Active Galaxies Newsletter
An electronic publication dedicated to the observations and theory of active galaxiesEdited by Megan Argo
The Active Galaxies Newsletter is an electronic publication dedicated to the observation and theory of active galaxies. It is intended to be used to notify others in the field of recently accepted papers, conference proceedings and dissertations, and also contains announcements of jobs and conferences. It is produced monthly and sent to over 600 subscribers.
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New job: Postdoctoral position, IAC Spain, deadline November 30th. See details.| Active | An electronic publication dedicated to |
| Galaxies | the observation and theory of |
| Newsletter | active galaxies |
| No. 217 -- November 2015 | Editor: Megan Argo (agnews@manchester.ac.uk) |
Jobs Adverts - Meetings Adverts - Special Announcements
Welcome to all the new subscribers, and thanks to everyone who contributed to this issue of the Active Galaxies Newsletter. This newsletter is intended to disseminate paper abstracts, meeting announcements, job adverts and other information which may be of interest to the active galaxies community. It is produced monthly and, whilst the deadline for contributions is the last day of the month, contributions may be submitted at any time.
The Latex macros for submitting abstracts and dissertation abstracts are appended to each issue of the newsletter and are also available on the web page. Please note that the editor may reject submissions which do not use the template. As always, any suggestions or feedback regarding the newsletter are welcome.
Thanks for your continued subscription.
The peculiar optical-UV X-ray spectra of the X-ray weak quasar PG0043+039
W. Kollatschny1, N. Schartel2, M. Zetzl1, M. Santos-Lleó2, P. M. Rodríguez-Pascual2, L. Ballo3, A. Talavera2
1. Institut für Astrophysik, Universität Göttingen, Friedrich-Hund Platz 1, D-37077 Göttingen, Germany
2. XMM-Newton Science Operations Centre, ESA, Villafranca del Castillo, Apartado 78, 28691 Villanueva de la Cañada, Spain
3. Osservatorio Astronomico di Brera (INAF), via Brera 28, I-20121 Milano, Italy
The object PG0043+039 has been identified as a broad absorption line (BAL)
quasar based on its UV spectra. However, this optical luminous quasar has
not been detected before in deep X-ray observations, making it the most
extreme X-ray weak quasar known today. This study aims to detect
PG0043+039 in a deep X-ray exposure. The question is what causes the extreme
X-ray weakness of PG0043+039? Does PG0043+039 show other spectral or
continuum peculiarities? We took simultaneous deep X-ray spectra with
XMM-Newton, far-ultraviolet (FUV) spectra with the Hubble Space Telescope
(HST), and optical spectra of PG0043+039 with the Hobby-Eberly Telescope
(HET) and Southern African Large Telescope (SALT) in July, 2013. We have
detected PG0043+039 in our X-ray exposure taken in 2013. We presented our
first results in a separate paper (Kollatschny et al. 2015). PG0043+039
shows an extreme αox gradient (αox = -2.37). Furthermore,
we were able to verify an X-ray flux of this source in a reanalysis of the
X-ray data taken in 2005. At that time, it was fainter by a factor of
3.8±0.9 with αox = -2.55. The X-ray spectrum is compatible
with a normal quasar power-law spectrum (Γ = 1.70+0.57
A&A in press
E-mail contact: wkollat@astro.physik.uni-goettingen.de
The hard X-ray emission of the luminous infrared galaxy NGC 6240 as observed by NuSTAR
S. Puccetti1,2, A. Comastri3, F. E. Bauer4,5,6,7, W. N. Brandt8,9,10, F. Fiore2, F. A. Harrison11, B. Luo8,9, D. Stern12, C. M. Urry13, D. M. Alexander14, A. Annuar14, P. Arévalo4,15, M. Balokovic11, S. E. Boggs16, M. Brightman11, F. E. Christensen17, W. W. Craig16,18, P. Gandhi14,19, C. J. Hailey20, M. J. Koss21, S. La Massa13, A. Marinucci22, C. Ricci4,5, D. J. Walton12,11, L. Zappacosta2, W. Zhang23
