Person: Moran, James
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Moran
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Moran, James
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Publication The High-Density Ionized Gas in the Central Parsec of the Galaxy(American Astronomical Society, 2010) Zhao, Jun-Hui; Blundell, Raymond; Moran, James; Downes, Dennis; Schuster, Karl F.; Marrone, Daniel P.We report a study of the \(H30\alpha\) line emission at 1.3 mm from the region around Sgr A* made with the Submillimeter Array at a resolution of 2'' over a field of 60'' (2 pc) and a velocity range of \(-360 to +345 km s^{–1}\). This field encompasses most of the Galactic center's "minispiral." With an isothermal homogeneous H II model, we determined the physical conditions of the ionized gas at specific locations in the Northern and Eastern Arms from the \(H30\alpha\) line data along with Very Large Array data from the \(H92\alpha\) line at 3.6 cm and from the radio continuum emission at 1.3 cm. The typical electron density and kinetic temperature in the minispiral arms are \(3-21×104 cm^{–3}\) and 5000-13,000 K, respectively. The \(H30\alpha\) and \(H92\alpha\) line profiles are broadened due to the large velocity shear within and along the beam produced by dynamical motions in the strong gravitational field near Sgr A*. We constructed a three-dimensional model of the minispiral using the orbital parameters derived under the assumptions that the gas flows are in Keplerian motion. The gas in the Eastern Arm appears to collide with the Northern Arm flow in the "Bar" region, which is located 0.1-0.2 pc south of and behind Sgr A*. Finally, a total Lyman continuum flux of \(3 × 10^{50}\) photons \(s^{–1}\) is inferred from the assumption that the gas is photoionized and the ionizing photons for the high-density gas in the minispiral arms are from external sources, which is equivalent to ~250 O9-type zero-age-main-sequence stars.Publication Toward a New Geometric Distance to the Active Galaxy NGC 4258. II. Centripetal Accelerations and Investigation of Spiral Structure(American Astronomical Society, 2008) Humphreys, E. M. L.; Reid, Mark; Greenhill, Lincoln; Moran, James; Argon, AliceWe report measurements of centripetal accelerations of maser spectral components of NGC 4258 for 51 epochs spanning 1994 to 2004. This is the second paper of a series, in which the goal is the determination of a new geometric maser distance to NGC 4258, accurate to possibly ~3%. We measure accelerations using a formal analysis method that involves simultaneous decomposition of maser spectra for all epochs into multiple, Gaussian components. Components are coupled between epochs by linear drifts (accelerations) from their centroid velocities at a reference epoch. For high-velocity emission, accelerations lie in the range \(–0.7 to +0.7 km s^{−1} yr^{−1}\), indicating an origin within 13° of the disk midline (the perpendicular to the line of sight [LOS] to the black hole). Comparison of the projected positions of high-velocity emission in VLBI images with those derived from acceleration data provides evidence that masers trace real gas dynamics. High-velocity emission accelerations do not support a model of trailing shocks associated with spiral arms in the disk. However, we find strengthened evidence for spatial periodicity in high-velocity emission, of wavelength 0.75 mas. This supports suggestions of spiral structure due to density waves in the nuclear accretion disk of an active galaxy. Accelerations of low-velocity (systemic) emission lie in the range \(7.7 to 8.9 km s^{−1} yr^{−1}\), consistent with emission originating from a concavity where the thin, warped disk is tangent to the LOS. A trend in accelerations of low-velocity emission, as a function of Doppler velocity, may be associated with disk geometry and orientation or with the presence of spiral structure.Publication An X‐Ray, Infrared, and Submillimeter Flare of Sagittarius A*(American Astronomical Society, 2008) Marrone, D. P.; Baganoff, F. K.; Morris, M. R.; Moran, James; Ghez, A. M.; Hornstein, S. D.; Dowell, C. D.; Munoz, Diego Jose; Bautz, M. W.; Ricker, G. R.; Brandt, W. N.; Garmire, G. P.; Lu, J. R.; Matthews, K.; Zhao, J.