Active Galactic Nuclei Candidates Research Articles

Variable Active Galactic Nuclei in the Galaxy Evolution Explorer Time Domain Survey

We searched the northern hemisphere fields of the Galaxy Evolution Explorer Time Domain Survey for galaxies with UV variability indicative of active galactic nuclei (AGNs). We identified 48 high-probability candidate AGNs from a parent sample of 1819 galaxies in the NASA Sloan Atlas catalog. We further characterized these systems using optical spectroscopic diagnostics, Wide-field Infrared Survey Explorer IR color selection criteria, and spectral energy distribution modeling. Of the 48 candidates, eight were identified as AGNs from optical emission lines, two were identified by their IR colors, and 28 were identified through spectral energy decomposition. Observational biases of each selection method are discussed in connecting these AGN subsamples to another. By selecting AGNs based on UV variability, we also identified six low-mass AGN candidates, all of which would have been missed by spectroscopic selection.

Search for Periodicities in High Energy AGNs with a Time Domain Approach

This paper investigates a new methodology to search for periods in light curves of high-energy gamma-ray sources such as active galactic nuclei (AGNs). High-energy light curves have significant stochastic components, making period detection somewhat challenging. In our model, periodic terms, drifts of the light curves, and random walk with a correlation between flux points due to colored noise are taken into account independently. The parameters of the model are obtained directly from a Markov Chain Monte Carlo minimization. The time periods found are compared to the output of the publicly available Agatha program. The search method is applied to high-energy periodic AGN candidates from the Fermi-LAT catalog. The significance of periodic models over pure noise models is discussed. Finally, the variability of the period and amplitude of oscillating terms is studied on the most significant candidates.

A Resolved Search for AGN in the Centers of Nearby Galaxies with WISE

We investigate the mid-infrared detection of active galactic nucleus (AGN) in nearby galaxies and the effects of contamination by starlight and dust emission from the host galaxy. We used a sample of ∼14,000 nearby galaxies from the z = 0 Multiwavelength Galaxy Synthesis to study the effect of isolating the galaxy center on AGN detection. We identify 39 known AGN and 9 additional previously selected AGN candidates using color selection in WISE Bands 1 and 2. Most AGN identified using the smallest apertures around the nucleus are lost from the WISE color selection at larger aperture radii. This suggests that when low spatial resolution or integrated galaxy measurements are used to identify AGN in the mid-IR, lower luminosity AGN may go undetected due to contamination from the galaxy’s dust emission and starlight.

SDSS-IV MaNGA: Identification and multiwavelength properties of Type-1 AGN in the DR15 sample

ABSTRACT We present a method to identify type-1 active galactic nuclei (AGNs) in the central 3 arcsec integrated spectra of galaxies in the MaNGA DR15 sample. It is based on flux ratios estimates in spectral bands flanking the expected h α broad component h αBC. The high signal-to-noise ratio obtained (mean S/N = 84) permits the identification of h αBC without prior subtraction of the host galaxy (HG) stellar component. A final sample of 47 type-1 AGN is reported out of 4700 galaxies at z < 0.15. The results were compared with those from other methods based on the SDSS DR7 and MaNGA data. Detection of type-1 AGN in those works compared to our method goes from 26 per cent to 81 per cent. Spectral indexes were used to classify the type-1 AGN spectra according to different levels of AGN-HG contribution, finding 9 AGN-dominated, 14 intermediate, and 24 HG-dominated objects. Complementary data in NIR-MIR allowed us to identify type I AGN-dominated objects as blue and HG-dominated as red in the WISE colours. From NVSS and FIRST radio continuum data, we identify 5 HERGs (high-excitation radio galaxies) and 4 LERGs (low-excitation radio galaxies), three showing evidence of radio-jets in the FIRST maps. Additional X-ray data from ROSAT allowed us to build [O iii] and h αBC versus X-ray, NIR-MIR, and radio continuum diagrams, showing that L(h αBC) and L([O iii]) provide good correlations. The range in h αBC luminosity is wide 38 < logL(h αBC) < 44, with log FWHM(h αBC) ∼ 3–4, covering a range of Eddington ratios of −5.15 < log Lbol/LEdd < 0.70. Finally, we also identify and report ten possible changing-look AGN candidates.

