Tidal Disruption Models Research Articles

Simulating emission line galaxies for the next generation of large-scale structure surveys

ABSTRACT We investigate emission line galaxies across cosmic time by combining the modified L-Galaxies semi-analytical galaxy formation model with the JiuTian cosmological simulation. We improve the tidal disruption model of satellite galaxies in L-Galaxies to address the time dependence problem. We utilize the public code cloudy to compute emission line ratios for a grid of H ii region models. The emission line models assume the same initial mass function as that used to generate the spectral energy distribution of semi-analytical galaxies, ensuring a coherent treatment for modelling the full galaxy spectrum. By incorporating these emission line ratios with galaxy properties, we reproduce observed luminosity functions for H α, H β, [O ii], and [O iii] in the local Universe and at high redshifts. We also find good agreement between model predictions and observations for autocorrelation and cross-correlation functions of [O ii]-selected galaxies, as well as their luminosity dependence. The bias of emission line galaxies depends on both luminosity and redshift. At lower redshifts, it remains constant with increasing luminosity up to around $\sim 10^{42.5}\, {\rm erg\, s^{-1}}$ and then rises steeply for higher luminosities. The transition luminosity increases with redshift and becomes insignificant above z = 1.5. Generally, galaxy bias shows an increasing trend with redshift. However, for luminous galaxies, the bias is higher at low redshifts, as the strong luminosity dependence observed at low redshifts diminishes at higher redshifts. We provide a fitting formula for the bias of emission line galaxies as a function of luminosity and redshift, which can be utilized for large-scale structure studies with future galaxy surveys.

Real-time discovery of AT2020xnd: a fast, luminous ultraviolet transient with minimal radioactive ejecta

ABSTRACT The many unusual properties of the enigmatic AT2018cow suggested that at least some subset of the empirical class of fast blue optical transients (FBOTs) represents a genuinely new astrophysical phenomenon. Unfortunately, the intrinsic rarity and fleeting nature of these events have made it difficult to identify additional examples early enough to acquire the observations necessary to constrain theoretical models. We present here the Zwicky Transient Facility discovery of AT2020xnd (ZTF20acigmel, the ‘Camel’) at z = 0.243, the first unambiguous AT2018cow analogue to be found and confirmed in real time. AT2018cow and AT2020xnd share all key observational properties: a fast optical rise, sustained high photospheric temperature, absence of a second peak attributable to ejection of a radioactively heated stellar envelope, extremely luminous radio, millimetre, and X-ray emission, and a dwarf-galaxy host. This supports the argument that AT2018cow-like events represent a distinct phenomenon from slower-evolving radio-quiet supernovae, likely requiring a different progenitor or a different central engine. The sample properties of the four known members of this class to date disfavour tidal disruption models but are consistent with the alternative model of an accretion powered jet following the direct collapse of a massive star to a black hole. Contextual filtering of alert streams combined with rapid photometric verification using multiband imaging provides an efficient way to identify future members of this class, even at high redshift.

ALMA Polarimetry of AT2018cow

Abstract We present the first radio polarimetric observations of a fast-rising blue optical transient, AT2018cow. Two epochs of polarimetry with additional coincident photometry were performed with the Atacama Large Millimeter/submillimeter Array. The overall photometric results based on simultaneous observations in the 100 and 230 GHz bands are consistent with the nonthermal radiation model reported by Ho et al. and indicate that the spectral peaks (∼110 GHz at the first epoch and ∼67 GHz at the second epoch) represent the synchrotron self-absorption frequency. The non-detection of linear polarization with <0.15% in the 230 GHz band at the phase when the effect of synchrotron self-absorption was quite small in the band may be explained by internal Faraday depolarization with high circumburst density and strong magnetic field. This result supports the stellar explosion scenario rather than the tidal disruption model. The maximum energy of accelerating particles at the shocks of AT2018cow-like objects is also discussed.

