1. The MIR spectra of seven sources are dominated by synchrotron emission, with no significant component of nuclear dust emission. In parabolic SED fits of the non-thermal cores FR-Is tend to have lower peak frequencies and stronger curvature than blazars. This is roughly consistent with the common picture in which the core emission in FR-Is is less strongly beamed than in blazars.

37 pages, 14 figures, accepted for publication in ApJ

References in corpus (22)

• The Host Galaxies and Classification of Active Galactic Nuclei
• Mid-IR Galaxy Classification Based on Silicate Obscuration and PAH Equivalent Width
• Spitzer Reveals Hidden Quasar Nuclei in Some Powerful FR II Radio Galaxies
• Spitzer IRS spectra of a large sample of Seyfert galaxies: a variety of infrared SEDs in the local AGN population
• An optical spectroscopic survey of the 3CR sample of radio galaxies with z<0.3. I. Presentation of the data
• Aromatic Features in AGN: Star-Forming Infrared Luminosity Function of AGN Host Galaxies
• Magnetic Fields in the Center of the Perseus Cluster
• SPITZER IRS spectra of Virgo early type galaxies: detection of stellar silicate emission
• Properties of polycyclic aromatic hydrocarbons in local elliptical galaxies revealed by the Infrared Spectrograph on Spitzer
• An infrared survey of brightest cluster galaxies: Paper I
• Mid-Infrared Diagnostics of LINERs
• On the origin of X-ray emission in some FR Is: ADAF or jet?
• The Mid-Infrared Emission of M87
• Hubble Space Telescope Near-Infrared Snapshot Survey of 3CR radio source counterparts at low redshift
• Multifrequency VLA observations of the FR I radio galaxy 3C 31: morphology, spectrum and magnetic field
• The origin of the infrared emission in radio galaxies I: new mid- to far-infrared and radio observations of the 2Jy sample
• Jet Speeds in Wide Angle Tailed Radio Galaxies
• The prevalence of FRI radio quasars
• Thermal and Non-Thermal Infrared Emission from M87
• Optical Polarimetry of the Jets of Nearby Radio Galaxies: I. The Data
• The structure of the jet in 3C 15 from multi-band polarimetry
• On the nature of optical nuclei in FR I radio-galaxies from ACS/HST imaging polarimetry

Cited by in corpus (11)

• Compact steep-spectrum and peaked-spectrum radio sources
• Far-infrared line spectra of active galaxies from the Herschel/PACS Spectrometer: the complete database
• Spitzer Mid-IR Spectroscopy of Powerful 2Jy and 3CRR Radio Galaxies. II. AGN Power Indicators and Unification
• The TeV-emitting radio galaxy 3C 264. VLBI kinematics and SED modeling
• A census of radio-selected AGN on the COSMOS field and of their FIR properties
• Estimating the Jet Power of Mrk\,231 During the 2017-2018 Flare
• Near-infrared Hubble Space Telescope polarimetry of a complete sample of narrow-line radio galaxies
• Profile comparison of the 6-9 $\mu$m polycyclic aromatic hydrocarbon bands in starburst-dominated galaxies
• Deep Herschel observations of the 2Jy sample: assessing the non-thermal and AGN contributions to the far-IR continuum
• The origin of X-ray emission in 3CRR sources: hints from mid-infrared Spitzer observations
• Searching for Nuclear Obscuration in the Infrared Spectra of Nearby FR I Radio Galaxies