Edge-on Accretion Disk Research Articles

Accretion disk versus jet orientation in H2O megamaser galaxies

Context. An essential part of the paradigm describing active galactic nuclei is the alignment between the radio jet and the associated rotation axis of the sub-pc accretion disks. Because of the small linear and angular scales involved, this alignment has not yet been checked in a sufficient number of low luminosity active galactic nuclei (LLAGNs). Aims. The project examines the validity of this paradigm by measuring the radio continuum on the same physical scale as the accretion disks to investigate any possible connection between these disks and the radio continuum. Methods. We observed a sample of 18 LLAGNs in the 4.8 GHz (6 cm) radio continuum using the Very Long Baseline Array (VLBA) with 3.3–6.5 ms resolution. The sources were selected to show both an edge-on accretion disk revealed by 22 GHz H2O megamaser emission and signatures of a radio jet. Furthermore, the sources were previously detected in 33 GHz radio continuum observations made with the Very Large Array. Results. Five out of 18 galaxies observed were detected at 8σ or higher levels (Mrk 0001, Mrk 1210, Mrk 1419, NGC 2273, and UGC 3193). While these five sources are known to have maser disks, four of them exhibit a maser disk with known orientation. For all four of these sources, the radio continuum is misaligned relative to the rotation axis of the maser disk, but with a 99.1% confidence level, the orientations are not random and are confined to a cone within 32° of the maser disk’s normal. Among the four sources the misalignment of the radio continuum with respect to the normal vector to the maser disk is smaller when the inner radius of the maser disk is larger. Furthermore, a correlation is observed between the 5 GHz VLBA radio continuum and the [OIII] luminosity and also with the H2O maser disk’s inner radius.

UNCOVERING THE OUTFLOW DRIVEN BY THE BROWN DWARF LS-RCrA 1: Hα AS A TRACER OF OUTFLOW ACTIVITY IN BROWN DWARFS

It is now apparent that classical T Tauri-like outflows commonly accompany the formation of young brown dwarfs (BDs). To date two optical outflows have been discovered, and results presented in this Letter increase this number to three. Using spectro-astrometry, the origin of the LS-RCrA 1 forbidden emission lines in a blueshifted outflow is confirmed. The nondetection of the redshifted component of the outflow in forbidden lines, along with evidence for some separation between low- and high-velocity outflow components, does not support the hypothesis that LS-RCrA 1 has an edge-on accretion disk. The key result of this analysis is the discovery of an outflow component to the Hα line. The Hα line profile has blueshifted and redshifted features in the wings which spectro-astrometry reveals to also originate in the outflow. The discovery that Hα emission in BDs can have a significant contribution from an outflow suggests that the use of Hα line widths as a proxy of mass accretion in BDs is not clear cut. This method assumes that any contribution to the Hα line flux from a possible outflow is negligible. Finally, the fact that the Hα line traces both lobes of the outflow while only the blueshifted lobe is seen in forbidden emission points to the presence of a dust hole in the accretion disk of LS-RCrA 1. This is commonly seen in classical T Tauri stars and is assumed to signal the onset of planet formation.

Discovery of Water Maser Emission in Five AGNs and a Possible Correlation Between Water Maser and Nuclear 2–10 keV Luminosities

We report the discovery of water maser emission in five active galactic nuclei (AGNs) with the 100 m Green Bank Telescope (GBT). The positions of the newly discovered masers, measured with the VLA, are consistent with the optical positions of the host nuclei to within 1 � (0B3 radio and 1B3 optical) and most likely mark the locations of the embedded central engines. The spectra of three sources, 2MASX J08362280+3327383, NGC 6264, and UGC 09618 NED02, display the characteristic spectral signature of emission from an edge-on accretion disk with maximum orbitalvelocityof � 700, � 800,and � 1300kms � 1 ,respectively.WealsopresentaGBTspectrumofapreviouslyknown source, Mrk 0034, and interpret the narrow Doppler components reported here as indirect evidence that the emission originatesinanedge-onaccretiondiskwithorbitalvelocityof � 500kms � 1 .Weobtainedadetectionrateof 12%(5out of 41) among Seyfert 2 and LINER systems with 10,000 km s � 1 < vsys < 15;000 km s � 1 . For the 30 nuclear water masers with available hard X-ray data, we report a possible relationship between unabsorbed X-ray luminosity (2Y10 keV) and total isotropic water maser luminosity, L2� 10 / L 0:5� 0:1 H2O , consistent with the model proposed by Neufeld and Maloney, in which X-ray irradiation and heating of molecular accretion disk gas by the central engine excites the maser emission. Subject headingg galaxies: active — galaxies: individual (2MASX J08362280+3327383, NGC 6264, UGC 09618 NED02, IRAS 03355+0104, SBS 0927+493, Markarian 0034, NGC 3393, NGC 5495, VII Zw 073, IC 0184, AM 2158� 380 NED02) — galaxies: Seyfert — ISM: jets and outflows — ISM: molecules — masers

Discovery of Water Maser Emission in Eight AGNs with 70 m Antennas of NASA’s Deep Space Network

