Active Galactic Nuclei Contribution Research Articles

EPOCHS Paper – VIII. An insight into MIRI-selected galaxies in SMACS-0723 and the benefits of deep MIRI photometry in revealing AGN and the dusty universe

ABSTRACT We present the analysis of the stellar population and star formation history of 181 MIRI selected galaxies at z = 0 − 3.5 in the massive galaxy cluster field SMACS J0723.3–7327, commonly referred to as SMACS0723, using the JWST Mid-Infrared Instrument (MIRI). We combine the data with the JWST Near Infrared Camera (NIRCam) catalogue, in conjunction with the Hubble Space Telescope (HST) WFC3/IR and ACS imaging. We find that the MIRI bands capture PAH features and dust emission, significantly enhancing the accuracy of photometric redshift and measurements of the physical properties of these galaxies. The median photo-z’s of galaxies with MIRI data are found to have a small 0.1 per cent difference from spectroscopic redshifts and reducing the error by 20 per cent. With MIRI data included in SED fits, we find that the measured stellar masses are unchanged, while the star formation rate is slightly lower by 0.1 dex. We also fit the median SED of active galactic nuclei (AGNs) and star-forming galaxies (SFG) separately. MIRI data provides tighter constraints on the AGN contribution, reducing the typical AGN contributions by ∼15 per cent. In addition, we also compare the median SED obtained with and without MIRI, and we find that including MIRI data yields steeper optical and UV slopes, indicating bluer colours, lower dust attenuation, and younger stellar populations. In the future, MIRI/MRS will enhance our understanding by providing more detailed spectral information and allowing for the study of specific emission features and diagnostics associated with AGN.

Active Galactic Nucleus Properties of ∼1 Million Member Galaxies of Galaxy Groups and Clusters at z < 1.4 Based on the Subaru Hyper Suprime-Cam Survey

Herein, we present the statistical properties of active galactic nuclei (AGNs) for approximately 1 million member galaxies of galaxy groups and clusters with 0.1 < cluster redshift (z cl) < 1.4 selected using the Subaru Hyper Suprime-Cam, the so-called CAMIRA clusters. In this research, we focused on the AGN power fraction (f AGN), which is defined as the proportion of the contribution of AGNs to the total infrared (IR) luminosity, L IR (AGN)/L IR, and examined how f AGN depends on (i) z cl and (ii) the distance from the cluster center. We compiled multiwavelength data using the ultraviolet–mid-IR range. Moreover, we performed spectral energy distribution fits to determine f AGN using the CIGALE code with the SKIRTOR AGN model. We found that (i) the value of f AGN in the CAMIRA clusters is positively correlated with z cl, with the correlation slope being steeper than that for field galaxies, and (ii) f AGN exhibits a high value at the cluster outskirts. These results indicate that the emergence of the AGN population depends on the redshift and environment and that galaxy groups and clusters at high redshifts are important in AGN evolution. Additionally, we demonstrated that cluster–cluster mergers may enhance AGN activity at the outskirts of particularly massive galaxy clusters. Our findings are consistent with a related study on the CAMIRA clusters that was based on the AGN number fraction.

