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A&A
Volume 699, June 2025
Article Number L4
Number of page(s) 7
Section Letters to the Editor
DOI https://doi.org/10.1051/0004-6361/202554987
Published online 27 June 2025

© The Authors 2025

Licence Creative CommonsOpen Access article, published by EDP Sciences, under the terms of the Creative Commons Attribution License (https://creativecommons.org/licenses/by/4.0), which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.

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1. Introduction

Extragalactic radio jets, emanating from active galactic nuclei (AGNs) at the centres of some galaxies, are among the most powerful astrophysical phenomena (Antonucci 1993; Netzer 2013). These are radio galaxies (RGs), often called radio-loud AGNs (RLAGNs; Urry & Padovani 1995), which are predominantly bright in the radio band. Their jets can extend to large distances beyond the boundaries of host galaxies; those rare RGs that reach sizes larger than 0.7 Mpc are called giant RGs (GRGs; e.g. Ishwara-Chandra & Saikia 1999; Kuźmicz et al. 2018; Dabhade et al. 2023). Jet activity typically persists for no more than a few tens of millions of years and a RG in which jet activity has ceased is referred to as a ‘remnant’ RG, where steep radio spectra can be observed in the outer lobes (Jamrozy et al. 2004; Parma et al. 2007; Murgia et al. 2011; Brienza et al. 2017; Quici et al. 2021). Some RGs also show evidence of episodic jet activity, with double-double lobed RGs (DDRG; Schoenmakers et al. 2000) standing out as particularly striking examples of recurrent jet activity (see reviews by Saikia & Jamrozy 2009; Mahatma 2023; Morganti 2024).

The vast majority of these RLAGNs are hosted predominantly by massive, gas–poor elliptical galaxies that lack significant star formation (Wilson & Colbert 1995; Urry & Padovani 1995). In contrast, AGNs in spiral galaxies are typically radio-quiet with radio luminosities several orders of magnitude lower than those of RLAGNs. Spiral galaxies typically emit radio waves primarily through thermal free–free emission from the ionised interstellar medium (which rises at higher radio frequencies), along with synchrotron emission from their diffuse magneto-ionic medium (Condon 1992). The occurrence of RLAGNs with extended lobes in spiral galaxies is extremely rare. The first such object identified was a 200 kpc long radio source, J0313−192, whose host galaxy emits a 42 kpc long jet (Ledlow et al. 1998). So far, only a select number of unambiguous spiral host galaxies have been identified, including Speca (Hota et al. 2011), J2345−0449 (Bagchi et al. 2014), J0836+0532 (Singh et al. 2015), J1649+2635 (Mao et al. 2015), and MCG+07−47−10 (Mulcahy et al. 2016). Moreover, only two of them – Speca at z = 0.137 and J2345−0449 at z = 0.0755 – extend to 1.4 Mpc and 1.6 Mpc, respectively, and each has multiple pairs of lobes indicating episodic AGN activity. It is worth mentioning that the sample of spiral-host RGs has been expanded recently (e.g. Wu et al. 2022; Yuan et al. 2024). However, many of the selected objects require careful re-verification. Moreover, the spiral-hosted DDRGs and GRGs do stand out and they should be considered different from typical RGs and jetted Seyfert galaxies.

