Publications
CARS Publications
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The Close AGN Reference Survey (CARS): Locating the [OIIII] wing component in luminous local Type 1 AGN
arXiv linkThe strong asymmetry in the optical [OIII] 5007 emission line is one of the best signatures of active galactic nuclei (AGN) driven warm (~104K) ionized gas outflows on host galaxy scales. While large spectroscopic surveys such as the sloan digital sky survey (SDSS) have characterized the kinematics of [OIII] for large samples of AGN, estimating the associated energetics requires spatially resolving these outflows with, for example, integral field unit (IFU) studies. As part of the Close AGN Reference Survey (CARS), we obtained spatially resolved IFU spectroscopy for a representative sample of 39 luminous type 1 AGN at 0.01<z<0.06 with the multi unit spectroscopic explorer (MUSE) and the visible multi object spectrograph (VIMOS) IFUs at the very large telescope (VLT) to infer the spatial location of the ionized gas outflows. We compared the 2D light distributions of the [OIII] wing to that of the Hbeta broad emission line region, a classical point source (PSF). We then used the PSF to distinguish between the unresolved and resolved [OIII] wing emission. We further determined its location using spectro-astrometry for the point-like sources. The [OIII] wing is spatially unresolved in 23 out of the 36 AGN with >80% of the flux associated with a point-like source. We measured <100pc offsets in the spatial location of the outflow from the AGN nucleus using the spectro-astrometry technique for these sources. For the other 13 AGN, the [OIII] wing emission is resolved and possibly extended on several kiloparsec scales.} We conclude that [OIII] wing emission can be compact or extended in an unbiased luminous AGN sample, where both cases are likely to appear. Electron density in the compact [OIII] wing regions (median ne~1900cm-3) is nearly a magnitude higher than in the extended ones (median ne~500cm-3). The presence of spatially extended and compact [OIII] wing emission is unrelated to the AGN bolometric luminosity and to inclination effects, which means other features such as time delays, or mechanical feedback (radio jets) may shape the ionized gas outflow properties.
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The Close AGN Reference Survey (CARS): No obvious signature of AGN feedback on star formation, but subtle trends
arXiv linkActive Galactic Nuclei (AGN) are thought to be responsible for the suppression of star formation in massive ~1010Msun galaxies. While this process is a key feature in numerical simulations of galaxy formation, it is not yet unambiguously confirmed in observational studies. 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 a few to 100Myr. 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. We construct integrated panchromatic spectral energy distributions (SED) to measure the FIR luminosity as a tracer for the recent (<100Myr) SFR. In addition we use integral-field unit (IFU) observation of the CARS targets to employ the Halpha luminosity decontaminated by AGN excitation as a proxy for the current (<5Myr) SFR. 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 is remaining 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 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. AGN can occur 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 2) the recent SFH is an additional tool to identify rapid changes in galaxy growth driven by the AGN or other processes.
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The Close AGN Reference Survey (CARS): IFU survey data and the BH mass dependence of long-term AGN variability
arXiv linkActive galactic nuclei (AGN) are thought to be intimately connected with their host galaxies through feeding and feedback processes. A strong coupling is predicted and supported by cosmological simulations of galaxy formation, but the details of the physical mechanisms are still observationally unconstrained. Galaxies are complex systems of stars and a multiphase interstellar medium (ISM). A spatially resolved multiwavelength survey is required to map the interaction of AGN with their host galaxies on different spatial scales and different phases of the ISM. The goal of the Close AGN Reference Survey (CARS) is to obtain the necessary spatially resolved multiwavelength observations for an unbiased sample of local unobscured luminous AGN. We present the overall CARS survey design and the associated wide-field optical integral-field unit (IFU) spectroscopy for all 41 CARS targets at z<0.06 randomly selected from the Hamburg/ESO survey of luminous unobscured AGN. This data set provides the backbone of the CARS survey and allows us to characterize host galaxy morphologies, AGN parameters, precise systemic redshifts, and ionized gas distributions including excitation conditions, kinematics, and metallicities in unprecedented detail. We focus our study on the size of the extended narrow-line region (ENLR) which has been traditionally connected to AGN luminosity. Given the large scatter in the ENLR size-luminosity relation, we performed a large parameter search to identify potentially more fundamental relations. Remarkably, we identified the strongest correlation between the maximum projected ENLR size and the black hole mass, consistent with an RENLR,max~MBH0.5 relationship. We interpret the maximum ENLR size as a timescale indicator of a single black hole (BH) radiative-efficient accretion episode for which we inferred <log(tAGN/[yr])> = (0.45+-0.08)log(MBH/[MSun]) + 1.78+0.54-0.67 using forward modeling. The extrapolation of our inferred relation toward higher BH masses is consistent with an independent lifetime estimate from the HeII proximity zones around luminous AGN at z~3. While our proposed link between the BH mass and AGN lifetime might be a secondary correlation itself or impacted by unknown biases, it has a few relevant implications if confirmed. For example, the famous AGN Eigenvector 1 parameter space may be partially explained by the range in AGN lifetimes. Also, the lack of observational evidence for negative AGN feedback on star formation can be explained by such timescale effects. Further observational tests are required to confirm or rule out our BH mass dependent AGN lifetime hypothesis.
