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Fig. 2 610 MHz (left panel) and 240 MHz (right panel) radio contours overlaid on their DSS optical images. The restoring beam is shown in lower left corner of each map. The contour levels are shown at the bottom of each map. The first lowest radio contour is about 4σ − 5σ of the rms noise value in each map. The source name and radio frequency is mentioned at the top left of each map. The same plotting convention is followed for other sources.

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	Fig. 4 Four-point (240 MHz, 610 MHz, 1.4 GHz, and 5.0 GHz) radio spectra of Seyfert galaxies in our sample. The dotted line connects the flux density points and dashed line shows the least chi-square linear fit to the spectral points. Radio spectra of Seyfert types 1s and 2s are shown in the left and right panels, respectively.
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Appendix A: Notes on individual sources

In this section we describe the radio properties of the individual sources in our sample.

Appendix A.1: MRK 6

Kharb et al. (2006) present a detailed study of MRK 6 radio morphology and report that the radio emission is seen on three different spatial scales i.e.,~7.5 kpc bubbles, ~1.5 kpc bubbles lying nearly orthogonal to each other, and a ~1 kpc radio jet lying orthogonal to the 1.5 kpc bubble. They suggest that the existence of kpc scale radio bubbles/lobes can be attributed to the radio relics related to past episodic nuclear activity. Our radio images at 610 MHz and 240 MHz show only a single component that is fitted with elliptical Gaussians of 10 and 2476, respectively. The radio emission at 610 MHz and 240 MHz are likely to include all the emitting components detected by Kharb et al. (2006) because the combined 5.0 GHz flux density of all the components in Kharb et al. (2006) follow the spectral shape determined by our 240 MHz, 610 MHz GMRT, and 1.4 GHz NVSS flux densities.

Appendix A.2: NGC 3227

The 8.4 GHz VLA observations show north-south elongated nuclear radio emission, and at sub-arcsec resolution, the core is resolved into 04 double sources (Mundell et al. 1995). The 5.0 GHz VLA “D” array observations show the kpc-scale extended radio emission, which is interpreted as the emission from star-forming host galaxy disk (Gallimore et al. 2006). Our GMRT images at 610 MHz and 240 MHz show radio emission as nearly unresolved point sources that are fitted with an elliptical Gaussian of 8 and 3202, respectively. The fitted powerlaw radio spectrum over 240 MHz to 5.0 GHz renders spectral index (α_int) ~  − 0.53, while there is an indication of spectral flattening toward lower frequencies.

Appendix A.3: NGC 3516

High-resolution VLA observations of NGC 3516 show a compact flat-spectrum core with a ~07 (~120 pc) one-sided northern extension along PA ≃ 8° (Nagar et al. 1999). At arcsec resolution, additional radio components are seen that extend out to ~4′′ (~740 pc) and align with the co-spatial S-shaped optical emission-line structure (Miyaji et al. 1992; Ferruit et al. 1998). At coarser resolution, a linear radio structure spanning ~45′′ (~8.3 kpc), oriented along PA ~ 44°, across the nucleus is also seen (Baum et al. 1993). In our GMRT observations, the 610 MHz radio emission is detected as marginally resolved point source fitted with an elliptical Gaussian of 1038. The integrated flux density at 610 MHz is substantially higher than the peak flux density, and also the fitted Gaussian size is larger than the synthesized beam size, and this may be indicative of the presence of extended emission at the kpc-scale. We fit the 240 MHz radio emission with a large Gaussian of 3731. There is hint of second component along the north-east direction from the central nuclear component that seems to be consistent with the radio morphology reported by Baum et al. (1993). NGC 3516 shows inverted spectrum between 1.4 GHz and 610 MHz, while a steep spectrum between 610 MHz and 240 MHz. The changing spectral behavior can be interpreted as the presence of at least two emitting components. Possibly, 5.0 GHz to 610 MHz is dominated by the compact AGN core having self absorbed synchrotron emission, and low-frequency emission at 610 MHz to 240 MHz is dominated by optically thin synchrotron emission from the extended component.

