Active Galactic Nuclei Activity Research Articles

A Closer Look at the Origin of LINER Emission in Later-type Galaxies and Its Connection to Evolved Stars with a Machine Learning Classification Scheme

Abstract Identifying the dominant ionizing sources in galaxies is essential for understanding their formation and evolution. Traditionally, spectra are classified based on their dominant ionizing source using strong emission lines and Baldwin, Phillips, & Terlevich (BPT) diagrams. The ionizing source is traditionally determined by the emission line ratios using the BPT diagrams. Low-ionization nuclear emission-line regions (LINERs) are a class of ionizing mechanisms that is observationally identified but with a poorly understood origin, unlike the case of star-forming regions and active galactic nuclei (AGN). LINERs, typically found in early-type galaxies, are often associated with low-luminosity AGN activity but may also be powered by aging stellar populations, particularly post-asymptotic giant branch (p-AGB) stars. In this study, we employ a machine-learning-based encoder, spender, to analyze the full MaNGA integral field unit spectra and identify key spectral features of LINERs. By examining the continuum and line emission of these spaxels, our approach aims to uncover hidden patterns and better understand the dominant ionizing sources. We show in this work that the neural-network-based encoder was able identify LINER sources from the stellar continuum alone. The characteristics of the stellar population underlying LINER regions are consistent with evolved low-mass stars, implying that the source driving LINER emission is probably p-AGB stars rather than AGN activity.

The Interplay Between Black Holes and Galaxy Formation: A Cosmological Perspective

The interplay between black holes and galaxy formation constitutes a crucial domain of research in cosmology, offering profound insights into the universe's evolution. This study explores the intricate relationship between supermassive black holes (SMBHs) and their host galaxies, emphasizing how their co-evolution shapes galaxy morphology, star formation rates, and the dynamics of galactic environments. Utilizing recent observational data from X-ray surveys and gravitational wave detections, we present compelling evidence for the regulatory role of SMBHs in star formation and the structural configuration of galaxies. Employing a robust combination of observational data analysis and theoretical modeling, our research elucidates the mechanisms through which SMBHs impact their host galaxies. We find that SMBHs grow not only through the accretion of matter but also significantly influence the surrounding gas dynamics. This leads to complex feedback processes that can either foster or inhibit star formation, thereby contributing to a nuanced understanding of cosmic evolution. The study of Active Galactic Nuclei (AGNs) across various galaxy types has garnered considerable attention due to their pivotal influence on cosmic evolution. We conduct empirical analyses to investigate the distribution of AGNs within different classifications, specifically focusing on elliptical, spiral, and irregular galaxies. Initial findings indicate a notable prevalence of AGNs in elliptical galaxies, suggesting a correlation between galaxy morphology and nuclear activity. Further exploration of the star formation rates (SFRs) in AGN-hosting galaxies versus their non-AGN counterparts reveals intriguing patterns, with histograms from simulated data illustrating a significant disparity in SFRs. This suggests that AGN activity may correlate with suppressed star formation, raising critical questions regarding the role of AGNs in galaxy evolution and the underlying feedback mechanisms. Moreover, to enhance our understanding of the relationship between gravitational wave events and black hole mergers, we analyze scatter plots depicting the mass distribution of merging black holes across varying redshifts. This analysis contributes to ongoing discussions about the connection between AGN activity and black hole formation, emphasizing the relevance of gravitational wave observations in astrophysics. Additionally, we examine the growth patterns of SMBHs over cosmic time through a hypothetical growth model, revealing potential exponential growth trends that underscore the dynamic nature of black hole evolution. Finally, we scrutinize the interplay between AGN feedback mechanisms and star formation rates, highlighting complex feedback loops that govern galaxy dynamics.

