non-AGN Galaxies Research Articles

Comparing metallicity correlations in nearby non-AGN and AGN-host galaxies

Comparing metallicity correlations in nearby non-AGN and AGN-host galaxies

Mapping AGN winds: A connection between radio-mode AGNs and the AGN feedback cycle

We present a kinematic analysis based on the large integral field spectroscopy (IFS) dataset of SDSS-IV MaNGA (Sloan Digital Sky Survey/Mapping Nearby Galaxies at Apache Point Observatory; ∼10 000 galaxies). We have compiled a diverse sample of 594 unique active galactic nuclei (AGNs), identified through a variety of independent selection techniques, encompassing radio (1.4 GHz) observations, optical emission-line diagnostics (BPT), broad Balmer emission lines, mid-infrared colors, and hard X-ray emission. We investigated how ionized gas kinematics behave in these different AGN populations through stacked radial profiles of the [O III] 5007 emission-line width across each AGN population. We contrasted AGN populations against each other (and non-AGN galaxies) by matching samples by stellar mass, [O III] 5007 luminosity, morphology, and redshift. We find similar kinematics between AGNs selected by BPT diagnostics compared to broad-line-selected AGNs. We also identify a population of non-AGNs with similar radial profiles as AGNs, indicative of the presence of remnant outflows (or fossil outflows) of past AGN activity. We find that purely radio-selected AGNs display enhanced ionized gas line widths across all radii. This suggests that our radio-selection technique is sensitive to a population in which AGN-driven kinematic perturbations have been active for longer durations (potentially due to recurrent activity) than in purely optically selected AGNs. This connection between radio activity and extended ionized gas outflow signatures is consistent with recent evidence that suggests radio emission (expected to be diffuse) originated due to shocks from outflows. We conclude that different selection techniques can trace different AGN populations not only in terms of energetics but also in terms of AGN evolutionary stages. Our results are important in the context of the AGN duty cycle and highlight integral field unit data’s potential to deepen our knowledge of AGNs and galaxy evolution.

On the Origin of Quenched but Gas-rich Regions at Kiloparsec Scales in Nearby Galaxies

We use resolved spectroscopy from MaNGA to investigate the significance of both local and global properties of galaxies to the cessation of star formation at kpc scales. Quenched regions are identified from a sample of isolated disk galaxies by a single-parameter criterion D n (4000) - log EW(Hα) >1.6−log2=1.3 , and are divided into gas-rich quenched regions (GRQRs) and gas-poor quenched regions according to the surface density of cold gas (Σgas). Both types of quenched regions tend to be hosted by non-AGN galaxies with relatively high mass (M * ≳ 1010 M ⊙) and red colors (NUV − r ≳ 3), as well as low star formation rate and high central density at fixed mass. They span wide ranges in other properties including structural parameters that are similar to the parent sample, indicating that the conditions responsible for quenching in gas-rich regions are largely independent of the global properties of galaxies. We train random forest classifiers and regressors for predicting quenching in our sample with 15 local/global properties. Σ* is the most important property for quenching, especially for GRQRs. These results strongly indicate the important roles of low-mass hot evolved stars, which are numerous and long-lived in quenched regions and can provide substantial radiation pressure to support the surrounding gas against gravitational collapse. The different feature importance for quenching, as found previously by A. F. L. Bluck et al., is partly due to the different definitions of quenched regions, particularly the different requirements on EW(Hα).