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The Close AGN Reference Survey (CARS) - A massive multi-phase outflow impacting the edge-on galaxy HE1353-1917
Paper LinkContext. Galaxy-wide outflows driven by star formation and/or an active galactic nucleus (AGN) are thought to play a crucial rule in the evolution of galaxies and the metal enrichment of the inter-galactic medium. Direct measurements of these processes are still scarce and new observations are needed to reveal the nature of outflows in the majority of the galaxy population.
Aims: We combine extensive, spatially-resolved, multi-wavelength observations, taken as part of the Close AGN Reference Survey (CARS), for the edge-on disc galaxy HE1353-1917 in order to characterise the impact of the AGN on its host galaxy via outflows and radiation.
Methods: Multi-color broad-band photometry was combined with spatially-resolved optical, near-infrared (NIR) and sub-mm and radio observations taken with the Multi-Unit Spectroscopy Explorer (MUSE), the Near-infrared Integral Field Spectrometer (NIFS), the Atacama Large Millimeter Array (ALMA), and the Karl G. Jansky Very Large Array (VLA) to map the physical properties and kinematics of the multi-phase interstellar medium.
Results: We detect a biconical extended narrow-line region ionised by the luminous AGN orientated nearly parallel to the galaxy disc, extending out to at least 25 kpc. The extra-planar gas originates from galactic fountains initiated by star formation processes in the disc, rather than an AGN outflow, as shown by the kinematics and the metallicity of the gas. Nevertheless, a fast, multi-phase, AGN-driven outflow with speeds up to 1000 km/s is detected close to the nucleus at 1 kpc distance. A radio jet, in connection with the AGN radiation field, is likely responsible for driving the outflow as confirmed by the energetics and the spatial alignment of the jet and multi-phase outflow. Evidence for negative AGN feedback suppressing the star formation rate (SFR) is mild and restricted to the central kpc. But while any SFR suppression must have happened recently, the outflow has the potential to greatly impact the future evolution of the galaxy disc due to its geometrical orientation. Conclusions.. Our observations reveal that low-power radio jets can play a major role in driving fast, multi-phase, galaxy-scale outflows even in radio-quiet AGN. Since the outflow energetics for HE1353-1917 are consistent with literature, scaling relation of AGN-driven outflows the contribution of radio jets as the driving mechanisms still needs to be systematically explored. -
The Close AGN Reference Survey (CARS) - Comparative analysis of the structural properties of star-forming and non-star-forming galaxy bars
Paper LinkThe absence of star formation in the bar region that has been reported for some galaxies can theoretically be explained by shear. However, it is not clear how star-forming (SF) bars fit into this picture and how the dynamical state of the bar is related to other properties of the host galaxy. We used integral-field spectroscopy from VLT/MUSE to investigate how star formation within bars is connected to structural properties of the bar and the host galaxy. We derived spatially resolved Hα fluxes from MUSE observations from the CARS survey to estimate star formation rates in the bars of 16 nearby (0.01 < z < 0.06) disc galaxies with stellar masses between 10^10 M☉ and 10611 M☉. We further performed a detailed multicomponent photometric decomposition on images derived from the data cubes. We find that bars clearly divide into SF and non-SF types, of which eight are SF and eight are non-SF. Whatever the responsible quenching mechanism is, it is a quick process compared to the lifetime of the bar. The star formation of the bar appears to be linked to the flatness of the surface brightness profile in the sense that only the flattest bars (nbar≤0.4) are actively SF (SFRb > 0.5 M☉/yr). Both parameters are uncorrelated with Hubble type. We find that star formation is 1.75 times stronger on the leading than on the trailing edge and is radially decreasing. The conditions to host non-SF bars might be connected to the presence of inner rings. Additionally, from testing an AGN feeding scenario, we report that the star formation rate of the bar is uncorrelated with AGN bolometric luminosity. The results of this study may only apply to type-1 AGN hosts and need to be confirmed for the full population of barred galaxies.