A multi-scale investigation into the diagnostic potential of the HCN/HCO+ ratio for active galactic nucleus and starburst activity in nearby galaxies

Context. The identification of active galactic nuclei (AGNs) and starburst (SB) regions in galaxies is crucial for understanding the role of various physical processes in galaxy evolution. Molecular line ratios, such as the HCN/HCO+ ratio, have been proposed as potential tracers of these distinct environments. Aims. We aim to assess the reliability of the HCN/HCO+ ratio, from J = 1–0 to J = 4–3 transitions, as a diagnostic tool for differentiating AGN and SB activity across a diverse sample of nearby galaxies. We focus on evaluating the effect of spatial resolution on the robustness of these ratios and investigate the underlying physical conditions that drive observed variations. Methods. We compiled observations of HCN and HCO+ lines across multiple J transitions from various sources, covering different galaxy types, including Seyferts, SBs, and (ultra-)luminous infrared galaxies. The observations span spatial scales from cloud-sized regions (tens of parsecs) to kiloparsec scales. We analysed the behaviour of these ratios at varying resolutions and employed non-local thermodynamic equilibrium (non-LTE) radiative transfer models to infer the physical conditions that drive the observed ratios. Results. We find that the HCN/HCO+ ratio from higher J transitions (e.g. J = 4–3) can differentiate between AGN and SB activity when observed at high spatial resolution (< 100 pc). This distinction occurs around unity, with HCN/HCO < 1 observed in SB-dominated and > 1 in AGN-dominated regions. However, at lower resolutions, contamination from multiple emission sources and beam averaging effects destroy these distinctions. Radiative transfer modelling suggests that elevated HCN/HCO+ ratios in AGN-dominated regions are largely driven by an increase in HCN abundance relative to HCO+, likely due to high-temperature chemistry or increased excitation. Conclusions. Our study confirms that the HCN/HCO+ ratio, particularly of higher J transitions, can be a reliable tracer of AGN versus SB activity if observations are conducted at sufficiently high spatial resolution. However, caution must be exercised in interpreting these ratios at larger spatial scales due to contamination effects. Further high-resolution observations are needed to refine the conditions under which these ratios can serve as reliable diagnostics.

Warm Ionized Gas Outflows in Active Galactic Nuclei: What Causes Them?

Abstract The driving force behind outflows, often invoked to understand the correlation between the supermassive black holes powering active galactic nuclei (AGN) and their host galaxy properties, remains uncertain. We provide new insights into the mechanisms that trigger warm ionized outflows in AGN, based on findings from the MaNGA survey. Our sample comprises 538 AGN with strong [O iii] λ5007 emission lines, of which 197 are detected in radio and 341 are radio-undetected. We analyzed the [O iii] λ5007 line in summed spectra, extracted over their central 500 × 500 pc2 region. The calculated Balmer 4000 Å break, D n 4000, is larger than 1.45 for ∼95% of the sources, indicating that the specific star formation rate in their central regions is less than 10−11.5 yr−1, which points to evidence of negative AGN feedback suppressing star formation. Considering the whole sample, radio-detected sources show a greater outflow detection rate (56% ± 7%) than radio-undetected sources (25% ± 3%). They also show higher velocity, mass outflow rate, outflow power, and outflow momentum rate. We noticed a strong correlation between outflow characteristics and bolometric luminosity in both samples, except that the correlation is steeper for the radio-detected sample. Our findings suggest that (a) warm ionized outflows are prevalent in all types of AGN, (b) radiation from AGN is the primary driver of these outflows, (c) radio jets are likely to play a secondary role in enhancing the gas kinematics over and above that caused by radiation, and (d) there is very little star formation in the central regions of the galaxies, possibly due to negative feedback from AGN activity.

The Interplay Between Supermassive Black Holes and Their Host Galaxies: A Multi-wavelength Approach

The interplay between supermassive black holes (SMBHs) and their host galaxies is a critical area of research in extragalactic astronomy, shedding light on the fundamental processes that govern galaxy formation and evolution. This study employs a multi-wavelength approach to investigate the correlation between SMBHs and their host galaxies, utilizing data from radio, optical, infrared, and X-ray observations. Recent advancements in observational technologies have enabled deeper insights into the mechanisms at play in this complex relationship. We begin by examining the fundamental connection between the mass of SMBHs and various properties of their host galaxies, such as stellar mass, bulge structure, and star formation rate. Our analysis reveals a significant correlation between SMBH mass and the central velocity dispersion of stars, consistent with the established M-sigma relation. However, deviations from this correlation suggest the influence of additional factors, such as environmental conditions and galaxy mergers. Furthermore, we explore the feedback mechanisms initiated by SMBHs, particularly through active galactic nuclei (AGN) activity. Multi-wavelength observations allow us to assess the impact of AGN feedback on star formation within host galaxies. We document cases where AGN activity suppresses star formation, resulting in a transition from star-forming to passive galaxies. Conversely, we also identify scenarios where SMBH feedback may trigger star formation, underscoring the dual role of SMBHs in galaxy evolution. In addition to examining individual cases, we utilize large galaxy survey data sets to analyze trends across different galaxy populations. Our findings indicate variations in SMBH-host galaxy relationships based on galaxy morphology and environment, suggesting that the evolution of both components is influenced by cosmic structures. This study highlights the importance of a multi-wavelength approach in understanding the complex dynamics between SMBHs and their host galaxies. By integrating diverse data sources, we provide a comprehensive view of how these colossal entities coexist and interact. Our results contribute to the broader discourse on galaxy formation theories and the role of SMBHs in shaping the universe, paving the way for future investigations that will deepen our understanding of cosmic evolution.