NuSTAR Observations of 52 Compton-thick Active Galactic Nuclei Selected by the Swift/Burst Alert Telescope All-sky Hard X-Ray Survey

We present systematic broadband X-ray spectral analysis of 52 Compton-thick () active galactic nucleus (CTAGN) candidates selected by the Swift/Burst Alert Telescope all-sky hard X-ray survey observed with Chandra, X-ray Multi-Mirror Mission-Newton (XMM-Newton), Swift/X-Ray Telescope, Suzaku, and NuSTAR. The XMM-Newton data of 10 objects and the NuSTAR data of 15 objects are published for the first time. We use an X-ray spectral model from a clumpy torus (XClumpy) to determine the torus properties. As a result, the hydrogen column density along the line of sight obtained from the XClumpy model indicates that 24 objects are Compton-thin AGNs and 28 objects are CTAGNs in a 90% confidence interval. The main reason is the difference in the torus model applied. The hydrogen column density along the equatorial direction of CTAGNs inferred from the XClumpy model is larger than that of less obscured AGNs. The Compton-thin torus covering factor C 22 obtained from the XClumpy model is consistent with that of Ricci et al. in the low Eddington ratio (), whereas C 22 inferred from the XClumpy model is larger than that of Ricci et al. in the high Eddington ratio (). The average value of the Compton-thick torus covering factor C 24 obtained from the XClumpy model is %. This value is larger than that of Ricci et al. (%) based on the assumption that all AGNs have intrinsically the same torus structure. These results suggest that the structure of CTAGNs may be intrinsically different from that of less obscured AGNs.

SNAD transient miner: Finding missed transient events in ZTF DR4 using k-D trees

We report the automatic detection of 11 transients (7 possible supernovae and 4 active galactic nuclei candidates) within the Zwicky Transient Facility fourth data release (ZTF DR4), all of them observed in 2018 and absent from public catalogs. Among these, three were not part of the ZTF alert stream. Our transient mining strategy employs 41 physically motivated features extracted from both real light curves and four simulated light curve models (SN Ia, SN II, TDE, SLSN-I). These features are input to a k-D tree algorithm, from which we calculate the 15 nearest neighbors. After pre-processing and selection cuts, our dataset contained approximately a million objects among which we visually inspected the 105 closest neighbors from seven of our brightest, most well-sampled simulations, comprising 89 unique ZTF DR4 sources. Our result illustrates the potential of coherently incorporating domain knowledge and automatic learning algorithms, which is one of the guiding principles directing the SNAD team. It also demonstrates that the ZTF DR is a suitable testing ground for data mining algorithms aiming to prepare for the next generation of astronomical data.

RESOLVE and ECO: Finding Low-metallicity z ∼ 0 Dwarf AGN Candidates Using Optimized Emission-line Diagnostics

Existing star-forming vs. active galactic nucleus (AGN) classification schemes using optical emission-line diagnostics mostly fail for low-metallicity and/or highly star-forming galaxies, missing AGN in typical z ∼ 0 dwarfs. To recover AGN in dwarfs with strong emission lines (SELs), we present a classification scheme optimizing the use of existing optical diagnostics. We use Sloan Digital Sky Survey emission-line catalogs overlapping the volume- and mass-limited REsolved Spectroscopy Of a Local VolumE (RESOLVE) and Environmental COntex (ECO) surveys to determine the AGN percentage in SEL dwarfs. Our photoionization grids show that the [O iii]/Hβ versus [S ii]/Hα diagram (S ii plot) and [O iii]/Hβ versus [O i]/Hα diagram (O i plot) are less metallicity sensitive and more successful in identifying dwarf AGN than the popular [O iii]/Hβ versus [N ii]/Hα diagnostic (N ii plot or “BPT diagram”). We identify a new category of “star-forming AGN” (SF-AGN) classified as star-forming by the N ii plot but as AGN by the S ii and/or O i plots. Including SF-AGN, we find the z ∼ 0 AGN percentage in dwarfs with SELs to be ∼3%–16%, far exceeding most previous optical estimates (∼1%). The large range in our dwarf AGN percentage reflects differences in spectral fitting methodologies between catalogs. The highly complete nature of RESOLVE and ECO allows us to normalize strong emission-line galaxy statistics to the full galaxy population, reducing the dwarf AGN percentage to ∼0.6%–3.0%. The newly identified SF-AGN are mostly gas-rich dwarfs with halo mass <1011.5 M ⊙, where highly efficient cosmic gas accretion is expected. Almost all SF-AGN also have low metallicities (Z ≲ 0.4 Z ⊙), demonstrating the advantage of our method.

