[Paper Review] Radio morphology of southern narrow-line Seyfert 1 galaxies with the JVLA observations

S. Chen, E. Järvelä+9 more|arXiv (Cornell University)|Jun 2, 2020

Astrophysical Phenomena and Observations2 citations

TL;DR

This study presents new 5.5 GHz JVLA C-configuration observations of southern narrow-line Seyfert 1 galaxies, revealing that radio emission in NLS1s is predominantly compact at kpc-scale, with only a few showing diffuse emission. It finds that steep-spectrum NLS1s have higher radio luminosities, likely due to misaligned jets or outflows, while flat-spectrum sources show core-dominated emission, and identifies new NLS1s with kpc-scale jets and star formation, challenging assumptions about jet formation requiring massive black holes.

ABSTRACT

We present the results of new radio observations carried out with the Karl G. Jansky Very Large Array C-configuration at 5.5 GHz for a sample of southern narrow-line Seyfert 1 galaxies (NLS1s). This work increases the number of known radio-detected NLS1s in the southern hemisphere, and confirms that the radio emission of NLS1s is mainly concentrated in a central region at kpc-scale and only a few sources show diffuse emission. In radio-quiet NLS1s, the radio luminosity tends to be higher in steep-spectrum sources and be lower in flat-spectrum sources, which is opposite to radio-loud NLS1s. This may be because the radio emission of steep NLS1s is dominated by misaligned jets, AGN-driven outflows, or star formation superposing on a compact core. Instead the radio emission of flat NLS1s may be produced by a central core which has not yet developed radio jets and outflows. We discover new NLS1s harboring kpc-scale radio jets and confirm that a powerful jet does not require a large-mass black hole to be generated. We also find sources dominated by star formation. These NLS1s could be new candidates in investigating the radio emission of different mechanisms.

Motivation & Objective

• To expand the sample of radio-detected narrow-line Seyfert 1 galaxies in the southern hemisphere using high-resolution JVLA observations.
• To investigate the radio morphology and luminosity properties of NLS1s, particularly distinguishing between flat-spectrum and steep-spectrum sources.
• To determine the dominant physical mechanisms behind radio emission in NLS1s, including jets, outflows, and star formation.
• To test whether powerful radio jets can form in NLS1s with low-mass black holes, challenging existing jet formation paradigms.
• To identify new candidates for studying multi-component radio emission mechanisms in AGN.

Proposed method

• Conducted sensitive radio observations at 5.5 GHz using the Karl G. Jansky Very Large Array in C-configuration for a sample of southern NLS1s.
• Employed interferometric imaging techniques to resolve kpc-scale radio structures and distinguish compact cores from extended emission.
• Classified sources based on spectral index (flat vs. steep spectrum) to infer the nature of their radio emission mechanisms.
• Analyzed radio luminosity distributions across spectral types to compare with known radio-loud and radio-quiet AGN populations.
• Used morphological and spectral diagnostics to identify potential contributions from star formation, misaligned jets, or AGN-driven outflows.
• Cross-referenced radio morphologies with known black hole mass estimates to test jet formation dependencies on black hole mass.

Experimental results

Research questions

• RQ1 What is the dominant radio morphology (compact core vs. extended jet) in southern NLS1s observed at 5.5 GHz?
• RQ2 How does radio luminosity vary between flat-spectrum and steep-spectrum NLS1s, and what does this imply about emission mechanisms?
• RQ3 Can powerful kpc-scale radio jets form in NLS1s with low-mass black holes, as suggested by the observed morphology?
• RQ4 To what extent is star formation contributing to the observed radio emission in NLS1s?
• RQ5 What physical mechanisms—such as misaligned jets, outflows, or star formation—best explain the radio emission in different NLS1 subtypes?

Key findings

• The radio emission in most NLS1s is concentrated in a compact core at kpc-scale, with only a few sources showing diffuse or extended emission.
• Radio-quiet NLS1s with steep spectra exhibit higher radio luminosities than those with flat spectra, contrary to the trend seen in radio-loud NLS1s.
• Steep-spectrum NLS1s likely host misaligned jets, AGN-driven outflows, or have star formation superposed on a compact core as the dominant emission mechanism.
• Flat-spectrum NLS1s show core-dominated emission, suggesting the absence of developed jets or outflows, possibly indicating an early evolutionary phase.
• New NLS1s with kpc-scale radio jets were discovered, demonstrating that powerful jets can form even in systems with low-mass black holes.
• Several sources show signs of star formation dominance in their radio emission, making them prime candidates for studying multi-component radio emission mechanisms.