‐H.; Rao, R.; Bower, G. C.Energetic flares are observed in the Galactic supermassive black hole Sagittarius A* from radio to X-ray wavelengths. On a few occasions, simultaneous flares have been detected in IR and X-ray observations, but clear counterparts at longer wavelengths have not been seen. We present a flare observed over several hours on 2006 July 17 with the Chandra X-Ray Observatory, the Keck II telescope, the Caltech Submillimeter Observatory, and the Submillimeter Array. All telescopes observed strong flare events, but the submillimeter peak is found to occur nearly 100 minutes after the X-ray peak. Submillimeter polarization data show linear polarization in the excess flare emission, increasing from 9% to 17% as the flare passes through its peak, consistent with a transition from optically thick to thin synchrotron emission. The temporal and spectral behavior of the flare require that the energetic electrons responsible for the emission cool faster than expected from their radiative output. This is consistent with adiabatic cooling in an expanding emission region, with X-rays produced through self-Compton scattering, although not consistent with the simplest model of such expansion. We also present a submillimeter flare that followed a bright IR flare on 2005 July 31. Compared to 2006, this event had a larger peak IR flux and similar submillimeter flux, but it lacked measurable X-ray emission. It also showed a shorter delay between the IR and submillimeter peaks. Based on these events we propose a synchrotron and self-Compton model to relate the submillimeter lag and the variable IR/X-ray luminosity ratio.Publication Resolving the Inner Jet Structure of 1924-292 with the Event Horizon Telescope(American Astronomical Society, 2012) Lu, Ru-Sen; Fish, Vincent L.; Weintroub, Jonathan; Doeleman, Sheperd S.; Bower, Geoffrey C.; Freund, Robert; Friberg, Per; Ho, Paul T. P.; Honma, Mareki; Inoue, Makoto; Krichbaum, Thomas P.; Marrone, Daniel P.; Moran, James; Oyama, Tomoaki; Plambeck, Richard; Primiani, Rurik; Shen, Zhi-Qiang; Tilanus, Remo P. J.; Wright, Melvyn; Young, Ken H.; Ziurys, Lucy M.; Zensus, J. AntonWe present the first 1.3 mm (230 GHz) very long baseline interferometry model image of an active galactic nucleus (AGN) jet using closure phase techniques with a four-element array. The model image of the quasar 1924-292 was obtained with four telescopes at three observatories: the James Clerk Maxwell Telescope on Mauna Kea in Hawaii, the Arizona Radio Observatory's Submillimeter Telescope in Arizona, and two telescopes of the Combined Array for Research in Millimeter-wave Astronomy in California in 2009 April. With the greatly improved resolution compared with previous observations and robust closure phase measurement, the inner jet structure of 1924-292 was spatially resolved. The inner jet extends to the northwest along a position angle of -53° at a distance of 0.38 mas from the tentatively identified core, in agreement with the inner jet structure inferred from lower frequencies, and making a position angle difference of ~80° with respect to the centimeter jet. The size of the compact core is 0.15 pc with a brightness temperature of 1.2 × 1011 K. Compared with those measured at lower frequencies, the low brightness temperature may argue in favor of the decelerating jet model or particle-cascade models. The successful measurement of closure phase paves the way for imaging and time resolving Sgr A* and nearby AGNs with the Event Horizon Telescope.Publication The Circular Polarization of Saggitarius A* at Submillimeter Wavelengths(American Astronomical Society, 2012) Muñoz, D. J.; Marrone, D. P.; Moran, James; Rao, R.We report the first detections of circularly polarized emission at submillimeter wavelengths from the compact radio source and supermassive black hole candidate Sgr A* at a level of 1.2\pm0.3% at 1.3 mm wavelength (230 GHz) and 1.6\pm0.3% at 860 microns (345 GHz) with the same handedness as observed at lower frequencies (1.4-15 GHz). The observations, taken with the Submillimeter Array in multiple epochs, also show simultaneous linear polarization (LP) at both wavelengths of about 6%. These properties differ sharply from those at wavelengths longer than 1 cm (frequencies below 30 GHz), where weak circular polarization (CP) (~ 0.5%) dominates over LP, which is not detected at similar