CHANG-ES – XXVII. A radio/X-ray catalogue of compact sources in and around edge-on galaxies

ABSTRACT We present catalogues of discrete, compact radio sources in and around the discs of 35 edge-on galaxies in the Continuum Halos in Nearby Galaxies – an EVLA Survey. The sources were extracted using the pybdsf program at both 1.6 GHz (L band) and 6.0 GHz (C band) from matching resolution (≈3 arcsec) data. We also present catalogues of X-ray sources from Chandra data sets for 27 of the galaxies. The sources at the two radio frequency bands were positionally cross-correlated with each other, and the result cross-correlated with the X-ray sources. All catalogues are included for download with this paper. We detect a total of 2507 sources at L band and 1413 sources at C band. 75 sources have been successfully cross-correlated in both radio bands plus X-ray. Three new nuclear sources are candidates for low luminosity active galactic nuclei in NGC 3877, NGC 4192, and NGC 5792; the one in NGC 3877 also appears to be variable. We also find new nuclear sources in two companion galaxies: NGC 4435 (companion to NGC 4438) and NGC 4298 (companion to NGC 4302). We have also discovered what appears to be a foreground double star; each star has X-ray emission and there is radio emission at both L band and C band in between them. This could be a colliding wind binary system. Suggestions for follow-up studies are offered.

Investigating the Accretion Nature of Binary Supermassive Black Hole Candidate SDSS J025214.67−002813.7

Abstract We present results of a multiwavelength analysis of SDSS J025214.67−002813.7, a system that has been previously classified as a binary active galactic nucleus (AGN) candidate based on periodic signals detected in the optical light curves. We use available radio−X-ray observations of the system to investigate the true accretion nature. Analyzing new observations from XMM-Newton and NuSTAR, we characterize the X-ray emission and search for evidence of circumbinary accretion. Although the 0.5–10 keV spectrum shows evidence of an additional soft emission component, possibly due to extended emission from hot nuclear gas, we find the spectral shape is consistent with that of a single AGN. Compiling a full multiwavelength spectral energy distribution (SED), we also search for signs of circumbinary accretion, such as a “notch” in the continuum due to the presence of minidisks. We find that the radio–optical emission agrees with the SED of a standard, radio-quiet, AGN; however, there is a large deficit in emission blueward of ∼1400 Å. Although this deficit in emission can plausibly be attributed to a binary AGN system, we find that the SED of SDSS J0252−0028 is better explained by emission from a reddened, single AGN. However, future studies of the expected hard X-ray emission associated with binary AGNs (especially in the unequal-mass regime) will allow for more rigorous analyses of the binary AGN hypothesis.