Analysis of the properties of known spiral galaxies with extended radio emission reveals several common features that characterise these unusual objects. One important property is the mass of the central supermassive black hole (SMBH), which in the case of spiral galaxies with powerful radio jets is comparable to that typically found in elliptical galaxies (Mulcahy et al. 2016; Keel et al. 2006; Mao et al. 2015). For example, Bagchi et al. (2014) found a SMBH of up to 109 M⊙ and a rapidly rotating galactic disc, with velocities from 400 to 500 km s−1. In the case of Speca, a rapidly rotating galactic disc with a velocity of 370 km s−1 was also found (Hota et al. 2014, 2016). The large mass of the black hole (BH) plays a key role in sustaining the activity of the central nucleus and producing the observed extended radio structures. Another important factor is the presence of interactions or mergers, which can trigger RLAGN activity in spiral galaxies, while preserving their spiral morphology (Kozieł-Wierzbowska et al. 2012). These interactions are thought to enhance the accretion of material onto the central SMBH, thereby powering the AGN and driving the production of radio jets. The surrounding environment also appears to be an important factor. Many of the RLAGN spiral galaxies are located in relatively dense environments, such as galaxy groups or clusters, which can provide the conditions necessary for extended radio emissions (Singh et al. 2015). Interestingly, spiral galaxies with extended radio emission often have ongoing star formation and AGN activity. This coexistence suggests a complex interplay between the phenomena mentioned above (Mao et al. 2015). Nevertheless, spiral RLAGNs, also known in the literature as Speca-like galaxies (Hota et al. 2011), spiral-DRAGNs (Mulcahy et al. 2016), and/or late-type galaxies with double radio lobes (Yuan et al. 2024), remain exceptionally rare, despite extensive efforts to find more of them.

In this Letter, we report the discovery of a spiral host LEDA 896325 in a GRG J1350−1634 that extends over 2 Mpc in projected size. Furthermore, we have detected evidence of two distinct episodes of lobe activity using radio observations. As we show later, this RG surpasses all previously known spiral-host RGs in size. We briefly discuss the properties of the target and explore possible jet-launching mechanisms in this spiralgalaxy.

Throughout the Letter, we adopt the flat ΛCDM cosmological model based on the Planck Collaboration (H0 = 67.8 km s−1 Mpc−1, Ωm = 0.308; Planck Collaboration XIII 2016). We use the convention S​ν ∝ να, where S​ν is the flux density at frequency ν and α is a spectral index (SI). The flux density scale is that of Baars et al. (1977). All positions and maps are given in the J2000.0 coordinate system. In the following, we use the designation J1350−1634 to describe the extended radio source, while we refer to its optical host galaxy asLEDA 896325.

2. Target

J1350−1634 was initially identified as a candidate for GRG by Proctor (2016) and later listed in the Kuźmicz et al. (2018) GRG catalogue. It was classified as Fanaroff-Riley type II RG (FR-II; Fanaroff & Riley 1974), with an angular size of its radio structure of 11′ measured on the NRAO VLA Sky Survey map (NVSS: Condon et al. 1998). LEDA 896325, located at the position of RA: 13h50m36 . s $ {{\overset{\text{s}}{.}}} $10, Dec: −16°34′50 . ″ $ {{\overset{\prime\prime}{.}}} $0, has been classified as either a quasar (Kuźmicz et al. 2018) or as a blazar (D’Abrusco et al. 2014). It has a spectroscopic redshift of zspec = 0.0877 (6dF Galaxy Survey; Jones et al. 2009).

The region of the sky containing J1350−1634 has extensive multi-wavelength survey coverage (optical through radio), and we analyse the relevant data in more detail later (see in Sect. 3). In addition, the galaxy is an X-ray source, appearing in the ROSAT Bright Source Catalogue (Voges et al. 1999) with a count rate of 8.58 × 10−2 s−1, and its corresponding photon flux in the 0.1−2.4 keV band, when assuming a power-law energy distribution, E−1.3dE, is 3.13 × 10−12 mW m−2. This source is also clearly detected in the eROSITA all-sky X-ray survey (Merloni et al. 2024).

3. Results and discussion

To understand how a spiral galaxy can host such an extended RG, we have examined several aspects of J1350−1634. First, we examine the morphology of LEDA 896325 (Sect. 3.1), then we estimate the central BH mass (Sect. 3.2). We consider possible triggers such as a companion or merger and the large-scale environment (Sect. 3.3). Finally, we describe the radio structure that reveals the episodic jet activity (Sect. 3.4), followed by the spectral ages of both activity episodes (Sect. 3.5).