Probing the interstellar medium of the quasar BRI 0952−0115

Context. The extent of the effect of active galactic nuclei (AGN) on their host galaxies at high-redshift is not apparent. The processes governing the co-eval evolution of the stellar mass and the mass of the central supermassive black hole, along with the effects of the supermassive black hole on the host galaxy, remain unclear. Studying this effect in the distant universe is a difficult process as the mechanisms of tracing AGN activity can often be inaccurately associated with intense star formation and vice versa. Aims. Our aim is to better understand the processes governing the interstellar medium (ISM) of the quasar BRI 0952−0952 at z = 4.432, specifically with regard to the individual heating processes at work and to place the quasar in an evolutionary context. Methods. We analyzed ALMA archival bands 3, 4, and 6 data and combined the results with high-resolution band-7 ALMA observations of the quasar. We detected [C I](2–1), [C II](2P3/2 − 2P1/2), CO(5–4), CO(7–6), CO(12–11), OH 2Π1/2(3/2 − 1/2), and H2O(211 − 202), and we report a tentative detection of OH+. We updated the lensing model and we used the radiative transfer code MOLPOP-CEP to produce line emission models which we compared with our observations. Results. We used the [C I] line emission to estimate the total molecular gas mass in the quasar. We present results from the radiative transfer code MOLPOP-CEP constraining the properties of the CO emission and suggest different possible scenarios for heating mechanisms within the quasar. We extended our results from MOLPOP-CEP to the additional line species detected in the quasar to place stronger constraints on the ISM properties. Conclusions. Modeling from the CO SLED suggests that there are extreme heating mechanisms operating within the quasar in the form of star formation or AGN activity; however, with the current data, it remains unclear which of the two is the preferred mechanism as both models reasonably reproduce the observed CO line fluxes. The updated lensing model suggests a velocity gradient across the [C II] line, suggestive of ongoing kinematical processes within the quasar. We find that the H2O emission in BRI 0952 is likely correlated with star-forming regions of the ISM. We used the molecular gas mass from [C I] to calculate a depletion time for the quasar. We conclude that BRI 0952−0952 is a quasar with a significant AGN contribution while also showing signs of extreme starburst activity, indicating that the quasar could be in a transitional phase between a starburst-dominated stage and an AGN-dominated stage.

The NuSTAR View of Perseus: The Intracluster Medium and a Peculiar Hard Excess

As the brightest galaxy cluster in the X-ray sky, Perseus is an excellent target for studying the intracluster medium (ICM), but until recently, its active galactic nucleus (AGN) made studies of the diffuse emission near its center nearly impossible to accomplish with NuSTAR, due to the extended wings of NuSTAR's point-spread function. The development of a new open-source software package—nucrossarf—now allows the contribution from point and diffuse sources to be modeled so that scattered light from the AGN can be accounted for. Using this technique, we present an analysis of diffuse hard X-ray (3–25 keV) emission from the ICM using three archival NuSTAR observations of the Perseus cluster. We find a ∼10% excess of emission beyond 20 keV not describable by purely thermal models. By performing similar analyses of AGNs in archival observations, we have characterized the systematic uncertainty of the modeled AGN contribution to be 3.4%. However, in order to explain the excess, the total scattered AGN emission would have to be 39% stronger than we have measured. We test physical explanations for the excess, such as diffuse inverse-Compton emission potentially originating from the radio mini-halo, but we determine that none of the models are compelling. An upper limit on the inverse-Compton flux (≤1.5 × 10−11 erg s−1 cm−2) and a corresponding lower limit on the global magnetic field strength (≥0.35 μG) are derived. We discuss the potential origin and implications of the excess and present our characterization of the nucrossarf systematic uncertainty, which should be useful for future work.

Exploring the nature of UV-bright z ≳ 10 galaxies detected by JWST: star formation, black hole accretion, or a non-universal IMF?

ABSTRACT We use the Cosmic Archaeology Tool (CAT) semi-analytical model to explore the contribution of Population (Pop) III/II stars and active galactic nuclei (AGNs) to the galaxy ultraviolet (UV) luminosity function (LF) evolution at 4 ≤ z ≤ 20. We compare in particular with recent JWST data in order to explore the apparent tension between observations and theoretical models in the number density of bright galaxies at z ≳ 10. The model predicts a star formation history dominated by UV faint (MUV &amp;gt; −18) galaxies, with a Pop III contribution of $\lesssim 10~{{\ \rm per\ cent}}$ ($\lesssim 0.5~{{\ \rm per\ cent}}$) at z ≃ 20 (z ≃ 10). Stars are the primary sources of cosmic reionization, with $5~{{\ \rm per\ cent}}\!-\!10~{{\ \rm per\ cent}}$ of ionizing photons escaping into the intergalatic medium at 5 ≤ z ≤ 10, while the contribution of unobscured AGNs becomes dominant only at z ≲ 5. The predicted stellar and AGN UV LFs reproduce the observational data at 5 ≲ z ≲ 9–10. At higher redshift, CAT predicts a steeper evolution in the faint-end slope (MUV &amp;gt; –18), and a number density of bright galaxies (MUV ≃ −20) consistent with data at z ∼ 10–11, but smaller by 0.8 dex at z ∼ 12–13, and 1.2 dex at z ∼ 14–16, when compared to the values estimated by recent studies. Including the AGN emission does not affect the above findings, as AGNs contribute at most to $\lesssim 10~{{\ \rm per\ cent}}$ of the total UV luminosity at MUV &amp;lt; –19 and z ≳ 10. Interestingly, considering a gradual transition in the stellar initial mass function, modulated by metallicity and redshift as suggested by recent simulations, the model agrees with JWST data at z ∼ 12–13, and the disagreement at z ∼ 14–16 is reduced to 0.5 dex.