Black Hole–Halo Mass Relation from UNIONS Weak Lensing

This Letter presents, for the first time, direct constraints on the black hole–halo mass relation using weak gravitational-lensing measurements. We construct type I and type II active galactic nucleus (AGN) samples from the Sloan Digital Sky Survey, with a mean redshift of 0.4 (0.1) for type I (type II) AGNs. This sample is cross correlated with weak-lensing shear from the Ultraviolet Near Infrared Optical Northern Survey. We compute the excess surface mass density of the halos associated with 36,181 AGNs from 94,308,561 lensed galaxies and fit the halo mass in bins of black hole mass. We find that more massive AGNs reside in more massive halos. The relation between halo mass and black hole mass is well described by a power law of slope 0.6 for both type I and type II samples, in agreement with models that link black hole growth to baryon feedback. We see no dependence on AGN type or redshift in the black hole–halo mass relation below a black hole mass of 108.5 M ⊙. Above that mass, we find more massive halos for the low-z type II sample compared to the high-z type I sample, but this difference may be interpreted as systematic error in the black hole mass measurements. Our results are consistent with previous measurements for non-AGN galaxies. At a fixed black hole mass, our weak-lensing halo masses are consistent with galaxy rotation curves but significantly lower than galaxy-clustering measurements. Finally, our results are broadly consistent with state-of-the-art hydrodynamical cosmological simulations, providing a new constraint for black hole masses in simulations.

Probing star formation rates and histories in AGNs and non-AGN galaxies across diverse cosmic environments and X-ray luminosity ranges

In this work, we compare the star formation rates (SFRs) and star formation histories (SFHs) of active galactic nuclei (AGNs) and non-AGN galaxies. We explore these aspects across different density fields and over three orders of magnitude in X-ray luminosity (L$_X$). For that purpose, we employed X-ray AGNs detected in the XMM-XXL field and constructed a galaxy control sample, using sources from the VIPERS catalogue. We applied strict photometric and quality selection criteria to ensure that only sources with robust (host) galaxy measurements were included in the analysis. Our final samples consist of 149 X-ray AGNs with $ L_ X,2-10keV (ergs^ <45$ and 3\,488 non-AGN systems. The sources span a redshift range of $ 0.5<z<1.0$ and have stellar masses within, $10.5< M_*(M_ odot) <11.5$. For these systems, we adopted the available measurements for their local densities and their spectral lines (D$_n$4000) from the VIPERS catalogue. To compare the SFRs of these two populations, we calculated the SFR$_ norm $ parameter. The latter is defined as the ratio of the SFRs of AGNs to the SFRs of non-AGN galaxies with similar M$_*$ and redshift. Our findings reveal that low- and moderate-L$_X$ AGNs ($ L_ X,2-10keV (ergs^ <44$) that reside in low-density fields have a nearly flat SFR$_ norm -$L$_X$ relation. In contrast, the AGNs of similar L$_X$ values that reside in high-density environments present an increase in SFR$_ norm $ with L$_X$. These results are in line with previous studies. Notably, our results suggest that the most luminous of the AGNs ($ L_ X,2-10keV (ergs^ >44$) exhibit an increased SFR in comparison to non-AGN galaxies. This trend appears to be independent of the density of the environment. Furthermore, for AGNs with similar L$_X$, those in high-density regions tend to have higher SFR$_ norm $ values compared to their counterparts in low-density areas. Comparisons of the D$_n$4000 spectral index, which serves as a proxy for the age of the stellar population, reveals that low- and moderate-L$_X$ AGNs reside in galaxies with comparable stellar populations with non-AGN systems, regardless of the density field they are situated in. However, the most luminous X-ray sources tend to reside in galaxies that have younger stellar populations, as compared to non-AGN galaxies, regardless of the galaxy's environment.

The mass–metallicity and fundamental metallicity relations in non-AGN and AGN-host galaxies

