SIMBAD references

Using the alternative data release of the TIFR GMRT Sky Survey (TGSS), we studied the low-frequency properties of FR 0 radio galaxies, the large population of compact radio sources associated with red massive early-type galaxies revealed by surveys at 1.4GHz. We considered TGSS observations from FR0CAT, a sample formed by 104 FR 0s at z<0.05: all but one of them are covered by the TGSS, and 43 of them are detected above a 5σ limit of 17.5mJy. No extended emission has been detected around the FR 0s, corresponding to a luminosity limit of ≤4x10²³W/Hz over an area of 100kpcx100kpc. All but eight FR 0s have a flat or inverted spectral shape (α<0.5) between 150 MHz and 1.4GHz: this spectral behavior confirms the general paucity of optically thin extended emission within the TGSS beam, as is expected for their compact 1.4GHz morphology. Data at 5GHz were used to build their radio spectra, which are also generally flat at higher frequencies. By focusing on a sub-sample of FR 0s with flux density >50mJy at 1.4GHz, we found that ∼75% of them have a convex spectrum, but with a smaller curvature than the more powerful gigahertz peaked-spectrum sources (GPS). The typical FR 0s radio spectrum is better described by a gradual steepening toward high frequencies, rather than to a transition from an optically-thick to an optically-thin regime, possibly observed in only ∼15% of the sample.