Strong [O iii] λ5007 Emission-line Compact Galaxies in LAMOST DR9: Blueberries, Green Peas, and Purple Grapes

Abstract Green Pea and Blueberry galaxies are well known for their compact size, low mass, strong emission lines, and analogs to high-z Lyα-emitting galaxies. In this study, 1547 strong [O iii] λ5007 emission-line compact galaxies with 1694 spectra are selected from LAMOST DR9 at the redshift range from 0.0 to 0.59. According to the redshift distribution, these samples can be separated into three groups: Blueberries, Green Peas, and Purple Grapes. Optical [Mg ii] λ2800 line feature, BPT diagram, multiwavelength spectral energy distribution (SED) fitting, mid-IR (MIR) color, and MIR variability are deployed to identify 23 active galactic nucleus candidates from these samples, which are excluded for the following star formation rate (SFR) discussions. We perform the multiwavelength SED fitting with GALEX UV and WISE MIR data. Color excess from the Balmer decrement shows that these strong [O iii] λ5007 emission-line compact galaxies are not highly reddened. The stellar mass of the galaxies is obtained by fitting LAMOST calibrated spectra with the emission lines masked. We find that the SFR is increasing with the increase of redshift, while for the sources within the same redshift bin the SFR increases with mass with a similar slope to the star-forming main sequence. These samples have a median metallicity of 12 + log(O/H) of 8.10. The metallicity increases with mass, and all the sources are below the mass–metallicity relation. The direct-derived T e -based metallicity from the [O iii] λ4363 line agrees with the empirical N2-based empirical gas-phase metallicity. Moreover, these compact strong [O iii] λ5007 lines are mostly in a less dense environment.

Revealing dual radio sources in a sub-kpc-scale binary active galactic nucleus candidate

ABSTRACT We present new imaging of a sub-kpc-scale binary active galactic nucleus (AGN) candidate from the Karl G. Jansky Very Large Array (VLA) and the Multi-Element Radio Linked Interferometer Network (e-MERLIN). Two unresolved radio sources of similar luminosity around 1022 WHz−1 are identified in ∼35 h of e-MERLIN 6 cm imaging. These radio sources have an angular separation of 0.19 ± 0.06 arcsec and position angle (PA) of 22° ± 10°, corresponding to a projected separation of 0.95 ± 0.29 kpc at the epoch of the source. Our results suggest the presence of a kpc-scale active black hole pair hosted by two galaxies in the late stage of a merger at z = 0.35. This work follows Woo et al., which presented two optical sources with a similar separation and PA, and a velocity separation of 200 km s−1. Our target adds to the currently limited sample of close-separation binary AGNs, which will aid in understanding the frequency of mergers and the stochastic gravitational wave background.

Compton-thick AGN in the NuSTAR Era VI: The Observed Compton-thick Fraction in the Local Universe

Abstract We present the analysis of simultaneous Nuclear Spectroscopic Telescope Array (NuSTAR) and XMM-Newton data of eight Compton-thick active galactic nuclei (CT-AGN) candidates selected in the Swift-BAT 100 month catalog. This work is part of an ongoing effort to find and characterize all CT-AGN in the Local (z ≤ 0.05) Universe. We used two physically motivated models, MYTorus and borus02, to characterize the sources in the sample, finding five of them to be confirmed CT-AGN. These results represent an increase of ∼19% over the previous NuSTAR-confirmed, BAT-selected CT-AGN at z ≤ 0.05, bringing the total number to 32. This corresponds to an observed fraction of ∼8% of all AGN within this volume-limited sample, although it increases to 20% ± 5% when limiting the sample to z ≤ 0.01. Out of a sample of 48 CT-AGN candidates, selected using BAT and soft (0.3−10 keV) X-ray data, only 24 are confirmed as CT-AGN with the addition of the NuSTAR data. This highlights the importance of NuSTAR when classifying local obscured AGN. We also note that most of the sources in our full sample of 48 Seyfert 2 galaxies with NuSTAR data have significantly different lines of sight and average torus column densities, favoring a patchy torus scenario.