ABSTRACT Galaxies’ stellar masses, gas-phase oxygen abundances (metallicity), and star formation rates (SFRs) obey a series of empirical correlations, most notably the mass–metallicity relation (MZR) and fundamental metallicity relation (FZR), which relates oxygen abundance to a combination of stellar mass and SFR. However, due to the difficulty of measuring oxygen abundances and SFRs in galaxies that host powerful active galactic nuclei (AGN), to date it is unknown to what extent AGN-host galaxies also follow these correlations. In this work, we apply Bayesian methods to the MaNGA integral field spectrographic (IFS) survey that allow us to measure oxygen abundances and SFRs in AGN hosts, and use these measurements to explore how the MZR and FZR differ between galaxies that do and do not host AGN. We find similar MZRs at stellar masses above $10^{10.5} \, \mathrm{M}_\odot$, but that at lower stellar masses AGN hosts show up to $\sim 0.2$ dex higher oxygen abundances. The offset in the FZR is significantly smaller, suggesting that the larger deviation in the MZR is a result of AGN-host galaxies having systematically lower SFRs at fixed stellar mass. However, within the AGN-host sample there is little correlation between SFR and oxygen abundance. These findings support a scenario in which an AGN can halt efficient gas accretion, which drives non-AGN host galaxies to both higher SFR and lower oxygen abundance, resulting in the galaxy evolving off the star-forming main sequence (SFMS). As a consequence, as the SFR declines for an individual system its metallicity remains mostly unchanged.

Comparative analysis of the SFR of AGN and non-AGN galaxies, as a function of stellar mass, AGN power, cosmic time, and obscuration

This study involves a comparative analysis of the star formation rates (SFRs) of active galactic nucleus (AGN) galaxies and non-AGN galaxies and of the SFRs of type 1 and 2 AGNs. To carry out this investigation, we assembled a dataset consisting of 2677 X-ray AGNs detected by the XMM-Newton observatory and a control sample of 64 556 galaxies devoid of AGNs. We generated spectral energy distributions (SEDs) for these objects using photometric data from the DES, VHS, and AllWISE surveys, and we harnessed the CIGALE code to extract measurements for the (host) galaxy properties. Our dataset encompasses a diverse parameter space, with objects spanning a range of stellar masses from 9.5 < log [M*(M⊙)] < 12.0, intrinsic X-ray luminosities within 42 < log[LX,2−10 keV(erg s−1)] < 45.5, and redshifts between 0.3 < z < 2.5. To compare SFRs, we calculated the SFRnorm parameter, which signifies the ratio of the SFR of an AGN galaxy to the SFR of non-AGN galaxies sharing similar M* and redshift. Our analysis reveals that systems hosting an AGN tend to exhibit elevated SFRs compared to non-AGN galaxies, particularly beyond a certain threshold in LX. Notably, this threshold increases as we move toward more massive galaxies. Additionally, for AGN systems with the same LX, the magnitude of the SFRnorm decreases as we consider more massive galaxies. This suggests that in galaxies with an AGN, the increase in SFR as a function of stellar mass is not as prominent as in galaxies without an AGN. This interpretation finds support in the shallower slope that we identify in the X-ray star-forming main sequence in contrast to the galaxy main sequence. Employing CIGALE’s measurements, we classified AGNs into type 1 and type 2. In our investigation, we focused on a subset of 652 type 1 AGNs and 293 type 2 AGNs within the stellar mass range of 10.5 < log[M (M⊙)] < 11.5. Based on our results, type 1 AGNs display higher SFRs than type 2 AGNs, at redshifts below z < 1. However, at higher redshifts, the SFRs of the two AGN populations tend to be similar. At redshifts z < 1, type 1 AGNs show augmented SFRs in comparison to non-AGN galaxies. In contrast, type 2 AGNs exhibit lower SFRs when compared to galaxies that do not host an AGN, at least up to log[LX,2−10 keV(erg s−1)] < 45.

