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Appendix A: Notes on individual targets

SDSS J153911.17+002600.7 (1):

this AGN is an NLS1 galaxy (Zhou et al. 2006; Williams et al. 2002). From its RASS observation, a hardness ratio of HRI = 0.46  ±  0.45 and a very soft photon index Γ = 2.8  ±  0.9 have been deduced by Williams et al. (2002). Its SDSS images exhibit some irregular structures around the nucleus. Part of this structure is a foreground star. The remaining faint features might belong to the host galaxy, or to some background galaxy. It is the radio-loudest AGN in our sample, when neglecting the two jet-dominated sources (9 and 11; see below).

SDSS J150521.92+014149.8 (2):

this NLS1 galaxy shows faint signatures of a spiral host galaxy. It also exhibits a strongly blueshifted [OIII] λ5007 emission line (by about 165 km s^-1), which is commonly found in NLS1s and might be related to outflows or inflows (Boroson 2005).

SDSS J134206.57+050523.8 (3):

this is an NLS1 Nagao et al. (2001); Zhou et al. (2006) and is also a member of the Li et al. (2008) sample.

SDSS J150407.51-024816.5 (4):

this elliptical LINER galaxy is the central galaxy of the compact X-ray luminous galaxy cluster RXC J1504-0248 with one of the most massive nearby cooling cores (Böhringer et al. 2005). The black-hole mass, estimated from the [SII] line width (cf., Komossa & Xu 2007) of about 3  ×  10⁷   M_⊙, is somewhat less than those estimated for the brightest cluster central galaxies (10^8 − 9   M_⊙, e.g., Rafferty et al. 2006; Fujita & Reiprich 2004).

In our MERLIN 18 cm images we detected two sources (4E[ast] and 4W[est]) at the optical position of the galaxy (Fig. 3). The two components are separated by about 05, which corresponds to 1750 pc at z = 0.217. In the VLA archive, we found a 3.5 cm data set at an angular resolution ( ≈ 0.25″) similar to that of our MERLIN image. Both components are detected at 3.5 cm, with F_peak(E) = 28.78  ±  0.07 mJy and F_peak(W) = 0.60  ±  0.07 mJy. The EVN 6 cm image recovers both components, while in the EVN 18 cm image, we only detected 4E. The 18 cm limiting peak flux density of 4W is 1.4 mJy. Figure A.1 displays the continuum spectra of 4E and 4W. The MERLIN/VLA two-point spectral index   ×  log (S_3.5   cm/S_18   cm) is 0.42 for 4E and 2.05 for 4W. The EVN two-point spectral index   ×  log (S_6   cm/S_18   cm) is 0.14 for 4E and  < 0.58 for 4W. The eastern component has a relatively flat 18-6-3.5 cm spectrum. The western component is steeper, but flattens toward shorter wavelengths. The flat nuclear spectrum might be the result of a set of closely spaced homogeneous synchrotron components or optically thin bremsstrahlung in a disk wind (cf., Blundell & Kuncic 2007). The SDSS image of the host galaxy is regular and shows no signs of a recent merger. Together with the steep spectral index, the western component does not appear to be a companion nucleus, but rather a jet component. This is consistent with an asymmetry seen in the central X-ray brightness distribution (Fig. 9 in Böhringer et al. 2005), which might be the result of interaction between the radio jet and the hot cluster medium. More conclusions are limited because the EVN 18 cm data were hampered by bad weather. More and deeper radio data are required to study the impact of the potential radio jet onto the surrounding environment.

SDSS J010649.39+010322.4 (5):

this LINER galaxy lies at the heart of the galaxy cluster RXC J0106.8+0103 or Zw 348 (e.g., Ebeling et al. 2000; Böhringer et al. 2000). In this cluster, the AGN is expected to be a major contaminant of the overall X-ray emission (Böhringer et al. 2000). However, from the low R_X and R ^∗  values in Fig. 5, it can be seen that the X-rays still appear to be dominated by the cluster emission. The FIRST image reveals a slight extended emission component to the southeast in addition to the compact core (the extend parameter θ_FIRST ≈ 1.3), which, being barely above the noise level, could be an indication for a jet component. Our MERLIN image does not reveal any extended emission, since it might resolve out faint extended emission. This galaxy is also luminous at UV wavelengths (based on GALEX data). It lies on the boundary of between large UV luminous galaxies (UVLGs) and compact UVLGs as defined by Hoopes et al. (2007). Large UVLGs are principally normal galaxies, but are very luminous primarily because of their large size. Compact UVLGs, on the other hand, are low-mass, relatively metal-poor systems that often have disturbed morphology. These systems are characterized by intense ongoing star formation. Hoopes et al. (2007) estimated the SFR by SED fitting. SFR_UV ≈ 2.4 is compatible with our FIRST estimated SFR (Table 3). Our MERLIN results show a much lower SFR, which indicates that the star formation is significantly extended throughout the host and is resolved out by the interferometer. The increasing brightness temperature at MERLIN angular resolution indicates an AGN/jet origin of the unresolved emission.

