Discovery of a Gas-enshrouded Broad-line Active Galactic Nucleus at z ∼ 7

Context. Investigating whether and how galaxy mergers affect black hole growth can be a determinant for black hole-galaxy coevolution models and, in particular, for understanding how early Universe seed black holes grew to become supermassive. However, while mergers have been observed to enhance the active galactic nucleus (AGN) activity and thus black hole growth in massive galaxies, it is not yet known how this relation and the role of the environment translates to dwarf galaxies (the most likely hosts of the early seed black holes) since there are scarce and mixed results in the literature. Aims. We seek to assess the impact of galaxy mergers and the environment on AGN triggering in dwarf galaxies. Methods. We used a sample of 3280 dwarf galaxies with integral-field spectroscopic data from the MaNGA survey to study the AGN fraction throughout the merger process and how it is affected by the environment (characterized by galaxy isolation, being in a void, and group richness). We also compare the fraction of interacting galaxies in AGN and non-AGN dwarf galaxies. Results. We find that dwarf galaxy mergers can ignite AGNs at separations below 20 kpc. The AGN fraction increases notoriously after the first pass and remains enhanced until the final stage. However, mergers are not the dominant AGN triggering mechanism. We also find that the environment has a non-negligible impact on AGN activity in dwarf galaxies, as the AGN fraction increases when moving to lower density environments. These findings provide the most statistically robust constraints to date on the effects of dwarf galaxy mergers and environment on AGN activity and black hole growth.

The most rapidly evolving regions of galaxies often display complex optical spectra with emission lines excited by massive stars, shocks and accretion onto supermassive black holes. Standard calibrations (such as for the star formation rate) cannot be applied to such mixed spectra. In this paper we isolate the contributions of star formation, shock excitation and active galactic nucleus (AGN) activity to the emission line luminosities of individual spatially resolved regions across the central 3 $\times$ 3 kpc$^2$ region of the active barred spiral galaxy NGC$\sim$613. The star formation rate and AGN luminosity calculated from the decomposed emission line maps are in close agreement with independent estimates from data at other wavelengths. The star formation component traces the B-band stellar continuum emission, and the AGN component forms an ionization cone which is aligned with the nuclear radio jet. The optical line emission associated with shock excitation is cospatial with strong $H_2$ and [Fe II] emission and with regions of high ionized gas velocity dispersion ($\sigma > 100$ km s$^{-1}$). The shock component also traces the outer boundary of the AGN ionization cone and may therefore be produced by outflowing material interacting with the surrounding interstellar medium. Our decomposition method makes it possible to determine the properties of star formation, shock excitation and AGN activity from optical spectra, without contamination from other ionization mechanisms.

We investigate the multi-wavelength properties of host galaxies of 3701 X-ray-selected active galactic nuclei (AGNs) out to z ∼ 5 in the Chandra-COSMOS Legacy Survey. Thanks to the extensive multi-wavelength photometry available in the COSMOS field, we derive AGN luminosities, host stellar masses, and star formation rates (SFRs) via a multi-component SED fitting technique. Type 1 and Type 2 AGNs follow the same intrinsic L 2–10 keV–L 6 μm relation, suggesting that mid-infrared emission is a reasonably good measure of the AGN accretion power regardless of obscuration. We find that there is a strong increase in Type 1 AGN fraction toward higher AGN luminosity, possibly due to the fact that Type 1 AGNs tend to be hosted by more massive galaxies. The AGN luminosity and SFR are consistent with an increase toward high stellar mass, while the M stellar dependence is weaker toward the high-mass end, which could be interpreted as a consequence of quenching both star formation and AGN activity in massive galaxies. AGN host galaxies tend to have SFRs that are consistent with normal star-forming galaxies, independent of AGN luminosities. We confirm that black hole accretion rate and SFR are correlated up to z ∼ 5, when forming stars. The majority (∼73%) of our AGN sample are faint in the far-infrared, implying that the moderate-luminosity AGNs seem to be still active after the star formation is suppressed. It is not certain whether AGN activity plays a role in quenching the star formation. We conclude that both AGN activity and star formation might be more fundamentally related to host stellar mass.

