Unveiling the kinematics of a central region in the triple AGN host NGC 7733-7734 interacting group

Stellar bars in galaxies are mainly characterised by their length, strength and pattern speed. Besides the bar length and pattern speed, the bar strength is a crucial characteristic. It signifies the bar’s contribution to the overall potential of the galaxy, which is hard to measure. But, there are many proxies to measure bar strength. For example, the maximum ellipticity (Laurikainen & Salo, 2002; Erwin, 2004) and the boxiness of the bar isophotes (Gadotti, 2011) have been used to estimate bar strength. Bar strength can also be estimated by measuring the torque exerted by the bar (Combes & Sanders, 1981; Buta & Block, 2001; Laurikainen & Salo, 2002) or by measuring the amplitude of the m=2 Fourier mode (Athanassoula, 2003). In this work, we are using one of the simplest definitions as given by Abraham & Merrifield (2000) and later used by Aguerri et al. (2009), as it is easy to determine from the ellipse fits. This method requires the measurement of the bar ellipticity ($\epsilon_{bar}$) at $r_{bar}$.

In order to measure the bar strength, first we need to deproject the galaxies according to the galaxy inclination (i). To estimate i of NGC 7733 and NGC 7734, we performed the isophotal analysis on $J$-band image (since, the $J$-band NIR images of NGC 7733 and NGC 7734 a have high signal-to-noise ratio (S/N) compared to other NIR images, a typical feature of IRSF observations (see, Nagayama et al. (2003)). The ellipse-fitting began a few arcsec away from the centre and extended to the outermost isophotes of the disc. All parameters, including the centres, were allowed to vary during the fitting. It allowed us to establish the ellipticity ($\epsilon$), position angle (PA), and mean intensity of the best-fit ellipse as a function of the semi-major axis. We estimated the $\epsilon$ corresponding to a surface brightness of 21 $mag/arcsec^{2}$, which is consistent with the surface brightness of 25 $mag/arcsec^{2}$ in B-band (Jarrett et al., 2003).

We determined, i, using $cos\ i=(1-\epsilon$). Now, we deproject the $J$-band NIR image of NGC 7733 into the sky plane using i = 57.23°and PA = 103.9°. Similarly, for NGC 7734, the deprojection has been done using i = 32.14°, PA = 144°. Once we deproject galaxy images, we use them for further analysis.

Several methods have been developed to measure the bar’s length. The three most popular methods are - the Fourier decomposition, the PA radial profile and the ellipticity radial profile. To estimate the bar length using Fourier decomposition, the Fourier analysis of azimuthal luminosity profiles is used (Ohta et al., 1990; Aguerri et al., 2000a). The other two methods use the isophotal analysis technique of fitting ellipses to photometric isophotes. In the PA radial profile method, the isophotes associated with the bar show nearly constant PA and then it changes to the outer disc orientation at large radii (Wozniak et al., 1995; Aguerri et al., 2000b). The bar length is determined at the radius where the PA changes by $\Delta$PA from the value corresponding to the local maxima of $\epsilon$. The value of $\Delta$PA used in literature is 5°(Aguerri et al., 2015; Guo et al., 2019). The radial ellipticity profile of a barred galaxy exhibits a rise from a central value of zero to a local maximum, where the bar dominates the isophotes. Then, it transitions to the disc-dominated isophotes and decreases to a local minimum, which corresponds to the end of the bar. Thus the local maximum represents the lower limit and the local minimum represents the upper limit of the bar length (Michel-Dansac & Wozniak, 2006). In this study, We adopt the radius reaching the local maximum $\epsilon$ where the PA of the bar isophotes’ remains constant (Barazza et al., 2008; Aguerri et al., 2009), as the bar length and the corresponding $\epsilon$ as bar ellipticity ($\epsilon_{bar}$). The bar strength ($f_{bar}$) was obtained using the bar’s axis ratio (b/a: where a and b are the semi-major and semi-minor axis, respectively), in line with the relation outlined in Aguerri et al. (2009) which is derived from the maximum value of the ellipticity profile along the bar, which usually happens at the end of the bar. The value of bar strength ranges from zero for an unbarred galaxy to close to unity for a strong bar (Abraham & Merrifield, 2000).