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The Close AGN Reference Survey (CARS). Discovery of a global [C II] 158 μm line excess in AGN HE 1353-1917
Paper LinkThe [C II]λ158 μm line is one of the strongest far-infrared (FIR) lines and an important coolant in the interstellar medium of galaxies that is accessible out to high redshifts. The excitation of [C II] is complex and can best be studied in detail at low redshifts. Here we report the discovery of the highest global [C II] excess with respect to the FIR luminosity in the nearby AGN host galaxy HE1353-1917. This galaxy is exceptional among a sample of five targets because the AGN ionization cone and radio jet directly intercept the cold galactic disk. As a consequence, a massive multiphase gas outflow on kiloparsec scales is embedded in an extended narrow-line region. Because HE1353-1917 is distinguished by these special properties from our four bright AGN, we propose that a global [C II] excess in AGN host galaxies could be a direct signature of a multiphase AGN-driven outflow with a high mass-loading factor.
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The Close AGN Reference Survey (CARS) - SOFIA Detects Spatially Resolved [C II] Emission in the Luminous AGN HE 0433-1028
Paper linkIn this paper we presented a joint analysis of the [CII] emission line as observed with FIFI-LS aboard of SOFIA and the Halpha as mapped with the VLT-MUSE integral field spectrograph. Both emission lines are supposed to trace ongoing star formation and are calibrated as star formation calibrators. Despite the low spatial resolution of FIFI-LS we were able to show that we indeed recovered the spatial extend of the star forming regions as probed by Halpha along a very prominent bar in this galaxy. A detailed comparison of the flux distribution taking the PSF of both observations into account confirms are rather good match between the emission lines in terms of their distribution and flux ratio. Hence, we conclude that [CII] and Halpha pre-dominately trace the ongoing star formation and that their is no significant impact of the AGN on reducing or enhancing the [CII] line.
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The Close AGN Reference Survey (CARS) - No evidence of galaxy-scale hot outflows in two nearby AGN
Paper LinkBased on deep Chandra X-ray observations of two nearby AGN (HE0227-0913 and HE0351+0240), M. Powell et al. reported no evidence of galaxy-wide hot gas outflows. After careful analysis of the Chandra PSF to deal with the bright type 1 AGN core, no significant extended emission could be detected. This is a surprising result since current theoretical models predict rather bright X-ray emission from hot gas outflows on kpc-scales powered by the AGN.
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The Close AGN Reference Survey (CARS) - Mrk 1018 halts dimming and experiences strong short-term variability
Paper linkAfter changing optical AGN type from 1.9 to 1 in 1984, the AGN Mrk 1018 recently reverted back to its type 1.9 state. Our ongoing monitoring now reveals that the AGN has halted its dramatic dimming, reaching a minimum around October 2016. The minimum was followed by an outburst rising with ~0.25 U-band mag/month. The rebrightening lasted at least till February 2017 as confirmed by joint Chandra and Hubble observations. Monitoring was resumed in July 2017 after the source emerged from sunblock, at which point the AGN was found only ~0.4 mag brighter than its minimum. The intermittent outburst was accompanied with the appearance of a red wing asymmetry in broad-line shape, indicative of an inhomogeneous broad line region. Mrk 1018's current flickering brightness following its rapid fade suggests either that the source has reignited, remains variable at a low level, or may continue dimming over the next few years. Discriminating between these possibilities demands continual multi-wavelength monitoring.
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The Close AGN Reference Survey (CARS)
Paper linkThe role of active galactic nuclei (AGN) in the evolution of galaxies remains a mystery. The energy released by these accreting supermassive black holes can vastly exceed the entire binding energy of their host galaxies, yet it remains unclear how this energy is dissipated throughout the galaxy, and how that might couple to the galaxy's evolution. The Close AGN Reference Survey (CARS) is a multi-wavelength survey of a representative sample of luminous Type I AGN at redshifts 0.01 < z < 0.06 to help unravel this intimate connection. These AGN are more luminous than very nearby AGN but are still close enough for spatially resolved mapping at sub-kpc scales with various state- of-the art facilities and instruments, such as VLT-MUSE, ALMA, JVLA, Chandra, SOFIA, and many more. In this article we showcase the power of CARS with examples of a multi-phase AGN outflow, diverse views on star formation activity and a unique changing-look AGN. CARS will provide an essential low-redshift reference sample for ongoing and forthcoming AGN surveys at high redshift.
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The Close AGN Reference Survey - What is causing Mrk 1018's return to the shadows after 30 years?