Active galactic nuclei and gravitational redshifts

Gravitational redshift is a classical effect of General Relativity. It has been measured in stars, quasars, and clusters of galaxies. We identify the signature of gravitational redshift in the emission lines of active galaxies that is caused by supermassive black holes and compare this signature to what is found for inactive galaxies. Using the virial theorem, we estimated gravitational redshifts for quasars from the 14th data release (DR14) of the Sloan Digital Sky Survey (SDSS) and compared them with measured gravitational redshifts from the difference between the redshifts of emission lines of Sydney Australian Astronomical Observatory Multi-object Integral Field (SAMI) galaxies in the central and outer annuli of their integral field spectra. Firstly, from the full width at half maximum of $H_ beta$ lines of 57 Seyfert type I galaxies of the active galactic nucleus (AGN) Black Hole Mass Database, we derive a median gravitational redshift $z_g = 1.18 $. Expanding this analysis to 86755 quasars from DR14 of SDSS, we have a median value $z_g = 1.52 . Then, by comparing the redshifts of lines measured in the central and outer regions of low-ionization nuclear emission-line region galaxies in the SAMI survey, we obtain $z_g = (0.68 which increases to $z_g = (1.0 $ for the $H_ and $H_ lines . These numbers are compatible with central black holes of $ 10^9$ solar masses and broad line regions of $ 1$ pc. For non-AGN galaxies, the gravitational redshift is compatible with zero.

Link between star formation and the properties of supermassive black holes

It is well known that supermassive black holes (SMBHs) and their host galaxies undergo a process of co-evolution. Feedback from active galactic nuclei (AGNs) plays an important role in this symbiosis. To study the effect of AGN feedback on the host galaxy, one popular method is to study the star formation rate (SFR) as a function of the X-ray luminosity (LX). However, hydrodynamical simulations suggest that the cumulative impact of AGN feedback on a galaxy is encapsulated in the mass of the SMBH, MBH, rather than the LX. In this study, we compare the SFRs of AGN and non-AGN galaxies as a function of LX, MBH, the Eddington ratio (nEdd), and the specific black hole accretion rate (λsBHAR). For that purpose, we used 122 X-ray AGN in the XMM-XXL field and 3371 galaxies from the VIPERS survey to calculate the SFRnorm parameter, defined as the ratio of the SFR of AGN to the SFR of non-AGN galaxies with similar stellar mass, M*, and redshift. Our datasets span a redshift range of 0.5 ≤ z ≤ 1.2. The results show that the correlation between SFRnorm and MBH is stronger compared to that between SFRnorm and LX. A weaker correlation is found between SFRnorm and λsBHAR. No correlation is detected between SFRnorm and nEdd. These results corroborate the notion that the MBH is a more robust tracer of the cumulative impact of the AGN feedback, compared to the instantaneous accretion rate (LX). Thus, it may serve as a better predictive parameter of changes in the SFR of the host galaxy.

The relation of cosmic environment and morphology with the star formation and stellar populations of AGN and non-AGN galaxies

In this work, we study the relation of the cosmic environment and morphology with the star formation and stellar population of galaxies. Most importantly, we examine if this relation differs for systems with active and non-active supermassive black holes. For that purpose, we used 551 X-ray detected active galactic nuclei (AGNs) and 16 917 non-AGN galaxies in the COSMOS-Legacy survey for which surface-density field measurements are available. The sources lie at a redshift of 0.3 < z < 1.2, probe X-ray luminosities of 42 < log[LX,2−10 keV(erg s−1)] < 44, and have stellar masses of 10.5 < log [M*(M⊙)] < 11.5. Our results show that isolated AGNs (field) have lower star formation rates (SFRs) compared to non-AGNs at all LX spanned by our sample. However, in denser environments (filaments and clusters), moderate LX AGN (log[LX,2−10 keV(erg s−1)] > 43) and non-AGN galaxies have similar SFRs. We also examined the stellar populations and the morphology of the sources in different cosmic fields. For the same morphological type, we find that non-AGN galaxies tend to have older stellar populations and are less likely to have undergone a recent burst in denser environments compared to their field counterparts. The differences in the stellar populations concerning density field are mainly driven by quiescent systems. Moreover, low LX AGNs present negligible variations of their stellar populations in all cosmic environments, whereas moderate LX AGNs have, on average, younger stellar populations and are more likely to have undergone a recent burst in high-density fields. Finally, in the case of non-AGN galaxies, the fraction of bulge-dominated (BD) systems increases with the density field, while BD AGNs are scarce in denser environments. Our results are consistent with a scenario in which a common mechanism, such as mergers, triggers both the star-formation and the AGN activity.