The $\epsilon_{bar}$ ($\epsilon_{bar}$ = 1 - $(b/a)_{bar}$) represents the maximum value of the ellipticity profile along the bar. Studies (Laurikainen et al., 2002, 2007) have shown that $\epsilon_{bar}$ correlates quite well with the measurement based on the maximum relative tangential force due to the bar (Buta & Block, 2001).

We have determined the bar strength ($f_{\text{bar}}$) to be 0.538 $\pm$ 0.007 for NGC 7733 and 0.267 $\pm$ 0.005 for NGC 7734. Since NGC 7733 is a highly inclined galaxy with a close companion, the bar ends are being affected due to the ongoing interaction with NGC 7734 as visible in Fig. 1. Hence the bar ends seem to be distorted and bar length and strength measurements are done as best as possible. The bar length and strength observed in the NGC 7733-34 system are consistent with the characteristics of late-type galaxies reported by Díaz-García et al. (2016), based on 3.6-$\mu$m imaging from the Spitzer Survey of Stellar Structure in Galaxies ($S^{4}G$). Notably, NGC 7733 displays a stronger bar compared to NGC 7734. This observation is particularly intriguing given that Seyfert galaxies generally do not exhibit strong bars (Shlosman et al., 2000). This discrepancy invites further numerical and theoretical investigations to explore the relationship between nuclear activity and stellar bar evolution.

NIR images are used for two-dimensional decomposition because the emission from the old stellar populations in galaxies dominates the NIR band, and dust has less of an impact on NIR emission. Therefore, NIR images are the best for modelling the light distribution in the bulge, bar, and discs of galaxies. We employed the two-dimensional (2-D) decomposition code GALFIT (Peng et al., 2002) to obtain measurements of structural components from NIR ($J$ and $K_{s}$) images of NGC 7733 and NGC 7734. GALFIT uses the Levenberg-Marquardt algorithm to minimise the $\chi^{2}$ between the observed image and the PSF-convolved model image (the sum of model components). We used two Sersic and one exponential profile to model the bulge, bar, and disc light distribution. Another Sersic profile was used to model the third galaxy, NGC 7733N, and details of the model parameters for this galaxy can be found in Yadav et al. (2021). Here, we present the model parameters for NGC 7733 and NGC 7734. The best-fit model is determined using a $\chi^{2}$ minimisation technique. The estimated errors on the recovered parameters in GALFIT models consider only the random (Poisson) noise due to the source brightness when the model fits the data perfectly. However, in the case of galaxy fitting, the discrepancies between data and model profile include not just Poisson sources but also errors arising from PSF variation in the image, parameter degeneracy, and sky background estimation errors (Peng et al., 2010). The unmodelled spiral arms cause further uncertainty on the retrieved values (Barway et al., 2020). However, Vika et al. (2013, 2014) estimate the associated errors of the fitted parameter based on the uncertainties in estimating the sky flux, which dominates the error budget. In bulge+disc decomposition, Vika et al. (2014) show the uncertainties associated with bulge $n$ and $R_{e}$ can vary by up to 25%. Kruk et al. (2018) considered the similar uncertainties in their bulge+bar+disc decomposition.

Since estimating the errors caused by each of these components is non-trivial, we present the best-fit parameters for both NGC 7733 and NGC 7734 without the associated errors in Table 1. The $J$-band NIR images, the model images, the residual images along with the 1-D surface brightness (hereafter - SB) profiles of NGC 7733 and NGC 7734 are shown in Fig 2. In the residual image of NGC 7734 (image (c) in the lower panel of Fig 2), we notice that some stellar contribution is present in the very central region. Also, from the 1-D SB profile (image (d) in the lower panel of Fig 2), we find some missing light (the model SB profile does not match the galaxy SB profile) in the very central 1 arcsec region. However, we cannot model it in our $J$-band data due to the resolution. We suspect that this missing light can be a contribution from a second bulge, which can be a classical bulge at the very centre of the galaxy. We tried to model the light distribution of NGC 7734 in HST/F606w band data using GALFIT, which did not return a good fit due to the contamination from dust and the structures in the NGC 7734’s central region. We then look into the central isophotes of NGC 7734 using HST data and find that the central ($\sim$230 pc) isophotes are nearly circular compared to the outer isophotes and it is shown in Fig 3. Studies on composite bulges (Méndez-Abreu et al., 2014; Erwin et al., 2015) have found the existence of a central classical bulge embedded in a disc-like bulge with the central isophotes becoming very round as we find in the centre of NGC 7734.