Active Galactic Nuclei in a Mid-infrared Selected Galaxy Sample at z > 0.13: [Ne v]λ3426 Line Emission as a Benchmark

We present a 24 μm-selected spectroscopic sample z > 0.13 (median 〈z〉 = 0.41) in the Lockman Hole field, consisting of 4035 spectra. Our aim is to identify active galactic nuclei (AGNs) and determine their fraction in this mid-infrared-selected sample. In this work, we use the [Ne v]λ3426 emission line to spectroscopically identify AGNs. Combined with broad-line Type I AGNs selected in our previous study, our sample consists of 887 (∼22%) spectroscopically confirmed AGNs. We perform a stacking analysis on the remaining spectra and find that in various mid-infrared (MIR) wedge-selected AGN candidates, the stacked spectra still show significant [Ne v]λ3426 emission. In contrast, no clear [Ne v]λ3426 signal is detected in non-AGN candidates falling outside the wedges. Assuming a range of AGN MIR spectral energy distribution (SED) slope of −0.3 <α < 0.7, and an average star-forming relation derived from 65 star-forming templates, we develop a robust method to separate the AGN and star-forming contributions to the MIR SEDs using the rest-frame L 12/L 1.6 versus L 4.5/L 1.6 diagram. We separate the objects into bins of L 12 and find that the AGN fraction increases with increasing L 12. We also find that the stacked [Ne v]λ3426 strength scales with L 12. The pure AGN luminosity at 12 μm exhibits a positive correlation with the star formation rates, indicating possible coevolution and common gas supply between the AGNs and their host galaxies. Varying population properties across the redshift range explored contribute to the observed correlation.

Study of star formation in dual nuclei galaxies using UVIT observations

ABSTRACT We have used the Ultraviolet Imaging Telescope (UVIT) aboard AstroSat to study star formation in a sample of nine dual nuclei galaxies with separations ⪅ 11 kpc, which is an expected outcome of galaxy mergers. To minimize the contribution of active galactic nuclei (AGN) emission, we have used mid-IR colour cut-offs and masked the AGN-dominated nuclei. The UV continuum slope (β) is used to calculate the internal extinction (AV) which ranges from 0.53 to 4.04 in the FUV band and 0.44 to 3.10 in the NUV band for the sample. We have detected 1−20 star-forming clumps in our sample galaxies. The extinction-corrected total FUV star formation rate (SFR) ranges from ∼0.35 to ∼32 M⊙ yr−1. Our analyses of AV, specific SFR (sSFR) show that dual nuclei sources are associated with dusty, star-forming galaxies. The FUV − NUV colour maps show redder colour in the nuclear and disc regions while bluer colour is observed in the outskirts of most galaxies which can be due to embedded dust or different stellar populations. We have found some signatures of possible stellar/AGN feedback like a ring of star formation, a redder ring around blue nuclei, etc. However, further observations are required to confirm this.

