[Paper Review] LoTSS jellyfish galaxies. III. The first identification of jellyfish galaxies in the Perseus cluster

Ian Roberts, R. J. van Weeren+5 more|arXiv (Cornell University)|Jan 1, 2022

Galaxies: Formation, Evolution, Phenomena107 references36 citations

TL;DR

This study presents the first identification of jellyfish galaxies in the Perseus cluster using 144 MHz radio continuum observations from LOFAR, revealing one-sided radio tails and optical morphologies consistent with ram pressure stripping. The key finding is enhanced star formation on the leading side of galaxies, along with flatter spectral indices in disks and steeper indices in stripped tails, indicating complex radio emission processes driven by environmental quenching and star formation.

ABSTRACT

In this paper we report the first identification of jellyfish galaxies in the Perseus cluster (Abell 426). We identified four jellyfish galaxies (LEDA 2191078, MCG +07-07-070, UGC 2654, UGC 2665) within the central 2° ×2° (2.6 Mpc × 2.6 Mpc) of Perseus based on the presence of one-sided radio continuum tails that were detected at 144 MHz by the LOw Frequency ARray (LOFAR). The observed radio tails, as well as the orientation of morphological features in the rest-frame optical, are consistent with these four galaxies being impacted by ram pressure stripping as they orbit through the Perseus intracluster medium. By combining the LOFAR imaging at 144 MHz with 344 MHz imaging from the Karl G. Jansky Very Large Array, we derived spectral indices for the disks and the stripped tails of these jellyfish galaxies. We show that the spectral indices over the galaxy disks are quite flat, while the indices of the stripped tails are substantially steeper. We also identified a number of compact Hα + [NII] sources with narrowband imaging from the Isaac Newton Telescope. These sources are brighter along the leading side of the galaxy (i.e., opposite to the direction of the stripped tail), which is consistent with ram pressure induced star formation. Lastly, consistent with previous works in other clusters, we find that these jellyfish galaxies show enhanced radio luminosities for their observed star formation rates. Given the small distance to the Perseus cluster (D ∼ 70 Mpc, 1″ ≃ 340 pc), these galaxies are excellent candidates for multiwavelength follow-up observations to probe the impact of ram pressure stripping on galaxy star formation at subkiloparsec scales.

Motivation & Objective

• To identify jellyfish galaxies in the Perseus cluster using low-frequency radio continuum observations.
• To investigate the impact of ram pressure stripping on star formation and radio emission in cluster galaxies.
• To measure spectral indices across galaxy disks and stripped tails to probe cosmic ray electron aging and magnetic field structure.
• To analyze compact Hα + [NII] sources to assess ram pressure-induced star formation on the leading side of galaxies.
• To evaluate whether these jellyfish galaxies exhibit enhanced radio luminosities relative to the standard radio-SFR relation.

Proposed method

• Utilized 144 MHz continuum imaging from the LOFAR Two-metre Sky Survey (LoTSS) covering a 2°×2° region in the Perseus cluster.
• Combined LOFAR 144 MHz data with 344 MHz imaging from the Karl G. Jansky Very Large Array to derive spectral indices across galaxy disks and stripped tails.
• Performed narrowband Hα + [NII] imaging using the Isaac Newton Telescope to detect compact star-forming regions.
• Conducted multiwavelength analysis including rest-frame optical imaging and spectroscopic data to assess galaxy morphology and star formation activity.
• Applied spectral index analysis to distinguish between synchrotron aging and injection spectral indices in radio-emitting regions.
• Used cosmological parameters (ΩM = 0.3, ΩΛ = 0.7, H0 = 70 km s⁻¹ Mpc⁻¹) and cluster-centric radii relative to NGC 1275 for spatial context.

Experimental results

Research questions

• RQ1 Are jellyfish galaxies present in the Perseus cluster, and can they be identified via one-sided radio continuum tails at 144 MHz?
• RQ2 Is there evidence of enhanced star formation on the leading side of galaxies undergoing ram pressure stripping, as predicted by simulations?
• RQ3 How do the spectral indices of radio emission vary between galaxy disks and stripped tails, and what do they reveal about cosmic ray electron aging?
• RQ4 Do these jellyfish galaxies exhibit excess radio luminosity relative to their star formation rates, and what might be the physical origin?
• RQ5 What is the spatial distribution of compact Hα + [NII] sources relative to the direction of the stripped tail, and does it support ram pressure-induced star formation?

Key findings

• Four jellyfish galaxies (LEDA 2191078, MCG +07-07-070, UGC 2654, UCG 2665) were identified in the central 2°×2° of the Perseus cluster via one-sided 144 MHz radio tails.
• Compact Hα + [NII] sources are brighter on the leading side of the galaxies, opposite the stripped tail, indicating ram pressure-induced star formation.
• Spectral indices over the galaxy disks are flat, likely due to ionization losses in a dense interstellar medium, while those in the stripped tails are steeper and consistent with synchrotron aging.
• The spectral indices of the stripped tails are consistent with both the expected injection index from star formation and moderate steepening due to aging, though poorly constrained.
• Globally, these galaxies exhibit enhanced 144 MHz luminosities relative to the standard low-frequency radio luminosity–star formation rate relation, indicating a radio excess similar to other jellyfish galaxies.
• The Perseus cluster, at ~70 Mpc distance, offers a favorable target for high-resolution, multiwavelength follow-up to study ram pressure stripping at sub-kiloparsec scales.