Late-time observations of the relativistic tidal disruption flare candidate Swift J1112.2−8238

We present late-time follow-up of the relativistic tidal disruption flare candidate Swift J1112.2-8238. We confirm the previously determined redshift of $z=0.8900\pm0.0005$ based on multiple emission line detections. {\em HST} imaging of the host galaxy indicates a complex and distorted morphology with at least two spatially distinct components. These are offset in velocity space by less than 350\,km\,s$^{-1}$ in VLT/X-Shooter observations, suggesting that the host is undergoing interaction with another galaxy. The transient position is consistent to 2.2$\sigma$ with the centre of a bulge-like component at a distance of 1.1$\pm$0.5\,kpc from its centre. Luminous, likely variable radio emission has also been observed, strengthening the similarities between Swift J1112.2-8238 and other previously identified relativistic tidal disruption flares. While the transient location is $\sim2\sigma$ from the host centroid, the disrupted nature of the host may provide an explanation for this. The tidal disruption model remains a good description for these events.

SUPERNOVAE IN THE CENTRAL PARSEC: A MECHANISM FOR PRODUCING SPATIALLY ANISOTROPIC HYPERVELOCITY STARS

Several tens of hyper-velocity stars (HVSs) have been discovered escaping our Galaxy. These stars share a common origin in the Galactic centre and are distributed anisotropically in Galactic longitude and latitude. We examine the possibility that HVSs may be created as the result of supernovae occurring within binary systems in a disc of stars around Sgr A* over the last 100 Myr. Monte Carlo simulations show that the rate of binary disruption is ~10^-4 yr^-1, comparable to that of tidal disruption models. The supernova-induced HVS production rate (\Gamma_HVS) is significantly increased if the binaries are hardened via migration through a gaseous disc. Moderate hardening gives \Gamma_HVS ~ 2*10^-7 yr^-1 and an estimated population of ~20 HVSs in the last 100 Myr. Supernova-induced HVS production requires the internal and external orbital velocity vectors of the secondary binary component to be aligned when the binary is disrupted. This leaves an imprint of the disc geometry on the spatial distribution of the HVSs, producing a distinct anisotropy.

THE ACS SURVEY OF GALACTIC GLOBULAR CLUSTERS. XI. THE THREE-DIMENSIONAL ORIENTATION OF THE SAGITTARIUS DWARF SPHEROIDAL GALAXY AND ITS GLOBULAR CLUSTERS

We use observations from the ACS study of Galactic globular clusters to investigate the spatial distribution of the inner regions of the disrupting Sagittarius dwarf spheroidal galaxy (Sgr). We combine previously published analyses of four Sgr member clusters located near or in the Sgr core (M54, Arp 2, Terzan 7 and Terzan 8) with a new analysis of diffuse Sgr material identified in the background of five low-latitude Galactic bulge clusters (NGC 6624, 6637, 6652, 6681 and 6809) observed as part of the ACS survey. By comparing the bulge cluster CMDs to our previous analysis of the M54/Sgr core, we estimate distances to these background features. The combined data from four Sgr member clusters and five Sgr background features provides nine independent measures of the Sgr distance and, as a group, provide uniformly measured and calibrated probes of different parts of the inner regions of Sgr spanning twenty degrees over the face of the disrupting dwarf. This allows us, for the first time, to constrain the three dimensional orientation of Sgr's disrupting core and globular cluster system and compare that orientation to the predictions of an N-body model of tidal disruption. The density and distance of Sgr debris is consistent with models that favor a relatively high Sgr core mass and a slightly greater distance (28-30 kpc, with a mean of 29.4 kpc). Our analysis also suggests that M54 is in the foreground of Sgr by ~2 kpc, projected on the center of the Sgr dSph. While this would imply a remarkable alignment of the cluster and the Sgr nucleus along the line of sight, we can not identify any systematic effect in our analysis that would falsely create the measured 2 kpc separation. Finally, we find that the cluster Terzan 7 has the most discrepant distance (25 kpc) among the four Sgr core clusters, which may suggest a different dynamical history than the other Sgr core clusters.