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.

Context. Hyperluminous infrared galaxies (HLIRGs) are shown to have been more abundant in early epochs. The small samples used in earlier studies are not sufficient to draw robust statistical conclusions regarding the physical properties and the power sources of these extreme infrared (IR) bright galaxies. Aims. We make use of multi-wavelength data of a large HLIRG sample to derive the main physical properties, such as stellar mass, star formation rate (SFR), volume density, and the contribution to the cosmic stellar mass density and the cosmic SFR density. We also study the black hole (BH) growth rate and its relationship with the SFR of the host galaxy. Methods. We selected 526 HLIRGs in three deep fields (Boötes, Lockman-Hole, and ELAIS-N1) and adopted two spectral energy distribution (SED) fitting codes: CIGALE, which assumes energy balance, and CYGNUS, which is based on radiative transfer models and does not adopt an energy balance principle. We used two different active galactic nucleus (AGN) models in CIGALE and three AGN models in CYGNUS to compare results that were estimated using different SED fitting codes and a range of AGN models. Results. The stellar mass, total IR luminosity, and AGN luminosity agree well among different models, with a typical median offset of 0.1 dex. The SFR estimates show the largest dispersions (up to 0.5 dex). This dispersion has an impact on the subsequent analysis, which may suggest that the previous contradictory results could partly have been due to the different choices in methods. HLIRGs are ultra-massive galaxies, with 99% of them having stellar masses larger than 1011 M⊙. Our results reveal a higher space density of ultra-massive galaxies than what was found by previous surveys or predicted via simulations. We find that HLIRGs contribute more to the cosmic SFR density as redshift increases. In terms of BH growth, the two SED fitting methods provide different results. We can see a clear trend in whereby SFR decreases as AGN luminosity increases when using CYGNUS estimates. This may possibly imply quenching by AGN in this case, whereas this trend is much weaker when using CIGALE estimates. This difference is also influenced by the dispersion between SFR estimates obtained by the two codes.

The main objective of this article is to check the Unified Model (UM) for the expected similar stellar velocity dispersions between Type 1 and Type 2 active galactic nuclei (AGNs) and then to provide further clues on black hole (BH) mass properties. Unlike previous comparisons of BH masses estimated from M BH–σ relations for Type 2 AGNs and from virial BH masses for Type 1 AGNs, reliable stellar velocity dispersions σ measured from absorption features around 4000 Å are directly compared between the thus far largest samples of 6260 low-redshift (z < 0.3) Type 1 AGNs and almost all Type 2 AGNs in SDSS DR12. Although half of Type 1 AGNs do not have a measured σ due to unapparent absorption features overwhelmed by AGN activities, both properties of the mean spectra of Type 1 AGNs with and without a measured σ and a positive dependence of σ on the [O iii] luminosity can lead to a statistically larger σ for all Type 1 AGNs compared to the 6260 Type 1 AGNs with measured stellar velocity dispersions. Then, direct σ comparisons can lead to a statistically larger σ in Type 1 AGNs, with a confidence level higher than 10σ, after considering the necessary effects of different redshifts and different central AGN activities. Although Type 1 AGNs have a σ of only about (9 ± 3)% larger than Type 2 AGNs, the difference cannot be well explained at the current stage. Unless there is strong evidence to support different M BH–σ relations or to support quite different evolutionary histories between Type 1 and Type 2 AGNs, the statistically larger σ in Type 1 AGNs provides a strong challenge to the UM of AGNs.

