Hole In NGC Research Articles

XMM-Newton and Chandra observations of the globular cluster NGC 6388

Context. By studying the optical brightness surface density of the globular cluster NGC 6388, it has been recently proposed that it harbors a central intermediate-mass black hole with mass ≃5.7 x 10 3 M ⊙ . Aims. We expect that the compact object in the center of NGC 6388 emits radiation in the X-ray band as a consequence of the accretion from the surrounding matter. We searched for XMM-Newton and Chandra observations towards NGC 6388 to test this hypothesis. Methods. We determine both the hardness ratios and luminosity with a minimum set of assumptions for each of the identified field sources. Results. The Chandra satellite disentangles several point-like X-ray sources, probably low mass X-ray binaries, well within the core radius of the globular cluster. However, three of them, coinciding with the cluster center of gravity, remain unresolved. Their total luminosity is L Obs X ≃ 2.7 x 10 33 erg s -1 . If one of these sources is the X-ray counterpart of the intermediate-mass black hole in NGC 6388, the corresponding upper limit on the accretion efficiency, with respect to the Eddington luminosity, is 3 x 10 -9 . This measurement could be tightened if moderately deep radio observations of the field were performed.

Locating the Two Black Holes in NGC 6240

Mergers play an important role in galaxy evolution and are key to understanding the correlation between central-black hole mass and host-galaxy properties. We used the new technology of adaptive optics at the Keck II telescope to observe NGC 6240, a merger between two disk galaxies. Our high-resolution near-infrared images, combined with radio and x-ray positions, revealed the location and environment of two central supermassive black holes. Each is at the center of a rotating stellar disk, surrounded by a cloud of young star clusters. The brightest of these young clusters lie in the plane of each disk, but surprisingly are seen only on the disks' receding side.

A Reverberation‐based Mass for the Central Black Hole in NGC 4151

We have undertaken a new ground-based monitoring campaign to improve the estimates of the mass of the central black hole in NGC 4151. We measure the lag time of the broad H? line response compared to the optical continuum at 5100 ? and find a lag of 6.6 days. We combine our data with the recent reanalysis of UV emission lines by Metzroth and coworkers to calculate a weighted mean of the black hole mass, MBH = (4.57) ? 107 M?. The absolute calibration of the black hole mass is based on normalization of the AGN black hole mass-stellar velocity dispersion (MBH-?*) relationship to that of quiescent galaxies by Onken and coworkers. The scatter in the MBH-?* relationship suggests that reverberation-mapping-based mass measurements are typically uncertain by a factor of 3-4.

The black hole in NGC 3379: a comparison of gas and stellar dynamical mass measurements with HST and integral-field data

We combine Hubble Space Telescope spectroscopy and ground-based integral-field data from the SAURON and OASIS instruments to study the central black hole in the nearby elliptical galaxy NGC 3379. From these data, we obtain kinematics of both the stars and the nuclear gaseous component. Axisymmetric three-integral models of the stellar kinematics find a black hole of mass 1.4 +2.6 -1.0 x 10 8 M ⊙ (3σ errors). These models also probe the velocity distribution in the immediate vicinity of the black hole and reveal a nearly isotropic velocity distribution throughout the galaxy and down to the black hole sphere of influence R BH . The morphology of the nuclear gas disc suggests that it is not in the equatorial plane; however the core of NGC 3379 is nearly spherical. Inclined thin-disc models of the gas find a nominal black hole of mass (2.0 ± 0.1) x 10 8 M ⊙ (3a errors), but the model is a poor fit to the kinematics. The data are better fit by introducing a twist in the gas kinematics (with the black hole mass assumed to be 2.0 x 10 8 M ⊙ ), although the constraints on the nature and shape of this perturbation are insufficient for more detailed modelling. Given the apparent regularity of the gas disc appearance, the presence of such strong non-circular motion indicates that caution must be used when measuring black hole masses with gas dynamical methods alone.