	Fig. A.1 Target 4 radio continuum spectra of eastern and western components: MERLIN at 1.67 GHz (open symbols represent EVN measurements), EVN at 5 GHz, and VLA at 8.46 GHz.
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SDSS J074738.38+245637.3 (6):

this early-type Seyfert 1 has a companion SDSS J074738.25+245626.1 at z = 0.131. Low surface-brightness features in the SDSS images are located between the two galaxies. Gravitational interaction could therefore be responsible for the SFR of  ~50   M_⊙ yr^-1 estimated from the large aperture data. MERLIN appears to resolve out a fraction of about 80% of the FIRST emission. The resulting SFR estimate is comparable to the [OII] one, which is about 10   M_⊙ yr^-1. This is the most radio-quiet source of the sample, and with the MERLIN measurement it becomes even more radio-quiet, . The X-ray luminosity is typical for Seyfert 1 galaxies, which in turn indicates that only a small fraction of the MERLIN flux density is related to star formation, to follow the X-ray/radio correlation. MERLIN probes galactic scales of  ~450 pc, while the 3′′ diameter SDSS fiber probes a region of about 7 kpc diameter. This suggests that the [OII] luminosity might be related to the extended, resolved out FIRST radio emission. Higher angular resolution radio observations are required to resolve this problem.

SDSS J030639.57+000343.1 (7):

this NLS1 has a spiral morphology. The galaxy is possibly a member of a group, with a projected distance of about 110 kpc to the nearest neighbor. It has a redshifted [OIII] λ5007 emission line (~46 km s^-1), which, as discussed above, indicates a complex narrow-line region kinematics (Boroson 2005).

SDSS J081026.07+234156.1 (8):

Whalen et al. (2006) classified this AGN as an NLS1 galaxy. Its optical appearance is compact. It is the radio-faintest object in our sample. With the MERLIN measurement, it becomes the second-most radio-quiet AGN, .

SDSS J162332.27+284128.7 (9):

this optically unresolved object has been classified as a BL Lac object (Plotkin et al. 2008). Owing to the absence of spectral features, no black-hole mass could be estimated. This might also be a problem for its redshift, which is taken from the SDSS database. This object is not particularly radio-loud (Fig. 5), though we are supposedly observing the jet almost face on.

SDSS J080322.48+433307.1 (10):

this SY1 galaxy shows some extremely redshifted [OIII] emission (~57 km s^-1,

Boroson 2005) and is also included in the large catalogs by Wang et al. (2006) and Li et al. (2008). Owing to a nearby guide star (SDSS J080324.87+433330.1), it is also suitable for AO-assisted observations.

SDSS J080644.41+484149.2 (11):

this source is the only FRII RL QSO (de Vries et al. 2006) in our sample, having a nearby natural guide star (SDSS J080645.63+484156.6). Its optical appearance is unresolved. Although it is RL in the classical sense, the R_X measurement would still result in a RQ AGN. We have only used the compact nuclear radio emission. This could mean that the 40 pc scale emission is not that strongly influenced by the jet component.

SDSS J092710.60+532731.6 (12):

this radio galaxy shows a passive, elliptical optical spectrum. It has a nearby natural guide star (SDSS J092707.09+532742.3) and is likely the brightest cluster galaxy in the Zw 2379 galaxy cluster (z = 0.205; Stott et al. 2008). Its high EVN brightness temperature underlines the AGN nature of the radio emission.

SDSS J134420.87+663717.6 (13):

IRAS 13428+6652 has been identified as Seyfert 1.5 by Moran et al. (1996). It appears to be a major merger with an extended tidal tail and possibly two nuclei. It is suitable for AO-assisted studies (SDSS J134427.10+663705.2). The source has been detected at 20 cm by NVSS. However, we could not detect any compact flux density at 18 cm with MERLIN. Since it is an IR luminous galaxy (L_FIR ≈ 5  ×  10¹¹   L_⊙), the radio emission is most likely dominated by extended star formation.

© ESO, 2012