Supermassive black hole (SMBH) binaries form due to galaxy mergers and minor accretion events. When the SMBHs are accreting, they form dual or binary AGN and can give rise to double-peaked emission lines in the optical spectra of the merger remnant. The double-peaked emission lines could also be due to jet-ISM interaction or rotating disks. One of the best ways to confirm dual/binary AGN in double-peaked AGN (DPAGN) is by using high resolution radio observations. We have observed a sample of 20 DPAGN at two or more frequencies using the Karl G. Jansky Very Large Array (VLA), of which one source is already published and the remaining 19 are presented in this paper. We have detected dual radio structures at separation of 10 kpc in three of our sample galaxies. Using the spectral index maps and optical spectra of the sources, we have confirmed that one of them is a dual AGN (DAGN), while the other two can be dual AGN or AGN+ star-forming nuclei pairs. Of the remaining sources, one has a clear core-jet structure and another source could be a core-jet structure or a DAGN. The remaining 13 sources are single cores while one source is not detected at any frequency. We find that for our dual AGN detection, the DPAGN emission lines do not originate from the dual/binary AGN. Instead, they could be due to outflows or jets. Hence, we conclude that DPAGN identified in low resolution SDSS spectra are not good indicators of dual/binary AGN. On the other hand, closely interacting galaxies or merger remnants are good candidates for detecting dual/binary AGN.
We present radio observations of the galaxy merger remnant Mrk 212 with the Karl G. Jansky Very Large Array (VLA) and the upgraded Giant Meter Radio Telescope (uGMRT). Mrk 212 has two previously known radio sources associated with the two optical nuclei, S1 and S2, with a projected separation of ∼6 kpc, making it a dual active galactic nuclei (AGN) candidate. Our new 15 GHz VLA observations reveal that S1 is a double radio source centred around the optical nucleus; its total extent is ∼750 parsec and its average 1.4−8.5 GHz spectral index is −0.81 ± 0.06. S1 therefore, resembles a compact symmetric object (CSO). The 15 GHz VLA image identifies the radio source at S2 to be a compact core. Our radio observations therefore strongly support the presence of a dual AGN in Mrk 212. The optical emission line flux ratios obtained from the Himalayan Chandra Telescope (HCT) observations however, show that S1 and S2 both fall in the AGN + SF (star formation) region of the BPT diagram. Weak AGN lying in the SF or AGN + SF intermediate regions in the BPT diagram have indeed been reported in the literature; our sources clearly fall in the same category. We find an extended radio structure in our newly reduced 8.5 GHz VLA data, that is offset by ∼1″ from the optical nucleus S2. New deep FUV and NUV observations with the Ultraviolet Imaging Telescope (UVIT) aboard AstroSat reveal SF knots around S2 as well as kpc-scale tidal tails; the SF knots around S2 coincide with the extended radio structure detected at 8.5 GHz. The radio spectral indices are consistent with SF. Any possible association with the AGN in S2 is unclear at this stage.
In this paper, we have modelled the dynamical and emission properties (in the presence of radiative losses and diffusive shock acceleration) of an observed S-shaped radio source (2MASX J12032061+131931) due to a precessing jet. In this regard, we have performed high-resolution 3D magnetohydrodynamic (MHD) simulations of a precessing jet in a galactic environment. We show the appearance of a distinct S-shape with two bright hotspots when the bow shock region weakens over time. The formed morphology is sensitive to the parameter selections. The increased interaction between the helical jet and the ambient medium and the deceleration of the jet due to MHD instabilities also greatly affect the resulting structure. Hence, kinematic models must be corrected for these deceleration effects in order to adequately predict the precession parameters. The synthetic spectral index map shows that the jet side and leading edges possess relatively steeper spectral index values than the jet ridge lines, whereas the hotspots show flat spectral index values. The jets are also found to be highly linearly polarized (up to 76%) and the magnetic field lines, in general, follow the jet locus which is formed due to the jet-ambient medium interaction. Diffusive shocks, in this context, keep the structure active during its course of evolution. Furthermore, we have demonstrated that these galaxies deviate significantly from the ‘equipartition’ approximation leading to a discrepancy in their spectral and dynamical age.