Embers of Active Galactic Nuclei: Tidal Disruption Events and Quasiperiodic Eruptions

Abstract Recent observations have confirmed the direct association between tidal disruption events (TDEs) and quasiperiodic eruptions (QPEs). In addition, TDE hosts and QPE hosts are statistically found to be similar in their morphological properties and in the strong overrepresentation of poststarburst galaxies. Particularly, both of them show an intriguing preference for extending emission line regions, which are indicative of recently faded active galactic nuclei (AGNs). This further suggests that QPEs might be produced following TDEs involving supermassive black holes at a particular stage, when the AGN activity has recently ceased. Moreover, in the framework of the “QPEs = extreme mass ratio inspiral (EMRI) + accretion disk” model, a large fraction of QPE EMRIs are inferred to be quasi-circular from the QPE timing, indicating that they are wet EMRIs that were formed in the AGN disk during a previous AGN phase. Based on these facts, we propose a unified scenario that connects these three phenomena: AGN activities boost both the TDE rate and the formation rate of low-eccentricity EMRIs; consequently, TDEs are preferentially found in recently faded AGNs instead of in ongoing AGNs due to selection effects; and QPEs are also preferentially found in recently faded AGNs where TDEs frequently feed a misaligned accretion disk to the EMRI.

Exploring the physical properties of type II quasar candidates at intermediate redshifts with CIGALE

Context. Active galactic nuclei (AGNs) play a vital role in the evolution of galaxies over cosmic time, significantly influencing their star formation and growth. As obscured AGNs are difficult to identify due to obscuration by gas and dust, our understanding of their full impact is still under study. It is essential to investigate their properties and distribution, in particular type II quasars (QSO2s), to comprehensively account for AGN populations and understand how their fraction evolves over time. Such studies provide critical insights into the co-evolution of AGNs and their host galaxies. Aims. Following our previous study, where a machine learning approach was applied to identify 366 QSO2 candidates from SDSS and WISE surveys (median z ∼ 1.1), we now aim to characterise this QSO2 candidate sample by analysing their spectral energy distributions (SEDs) and deriving their physical properties. Methods. We estimated relevant physical properties of the QSO2 candidates, including the star formation rate (SFR), stellar mass (M*), AGN luminosity, and AGN fraction, using SED fitting with CIGALE. We compared the inferred properties with analogous populations in the semi-empirical simulation SPRITZ, placing these results in the context of galaxy evolution. Results. The physical properties derived for our QSO2 candidates indicate a diverse population of AGNs at various stages of evolution. QSO2 candidates cover a wide range in the SFR–M* diagram, with numerous high-SFR sources lying above the main sequence at their redshift, suggesting a link between AGN activity and enhanced star formation. Additionally, we identify a population of apparently quenched galaxies, which may be due to obscured star formation or AGN feedback. Furthermore, the physical parameters of our sample align closely with those of composite systems and type 2 AGNs from SPRITZ, supporting the classification of these candidates as obscured AGNs. Conclusions. This study confirms that our QSO2 candidates, selected via a machine learning approach, exhibit properties consistent with being AGN-host galaxies. This method can identify AGNs within large galaxy samples by considering AGN fractions and their contributions to the infrared luminosity, going beyond the limitations of traditional colour–colour selection techniques. The diverse properties of our candidates demonstrate the capability of this approach to identify complex AGN-host systems that might otherwise be missed. This shows the help that machine learning can provide in refining AGN classifications and advancing our understanding of galaxy evolution driven by AGN activity with new target selection.

