Massive Dark Objects Research Articles

WISDOM project – XIV. SMBH mass in the early-type galaxies NGC 0612, NGC 1574, and NGC 4261 from CO dynamical modelling

ABSTRACT We present a CO dynamical estimate of the mass of the supermassive black hole (SMBH) in three nearby early-type galaxies: NGC 0612, NGC 1574, and NGC 4261. Our analysis is based on Atacama Large Millimeter/submillimeter Array (ALMA) Cycle 3–6 observations of the 12CO(2–1) emission line with spatial resolutions of 14–58 pc (0.01″–0.26″). We detect disc-like CO distributions on scales from ≲ 200 pc (NGC 1574 and NGC 4261) to ≈10 kpc (NGC 0612). In NGC 0612 and NGC 1574 the bulk of the gas is regularly rotating. The data also provide evidence for the presence of a massive dark object at the centre of NGC 1574, allowing us to obtain the first measure of its mass, MBH = (1.0 ± 0.2) × 108 M⊙ (1σ uncertainty). In NGC 4261, the CO kinematics is clearly dominated by the SMBH gravitational influence, allowing us to determine an accurate black hole mass of (1.62 ± 0.04) × 109 M⊙ (1σ uncertainty). This is fully consistent with a previous CO dynamical estimate obtained using a different modelling technique. Signs of non-circular gas motions (likely outflow) are also identified in the inner regions of NGC 4261. In NGC 0612, we are only able to obtain a (conservative) upper limit of MBH ≲ 3.2 × 109 M⊙. This has likely to be ascribed to the presence of a central CO hole (with a radius much larger than that of the SMBH sphere of influence), combined with the inability of obtaining a robust prediction for the CO velocity curve. The three SMBH mass estimates are overall in agreement with predictions from the MBH − σ* relation.

Dilaton-axion black hole lensing and its relativistic images

Appraising a massive dark object at the centre of our galaxy, we analyse gravitational lensing effect for dilaton-axion black hole. We have explored angular positions, magnifications, time delay, effective deflection angle as well as differential time delay of both primary and secondary first order as well as second order images for such kind of black hole spacetime.

Black Holes and the Supermassive Compact Object at the Galactic Center: Multi-arts of Thought and Nature

Black Holes and the Supermassive Compact Object at the Galactic Center: Multi-arts of Thought and Nature

The role of self-interacting right-handed neutrinos in galactic structure

It has been shown previously that the DM in galactic halos can be explained by a self-gravitating system of massive keV fermions (`inos') in thermodynamic equilibrium, and predicted the existence of a denser quantum core of inos towards the center of galaxies. In this article we show that the inclusion of self-interactions among the inos, modeled within a relativistic mean-field-theory approach, allows the quantum core to become massive and compact enough to explain the dynamics of the S-cluster stars closest to the Milky Way's galactic center. The application of this model to other galaxies such as large elliptical harboring massive central dark objects of ∼ 109 M⊙ is also investigated. We identify these interacting inos with sterile right-handed neutrinos pertaining to minimal extensions of the Standard Model, and calculate the corresponding total cross-section σ within an electroweak-like formalism to be compared with other observationally inferred cross-section estimates. The coincidence of an ino mass range of few tens of keV derived here only from the galactic structure, with the range obtained independently from other astrophysical and cosmological constraints, points towards an important role of the right-handed neutrinos in the cosmic structure.

Probing hybrid modified gravity by stellar motion around Galactic Center

We consider possible signatures for the so called hybrid gravity within the Galactic Central Parsec. This modified theory of gravity consists of a superposition of the metric Einstein–Hilbert Lagrangian with an f(R) term constructed à la Palatiniand can be easily reduced to an equivalent scalar–tensor theory. Such an approach is introduced in order to cure the shortcomings related to f(R) gravity, in general formulated either in metric or in metric-affine frameworks. Hybrid gravity allows to disentangle the further gravitational degrees of freedom with respect to those of standard General Relativity. The present analysis is based on the S2 star orbital precession around the massive compact dark object at the Galactic Center where the simulated orbits in hybrid modified gravity are compared with astronomical observations. These simulations result with constraints on the range of hybrid gravity interaction parameter ϕ0, showing that in the case of S2 star it is between −0.0009 and −0.0002. At the same time, we are also able to obtain the constraints on the effective mass parameter mϕ, and found that it is between −0.0034 and −0.0025 AU−1 for S2 star. Furthermore, the hybrid gravity potential induces precession of S2 star orbit in the same direction as General Relativity. In previous papers, we considered other types of extended gravities, like metric power law f(R)∝Rn gravity, inducing Yukawa and Sanders-like gravitational potentials, but it seems that hybrid gravity is the best among these models to explain different gravitational phenomena at different astronomical scales.