Uncovering a Massive z ∼ 7.7 Galaxy Hosting a Heavily Obscured Radio-loud Active Galactic Nucleus Candidate in COSMOS-Web

In this Letter, we report the discovery of the highest redshift, heavily obscured, radio-loud (RL) active galactic nucleus (AGN) candidate selected using JWST NIRCam/MIRI, mid-IR, submillimeter, and radio imaging in the COSMOS-Web field. Using multifrequency radio observations and mid-IR photometry, we identify a powerful, RL, growing supermassive black hole with significant spectral steepening of the radio spectral energy distribution (f 1.28 GHz ∼ 2 mJy, q 24 μm = −1.1, α 1.28−3 GHz = − 1.2, Δα = − 0.4). In conjunction with ALMA, deep ground-based observations, ancillary space-based data, and the unprecedented resolution and sensitivity of JWST, we find no evidence of AGN contribution to the UV/optical/near-infrared (NIR) data and thus infer heavy amounts of obscuration (N H > 1023 cm−2). Using the wealth of deep UV to submillimeter photometric data, we report a singular solution photo-z of z phot = 7.7−0.3+0.4 and estimate an extremely massive host galaxy (logM⋆=11.92±0.5M⊙) hosting a powerful, growing supermassive black hole​​​​​ (L Bol = 4−12x × 1046 erg s−1). This source represents the farthest known obscured RL AGN candidate, and its level of obscuration aligns with the most representative but observationally scarce population of AGN at these epochs.

Sub-mJy radio emission from high-redshift active galactic nuclei in the footprint of the VLA Sky Survey

ABSTRACT Using empty-field ‘Quick Look’ images from the first two epochs of the VLA Sky Survey (VLASS) observations, centred on the positions of ∼3700 individually radio-non-detected active galactic nuclei (AGNs) at z ≥ 4, we performed image stacking analysis to examine the sub-mJy emission at 3 GHz. We found characteristic monochromatic radio powers of Pchar = (2–13) × 1024 W Hz−1, indicating that AGN-related radio emission is widespread in the sample. The signal-to-noise ratios of the redshift-binned median stacked maps are between 4–6, and we expect that with the inclusion of the yet to be completed third-epoch VLASS observations, the detection limit defined as signal-to-noise ratio SNR ≥ 6 could be reached, and the redshift dependence can be determined. To obtain information on the general spectral properties of the faint radio emission in high-redshift AGNs, we confined the sample to ∼3000 objects covered by both the VLASS and the Faint Images of the Radio Sky at Twenty-centimeters (FIRST) survey. We found that the flux densities from the median stacked maps show a characteristic spectral index of α* = −0.30 ± 0.15, which is in agreement with the median spectral index of the radio-detected z ≥ 4 AGNs from our high-redshift AGN catalogue. The three-band mid-infrared colour–colour diagram based on Wide-field Infrared Survey Explorer observations provides further support regarding the AGN contribution to the radio emission in the sub-mJy sample.

VICTORIA project: The LOFAR HBA Virgo Cluster Survey

Context. The Virgo cluster is the nearest (d = 16.5 Mpc) massive (M ≥ 1014 M⊙) galaxy cluster and is therefore a prime target for studying astrophysical processes in dense large-scale environments. In the radio band, we can probe the nonthermal components of the interstellar medium, the intracluster medium (ICM), and of active galactic nuclei (AGN). This allows an investigation of the impact of the environment on the evolution of galaxies and the contribution of AGN to ICM heating. With the ViCTORIA (VIrgo Cluster multi-Telescope Observations in Radio of Interacting galaxies and AGN) project, we are carrying out multiple wide-field surveys of the Virgo cluster at different frequencies. Aims. We aim to investigate the impact of the environment on the evolution of galaxies and the contribution of AGN to ICM heating – from the inner cluster regions out to beyond the virial radius. Methods. We performed a survey of the cluster at 120–168 MHz using the LOw-Frequency ARray (LOFAR). We imaged a 132 deg2 region of the cluster, reaching an order-of-magnitude greater sensitivity than existing wide-field radio surveys of this field at three times higher spatial resolution compared to other low-frequency observations. We developed a tailored data processing strategy to subtract the bright central radio galaxy M 87 from the data. This allowed us to correct for systematic effects due to ionospheric variation as a function of time and direction. Results. In the final mosaic, which has a resolution of 9″ × 5″, we reach a median noise level of 140 μJy beam−1 inside the virial radius and 280 μJy beam−1 for the full area. We detect 112 Virgo member galaxies and 114 background galaxies. In at least 18 cases, the radio morphology of the cluster member galaxies shows clear signs of ram-pressure stripping. This includes three previously unreported candidates. In addition, we reveal previously undiscovered tails of 150 kpc in length from a previous epoch of AGN activity for NGC 4472 (M 49). While no cluster-scale diffuse radio sources are discovered, we find the presence of an extended radio signature of the W′ group. This feature is coincident with an X-ray filament detected with SRG/eROSITA in the outskirts of the cluster. We speculate that this emission is synchrotron radiation, which could be related to shocks or turbulence from accretion processes. Conclusions. The data published in this paper serve as a valuable resource for future studies. In the follow-up work of the ViCTORIA project, we will use these data for an analysis of environmental effects on the radio properties of star-forming galaxies in Virgo.