Based on the best-fitted model effective radius values ($R_{e}$), we found that the bulge and bar of NGC 7733 are larger than the respective components of NGC 7734. However, when taking into account the error bars as discussed earlier, both bulges could be consistent in size. Additionally, the disc of NGC 7733 is approximately twice the size of NGC 7734, as estimated from the disc scale length ($R_{s}$). Using the Sersic index ($n$) value, we found that NGC 7734 hosts a disc-like bulge ($1<n<2$) whereas NGC 7733 hosts a classical bulge ($n>2$). Although some studies (Costantin et al., 2018) suggest that sersic index alone is not a valid method for identifying the nature of bulges, it is extensively used to classify the bulge type. However, NGC 7733 hosts a disc-like bulge rather than a classical bulge with an uncertainty of 25% in $n$, which makes $n<2$. We also determined the mass of individual components in the $K_{s}$ band using $M/L=0.6$ (McGaugh & Schombert, 2014). We did not perform reddening correction due to galactic extinction since it is negligible in the $K_{s}$ band.

The existence of a disc-like bulge in NGC 7733 and NGC 7734 indicates that, most likely, it has been formed through secular evolution due to the presence of a bar.

The analysis of fine nuclear structural features in the central region of galaxies involves the use of a variety of image-processing techniques. One such technique, known as Structure Map, was introduced by Pogge & Martini (2002). This method can resolve structures as small as an image’s point spread function (PSF) scale. It effectively eliminates the smooth large-scale light distribution and enhances the visibility of narrow dust lanes and emission-line gas in nearby galaxies. We have applied this method to the HST/$F606W$ images of NGC 7733 and NGC 7734. The process involves convolving the image with a PSF for the PC1 camera corresponding to the filter band-pass generated using TINYTIM (Krist et al., 2011). The original image is then divided by the PSF-convolved image, and the resulting ratio is further convolved with the transpose of the model PSF. Mathematically, a structure map S is defined as:

Where $I$ is the original image, $P$ is the model PSF, $P^{t}$ is the transpose of the PSF, and $\otimes$ is the convolution operator. This technique is based on the Richardson-Lucy (RL) image restoration algorithm. The structure maps for the central 8 arcsec² and 6 arcsec² square region of NGC 7733 and NGC 7734, respectively, are shown in Fig. 4. Dark regions represent the dust-obscured areas, in contrast, bright regions correspond to either the location of heightened stellar light (for example, star-forming regions) or emission-line regions (the $F606W$ filter reveals several bright emission lines from high surface-brightness regions due to its wide bandwidth). In NGC 7733, we identified a nuclear disc-like structure that appears like a nuclear ring due to presence of dust. The semi-major axis of this nuclear disc is $\sim$ $1.116$ kpc. Conversely, the central feature in NGC 7734 resembles a disc and spiral arms-like structure in the outer parts as depicted in Fig. 4.

We utilized the wide field mode (WFM) of the MUSE IFS, which provides an archival science-ready data cube of the galaxy group NGC 7733-34. The data cube was analysed using the 3.1.0 version of Galaxy IFU Spectroscopy Tool (GIST) (Bittner et al., 2019), a comprehensive scientific analysis framework for fully reduced (integral-field) spectroscopic data. GIST leverages the penalized pixel-fitting code (pPXF) (Cappellari & Emsellem, 2004; Cappellari, 2017, 2022) to extract stellar line-of-sight velocity distribution (LOSVD), that is, stellar kinematics, and the Gas and Absorption Line Fitting (GandALF) (Sarzi et al., 2006; Falcón-Barroso et al., 2006) to determine the emission line fluxes and gaseous kinematics. Voronoi binning (Cappellari & Copin, 2003) was used for spatially binning the data within the wavelength range $480-580$ nm to achieve a S/N of $30$. Spaxels with S/N greater than $30$ remain unbinned, while those with S/N less than three were excluded to eliminate noisy data before binning. Additionally, all spectra were corrected for galactic extinction values in the direction of the target. It is important to keep in mind that the selected wavelength range includes a potentially strong emission line ($H\beta$). However, in the NGC 7733-34 group, $H\beta$ emission is significantly low, thus the Voronoi binning will not be substantially affected by the selected wavelength range.