Relighting the fire in Hickson Compact Group (HCG) 15: Magnetised fossil plasma revealed by the SKA Pathfinders and Precursors

In the context of the life cycle and evolution of active galactic nuclei (AGNs), environment plays a key role. In particular, the over-dense environments of galaxy groups, where dynamical interactions and bulk motions have significant impact, offer an excellent but under-explored window into the life cycles of AGNs and the processes that shape the evolution of relativistic plasma. Pilot survey observations with the Australian Square Kilometre Array Pathfinder (ASKAP) Evolutionary Map of the Universe (EMU) survey have recovered diffuse emission associated with the nearby (z = 0.0228) galaxy group HCG15, which was revealed to be strongly linearly polarised. We studied the properties of this emission in unprecedented detail to settle questions about its nature and its relation to the group-member galaxies. We performed a multi-frequency spectropolarimetric study of HCG15, incorporating our ASKAP EMU observations as well as new data from MeerKAT, the LOw-Frequency ARray (LOFAR), Giant Metrewave Radio Telescope (GMRT), and Karl G. Jansky Very Large Array (VLA), along with X-ray data from XMM-Newton and optical spectra from Himalayan Chandra Telescope (HCT). Our study confirms that the diffuse structure represents remnant emission from historic AGN activity that is likely to be associated with HCG15-D, some $80 - 86$ Myr ago (based on an ageing analysis). We detected significant highly linearly-polarised emission from a diffuse `ridge-like' structure with a highly ordered magnetic field. Our analysis suggests that this emission is generated by the draping of magnetic field lines in the intra-group medium (IGrM). Subsequent investigations with simulations would further improve our understanding of this phenomenon. We confirm that HCG15-C is a group-member galaxy. Finally, we report the detection of thermal emission associated with a background cluster at a redshift of z ≈ 0.87 projected onto the IGrM of HCG15, which matches the position and redshift of the recent Sunyaev-Zel'dovich (SZ) detection of ACT-CL J0207.8+0209.

The Role of Active Galactic Nuclei Feedback in Shaping the Dynamics of Galaxy Cluster Centers

The role of Active Galactic Nuclei (AGN) feedback in shaping the dynamics of galaxy cluster centers has emerged as a pivotal research area in contemporary astrophysics. Recent observations, particularly those revealing cavities in the intracluster medium (ICM), have underscored the significance of feedback mechanisms driven by supermassive black holes (SMBHs) located at the centers of galaxies. This feedback is now recognized as a key factor in accurately modeling the evolution of both galactic and extragalactic systems. The current era of X-ray astronomy, marked by missions such as Chandra and XMM-Newton, has revolutionized our understanding of "cool-core" (CC) galaxy clusters and groups. Rather than the traditional view, which emphasized the cooling of hot gas and its subsequent inflow toward the cluster center, a more nuanced picture has emerged. This new paradigm illustrates a complex dynamical interplay within the ICM, where AGN activity induces heating that counteracts cooling processes, maintaining a delicate balance. In this study, we specifically investigate AGN feedback processes occurring in the centers of galaxy clusters. We analyze how AGN feedback leads to the formation of periodic jets and examine their impact on the surrounding ICM. By correlating the duty cycle of episodic jet activity with the cooling time (CT) of the central ICM, we aim to determine whether the central AGN is engaged in a feedback loop with the ICM, thereby influencing its thermal and dynamical state. Additionally, we explore the critical differences between galaxy clusters and groups within the framework of ICM cooling and AGN feedback. Our hypothesis suggests that a larger fraction of gas contributes to star formation in galaxy groups compared to clusters, where a significant portion of the gas is thought to be funneled into the central AGN. By examining these distinctions, we seek to clarify the mechanisms governing star formation and AGN activity in different environments. Ultimately, this research aims to elucidate the intricate role of AGN feedback in shaping the dynamics of galaxy cluster centers, enhancing our understanding of its broader implications for galaxy formation and evolution across various cosmic structures. Through this investigation, we hope to provide valuable insights into the complex interplay between AGN feedback, ICM cooling, and star formation processes, thereby contributing to a more comprehensive understanding of galaxy evolution in the universe.