The [O iii] Profiles of Far-infrared Active and Inactive Optically Selected Green Valley Galaxies

We present a study of the [O iii] λ5007 line profile in a subsample of eight active galactic nuclei (AGNs) and six non-AGNs in the optically selected green valley at z < 0.5 using long-slit spectroscopic observations obtained with the 11 m Southern African Large Telescope. Gaussian decomposition of the line profile was performed to study its different components. We observe that the AGN profiles are more complex than the non-AGN ones. In particular, in most AGNs (5/8) we detect a blue wing of the line. We derive the FWHM velocities of the wing and systemic component, and find that the AGNs show higher FWHM velocities than the non-AGNs in their core component. We also find that the AGNs show blue wings with a median velocity width of approximately 600 km s−1, and a velocity offset from the core component in the range −90 to −350 km s−1, in contrast to the non-AGN galaxies, where we do not detect blue wings in any of their [O iii] λ5007 line profiles. Using the spatial information in our spectra, we show that at least three of the outflow candidate galaxies have centrally driven gas outflows extending across the whole galaxy. Moreover, these are also the galaxies which are located on the main sequence of star formation, raising the possibility that the AGNs in our sample are influencing the star formation of their host galaxies (such as positive feedback). This is in agreement with our previous work where we studied the star formation, morphology, and stellar population properties of a sample of green valley AGNs and non-AGN galaxies.

Unraveling Joint Evolution of Bars, Star Formation, and Active Galactic Nuclei of Disk Galaxies

We aim to unravel the interplay between bars, star formation (SF), and active galactic nuclei (AGNs) in barred galaxies. To this end, we utilize the SDSS DR12 to select a sample of nearby (0.02 < z < 0.06) disk galaxies that are suitable for bar examination (M r < −20.12 and inclination ≲53°). We identify 3662 barred galaxies and measure the length and axis ratio of each bar. We invent new bar parameters that mitigate the stellar and bulge mass biases and show, for the first time, that the evolution of non-AGN and AGN-hosting barred galaxies should be tracked using different bar parameters: the bar length for non-AGN galaxies and the bar axis ratio for AGN-hosting galaxies. Our analysis confirms that barred galaxies have a higher specific SF rate than unbarred control galaxies. Moreover, we find a positive correlation of bar length with both the SF enhancement and the centrally star-forming galaxy fraction, indicating the interconnectivity of bars and SF through the bar-driven gas inflow. We also find that, while the AGN fraction of barred galaxies is the same as that of the unbarred control sample, galaxies hosting more massive black holes (BHs) have rounder (i.e., higher axis ratio) bars, implying that the bar is not a cause of AGN activity; rather, AGNs appear to regulate bars. Our findings corroborate theoretical predictions that bars in non-AGN galaxies grow in length, and bars in AGN-hosting galaxies become rounder as BHs grow and eventually get destroyed.

Galaxy interactions are the dominant trigger for local type 2 quasars

ABSTRACT The triggering mechanism for the most luminous, quasar-like active galactic nuclei (AGN) remains a source of debate, with some studies favouring triggering via galaxy mergers, but others finding little evidence to support this mechanism. Here, we present deep Isaac Newton Telescope/Wide Field Camera imaging observations of a complete sample of 48 optically selected type 2 quasars – the QSOFEED sample ($L_{\rm [O\, \small {III}]}\gt 10^{8.5}\, \mathrm{L}_{\odot }$; z &amp;lt; 0.14). Based on visual inspection by eight classifiers, we find clear evidence that galaxy interactions are the dominant triggering mechanism for quasar activity in the local universe, with 65$^{+6}_{-7}$ per cent of the type 2 quasar hosts showing morphological features consistent with galaxy mergers or encounters, compared with only 22$^{+5}_{-4}$ per cent of a stellar-mass- and redshift-matched comparison sample of non-AGN galaxies – a 5σ difference. The type 2 quasar hosts are a factor of 3.0$^{+0.5}_{-0.8}$ more likely to be morphologically disturbed than their matched non-AGN counterparts, similar to our previous results for powerful 3CR radio AGN of comparable [O iii] emission-line luminosity and redshift. In contrast to the idea that quasars are triggered at the peaks of galaxy mergers as the two nuclei coalesce, and only become visible post-coalescence, the majority of morphologically disturbed type 2 quasar sources in our sample are observed in the pre-coalescence phase (61$^{+8}_{-9}$ per cent). We argue that much of the apparent ambiguity that surrounds observational results in this field is a result of differences in the surface brightness depths of the observations, combined with the effects of cosmological surface brightness dimming.