1. ASDC-ASI, Via del Politecnico, 00133 Roma, Italy
We present a broad-band (∼0.3-70 keV) spectral and
temporal analysis of NuSTAR observations of the luminous
infrared galaxy NGC 6240, combined with archival
Chandra, XMM-Newton and BeppoSAX data. NGC
6240 is a galaxy in a relatively early merger state with two
distinct nuclei separated by ∼1."5. Previous Chandra
observations have resolved the two nuclei, showing that they are
both active and obscured by Compton-thick material. Although they
cannot be resolved by NuSTAR, thanks to the unprecedented
quality of the NuSTAR data at energies >10 keV, we clearly
detect, for the first time, both the primary and the reflection
continuum components. The NuSTAR hard X-ray spectrum is
dominated by the primary continuum piercing through an absorbing
column density which is mildly optically thick to Compton scattering
(τ ≃ 1.2, NH ∼ 1.5 × 1024
cm-2). We detect moderate hard X-ray (> 10 keV) flux
variability up to 20% on short (15-20 ksec) timescales. The
amplitude of the variability is maximum at ∼30 keV and is
likely to originate from the primary continuum of the southern
nucleus. Nevertheless, the mean hard X-ray flux on longer
timescales (years) is relatively constant. Moreover, the two nuclei
remain Compton-thick, although we find evidence of variability of
the material along the line of sight with column densities NH
≤2×1023 cm-2 over long
(∼3-15 years) timescales. The observed X-ray emission in the
NuSTAR energy range is fully consistent with the sum of the
best-fit models of the spatially resolved Chandra spectra of
the two nuclei.
Accepted for publication in A&A
E-mail contact: puccetti@asdc.asi.it
A NuSTAR Survey of Nearby Ultraluminous Infrared Galaxies
Stacy H. Teng1, 2, 3, Jane R. Rigby1,
Daniel Stern4, Andrew Ptak1, D. M. Alexander5, Franz E. Bauer6,7,8, Stephen E. Boggs9, W. Niel Brandt10,11, Finn E. Christensen12, Andrea Comastri13, William W. Craig9,14, Duncan Farrah15, Poshak Gandhi16, Charles J. Hailey17, Fiona A. Harrison18, Ryan C. Hickox19, Michael Koss20, Bin Luo10,11, Ezequiel Treister21,
and William W. Zhang1
1. Astrophysics Science Division, NASA Goddard Space Flight Center, Greenbelt, MD 20771, USA
We present a NuSTAR, Chandra, and XMM-Newton survey of nine of the
nearest ultraluminous infrared galaxies (ULIRGs). The unprecedented sensitivity of
NuSTAR at energies above 10 keV enables spectral modeling with far better precision
than was previously possible. Six of the nine sources observed were
detected sufficiently well by NuSTAR to model in detail their broadband X-ray spectra,
and recover the levels of obscuration and intrinsic X-ray luminosities. Only one source
(IRAS 13120-5453) has a spectrum consistent with a Compton-thick AGN, but we cannot rule out that a second source (Arp 220) harbors an extremely highly obscured
AGN as well. Variability in column density (reduction by a factor of a few compared to older observations) is seen in IRAS 05189-2524 and Mrk 273, altering the classification of these border-line sources from Compton-thick to Compton-thin.
The ULIRGs in our sample have surprisingly low observed fluxes in high energy (>10 keV) X-rays, especially compared to their bolometric luminosities.
They have lower ratios of unabsorbed 2-10 keV to bolometric luminosity, and
unabsorbed 2-10 keV to mid-IR [O IV] line luminosity than do Seyfert 1 galaxies.
We identify IRAS 08572+3915 as another candidate
intrinsically X-ray weak source, similar to Mrk 231.
We speculate that the X-ray weakness of IRAS 08572+3915 is related
to its powerful outflow observed at other wavelengths.