For the analysis of stellar kinematics, pPXF utilizes a non-negative linear combination of template spectral libraries convolved with the LOSVD in pixel space. The method employs a least square minimisation technique to determine the best fit LOSVD parameters. In the current analysis, to prevent the contamination from the redder wavelength, the fitting of the spectra is carried out between the wavelength range $480-580$ nm, as suggested by Bittner et al. (2019, 2021). During the fit, prominent emission lines within this range are masked. An 8th-order multiplicative Legendre polynomial is incorporated into the fit to address any minor differences in the continuum between observed and template spectra. Taking these best-fit values into account, spatial maps of the stellar velocity ($V$) in the galaxy’s rest frame, velocity dispersion ($\sigma$), and higher order Gauss-Hermite moments ($h_{3}$ and $h_{4}$) of the galaxies are constructed. In this work, we are using V, $\sigma$ and $h_{3}$ maps for further discussions. The $h_{4}$ moment is not used because it does not provide relevant information for this work; thus, we haven’t included a corresponding map of $h_{4}$ moment.

In the science-ready $FUV$ and narrow band $H\alpha$ images of NGC 7733 and NGC 7734, the star-forming regions appear as bright clumps. To identify these clumps, we utilized the Source Extractor Software (SExtractor) (Bertin & Arnouts, 1996). This software takes a threshold value as input to detect the source, with pixels exceeding the threshold count identified as a source. For the $FUV$ image, we set the detection threshold at 1.5$\sigma$, and for the $H\alpha$ image, it is $3\sigma$, where $\sigma$ represents the global background noise. In the image of NGC 7733, we detected 71 regions in $FUV$ and 53 regions in $H\alpha$. Similarly, in the image of NGC 7734, we ascertained 181 regions in $FUV$ and 64 regions in $H\alpha$. After correcting for instrumental resolution, we found 41 $FUV$ and 51 $H\alpha$ regions in the image of NGC 7733, with three of the regions associated with nuclear emission. For the image of NGC 7734, we obtained 73 $FUV$ and 51 $H\alpha$ regions. Among these, 11 $FUV$ and 4 $H\alpha$ regions are located along the bar.

In order to conduct aperture photometry on the identified sources, we employed Photutils, which is a Python astropy package³³3https://photutils.readthedocs.io/en/stable/aperture.html. The star-forming regions represent a group of young, vibrant stars, and the magnitude calculated from these regions is influenced by both galactic and internal extinction. We determined galactic extinction in $UV$ and $H\alpha$ by utilizing the extinction law outlined by Cardelli et al. (1989) -

Here, x is the wave number, a(x) and b(x) were evaluated from Cardelli et al. (1989), $R_{v}=3.1$ for Milky Way and A(V) = 0.073 for NGC 7733 and 0.074 for NGC 7734.

For star-forming disc galaxies, Kennicutt (1998) suggested $H\alpha$ extinction, $A_{H\alpha}=1.1$ mag. To correct for internal extinction we used $A_{H\alpha}=1.1$ mag and $A_{FUV}/A_{H\alpha}=3.6$ (Leroy et al., 2008). We derived the SFR in the $FUV$ filter using the following relation (Leroy et al., 2008) -

To measure the SFR of the $H\alpha$ star-forming regions we used the following relation (Calzetti et al., 2007) -

The luminosity in both the equations (Eqs. 4 and  5) is the intrinsic luminosity.