The AGN Fraction in Dwarf Galaxies from eROSITA: First Results and Future Prospects

Abstract Determining the fraction of nearby dwarf galaxies hosting massive black holes (BHs) can inform our understanding of the origin of “seed” BHs at high redshift. Here we search for signatures of accreting massive BHs in a sample of dwarf galaxies (M ⋆ ≤ 3 × 109 M ⊙, z ≤ 0.15) selected from the NASA-Sloan Atlas (NSA) using X-ray observations from the eROSITA Final Equatorial Depth Survey (eFEDS). On average, our search is sensitive to active galactic nuclei (AGNs) in dwarf galaxies that are accreting at ≳1% of their Eddington luminosity. Of the ∼28,000 X-ray sources in eFEDS and the 495 dwarf galaxies in the NSA within the eFEDS footprint, we find six galaxies hosting possible active massive BHs. If the X-ray sources are indeed associated with the dwarf galaxies, the X-ray emission is above that expected from star formation, with X-ray source luminosities of L 0.5–8 keV ∼ 1039–40 erg s−1. Additionally, after accounting for chance alignments of background AGNs with dwarf galaxies, we estimate there are between zero and nine real associations between dwarf galaxies and X-ray sources in the eFEDS field at the 95% confidence level. From this we find an upper limit on the eFEDS-detected dwarf galaxy AGN fraction of ≤1.8%, which is broadly consistent with similar studies at other wavelengths. We extrapolate these findings from the eFEDS sky coverage to the planned eROSITA All-Sky Survey and estimate that upon completion, the all-sky survey could yield as many as ∼1350 AGN candidates in dwarf galaxies at low redshift.

The Physics of the Coronal-line Region for Galaxies in Mapping Galaxies at Apache Point Observatory

Abstract The fundamental nature and extent of the coronal-line region (CLR), which may serve as a vital tracer for active galactic nucleus (AGN) activity, remain unresolved. Previous studies suggest that the CLR is produced by AGN-driven outflows and occupies a distinct region between the broad-line region and the narrow-line region, which places it tens to hundreds of parsecs from the galactic center. Here, we investigate 10 coronal line (CL; ionization potential ≳100 eV) emitting galaxies from the Sloan Digital Sky Survey IV Mapping Galaxies at Apache Point Observatory (MaNGA) catalog with emission from one or more CLs detected at ≥5σ above the continuum in at least 10 spaxels—the largest such MaNGA catalog. We find that the CLR is far more extended, reaching out to 1.3–23 kpc from the galactic center. We crossmatch our sample of 10 CL galaxies with the largest existing MaNGA AGN catalog and identify seven in it; two of the remaining three are galaxy mergers and the final one is an AGN candidate. Further, we measure the average CLR electron temperatures as ranging between 12,331 and 22,530 K, slightly above the typical threshold for pure AGN photoionization (∼20,000 K) and indicative of shocks (e.g., merger induced or from supernova remnants) in the CLR. We reason that ionizing photons emitted by the central continuum source (i.e., AGN photoionization) primarily generate the CLs, and that energetic shocks are an additional ionization mechanism that likely produce the most extended CLRs we measure.

Swift/UVOT follow-up of gravitational wave alerts in the O3 era

ABSTRACT In this paper, we report on the observational performance of the Swift Ultra-violet/Optical Telescope (UVOT) in response to the gravitational wave (GW) alerts announced by the Advanced Laser Interferometer Gravitational Wave Observatory and the Advanced Virgo detector during the O3 period. We provide the observational strategy for follow-up of GW alerts and provide an overview of the processing and analysis of candidate optical/UV sources. For the O3 period, we also provide a statistical overview and report on serendipitous sources discovered by Swift/UVOT. Swift followed 18 GW candidate alerts, with UVOT observing a total of 424 deg2. We found 27 sources that changed in magnitude at the 3σ level compared with archival u- or g-band catalogued values. Swift/UVOT also followed up a further 13 sources reported by other facilities during the O3 period. Using catalogue information, we divided these 40 sources into five initial classifications: 11 candidate active galactic nuclei (AGNs)/quasars, three cataclysmic variables (CVs), nine supernovae, 11 unidentified sources that had archival photometry, and six uncatalogued sources for which no archival photometry was available. We have no strong evidence to identify any of these transients as counterparts to the GW events. The 17 unclassified sources are likely a mix of AGN and a class of fast-evolving transient, and one source may be a CV.