We present high resolution radio continuum observations with the Karl G. Jansky Very Large Array at 6, 8.5, 11.5 and 15 GHz of the double-peaked emission-line galaxy 2MASXJ12032061+1319316. The radio emission has a prominent S-shaped morphology with highly symmetric radio jets that extend over a distance of ∼ 1.5 (1.74 kpc) on either side of the core of size ∼ 0.1 (116 pc). The radio jets have a helical structure resembling the precessing jets in the galaxy NGC 326 which has confirmed dual active galactic nuclei (AGN). The nuclear bulge velocity dispersion gives an upper limit of (1.56±0.26)×108 M for the total mass of nuclear black hole(s). We present a simple model of precessing jets in 2MASXJ1203 and find that the precession timescale is around 10 5 years: this matches the source lifetime estimate via spectral aging. We find that the expected super massive black hole (SMBH) separation corresponding to this timescale is 0.02 pc. We used the double peaked emission lines in 2MASXJ1203 to determine an orbital speed for a dual AGN system and the associated jet precession timescale, which turns out to be more than the Hubble time, making it unfeasible. We conclude that the S-shaped radio jets are due to jet precession caused either by a binary/dual SMBH system, a single SMBH with a tilted accretion disk or a dual AGN system where a close pass of the secondary SMBH in the past has given rise to jet precession.
We studied the broadband X-ray spectra of Swift/BAT selected low-accreting AGNs using the observations from XMM-Newton, Swift, and NuSTAR in the energy range of 0.5 − 150 keV. Our sample consists of 30 AGNs with Eddington ratio, λEdd < 10−3. We extracted several coronal parameters from the spectral modelling, such as the photon index, hot electron plasma temperature, cutoff energy, and optical depth. We tested whether there exists any correlation/anti-correlation among different spectral parameters. We observe that the relation of hot electron temperature with the cutoff energy in the low accretion domain is similar to what is observed in the high accretion domain. We did not observe any correlation between the Eddington ratio and the photon index. We studied the compactness-temperature diagram and found that the cooling process for extremely low-accreting AGNs is complex. The jet luminosity is calculated from the radio flux, and observed to be related to the bolometric luminosity as $L_{\rm jet} \propto L_{\rm bol}^{0.7}$, which is consistent with the standard radio-X-ray correlation.
The Seyfert galaxy NGC 2639 was known to exhibit three episodes of AGN jet/lobe activity. We present here the upgraded Giant Metrewave Radio Telescope (uGMRT) 735 MHz image of NGC 2639 showing a fourth episode as witnessed by the discovery of ∼9 kpc radio lobes misaligned with the previously known ∼1.5 kpc, ∼360 parsec, and ∼3 parsec jet features detected through the Karl G. Jansky Very Large Array (VLA) and the Very Long Baseline Array (VLBA), respectively. Using the spectral ageing software BRATS, we derive the ages of the ∼9 kpc, ∼1.5 kpc, and ∼360 parsec episodes to be, respectively, $34^{+4}_{-6}$ Myr, $11.8^{+1.7}_{-1.4}$ Myr, and $2.8^{+0.7}_{-0.5}$ Myr, and conclude that minor mergers occurred 9 − 22 Myr apart. NGC 2639 shows a deficit of molecular gas in its central ∼6 kpc region. The GALEX NUV image also shows a deficiency of recent star-formation in the same region, while the star formation rate (SFR) surface density in NGC 2639 is lower by a factor of 5 − 18 compared to the global Schmidt law of star-forming galaxies. This makes NGC 2639 a rare case of a Seyfert galaxy showing episodic jet activity and possible signatures of jet-driven AGN feedback.
Simulations expect an enhanced star-formation and active galactic nuclei (AGN) activity during galaxy mergers, which can lead to formation of binary/dual AGN. AGN feedback can enhance or suppress star-formation. We have carried out a pilot study of a sample of ˜10 dual nuclei galaxies with AstroSat’s Ultraviolet Imaging Telescope (UVIT). Here, we present the initial results for two sample galaxies (Mrk 739, ESO 509) and deep multi-wavelength data of another galaxy (Mrk 212). UVIT observations have revealed signatures of positive AGN feedback in Mrk 739 and Mrk 212, and negative feedback in ESO 509. Deeper UVIT observations have recently been approved; these will provide better constraints on star-formation as well as AGN feedback in these systems.
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