Appendix A.4: NGC 4151

The nuclear radio source in NGC 4151 resolves into compact knots aligned in a slightly curved jet structure spanning ~5′′ (~340 parsec) across the nucleus and oriented along PA ~ 80° (Ulvestad et al. 1981; Booler et al. 1982; Wilson & Ulvestad 1982b; Pedlar et al. 1993; Mundell et al. 2003). The WSRT observations of NGC 4151 revealed a ~15′′ (~1 kpc) linear structure, roughly aligned with the inner jet, and a bracketing pair of radio continuum arcs located at ~45′′ (~3 kpc) from the radio nucleus (Baum et al. 1993). In our GMRT observations, the 610 MHz radio emission is double-peaked with the weaker peak at a distance of ~854 along the PA ~ 65°.2 from the central component. The 610 MHz radio emission can be fitted with two elliptical Gaussian components with the central component having a peak flux density ~312.9 mJy/beam and convolved size ~828, while the second Gaussian component has peak flux density of ~218.1 mJy/beam and convolved size ~874. Owing to its larger beam-size, the 240 MHz radio image shows a nearly unresolved point source fitted with a Gaussian of ~1764. The four-point radio spectrum remains fairly steep (α_int ~  − 0.76) over 240 MHz to 5.0 GHz.

Appendix A.5: MRK 766

The 8.4 GHz VLA “A” and “C” array observations of MRK 766 show an unresolved point source emission and no evidence of emission on intermediate scale (Kukula et al. 1995). In our GMRT observations, the 610 MHz and 240 MHz radio emission is seen as unresolved point sources that are fitted with Gaussian of ~781 and ~90, respectively. The four-point integrated radio spectral index (α_int ~  − 0.47) is less steep than average spectral index for our sample Seyfert galaxies.

Appendix A.6: MRK 279

VLA observations of MRK 279 at 8.4 GHz show an unresolved point source emission in both “A” and “C” array configurations and no evidence of emission on intermediate scale (Kukula et al. 1995). Our GMRT observations at 610 MHz and 240 MHz show radio emission as an unresolved point source fitted with the Gaussians of sizes ~754 and ~1752, respectively. The four-point radio spectrum of MRK 279 is fairly steep with an integrated spectral index (α_int) ~  −0.88.

Appendix A.7: NGC 5548

VLA observations of NGC 5548 revealed a compact core between two diffuse lobes separated by ~15′′ (Wilson & Ulvestad 1982a). Using VLA “D” array observations, Gallimore et al. (2006) detected marginally resolved lobes along with the nuclear point source emission. In our GMRT observations, we fit the 610 MHz radio emission with a Gaussian of ~1411. We note that the 610 MHz total flux density is significantly higher than the peak flux density, and also the fitted Gaussian size is larger than the synthesized beam size. This may infer the presence of kpc-scale extended radio emission. At 240 MHz, the radio emission is nearly an unresolved point source fitted with a Gaussian of ~2383. The four-point radio spectrum of NGC 5548 is fitted with a spectral index of (α_int) ~  − 0.68.

Appendix A.8: ARK 564

The 8.4 GHz VLA observations of ARK 564 show a triple radio source along the north-south direction (PA ~ 6°), extended to ~320 pc (Moran 2000). In our GMRT observations, the radio emission at 610 MHz and 240 MHz is nearly point-source emission fitted with a Gaussian of ~791 and ~2492, respectively. The four-point radio spectrum over 240 MHz to 5.0 GHz is fairly steep with an integrated spectral index (α_int) ~  − 0.88.

Appendix A.9: NGC 7469

The 1.6 GHz VLBI observations resolved the core-jet structure into five different components, lying in an east-west line which extends up to ~55 pc (Lonsdale et al. 2003). A variety of observations at high spatial resolution indicate that the AGN in NGC 7469 is surrounded by a ring of starburst (Mauder et al. 1994; Genzel et al. 1995) with radio observations showing an unresolved central component surrounded by the ring-like structure (Wilson et al. 1991). In our GMRT observations, the radio emission at 610 MHz and 240 is fitted with single Gaussian components with sizes of ~1070 and ~3768, respectively. The integrated flux density at 610 MHz is substantially higher than the peak flux density, and the fitted Gaussian size is also larger than the synthesized beam size. This may be considered as an indication of kpc-scale extended emission in NGC 7469. The four-point radio spectrum of NGC 7469 is fairly steep with integrated spectral index (α_int) ~  − 0.82.