Sw 1644+57/GRB 110328A: THE PHYSICAL ORIGIN AND THE COMPOSITION OF THE RELATIVISTIC OUTFLOW

Sw 1644+57/GRB 110328A is a remarkable cosmological X-ray outburst detected by the {\it Swift} satellite. Its early-time ($t\lesssim 0.1$ days since the trigger) X-ray emission resembles some gamma-ray bursts (GRBs), e.g., GRB 090417B. But the late-time flaring X-ray plateau lasting $> 40$ days renders it unique. We examine the possibilities that the outburst is a super-long GRB powered either by the fallback accretion onto a nascent black hole or by a millisecond pulsar, and find out that these two scenarios can address some but not all of the main observational features. We then focus on the model of tidal disruption of a (giant) star by a massive black hole. The mass of the tidal-disrupted star is estimated to be $\gtrsim$ a few solar masses. A simple/straightforward argument for a magnetic origin of the relativistic outflow is presented.

A NEW CLASS OF GAMMA-RAY BURSTS FROM STELLAR DISRUPTIONS BY INTERMEDIATE-MASS BLACK HOLES

It has been argued that the long gamma-ray burst (GRB) of GRB 060614 without an associated supernova (SN) has challenged the current classification and fuel model for long GRBs, and thus a tidal disruption model has been proposed to account for such an event. Since it is difficult to detect SNe for long GRBs at high redshift, the absence of an SN association cannot be regarded as the solid criterion for a new classification of long GRBs similar to GRB 060614, called GRB 060614-type bursts. Fortunately, we now know that there is an obvious periodic substructure observed in the prompt light curve of GRB 060614. We thus use such periodic substructure as a potential criterion to categorize some long GRBs into a new class of bursts, which might have been fueled by an intermediate-mass black hole (IMBH) gulping a star, rather than a massive star collapsing to form a black hole. Therefore, the second criterion to recognize for this new class of bursts is whether they fit the tidal disruption model. From a total of 328 Swift GRBs with accurately measured durations and without SN association, we find 25 GRBs satisfying the criteria for GRB 060614-type bursts: seven of them are with known redshifts and 18 with unknown redshifts. These new bursts are ~6% of the total Swift GRBs, which are clustered into two subclasses: Type I and Type II with considerably different viscous parameters of accretion disks formed by tidally disrupting their different progenitor stars. We suggest that the two different kinds of progenitors are solar-type stars and white dwarfs: the progenitors for four Type I bursts with viscous parameter of around 0.1 are solar-type stars, and the progenitors for 21 Type II bursts with viscous parameter of around 0.3 are white dwarfs. The potential applications of this new class of GRBs as cosmic standard candles are discussed briefly

Stellar Over-Densities in the Outer Halo of the Milky Way

AbstractThis study presents a tomographic survey of a subset of the outer halo (10–40 kpc) drawn from the Sloan Digital Sky Survey Data Release 6. Halo substructure on spatial scales of >3 degrees is revealed as an excess in the local density of sub-giant stars. With an appropriate assumption of a model stellar isochrone it is possible for us to then derive distances to the sub-giant population. We describe three new candidate halo substructures; the 160- and 180-degree over-densities (at distances of 17 and 19 kpc respectively and radii of 1.3 and 1.5 kpc respectively) and an extended feature at 28 kpc that covers at least 162 deg2, the Virgo Equatorial Stream. In addition, we recover the Sagittarius dwarf galaxy (Sgr) leading-arm material and the Virgo Over-Density.The derived distances, together with the number of sub-giant stars associated with each substructure, enables us to derive the integrated luminosity for the features. The tenuous, low surface brightness of the features strongly suggests an origin from the tidal disruption of an accreted galaxy or galaxies. Given the dominance of the tidal debris of Sgr in this region of the sky we investigate if our observations can be accommodated by tidal disruption models for Sgr. The clear discordance between observations and model predictions for known Sgr features means it is difficult to tell unambiguously if the new substructures are related to Sgr or not. Radial velocities in the stellar over-densities will be critical in establishing their origins.