Streaming Motions toward the Supermassive Black Hole in NGC 1097

We have used GMOS-IFU and high-resolution HST-ACS observations to map, in unprecedented detail, the gas velocity field and structure within the 0.7 kpc circumnuclear ring of the SBb LINER/Seyfert 1 galaxy NGC 1097. We find clear evidence of radial streaming motions associated with spiral structures leading to the unresolved (<3.5 pc) nucleus, which we interpret as part of the fueling chain by which gas is transported to the nuclear starburst and supermassive black hole.

Precession of the super-massive black hole in NGC 1275 (3C 84)?

The X-ray holes at the centre of the Perseus Cluster of galaxies are not all at the same position angle with respect to the centre of the cluster. This configuration would result if the jet inflating the bubbles is precessing, or moving around, and the bubbles detach at different times. The orientations which best fit the observed travel directions are an inclination of the precession axis to the line of sight of 120 degrees and an opening angle of 50 degrees. From the timescales for the bubbles seen in the cluster, the precession timescale, t_prec, is around 3.3x10^7 yrs. The bubbles rising up through different parts of the cluster may have interacted with the central cool gas, forming the whorl of cool gas observed in the temperature structure of the cluster. The dynamics of bubbles rising in fluids is discussed. The conditions present in the cluster are such that oscillatory motion, observed for bubbles rising in fluids on Earth, should take place. However the timescale for this motion is longer than that taken for the bubbles to evolve into spherical cap bubbles, which do not undergo a path instability, so such motion is not expected to occur.

The Low End of the Supermassive Black Hole Mass Function: Constraining the Mass of a Nuclear Black Hole in NGC 205 via Stellar Kinematics

Hubble Space Telescope (HST) images and spectra of the nucleated dwarf elliptical galaxy NGC 205 are combined with 3-integral axisymmetric dynamical models to constrain the mass (M_BH) of a putative nuclear black hole. This is only the second attempt, after M33, to use resolved stellar kinematics to search for a nuclear black hole with mass below 10^6 solar masses. We are unable to identify a best-fit value of M_BH in NGC 205; however, the data impose a upper limit of 2.2x10^4 M_sun (1sigma confidence) and and upper limit of 3.8x10^4 M_sun (3sigma confidence). This upper limit is consistent with the extrapolation of the M_BH-sigma relation to the M_BH < 10^6 M_sunregime. If we assume that NGC 205 and M33 both contain nuclear black holes, the upper limits on M_BH in the two galaxies imply a slope of ~5.5 or greater for the M_BH-sigma relation. We use our 3-integral models to evaluate the relaxation time (T_r) and stellar collision time (T_coll) in NGC 205; T_r~10^8 yr or less in the nucleus and T_coll~10^11 yr. The low value of T_r is consistent with core collapse having already occurred, but we are unable to draw conclusions from nuclear morphology about the presence or absence of a massive black hole.

Supermassive black hole mass measurements for NGC 1300 and 2748 based on Hubble Space Telescope emission-line gas kinematics

We present Space Telescope Imaging Spectrograph emission-line spectra of the central regions of the spiral galaxies NGC 1300 and 2748. From the derived kinematics of the nuclear gas we have found evidence for central supermassive black holes in both galaxies. The estimated masses of the black holes in NGC 1300 and 2748 are (6.6 +6.3) × 10 7 and (4.4 +3.5) × 10 7 M� , respectively (both at the 95 per cent confidence level). These two black hole mass estimates contribute to the poorly sampled low-mass end of the nuclear black hole mass spectrum. Ke yw ords: black hole physics ‐ galaxies: individual: NGC 1300 ‐ galaxies: individual: NGC 2748 ‐ galaxies: kinematics and dynamics ‐ galaxies: nuclei ‐ galaxies: spiral.