Accepted by The Astrophysical Journal
E-mail contact: jane.rigby@nasa.gov
The sign of active galactic nucleus quenching in a merger remnant with radio jets
K. Ichikawa1, J. Ueda1,2, M. Shidatsu3, T. Kawamuro4, K. Matsuoka4
1. National Astronomical Observatory of Japan, 2-21-1 Osawa, Mitaka, Tokyo 181-8588, Japan
We investigate optical, infrared, and radio active galactic nucleus (AGN) signs in the merger remnant Arp 187, which hosts luminous jets launched in the order of 105 yr
ago but whose present-day AGN activity is still unknown.
We find AGN signs from the optical BPT diagram and infrared [OIV]25.89 μm line, originating from the narrow line regions of AGN.
On the other hand, Spitzer/IRS show the host galaxy dominated spectra,
suggesting that the thermal emission from the AGN torus is considerably small or already diminished.
Combining the black hole mass, the upper limit of radio luminosity of the core, and the fundamental plane of the black hole enable us to estimate X-ray luminosity, which gives <1040 erg s-1.
Those results suggest that the AGN activity of Arp 187 has already been quenched, but the narrow line region is still alive owing to the time delay of emission from the
past AGN activity.
Accepted by PASJ
E-mail contact: kohei.ichikawa@nao.ac.jp
-0.45
with moderate intrinsic absorption (NH = 5.5+6.9
-3.9 × 1021 cm-2) and reflection.
The UV/optical flux of PG0043+039 has increased by a factor of 1.8 compared
to spectra taken in the years 1990-1991. The FUV spectrum is highly peculiar
and dominated by broad bumps besides Lyα. There is no detectable Lyman
edge associated with the BAL absorbing gas seen in the CIV line. PG0043+039
shows a maximum in the overall continuum flux at around λ ≈
2500 Å in contrast to most other AGN where the maximum is found at
shorter wavelengths. All the above is compatible with an intrinsically X-ray
weak quasar, rather than an absorbed X-ray emission. Besides strong FeII
multiplets and broad Balmer and HeI lines in the optical band we only detect a
narrow [OII]λ3727 emission line and a BAL system in the
CaH λ3968, CaK λ3934 lines (blueshifted by 4900
kms-1) and in the HeI λ3889 line (blueshifted by 5600
kms-1).
Preprint available at http://arxiv.org/abs/1510.02681
2. INAF-Osservatorio Astronomico di Roma, via Frascati 33, 00078 Monte Porzio Catone (RM), Italy
3. INAF-Osservatorio Astronomico di Bologna, via Ranzani 1, 40127 Bologna, Italy
4. EMBIGGEN Anillo, Concepción, Chile
5. Instituto de Astrofísica, Facultad de Física, Pontificia Universidad Católica de Chile, 306, Santiago 22, Chile
6. Millenium Institute of Astrophysics, Santiago, Chile
7. Space Science Institute, 4750 Walnut Street, Suite 205, Boulder, Colorado 80301
8. Department of Astronomy & Astrophysics, 525 Davey Laboratory, Pennsylvania State University, University Park, PA 16802, USA
9. Institute for Gravitation and the Cosmos, Pennsylvania State University, University Park, PA 16802, USA
10. Department of Physics, 104 Davey Laboratory, Pennsylvania State University, University Park, PA 16802, USA
11. Cahill Center for Astrophysics, California Institute of Technology, 1216 East California Boulevard, Pasadena, CA 91125, USA
12. Jet Propulsion Laboratory, California Institute of Technology, 4800 Oak Grove Drive, Mail Stop 169-221, Pasadena, CA 91109, USA
13. Yale Center for Astronomy and Astrophysics, Physics Department, Yale University, PO Box 208120, New Haven, CT 06520-8120, USA
14. Department of Physics, Durham University, Durham DH1 3LE, UK
15. Instituto de Física y Astronomía, Facultad de Ciencias, Universidad de Valparaíso, Gran Bretana N 1111, Playa Ancha, Valparaíso, Chile
16. Space Sciences Laboratory, University of California, Berkeley CA 94720, USA
17. DTU Space, National Space Institute, Technical University of Denmark, Elektrovej 327, DK-2800 Lyngby, Denmark
18. Lawrence Livermore National Laboratory, Livermore, CA 94550, USA