Advanced LIGO and Advanced Virgo are detecting a large number of binary stellar origin black hole (BH) mergers. A promising channel for accelerated BH merger lies in active galactic nucleus (AGN) discs of gas around supermasssive BHs. Here, we investigate the relative number of compact object (CO) mergers in AGN disc models, including BH, neutron stars (NS), and white dwarfs, via Monte Carlo simulations. We find the number of all merger types in the bulk disc grows ∝ t1/3 which is driven by the Hill sphere of the more massive merger component. Median mass ratios of NS–BH mergers in AGN discs are $\tilde{q}=0.07\pm 0.06(0.14\pm 0.07)$ for mass functions (MF) M−1(− 2). If a fraction fAGN of the observed rate of BH–BH mergers (RBH–BH) come from AGN, the rate of NS–BH (NS–NS) mergers in the AGN channel is ${R}_{\mathrm{ BH}\!-\!\mathrm{ NS}} \sim f_{\mathrm{ AGN}}[10,300]\, \rm {Gpc}^{-3}\, \rm {yr}^{-1},({\mathit{ R}}_{NS\!-\!NS} \le \mathit{ f}_{AGN}400\, \rm {Gpc}^{-3}\, \rm {yr}^{-1}$). Given the ratio of NS–NS/BH–BH LIGO search volumes, from preliminary O3 results the AGN channel is not the dominant contribution to observed NS–NS mergers. The number of lower mass gap events expected is a strong function of the nuclear MF and mass segregation efficiency. CO merger ratios derived from LIGO can restrict models of MF, mass segregation, and populations embedded in AGN discs. The expected number of electromagnetic (EM) counterparts to NS–BH mergers in AGN discs at z &amp;lt; 1 is $\sim [30,900]\, {\rm {yr}}^{-1}(f_{\mathrm{ AGN}}/0.1)$. EM searches for flaring events in large AGN surveys will complement LIGO constraints on AGN models and the embedded populations that must live in them.

We present integral field spectroscopy observations, covering the [O III]4959,5007 emission-line doublet of eight high-redshift (z=1.4-3.4) ultra-luminous infrared galaxies (ULIRGs) that host Active Galactic Nuclei (AGN) activity, including known sub-millimetre luminous galaxies (SMGs). The targets have moderate radio luminosities that are typical of high-redshift ULIRGs (L(1.4GHz)=10^(24)-10^(25)W/Hz) and therefore are not radio-loud AGN. We de-couple kinematic components due to the galaxy dynamics and mergers from those due to outflows. We find evidence in the four most luminous systems (L([O III])>~10^(43)erg/s) for the signatures of large-scale energetic outflows: extremely broad [O III] emission (FWHM ~ 700-1400km/s) across ~4-15kpc, with high velocity offsets from the systemic redshifts (up to ~850km/s). The four less luminous systems have lower quality data displaying weaker evidence for spatially extended outflows. We estimate that these outflows are potentially depositing energy into their host galaxies at considerable rates (~10^(43)-10^(45)erg/s); however, due to the lack of constraints on the density of the outflowing material and the structure of the outflow, these estimates should be taken as illustrative only. Based on the measured maximum velocities (v(max)~400-1400km/s) the outflows observed are likely to unbind some fraction of the gas from their host galaxies, but are unlikely to completely remove gas from the galaxy haloes. By using a combination of energetic arguments and a comparison to ULIRGs without clear evidence for AGN activity, we show that the AGN activity could be the dominant power source for driving all of the observed outflows, although star formation may also play a significant role in some of the sources.

Differentiating between active galactic nucleus (AGN) activity and star formation in z ∼ 2 galaxies is difficult because traditional methods, such as line-ratio diagnostics, change with redshift, while multi-wavelength methods (X-ray, radio, IR) are sensitive to only the brightest AGNs. We have developed a new method for spatially resolving emission lines using the Hubble Space Telescope/Wide Field Camera 3 G141 grism spectra and quantifying AGN activity through the spatial gradient of the [O iii]/Hβ line ratio. Through detailed simulations, we show that our novel line-ratio gradient approach identifies ∼40% more low-mass and obscured AGNs than obtained by classical methods. Based on our simulations, we developed a relationship that maps the stellar mass, star formation rate, and measured [O iii]/Hβ gradient to the AGN Eddington ratio. We apply our technique to previously studied stacked samples of galaxies at z ∼ 2 and find that our results are consistent with these studies. This gradient method will also be able to inform other areas of galaxy evolution science, such as inside-out quenching and metallicity gradients, and will be widely applicable to future spatially resolved James Webb Space Telescope data.

