Browsing by Author "Iwasawa, K."
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- ItemA hard X-ray view of luminous and ultra-luminous infrared galaxies in GOALS - I. AGN obscuration along the merger sequence(2021) Ricci, C.; Privon, G. C.; Pfeifle, R. W.; Armus, L.; Iwasawa, K.; Torres-Albà, N.; Satyapal, S.; Bauer, F. E.; Treister, E.; Ho, L. C.; Aalto, S.; Arévalo, P.; Barcos-Muñoz, L.; Charmandaris, V.; Diaz-Santos, T.; Evans, A. S.; Gao, T.; Inami, H.; Koss, M. J.; Lansbury, G.; Linden, S. T.; Medling, A.; Sanders, D. B.; Song, Y.; Stern, D.; U, V.; Ueda, Y.; Yamada, S.The merger of two or more galaxies can enhance the inflow of material from galactic scales into the close environments of active galactic nuclei (AGNs), obscuring and feeding the supermassive black hole (SMBH). Both recent simulations and observations of AGN in mergers have confirmed that mergers are related to strong nuclear obscuration. However, it is still unclear how AGN obscuration evolves in the last phases of the merger process. We study a sample of 60 luminous and ultra-luminous IR galaxies (U/LIRGs) from the GOALS sample observed by NuSTAR. We find that the fraction of AGNs that are Compton thick (CT;N-H >= 10(24)cm(-2) ) peaks at at a late merger stage, prior to coalescence, when the nuclei have projected separations (d(sep)) of 0.4-6 kpc. A similar peak is also observed in the median N-H [[(1.6 +/- 0.5) x 10(24) cm(-2)].]. The vast majority (85(-9)(+7) per cent)) of the AGNs in the final merger stages (d(sep) less than or similar to 10 kpc) are heavily obscured (N-H = 10(23) cm(-2)), and the median N-H of the accreting SMBHs in our sample is systematically higher than that of local hard X-ray-selected AGN, regardless of the merger stage. This implies that these objects have very obscured nuclear environments, with the gas almost completely covering the AGN in late mergers. CT AGNs tend to have systematically higher absorption-corrected X-ray luminosities than less obscured sources. This could either be due to an evolutionary effect, with more obscured sources accreting more rapidly because they have more gas available in their surroundings, or to a selection bias. The latter scenario would imply that we are still missing a large fraction of heavily obscured, lower luminosity (L2-10 less than or similar to 10(43) erg s(-1)) AGNs in U/LIRGs.
- ItemA Herschel/PACS Far-infrared Line Emission Survey of Local Luminous Infrared Galaxies(IOP PUBLISHING LTD, 2017) Diaz Santos, T.; Armus, L.; Charmandaris, V.; Lu, N.; Stierwalt, S.; Stacey, G.; Malhotra, S.; van der Werf, P. P.; Howell, J. H.; Privon, G. C.; Mazzarella, J. M.; Goldsmith, P. F.; Murphy, E. J.; Barcos Munoz, L.; Linden, S. T.; Inami, H.; Larson, L.; Evans, A. S.; Appleton, P.; Iwasawa, K.; Lord, S.; Sanders, D. B.; Surace, J. A.We present an analysis of [O I](63), [O III](88), [N II](122), and [C II](158) far-infrared (FIR) fine-structure line observations obtained with Herschel/PACS, for similar to 240 local luminous infrared galaxies (LIRGs) in the Great Observatories All-sky LIRG Survey. We find pronounced declines ("deficits") of line-to-FIR continuum emission for [N II](122), [O I](63), and [C II](158) as a function of FIR color and infrared luminosity surface density, Sigma(IR). The median electron density of the ionized gas in LIRGs, based on the [N II](122)/[N II](205) ratio, is n(e) = 41 cm(-3). We find that the dispersion in the [C II](158) deficit of LIRGs is attributed to a varying fractional contribution of photodissociation regions (PDRs) to the observed [C II](158) emission, f ([C II](158)(PDR)) = [C II](158)(PDR)/C II](158), which increases from similar to 60% to similar to 95% in the warmest LIRGs. The [O I](63)/[C II](158)(PDR) ratio is tightly correlated with the PDR gas kinetic temperaturein sources where [O I] 63 is not optically thick or self-absorbed. For each galaxy, we derive the average PDR hydrogen density, n(H), and intensity of the interstellar radiation field, G, in units of G(0) and find G/n(H) ratios of similar to 0.1-50 G(0) cm(3), with ULIRGs populating the upper end of the distribution. There is a relation between G/n(H) and Sigma(IR), showing a critical break at Sigma(IR)* similar or equal to 5 x 10(10) L-circle dot kpc(-2). Below Sigma(IR)*, G/n(H) remains constant, similar or equal to 0.32G(0) cm(3), and variations in Sigma(IR) are driven by the number density of star-forming regions within a galaxy, with no change in their PDR properties. Above Sigma(IR)*, G/n(H) increases rapidly with Sigma(IR), signaling a departure from the typical PDR conditions found in normal star-forming galaxies toward more intense/harder radiation fields and compact geometries typical of starbursting sources.