The jet paths of radio active galactic nuclei and their cluster weather

We studied bent radio sources within X-ray galaxy groups in the COSMOS and XMM-LSS fields. The radio data were obtained from the MeerKAT International GHz Tiered Extragalactic Explorations data release 1 (MIGHTEE-DR1) at 1.2–1.3 GHz, with angular resolutions of 8.9″ and 5″, and median noise levels of rmsmed ∼ = 3.5 and 5.5 μJy/beam. Bent radio active galactic nuclei (AGN) were identified through visual inspection. Our analysis included 19 bent radio AGN in the COSMOS field and 17 in the XMM-LSS field that lie within X-ray galaxy groups (2 × 1013 ≲ M200c/M⊙ ≤ 3 × 1014). We investigated the relationship between their bending angle (BA) – the angle formed by the jets or lobes of two-sided radio sources associated with AGN – and the properties of their host galaxies and large-scale environment probed by the X-ray galaxy groups. Our key findings are: (a) In the XMM-LSS field, we observed a strong correlation between the linear projected size of the bent AGN, the group halo mass, and the projected distance from the group centre. This trend, consistent with previous studies, was not detected in the COSMOS sample. (b) The BA is a function of environmental density, with the type of medium playing a significant role. Additionally, at z ≤ 0.5 we found a higher number of bent sources (BA ≤ 160°) compared to higher redshifts (z ∼ 1), by a factor of > 1.5. This trend aligns with magneto-hydrodynamic simulations, which suggest that denser environments and longer interaction times at lower redshifts contribute to this effect. A comparison with the literature suggests that jet bending in galaxy groups within the redshift range 0.1 < z < 1.2 is primarily driven by ram pressure exerted on the jets, which occurs during quiescent phases of AGN activity. This study underscores the role of environmental interactions in shaping the morphology of radio AGN within galaxy groups, providing insights into the interplay between large-scale structure and AGN physics.

Active Galactic Nucleus Feedback in Quiescent Galaxies at Cosmic Noon Traced by Ionized Gas Emission

Abstract We analyze ionized gas emission lines in deep rest-frame optical spectra of 14 massive ( log M * > 10.2 M ⊙) quiescent galaxies at redshifts 1.7 < z < 3.5 observed with JWST/NIRSpec by the Blue Jay survey. Robust detection of emission lines in 71% of the sample indicates the presence of ongoing ionizing sources in this passive population. The Hα line luminosities confirm that the population is quiescent, with star formation rates that are at least 10 times lower than the main sequence of star formation at z ∼ 2. The quiescent sample is clearly separate from the star-forming population in line diagnostic diagrams, and occupies a region usually populated by active galactic nuclei (AGN). Analysis of the observed line ratios, equivalent widths, and velocity dispersions leads us to conclude that in most cases the gas is ionized by AGN activity, despite the lack of X-ray detections. We measure generally low values of the bolometric luminosity L bol ∼ 1044 erg s−1 and Eddington ratio λ ∼ 10−2–10−3 for the central engines, typical of low-luminosity AGN. A subset of the sample also hosts ionized and neutral outflows, with ionized outflow velocities of the order of ∼1000 km s−1. Our results show, for the first time using a representative sample, that low-luminosity AGN are extremely common among quiescent galaxies at high redshift. These low-luminosity AGN may play a key role in quenching star formation and in maintaining massive galaxies quiescent from Cosmic Noon to z ∼ 0.

Impacts of UV Radiation from an AGN on Planetary Atmospheres and Consequences for Galactic Habitability

Abstract We present a study of the effects of ultraviolet (UV) emission from active galactic nuclei (AGN) on the atmospheric composition of planets and potential impact on life. It is expected that all supermassive black holes, which reside at galactic centers, have gone through periods of high AGN activity in order to reach their current masses. We examine potential damaging effects on lifeforms on planets with different atmosphere types and receiving different levels of AGN flux, using data on the sensitivity of various species’ cells to UV radiation to determine when radiation becomes “dangerous.” We also consider potential chemical changes to planetary atmospheres as a result of UV radiation from AGN, using the Platform for Atmosphere, Land, Earth, and Ocean photochemical model. We find that the presence of sufficient initial oxygen (surface mixing ratio ≥10−3 mol mol−1) in the planet’s atmosphere allows a thicker ozone layer to form in response to AGN radiation, which reduces the level of dangerous UV radiation incident on the planetary surface from what it was in absence of an AGN. We estimate the fraction of solar systems in galaxies that would be affected by substantial AGN UV radiation, and find that the impact is most pronounced in compact galaxies such as “red nugget relics,” as compared to typical present-day ellipticals and spirals (using M87 and the Milky Way as examples).