Nearby active galactic nuclei and starburst galaxies as sources of the measured UHECRs anisotropy signal

The Pierre Auger and the Telescope Array observatories have measured independent and statistical significant anisotropy in the arrival direction of ultra-high-energy cosmic rays (UHECR). Three hotspot regions with relative excess of events and a dipole signal have been identified in different regions of the sky and energy ranges. In this paper, we investigate the conditions under which these anisotropy signal could be generated by nearby (<23 Mpc) active galactic nuclei (AGN) and/or starburst galaxies (SBG). We studied a wide range of possibilities including injected nuclei (p, He, N, Si, and Fe), three UHECR luminosity proxies and three extragalactic magnetic field models. The results shows that both local AGN and SBG are needed to describe all the anisotropy signal. The contribution of AGN to hotspots and to the generation of the dipole is dominant in most cases. SBG is required only to explain the hotspot measured by the Telescope Array Observatory.

Optical and mid-infrared line emission in nearby Seyfert galaxies

Line ratio diagnostics provide valuable clues as to the source of ionizing radiation in galaxies with intense black hole accretion and starbursting events, such as local Seyfert galaxies or galaxies at the peak of their star formation history. We aim to provide a reference joint optical and mid-IR line ratio analysis for studying active galactic nucleus (AGN) identification via line-ratio diagnostics and testing predictions from photoionization models. We first obtained homogenous optical spectra with the Southern Africa Large Telescope for 42 Seyfert galaxies with available Spitzer/IRS spectroscopy, along with X-ray to mid-IR multiband data. After confirming the power of the main optical ([O III]λ5007) and mid-IR ([Ne V]14.3 μm, [O IV]25.9 μm, [Ne III]15.7 μm) emission lines in tracing AGN activity, we explored diagrams based on ratios of optical and mid-IR lines by exploiting photoionization models of different ionizing sources (AGN, star formation, and shocks). We find that pure AGN photoionization models are good at reproducing observations of Seyfert galaxies with an AGN fractional contribution to the mid-IR (5 − 40 μm) continuum emission larger than 50 per cent. For targets with a lower AGN contribution, even assuming a hard ionizing field from the central accretion disk (Fν ∝ να, with α ≈ −0.9), these same models do not fully reproduce the observed mid-IR line ratios. Mid-IR line ratios such as [Ne V]14.3 μm/[Ne II]12.8 μm, [O IV]25.9 μm/[Ne II]12.8 μm, and [Ne III]15.7 μm/[Ne II]12.8 μm show a dependence on the AGN fractional contribution to the mid-IR, unlike optical line ratios. An additional source of ionization, either from star formation or radiative shocks, can help explain the observations in the mid-IR. While mid-IR line ratios are good tracers of the AGN activity versus star formation, among the combinations of optical and mid-IR diagnostics in line-ratio diagrams, only those involving the [O I]/Hα ratio are promising diagnostics for simultaneously unraveling the relative roles of AGN, star formation, and shocks. A proper identification of the dominant source of ionizing photons would require the exploitation of analysis tools based on advanced statistical techniques as well as spatially resolved data.