Probable intermediate-mass black holes in NGC 4559: XMM-Newton spectral and timing constraints

We have examined X-ray and optical observations of two ultraluminous X-ray sources, X7 and X10 in NGC 4559, using XMM-Newton, Chandra and the Hubble Space Telescope (HST). The ultraviolet/X-ray luminosity of X7 exceeds 2.1 x 10(40) erg s(-1) in the XMM-Newton observation, and that of X10 is > 1.3 x 10(40) erg s(-1). X7 has both thermal and power-law spectral components, The characteristic temperature of the thermal component is 0.12 keV. The power-law components in the two sources both have slopes with photon index similar or equal to2.1. A timing analysis of X7 indicates a break frequency at 28 MHz in the power spectrum, while that for X10 is consistent with an unbroken power law. The luminosity of the blackbody component in the X-ray spectrum of X7 and the nature of its time-variability provides evidence that this object is an intermediate-mass black hole accreting at sub-Eddington rates, but other scenarios which require high advection efficiencies from a hollowed-out disc might be possible. The emission from X10 can be characterized by a single power-law. This source can be interpreted either as an intermediate-mass black hole, or as a stellar mass black hole with relativistically beamed Comptonized emission. There are four optical counterparts in the error circle of X7. No counterparts are evident in the error circle for X10.

On the origin of circular and hexagonal formations in galaxies

Round and arc-shaped formations are known in some galaxies, the Bubble complex (the Hodge object) in NGC 6946 being the most remarkable. The rim of the complex has the form of a regular arc in which part of a hexagonal structure is embedded. A similar morphology is recognized in the NGC 7421 galaxy in the part of its rim which is leading in the galaxy motion through the intergalactic gas, as suggested by the bow-shock appearance of the H I halo of the galaxy. A hexagonal shape is also found in the NGC 4676A galaxy. The H II radial velocities across the Bubble complex are compatible with its retrograde rotation and drift, which are characteristic of solitary vortices known in nonlinear hydrodynamics. The drift motion may explain the location of the Bubble complex at the tip of the largest elliptical H I hole in NGC 6946. The hexagonal vortices in the atmospheres of Jupiter and Saturn are within the gas streams, which seems to be suggestive as well. It is conjectured that the hexagonal rims of stellar systems might be relicts of flat segments of the shock wave produced by the ram pressure. The giant stellar arcs in NGC 300 and M33 are associated with the high-energy X-ray sources P42 and X-4 respectively and these might be the relics of hypernovae.

X‐Ray Emission from a Merger Remnant, NGC 7252 (the “Atoms‐for‐Peace” Galaxy)

We observed a nearby merger remnant NGC 7252 with the X-ray satellite ASCA and detected X-ray emission with the X-ray flux of (1.8 ± 0.3) × 10-13 ergs s-1 cm-2 in the 0.5-10 keV band. This corresponds to the X-ray luminosity of 8.1 × 1040 ergs s-1. The X-ray emission is well described with a two-component model: a soft component with kT = 0.72 ± 0.13 keV and a hard component with kT > 5.1 keV. Although NGC 7252 is referred to as a dynamically young protoelliptical, the 0.5-4 keV luminosity of the soft component is about 2 × 1040 ergs s-1, which is low for an early-type galaxy. The ratio of LX/LFIR suggests that the soft component originated from the hot gas due to star formation. Its low luminosity can be explained by the gas ejection from the galaxy as galaxy winds. Our observation reveals the existence of hard X-ray emission with the 2-10 keV luminosity of 5.6 × 1040 ergs s-1. This may indicate the existence of nuclear activity or an intermediate-mass black hole in NGC 7252.