In this section, we examine the signatures present in the kinematic maps obtained from MUSE data, which indicate the existence of various structural components. The higher-order $h_{3}$ moment which quantifies the skewness of LOSVD is crucial to characterize the stellar orbital structure.

To measure emission line properties such as emission line fluxes, gas kinematics, and emission-free continuum spectra, GIST utilizes the GandALF module (Sarzi et al., 2006; Falcón-Barroso et al., 2006). Each user-specified emission line is treated as a Gaussian template additional to the stellar templates. The best-fitting gaseous properties are estimated using a linear combination of these emission line templates with the spectral library template. We have generated gas ($H\alpha$) velocity and velocity dispersion maps for NGC 7733 (top) and NGC 7734 (bottom), as shown in Fig. 7.

In our investigation, we have conducted a multi-wavelength analysis to examine the occurrence of $H\alpha$ and $FUV$ emission along the bar of the barred spiral galaxy NGC 7734 in the triple AGN group NGC 7733-34. A recent study by Yadav et al. (2023) examined the SF in NGC 7733 and NGC 7734 using $FUV$ data from UVIT and $H\alpha$ data from MUSE. Our measured mean $\Sigma_{SFR}$ aligns with their estimated values for both galaxies. Additionally, they documented the presence of $H\alpha$ emission along the bar of NGC 7734.

We conducted a similar analysis on both the $FUV$ and $H\alpha$ images of NGC 7734. Remarkably, we observed the presence of $FUV$ emission along with $H\alpha$ in the bar region of NGC 7734. We identified and characterised all the SFCs in the $FUV$ and $H\alpha$ images and calculated their $\Sigma_{SFR}$. We categorized the SFCS into three regions: 1) Central region, which encompasses the central part of the galaxy, including the bar and bar ends, 2) Inner ring and 3) Outer ring. The detailed discussion on the SF in NGC 7734 is given is Appendix A. The number of detected clumps along with the median value of log $\Sigma_{SFR}$ for the three regions as described above are presented in Table 2.

In previous research, the impact of the bar on central SF has been documented (Combes & Gerin, 1985). Understanding SF along the bar is crucial for gaining insights into the role of the bar in galaxy evolution. In a recent study, Fraser-McKelvie et al. (2020) identified the presence of $H\alpha$ emissions along the bar and at the bar ends in a sample of MaNGA galaxies, particularly those in low-density environments. Their findings indicate that the $H\alpha$ bar leads the stellar bar, as evidenced by measuring the respective $H\alpha$ and stellar bar position angles.

In Fig. 8, we present the UVIT $FUV$ image (left panel) and MUSE $H\alpha$ image (right panel) of NGC 7734. We have overlaid the $J$ band bar PA on both the $FUV$ and $H\alpha$ images passing through the galaxies’ photometric centre, which we determined from the isophotal analysis. The PA of the bar is measured from isophotal analysis on $J$ band image as discussed in Sec. 3.1. The estimated bar PA of NGC 7734 is 22.48°$\pm$ 0.79°. We found that there is an observable difference in the position angle between the stellar bar and $H\alpha$ along the stellar bar, whereas the $FUV$ bar is primarily aligned with the stellar bar. The presence of $H\alpha$ emission along the bar is intriguing as it suggests recent SF (around 10 million years ago). Additionally, the coexistence of $FUV$ and $H\alpha$ emissions along the bar indicates the presence of young stars in this region (approximately 100 million years old). It is well known that bar-induced gas inflow triggers SF in the central regions of galaxies, and it has been observed that barred galaxies tend to have higher gas concentrations than their unbarred counterparts, which correlates with increased rates of central SF (see, Sakamoto et al. (1999); Jogee et al. (2005)).

Additionally, the $g-r$ colour image of NGC 7734 bar is displayed in the left panel of Fig. 9, with contours taken from the $g$-band image. A detailed examination of the bar reveals clumpy stellar light within the optical contour, which we have marked as (1, 2, 3, and 4, respectively). Clumps 1 and 4 are located at the northern and southern ends of the bar respectively, while clump 2 represents the central region, identified as a disc-like bulge based on the Sersic index. Clump 3 is the clump present along the bar on the southern side of the bulge, it has also been marked in Fig. 1 and bottom panel of Fig. 4. The presence of a clumpy structure, particularly clump 3, along the bar in the optical image, is noteworthy. We observe $FUV$ emission around the clumpy region in the left panel of Fig. 8, while the $H\alpha$ gas is not present there, having instead moved eastward.