It has long been known that galaxy interactions are associated with enhanced star formation. In a companion paper, we explored this connection by applying a variety of statistics to Sloan Digital Sky Survey (SDSS) data. In particular, we showed that specific star formation rates of galaxies are higher if they have close neighbours. Here, we apply exactly the same techniques to active galactic nuclei (AGN) in the survey, showing that close neighbours are not associated with any similar enhancement of nuclear activity. Star formation is enhanced in AGN with close neighbours in exactly the same way as in inactive galaxies, but the accretion rate on to the black hole, as estimated from the extinction-corrected [O iii] luminosity, is not influenced by the presence or absence of companions. Previous work has shown that galaxies with more strongly accreting black holes contain more young stars in their inner regions. This leads us to conclude that star formation induced by a close companion and star formation associated with black hole accretion are distinct events. These events may be part of the same physical process, for example a merger, provided they are separated in time. In this case, accretion on to the black hole and its associated star formation would occur only after the two interacting galaxies have merged. The major caveat in this work is our assumption that the extinction-corrected [O iii] luminosity is a robust indicator of the bolometric luminosity of the central black hole. It is thus important to check our results using indicators of AGN activity at other wavelengths.

We use the Galaxy and Mass Assembly (GAMA) and the Deep Extragalactic Visible Legacy Survey (DEVILS) observational data sets to calculate the cosmic star formation rate (SFR) and active galactic nuclei (AGN) bolometric luminosity history (CSFH/CAGNH) over the last 12.5 billion years. SFRs and AGN bolometric luminosities were derived using the spectral energy distribution fitting code ProSpect, which includes an AGN prescription to self-consistently model the contribution from both AGN and stellar emission to the observed rest-frame ultra-violet to far-infrared photometry. We find that both the CSFH and CAGNH evolve similarly, rising in the early Universe up to a peak at look-back time ≈10 Gyr (z ≈ 2), before declining towards the present day. The key result of this work is that we find the ratio of CAGNH to CSFH has been flat ($\approx 10^{42.5}\, \mathrm{erg \, s^{-1}\, {\rm M}_{\odot }^{-1}\, yr}$) for 11 Gyr up to the present day, indicating that star formation and AGN activity have been coeval over this time period. We find that the stellar masses of the galaxies that contribute most to the CSFH and CAGNH are similar, implying a common cause, which is likely gas inflow. The depletion of the gas supply suppresses cosmic star formation and AGN activity equivalently to ensure that they have experienced similar declines over the last 10 Gyr. These results are an important milestone for reconciling the role of star formation and AGN activity in the life cycle of galaxies.

We studied the circumnuclear mid-IR emission in a sample of 19 local active galactic nuclei (AGNs) with high spatial resolution spectra using T-ReCS (Gemini) and CanariCam (GTC), together with Spitzer/IRS observations. We measured the flux and the equivalent width for the 11.3 μm PAH feature and the [S iv] line emission as a function of galactocentric distance. This allowed us to study the star formation (SF) at subkiloparsec scales from the nucleus for a large sample of nearby AGNs. The [S iv] line emission could be tracing the AGN radiation field within a few thousand times the sublimation radius (R sub), but it often peaks at distances greater than 1000 R sub. One possibility is that the SF is contributing to the [S iv] total flux. We found an 11.3 μm PAH emission deficit within the inner few tens of parsecs from the AGN. This deficit might be due to the destruction of the molecules responsible for this feature or the lack of SF at these distances. We found a sensible agreement in the expected shift of the relation of the AGN bolometric luminosity and the SF rate. This indicates that numerical models attributing the link between AGN activity and host galaxy growth to mergers are in agreement with our data, for most inner galaxy parts.