ITAL]Chandra[/ITAL] Limits on X-Ray Emission Associated with the Supermassive Black Holes in Three Giant Elliptical Galaxies

Elliptical galaxy nuclei are the sites of the largest black holes known but typically show little or no nuclear activity. We investigate this extreme quiescence using Chandra X-Ray Observatory observations of the giant elliptical galaxies NGC 1399, NGC 4472, and NGC 4636. The unique Chandra imaging power enables us to place upper limits of 7.3, 15, and 28 × 10-9LEdd for the ~108-109 M☉ black holes in NGC 1399, NGC 4472, and NGC 4636, respectively. The corresponding radiative efficiencies in this band are 4.1, 24, and 620 × 10-6 using Bondi accretion rates derived from the Chandra hot interstellar gas surface brightness profiles. These limits are inconsistent with basic advection-dominated accretion flow models for NGC 1399 and NGC 4472, indicating accretion onto the black hole at 10% of the Bondi rate.

Axisymmetric, Three-Integral Models of Galaxies: A Massive Black Hole in NGC 3379

We fit axisymmetric three-integral dynamical models to NGC 3379 using the line-of-sight velocity distribution obtained from Hubble Space Telescope FOS spectra of the galaxy center and ground-based long-slit spectroscopy along four position angles, with the light distribution constrained by WFPC2 and ground-based images. We have fitted models with inclinations from 29° (intrinsic galaxy type E5) to 90° (intrinsic E1) and black hole masses from 0 to 109 M⊙. The best-fit black hole masses range from 6 × 107 to 2 × 108 M⊙, depending on inclination. The preferred inclination is 90° (edge-on); however, the constraints on allowed inclination are not very strong, owing to our assumption of constant M/LV. The velocity ellipsoid of the best model is not consistent with either isotropy or a two-integral distribution function. Along the major axis, the velocity ellipsoid becomes tangential at the innermost bin, radial in the midrange radii, and tangential again at the outermost bins. The rotation rises quickly at small radii owing to the presence of the black hole. For the acceptable models, the radial-to-tangential [(σ + σ)/2] dispersion in the midrange radii ranges over 1.1 < σr/σt < 1.7, with the smaller black holes requiring larger radial anisotropy. Compared with these three-integral models, two-integral isotropic models overestimate the black hole mass since they cannot provide adequate radial motion. However, the models presented in this paper still contain restrictive assumptions—namely, assumptions of constant M/LV and spheroidal symmetry—requiring yet more models to study black hole properties in complete generality.

Stellar and Ionized Gas Kinematics in the Circumnuclear Region of the Galaxy NGC 7331

We present simultaneous two-dimensional spectroscopy of the circumnuclear region (12'' × 9'') of the galaxy NGC 7331, obtained with an optical fiber system coupled to the ISIS double spectrograph of the 4.2 m William Herschel Telescope. The system allows simultaneous observation of 125 regions of this galaxy in two spectral ranges: 4590-5400 A at high resolution (1.5 A) and 6400-9620 A at low resolution (5 A). These spectra are mainly used to study the stellar and gas kinematics in the innermost region of this galaxy. The stellar velocity fields inferred from the Mg I b and Ca II absorption lines are in good agreement. They show a solid-body rotational pattern with the line of nodes along the position angle of the apparent major axis of the galaxy. The relatively large local stellar velocity dispersion suggests that we are observing the bulge rather than the disk kinematics. The two-dimensional kinematic data agree with previous one-dimensional studies that found no evidence for a massive black hole in NGC 7331. The [O III] emission lines are split into three components. One is distributed around the systemic velocity, another is systematically blueshifted, and the last is systematically redshifted. We propose that these arise from two distinct gaseous systems: a warped disk of irregular rotational pattern with the kinematic axes shifted by about 30° with respect to those of the stars, and a shell of gas flowing radially. Although alternative interpretations in terms of inflow driven by a central bar or outflow produced by a galactic wind are possible, the latter seems preferable. In NGC 7331 the ionized gas and stars are kinematically decoupled, the velocity dispersion of the ionized gas being substantially lower than that of the stars. This last result differs from what is generally found in Seyfert galaxies. However, NGC 7331 and M31 show a large degree of similarity, and the type of LINERs that they harbor are probably produced by the same type of phenomenon.