The Geometry of and Mass Accretion Rate through the Maser Accretion Disk in NGC 4258

By J. Herrnstein, James M. Moran, L. Greenhill, A. Trotter. 2005

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A maximum likelihood analysis of the NGC 4258 maser positions and velocities reveals a ~2 σ deviation from Keplerian motion in the projected rotation curve of the high-velocity features, corresponding to a ~9 km s-1, or 0.8%, flattening of the LOS velocities with respect to Keplerian motion over the range of the high-velocity masers. While there are a number of potential explanations for this flattening, we argue for pure Keplerian rotation in an inclination-warped disk on the basis of the ability of this model to explain a number of otherwise puzzling features of the system. A radial gradient in the disk inclination of 0.034 mas-1 is not only consistent with the observed rotation curve, but it generates a bowl along the near edge of the disk that naturally explains the otherwise puzzling narrow spread in the declinations of the systemic masers. It also explains the existence and location of an apparently recurring flare among the systemic masers. There is no significant evidence for non-Keplerian rotation in the inclination-warped disk. An additional implication of the inclination warp is that the disk rises in front of and obscures the central engine at a disk radius of about 8.3 mas, or 0.29 pc. By comparing the observed X-ray column to conditions in the disk at this radius, we argue that the disk must be atomic at 0.29 pc. Hence, we conclude that the molecular-to-atomic transition occurs just beyond the outermost maser at 0.28 pc, and from this we infer an accretion rate of ~10-4α M☉ yr-1, where α (≲1) is the standard dimensionless parameterization of the kinematic viscosity. Our model suggests that most of the observed X-ray column arises in the warped accretion disk at 0.29 pc and that the maser emission is truncated at large radii predominantly as a result of the molecular-to-atomic phase transition originally proposed by Neufeld & Maloney. The inferred accretion rate is consistent with the jet-dominated accretion models of Yuan et al.

Subfields: Astronomy and Astrophysics

View Paper: https://www.semanticscholar.org/paper/cfea388633a6538664f416d6ceb287961396c787

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In Astronomy and Astrophysics

Citations in the corpus

TOWARD A NEW GEOMETRIC DISTANCE TO THE ACTIVE GALAXY NGC 4258. III. FINAL RESULTS AND THE HUBBLE CONSTANT (2013, methodology): “Another difference between this work and the investigation of disk warping performed by Herrnstein et al. (2005) is that they only performed a fit to the high-velocity maser emission.”
PRECISE BLACK HOLE MASSES FROM MEGAMASER DISKS: BLACK HOLE–BULGE RELATIONS AT LOW MASS (2010, background): “Other observations provide detailed constraints on the thickness, velocity structure, and toroidal magnetic field in an accretion disk (e.g., Modjaz et al. 2005; Herrnstein et al. 2005; Argon et al. 2007; Humphreys et al. 2008).”
ASTROPHYSICAL TESTS OF MODIFIED GRAVITY: CONSTRAINTS FROM DISTANCE INDICATORS IN THE NEARBY UNIVERSE (2012, result): “The two distance estimates obtained from the maser data are in excellent agreement; see Herrnstein et al. (2005) and Humphreys et al. (2008) for recent studies.”
Microarcsecond Radio Astrometry (2013, background): “Observations of the archetypal megamaser galaxy, NGC 4258, demonstrated the power of radio astrometric observations for better understanding of AGN accretion disks (Herrnstein et al. 2005) and yielded an accurate distance of 7.2± 0.5 Mpc to the galaxy (Herrnstein et al. 1999).”
Measuring the Masses of Supermassive Black Holes (2014, unknown): “14 [1]Herrnstein et al. (2005).”
Black Hole Spin via Continuum Fitting and the Role of Spin in Powering Transient Jets (2013, background): “…holes (McClintock & Remillard 2006; ¨Ozel et al. 2010; Orosz et al. 2011a; Steeghs et al. 2013), as well as for several super-massive black holes, e.g., Sgr A* (Ghez et al. 2008; Gillessen et al. 2009), NGC 4258 (Herrnstein et al. 2005), and others (G¨ultekin et al. 2009, and references therein).”
REVISITING THE SCALING RELATIONS OF BLACK HOLE MASSES AND HOST GALAXY PROPERTIES (2012, unknown): “…& de Zeeuw 2010) ; (25 = Kondratko et al. 2008) ; (26 = Gültekin et al. 2009b) ; (27 = McConnell et al. 2011a) ; (28 = Walsh et al. 2012) ; (29 = Herrnstein et al. 2005) ; (30 = Ferrarese et al. 1996) ; (31 = Cretton & van den Bosch 1999a) ; (32 = Walsh et al. 2010) ; (33 = Gebhardt et al.…”
A systematic search for close supermassive black hole binaries in the Catalina Real-time Transient Survey (2015, background): “Warped features are known to exist when the data is of sufficient quality to identify them, e.g. Herrnstein et al. (2005) for NGC 4258, and may be common to most AGN, according to high resolution simulations of gas inflow in active galaxies (Hopkins & Quataert 2010).”