3.1. The morphology of LEDA 896325

The high-resolution Dark Energy Spectroscopic Instrument (DESI) Legacy Imaging Surveys, Data Release-10 (DESCal DR-10; Dey et al. 2019) image clearly reveals the spiral-like structure of the host galaxy, as is shown in the lower left corner of Fig. 1. The 6dF optical spectrum shows a relatively weak continuum and a broad Hα emission line, suggesting that the host galaxy is more likely to be classified as a broad-line RG rather than a quasar.

thumbnail Fig. 1.

False-colour image of J1350−1634, in which red and blue colours represent GLEAM (200 MHz, with a root mean square (rms) of 15 mJy beam−1) and NVSS (1400 MHz, with a rms of 0.45 mJy beam−1), respectively. The thin black contours of RACS-mid (887 MHz, with a rms of 0.3 mJy beam−1) are plotted at 3 rms × 2n (n = 0, 1, 2, 3 …). Both red and blue pixels show values above 3 × rms for the respective data. The outer and inner lobes, as well as the core, are marked with yellow. Unrelated background radio sources are labelled ‘bg’, ‘bb’, ‘bc’, and ‘bd’. Two insets in the lower left corner show the colourful DESCal DR-10 optical image of the host galaxy LEDA 896325, and the VLBI-scale radio core with a one-sided jet, represented by 8.65 GHz contours.

To analyse the morphology of LEDA 896325 and support its classification as a spiral galaxy, we modelled its surface brightness profile using a g-band DESCal DR-10 image. We performed a structural decomposition with GALFIT 3.0 (Peng et al. 2007), fitting analytical models to the galaxy’s light distribution to separate its main structural components, such as the bulge and the disc, allowing for a quantitative characterisation of its morphology. We applied two different modelling approaches. In the first approach (Model 1), we used a two-component model with a point spread function (PSF) for the AGN contribution combined with a single Sérsic profile for the whole galaxy. The second approach (Model 2) uses a three-component model – a PSF for the AGN, an exponential disc, and a Sérsic profile for the bulge component. In both cases, the PSF of the AGN is included, since the optical spectrum of the host galaxy of LEDA 896325 has a broad Hα emission line, and the galaxy is a source of radio and X-ray emission. To remove the light contribution from foreground objects, our model includes two point sources visible in Fig. 2 (left panel), modelled using PSF profiles, and the foreground galaxy (labelled as ‘g2’, see Fig. B.1), overlapping LEDA 896325, which was fitted with a two-component model consisting of a disc and a bulge. As a result of modelling, in the two-component model, we obtained the Sérsic index for the whole galaxy equal to n = 1.8, indicating a morphology intermediate between a pure disc and a classical elliptical profile. In contrast, the three-component model yields a Sérsic index of n = 0.8 for the disc component, consistent with an exponential light profile characteristic of galactic discs, and n = 1.45 for the bulge, indicating the presence of a pseudo-bulge rather than a classical de Vaucouleurs bulge (n ≃ 4). The residual images for both models, presented in Fig. 2 (middle and right panels), clearly reveal the spiral- or ring-like structure of the host galaxy. In Fig. A.1, we show the surface brightness profiles along the galaxy’s semi-major axis with both fitted models superimposed, including their individual components. Both modelling approaches give a comparable quality of fit to the data. To highlight the differences between them, we also show residuals obtained by subtracting one model from the other. The most significant discrepancies are observed in the region close to the central AGN. Although the two models provide different interpretations of the morphology of the galaxy, i.e. the two-component model suggests an intermediate structure between a spiral and an elliptical galaxy, while the three-component model classifies it as a disc galaxy with a pseudo-bulge. Both models show that LEDA 896325 clearly exhibits disc-like features with spiral structures. This suggests that the galaxy has evolved by processes that have preserved its spiral structure, most likely through secular evolution or minor interactions, rather than major disruptive events.

thumbnail Fig. 2.

