CARS Publications

  • No evidence of galaxy-scale hot outflows in two nearby AGN

    M. C. Powell, B. Husemann, G. R. Tremblay et al. , 2018, arXiv:1807.00839, ,

    Based 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.

  • The Close AGN Reference Survey (CARS) - Mrk 1018 halts dimming and experiences strong short-term variability

    Krumpe, M., Husemann, B., Tremblay, G. R., Urrutia, T., Powell, M., Davis, T. A., Scharwächter, J., Dexter, J., Busch, G., Combes, F., Croom, S. M., Eckart, A., McElroy, R. E., Perez-Torres, M., Leung, G., 2017, A&A, ,

    After 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.

  • The Close AGN Reference Survey (CARS)

    Husemann, B., Tremblay, G., Davis, T., Busch, G., McElroy, R., Neumann, J., Urrutia, T., Krumpe, M., Scharwächter, J., Powell, M., Perez-Torres, M., 2017, The ESO Messenger, 169, 42

    The 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.

  • The Close AGN Reference Survey - What is causing Mrk 1018's return to the shadows after 30 years?

    B. Husemann, T. Urrutia, G. R. Tremblay, M. Krumpe, J. Dexter, G. Busch, F. Combes, S. M. Croom, T. A. Davis, A. Eckart, R. E. McElroy, M. Perez-Torres, M. Powell, J. Scharwaechter, 2016, A&A, 593, L9

    We 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.

  • The Close AGN Reference Survey - Mrk 1018's return to the shadows after 30 years as a Seyfert 1

    R. E. McElroy, B. Husemann, S. M. Croom, T. A. Davis, V. N. Bennert, G. Busch, F. Combes, A. Eckart, M. Perez-Torres, M. Powell, J. Scharwaechter, G. R. Tremblay, T. Urrutia, 2016, A&A, 593, L8

    We 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

  • A low-luminosity type-1 QSO sample IV - Molecular gas contents and conditions of star formation in three nearby Seyfert galaxies

    Moser, L., Krips, M., Busch, G., Scharwächter, J., König, S., Eckart, A., Smajić, S., García-Marin, M., Valencia-S., M., Fischer, S., Dierkes, J., 2016, A&A, 587, A137

    We 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.

  • A low-luminosity type-1 QSO sample. V - Overluminous host spheroids and their excitation mechanisms

    Busch, G., Fazeli, N., Eckart, A., Valencia-S., M., Smajić, S., Moser, L., Scharwächter, J., Dierkes, J., Fischer, S., 2016, A&A, 576, A138

    We 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.

  • A low-luminosity type-1 QSO sample. I. Overluminous host spheroidals or undermassive black holes

    G. Busch, J. Zuther, M. Valencia-S., L. Moser, S. Fischer, A. Eckart, J. Scharwächter, D. A. Gadotti, L. Wisotzki, 2014, A&A, 561, A140

    Deep 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.

  • A low-luminosity type-1 QSO sample: II. Tracing circumnuclear star formation in HE1029-1831 with SINFONI

    G. Busch, S. Smajic, J. Scharwächter, A. Eckart, M. Valencia-M., L. Moser, B. Husemann, M. Kirps, J. Zuther, 2015, A&A, 575, A128

    The 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.

  • HI in nearby low-luminosity QSO host galaxies

    S. König, A. Eckart, M. Garcia-Marin, W. K. Huchtmeier, 2009, A&A, 507, 757

    This 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.

  • Molecular gas in nearby low-luminosity QSO host galaxies

    T. Bertram, A. Eckart, S. Fischer, J. Zuther, C. Straubmeier, L. Wisotzki, M. Krips, 2007, A&A, 470, 571

    This 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.

  • A low-luminosity type-1 QSO sample. III - Optical spectroscopic properties and activity classification

    Tremou, E., Garcia-Marin, M., Zuther, J., Eckart, A., Valencia-Schneider, M., Vitale, M., Shan, C., 2015, A&A, 580, A114

    Context. 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.