We report the discovery of water maser emission in eight active galactic nuclei (AGNs) with the 70 m NASA Deep Space Network (DSN) antennas at Tidbinbilla, Australia, and Robledo, Spain. The positions of the newly discovered masers, measured with the VLA, are consistent with the optical positions of the host nuclei to within 1 σ (03 radio and 13 optical) and most likely mark the locations of the embedded central engines. The spectra of two sources, NGC 3393 and NGC 5495, display the characteristic spectral signature of emission from an edge-on accretion disk, with orbital velocities of ~600 and ~400 km s-1, respectively. In a survey with DSN facilities of 630 AGNs selected from the NASA Extragalactic Database, we have discovered a total of 15 water maser sources. The resulting incidence rate of maser emission among nearby (vsys < 7000 km s-1) Seyfert 1.8-2.0 and LINER systems is ~10% for a typical rms noise level of ~14 mJy over 1.3 km s-1 spectral channels. As a result of this work, the number of nearby AGNs (vsys < 7000 km s-1) observed with <20 mJy rms noise has increased from 130 to 449.

The Most Detailed Picture Yet of an Embedded High Mass YSO

High-mass star formation is not well understood chiefly because examples are deeply embedded, relatively distant, and crowded with sources of emission. Using VLA and VLBA observations of H2O and SiO maser emission, we have mapped in detail the structure and proper motion of material 20-500 AU from the closest high-mass YSO, radio source I in the Orion KL region. We observe streams of material driven in a rotating, wide angle, bipolar wind from the the surface of an edge-on accretion disk. The example of source I provides strong evidence that high-mass star formation proceeds via accretion.

A Warped Accretion Disk and Wide‐Angle Outflow in the Inner Parsec of the Circinus Galaxy

We present the first VLBI maps of H2O maser emission (lambda 1.3cm) in the nucleus of the Circinus Galaxy, constructed from data obtained with the Australia Telescope Long Baseline Array. The maser emission traces a warped, edge-on accretion disk between radii of 0.11+/-0.02 and ~0.40 pc, as well as a wide-angle outflow that extends up to ~1 pc from the estimated disk center. The disk rotation is close to Keplerian (v varies as 1/sqrt(r)), the maximum detected rotation speed is 260 km/s, and the inferred central mass is 1.7+/-0.3 x 10^6 solar masses. The outflowing masers are irregularly distributed above and below the disk, with relative outflow velocities up to ~+/-160 km/s, projected along the line of sight. The flow probably originates closer than 0.1 pc to the central engine, possibly in an inward extension of the accretion disk, though there is only weak evidence of rotation in the outward moving material. We observe that the warp of the disk appears to collimate the outflow and to fix the extent of the ionization cone observed on larger angular scales. This study provides the first direct evidence (i.e., through imaging) of dusty, high-density, molecular material in a nuclear outflow <1 pc from the central engine of a Seyfert galaxy, as well as the first graphic evidence that warped accretion disks can channel outflows and illumination patterns in AGN. We speculate that the same arrangement, which in some ways obviates the need for a geometrically thick, dusty torus, may apply to other type-2 AGN.

The X-Ray System R Aquarii: A Two-sided Jet and Central Source

We report Chandra ACIS-S3 X-ray imaging and spectroscopy of the R Aquarii binary system that show a spatially resolved two-sided jet and an unresolved central source. This is the first published report of such an X-ray jet seen in an evolved ∼2–3 M, stellar system. At keV, the X-ray jet extends to both the northeast E ! 1 (NE) and southwest (SW) relative to the central binary system. At keV, R Aqr is a pointlike source 1 ! E ! 7.1 centered on the star system. While both 3.5 cm radio continuum emission and X-ray emission appear coincident in projection and have maximum intensities at ∼7 .5 NE of the central binary system, the next strongest X-ray component is located ∼30 SW of the central binary system and has no radio continuum counterpart. The X-ray jets are likely shock-heated in the recent past and are not in thermal equilibrium. The strongest SW X-ray jet component may have been shocked recently since there is no relic radio emission as expected from an older shock. At the position of the central binary, we detect X-ray emission below 1.6 keV consistent with blackbody emission at K. There is also a prominent 6.4 keV feature, a possible fluorescence or collisionally 6 T ∼ 2 # 10 excited Fe Ka line from an accretion disk or from the wind of the giant star. For this excitation to occur, there must be an unseen hard source of X-rays or particles in the immediate vicinity of the hot star. Such a source would be hidden from view by the surrounding edge-on accretion disk. Subject headings: binaries: symbiotic — circumstellar matter — radio continuum: stars — stars: individual (R Aquarii) — stars: winds, outflows — white dwarfs — X-rays: general

Constraining the Black Hole Mass and Accretion Rate in the Narrow‐Line Seyfert 1 Galaxy RE J1034+396