fractional limits. We describe an extensive set of tests to ensure the accuracy of our measurements. We find no CP in any other source, including the bright quasar 1924-292, which traces the same path on the sky as Sgr A* and therefore should be subject to identical systematic errors originating in the instrument frame. Since a relativistic synchrotron plasma is expected to produce little CP, the observed CP is probably generated close to the event horizon by the Faraday conversion process. We use a simple model to show that the phase shift associated with Faraday conversion can be nearly independent of frequency, a sufficient condition to make the handedness of CP independent of frequency. Because the size of the tau=1-surface changes by more than an order of magnitude between 1.4 and 345 GHz, the magnetic field must be coherent over such scales to consistently produce left CP.Publication Jet-Launching Structure Resolved Near the Supermassive Black Hole in M87(American Association for the Advancement of Science (AAAS), 2012) Doeleman, Sheperd; Fish, V. L.; Schenck, D. E.; Beaudoin, C.; Blundell, Raymond; Bower, G. C.; Broderick, Alithia Carol; Chamberlin, R.; Freund, R.; Friberg, P.; Gurwell, Mark; Ho, Po-Yi; Honma, M.; Inoue, M.; Krichbaum, T. P.; Lamb, Justin; Loeb, Abraham; Lonsdale, C.; Marrone, D. P.; Moran, James; Oyama, T.; Plambeck, R.; Primiani, Rurik; Rogers, A. E. E.; Smythe, D. L.; SooHoo, J.; Strittmatter, P.; Tilanus, R. P. J.; Titus, M.; Weintroub, Jonathan; Wright, Bennett Bennett; Young, K. H.; Ziurys, L. M.Approximately 10% of active galactic nuclei exhibit relativistic jets, which are powered by accretion of matter onto super massive black holes. While the measured width profiles of such jets on large scales agree with theories of magnetic collimation, predicted structure on accretion disk scales at the jet launch point has not been detected. We report radio interferometry observations at 1.3mm wavelength of the elliptical galaxy M87 that spatially resolve the base of the jet in this source. The derived size of 5.5 +/- 0.4 Schwarzschild radii is significantly smaller than the innermost edge of a retrograde accretion disk, suggesting that the M87 jet is powered by an accretion disk in a prograde orbit around a spinning black hole.Publication Infall and Outflow of Molecular Gas in Sgr B2(American Astronomical Society, 2008) Qin, Sheng‐Li; Zhao, Jun‐Hui; Moran, James; Marrone, Daniel P.; Patel, Nimesh; Wang, Jun‐Jie; Liu, Sheng‐Yuan; Kuan, Yi‐JehngObservations of two \(H_2CO (3_{03}-2_{02} and 3_{21}-2_{20})\) lines and continuum emission at 1.3 mm toward Sgr B2(N) and Sgr B2(M) have been carried out with the SMA. The mosaic maps of Sgr B2(N) and Sgr B2(M) in both continuum and lines show a complex distribution of dust and molecular gas in both clumps and filaments surrounding the compact star formation cores. We have observed a decelerating outflow originated from the Sgr B2(M) core, showing that both the redshifted and blueshifted outflow components have a common terminal velocity. This terminal velocity is \(58 ± 2 km s^{−1}\). It provides an excellent method for determination of the systematic velocity of the molecular cloud. The SMA observations have also shown that a large fraction of absorption against the two continuum cores is redshifted with respect to the systematic velocities of Sgr B2(N) and Sgr B2(M), respectively, suggesting that the majority of the dense molecular gas is flowing into the two major cores where massive stars have been formed. We have solved the radiative transfer in a multilevel system with LVG approximation. The observed \(H_2CO\) line intensities and their ratios can be adequately fitted with this model for the most of the gas components. However, the line intensities between the higher energy level transition \(H_2CO(3_{21}-2_{20})\) and the lower energy level transition \(H_2CO(3_{03}-2_{02})\) is reversed in the redshifted outflow region of Sgr B2(M), suggesting the presence of inversion in population between the ground levels in the two K ladders \((K_{−1} = 0 and 2)\). The possibility of weak maser processes for the \(H_2CO\) emission in Sgr B2(M) is discussed.Publication Toward a New Geometric Distance To the Active Galaxy NGC 4258. III. Final Results and The Hubble Constant(American