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1.
Data on the positions of gamma-ray bursts (GRBs) in galaxies are used to construct the radial distributions of their surface density. The gradient in GRB surface density is shown to decrease sharply at a galactocentric distance equal to the effective galactic radius. In central galactic regions, the GRB density distribution agrees with the galactic surface-brightness distribution; in outer regions, the GRB density decreases more slowly than does the surface brightness. Based on improved statistics, we analyze the radial distribution of type Ib/c supernovae. We show that it differs insignificantly from the distributions of other types of supernova and exhibits a much closer similarity to the distribution of star-forming regions than do GRBs. Although the statistics for GRBs is poor, the deviation of their distribution from the distribution of active star-forming regions in nearby galaxies seems to have been firmly established. A correlation of GRBs with the distribution of dark matter in outer galactic regions is not ruled out.  相似文献   

2.
We describe the Sternberg Astronomical Institute (SAI) catalog of supernovae. We show that the radial distributions of type-Ia, type-Ibc, and type-II supernovae differ in the central parts of spiral galaxies and are similar in their outer regions, while the radial distribution of type-Ia supernovae in elliptical galaxies differs from that in spiral and lenticular galaxies. We give a list of the supernovae that are farthest from the galactic centers, estimate their relative explosion rate, and discuss their possible origins.  相似文献   

3.
Rotating black holes can power the most extreme non-thermal transient sources. They have a long-duration viscous time-scale of spin-down, and produce non-thermal emissions along their spin-axis, powered by a relativistic capillary effect. We report on the discovery of exponential decay in Burst and Triensient Source Experiment (BATSE) light curves of long gamma-ray bursts (GRBs) by matched filtering, consistent with a viscous time-scale, and identify ultra-high energy cosmic rays (UHECRs) about the Greisen–Zatsepin–Kuzmin (GZK) threshold with linear acceleration of ion contaminants along the black hole spin-axis, consistent with black hole masses and lifetimes of Fanaroff–Riley type II (FR II) active galactic nuclei (AGN). We explain the absence of UHECRs from BL Lac objects due to UHECR emissions preferably at appreciable angles away from the black hole spin-axis. Black hole spin may be the key to unification of GRBs and their host environments, and to AGN and their host galaxies. Our model points to long-duration bursts in radio from long GRBs without supernovae and gravitational waves from all long GRBs.  相似文献   

4.
We analyse the relation between active galactic nuclei (AGN) host properties and large-scale environment for a representative red and blue AGN host galaxy sample selected from the Data Release 4 Sloan Digital Sky Survey. A comparison is made with two carefully constructed control samples of non-active galaxies, covering the same redshift range and colour baseline. The cross-correlation functions show that the density distribution of neighbours is almost identical for blue galaxies, either active or non-active. Although active red galaxies inhabit environments less dense compared to non-active red galaxies, both reside in environments considerably denser than those of blue hosts. Moreover, the radial density profile of AGN relative to galaxy group centres is less concentrated than galaxies. This is particularly evident when comparing red AGN and non-active galaxies.
The properties of the neighbouring galaxies of blue and red AGN and non active galaxies reflect this effect. While the neighbourhood of the blue samples is indistinguishable, the red AGN environs show an excess of blue-star-forming galaxies with respect to their non-active counterpart. On the other hand, the active and non-active blue systems have similar environments but markedly different morphological distributions, showing an excess of blue early-type AGN, which are argued to be late-stage mergers. This comparison reveals that the observable differences between active red and blue host galaxy properties including star formation history and AGN activity depends on the environment within which the galaxies form and evolve.  相似文献   

5.
The study of short-duration gamma-ray bursts (GRBs) experienced a complete revolution in recent years thanks to the discovery of the first afterglows and host galaxies starting in May 2005. These observations demonstrated that short GRBs are cosmological in origin, reside in both star forming and elliptical galaxies, are not associated with supernovae, and span a wide isotropic-equivalent energy range of ～1048–1052 erg. However, a fundamental question remains unanswered: What are the progenitors of short GRBs? The most popular theoretical model invokes the coalescence of compact object binaries with neutron star and/or black hole constituents. However, additional possibilities exist, including magnetars formed through prompt channels (massive star core-collapse) and delayed channels (binary white dwarf mergers, white dwarf accretion-induced collapse), or accretion-induced collapse of neutron stars. In this review I summarize our current knowledge of the galactic and sub-galactic environments of short GRBs, and use these observations to draw inferences about the progenitor population. The most crucial results are: (i) some short GRBs explode in dead elliptical galaxies; (ii) the majority of short GRBs occur in star forming galaxies; (iii) the star forming hosts of short GRBs are distinct from those of long GRBs, and instead appear to be drawn from the general field galaxy population; (iv) the physical offsets of short GRBs relative to their host galaxy centers are significantly larger than for long GRBs; (v) there is tentative evidence for large offsets from short GRBs with optical afterglows and no coincident hosts; (vi) the observed offset distribution is in good agreement with predictions for NS–NS binary mergers; and (vii) short GRBs trace under-luminous locations within their hosts, but appear to be more closely correlated with the rest-frame optical light (old stars) than the UV light (young massive stars). Taken together, these observations suggest that short GRB progenitors belong to an old stellar population with a wide age distribution, and generally track stellar mass. These results are fully consistent with NS–NS binary mergers and rule out a dominant population of prompt magnetars. However, a partial contribution from delayed magnetar formation or accretion-induced collapse is also consistent with the data.  相似文献   