- ItemExcitation Mechanisms for HCN (1-0) and HCO+ (1-0) in Galaxies from the Great Observatories All-sky LIRG Survey.(2015) Privon, G. C.; Treister, Ezequiel; Herrero-Illana, R.; Evans, Aaron S.; Iwasawa, K.; Perez-Torres, M. A.; Armus, Lee; Díaz-Santos, T.; Murphy, E. J.; Stierwalt, S.; Aalto, S.
- ItemGrowing supermassive black holes in the late stages of galaxy mergers are heavily obscured.(2017) Ricci, Claudio; Bauer, Franz Erik; Treister, Ezequiel; Privon, G. C.; Schawinski, K.; Blecha, L.; Arevalo, P.; Armus, Lee; Harrison, F.; Ho, L. C.; Iwasawa, K.; Sanders, David B.; Stern, Daniel
- ItemNuSTAR catches the unveiling nucleus of NGC 1068(2016) Bauer, Franz Erik; Ricci, Claudio; Marinucci, A.; Bianchi, S.; Matt, G.; Alexander, D.; Balokovic, M.; Brandt, W.; Gandhi, P.; Guainazzi, M.; Harrison, F.; Iwasawa, K.; Koss, M.; Madsen, K.; Nicastro, F.; Puccetti, S.; Stern, D.; Walton, D.
- ItemNUSTAR Unveils a Heavily Obscured Low-luminosity Active Galactic Nucleus in the Luminous Infrared Galaxy NGC 6286.(2016) Ricci, Claudio; Bauer, Franz Erik; Treister, Ezequiel; Romero-Cañizales, C.; Arevalo, P.; Iwasawa, K.; Privon, G. C.; Sanders, David B.; Schawinski, K.; Stern, D.; Imanishi, M.
- ItemProbing the circumnuclear absorbing medium of the buried AGN in NGC 1068 through NuSTAR observations(OUP, 2019) Zaino, A.; Bianchi, S.; Marinucci, A.; Matt, G.; Bauer, Franz Erik; Brandt, W. N.; Gandhi, P.; Guainazzi, M.; Iwasawa, K.; Puccetti, S.; Ricci, Claudio; Walton, D. J.We present the results of the latest NuSTAR monitoring campaign of the Compton-thick Seyfert 2 galaxy NGC 1068, composed of four ∼50 ks observations performed between 2017 July and 2018 February to search for flux and spectral variability on time-scales from 1 to 6 months. We detect one unveiling and one eclipsing event with time-scales less than 27 and 91 d, respectively, ascribed to Compton-thick material with N H = (1.8 ± 0.8) × 10 24 and ≥ (2.4 ± 0.5) × 10 24 cm −2 moving across our line of sight. This gas is likely located in the innermost part of the torus or even further inward, thus providing further evidence of the clumpy structure of the circumnuclear matter in this source. Taking advantage of simultaneous Swift–XRT observations, we also detected a new flaring ULX, at a distance d ∼ 30 arcsec (i.e. ∼2 kpc) from the nuclear region of NGC 1068, with a peak X-ray intrinsic luminosity of (3.0 ± 0.4) × 10 40 erg s −1 in the 2–10 keV band.
- ItemThe Chandra COSMOS-Legacy Survey: Source X-Ray Spectral Properties(2016) Marchesi, Stefano; Treister, Ezequiel; Lanzuisi, G.; Civano, Francesca; Iwasawa, K.; Suh, H.; Comastri, A.; Zamorani, G.; Allevato, Viola; Griffiths, R.; Miyaji, T.
- ItemThe incidence of obscuration in active galactic nuclei.(2014) Merloni, A.; Treister, Ezequiel; Bongiorno, A.; Brusa, Marcella; Iwasawa, K.; Mainieri, V.; Magnelli, B.; Salvato, M.; Berta, S.; Cappelluti N; Comastri, A.
- ItemThe XMM deep survey in the CDF-S IX. An X-ray outflow in a luminous obscured quasar at z ≈ 1.6(2015) Vignali, C.; Iwasawa, K.; Comastri, A.; Gilli, R.; Lanzuisi, G.; Ranalli, P.; Cappelluti, N.; Mainieri, V.; Georgantopoulos, I.; Bauer, Franz Erik; Fritz, J.; Brusa, M.; Brandt, W.; Carrera, F.; Fiore, F.; Tombesi, F.