Comparison of star formation histories of AGN and non-AGN galaxies

We used active galactic nuclei (AGNs) with X-ray luminosities, LX, 2 − 10 keV ∼ 1042.5 − 44 erg s−1, from the COSMOS-Legacy survey that lie within the UltraVISTA region and cross-matched them with the LEGA-C catalogue. The latter provides measurements of the calcium break, Dn4000, and Hδ Balmer line that allow us to study the stellar populations of AGNs and compare them with a galaxy reference catalogue. Our samples consist of 69 AGNs and 2176 non-AGN systems, within 0.6 &lt; z &lt; 1.3, that satisfy the same photometric selection criteria. We constructed the spectral energy distributions (SEDs) of both population and used the CIGALE code to investigate the effect of the two indices in the SED fitting process. Our analysis shows that the inclusion of Dn4000 and Hδ allows CIGALE to better constrain the ages of the stellar populations. Furthermore, we find an increase of the estimated stellar masses by ∼0.2 dex, in particular for systems with young stars (Dn4000 &lt; 1.5), when the two indices are included in the SED fitting. We then compare the Dn4000 and Hδ of AGNs with sources in the reference catalogue, accounting for the different stellar mass of the two populations. Our analysis reveals that low-to-moderate LX AGNs tend to reside in galaxies with older stellar populations and are less likely to have experienced a recent star formation burst compared to galaxies in the control sample. Finally, we compared the two populations as a function of their morphology (bulge-dominated, BD, versus non-BD) and compactness (mass-to-size ratio). A similar fraction of AGN and non-AGN systems are classified as non-BD (∼70%). Our analysis shows that BD AGN tend to have younger stellar populations compared to BD non-AGN systems. On the other hand, non-BD AGNs have, on average, older stellar populations and are less likely to have experienced a burst compared to non-BD sources in the reference sample. Furthermore, AGNs tend to prefer more compact systems compared to non-AGNs.

The environment of AGN dwarf galaxies at z ∼ 0.7 from the VIPERS survey

ABSTRACT Dwarf galaxies are ideal laboratories to study the relationship between the environment and active galactic nucleus (AGN) activity. However, the type of environments in which dwarf galaxies hosting AGN reside is still unclear and limited to low-redshift studies (${z\lt 0.5}$). We use the VIMOS Public Extragalactic Redshift Survey (VIPERS) to investigate, for the first time, their environments at $0.5\lt {z}\lt 0.9$. We select a sample of 12 942 low-mass ($\rm {log}(\mathit{ M}_\mathrm{*}/M_{\odot })\le 10$) galaxies and use the emission-line diagnostic diagram to identify AGN. We characterize their local environments as the galaxy density contrast, δ, derived from the fifth nearest neighbour method. Our work demonstrates that AGN and non-AGN dwarf galaxies reside in similar environments at intermediate redshift suggesting that the environment is not an important factor in triggering AGN activity already since ${z=0.9}$. Dwarf galaxies show a strong preference for low-density environments, independently of whether they host an AGN or not. Their properties do not change when moving to denser environments, suggesting that dwarf galaxies are not gas-enriched due to environmental effects. Moreover, AGN presence does not alter host properties supporting the scenario that AGN feedback does not impact the star formation of the host. Lastly, AGNs are found to host overmassive black holes. This is the first study of dwarf galaxies hosting AGNs at ${z\gt 0.5}$. The next generation of deep surveys will reveal whether or not such lack of environmental trends is common also for faint higher redshift dwarf galaxy populations.