The host galaxies of radio AGN: New views from combining LoTSS and MaNGA observations

The role of radio mode active galactic nuclei (AGN) feedback on galaxy evolution is still under debate. In this study we utilized a combination of radio continuum observations and optical integral field spectroscopic (IFS) data to explore the impact of radio AGN on the evolution of their host galaxies at global and subgalactic scales. We constructed a comprehensive radio-IFS sample comprising 5548 galaxies with redshift z < 0.15 by cross-matching the LOFAR Two-Metre Sky Survey (LoTSS) with the Mapping Nearby Galaxies at APO (MaNGA) survey. We revisited the tight linear radio continuum–star formation relation and quantify its intrinsic scatter, then used the relation to classify 616 radio-excess AGN with excessive radio luminosities over the values expected from their star formation rates. Massive radio AGN host galaxies are predominantly quiescent systems, but the quenching level shows no correlation with the jet luminosity. The mass assembly histories derived from the stellar population synthesis model fitting agree with the cosmological simulations incorporating radio-mode AGN feedback models. We observe that radio AGN hosts grow faster than a control sample of galaxies matched in stellar mass, and the quenching age (∼5 Gyr) is at larger lookback times than the typical radio jet age (< 1 Gyr). By stacking the spectra in different radial bins and comparing results for radio AGN hosts and their controls, we find emission line excess features in the nuclear region of radio AGN hosts. This excess is more prominent in low-luminosity, low-mass, and compact radio AGN. The [N II]/Hα ratios of the excessive emission line indicate that radio AGN or related jets are ionizing the surrounding interstellar medium in the vicinity of the nucleus. Our results support the scenario that the observed present-day radio AGN activity may help their host galaxies maintain quiescence through gas ionization and heating, but it is not responsible for the past quenching of their hosts.

A Dual Active Black Hole Candidate with Mass Ratio ~7:1 in a Disk Galaxy

Abstract Dual active galactic nuclei (AGNs) with comparable masses are commonly witnessed among the major merged galaxies with interaction remnants. Considering almost every massive galaxy is associated with multiple dwarf satellites around it, minor mergers involving galaxies with disproportional stellar masses should be much more common than major mergers, which would naturally lead to black hole (BH) pairs with significantly different masses. However, dual AGNs generated by minor mergers involving one or two dwarf galaxies are exceptionally rare and understudied. Moreover, good estimates of the masses of both BHs are not yet available to test this idea. Here we report the evidence of a dual AGN candidate with mass ratio ~7:1 located in an undisturbed disk galaxy. We identify the central BH with mass of 9.4 × 106 M ⊙ from its radio emission as well as AGN-driven galactic-scale biconical outflows. The off-centered BH generates obvious broad and narrow emission-line regions, which gives us a robust estimation of a 1.3 × 106 M ⊙ BH mass. We explore alternative scenarios for explaining the observational features of this system, including the complex gas kinematics triggered by central AGN activity and dust attenuation of the broad-line region of the central BH, finding that they failed to fully account for the kinematics of both the redshifted off-centered broad and narrow emission-line components.

ALMA/SCUBA-2 COSMOS Survey: Properties of X-Ray- and SED-selected Active Galactic Nuclei in Bright Submillimeter Galaxies