Investigation of Stellar Kinematics and Ionized Gas Outflows in Local (U)LIRGs

We explore the properties of stellar kinematics and ionized gas in a sample of 1106 local (U)LIRGs from the AKARI telescope. We combine data from Wide-field Infrared Survey Explorer and Sloan Digital Sky Survey Data Release 13 to fit the spectral energy distribution (SED) of each source to constrain the contribution of active galactic nuclei (AGNs) to the total IR luminosity and estimate physical parameters such as stellar mass and star formation rate (SFR). We split our sample into AGNs and weak/non-AGNs. We find that our sample is considerably above the main sequence. The highest SFRs and stellar masses are associated with ULIRGs. We also fit the Hβ and Hα regions to characterize the outflows. We find that the incidence of ionized gas outflows in AGN (U)LIRGs (∼72%) is much higher than that in weak/non-AGN ones (∼39%). The AGN ULIRGs have extreme outflow velocities (up to ∼2300 km s−1) and high mass-outflow rates (up to ∼60 M ⊙ yr−1). Our results suggest that starbursts are insufficient to produce such powerful outflows. We explore the correlations of SFR and specific SFR (sSFR) with ionized gas outflows. We find that AGN hosts with the highest SFRs exhibit a negative correlation between outflow velocity and sSFR. Therefore, in AGNs containing large amounts of gas, the negative feedback scenario might be suggested.

Spatially resolved dust properties and quasar-galaxy decomposition of a hyper-luminous infrared galaxy at z = 4.4

ABSTRACT We report spatially resolved dust properties of the quasar host galaxy BRI1335−0417 at redshift z = 4.4 constrained by the Atacama Large Millimetre/submillimetre Array observations. The dust temperature map, derived from a greybody fit to rest frame 90 and 161 μm continuum images, shows a steep increase towards the centre, reaching 57.1 ± 0.3 K and a flat median profile at the outer regions of ∼38 K. Image decomposition analysis reveals the presence of a point source in both dust continuum images spatially coincident with the highest temperature peak and the optical quasar position, which we attribute to warm dust heated by an active galactic nucleus (AGN). We show that a model including this warm component along with cooler dust heated by star formation describes the global spectral energy distribution better than a single-component model, with dust temperatures of 87.1$^{+34.1}_{-18.3}$ K (warm component) and 52.6$^{+10.3}_{-11.0}$ K (cold component). The star-formation rate (SFR) estimated from the cold dust component is $1700_{-400}^{+500}\ \mathrm{M}_\odot$ yr−1, a factor of three smaller than previous estimates due to a large AGN contribution ($53^{+14}_{-15}$ per cent). The unresolved warm dust component also explains the steep temperature gradient, as the temperature profile derived after the point source subtraction is flat. The point source subtraction also reduces the estimated central SFR surface density ΣSFR by over a factor of three. With this correction, spatially resolved measurements of ΣSFR and the surface gas mass density Σgas form a roughly linear sequence in the Kennicutt–Schmidt diagram with a constant gas depletion time of 50–200 Myr. The demonstrated AGN-host galaxy decomposition reveals the importance of spatially resolved data for accurate measurements of quasar host galaxy properties, including dust temperature, SFRs, and size.

High-z galaxies with JWST and local analogues – it is not only star formation

ABSTRACT I present an analysis of the JWST NIRSpec data of SMACS 0723 released as Early Release Observations. As part of this three new redshifts are provided, bringing the total of reliable redshifts to 14. I propose a modification to the direct abundance determination method that reduces sensitivity to flux calibration uncertainties by a factor of ∼3 and show that the resulting abundances are in good agreement with Bayesian photoionization models of the rest-frame optical spectrum. I also show that 6355 is most likely a narrow-line active galactic nucleus (AGN) with $M_*\lt 10^9\, \mathrm{M}_\odot$ at z = 7.66 and argue that 10 612 might also have an AGN contribution to its flux through comparison to photoionization models and low-redshift analogues. Under the assumption that the lines come from star formation, I find that the galaxies have gas depletion times of ∼107 yr, comparable to similar galaxies locally. I also identify a population of possibly shock-dominated galaxies at z &amp;lt; 3, whose near-IR emission lines plausibly come nearly all from shocks and discuss their implications. I close with a discussion of the potential for biases in the determination of the mass–metallicity relation using samples defined by detected [O iii]4363 and show using low-z galaxies that this can lead to biases of up to 0.5 dex with a systematic trend with mass.

