Recent JWST Science Abstracts - AGN

Active Galactic Nucleus and Quasar Science with Aperture Masking Interferometry on the James Webb Space Telescope

Paper abstract:- Due to feedback from accretion onto supermassive black holes (SMBHs), active galactic nuclei (AGNs) are believed to play a key role in ΛCDM cosmology and galaxy formation. However, AGNs extreme luminosities and the small angular size of their accretion flows create a challenging imaging problem. We show that the James Webb Space Telescope’s Near Infrared Imager and Slitless Spectrograph (JWST-NIRISS) Aperture Masking Interferometry (AMI) mode will enable true imaging (i.e., without any requirement of prior assumptions on source geometry) at ∼65 mas angular resolution at the centers of AGNs. This is advantageous for studying complex extended accretion flows around SMBHs and in other areas of angular-resolution-limited astrophysics. By simulating data sequences incorporating expected sources of noise, we demonstrate that JWST-NIRISS AMI mode can map extended structure at a pixel-to-pixel contrast of ∼10−2 around an L = 7.5 point source, using short exposure times (minutes). Such images will test models of AGN feedback, fueling, and structure (complementary with ALMA observations), and are not currently supported by any ground-based IR interferometer or telescope. Binary point source contrast with NIRISS is ∼10−4 (for observing binary nuclei in merging galaxies), significantly better than current ground-based optical or IR interferometry. JWST-NIRISS’s seven-hole non-redundant mask has a throughput of 15%, and utilizes NIRISS’s F277W (2.77 μm), F380M (3.8 μm), F430M (4.3 μm), and F480M (4.8 μm) filters. NIRISS’s square pixels are 65 mas per side, with a field of view ∼2′ ? 2′. We also extrapolate our results to AGN science enabled by non-redundant masking on future 2.4 m and 16 m space telescopes working at long-UV to near-IR wavelengths.

Reference: Saavik Ford,City University of New York, Co-authors:-B. McKernan, A. Sivaramakrishnan, A. R. Martel, A. Koekemoer, D. Lafreniere, S. Parmentier, 2014ApJ, 783, 73F

The Dependency of AGN Infrared Colour-Selection on Source Luminosity and Obscuration. An Observational Perspective in CDFS and COSMOS

Paper abstract:- This work addresses the AGN IR-selection dependency on intrinsic source luminosity and obscuration, in order to identify and characterise biases that could affect conclusions in studies. Methods: We study IR-selected AGN in the Chandra Deep Field South (CDFS) survey and in the Cosmological Survey (COSMOS). The AGN sample is divided into low and high X-ray luminosity classes and into unobscured (type-1) and obscured (type-2) classes by means of X-ray and optical spectroscopy data. Specifically in the X-ray regime, we adopt the intrinsic luminosity taking the estimated column density (NH) into account. We also take the opportunity to highlight important differences resulting from adopting different methods of assessing AGN obscuration. Results: In agreement with previous studies, we also find that AGN IR-selection efficiency shows a decrease with decreasing source AGN X-ray luminosity. For the intermediate-luminosity AGN population (43.3 <= log(Lx[erg/s]) <= 44), the efficiency also worsens with increasing obscuration (NH). The same sample also shows an evolution with cosmic time of the obscured fraction at the highest X-ray luminosities, independently of the adopted type-1/type-2 classification method. Conclusions: We confirm that AGN IR-selection is genuinely biased towards unobscured AGNe, but only at intermediate luminosities. At the highest luminosities, where AGN IR-selection is more efficient, there is no obscuration bias. We show that type-1 AGNe are intrinsically more luminous than type-2 AGNe only at z <~ 1.6, thus resulting in more type-1 AGN being selected when the IR survey is shallower. Based on this and other studies, we conclude that deep hard-X-ray coverages, high-resolution IR imaging, or a combination of IR and radio data are required to recover the lower luminosity obscured AGN population. In addition, wide IR surveys are needed to recover the rare powerful, obscured AGN population. Finally, when the James Webb Space Telescope comes online, the broad-band filters 2.0 μm, 4.4 μm, 7.7 μm, and 18 μm will be essential for disentangling AGN from non-AGN dominated SEDs at depths where spectroscopy becomes impractical.

Reference: Hugo Messias, Instituto de Astrofísica e Ciências do Espaço, Universidade de Lisboa, OAL, Tapada da Ajuda, PT1349-018 Lisboa, Portugal, Co-authors:- Jose M Afonso, Mara Salvato, Bahram Mobasher, Andrew M Hopkins, 2014, A&A, 562A, 144M