Abstract We investigate the properties of active galactic nuclei (AGNs) in the brightest submillimeter galaxies (SMGs) in the COSMOS field. We utilize the bright sample of the ALMA/SCUBA-2 COSMOS Survey (AS2COSMOS), which consists of 260 SMGs with S 870 μm = 0.7–19.2 mJy at z = 0–6. We perform optical to millimeter spectral energy distribution (SED) modeling for the whole sample. We identify 24 AGN-host galaxies from the SEDs. Supplemented by 23 X-ray-detected AGNs (X-ray AGNs), we construct an overall sample of 40 AGN-host galaxies. The X-ray luminosity upper bounds indicate that the X-ray-undetected SED-identified AGNs are likely to be nearly Compton thick or have unusually suppressed X-ray emission. From visual classification, we identify 2 5 − 5 + 6 % of the SMGs without AGNs as major merger candidates. This fraction is almost consistent with the general galaxy population at z ∼ 2, suggesting that major mergers are not necessarily required for the enhanced star formation in SMGs. We also identify 4 7 − 15 + 16 % of the AGN hosts as major merger candidates, which is about twice as high as that in the SMGs without AGNs. This suggests that major mergers play a key role in triggering AGN activity in bright SMGs.

Can Active Galactic Nuclei Activity Be Enhanced by Ram Pressure Stripping?—X-Ray Perspective

Abstract Ram pressure stripping (RPS) is an important process that plays a significant role in shaping the evolution of cluster galaxies and their surrounding environment. Despite its recognized significance, the potential connection between RPS and active galactic nuclei (AGN) activity in cluster galaxies remains poorly understood. Recent claims, based on optical emission-line diagnostics, have suggested such a connection. Here, we investigate this relationship from an X-ray perspective, using a sample of galaxies undergoing RPS in four nearby galaxy clusters: A1656, A1367, A426, and A3627. This study is the first to test such a connection from an X-ray standpoint. Our analysis reveals no signs of enhanced X-ray AGN activity in our sample, with most RPS galaxies (~90%) showing X-ray luminosities below 1041 erg s−1 in their central point sources. Moreover, there is no noticeable difference in X-ray AGN activity among RPS galaxies compared to a control sample of non-RPS galaxies, as demonstrated by the similar X-ray luminosities observed in their central point sources. While the most luminous X-ray AGN in our sample is found in ESO 137-002, a galaxy undergoing RPS in A3627, there is no evidence for a widespread enhancement of X-ray AGN activity due to RPS. Given the limited sample size of our study, this could also indicate that either the X-ray AGN enhancement from RPS is at most weak or the timescale for the X-ray AGN enhancement is short. This emphasizes the need for further investigations with larger X-ray samples to better understand the impact of RPS on AGN activity in cluster galaxies.

Host Galaxy Properties and AGN Clustering: Insights from X-ray Observations and Their Impact on Cosmic Evolution

This review examines the connection between X-ray-selected Active Galactic Nuclei (AGN) and their host galaxies, focusing on how X-ray observations provide insights into AGN structure and clustering. AGNs, powered by supermassive black holes, are key drivers of galaxy evolution, and X-ray data play a critical role in studying these energetic phenomena. The unified model of AGNs, which attributes differences between type 1 (unobscured) and type 2 (obscured) AGNs to orientation effects, is discussed. However, variations in clustering between these two types challenge this model, suggesting additional factors influence their evolution. Detecting AGN clusters in the X-ray band remains difficult due to observational biases and limitations, but such studies are vital for understanding how AGNs form and interact within large-scale structures. Host galaxy properties, including luminosity, stellar mass, and star formation rate, are analyzed for their impact on AGN clustering. Research indicates that AGN luminosity is strongly linked to the mass of the dark matter halos surrounding their host galaxies. This relationship may vary depending on the triggering mechanism of the AGN, such as galaxy mergers or internal instabilities. Differences in AGN clustering patterns provide insights into the diverse pathways through which AGNs are activated. AGN feedback, which describes how AGNs influence star formation in their host galaxies, is another key focus. Observations suggest that at higher redshifts, brighter AGNs tend to enhance star formation rates, showing a complex interplay between AGN activity and galaxy growth. By synthesizing recent observational results, this review highlights the central role of AGNs in shaping galaxies and their environments. It provides a deeper understanding of how AGNs interact with their host galaxies and larger cosmic structures, offering valuable insights into the processes driving galaxy evolution over cosmic time.