UV-FIR SED modelling of AGNs in IR-luminous galaxies up to z ∼ 2.5: understanding the effects of torus models

ABSTRACT UV-FIR spectral energy distribution (SED) modelling is an effective way to disentangle emission between star formation (SF) and active galactic nuclei (AGNs) in galaxies; however, this approach becomes uncertain for composite AGNs/SF galaxies that comprise 50–70 per cent of IR-samples. Cosmic X-ray background (XRB) models require a large fraction of obscured AGNs to reproduce the observed XRB peak, motivating reliable SED analyses in objects where the AGNs may be ‘buried’ in the galaxy and in the mid-IR to far-IR SED. In this paper, we study a 24 $\mu$m-selected (S24 &amp;gt; 100 $\mu$Jy) sample of 95 galaxies with $0~{{\ \rm per\ cent}} \lt f_{\mathrm{ MIR},\mathrm{ AGN}} \lt 100~{{\ \rm per\ cent}}$, 0.4 &amp;lt; z &amp;lt; 2.7, and 1011L⊙ &amp;lt; LIR &amp;lt; 1013L⊙. We test the performance of AGN models ranging in torus optical depth via SED fitting, comparing results with Spitzer mid-infrared spectroscopy and X-ray observations. The best-fitting torus optical depth can shed light on whether these galaxies host a luminous obscured AGN population. We find that permitting a broader AGN SED parameter space results in improved fit quality with higher optical depths, higher FIR AGN contributions, and higher LBol, impacting the bright end of the LBol luminosity function. Our results suggest there may be a population of dust-obscured composites that are bolometrically significant but have their AGNs mostly hidden in the mid-IR SED. If so, literature applications of SED fitting that often simplify AGN models or omit optically thick tori may largely underestimate AGN contribution from composite sources, as these sources are both numerous and have solutions sensitive to the assumed range of AGN models.

Molecular Outflows in z > 6 Unobscured QSO Hosts Driven by Star Formation

Feedback and outflows in galaxies that are associated with a quasar phase are expected to be pivotal in quenching the most massive galaxies. However, observations targeting the molecular outflow phase, which dominates both the mass and momentum and removes the immediate fuel for star formation, are limited in high-z QSO hosts. Massive quiescent galaxies found at z ∼ 4 are predicted to have quenched star formation already by z ∼ 5 and undergone their most intense growth at z > 6. Here, we present two Atacama Large Millimeter/submillimeter Array (ALMA) detections of molecular outflows, traced by blueshifted absorption of the OH 119 μm doublet, from a sample of three z > 6 infrared luminous QSO hosts: J2310+1855 and P183+05. OH 119 μm is also detected in emission from P183+05, and tentatively in the third source: P036+03. Using similar assumptions as for high-z dusty star-forming galaxy outflows, we find that our QSOs drive molecular outflows with comparable mass outflow rates, which are comparably energetic except for J2310+1855's significantly lower outflow energy flux. We do not find evidence, nor require additional input from the central active galactic nucleus (AGN) to drive the molecular outflow in J2310+1855, but we cannot rule out an AGN contribution in P183+05 if a significant AGN contribution to L FIR is assumed and/or if the outflow covering fraction is high (≥53%), which evidence from the literature suggests is unlikely in these sources. Differences observed in the blueshifted absorption spectral properties may instead be caused by the QSO hosts’ more compact dust continuums, limiting observations to lower altitude and more central regions of the outflow.