We present a comprehensive study of the spectrum of the narrow-line Seyfert 1 (NLS1) galaxy RE J1034+396, summarizing the information obtained from the optical to X-rays with observations from the William Herschel 4.2 m Telescope, the Hubble Space Telescope, the Extreme Ultraviolet Explorer, ROSAT, ASCA, and BeppoSAX. The BeppoSAX spectra reveal a soft component which is well represented by two blackbodies with kTeff = 60 and 160 eV, mimicking that expected from a hot, optically thick accretion disk around a low-mass black hole. This is borne out by our modeling of the optical-to-X-ray nuclear continuum, which constrains the physical parameters of a NLS1 for the first time. The models demonstrate that RE J1034+396 is likely to be a system with a nearly edge-on accretion disk (60°-75° from the disk axis), accreting at nearly Eddington rates (0.3-0.7LEdd) onto a low-mass black hole (Mbh ~ 2-10 × 106 M☉). This is consistent with the hypothesis that NLS1s are Seyfert-scale analogies of galactic black hole candidates. The unusually high temperature of the big blue bump reveals a flat power-law-like continuum in the optical/UV which is consistent with an extrapolation to the hard X-ray power law, and which we speculate may be similar to the continuum component observed in BL Lac objects in their quiescent periods. From the BeppoSAX and ASCA data, we find that the slope of the hard X-ray power law depends very much on the form of the soft component which is assumed. For our best-fitting models, it lies somewhere between α = 0.7 and 1.3 and thus may not be significantly softer than active galactic nuclei in general.

Accretion and Outflow Traced by H2O Masers in the Circinus AGN

The first VLBI images of H2O maser emission in the Circinus Galaxy AGN show both a warped, edge-on accretion disk and an outflow 0.1 to 1 pc from the central engine. The inferred central mass is 1.3 × 106 M⊙, while the disk mass may be on the order of 105 M⊙, based on a nearly Keplerian rotation curve. The bipolar, wide-angle outflow appears to contain “bullets” ejected from within &lt; 0.1 pc of the central mass. The positions of filaments and bullets observed in the AGN ionization cone on kpc-scales suggest that the disk channels the flow to a radius of ∼ 0.4 pc, at which the flow appears to disrupt the disk.

A Variable Asymmetry in the Circumstellar Disk of HH 30

We report Hubble Space Telescope observations of variability within the reflection nebulosity of HH 30, a compact bipolar nebula which is a nearly edge-on accretion disk system.

Symmetric Parsec-Scale Radio Jets in NGC 4261

AbstractVLBA observations of NGC 4261 (3C 270) reveal highly symmetric radio structures at both 1.6 and 8.4 GHz. There is little evidence for free-free absorption in the inner few pc, despite the fact that HST imaging shows this galaxy to contain a nearly edge-on disk of gas and dust in its nucleus. However, at our highest resolution we find a narrow gap in emission just east of the radio core which we interpret as evidence for a small (sub-parsec) nearly edge-on accretion disk which is obscuring the base of the counterjet. The position angle of the pc-scale radio axis agrees with the position angle of the VLA-scale jets, which differs from the apparent rotation axis of the nuclear disk seen by HST.

The Nuclear Region of M51 Imaged with the HST Planetary Camera

We present high-resolution, broad- and narrow-band, pre-refurbishment images of the central region of M51 taken with the Planetary Camera of the Hubble Space Telescope. The V-band images show a rather chaotic distribution of dust lanes, though some are oriented radially, roughly aligned with the major axis of the bar, and may be transporting gas to the AGN in the nucleus. The dust lane obscuring the nucleus of the galaxy, which was previously thought to be an edge-on accretion disk feeding the AGN, is not centered on the nucleus. It is unlikely that this is a stable configuration, suggesting that the material has only recently entered the nuclear region. The nucleus is contained within a cluster of stars having a total luminosity of order 5x10^7 L_0. Fitting a King model to the least obscured portions of the cluster yields a maximum core radius of 14 pc. The morphology apparent in the forbidden-line images of the extra-nuclear cloud is consistent with a narrow jet striking and scattering off the boundary of a relatively dense cocoon of gas in the disk of the galaxy. The emission-line regions are concentrated along the inner borders of dust filaments, supporting the view that the nuclear jet is ramming into and stirring up the ISM of the disk.

Further probing of the X-ray source in NGC 4151: new constraints on the nuclear geometry

We report on the results of new Ginga observations of the archetypal Seyfert galaxy, NGC 4151, performed over an 18-month period between early 1990 and mid-1991. The present program complements earlier extensive monitoring of this source in the medium-energy X-ray band by both EXOSAT and Ginga to give a combined data set of some 36 separate observations made over a period of 8 years. The new observations bring to light a remarkable transient change in the low-energy extinction and soft X-ray excess apparent in the X-ray spectrum of NGC 4151. The spectrum became systematically softer below about 4 keV from mid-1988, with the spectral softness peaking in mid-1990 and then reverting to its former state by late 1990. Interpreting this in terms of the partial covering model, the covered fraction of the source, which normally takes a value of 80-90 percent, underwent a sharp decline to about 20 percent over a 2-year period and then returned to the canonical level over the following six months. This observation favors the presence of a normally stable 'bulk' structure such as an edge-on accretion disk. A transitory change of azimuthal structure in the disk could then account for the apparent dip in the covered fraction. If the central X-ray source radiates isotropically then the medium producing the bulk of the iron-line emission must deviate from a spherically symmetric distribution.