19. School of Physics & Astronomy, University of Southampton, Highfield, Southampton SO17 1BJ UK
20. Columbia Astrophysics Laboratory, Columbia University, New York, NY 10027, USA
21. Institute for Astronomy, Department of Physics, ETH Zurich, Wolfgang-Pauli-Strasse 27, CH-8093 Zurich, Switzerland
22. Dipartimento di Matematica e Fisica, Universitá degli Studi Roma Tre, via della Vasca Navale 84, I-00146 Roma, Italy
23. NASA Goddard Space Flight Center, Greenbelt, MD 20771, USA
Preprint available at http://arxiv.org/abs/1510.04477
2. Department of Astronomy, University of Maryland, College Park, MD 20742, USA
3. Current address: Science and Technology Division, Institute for Defense Analyses, 4850 Mark Center Drive, Alexandria, VA 22311, USA
4. Jet Propulsion Laboratory, California Institute of Technology, Pasadena, CA 91109, USA
5. Department of Physics, Durham University, Durham, DH1 3LE, UK
6. Instituto de Astrofísica, Facultad de Física, Pontificia Universidad Católica de Chile, 306, Santiago 22, Chile
7. Millennium Institute of Astrophysics, Santiago, Chile
8. Space Science Institute, 4750 Walnut Street, Suite 205, Boulder, Colorado 80301
9. Space Sciences Laboratory, University of California, Berkeley, CA 94720, USA
10. Department of Astronomy and Astrophysics, The Pennsylvania State University, 525 Davey Lab, University Park, PA 16802, USA
11. Institute for Gravitation and the Cosmos, The Pennsylvania State University, University Park, PA 16802, USA
12. DTU Space-National Space Institute, Technical University of Denmark, Elektrovej 327, DK-2800 Lyngby, Denmark
13. INAF-Osservatorio Astronomico di Bologna, via Ranzani 1, I-40127 Bologna, Italy
14. Lawrence Livermore National Laboratory, Livermore, CA 94550, USA
15. Department of Physics, Virginia Tech, Blacksburg, VA 24061, USA
16. School of Physics & Astronomy, University of Southampton, Highfield, Southampton, SO17 1BJ, UK
17. Columbia Astrophysics Laboratory, Columbia University, New York, NY 10027, USA
18. Cahill Center for Astronomy and Astrophysics, California Institute of Technology, Pasadena, CA 91125, USA
19. Department of Physics and Astronomy, Dartmouth College, 6127 Wilder Laboratory, Hanover, NH 03755, USA
20. Institute for Astronomy, Department of Physics, ETH Zurich, Wolfgang-Pauli-Strasse 27, CH-8093 Zurich, Switzerland
21. Departamento de Astronomía Universidad de Concepción, Casilla 160-C, Concepción, Chile
Preprint available at http://arxiv.org/abs/1510.04453
2. Harvard-Smithsonian Center for Astrophysics, 60 Garden Street, Cambridge, MA 02138, USA
3. MAXI team, RIKEN, 2-1 Hirosawa, Wako, Saitama 351-0198, Japan
4. Department of Astronomy, Kyoto University, Kitashirakawa-Oiwake-cho, Sakyo-ku, Kyoto 606-8502, Japan
Preprint available at http://arxiv.org/abs/1510.06037
Unveiling the X-ray/UV properties of disk winds in active galactic nuclei using broad and mini-broad absorption line quasars
Margherita Giustini1
1. SRON - Netherlands Institute for Space Research, Sorbonnelaan 2, 3584 CA Utrecht, Netherlands
We present the results of the uniform analysis of 46 XMM-Newton observations of six BAL and seven mini-BAL QSOs belonging to the Palomar-Green Quasar catalogue. Moderate-quality X-ray spectroscopy was performed with the EPIC-pn, and allowed to characterise the general source spectral shape to be complex, significantly deviating from a power law emission. A simple power law analysis in different energy bands strongly suggests absorption to be more significant than reflection in shaping the spectra. If allowing for the absorbing gas to be either partially covering the continuum emission source or to be ionised, large column densities of the order of 1022-24 cm-2 are inferred. When the statistics was high enough, virtually every source was found to vary in spectral shape on various time scales, from years to hours. All in all these observational results are compatible with radiation driven accretion disk winds shaping the spectra of these intriguing cosmic sources.