We suspect that clump 3 can be a compact galaxy projected in a way that it appears to be part of the bar. In order to confirm this, we extracted the spectra from the MUSE cube by taking a circular aperture with a radius of 2.26 arcsec around the clump as well as around the centre of NGC 7734. The continuum subtracted observed spectra for bulge and clump 3 are shown by black and blue lines respectively in the right panel of Fig 9. We zoomed in the spectrum around the H$\alpha$ and [NII] doublet emission lines. We fitted Gaussian profiles to all the three spectral lines and the fitted spectra are shown in red. We also plotted the peaks of the emission lines along with their respective observed wavelength. We estimated the red-shift using $H\alpha$ and [NII] lines from the MUSE data cube and found it to be 0.03508 $\pm$ 0.00003, which is similar to the red-shift of the host galaxy (z = 0.03527 $\pm$ 0.00006) (Yadav et al., 2021). Thus, the clump is moving with a velocity of 57 $km$ $s^{-1}$ with respect to the galaxy NGC 7734. So, the redshift measurement does not support our assumption. We are unable to detect any velocity gradient surrounding the clump in our stellar velocity map (see, Fig. 6), similar to Yadav et al. (2021)’s discovery of NGC 7733N.

However, the size and prominence of clump 3 in the optical images enforces us to estimate its mass. We measured its mass using the $g-r$ colour following the relation of Bell et al. (2003). By visually inspecting a circular region with a radius of 2.26 arcsec (approximately 1.73 kpc at the distance of NGC 7734), we determined the galactic extinction corrected colour and, hence, the mass to be (3.37 $\pm$ 0.44) $\times$ 10⁷ $M_{\odot}$. Additionally, it appears red in the $g-r$ colour map with a colour value of 0.826 $\pm$ 0.05, indicating that it is not merely a star-forming clump.

Studies of compact elliptical galaxies (cEs) suggest that they have stellar masses of $10^{8}M_{\odot}-10^{10}M_{\odot}$ with sizes in the range of 100 - 900 pc and thus they have very high stellar density (Faber, 1973; Choi et al., 2002). These low mass cEs are preferentially observed near the giant galaxies (like the presence of M32-like compact object in the close proximity of the M31 galaxy) (Nieto & Prugniel, 1987). The kinematical study of cEs by Ferré-Mateu et al. (2021) shows that the LOS stellar velocity of these galaxies have a maximum value of around 20-60 $km$ $s^{-1}$. Utilizing the GIST workflow on the MUSE data cube as discussed in Sec. 3.4, we derived the LOS stellar kinematics of clump 3. The stellar velocity map is shown in the right panel of Fig. 9. We estimated the median value of LOS velocity of clump 3 by considering a circular region of radius 2.26 arcsec. The velocity value is 26 $\pm$ 4 $km$$s^{-1}$.

Although the estimated stellar mass of clump 3 is slightly less compared to the CEs, it falls in the regime of ultra-compact dwarf galaxies (UCDs). The UCDs have stellar masses of $10^{6}M_{\odot}-10^{8}M_{\odot}$ with a projected radius of up to 20 pc, making them the most compact galaxies in the universe (Drinkwater et al., 2000; Brodie et al., 2011). In our analysis, the stellar mass of clump 3 falls in the regime of UCDs, but its size is large, rejecting its possibility of being a UCD. Thus, based on the mass and size of the clump, we are speculating that it can be a compact galaxy. Also, the LOS velocity measurement can be contaminated due to the presence of the bar in NGC7734, which is along the line of nodes of the galaxy, so the LOS velocity measurement associated with clump 3 is limited. It will represent the upper limit of the velocity of clump 3. Hence, the mass and the LOS velocity measurement of clump 3 follow the classification of cEs. So there is a possibility that clump 3 is a compact elliptical galaxy (cE) and hence it could be the fourth galaxy in this interacting group. We named it as NGC 7734S. This interaction seems to be the primary factor driving the continuous formation of stars in the central region. Additionally, the effect of this interaction may affect the kinematics (both stellar and gas) of the galaxy centre (despite the galaxy containing a disc-like bulge) and this has been discussed in Sec. 4.1.2 and Sec. 4.2.2.