Paper linkWe recently discovered that the active galactic nucleus (AGN) of Mrk 1018 has changed optical type again after 30 years as a type 1 AGN. Here we combine Chandra, NuStar, Swift, Hubble Space Telescope and ground-based observations to explore the cause of this change. The 2-10keV flux declines by a factor of 8 between 2010 and 2016. We show with our X-ray observation that this is not caused by varyinng neutral hydrogen absorption along the line-of-sight up to the Compton-thick level. The optical-UV spectral energy distributions are well fit with a standard geometrically thin optically thick accretion disc model that seems to obey the expected L~T^4 relation. It confirms that a decline in accretion disc luminosity is the primary origin for the type change. We detect a new narrow-line absorber in Lya blue-shifted by ~700km/s with respect to the systemic velocity of the galaxy. This new Lya absorber could be evidence for the onset of an outflow or a companion black hole with associated gas that could be related to the accretion rate change. However, the low column density of the absorber means that it is not the direct cause for Mrk 1018's changing-look nature.
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The Close AGN Reference Survey - Mrk 1018's return to the shadows after 30 years as a Seyfert 1
Paper linkWe report the discovery that the known `changing look' AGN Mrk 1018 has changed spectral type for a second time. New VLT-MUSE data taken in 2015 as part of the Close AGN Reference Survey (CARS) shows that the AGN returned to its original Seyfert 1.9 classification. The CARS sample is selected to contain only bright type 1 AGN, but Mrk 1018's broad emission lines and continuum, typical of type 1 AGN, have almost entirely disappeared. We use spectral fitting of the MUSE spectrum and previously available spectra to determine the drop in broad line flux and the Balmer decrement. We find that the broad line flux has decreased by a factor of 4.75+-0.5 in Ha since an SDSS spectrum was taken in 2000. The Balmer decrement has not changed significantly implying no enhanced reddening with time, but the remaining broad lines are more asymmetric than those present in the type 1 phase. We posit that the change is due to an intrinsic drop in flux from the accretion disk rather than variable extinction or a tidal disruption event.
Parent Sample Publications
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A low-luminosity type-1 QSO sample IV - Molecular gas contents and conditions of star formation in three nearby Seyfert galaxies
Paper linkWe present a pilot study of ~3'' resolution observations of low CO transitions with the Submillimeter Array in three nearby Seyfert galaxies, which are part of the low-luminosity quasi-stellar object (LLQSOs) sample consisting of 99 nearby (z = 0.06) type-1 active galactic nuclei (AGN) taken from the Hamburg/ESO quasi-stellar object (QSO) survey. Two sources were observed in 12CO(2-1) and 13CO(2-1) and the third in 12CO(3-2) and HCO+(4-3). None of the sources is detected in continuum emission. More than 80% of the 12CO detected molecular gas is concentrated within a diameter (FWHM) < 1.8 kpc. 13CO is tentatively detected, while HCO+ emission could not be detected. All three objects show indications of a kinematically decoupled central unresolved molecular gas component. The molecular gas masses of the three galaxies are in the range Mmol = (0.7-8.7) × 109M⊙. We give lower limits for the dynamical masses of Mdyn> 1.5 × 109M⊙ and for the dust masses of Mdust> 1.6 × 106M⊙. The R21 = 12CO/13CO(2-1) line luminosity ratios show Galactic values of R21 ~ 5-7 in the outskirts and R21 ≳ 20 in the central region, similar to starbursts and (ultra)luminous infrared galaxies ((U)LIRGs; i.e. LIRGs and ULIRGs), implying higher temperatures and stronger turbulence. All three sources show indications of 12CO(2-1)/12CO(1-0) ratios of ~0.5, suggesting a cold or diffuse gas phase. Strikingly, the 12CO(3-2)/(1-0) ratio of ~1 also indicates a higher excited phase. Since these galaxies have high infrared luminosities of LIR ≥ 1011L⊙ and seem to contain a circumnuclear starburst with minimum surface densities of gas and star formation rate (SFR) around Σmol = 50-550 M⊙pc-2 and ΣSFR = 1.1-3.1 M⊙ kpc-2 yr-1, we conclude that the interstellar medium in the centers of these LIRG Seyferts is strongly affected by violent star formation and better described by the ULIRG mass conversion factor.