Accepted by Astronomische Nachrichten.
E-mail contact: m.giustini@sron.nl
Preprint available at http://arxiv.org/abs/1510.04545
Dichroic polarization at mid-infrared wavelengths: a Bayesian approach
E. Lopez-Rodriguez1,2
1. Department of Physics & Astronomy, University of Texas at San Antonio, One UTSA Circle, San Antonio, TX 78249, USA
2. Department of Astronomy, University of Texas at Austin, 1 University Station C1400, Austin, TX 78712, USA
A fast and general Bayesian inference framework to infer the physical properties of dichroic polarization using mid-infrared imaging- and spectro-polarimetric observations is presented. The Bayesian approach is based on a hierarchical regression and No-U-Turn Sampler method. This approach simultaneously infers the normalized Stokes parameters to find the full family of solutions that best describe the observations. In comparison with previous methods, the developed Bayesian approach allows the user to introduce a customized absorptive polarization component based on the dust composition, and the appropriate extinction curve of the object. This approach allows the user to obtain more precise estimations of the magnetic field strength and geometry for tomographic studies, and information about the dominant polarization components of the object. Based on this model, imaging-polarimetric observations using two or three filters located in the central 9.5-10.5 μm, and the edges 8-9 μm and/or 11-13 μm, of the wavelength range are recommended to optimally disentangle the polarization mechanisms.
Accepted by MNRAS
E-mail contact: enrique.lopezrodriguez@utsa.edu
Preprint available at http://arxiv.org/abs/1510.06741
The Search for Active Black Holes in Nearby Low-Mass Galaxies using Optical and mid-IR data
Lia Sartori1, Kevin Schawinski1, Ezequiel Treister2, Benny Trakhtenbrot1, Michael Koss1, Maryam Shirazi1, Kyuseok Oh1,3
1. Institute for Astronomy, Department of Physics, ETH Zurich, Wolfgang-Pauli-Strasse 27, CH-8093 Zurich, Switzerland
2. Universidad de Concepcion, Departamento de Astronomia, Casilla 160-C, Concepcion, Chile
3. Department of Astronomy, Yonsei University, Seoul 120-749, Republic of Korea
We investigated AGN activity in low-mass galaxies, an important regime that can shed light on to black hole (BH) formation and evolution, and their interaction with their host galaxies. We identified 336 AGN candidates from a parent sample of ∼48,000 nearby low-mass galaxies (M☆ ≤ 109.5 M⊙, z < 0.1) in the Sloan Digital Sky Survey. We selected the AGN using the classical BPT diagram, a similar optical emission line diagnostic based on the HeII λ4686 line, and mid-IR colour cuts. Different criteria select host galaxies with different physical properties such as stellar mass and optical colour and only 3 out of 336 sources fulfil all three criteria. This could be in part due to selection biases. The resulting AGN fraction of ∼0.7% is at least one order of magnitude below the one estimated for more massive galaxies. At optical wavelengths, the HeII-based AGN selection appears to be more sensitive to AGN hosted in star-forming galaxies than the classical BPT diagram, at least in the low-mass regime. The archival X-ray and radio data available for some of the optically selected AGN candidates seem to confirm their AGN nature, but follow-up observations are needed to confirm the AGN nature of the rest of the sample, especially in the case of mid-IR selection. Our sample will be important for future follow-up studies aiming to understand the relation between BHs and host galaxies in the low-mass regime.