The interaction between galaxies can result in gas exchange and gas inflow towards the central region, triggering the formation of central stars (Di Matteo et al., 2007; Hopkins et al., 2008). While this interaction can also trigger an AGN, it is not the sole cause of AGN activity (Ellison et al., 2011). Some studies have found evidence of mergers associated with AGN activity (Surace et al., 1998; Smirnova et al., 2006; Combes et al., 2009), while others have claimed that statistically there is no evidence of a merger associated with AGN activity, with a similar percentage found in both active and inactive galaxies (Coldwell & Lambas, 2006). Conversely, AGN feedback can lead to the cessation of SF in the central region. Jahan-Miri & Khosroshahi (2001) have shown that the nuclei of both galaxies in the NGC 7733-34 galaxy group are redder compared to the other parts of the galaxies, indicating the absence of nuclear starburst activity in the pair.

In this study, we investigate the SF along the bar in NGC 7734 and bar quenching and/or inside-out quenching resulting from AGN activity in NGC 7733 of this interacting system of galaxies. The feedback from an active AGN depletes gas from the central region, leading to the cessation of SF. Studies by Ellison et al. (2018); Bluck et al. (2020); Lammers et al. (2022) examined central SF suppression (inside-out quenching) in a large sample of MaNGA galaxies. They concluded that AGN feedback suppresses central (kpc scale) SF in nearby galaxies, it can also cause SF quenching along the bar, known as bar quenching. Additionally, Lammers et al. (2022) demonstrated that AGN feedback could not drive galaxy-wide quenching in our nearby universe, instead leaving galaxies in the green valley. Feedback from the active AGN heats the interstellar medium (ISM), preventing the gas from cooling and ceasing the gas inflow towards the centre, suppressing the SF along the bar. This result provides direct observational evidence of AGN feedback suppressing SF. Our findings indicate the absence of SF in the bar of NGC 7733, which appears redder. Notably, NGC 7733 hosts a Seyfert 2 AGN as identified by Yadav et al. (2021). Ongoing interaction with NGC 7733N and NGC 7734 has led to continued SF in the outer ring/spiral arm of NGC 7733. The SFR is higher towards the northern spiral arm, likely due to the presence of NGC 7733N. The lack of SF along the bar could be attributed to the negative feedback from the active AGN.

Strong bars are evident and long and are more frequently associated with the presence of AGNs than weak bars, which are typically smaller and fainter (Garland et al., 2024). Observations suggest that strong bars are more commonly found in quiescent galaxies, contrasting with the weaker bars, indicating that either the presence of a strong bar contributes to the cessation of star formation or that strong bars more readily form in quiescent environments (Géron et al., 2021). A comparison of bar properties in NGC 7733 and NGC 7734 reveals that the bar in NGC 7733 is both longer and stronger. A comprehensive analysis of a sample of interacting galaxies hosting bars and AGNs is necessary to explore the relationship between bar length and strength, star formation, and AGN activity in barred galaxies undergoing close interaction. Such study then can be compared with isolated barred galaxies Guo et al. (2019). It has been reported that the gas funnelling by the bar towards the centre increases the central SF as well as increases the gas consumption from the disc, and the galaxy turns into quenched from star-forming (Kormendy & Kennicutt, 2004; Masters et al., 2010). Géron et al. (2021) have shown that stronger bars help to quench the host galaxies through secular evolution. Our system is interacting, and we found that NGC 7733 hosts a strong and large bar with SF in the spiral arm and inside-out quenching/bar quenching. Despite having a strong bar, the $H\alpha$ and $FUV$ emission along the bar is absent in NGC 7733. Thus, a negative feedback of AGN can be a possible scenario of bar quenching in NGC 7733.