Active galactic nuclei catalog from the AKARI NEP-Wide field

Context. The north ecliptic pole (NEP) field provides a unique set of panchromatic data that are well suited for active galactic nuclei (AGN) studies. The selection of AGN candidates is often based on mid-infrared (MIR) measurements. Such methods, despite their effectiveness, strongly reduce the breadth of resulting catalogs due to the MIR detection condition. Modern machine learning techniques can solve this problem by finding similar selection criteria using only optical and near-infrared (NIR) data. Aims. The aim of this study is to create a reliable AGN candidates catalog from the NEP field using a combination of optical SUBARU/HSC and NIR AKARI/IRC data and, consequently, to develop an efficient alternative for the MIR-based AKARI/IRC selection technique. Methods. We tested set of supervised machine learning algorithms for the purposes of carrying out an efficient process for AGN selection. The best models were compiled into a majority voting scheme, which used the most popular classification results to produce the final AGN catalog. An additional analysis of the catalog properties was performed as a spectral energy distribution fitting via the CIGALE software. Results. The obtained catalog of 465 AGN candidates (out of 33 119 objects) is characterized by 73% purity and 64% completeness. This new classification demonstrates a suitable consistency with the MIR-based selection. Moreover, 76% of the obtained catalog can be found solely using the new method due to the lack of MIR detection for most of the new AGN candidates. The training data, codes, and final catalog are available via the github repository. The final catalog of AGN candidates is also available via the CDS service. Conclusions. The new selection methods presented in this paper are proven to be a better alternative for the MIR color AGN selection. Machine learning techniques not only show similar effectiveness, but also involve less demanding optical and NIR observations, substantially increasing the extent of available data samples.

A Chandra and HST View of WISE-selected AGN Candidates in Dwarf Galaxies

Abstract Reliably identifying active galactic nuclei (AGNs) in dwarf galaxies is key to understanding black hole (BH) demographics at low masses and constraining models for BH seed formation. Here we present Chandra X-ray Observatory observations of 11 dwarf galaxies that were chosen as AGN candidates using Wide-field Infrared Survey Explorer (WISE) mid-infrared (mid-IR) color–color selection. Hubble Space Telescope images are also presented for 10 of the galaxies. Based on Sloan Digital Sky Survey spectroscopy, six galaxies in our sample have optical evidence for hosting AGNs and five are classified as star-forming. We detect X-ray point sources with luminosities above that expected from X-ray binaries in the nuclei of five of the six galaxies with optical evidence of AGNs. However, the X-ray emission from these AGNs is generally much lower than expected based on AGN scaling relations with infrared and optical tracers. We do not find compelling evidence for AGNs in the five optically-selected star-forming galaxies despite having red mid-IR colors. Only two are detected in X-rays and their properties are consistent with stellar-mass X-ray binaries. Based on this multiwavelength study, we conclude that two-color mid-IR AGN diagnostics at the resolution of WISE cannot be used to reliably select AGNs in optically-star-forming dwarf galaxies. Future observations in the infrared with the James Webb Space Telescope offer a promising path forward.

The Effect of the Morphological Quenching Mechanism on Star Formation Activity at 0.5 &lt; z &lt; 1.5 in 3D-HST/CANDELS

Abstract Several mechanisms for the transformation of blue star-forming to red quiescent galaxies have been proposed, and the green valley (GV) galaxies amid them are widely accepted in a transitional phase. Thus, comparing the morphological and environmental differences of the GV galaxies with early-type disks (ETDs; bulge dominated and having a disk) and late-type disks (LTDs; disk dominated) is suitable for distinguishing the corresponding quenching mechanisms. A large population of massive (M * ≥ 1010 M ⊙) GV galaxies at 0.5 ≤ z ≤ 1.5 in 3D-HST/CANDELS is selected using extinction-corrected (U–V)rest color. After eliminating any possible active galactic nucleus candidates and considering the “mass-matching,” we finally construct two comparable samples of GV galaxies with either 319 ETD or 319 LTD galaxies. Compared to the LTD galaxies, it is found that the ETD galaxies possess higher concentration index and lower specific star formation rate, whereas the environments surrounding them are not different. This may suggest that the morphological quenching may dominate the star formation activity of massive GV galaxies rather than the environmental quenching. To quantify the correlation between the galaxy morphology and the star formation activity, we define a dimensionless morphology quenching efficiency Q mor and find that Q mor is not sensitive to the stellar mass and redshift. When the difference between the average star formation rate of ETD and LTD galaxies is about 0.7 M ⊙ yr−1, the probability of Q mor ≳ 0.2 is higher than 90%, which implies that the degree of morphological quenching in GV galaxies might be described by Q mor ≳ 0.2.