Multiwavelength Properties of Infrared-faint Radio Sources Based on Analysis of Their Spectral Energy Distribution

Abstract Infrared-faint radio sources (IFRSs) are believed to be a rare class of radio-loud active galactic nuclei (AGNs) characterized by their high radio-to-infrared flux density ratios of up to several thousand. Previous studies have shown that a fraction of IFRSs are likely to be hosted in dust-obscured galaxies. In this paper, our aim is to probe the dust properties, star formation rate (SFR), and AGN activity of IFRSs by modeling the UV-to-infrared spectral energy distribution (SED) of 20 IFRSs with spectroscopic redshifts ranging from 1.2 to 3.7. We compare the Bayesian evidence of a three-component model (stellar, AGN, and cold dust) with that of a two-component model (stellar and cold dust) for six IFRSs in our sample with far-infrared photometry and find that the three-component model has significantly higher Bayesian evidence, suggesting that IFRSs are most likely to be AGNs. The median SED of our IFRS sample shows similarities to an AGN–starburst composite in the IR regime. The derived IR luminosities of IFRSs indicate that they are low-luminosity counterparts of high-redshift radio galaxies. We disentangle the contributions of AGN-heated and star formation-heated dust to the IR luminosity of IFRSs and find that our sample is likely AGN-dominated. However, despite the evidence for significant impact of an AGN on the host galaxy, the AGN luminosity of our sample does not show correlation with the SFR of the sources.

Radio Active Galactic Nuclei Activity in Low Redshift Galaxies Is Not Directly Related to Star Formation Rates

We examine the demographics of radio-emitting active galactic nuclei (AGN) in the local Universe as a function of host galaxy properties, most notably both stellar mass (M ⋆) and star formation rate (SFR). Radio AGN activity is theoretically implicated in helping reduce the SFR of galaxies, and therefore it is natural to investigate the relationship between these two galaxy properties. We use the Mapping Nearby Galaxies at Apache Point Observatory (MaNGA) optical IFU catalog in conjunction with the NVSS and Faint Images of the Radio Sky at Twenty radio catalogs. MaNGA's high precision determinations of SFR allow us to impose a clean cut to reliably identify radio AGN from star formers. Using this sample of AGN, the well-measured stellar velocity dispersions from MaNGA, and the black hole M–σ relationship, we examine the Eddington ratio distribution (ERD) and its dependence on M ⋆ and SFR. We find that the ERD depends strongly on M ⋆, with more massive galaxies having larger Eddington ratios (λ). Interpreting our model fit to the data leads to a completeness-corrected estimate of F AGN(λ > 0.001), the fraction of galaxies with radio AGN with λ > 0.001. At logM⋆/M⊙∼11 , we estimate F AGN = 0.02. The AGN fraction increases rapidly with M ⋆, and at logM⋆/M⊙∼12 , we estimate F AGN ∼ 0.24. We do not find any dependence on SFR, specific star formation rate, or velocity dispersion when controlling for stellar mass. We conclude that galaxy SFRs appear to be unrelated to the presence or absence of a radio AGN, which may be useful in constraining theoretical models of AGN feedback.

Dark Matter Halos of Luminous Active Galactic Nuclei from Galaxy–Galaxy Lensing with the HSC Subaru Strategic Program

We assess the dark matter halo masses of luminous active galactic nuclei (AGNs) over the redshift range 0.2–1.2 using galaxy–galaxy lensing based on imaging data from the Hyper Suprime-Cam Subaru Strategic Program (HSC-SSP). We measure the weak lensing signal of a sample of 48,907 AGNs constructed using HSC and Wide-field Infrared Survey Explorer photometry. As expected, we find that the lensing mass profile of total AGN sample is consistent with that of massive galaxies ( log(M*/h−2M⊙)∼ 10.61). Surprisingly, the lensing signal remains unchanged when the AGN sample is split into four host galaxy stellar mass bins. Specifically, we find that the excess surface density of AGNs residing in galaxies with high stellar masses significantly differs from that of the control sample. We further fit a halo occupation distribution model to the data to infer the posterior distribution of parameters including the average halo mass. We find that the characteristic halo mass of the full AGN population lies near the knee ( log(Mh/h−1M⊙)=12.0 ) of the stellar-to-halo mass relation (SHMR). Illustrative of the results given above, the halo masses of AGNs residing in host galaxies with high stellar masses (i.e., above the knee of the SHMR) fall below the calibrated SHMR while the halo masses of the low stellar mass sample are more consistent with the established SHMR. These results indicate that massive halos with a higher clustering bias tend to suppress AGN activity, probably due to the lack of available gas.