Accepted by MNRAS
E-mail contact: lia.sartori@phys.ethz.ch
Preprint available at http://arxiv.org/abs/1509.08483
Rest-frame UV single-epoch black hole mass estimates of low-luminosity AGN at intermediate redshifts
Marios Karouzos1, Jong-Hak Woo1, Kenta Matsuoka2, Christopher S. Kochanek3, Christopher A. Onken4, Juna A. Kollmeier5, Dawoo Park1, Tohru Nagao6, and Sang Chul Kim7,8
1. Astronomy Program, Department of Physics & Astronomy, Seoul National University, Gwanak-gu, Seoul, Republic of Korea
2. Department of Astronomy, Kyoto University, Oiwake-cho, Sakyo-ku, Kyoto 606-8502, Japan
3. Department of Astronomy and the Center for Cosmology and Astroparticle Physics, Ohio State University, Columbus, Ohio, 43210, USA
4. Research School of Astronomy and Astrophysics, Australian National University, Canberra, ACT 2611, Australia
5. Carnegie Observatories, 813 Santa Barbara Street, Pasadena, California, 91101, USA
6. Research Center for Space and Cosmic Evolution, Ehime University, Bunkyo-cho 2-5, Matsuyama, Ehime 790-8577, Japan
7. Korea Astronomy and Space Science Institute (KASI), Daejeon 305-348, Republic Korea
8. Korea University of Science and Technology (UST), Daejeon 305-350, Republic Korea
The ability to accurately derive black hole (BH) masses at progressively higher redshifts and over a wide range of continuum luminosities has become indispensable in the era of large-area extragalactic spectroscopic surveys. In this paper we present an extension of existing comparisons between rest-frame UV and optical virial BH mass estimators to intermediate redshifts and luminosities comparable to the local Hβ reverberation mapped active galactic nuclei (AGN). We focus on the MgII, CIV, and CIII] broad emission lines and compare them to both Hα and Hβ. We use newly acquired near-infrared spectra from the FMOS instrument on the Subaru telescope for 89 broad-lined AGN at redshifts between 0.3 and 3.5, complemented by data from the AGES survey. We employ two different prescriptions for measuring the emission line widths and compare the results. We confirm that MgII shows a tight correlation with Hα and Hβ, with a scatter of ∼0.25 dex. The CIV and CIII] estimators, while showing larger scatter, are viable virial mass estimators after accounting for a trend with the UV-to-optical luminosity ratio. We find an intrinsic scatter of ∼0.37 dex between Balmer and carbon virial estimators by combining our dataset with previous high redshift measurements. This updated comparison spans a total of 3 decades in BH mass. We calculate a virial factor for CIV/CIII] log fCIV/CIII] = 0.87 with an estimated systematic uncertainty of ∼0.4 dex and find excellent agreement between the local reverberation mapped AGN sample and our high-z sample.
Accepted by Astrophysical Journal
E-mail contact: mkarouzos@astro.snu.ac.kr
Preprint available at http://arxiv.org/abs/1510.07626
PAGaN I: Multi-Frequency Polarimetry of AGN Jets with KVN
Jae-Young Kim1,2, Sascha Trippe1, Bong Won Sohn3, Junghwan Oh1, Jong-Ho Park1, Sang-Sung Lee3, Taeseok Lee1, Daewon Kim1
1. Department of Physics and Astronomy, Seoul National University, Seoul 08826, South Korea
2. Max-Planck Institut für Radioastronomie, D-53121 Bonn, Germany
3. Korea Astronomy and Space Science Institute, Daejeon 34055, South Korea
Active Galactic Nuclei (AGN) with bright radio jets offer the opportunity to study the structure of and physical conditions in relativistic outflows. For such studies, multi-frequency polarimetric very long baseline interferometric (VLBI) observations are important as they directly probe particle densities, magnetic field geometries, and several other parameters. We present results from first-epoch data obtained by the Korean VLBI Network (KVN) within the frame of the Plasma Physics of Active Galactic Nuclei (PAGaN) project. We observed seven radio-bright nearby AGN at frequencies of 22, 43, 86, and 129 GHz in dual polarization mode. Our observations constrain apparent brightness temperatures of jet components and radio cores in our sample to >108.01 K and >109.86 K, respectively. Degrees of linear polarization mL are relatively low overall: less than 10%. This indicates suppression of polarization by strong turbulence in the jets. We found an exceptionally high degree of polarization in a jet component of BL Lac at 43 GHz, with mL ∼ 40%. Assuming a transverse shock front propagating downstream along the jet, the shock front being almost parallel to the line of sight can explain the high degree of polarization.
