Towards a 3% Geometric Distance to NGC 4258A. Argon, L. Greenhill, M. Reid, J. Moran & E. Humphreys (Harvard-Smithsonian CfA)20 April 2007Adam Trotter (UNC-Chapel Hill)
Palomar ObservatoryJ. Kagaya (Hoshi No Techou)
The Host GalaxyNGC 4258 (M106)Barred spiral SABbcSeyfert 1.9, D=7.2 MpcAnomalous spiral arms detected in H and radio continuumRecent Chandra, XMM, Spitzer and other images highlight the dual nature of spiral arms normal + jet impinging on ISM
Palomar ObservatoryWilson, Yang & Cecil 2001http://chandra.harvard.edu/photo/2007/ngc4258/
Angular resolution = 200 as (0.006 pc at 7.2 Mpc)Spectral resolution < 1 km s-1VLBA
H2O Masers Conditions requiredDense(108 - 1010 cm-3)Warm(300 - 800 K)Quiescent(v ~ vD)
The Nuclear MegamaserDiscovered by Claussen, Heiligman & Lo (1984)Centered on galactic systemic vsys = 470 km s-1Isotropic Luminosity ~120 LANakai et al. (1993) discovered emission at 1000 km s-1
Owens Valley Radio Observatory, 40-m antenna Greenhill et al. 1995: VLBI Observations of systemic emission show linear structure. Secular velocity drift implies centripetal acceleration in a flat disk.
The Big PictureMiyoshi et al. (1995) present VLBI images of full velocity range of maser emissionSystemic emission in narrow band S of radio continuum (jet)High-velocity emission distributed 0.3 pc to either sideHigh-velocity emission exhibits nearly perfect Keplerian rotation curve
Global Model FitsAssume warped disk (position angle and inclination change as functions of radius)Systemic velocity v0 = 4793 km s-1Central Mass M0=3.780.01x107 MAPosition of disk center determined to 30asPlummer model of central cluster would require central density c > 5.7x1011 MA pc-3 : unstable to collapse/disruption in lifetime of galaxyMassive disk model would imply densities 10-1000x too great to support water maser emissionMust be a supermassive black hole!
TO OBSERVER0.1pcObservers viewTop ViewHighBowlRedshiftedmasersBlueshiftedmasersSystemicMasersCourtesy CfA Maser Group, Humphreys, et al. (in prep)NGC4258 Inclination warp (flattening of high velocity rotation curve): 8 across redsPosition angle warp (declinations): 9 across redsDisk obscures much of central regionSystemic masers in bowl on front side of disk0.1pc
Warp is Well-Characterized
Natural explanation for:Faint blue high velocity feature (free-free absorption along the line-of-sight)Strongest red high velocity feature ~1306 km s-1 (where i=90)Strongest systemic maser flares at ~490 km s-1 (optimum coherence path)X-ray absorbing layer (nH ~ 1023 cm-2) radius = 0.29 pc where disk crosses line-of-sight (Fruscione et al. 2005)
How to Get a Distance? Measure accelerations & proper motions
Herrnstein et al. 1999
The ResultAcceleration Distance:
Proper Motion Distance:Including all systematic model uncertainties, a 5% geometric distance measurement:
Comparison to Other MeasurementsD = 7.2 0.3 MpcH-band Tully Fisher (Aaronson et al. 1982)D = 7.1 1.1 MpcBlue Tully Fisher (Richter & Huchtmeier 1984)D = 7.9 1.8 MpcLuminosity Class Estimate (Rowan-Robinson 1985)D = 8.4 2.2 MpcCepheid VariablesD = 8.1 0.4 Mpc (Maoz et al. 1999 - 15 Cepheids)
D = 7.8 0.3 0.5 Mpc (Newman et al. 2001 - same 15 Cepheids)
D = 7.4 Mpc (Macri et al 2006 - 300 Cepheids)
All these depend on Cepheid calibrations
Towards a 3% Distance MeasurementArgon et al. 2007 (in preparation)18 epochs of VLBI observations, 1997 March 2000 August, using VLBA, VLA Phased Array and Effelsberg 100-m antennaWider bandwidth Detection of new high-velocity features 30% closer to disk centerQuantification of maser disk thickness, h~5 as, will lead to more accurate models and estimates of mass accretion rate ADAF?More robust genetic modeling algorithm to refine warped disk shape and reduce systematic uncertaintiesInclusion of possible spiral structure in high-velocity masers, and ellipticity in systemic maser orbitsHST observations (in progress) of Cepheids in NGC4258 to provide independent calibration of Cepheid distance scaleUltimately, a new measurement of H0, though at a distance of 7.2 Mpc, unmodeled local velocity field perturbations may limit accuracy of the result.
Mai: Les Tres Riches Heures du Duc de Berry, c. 1410The May jaunt, a pageant celebrating the "joli mois de Mai" in which one had to wear green garments known as livree de mai. The riders are young noblemen and women, with princes and princesses.
Optical Image courtesy of Credit: Bernie and Jay Slotnick, Adam Block, AOP, NOAO, AURA, NSF
CHANDRAChandra Observations and the Nature of the Anomalous Arms of NGC 4258 (M106)Author(s) A. S. Wilson, Y. Yang, and G. CecilIdentifiers The Astrophysical Journal, volume 560, part 1 (2001), pages 689697 NGC 4258 (M106): Mysterious Arms Revealed Credit: X-ray: NASA/CXC/Univ. of Maryland/A.S. Wilson et al.; Optical: Pal.Obs. DSS; IR: NASA/JPL-Caltech; VLA: NRAO/AUI/NSF JPEG (246.4 kb), Tiff (42.9 MB), PS (7.2 MB) A combination of space and ground-based observations, including X-ray data from Chandra, has helped reveal the nature of the so-called anomalous arms in the spiral galaxy NGC 4258 (also known as M106). These arms have been known for decades, but their origin remained mysterious to astronomers. NGC 4258 X-ray Image In visible (shown in gold) and infrared (red) light, two prominent arms emanate from the bright nucleus and spiral outward. These arms are dominated by young, bright stars, which light up the gas within the arms. But in radio (purple) and Chandra's X-ray (blue) images, two additional spiral arms are seen. Multiwavelength Animation of NGC 4258By analyzing data from XMM-Newton, Spitzer, and Chandra, scientists have confirmed earlier suspicions that the ghostly arms represent regions of gas that are being violently heated by shock waves. Previously, some astronomers had suggested that the anomalous arms are jets of particles being ejected by a supermassive black hole in nucleus of NGC 4258. But radio observations at the Very Large Array later identified another pair of jets originating in the core. However, the jets do heat the gas in their line of travel, forming an expanding cocoon. Because the jets lie close to M106's disk, the cocoon generates shock waves and heat the gas in the disk to millions of degrees, causing it to radiate brightly in X-rays and other wavelengths. Water-vapor maser emission from galactic nucleiAuthors: Claussen,M.J.; Heiligman,G.M.; Lo,K.Y.Affiliation: AA(Owens Valley Radio Observatory, Pasadena, CA), AB(Owens Valley Radio Observatory, Pasadena, CA), AC(Owens Valley Radio Observatory, Pasadena, CA)Publication: Nature (ISSN 0028-0836), vol. 310, July 26, 1984, p. 298-300. (Nature Homepage)