Left: DESI g-band image of LEDA 896325, with a magenta line indicating the cross section along the semi-major axis of the galaxy. Middle: Residual image for two components (PSF + Sersic from the whole galaxy). Right: Residual image for the three-component model (PSF + disc + bulge).

3.2. BH mass

To evaluate the BH mass of LEDA 896325 we derived the stellar velocity dispersion from the 6dF spectrum using the simple stellar population synthesis code STARLIGHT (Cid Fernandes et al. 2005). This code models the observed spectrum by fitting the galaxy’s spectral continuum with a combination of template spectra. As the 6dF spectra are not flux-calibrated, we normalised the spectrum of LEDA 896325 before modelling to minimise instrumental effects. Although STARLIGHT has been used previously to model 6dF spectra (e.g. Gomes & Papaderos 2012), its use is not recommended to infer stellar populations, ages, or galaxy masses due to the lack of flux calibration. However, the code can be used for kinematic analyses, such as the determination of stellar velocity dispersion. After applying corrections for instrumental and stellar base dispersion, the resulting stellar velocity dispersion of LEDA 896325 is σ* = 240 km s−1. Using the MBH − σ* relation (Gebhardt et al. 2000) and adopting the constants from Batiste et al. (2017) derived for the AGN sample, we estimate the BH mass of LEDA 896325 to be MBH = 2.4 × 108 M⊙. This value is in the range of BH masses of giant elliptical galaxies, although spiral galaxies with central AGNs can also reach analogically high values. For example, Bagchi et al. (2014) obtained a very similar value for the spiral galaxy J2345−0449, which is also a DDRG of size 1.6 Mpc. This supports the idea that a sufficiently massive BH is a crucial ingredient for the launch of extended radio jets even in a spiral host. While a high-mass BH is one key ingredient, external factors such as interactions could have also enabled RLAGN activity.

3.3. Merging scenario and environment

The possibility of interactions or mergers with neighbouring galaxies remains an important aspect of galaxy evolution. In the case of LEDA 896325, the presence of an extended object located 12″ south of its centre (labelled as ‘g2’ in Fig. B.1) supports an interaction scenario. This object could represent a small companion galaxy that is currently undergoing an interaction or merger with the host galaxy. Such interactions could play a crucial role in shaping the dynamical evolution of the system, potentially facilitating bulge growth and triggering AGN activity (Kormendy & Ho 2013). However, the redshift of ‘g2’ remains unknown, leaving open the possibility that it could be a foreground object unrelated to the host.

Another interesting galaxy in the same region is LEDA 896133 (labelled as ‘bg’ in Figs. 1 and B.1). This galaxy is located to the south-east of LEDA 896325 at an angular separation of 2 . ′ 13 $ 2{{\overset{\prime}{.}}}13 $. Its photometric redshift is zphot = 0.076 (Bilicki et al. 2014). Assuming that both galaxies are equidistant and that LEDA 896133 has the same redshift as LEDA 896325, their projected separation would be approximately 216 kpc (i.e. about 3.5 times closer than the distance to M31). In particular, LEDA 896133 has an ambiguous morphology of a lenticular or spiral type with some kind of ring-like structure and is also a bright and compact radio source (see Fig. 1). These two large galaxies are most likely interacting.

In addition to these immediate companions, we examined the larger environment of LEDA 896325 to see if nearby galaxy groups or clusters might influence its AGN activity. We searched for galaxies using the GLADE+ galaxy catalogue (Dálya et al. 2022) and for galaxy groups and clusters using the catalogues of Wen et al. (2012, 2018) and Wen & Han (2024) in the redshift range z ± Δz = 0.0877 ± 0.0033 (i.e. from 0.0844 to 0.0910). No galaxy clusters or galaxy groups were identified within a radius of 6 Mpc (i.e. 1°) around the host, suggesting that LEDA 896325 resides in a relatively sparse environment. Only a few candidate galaxies with a similar photometric redshift were randomly located around the host. Future spectroscopic observations will be essential to confirm the merging scenario and to accurately characterise the surrounding environment.