Appendix A.10: MRK 530

VLA observations of MRK 530 at 8.4 GHz show a compact point source emission with a slight extension (Kukula et al. 1995). The milli-arcsec resolution VLBI observations show a compact core emission with extension along the east-west direction at fainter levels (Lal et al. 2004). In our GMRT observations, the radio emission at 610 MHz and 240 MHz is seen as nearly point source that is fitted with single Gaussian components of sizes ~718 and ~4646, respectively. The four-point radio spectrum of MRK 530 is fairly steep (α_int) ~  − 0.77.

Appendix A.11: MRK 348

In MRK 348, the radio continuum emission is dominated by a variable, subparsec-scale (~0.5 pc) jet that feeds into a larger (~60 pc) linear radio structure oriented roughly north-south (Neff & de Bruyn 1983; Ulvestad et al. 1999; Antón et al. 2002). Baum et al. (1993) observed large-scale radio lobes (~6 kpc extent) that roughly align with the small-scale jet structure. Using 5.0 GHz VLA “D” array observations, Gallimore et al. (2006) report the presence of extended emission such that the large-scale lobes are marginally resolved after the nuclear point source subtraction. In our GMRT observations, the radio emission 610 MHz and 240 MHz is seen as nearly point source, which we fit with single Gaussian components of sizes ~681 and ~81, respectively. The radio spectrum of MRK 348 fitted over 240 MHz to 1.4 GHz has index (α_int) ~  − 0.58. The 5.0 GHz flux density appears to be dominated by variable AGN core component and does not fit with the spectral index measured over 240 MHz to 1.4 GHz.

Appendix A.12: MRK 1

VLA observations of MRK 1 show an unresolved point source radio emission from AGN (Kinney et al. 2000). In our GMRT observations, 610 MHz and 240 MHz radio images are like point-source emission and are fitted with single Gaussian components of sizes ~632 and ~1736, respectively. The four-point radio spectrum of MRK 1 is fitted with an index (α_int) ~  − 0.58.

Appendix A.13: MRK 1066

The 4.9 GHz VLA observations of MRK 1066 show a linear, probably triple, source extending ~28 along PA ~ 134° (Ulvestad & Wilson 1989). Using 1.4 GHz and 8.4 GHz VLA observations Nagar et al. (1999) reported that the 1.4 GHz radio emission can be fitted with a single Gaussian component and 8.4 GHz radio emission displays the central source and northwest extension along the position angle ~305° with respect to the core. A more diffuse southeast extension along the position angle ~140° with respect to the core also seems to be present (Nagar et al. 1999). In our GMRT observations, 610 MHz and 240 MHz radio images show nearly point-source emission and are fitted with single Gaussian components of sizes ~663 and ~1753, respectively. The integrated radio spectral index fitted over 240 MHz to 5.0 GHz is ~  − 0.72.

Appendix A.14: NGC 2110

VLA observations show a symmetrical, jet-like radio emission, extending ~4′′ in the north-south direction and straddling a central compact core (Ulvestad & Wilson 1984b). Using 1.4 GHz and 8.4 GHz VLA (A and AnB hybrid array configuration) observations, Nagar et al. (1999) reported 1.4 GHz emission as a point-source emission, while at 8.4 GHz a linear jet-like structure was noticed along the position angle ~9°. In our GMRT observations, the radio emission at 610 MHz and 240 MHz are are seen as nearly point-source emission. We fit 610 MHz and 240 MHz emission with single Gaussian components of sizes ~711 and ~3847, respectively. The four-point radio spectrum of NGC 2110 is steep with an integrated spectral index (α_int) ~  − 0.72.

Appendix A.15: NGC 2273

The 5.0 GHz sub-arcsec resolution VLA observations of NGC 2273 show an unequal double with a separation of ~12 (~145 pc) at PA 90°. While observations at 1.4 GHz show the double structure embedded in a more amorphous structure with an extent of 25 (~300 pc) along PA 20° (Ulvestad & Wilson 1984b). The 5.0 GHz WSRT observations show an additional amorphous structure on a larger scale and suggest an extended emission with a total extent of ~9′′ (~1 kpc) along PA 160° (Baum et al. 1993). In our GMRT observations, the radio images at 610 MHz and 240 MHz show nearly point source emission that is fitted with single Gaussian components of ~8 and ~2053, respectively. The 610 MHz radio image appears to be marginally resolved. The four-point radio spectrum of NGC 2273 is relatively flat with an integrated spectral index (α_int) ~  − 0.37.