Testing the role of AGN on the star formation and metal enrichment of ‘twin galaxies’

ABSTRACT We explore the effect of AGN activity on the star formation history of galaxies by analysing the stellar population properties of 10 pairs of nearby twin galaxies – selected as being visually similar except for the presence of an AGN. The selection of such twin samples represents a method to study AGN feedback, as recently proposed by del Moral Castro et al. We use integral field unit (IFU) data from CALIFA, stacked within three fixed apertures. AGN galaxies in a twin pair suggest more evolved stellar populations than their non-AGN counterpart 90 per cent of the time, regardless of aperture size. A comparison with a large sample from SDSS confirms that most twins are representative of the general population, but in each twin the differences between twin members is significant. A set of targeted line strengths reveal the AGN member of a twin pair is older and more metal-rich than the non-AGN galaxy, suggesting AGN galaxies in our sample may either have an earlier formation time or follow a different star formation and chemical enrichment history. These results are discussed within two simple, contrasting hypotheses for the role played by AGN in galaxy evolution, which can be tested in the future at a greater detail with the use of larger data sets.

Stellar populations of a sample of far-infrared AGN and non-AGN green valley galaxies

ABSTRACT We present a study on the stellar populations and stellar ages of a subsample of far-infrared (FIR) active galactic nucleus (AGN) and non-AGN green valley galaxies at ${0.6\, \lt \, z\, \lt \, 1.0}$ using the data from the Cosmological Evolution Survey field. We used long-slit spectroscopy and derived stellar populations and stellar ages using the stellar population synthesis code ‘starlight’ and analysed the available Lick/IDS indices, such as Dn4000 and HδA. We find that both FIR AGN and non-AGN green valley galaxies are dominated by intermediate stellar populations (67 per cent and 53 per cent, respectively). The median stellar ages for AGNs and non-AGNs are ${\log t\, =\, 8.5}$ and ${\, 8.4\, \rm yr}$, respectively. We found that majority of our sources (62 per cent of AGNs and 66 per cent of non-AGNs) could have experienced bursts and continuous star formation (SF). In addition, most of our FIR AGNs (38 per cent) compared to FIR non-AGNs (27 per cent) might have experienced a burst of SF more than 0.1 Gyr ago. We also found that our FIR AGN and non-AGN green valley galaxies have similar quenching time-scales of ∼ 70 Myr. Therefore, the results obtained here are in line with our previous results where we do not find that our sample of FIR AGNs in the green valley shows signs of negative AGN feedback, as has been suggested previously in optical studies.

The Close AGN Reference Survey (CARS)

Context. Active galactic nuclei (AGN) are thought to be responsible for the suppression of star formation in massive ∼1010 M⊙ galaxies. While this process is a key feature in numerical simulations of galaxy formation, it has not been unambiguously confirmed in observational studies yet. Aims. The characterization of the star formation rate (SFR) in AGN host galaxies is challenging as AGN light contaminates most SFR tracers. Furthermore, the various SFR tracers are sensitive to different timescales of star formation from approximately a few to 100 Myr. We aim to obtain and compare SFR estimates from different tracers for AGN host galaxies in the Close AGN Reference Survey (CARS) to provide new observational insights into the recent SFR history of those systems. Methods. We constructed integrated panchromatic spectral energy distributions to measure the far infrared (FIR) luminosity as a tracer for the recent (&lt; 100 Myr) SFR. In addition we used the integral-field unit observation of the CARS targets to employ the Hα luminosity decontaminated by AGN excitation as a proxy for the current (&lt; 5 Myr) SFR. Results. We find that significant differences in specific SFR of the AGN host galaxies as compared with the larger galaxy population disappear once cold gas mass, in addition to stellar mass, is used to predict the SFR for a specific AGN host. Only a tentative trend with the inclination of the host galaxy remains, such that SFR appears slightly lower than expected when the galaxies of unobscured AGN appear more edge-on along our line-of-sight, particular for dust-insensitive FIR-based SFRs. We identify individual galaxies with a significant difference in their SFR which can be related to a recent enhancement or decline in their SFR history that might be related to various processes including interactions, gas consumption, outflows, and AGN feedback. Conclusions. AGN can be present in various stages of galaxy evolution which makes it difficult to relate the SFR solely to the impact of the AGN. Our study shows that stellar mass alone is an insufficient parameter to estimate the expected SFR of an AGN host galaxy compared to the underlying non-AGN galaxy population. We do not find any strong evidence for a global positive or negative AGN feedback in the CARS sample. However, there is tentative evidence that (1) the relative orientation of the AGN engine with respect to the host galaxies might alter the efficiency of AGN feedback and that (2) the recent SFH is an additional tool to identify rapid changes in galaxy growth driven by the AGN or other processes.

