The Optical Properties of Host Galaxies of Radio Sources in the Coma Cluster

Abstract

We present a comprehensive study of host galaxies of radio sources within the 1.35$R_{200}$ of the Coma cluster by combining deep 144MHz observations from the LOFAR Two-Metre Sky Survey (LoTSS-DR2) with optical spectroscopy and photometry from DESI and SDSS. We identify 79 spectroscopically confirmed cluster members with reliable radio emission and classify them into compact, extended, and tailed subsamples according to their radio morphologies. By combining their radio and optical properties, we find compact radio sources are predominantly associated with massive, quiescent galaxies driven by AGN activity, while tailed sources are largely hosted by star-forming galaxies, tracing ongoing ram pressure stripping (RPS). Using phase-space analysis and a projected infall time proxy ($d_R$), we find that extended sources are preferentially located in the cluster outskirts ($d_R > 1$), while tailed sources are concentrated in the intermediate infall region ($0.4 < d_R < 1.0$), highlighting the influence of the dense intracluster medium.

Figures (14)

• Figure S1: Spectroscopic data completeness. (Upper panel): Spectroscopic completeness as a function of r-band magnitude with in 1.35$R_{200}$. The vertical dashed line denotes $r = 19.5$ mag. (Bottom panel): Spatial distribution of the spectroscopic completeness. The colorbar represents the completeness at $r < 19.5$. The red solid circle indicates the radius of $R_{200}$, and red dashed circle indicates 1.35$R_{200}$.
• Figure S2: The $R-V$ diagram ($R/R_{200}$ vs. $V_{los}$) of galaxies in the Coma Cluster field. Grey points represent spectroscopic galaxies with $r < 19.5$ mag. The black dashed curves indicate the caustic lines. Blue points denote confirmed Coma cluster members located within the caustic boundaries. The 79 galaxies with detected radio emission (LOFAR 144 MHz) are highlighted by red squares.
• Figure S3: The LoTSS-DR2 radio continuum image of the Coma cluster region. This $4^\circ \times 4^\circ$ field is centered on NGC 4874, the brightest central galaxy of the cluster. Red circles are the same as Figure \ref{['fig:comp']}.
• Figure S4: Euclidean-normalized differential source counts at 144 MHz within $1.35R_{200}$. Data points show the total counts in the Coma field (purple circles) and confirmed cluster members (golden triangles). Overlaid are models from Galluzzi2025 (grey dash-dotted line) and Bonato2017 (black dotted line), accounting for diverse extragalactic radio populations. Error bars indicate $1\sigma$ uncertainties.
• Figure S5: Examples of radio sources classified by morphology: extended (E), compact (C), and tailed (T). The (top panels) display the LOFAR 144 MHz radio continuum images, each covering a field of view of 100$^{\prime\prime} \times 100^{\prime\prime}$, while the (bottom panels) show the corresponding optical images from DESI. In all panels, green "x" symbols indicate the optical galactic centers, and white crosses denote the centroids of the radio emission. The red dashed ellipses in the radio images represent the morphology detections of the radio emission. The white circles in the optical images have a radius of $6^{\prime\prime}$.