3.4. Radio morphology and episodic activity

The radio morphology of J1350−1634, as is shown in Fig. 1, reveals a complex structure that provides evidence of episodic jet activity. We noticed two pairs of lobes in J1350−1634, i.e. (1a) the north-eastern (NE) outer lobe, which was not recognised before and is more prominent in the Galactic and Extragalactic All-sky Murchison Widefield Array survey (GLEAM; Hurley-Walker et al. 2017) but faintly visible in the NVSS; (1b) a south-western (SW) outer lobe; (2a) a SW inner lobe also not recognised before, visible only on the Rapid Australian Square Kilometre Array Pathfinder (ASKAP) Continuum Survey-low (RACS–low; McConnell et al. 2020); (2b) a NE inner lobe, which is ∼2 times longer in angular size and ∼14 times brighter than its SW counterpart. These two newly recognised structures correspond to an outer and an inner pair of lobes, confirming that J1350−1634 has undergone two distinct cycles of AGN activity. The largest angular size (LAS) of the outer lobes is 22′, corresponding to 2.24 Mpc, while the angular size of the inner lobes is 7′, corresponding to 0.71 Mpc. This makes J1350−1634 not only the largest spiral host GRG, but also the largest spiral host DDRG known to date.

The well-separated radio core is clearly visible over a wide range of frequencies and its flux density increases with increasing frequency (see Table C.1). Its records for different epochs also suggest that it may be variable. The radio core is also visible in the Very Long Baseline Array (VLBA) map (see lower left panel of Fig. 1), which was obtained from the Astrogeo VLBI FITS image database1. The VLBA core coincides exactly with the central position of LEDA 896325. In the VLBA map there is also a NE extension that lies in the same direction as the NE outer lobe of this RG. This extension could be either a still-visible jet from the latest activity or the beginning of a new episode. If a new episode is confirmed, J1350−1634 would be only the fifth known case of a known ‘triple-double’ RG (Chavan et al. 2023). Further dedicated VLBA imaging or monitoring is required to confirm this. It may reveal a new episode or help us to monitor the jet’s propagation. The counterjet is not visible at all, which may be due to the projection effect; the counterjet is away from our line of sight on the plane of the sky.

As was mentioned above, the RG analyzed here is quite extended in the sky and there are several radio-loud objects in its vicinity. Most of them have a low radio brightness that does not affect the flux density measurements of J1350−1634. However, several of them are noteworthy and should be taken into account. One of them is a background double RG (marked in Fig. 1 and in Table C.1 as ‘bd’) and there are two point-like radio objects (marked as ‘bb’ and ‘bc’ in Fig. 1, while in Table C.1 only the brightest source ‘bc’ is marked), where both the brightest objects are located at the head of the SW outer lobe (see Fig. 1). J1350−1634 has radio flux density measurements over a wide range of frequencies and the values are listed in Table C.1. These multi-frequency flux measurements allow us to derive the SI distribution and spectral ages of different lobes, as is discussed next. These ages confirm two separate jet activities – consistent with the idea of recurrent activity in the same galaxy.

3.5. Spectral age

First, we obtained a SI map of J1350−1634 between 200 MHz (GLEAM) and 1400 MHz (NVSS). At the beginning, the highest-resolution map was convolved to the resolution of the GLEAM map. Then the AIPS (Greisen 2003) tasks HGEOM and COMB (with opcode ‘SPIX’) were used to align the geometry of the two maps and finally to produce the SI map shown in Fig. C.1 (left panel). In this map there are four easily visible distinct structures: the core, the two outer lobes, and the NE inner lobe. The core emission dominates the central part of the source, influencing and mimicking the SW inner lobe and the inner parts of the NE inner lobe. The core has a SI value of about 0. The SW outer lobe shows typical signs of FRII-type SI behaviour, i.e. a flatter spectrum with a value of about −0.8 at the front edge, where the presumed hotspot was located, and smooth gradient of steepening SI towards the centre. This steepening towards the core is caused by the backflowing lobe plasma, where the aged plasma accumulates. The NE outer lobe also shows a steepening of the SI from the hotspot region towards the centre. The SI of the NE inner lobe is constant with the value of −0.8. However, there is a steeper region at its northern edges with a value of about −0.9 and this is probably related to the backflow of the NE outer lobe. The appearance of the SI described above is due to the radiation of relativistic charged particles in the presence of the magnetic field. In the synchrotron process higher-energy particles lose energy much faster than their lower-energy counterparts. This causes the multi-wavelength spectra to become increasingly curved over time.