An ACA 1 mm survey of HzRGs in the ELAIS-S1: survey description and first results

ABSTRACT Radio-emitting jets might be one of the main ingredients shaping the evolution of massive galaxies in the Universe since early cosmic times. However, identifying early radio active galactic nuclei (AGNs) and confirming this scenario have been hard to accomplish, with studies of samples of radio AGN hosts at z &amp;gt; 2 becoming routinely possible only recently. With the above in mind, we have carried out a survey with the Atacama Compact Array (ACA or Morita Array) at 1.3 mm (rms = 0.15 mJy) of 36 high-redshift radio AGN candidates found within 3.9 deg2 in the ELAIS-S1 field. The work presented here describes the survey and showcases a preliminary set of results. The selection of the sample was based on three criteria making use of infrared (IR) and radio fluxes only. The criterion providing the highest selection rate of high-redshift sources (86 per cent at z &amp;gt; 0.8) is one combining an IR colour cut and radio flux cut (S5.8μm/S3.6μm &amp;gt; 1.3 and $S_{\rm 1.4\, GHz}\gt 1\,$ mJy). Among the sample of 36 sources, 16 show a millimetre (mm) detection. In eight of these cases, the emission has a non-thermal origin. A zsp = 1.58 object, with a mm detection of non-thermal origin, shows a clear spatial offset between the jet-dominated mm continuum emission and that of the host’s molecular gas, as traced by serendipitously detected CO(5-4) emission. Among the objects with serendipitous line detections there is a source with a narrow jet-like region, as revealed by CS(6-5) emission stretching 20 kpc out of the host galaxy.

Optical Identification of Candidates for Active Galactic Nuclei Detected by the Mikhail Pavlinsky ART-XC Telescope Onboard the SRG Observatory during an All-Sky X-ray Survey

We present the results of our identification of eight objects from a preliminary catalogue of X-ray sources detected in the 4-12 keV energy band by the Mikhail Pavlinsky ART-XC telescope aboard the SRG observatory during its first all-sky survey. Three of them (SRGAJ005751.0+210846,SRGAJ014157.0-032915, SRGAJ232446.8+440756) have been discovered by ART-XC, while five were already known previously as X-ray sources, but their nature remained unknown. The last five sources have also been detected in soft X-rays by the eROSITA telescope of the SRG observatory. Our optical observations were carried out at the 1.6-m AZT-33IK telescope of the Sayan Observatory and the 1.5-m Russian-Turkish telescope (RTT-150). All of the investigated objects have turned out to be active galactic nuclei (AGNs) at redshifts from 0.019 to 0.283. Six of them are Seyfert 2 galaxies(including one Seyfert 1.9 galaxy), one (SRGAJ005751.0+210846) is a "hidden" AGN (in an edge-on galaxy), and one (SRGAJ224125.9+760343) is a narrow-line Seyfert 1 galaxy. The latter object is characterized by a high X-ray luminosity (~(2-13)*10^44 erg/s in the 4-12 keV band) and,according to our black hole mass estimate (~2*10^7 M_sun), an accretion rate close to the Eddington limit. All three AGNs discovered by the ART-XC telescope (which are not detected by the eROSITA telescope) are characterized by a high absorption column density (N_H > 3*10^23 cm^-2). The results obtained confirm the expectations that the ART-XC telescope is an efficient instrument for searches of heavily obscured and other interesting AGNs in the nearby (z<0.3) Universe. The SRG all-sky survey will last for more than 3 years more, which will allow many such objects to be discovered.