Properties of resonantly produced sterile neutrino dark matter subhaloes

The anomalous 3.55 keV X-ray line recently detected towards a number of massive dark matter objects may be interpreted as the radiative decays of 7.1 keV mass sterile neutrino dark matter. Depending on its parameters, the sterile neutrino can range from cold to warm dark matter with small-scale suppression that differs in form from commonly-adopted thermal warm dark matter. Here, we numerically investigate the subhalo properties for 7.1 keV sterile neutrino dark matter produced via the resonant Shi-Fuller mechanism. Using accurate matter power spectra, we run cosmological zoom-in simulations of a Milky Way-sized halo and explore the abundance of massive subhalos, their radial distributions, and their internal structure. We also simulate the halo with thermal 2.0 keV warm dark matter for comparison and discuss quantitative differences. We find that the resonantly produced sterile neutrino model for the 3.55 keV line provides a good description of structures in the Local Group, including the number of satellite dwarf galaxies and their radial distribution, and largely mitigates the too-big-to-fail problem. Future searches for satellite galaxies by deep surveys, such as the Dark Energy Survey, Large Synoptic Survey Telescope, and Wide Field Infrared Survey Telescope, will be a strong direct test of warm dark matter scenarios.

Constraining the range of Yukawa gravity interaction from S2star orbits

We consider possible signatures for Yukawa gravity within theGalactic Central Parsec, based on our analysis of the S2 star orbitalprecession around the massive compact dark object at the GalacticCentre, and on the comparisons between the simulated orbits in Yukawa gravityand two independent sets of observations. Our simulations resulted in strongconstraints on the range of Yukawa interaction Λ and showed that itsmost probable value in the case of S2 star is around 5000 - 7000 AU. Atthe same time, we were not able to obtain reliable constrains onthe universal constant δ of Yukawa gravity, because thecurrent observations of S2 star indicated that it may be highlycorrelated with parameter Λ in the range (0 < δ < 1).For δ > 2 they are not correlated. However, the same universal constant whichwas successfully applied to clusters of galaxies and rotation curvesof spiral galaxies (δ = 1/3) also gives a satisfactory agreement withthe observed orbital precession of the S2 star, and in that casethe most probable value for the scale parameter is Λ ≈ 3000±1500 AU. Also, the Yukawa gravity potential induces precession of S2 starorbit in the same direction as General Relativity for δ > 0 and forδ < −1, and in the opposite direction for −1 < δ < 0. The futureobservations with advanced facilities, such as GRAVITY or/and European ExtremelyLarge Telescope, are needed in order to verify these claims.

Catalog of nearby isolated galaxies in the volume z &lt; 0.01

We present a catalog of 520 most isolated nearby galaxies with angular velocities V LG < 3500 km/s, covering the entire sky. This population of “space orphans” makes up 4.8% among 10 900 galaxies with measured radial velocities. We describe the isolation criterion used to select our sample, called the “Local Orphan Galaxies”(LOG), and discuss their basic optical and HI properties. A half of the LOG catalog is occupied by the Sdm, Im and Ir morphological type galaxies without a bulge. The median ratio M gas/M star in the LOG galaxies exceeds 1. The distribution of the catalog galaxies on the sky looks uniform with some signatures of a weak clustering on the scale of about 0.5 Mpc. The LOG galaxies are located in the regions where the mean local density of matter is approximately 50 times lower than the mean global density. We indicate a number of LOG galaxies with distorted structures, which may be the consequence of interaction of isolated galaxies with massive dark objects.