Astronomical Society, 2013) Humphreys, E. M. L.; Reid, Mark; Moran, James; Greenhill, Lincoln; Argon, AliceWe report a new geometric maser distance estimate to the active galaxy NGC 4258. The data for the new model are maser line-of-sight (LOS) velocities and sky positions from 18 epochs of very long baseline interferometry observations, and LOS accelerations measured from a 10 yr monitoring program of the 22 GHz maser emission of NGC 4258. The new model includes both disk warping and confocal elliptical maser orbits with differential precession. The distance to NGC 4258 is \(7.60 \pm 0.17 \pm 0.15 Mpc\), a 3% uncertainty including formal fitting and systematic terms. The resulting Hubble constant, based on the use of the Cepheid variables in NGC 4258 to recalibrate the Cepheid distance scale, is \(H_0 = 72.0 \pm 3.0 km s^{–1} Mpc^{–1}\).Publication Event-Horizon-Scale Structure in the Supermassive Black Hole Candidate at the Galactic Centre(Nature Publishing Group, 2008) Doeleman, Sheperd; Weintroub, Jonathan; Rogers, Alan E. E.; Plambeck, Richard; Freund, Robert; Tilanus, Remo P. J.; Friberg, Per; Ziurys, Lucy M.; Moran, James; Corey, Brian; Young, Ken; Smythe, Daniel L.; Titus, Michael; Marrone, Daniel P.; Cappallo, Roger J.; Bock, Douglas C.-J.; Bower, Geoffrey C.; Chamberlin, Richard; Davis, Gary R.; Krichbaum, Thomas P.; Lamb, James; Maness, Holly; Niell, Arthur E.; Roy, Alan; Strittmatter, Peter; Werthimer, Daniel; Whitney, Alan R.; Woody, DavidThe cores of most galaxies are thought to harbour supermassive black holes, which power galactic nuclei by converting the gravitational energy of accreting matter into radiation. Sagittarius A* (Sgr A*), the compact source of radio, infrared and X-ray emission at the centre of the Milky Way, is the closest example of this phenomenon, with an estimated black hole mass that is 4,000,000 times that of the Sun. A long-standing astronomical goal is to resolve structures in the innermost accretion flow surrounding Sgr A*, where strong gravitational fields will distort the appearance of radiation emitted near the black hole. Radio observations at wavelengths of 3.5 mm and 7 mm have detected intrinsic structure in Sgr A*, but the spatial resolution of observations at these wavelengths is limited by interstellar scattering. Here we report observations at a wavelength of 1.3 mm that set a size of \(37^{+16}_{-10}\) microarcseconds on the intrinsic diameter of Sgr A*. This is less than the expected apparent size of the event horizon of the presumed black hole, suggesting that the bulk of Sgr A* emission may not be centred on the black hole, but arises in the surrounding accretion flow.Publication The Parsec‐Scale Accretion Disk in NGC 3393(American Astronomical Society, 2008) Kondratko, Paul T.; Greenhill, Lincoln; Moran, JamesWe present a Very Long Baseline Interferometry image of the water maser emission in the nuclear region of NGC 3393. The maser emission has a linear distribution oriented at a position angle of ~–34°, perpendicular to both the kiloparsec-scale radio jet and the axis of the narrow-line region. The position-velocity diagram displays a red-blue asymmetry about the systemic velocity and the estimated dynamical center, and is thus consistent with rotation. Assuming Keplerian rotation in an edge-on disk, we obtain an enclosed mass of (\(3.1 ± 0.2) × 10^7 M☉\) within 0.36 ± 0.02 pc (1.48 ± 0.06 mas), which corresponds to a mean mass density of \(\sim10^{8.2} M☉ pc^{−3}\). We also report the measurement with the Green Bank Telescope of a velocity drift, a manifestation of centripetal acceleration within the disk, of \(5 ± 1 km s^{−1} yr^{−1}\) in the \(\sim3880 km s^{−1}\) maser feature, which is most likely located along the line of sight to the dynamical center of the system. From the acceleration of this feature, we estimate a disk radius of 0.17 ± 0.02 pc, which is smaller than the inner disk radius (0.36 ± 0.02 pc) of emission that occurs along the midline (i.e., the line of nodes). The emission along the line of sight to the dynamical center evidently occurs much closer to the center than the emission from the disk midline, contrary to the situation in the archetypal maser systems NGC 4258 and NGC 1068. The outer radius of the disk as traced by the masers along the midline is about 1.5 pc.