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A low-luminosity type-1 QSO sample. V - Overluminous host spheroids and their excitation mechanisms
Paper linkWe present near-infrared (NIR) H + K-band long-slit spectra of eleven galaxies that were obtained with SOFI at the NTT (ESO). The galaxies are chosen from the low-luminosity type-1 quasi-stellar object (LLQSO) sample, which comprises the 99 closest (z ≤ 0.06) QSOs from the Hamburg/ESO survey for bright UV-excess QSOs. These objects are ideal targets to study the gap between local Seyfert galaxies and high-redshift quasars because they show much stronger AGN activity than local objects, but are still close enough for a detailed structural analysis. We fit hydrogen recombination, molecular hydrogen, and [Fe ii] lines after carefully subtracting the continuum emission. From the broad Paα components, we estimated black hole masses and enlarged the sample of LLQSOs that deviate from the MBH - Lbulge relations of inactive galaxies from 12 to 16 objects. All objects show emission from hot dust (T ~ 1200 K) as well as stellar contribution. However, the respective fractions vary strongly among the objects. More than half of the objects show H2 emission lines, which indicate a large reservoir of molecular gas that is needed to feed the AGN and star formation. In the NIR diagnostic diagram all objects lie in the location of AGN-dominated objects. However, most of the objects show indications of star formation activity, suggesting that their offset location with respect to MBH-Lbulge relations of inactive galaxies may be a consequence of overluminous bulges.
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A low-luminosity type-1 QSO sample. I. Overluminous host spheroidals or undermassive black holes
ADS LinkDeep NIR J/H/K band imaging for a sample of 20 QSO host galaxies is presented in this paper from the parent sample of CARS. A QSO-host image decomposition was done to measure the mass of the bulge component of the host. This is compared to the BH mass inferred from longslit spectroscopy to probe the BH mass-bulge mass relation. The authors found that most of the bulge are below the local BH mass-bulge mass relation established for inactive galaxies.
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A low-luminosity type-1 QSO sample: II. Tracing circumnuclear star formation in HE1029-1831 with SINFONI
ADS LinkThe paper presents high spatial resolution NIR H+K band IFU observations of the central regions of HE1029-1401 which is also part of the CARS sample and observed with MUSE.
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HI in nearby low-luminosity QSO host galaxies
ADS LinkThis paper present HI observations for the majority of CARS galaxies with the 100m Effelsberg single-dish radio telescope. 12 QSO host galaxies have been detected in HI and upper limits are presented for the remaining 15 targets.
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Molecular gas in nearby low-luminosity QSO host galaxies
ADS LinkThis paper reports the CO(1-0) and CO(2-1) for a sample of QSO selected from the Hamburg ESO survey at 0.01<z<0.06 to probe their molecular gas content. It represent the basis for the CARS sample.
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A low-luminosity type-1 QSO sample. III - Optical spectroscopic properties and activity classification
Paper linkContext. We report on the optical spectroscopic analysis of a sample of 99 low-luminosity quasi-stellar objects (LLQSOs) at z ≤ 0.06 base the Hamburg/ESO QSO Survey (HES). To better relate the low-redshift active galactic nucleus (AGN) to the QSO population it is important to study samples of the latter type at a level of detail similar to that of the low-redshift AGN. Powerful QSOs, however, are absent at low redshifts due to evolutionary effects and their small space density. Our understanding of the (distant) QSO population is, therefore, significantly limited by angular resolution and sensitivity. The LLQSOs presented here offer the possibility of studying the faint end of this population at smaller cosmological distances and, therefore, in greater detail.Aims: In comparing two spectroscopic methods, we aim to establish a reliable activity classification scheme of the LLQSOs sample. Our goal is to enrich our systematic multiwavelength analysis of the AGN/starburst relation in these systems and give a complementary information on this particular sample of LLQSOs from the Hamburg ESO survey.Methods: Here, we present results of the analysis of visible wavelength spectroscopy provided by the HES and the 6 Degree Field Galaxy Survey (6dFGS). These surveys use different spectroscopic techniques, long-slit and circular fiber, respectively. These allow us to assess the influence of different apertures on the activity of the LLQSOs using classical optical diagnostic diagrams. We perform a Gaussian fitting of strong optical emission lines and decompose narrow and broad Balmer components.Results: A small number of our LLQSO present no broad component, which is likely to be present but buried in the noise. Two sources show double broad components, whereas six comply with the classic NLS1 requiremnts. As expected in NLR of broad line AGNs, the [Sii]-based electron density values range between 100 and 1000 Ne/cm3. Using the optical characteristics of Populations A and B, we find that 50% of our sources with Hβ broad emission are consistent with the radio-quiet sources definition. The remaining sources could be interpreted as low-luminosity radio-loud quasar. The BPT-based classification renders an AGN/Seyfert activity between 50 to 60%. For the remaining sources, the possible starburst contribution might control the LINER and Hii classification. Finally, we discuss the aperture effect as responsible for the differences found between data sets, although variability in the BLR could play a significant role as well.