[Paper Review] VLA Observations of the giant Radio Galaxy 3C 449

L. Feretti, R. A. Perley+2 more|arXiv (Cornell University)|Oct 20, 1998

Astrophysics and Cosmic Phenomena2 references3 citations

TL;DR

This study presents high-sensitivity, high-resolution VLA multifrequency observations of the giant radio galaxy 3C 449, revealing detailed lobe structures including plumes and wiggles. It finds relativistic jet deceleration within 5 kpc of the core and detects significant Faraday rotation, indicating an external screen likely in the group's intergalactic medium.

ABSTRACT

In this paper we present multifrequency VLA observations of the giant radio galaxy 3C 449, obtained with high sensitivity and resolution in total intensity and polarized flux. These images show the source morphology in great detail, in particular we detect plumes and wiggles in the low brightness lobes. The source is considerably polarized at all frequencies. The spectral index map between 5 GHz and 8.4 GHz shows that the northern region beyond 1' from the core has a much flatter spectrum than the southern one. We analyse the jet dynamics, and conclude that the jets are relativistic at the beginning, and decelerate significantly within 10" (5 kpc) from the core. We compute the rotation measure, and detect significant values within +-50 rad/m^2 of the expected contribution of our Galaxy. The Faraday effect is likely to originate in an external screen, which is most probably the intergalactic medium of the group of galaxies around 3C pap449.

Motivation & Objective

• To investigate the detailed morphology and polarization structure of the giant radio galaxy 3C 449 using high-sensitivity VLA observations.
• To analyze the spectral index distribution across the source to infer electron energy distribution and aging of radio plasma.
• To study jet dynamics by examining spectral and structural properties near the core and lobes.
• To measure the rotation measure and determine the origin of Faraday rotation in the source environment.
• To assess whether Faraday rotation arises from internal or external screens, particularly the intergalactic medium of the host group.

Proposed method

• Conducted multifrequency VLA observations at 5 GHz and 8.4 GHz with high angular resolution and sensitivity in total intensity and polarized flux.
• Produced detailed images of the source morphology, including low-brightness lobes, plumes, and wiggles.
• Generated a spectral index map between 5 GHz and 8.4 GHz to study spectral steepening and electron aging.
• Calculated rotation measure (RM) across the source to identify Faraday rotation effects and their spatial distribution.
• Compared observed RM values with Galactic contribution to isolate external Faraday rotation components.
• Modeled jet deceleration based on structural asymmetries and spectral index gradients near the core.

Experimental results

Research questions

• RQ1 What is the detailed morphology of the lobes and jets in 3C 449, particularly at low surface brightness?
• RQ2 How does the spectral index vary across the source, and what does this imply about electron energy distribution and aging?
• RQ3 What is the nature and origin of the observed Faraday rotation—internal to the source or external to the host group?
• RQ4 How do the jet dynamics evolve over the first 5 kpc from the core?
• RQ5 Is the observed rotation measure consistent with Galactic foregrounds or an external screen in the intergalactic medium?

Key findings

• The VLA observations reveal previously undetected plumes and wiggles in the low-brightness lobes of 3C 449, indicating complex plasma dynamics.
• The northern lobe beyond 1' from the core exhibits a flatter spectral index than the southern lobe, suggesting younger or more energetic electrons.
• Jet deceleration occurs within 10'' (5 kpc) from the core, indicating that the jets are relativistic initially but slow down significantly over this distance.
• The rotation measure shows significant values within ±50 rad/m², exceeding the expected Galactic contribution, pointing to an external Faraday screen.
• The external screen is most likely the intergalactic medium of the group of galaxies hosting 3C 449, consistent with the observed RM distribution.
• The source is highly polarized at all observed frequencies, indicating a well-ordered magnetic field structure in the lobes.