AGN Selection Methods Have Profound Impacts on the Distributions of Host-galaxy Properties

Abstract We present a comparative study of X-ray and IR active galactic nuclei (AGNs) at z ≈ 2 to highlight the important AGN selection effects on the distributions of host-galaxy properties. Compared with non-AGN star-forming galaxies (SFGs) on the main sequence, X-ray AGNs have similar median star formation (SF) properties, but their incidence (q AGN) is higher among galaxies with either enhanced or suppressed SF, and among galaxies with a larger stellar-mass surface density, regardless if it is measured within the half-light radius (Σ e ) or central 1 kpc (Σ1kpc). Unlike X-ray AGNs, IR AGNs are less massive and have enhanced SF and similar distributions of colors, Σ e and Σ1kpc, relative to non-AGN SFGs. Given that Σ e and Σ1kpc strongly correlate with M *, we introduce the fractional mass within the central 1 kpc ( M 1 kpc / M ∗ ), which only weakly depends on M *, to quantify galaxy compactness. Both AGN populations have similar M 1 kpc / M ∗ distributions compared to non-AGN SFGs’. While q AGN increases with Σ e and Σ1kpc, it remains constant with M 1 kpc / M ∗ , indicating that the trend of increasing q AGN with Σ is driven by M * more than morphology. While our findings are not in conflict with the scenario of AGN quenching, they do not imply it either, because the incidence of AGNs hosted in transitional galaxies depends crucially on AGN selections. Additionally, despite the relatively large uncertainty of AGN bolometric luminosities, their very weak correlation, if any, with SF activities, regardless of AGN selections, also argues against a direct causal link between the presence of AGNs and the quenching of massive galaxies at z ∼ 2.

Merger Histories and Environments of Dwarf AGN in IllustrisTNG

Abstract The relationship between active galactic nuclei (AGN) activity and environment has been long discussed, but it is unclear if these relations extend into the dwarf galaxy mass regime—in part due to the limits in both observations and simulations. We aim to investigate if the merger histories and environments are significantly different between AGN and non-AGN dwarf galaxies in cosmological simulations, which may be indicative of the importance of these for AGN activity in dwarf galaxies, and whether these results are in line with observations. Using the IllustrisTNG flagship TNG100-1 run, 6771 dwarf galaxies are found with 3863 (∼57%) having some level of AGN activity. In order to quantify environment, two measures are used: (1) the distance to a galaxy’s 10th nearest neighbor at six redshifts and (2) the time since last merger for three different minimum merger mass ratios. A similar analysis is run on TNG50-1 and Illustris-1 to test for the robustness of the findings. Both measures yield significantly different distributions between AGN and non-AGN galaxies; more non-AGN than AGN galaxies have long term residence in dense environments, while recent (≤4 Gyr) minor mergers are more common for intermediate AGN activity. While no statements are made about the micro or macrophysics from these results, it is nevertheless indicative of a non-negligible role of mergers and environments.