Accepted by J. Korean Astron. Soc.
E-mail contact: trippe@astro.snu.ac.kr
arXiv preprint: http://arxiv.org/abs/1510.08150
PAGaN II: The Evolution of AGN jets on Sub-Parsec Scales
Junghwan Oh1, Sascha Trippe1, Sincheol Kang2,3, Jae-Young Kim1,4, Jong-Ho Park1, Taeseok Lee1, Daewon Kim1, Motoki Kino3, Sang-Sung Lee3, Bong Won Sohn3
1. Department of Physics and Astronomy, Seoul National University, Seoul 08826, South Korea
2. University of Science and Technology, Daejeon 34113, South Korea
3. Korea Astronomy and Space Science Institute, Daejeon 34055, South Korea
4. Max-Planck Institut für Radioastronomie, D-53121 Bonn, Germany
We report first results from KVN and VERA Array (KaVA) VLBI observations obtained in the frame of our Plasma-physics of Active Galactic Nuclei (PAGaN) project. We observed eight selected AGN at 22 and 43 GHz in single polarization (LCP) between March 2014 and April 2015. Each source was observed for 6 to 8 hours per observing run to maximize the uv-coverage. We obtained a total of 15 deep high-resolution images permitting the identification of individual circular Gaussian jet components and three spectral index maps of BL Lac, 3C 111 and 3C 345 from simultaneous dual-frequency observations. The spectral index maps show trends in agreement with general expectations - flat core and steep jets - while the actual value of the spectral index for jets shows indications for a dependence on AGN type. We analyzed the kinematics of jet components of BL Lac and 3C 111, detecting superluminal proper motions with maximum apparent speeds of about 5c. This constrains the lower limits of the intrinsic component velocities to ∼0.98c and the upper limits of the angle between jet and line of sight to ∼20°. In agreement with global jet expansion, jet components show systematically larger diameters d at larger core distances r, following the global relation d≈0.2r, albeit within substantial scatter.
Accepted by J. Korean Astron. Soc.
E-mail contact: trippe@astro.snu.ac.kr
arXiv preprint: http://arxiv.org/abs/1510.08153
A Search for AGN Intra-day Variability with KVN
Taeseok Lee1, Sascha Trippe1, Junghwan Oh1, Do-Young Byun2, Bong-Won Sohn2, Sang-Sung Lee2
1. Department of Physics and Astronomy, Seoul National University, Seoul 08826, South Korea
2. Korea Astronomy and Space Science Institute, Daejeon 34055, South Korea
Active galactic nuclei (AGN) are known for irregular variability on all time scales, down to intra-day variability with relative variations of a few percent within minutes to hours. On such short timescales, unexplored territory, such as the possible existence of a shortest characteristic time scale of activity and the shape of the high frequency end of AGN power spectra, still exists. We present the results of AGN single-dish fast photometry performed with the Korean VLBI Network (KVN). Observations were done in a "anti-correlated" mode using two antennas, with always at least one antenna pointing at the target. This results in an effective time resolution of less than three minutes. We used all four KVN frequencies, 22, 43, 86, and 129 GHz, in order to trace spectral variability, if any. We were able to derive high-quality light curves for 3C 111, 3C 454.3, and BL Lacertae at 22 and 43 GHz, and for 3C 279 at 86 GHz, between May 2012 and April 2013. We performed a detailed statistical analysis in order to assess the levels of variability and the corresponding upper limits. We found upper limits on flux variability ranging from ∼1.6% to ∼7.6%. The upper limits on the derived brightness temperatures exceed the inverse Compton limit by three to six orders of magnitude. From our results, plus comparison with data obtained by the University of Michigan Radio Astronomy Observatory, we conclude that we have not detected source-intrinsic variability which would have to occur at sub-per cent levels.
Accepted by J. Korean Astron. Soc.