The extent of black hole growth during different galaxy evolution phases and the connection between galaxy compactness and active galactic nucleus (AGN) activity remain poorly understood. We use Hubble Space Telescope imaging of the CANDELS fields to identify star-forming and quiescent galaxies at z = 0.5–3 in both compact and extended phases and use Chandra X-ray imaging to measure the distribution of AGN accretion rates and track black hole growth within these galaxies. We show that accounting for the impact of AGN light changes ∼20 per cent of the X-ray sources from compact to extended galaxy classifications. We find that ∼10–25 per cent of compact star-forming galaxies host an AGN, a mild enhancement (by a factor ∼2) compared to extended star-forming galaxies or compact quiescent galaxies of equivalent stellar mass and redshift. However, AGNs are not ubiquitous in compact star-forming galaxies and this is not the evolutionary phase, given its relatively short time-scale, where the bulk of black hole mass growth takes place. Conversely, we measure the highest AGN fractions (∼10–30 per cent) within the relatively rare population of extended quiescent galaxies. For massive galaxies that quench at early cosmic epochs, substantial black hole growth in this extended phase is crucial to produce the elevated black hole mass-to-galaxy stellar mass scaling relation observed for quiescent galaxies at z ∼ 0. We also show that AGN fraction increases with compactness in star-forming galaxies and decreases in quiescent galaxies within both the compact and extended subpopulations, demonstrating that AGN activity depends closely on the structural properties of galaxies.

We investigate star formation (SF) activity in the central kpc of a sample of nearby Active Galactic Nuclei (AGNs). AGN activities are expected to either trigger SF via accreting ISM to the central regions of the host galaxies or quench the SF via the energy feedback of the AGNs. To study the AGN-SF relation we select 113 nearby galaxies that host 8 GHz central radio sources. We use 8 GHz radio emission to represent the AGN activity and 8 micron dust emission in the central kpc regions of these galaxies to estimate the SF rate (SFR). The SFR is found to be correlated with the stellar mass for stellar mass greater than 1010 solar mass and looks scattered for stellar mass less than 1010 solar mass. There is no correlation between the specific SFR (SSFR) and the AGN activity for all sources. However, if we exclude the sources with the central stellar mass greater than 1010 solar mass, we find that the 8 GHz radio emission is well correlated with the SSFR. These results suggest that the AGN activity is significant in triggering SF activity only for small galaxies. Besides, we also select about 20 nearby AGN galaxies to investigate the radial variation of their surface specific star formation rate.

[Aims]: The relationship between star formation and super-massive black hole growth is central to our understanding of galaxy formation and evolution. Hyperluminous infrared galaxies (HLIRG) are unique laboratories to investigate the connection between starburst (SB) and active galactic nuclei (AGN), because they exhibit extreme star-formation rates, and most of them show evidence of harbouring powerful AGN.&#13;\n[Methods]: Our previous X-ray study of a sample of HLIRG shows that the X-ray emission of most of these sources is dominated by AGN activity. To improve our estimate of the relative contribution of the AGN and SB emission to its total bolometric output, we have built multi-wavelength (from radio to X-rays) spectral energy distributions (SED) for these HLIRG and fitted standard empirical AGN and SB templates to these SED.&#13;\n[Results]: In broad terms, most sources are well fitted with this method, and we found AGN and SB contributions similar to those obtained by previous studies of HLIRG. We have classified the HLIRG SED into two groups, class A and class B. Class A HLIRG show a flat SED from the optical to the infrared energy range. Three out of seven class A sources can be modelled with a pure luminosity-dependent quasar template, while the rest of them require a type 1 AGN template and a SB template. The SB component is dominant in three out of four class A objects. Class B HLIRG show SED with a prominent and broad IR bump. These sources cannot easily be modelled with a combination of pure AGN and pure SB, they require templates of composite objects, suggesting that of their emission comes from stellar formation processes.&#13;\n[Conclusions]: We propose that our sample is actually composed of three different populations: very luminous quasars (class A objects with negligible SB contribution), young galaxies going through their maximal star-formation period (class A objects with significant SB emission) and the high luminosity tail of the ultraluminous infrared galaxies population distribution (class B sources).