We fitted the resulting observed radio spectra of the both outer lobes and the NE inner lobe (presented in Fig. C.1, right panel) using the SYNAGE package (Murgia 1996). Using the Jaffe & Perola (JP; Jaffe & Perola 1973) model, we estimated the radiative losses of the two outer lobes and the NE inner lobe, respectively. Assuming and fixing the injection SI value to 0.5, we evaluated the break frequencies to be 0.9 and 10 GHz for both the outer (SW & NE) and the NE inner lobe, respectively. The fitting details were similar to those described by Sethi et al. (2024). To calculate the synchrotron age, we used, similar to for example Lusetti et al. (2024), the minimum magnetic field value of B min = 3.18 ( 1 + z ) 2 / 3 = 2.2 μ $ B_{\mathrm{min}} = 3.18(1+z)^2/\sqrt{3} = 2.2\,{\upmu} $G, which minimises the radiative losses and maximises the lifetime of the radio source, providing an upper limit. The resulting ages are 120 and 35 Myr for the outer and the NE inner lobes, respectively. These age values, when compared with those for other DDRGs (e.g. Marecki et al. 2021; Konar et al. 2013), do not appear to be special.

4. Conclusion

In summary, we have identified J1350−1634 as the largest of only three known spiral-host DDRGs with a size > 2 Mpc. This exceptional source shows that spiral galaxies, although rarely, can launch and sustain powerful, large-scale radio jets without losing their disc morphology. The central BH of LEDA 896325 is as massive as those in giant ellipticals, likely facilitating its active jets, and the preserved spiral structure of the host suggests a gentle evolution (secular processes or small mergers rather than major disruptive events). These results challenge the traditional view that only ellipticals can produce giant RLANGs: given a massive BH and the right conditions, even a star-forming spiral can host episodic radio jets. This raises important questions, such as why such systems are so uncommon, and what special conditions or trigger mechanisms (e.g. particular interactions or environments) enable a spiral to ignite radio jets on the scale of millions of parsecs. Our discovery underscores the need for further investigation – both observational and theoretical – to understand how jets are launched in disc galaxies and how these galaxies maintain their structure. Continued further searches for similar objects and follow-up studies (e.g. deeper high-resolution radio imaging and spectroscopic observations of neighbours) will help to unravel the underlying processes that allow dual spiral+jet properties, shedding new light on AGN physics and galaxy evolution in unique environments.

Acknowledgments

We thank the reviewer Prof. Ananda Hota for his very detailed and valuable comments that helped significantly improve the article. S.S., A.K., and M.J. were partly supported by the Polish National Science Centre (NCN) grant UMO-2018/29/B/ST9/01793. S.S. also acknowledges the Jagiellonian University grants: 2022-VMM U1U/272/NO/10, 2022-SDEM U1U/272/NO/15, and VMM-2023 U1U/272/NO/10. M.J. acknowledges access to the SYNAGE software kindly provided by Matteo Murgia. We gratefully acknowledge Polish high-performance computing infrastructure PLGrid (HPC Center: ACK Cyfronet AGH) for providing computer facilities and support within computational grant no. PLG/2024/016935 and PLG/2025/017961. We used in our work the Astrogeo VLBI FITS image database, DOI: 10.25966/kyy8-yp57, maintained by Leonid Petrov. We acknowledge APLPY (Robitaille & Bressert 2012), ASTROPY (Astropy Collaboration 2022) and MATPLOTLIB (Hunter 2007) being used in the paper to create all the plots.