Transient X-ray emission from normal galactic nuclei

X-ray transients appeared in optically non-active galactic nuclei have been observed in recent years. The most popular model explaining this kind of phenomena is the conventional tidal disruption model. In this model, when a star moves within the tidal radius of a black hole, part of the star materials will fall into the black hole through an accretion disk, which gives rise to the luminous flare. We propose that the X-ray emission may not necessarily come from radiation of the accretion disk alone. Instead, it may be related to a jet. As the jet travels in the interstellar medium, a shock is produced and synchrotron radiation is expected. We compared the model light curve and the synchrotron radiation spectrum with the observed data, and find that our model explains the observed light curve and late-time spectrum well. Our model predicts that these transient active galactic nuclei could be sources of the future gamma-ray satellites, e.g. GLAST and the emission region will be expanding with time.

Candidate tidal disruption events from the XMM-Newton slew survey

Context. In recent years, giant amplitude X-ray flares have been observed from a handful of non-active galaxies. The most plausible scenario of these unusual phenomena is tidal disruption of a star by a quiescent supermassive black hole at the centre of the galaxy. Aims. Only a small number of these type of events have been observed and confirmed to date. The discovery of more cases would allow a number of fundamental conclusions to be drawn about properties such as the frequency of tidal disruption events, the distribution of quiescent black hole masses and their influence in the context of galaxy/AGN formation and evolution among others. Methods. Comparing the XMM-Newton Slew Survey Source Catalogue with the ROSAT PSPC All-Sky Survey five galaxies have been detected a factor of up to 88 brighter in XMM-Newton with respect to ROSAT PSPC upper limits and presenting a soft X-ray colour. X-ray luminosities of these sources derived from slew observations have been found in the range 10 41 −10 44 erg s −1 , fully consistent with the tidal disruption model. This model predicts that during the peak of the outburst, flares reach X-ray luminosities up to 10 45 erg s −1 , which is close to the Eddington luminosity of the black hole, and afterwards a decay of the flux on a time scale of months to years is expected. Multi-wavelength follow-up observations have been performed on these highly variable objects in order to disentangle their nature and to investigate their dynamical evolution. Results. Here we present sources coming from the XMM-Newton Slew Survey that could fit in the paradigm of tidal disruption events. X-ray and optical observations revealed that two of these objects are in full agreement with that scenario and three other sources that, showing signs of optical activity, need further investigation within the transient galactic nuclei phenomena.

Tidal disruption model for the interacting pair of galaxies VV 117 (NGC 2444/45)

A series of N-body simulations have been performed to interpret the interacting pair of galaxies VV 117 (NGC 2444/45). The galaxies have been modelled assuming a mass ratio two. The simulations use various values for the distance of closest approach and the eccentricity of the relative orbit of the pair. A plausible scenario for the tidal disruption of the less massive galaxy is proposed. NGC2444, having double the mass of NGC 2445, has undergone penetrating collision with the latter in a hyperbolic or a parabolic orbit. After the first collision, the orbit has become bound. Our results show that VV 117 has either just emerged from the first collision or are on the verge of a second collision. NGC 2445suffers considerable disruption and mass loss. NGC 2444 is not affected much. The second collision is expected to culminate in the merger of the two galaxies.

The Davy Crater Chain: Implications for tidal disruption in the Earth‐Moon System and elsewhere

Linear crater chains on Ganymede and Callisto apparently provide an impact record of tidally disrupted bodies, like Comet Shoemaker‐Levy 9, at Jupiter. We propose that the Davy crater chain on the Earth's Moon records a similar tidal disruption event in the Earth‐Moon system. Most lunar crater chains result from either volcanism or secondary impacts, but the Davy chain differs in setting and appearance from these crater chains and instead shows morphologic similarities to the Jovian crater chains. While the Davy chain is much smaller than the Jovian crater chains, tidal disruption models indicate that this smaller size is consistent with the Earth's lower mass. The disruption models also indicate that most Earth‐crossing comets and asteroids are moving too fast for fragment dispersion before impact to produce the observed crater chain length. Thus, the Davy and Jovian crater chains apparently result from bodies with different orbital characteristics. In addition, the limited dispersion of high velocity fragments at the Moon suggests that crater chains may not form for all disruption events or on all planetary satellites. Based on modeled fragment dispersions elsewhere in the solar system, we suggest that similar crater chains may be present on Iapetus, and possibly on Titan, Titania or Oberon.