Relativistic images of Schwarzschild black hole lensing

We model massive dark objects at centers of many galaxies as Schwarzschild black hole lenses and study gravitational lensing by them in detail. We show that the ratio of mass of a Schwarzschild lens to the differential time delay between outermost two relativistic images (both of them either on the primary or on the secondary image side) is extremely insensitive to changes in the angular source position as well as the lens-source and lens-observer distances. Therefore, this ratio can be used to obtain very accurate values for masses of black holes at centers of galaxies. Similarly, angular separations between any two relativistic images are also extremely insensitive to changes in the angular source position and the lens-source distance. Therefore, with the known value of mass of a black hole, angular separation between two relativistic images would give a very accurate result for the distance of the black hole. Accuracies in determination of masses and distances of black holes would however depend on accuracies in measurements of differential time delays and angular separations between images. Deflection angles of primary and secondary images as well as effective deflection angles of relativistic images on the secondary image side are always positive. However, the effective deflection angles of relativistic images on the primary image side may be positive, zero, or negative depending on the value of angular source position and the ratio of mass of the lens to its distance. We show that effective deflection angles of relativistic images play significant role in analyzing and understanding strong gravitational field lensing.

Time delay and magnification centroid due to gravitational lensing by black holes and naked singularities

We model the massive dark object at the center of the Galaxy as a Schwarzschild black hole as well as Janis-Newman-Winicour naked singularities, characterized by the mass and scalar charge parameters, and study gravitational lensing (particularly time delay, magnification centroid, and total magnification) by them. We find that the lensing features are qualitatively similar (though quantitatively different) for Schwarzschild black holes, weakly naked, and marginally strongly naked singularities. However, the lensing characteristics of strongly naked singularities are qualitatively very different from those due to Schwarzschild black holes. The images produced by Schwarzschild black hole lenses and weakly naked and marginally strongly naked singularity lenses always have positive time delays. On the other hand, strongly naked singularity lenses can give rise to images with positive, zero, or negative time delays. In particular, for a large angular source position the direct image (the outermost image on the same side as the source) due to strongly naked singularity lensing always has a negative time delay. We also found that the scalar field decreases the time delay and increases the total magnification of images; this result could have important implications for cosmology. As the Janis-Newman-Winicour metric also describes the exterior gravitational field of a scalar star, naked singularities as well as scalar star lenses, if these exist in nature, will serve as more efficient cosmic telescopes than regular gravitational lenses.

Probe of Dark Galaxies via Disturbed/Lopsided Isolated Galaxies

AbstractSearching for lopsided/interacting objects among 1500 isolated galaxies yields only eight strongly disturbed galaxies which may be explained as a result of their interaction with massive dark objects. We present results of spectral and photometric observations of these galaxies performed with the 6-m telescope that lead to significant restriction on cosmic abundance of dark galaxies.

Microlensing Surveys of M31 in the Wide‐Field Imaging Era

The Andromeda Galaxy (M31) is the closest large galaxy to the Milky Way, thus it is an important laboratory for studying massive dark objects in galactic halos (MACHOs) by gravitational microlensing. Such studies strongly complement the studies of the Milky Way halo using the the Large and Small Magellanic Clouds. We consider the possibilities for microlensing surveys of M31 using the next generation of wide field imaging telescopes with fields of view in the square degree range. We consider proposals for such imagers both on the ground and in space. For concreteness, we specialize to the SNAP proposal for a space telescope and the LSST proposal for a ground based telescope. We find that a modest space-based survey of 50 visits of one hour each is considerably better than current ground based surveys covering 5 years. Crucially, systematic effects can be considerably better controlled with a space telescope because of both the infrared sensitivity and the angular resolution. To be competitive, 8 meter class wide-field ground based imagers must take exposures of several hundred seconds with several day cadence.

Microlensing Candidates in M87 and the Virgo Cluster with theHubble Space Telescope

The position of the giant elliptical galaxy M87 at the center of the Virgo Cluster means that the inferred column density of dark matter associated with both the cluster halo and the galaxy halo is quite large. This system is thus an important laboratory for studying massive dark objects in elliptical galaxies and galaxy clusters by gravitational microlensing, strongly complementing the studies of spiral galaxy halos performed in the Local Group. We have performed a microlensing survey of M87 with the WFPC2 instrument on the Hubble Space Telescope. Over a period of 30 days, with images taken once daily, we discover seven variable sources. Four are variable stars of some sort, two are consistent with classical novae, and one exhibits an excellent microlensing light curve, although with a very blue color, implying the somewhat disfavored possibility of a horizontal-branch source being lensed. On the basis of sensitivity calculations from artificial stars and from artificial light curves, we estimate the expected microlensing rate. We find that the detection of one event is consistent with a dark halo with a 20% contribution of microlensing objects for both M87 and the Virgo Cluster, similar to the value found from observations in the Local Group. Further work is required to test the hypothesized microlensing component to the cluster.