E-mail contact: trippe@astro.snu.ac.kr
arXiv preprint: http://arxiv.org/abs/1510.08156
Constraining the dynamical importance of hot gas and radiation pressure in quasar outflows using emission line ratios
Jonathan Stern1, Claude-André Faucher-Giguère2, Nadia L. Zakamska3, and Joseph F. Hennawi1
1. Max Planck Institut für Astronomie, Königstuhl 17, D-69117, Heidelberg, Germany
2. Department of Physics and Astronomy and CIERA, Northwestern University, 2145 Sheridan Road, Evanston, IL 60208, USA
3. Department of Physics & Astronomy, Johns Hopkins University, Bloomberg Center, 3400 N. Charles St., Baltimore, MD 21218, USA
Quasar feedback models often predict an expanding hot gas bubble which drives a galaxy-scale outflow. In many circumstances the hot gas is predicted to radiate inefficiently, making the hot bubble hard to observe directly. We present an indirect method to detect the presence of a hot bubble using hydrostatic photoionization models of the cold (∼104 K) line-emitting gas. These models assume that the cold gas is in pressure equilibrium with either the hot gas pressure or with the radiation pressure, whichever is larger. We compare our models with observations of the broad line region (BLR), the inner face of the dusty torus, the narrow line region (NLR), and the extended NLR, and thus constrain the hot gas pressure over a dynamical range of 105 in radius, from ∼0.1 pc to ∼10 kpc. We find that the emission line ratios observed in the average quasar spectrum are consistent with radiation-pressure-dominated models on all scales. On scales <40 pc a dynamically significant hot gas pressure is ruled out for an average quasar spectrum, while on larger scales the hot gas pressure cannot exceed six times the local radiation pressure. In individual quasars, ≈25% of the objects exhibit narrow line ratios that are inconsistent with radiation-pressure-dominated models by a factor of ∼2, though in these objects the hot gas pressure is also unlikely to exceed the radiation pressure by an order of magnitude or more. The upper limits we derive on the hot gas pressure imply that the instantaneous gas pressure force acting on galaxy-scale outflows falls short of the time-averaged force needed to explain the large momentum fluxes ṗ ≫ LAGN/c inferred for galaxy-scale outflows in luminous quasars. This apparent discrepancy can be reconciled if the optical quasars observed today previously experienced a buried, fully-obscured phase during which the hot gas bubble was more effectively confined and during which most of the galactic wind acceleration occurred.
SUBMITTED to ApJ on Oct 24th 2015
E-mail contact: stern@mpia.de
DRAFT is available at http://arxiv.org/abs/1510.07690
Nearby Active Galactic Nuclei
Super-massive black holes (SBHs) have long been identified as the engines of active galactic nuclei (AGNs) and are now considered to play a key role in galaxy evolution. In this dissertation I present results from two observational studies conducted on nearby AGNs with the aim of furthering our understanding of SBH growth and their interplay with the host galaxies.
The first study is an observational search for SBHs spatially offset from the center of their host galaxies. Such offsets can be considered signatures of gravitational recoil following the coalescence of an SBH binary system (formed in the aftermath of a galaxy merger) due to emission of gravitational waves. The study is based on a photometric analysis of fourteen nearby elliptical galaxies observed with the Hubble Space Telescope. I find that parsec-scale offsets are common. However, while these are individually consistent with residual gravitational recoil oscillations, there is a high probability that larger offsets than those actually observed should have been found in the sample as a whole. There are a number of possible explanations for this result: the galaxy merger rate may be lower than current estimates; SBH-binaries may reach the merger stage with a configuration which minimizes recoil velocities; or the SBH oscillations are more quickly damped than predicted.
In the second study I use integral field spectroscopy obtained with the Gemini South telescope to investigate the kinematics of the circum-nuclear ionized gas in two active galaxies: NGC 1386, a Seyfert 2, and NGC 1365, a Seyfert 1. The goal of the study is to investigate outflows in low-luminosity AGNs, and the mechanisms channeling gas (the SBH fuel) from the inner kiloparsec down to a few tens of parsecs from the SBH. I find that the dominant kinematic components can be explained as a combination of rotation in the large-scale galactic disk and compact outflows along the axis of the AGN radiation cone. However, in the case of NGC 1386, there is also compelling evidence for an equatorial outflow, which provides a new clue to the physical processes operating in AGNs.