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Appendix A: The surface brightness profiles along the cross-section, as indicated in Fig. 2

thumbnail Fig. A.1.

The surface brightness profiles along the cross-section, as indicated in Fig. 2, for two different models: Model 1 (PSF + Sérsic) and Model 2 (PSF + disc + bulge). In each plot, we present the overall model together with its individual components. The bottom panel shows the residuals obtained by subtracting Model 2 from Model 1, highlighting the differences between these two approaches.

Appendix B: Optical image of LEDA 896325 galaxy

thumbnail Fig. B.1.

Optical image of the LEDA 896325 galaxy from the DESCal DR-10 survey, with potential companion galaxies labelled as ‘g2’ and ‘bg’.

Appendix C: Integrated flux densities of different components of J1350–1634

Table C.1.

Observed flux densities of different components of J1350−1634 and unrelated sources

thumbnail Fig. C.1.

The left panel shows the RACS-mid (887 MHz, with rms of 0.3 mJy beam−1) contours on the SI map between 200 MHz GLEAM and the convolved 1400 MHz NVSS maps. The RACS-mid contours are plotted at 3 rms × 2n (n = 0, 1, 2, 3 ...). The right panel shows the radio spectra of both outer lobes (SW and NE) and NE inner of the target source fitted with the JP model with SYNAGE (for details, see Sect. 3.5).

All Tables

Table C.1.

Observed flux densities of different components of J1350−1634 and unrelated sources

In the text

All Figures

thumbnail Fig. 1.

False-colour image of J1350−1634, in which red and blue colours represent GLEAM (200 MHz, with a root mean square (rms) of 15 mJy beam−1) and NVSS (1400 MHz, with a rms of 0.45 mJy beam−1), respectively. The thin black contours of RACS-mid (887 MHz, with a rms of 0.3 mJy beam−1) are plotted at 3 rms × 2n (n = 0, 1, 2, 3 …). Both red and blue pixels show values above 3 × rms for the respective data. The outer and inner lobes, as well as the core, are marked with yellow. Unrelated background radio sources are labelled ‘bg’, ‘bb’, ‘bc’, and ‘bd’. Two insets in the lower left corner show the colourful DESCal DR-10 optical image of the host galaxy LEDA 896325, and the VLBI-scale radio core with a one-sided jet, represented by 8.65 GHz contours.
In the text
thumbnail Fig. 2.

Left: DESI g-band image of LEDA 896325, with a magenta line indicating the cross section along the semi-major axis of the galaxy. Middle: Residual image for two components (PSF + Sersic from the whole galaxy). Right: Residual image for the three-component model (PSF + disc + bulge).
In the text
thumbnail Fig. A.1.

The surface brightness profiles along the cross-section, as indicated in Fig. 2, for two different models: Model 1 (PSF + Sérsic) and Model 2 (PSF + disc + bulge). In each plot, we present the overall model together with its individual components. The bottom panel shows the residuals obtained by subtracting Model 2 from Model 1, highlighting the differences between these two approaches.
In the text
thumbnail Fig. B.1.

Optical image of the LEDA 896325 galaxy from the DESCal DR-10 survey, with potential companion galaxies labelled as ‘g2’ and ‘bg’.
In the text
thumbnail Fig. C.1.

The left panel shows the RACS-mid (887 MHz, with rms of 0.3 mJy beam−1) contours on the SI map between 200 MHz GLEAM and the convolved 1400 MHz NVSS maps. The RACS-mid contours are plotted at 3 rms × 2n (n = 0, 1, 2, 3 ...). The right panel shows the radio spectra of both outer lobes (SW and NE) and NE inner of the target source fitted with the JP model with SYNAGE (for details, see Sect. 3.5).
In the text

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