The Detection of Pure Dark Matter Objects with Bent Multiply Imaged Radio Jets

When a gravitational lens produces two or more images of a quasar's radio jet the images can be compared to reveal the presence of small structures along one or more of the lines of sight. If mass is distributed smoothly on scales of <~ 10^7 Msun independent bends in the jet images on milli-arcsecond scales will not be produced. All three of the well collimated multiply imaged radio jets that have been mapped on milli-arcsecond scales show some evidence of independent bends in their images. Using existing data we model the lens system B1152+199 and show that it likely contains a substructure of mass ~10^5 - 10^7 h^-1 Msun or a velocity dispersion of ~ 10 km/s. An alternative explanation is that an intrinsic bend in the jet is undetected in one image and magnified in the other. This explanation is disfavored and future observations could remove any ambiguity that remains. The probability of a radio jet being bent by small scale structure both inside and outside of the host lens is then investigate. The known populations of dwarf galaxies and globular clusters are far too small to make this probability acceptable. A previously unknown population of massive dark objects is needed. The standard Cold Dark Matter (CDM) model might be able to account for the observations if small mass halos are sufficiently compact. In other cosmological models where small scale structure is suppressed, such as standard Warm Dark Matter (WDM), the observed bent jets would be very unlikely to occur.

Dynamical modeling of the stellar nucleus of M 31

We present stellar dynamical models of the lopsided, double{peaked nucleus of M 31, derived from Hubble Space Telescope (HST) photometry. A Schwarzschild{type method, in conjunction with Richardson{Lucy deconvolution, was employed to construct steadily rotating, hot, stellar disks. The stars orbit a massive dark object, on prograde and retrograde quasi{periodic loop orbits. Our results support Tremaine's eccentric disk model, extended to include a more massive disk, non zero pattern speed (), and dierent viewing angle. Most of the disk mass populated prograde orbits, with'3.4% on retrograde orbits. The best ts to photometric and kinematic maps were disks with' 16 km s 1 pc 1 . We speculate on the origins of the lopsidedness, invoking recent work on the linear overstability of nearly Keplerian disks, that possess even a small amount of a counter { rotating component. Accretion of material { no more massive than a globular cluster { onto a preexisting stellar disk, will account for the mass in our retrograde orbits, and could have stimulated the lopsidedness seen in the nucleus of M 31.

Gravitational lensing by naked singularities

We model massive dark objects in galactic nuclei as spherically symmetric static naked singularities in the Einstein massless scalar field theory and study the resulting gravitational lensing in detail. Based on whether or not a naked singularity is covered within a photon sphere we classify naked singularities into two kinds: weakly naked (those contained within at least one photon sphere) and strongly naked (those not contained within any photon sphere). The qualitative features of gravitational lensing due to a weakly naked singularity are similar to those due to a Schwarzschild black hole (these give rise to one Einstein ring but no radial critical curve). However, the gravitational lensing due to a strongly naked singularity is qualitatively different from that due to a Schwarzschild black hole; a strongly naked singularity gives rise to either two or nil Einstein ring(s) and one radial critical curve. A light ray passing close to a photon sphere of a black hole or a weakly naked singularity goes around its photon sphere once, twice, or many times (before reaching an observer) depending upon the impact parameter and thus gives rise to a sequence of theoretically infinite number of relativistic images, which are highly demagnified. A strongly naked singularity produces no relativistic images.

Supermassive Black Holes in Galactic Nuclei

We discuss the link between the observations of distant quasars and those of massive dark objects in the cores of many local galaxies. We show how the formation of early black holes gives rise to the luminosity function of high-z quasars, while it imprints into their dark local relics a related shape of the correlation between masses and galaxy velocity dispersions. We propose that in its lower section, the correlation slope will reveal the (otherwise uncertain) strength of the feedback effects from the later quasar activity on the host galaxies.