Gas clouds from tidally disrupted stars in active galactic nuclei

view Abstract Citations (35) References (111) Co-Reads Similar Papers Volume Content Graphics Metrics Export Citation NASA/ADS Gas Clouds from Tidally Disrupted Stars in Active Galactic Nuclei Roos, Nico Abstract A direct implication of the presence of massive black holes in galactic nuclei is the occasional tidal disruption of a star in the vicinity of the hole. The tidal disruption rate will be enhanced as a result of perturbations of the star cluster around the hole (for instance during the final stage of a merger with a smaller galaxy) leading to prolonged periods of activity. Recent investigations of the tidal break- up of solar-type stars near massive black holes have shown that debris gas will be distributed throughout the galactic nucleus. About half of the stellar debris mass is strongly bound to the hole and will quickly be swallowed while the rest is expelled with typical velocities of order 5000M^1/6^_6_ km s^-1^, where M_6_ = M_hole_/10^6^ M_sun_. In this paper the structure and properties of freely expanding (unbound) remnant clouds irradiated by the central continuum source of an AGN are explored. It is argued that the remnant cloud fragments into cold clumps of gas (T~10^4^K) surrounded by hot gas at the Compton temperature (T_c_~10^7-8^K) when the ionization parameter {XI} (defined as the ratio of the ionizing radiation pressure to the gas pressure) reaches the critical value {XI}_c_ ~ 10. Subsequently the fraction of hot gas slowly increases at the expense of the cold component while the ionization parameter of both components remains equal to {XI}_c_. Photoionization of cold gas in the outmoving and radially elongated remnant clouds produces a broad line region at a distance of ~10^16-17^ cm in Seyferts and ~10^17-18^ cm in quasars. The broad line region (BLR) has an outer boundary where the remnant clouds become optically thin to the ionizing radiation from the central source. The densities and column densities in the BLR are in the range ~10^9-11 cm^-3^ and ~10^24-27^ cm^-2^, respectively ({XI}~10). Bound debris orbiting at ~10^15-16^M^2/3^_6_ cm with characteristic densities >= 10^11^ cm^-3^ may contribute to the inner part of the broad line region yielding symmetric lines, whereas a relatively small number (~10-100) of large outmoving remnant clouds produces a more asymmetric and bumpy line profile. There are two potential problems with this new model for the BLR: First, a high tidal disruption rate of order >= 0.1 M_sun_ yr^-1^ seems required to replenish the gas in the BLR in Seyferts as well as in QSOs. Second, in some AGN the central continuum source may be obscured by optically thick remnant clouds along our line of site. A very attractive property of the tidal disruption model is that it offers a natural interpretation not only for the broad emission lines but for a number of other features in AGN spectra as well. Tidal disruption will provide cold, dense gas close to the central source which can reprocess the radiation from the central source and produce a thermal bump in the optical/UV as well as several characteristic X-ray features. Optically thin remnants moving along our line of site outside the BLR at about 10^18-19^ cm may produce broad absorption lines similar to those observed in broad absorption line QSOs. The radially outmoving remnants are decelerated and compressed by the interstellar medium at radii >= 10^19^ cm, where they will emit narrow forbidden lines. Publication: The Astrophysical Journal Pub Date: January 1992 DOI: 10.1086/170919 Bibcode: 1992ApJ...385..108R Keywords: Active Galactic Nuclei; Black Holes (Astronomy); Gravitational Collapse; High Temperature Gases; Interstellar Gas; Star Clusters; Gas Ionization; Gas Pressure; Perturbation Theory; Photoionization; Quasars; Seyfert Galaxies; Spectral Line Width; Tides; Astrophysics; BLACK HOLE PHYSICS; GALAXIES: KINEMATICS AND DYNAMICS; GALAXIES: NUCLEI; GALAXIES: SEYFERT; GALAXIES: QUASARS: GENERAL full text sources ADS | data products SIMBAD (3) MAST (1)