Appendix A.16: NGC 5252

The 1.4 GHz and 5 GHz VLA observations show a radio structure consisting of a central, compact core, with a relatively flat spectrum and a weaker emission extending ~2′′ north and south of the core (Wilson & Tsvetanov 1994). Nagar et al. (1999) confirm the overall flatter spectrum of the core () and the radio continuum features seen in the earlier observations. In our GMRT observations, we fit the radio emission at 610 MHz and 240 MHz with single Gaussian components of sizes ~1066 and ~4631, respectively. The four-point radio spectrum of NGC 5252 is flat with integrated spectral index (α_int) ~  − 0.14, suggesting that the radio emission over 240 MHz to 5.0 GHz is dominated by a compact AGN core.

Appendix A.17: NGC 5728

The 5.0 GHz and 14.9 GHz VLA observations of NGC 5728 show a compact core and a faint radial feature extending along north-east (Schommer et al. 1988). In our 610 MHz GMRT image we noticed a double-peaked emission where the second off-nuclear component may correspond to the nuclear star-forming region reported in previous studies (Schommer et al. 1988; Mazzuca et al. 2008). The peaks of the two emitting components are separated by ~107 (~2.0 kpc) with the off-nuclear component residing along PA ~ 67° from the central nuclear component. The two components have peak flux densities of ~25.6 mJy/beam and 17.5 mJy/beam and are fitted with Gaussians of ~1246 and ~1639, respectively. The 240 MHz radio image shows one component of emission (possibly due larger synthesized beam-size) fitted with a Gaussian of ~20. The four-point radio spectrum exhibits inverted shape with turnover between 610 MHz and 1.4 GHz.

Appendix A.18: NGC 7212

VLA observations of NGC 7212 show a compact double source separated by ~07 in the north-south direction, and the northern blob appears to be slightly elongated (Falcke et al. 1998). In our GMRT observations, the 610 MHz image shows two emission components. The radio contours overlaid on DSS optical image clearly show that the second radio component is associated with the neighboring galaxy NGC 7213. The radio emission component associated with NGC 7212 is fitted with a single

Gaussian of ~885. Owing the large synthesized beam size (i.e.,~4061), the 240 MHz radio image shows only one emission component that includes emission from NGC 7213 too. The 240 MHz radio emission is fitted with a Gaussian of ~3279. The large beam size at 240 MHz does not allow us to estimate the flux densities of NGC 7212 and NGC 7213 separately. Therefore, 240 MHz flux density measurement of NGC 7212 is contaminated and over-estimated. The four-point integrated radio spectral index of NGC 7212 is ~−0.79. We note that spectral steepening seen over 610 MHz to 240 MHz is likely to be caused by the over-estimated 240 MHz flux density. It can also give rise to the steeper value of the integrated spectral index than the actual value.

Appendix A.19: NGC 7682

The 8.4 GHz VLA observations of NGC 7682 show unresolved point-source nuclear emission (Kukula et al. 1995); however, the milli-arcsec 5.0 GHz VLBI observations show a point source with extension along the southern (PA ~ 180°) and the south-eastern (PA ~ 120°) directions (Lal et al. 2004). Our GMRT images at 610 MHz and 240 MHz are fitted with single Gaussian components of sizes ~1082 and ~3823, respectively. The four-point spectrum of NGC 7682 is steep with spectral index (α_int) ~  − 0.72.

Appendix A.20: MRK 533

VLA “C” array observations of MRK 533 at 8.4 GHz show a slightly extended nuclear emission, which is seen as resolved into a 0.5 arcsec double structure in VLA “A” array observations (Kukula et al. 1995). VLA and EVN observations reveal a linear triple radio source of ~07 angular extent with the components at ~05 west and ~015 east of the main peak (Unger et al. 1988). Momjian et al. (2003) made more sensitive observations of MRK 533 using VLBA, phased VLA and Arecibo at 1.4 GHz and report the triple source and additional low-surface-brightness emission forming an S-shaped structure. Our GMRT images at 610 MHz and 240 MHz show nearly point-source radio emission that is fitted with single Gaussian components of sizes ~626 and ~2004, respectively. The radio spectrum of MRK 533 over 240 MHz to 5.0 MHz is fairly steep with spectral index (α_int) ~  − 0.78.

© ESO, 2013