Formation of a proto-quasar from accretion flows in a halo

We present a detailed model for the formation of massive objects at the centers of galaxies. The effects of supernovae heating and the conditions of gas loss are revisited. The escape time of the gas is compared with the cooling time, which provides an additional condition not previously considered. Its consequences for the allowed mass range of the halo is calculated and parameterized in terms of the spin parameter, , the redshift of collapse, zc, the fraction of baryons in stars, , and the efficiency of supernovae, ν. It is shown that sufficient gas is retained to form massive dark objects and quasars even for moderately massive halos but a decline is expected at low redshifts. Subsequently, a gaseous disk forms with a radial extent of a kpc, spun up by tidal torques and magnetized by supernovae fields with fields strengths of 10-100 . In a model of a self-similar accretion flow in an initially dominant halo, it is shown that for typical halo parameters, about accretes via small magnetic stresses (or alternatively by self-gravity induced instability or by alpha viscosity) in 108 years into a compact region. A model of a self-gravitating evolution of a compact magnetized disk ( pc), which is relevant when a significant fraction of the disk mass falls in, is presented, and it has a rapid collapse time scale of a million years. The two disk solutions, one for accretion in an imposed halo potential and the other for a self-gravitating disk, obtained here, have general utility and can be adapted to other contexts like protostellar disks as well. Implications of this work for dwarf galaxy formation, and a residual large scale seed field, are also breifly discussed.

Evidence for a massive dark object in NGC 4350

ABSTRACT In this work we build a detailed dynamic model for a S0 galaxy possibly hostinga central massive dark object (MDO). We show that the photometric profiles and thekinematics along the major and minor axes, including the h 3 and h 4 profiles, imply thepresence of a central MDO of mass M MDO ∼ 1.5−9.7· 10 8 M ⊙ , i.e. 0.3−2.8% of themass derived for the stellar spheroidal component. Models without MDO are unableto reproduce the kinematic properties of the inner stars and of the rapidly rotatingnuclear gas.The stellar population comprise of an exponential disc (27% of the light) anda diffuse spheroidal component (73% of the light) that cannot be represented by asimple de Vaucouleurs profile at any radius. The M/L ratios we found for the stellarcomponents (respectively 3.3 and 6.6) are typical of those ofdisc and elliptical galaxies.Key words: galaxies: individual: NGC 4350 – galaxies: kinematics and dynamics –galaxies: structure – galaxies: nuclei – dark matter 1 INTRODUCTIONThere is increasing evidence that most galaxies with a largespheroidal component host a Massive Dark Object (MDO)at their centre, with masses ranging from ∼ 10

The temperatures of dust-enshrouded active galactic nuclei

A high density of massive dark objects (MDOs), probably supermassive black holes, in the centres of nearby galaxies has been inferred from recent observations. There are various indications that much of the accretion responsible for producing these objects took place in dust-enshrouded active galactic nuclei (AGNs). If so, then measurements of the intensity of background radiation and the source counts in the far-infrared and submillimetre wavebands constrain the temperature of dust in these AGNs. An additional constraint comes from the hard X-ray background, if this is produced by accretion. One possibility is that the dust shrouds surrounding the accreting AGNs are cold, about 30 K. In this event, the dusty AGNs could be some subset of the population of luminous distant sources discovered at 850 microns using the SCUBA array on the JCMT, as proposed by Almaini et al. (1999). An alternative is that the dust shrouds surrounding the accreting AGNs are much hotter (> 60 K). These values are closer to the dust temperatures of a number of well-studied low-redshift ultraluminous galaxies that are thought to derive their power from accretion. If the local MDO density is close to the maximum permitted, then cold sources cannot produce this density without the submillimetre background being overproduced if they accrete at high radiative efficiency, and thus a hot population is required. If the dust-enshrouded accretion occurred at similar redshifts to that taking place in unobscured optical quasars, then a significant fraction of the far-infrared background radiation measured by COBE at 140 microns, but very little of the submilllimetre background at 850 microns, may have been produced by hot dust-enshrouded AGNs which may have already been seen in recent X-ray surveys.