The cosmic radio background from 150 MHz to 8.4 GHz and its division into AGN and star-forming galaxy flux

ABSTRACT We present a revised measurement of the extragalactic background light (EBL) at radio frequencies based on a near complete compendium of radio source counts. We present the radio-EBL at 150 MHz, 325 MHz, 610 MHz, 1.4 GHz, 3 GHz, 5 GHz, and 8.4 GHz. In all cases the contribution to the radio-EBL, per decade of flux, exhibits a two-humped distribution well matched to the active galactic nucleus (AGN) and star-forming galaxy (SFG) populations, and with each population contributing roughly equal energy. Only at 3 GHz are the source count contributions to the EBL fully convergent, and hence we report empirical lower limits to the radio-EBL in the remaining bands. Adopting predictions from the SHARK semi-analytic model for the form of the SFG population, we can fit the fainter source counts providing measurements of the total contribution to the radio-EBL for the SFG and the AGN populations separately. This constitutes an empirically constrained model-dependent measurement for the SFG contribution, but a fully empirical measurement of the AGN contribution. Using the ProSpect spectral energy distribution code we can model the ultraviolet-optical-infrared-mm-radio SFG EBL at all frequencies from the cosmic star-formation history and the adoption of a Chabrier initial mass function. However, significant discrepancy remains (5 ×) between our source-count estimates of the radio-EBL and the direct measurements reported from the Absolute Radiometer for Cosmology, Astrophysics, and Diffuse Emission-2 (ARCADE-2) experiment. We can rule out a significant missing discrete source radio population and suggest that the cause of the high ARCADE-2 radio-EBL values may need to be sought either in the foreground subtraction or as a yet unknown diffuse component in the radio sky.

SPARCS-North Wide-field VLBI Survey: exploring the resolved μJy extragalactic radio source population with EVN + e-MERLIN

ABSTRACT The SKA PAthfinder Radio Continuum Surveys (SPARCS) are providing deep-field imaging of the faint (sub-mJy) extragalactic radio source populations through a series of reference surveys. One of the key science goals for SPARCS is to characterize the relative contribution of radio emission associated with active galactic nucleus (AGN) from star formation (SF) in these faint radio source populations, using a combination of high sensitivity and high angular resolution imaging over a range of spatial scales (arcsec to mas). To isolate AGN contribution from SF, we hypothesize that there exists a brightness temperature cut-off point separating pure AGN from SF. We present a multiresolution (10–100 mas) view of the transition between compact AGN and diffuse SF through a deep wide-field EVN + e-MERLIN, multiple phase centre survey of the centre of the Northern SPARCS (SLOAN) reference field at 1.6 GHz. This is the first (and only) VLBI (+ e-MERLIN) milliarcsecond angular resolution observation of this field, and of the wider SPARCS reference field programme. Using these high spatial resolution (9 pc–0.3 kpc at z ∼ 1.25) data, 11 milliarcsec-scale sources are detected from a targeted sample of 52 known radio sources from previous observations with the e-MERLIN, giving a VLBI detection fraction of $\sim 21{{\ \rm per\ cent}}$. At spatial scales of $\sim 9\,$pc, these sources show little to no jet structure whilst at $\sim 0.3\,$kpc one-sided and two-sided radio jets begin to emerge on the same sources, indicating a possible transition from pure AGN emissions to AGN and SF systems.

Seeking neutrino emission from AGN through temporal and spatial cross-correlation

Active galactic nuclei (AGN) are a promising source for high-energy astrophysical neutrinos (HEANs). By the end of 2022, the Vera C. Rubin Observatory (VRO) will begin to observe $\gtrsim10$ million AGN with a regular and high cadence. Here, we evaluate the capacity of VRO, in tandem with various current and upcoming neutrino telescopes, to establish AGN as HEAN emitters. To do so, we assume that the neutrino luminosity from any given AGN at any given time is proportional to the electromagnetic luminosity. We then estimate the error with which this fraction can be measured through spatial and temporal cross-correlation of VRO light curves with IceCube, KM3NeT, and Bakail-GVD. We find that it may be possible to detect AGN contributions at the $\sim3 \sigma$ level to the HEAN flux even if these AGN contribute only $\sim10\%$ of the HEAN flux. The bulk of this information comes from spatial correlations, although the temporal information improves the sensitivity a bit. The results also imply that if an angular correlation is detected with high signal-to-noise, there may be prospects to detect a correlation between AGN variability and neutrino arrival times. The small HEAN fraction estimated here to be accessible to the entirety of the VRO AGN sample suggests that valuable information on the character of the emitting AGN may be obtained through similar analyses on different sub-populations of AGN.