6.
We present millimetre (mm) and submillimetre (submm) photometry of a sample of five host galaxies of gamma-ray bursts (GRBs), obtained using the Max Planck Millimetre Bolometer (MAMBO2) array and Submillimetre Common-User Bolometer Array (SCUBA). These observations were obtained as part of an ongoing project to investigate the status of GRBs as indicators of star formation. Our targets include two of the most unusual GRB host galaxies, selected as likely candidate submm galaxies: the extremely red  ( R − K ≈ 5)  host of GRB 030115, and the extremely faint  ( R > 29.5)  host of GRB 020124. Neither of these galaxies is detected, but the deep upper limits for GRB 030115 impose constraints on its spectral energy distribution, requiring a warmer dust temperature than is commonly adopted for submillimetre galaxies (SMGs).
As a framework for interpreting these data, and for predicting the results of forthcoming submm surveys of Swift -derived host samples, we model the expected flux and redshift distributions based on luminosity functions of both submm galaxies and GRBs, assuming a direct proportionality between the GRB rate density and the global star formation rate density. We derive the effects of possible sources of uncertainty in these assumptions, including (1) introducing an anticorrelation between GRB rate and the global average metallicity, and (2) varying the dust temperature.  相似文献   

7.
We present N -body simulations of galaxy groups embedded in a common halo of matter. We study the influence of the different initial conditions upon the evolution of the group and show that denser configurations evolve faster, as expected. We then concentrate on the influence of the initial radial density profile of the common halo and of the galaxy distribution. We select two kinds of density distributions, a singular profile (modelled by a Hernquist distribution) and a profile with a flat core (modelled by a Plummer sphere). In all cases we witness the formation of a central massive object owing to mergings of individual galaxies and to accretion of stripped material, but both its formation history and its properties depend heavily on the initial distribution. In Hernquist models the formation is caused by a 'burst' of mergings in the inner parts, owing to the large initial concentration of galaxies in the centre. The merging rate is much slower in the initial phases of the evolution of a Plummer distribution, where the contribution of accretion to the formation of the central object is much more important. The central objects formed within Plummer distributions have projected density profiles which are not in agreement with the radial profiles of observed brightest cluster members, unless the percentage of mass in the common halo is small. In contrast, the central object formed in initially cusped models has projected radial profiles in very good agreement with those of brightest cluster members, sometimes also showing luminosity excess over the r 1/4 law in the outer parts, as is observed in cD galaxies.  相似文献   

8.
We present the results of spectroscopic observations of three S0-Sa galaxies: NGC 338, NGC 3245, and NGC 5440 at the SAO RAS 6-m BTA telescope. The radial distributions of the line-ofsight velocities and radial velocity dispersions of stars and ionized gas were obtained, and rotation curves of galaxies were computed. We construct the numerical dynamic N-body galaxy models with N ?? 106 points. The models include three components: a ??live?? bulge, a collisionless disk, dynamically evolving to the marginally stable state, and a pseudo-isothermal dark halo. The estimates of radial velocities and velocity dispersions of stars obtained from observations are compared with model estimates, projected onto the line of sight. We show that the disks of NGC 5440 and the outer regions of NGC 338 are dynamically overheated. Taking into account the previously obtained observations, we conclude that the dynamic heating of the disk is present in a large number of early-type disk galaxies, and it seems to ensue from the external effects. The estimates of the disk mass and relative mass of the dark halo are given, as well as the disk mass-to-luminosity ratio for seven galaxies, observed at the BTA.  相似文献   

9.
This talk focuses on the various aspects we learnt from multiband observations of GRBs both, before and during the afterglow era. A statistical analysis to estimate the probable redshifts of host galaxies using the luminosity function of GRBs compatible with both the afterglow redshift data as well as the overall population of GRBs is discussed. We then address the question whether the observed fields of GRBs with precise localizations from third Inter-Planetary Network (IPN3) contain suitable candidates for their host galaxies.  相似文献   

10.
We present distributions of the orbital parameters of dark matter substructures at the time of merging into their host halo. Accurate knowledge of the orbits of dark matter substructures is a crucial input to studies which aim to assess the effects of the cluster environment on galaxies, the heating of galaxy discs and many other topics. Orbits are measured for satellites in a large number of N -body simulations. We focus on the distribution of radial and tangential velocities, but consider also distributions of orbital eccentricity and semimajor axis. We show that the distribution of radial and tangential velocities has a simple form and provide a fitting formula for this distribution. We also search for possible correlations between the infall directions of pairs of satellites, finding evidence for positive correlation at small angular separations as expected if some infall occurs along filaments. We also find (weak) evidence for correlations between the direction of the infall and infall velocity and the spin of the host halo.  相似文献   

11.
The observed rotation curves of four low-surface-brightness galaxies are compared with the predictions of three models of the dark matter distribution with various degrees of singularity at the center or without it. Contrary to the assertions in the literature, the results of fitting the rotation curves by the least-squares method using a chi-square distribution with optimal parameters (dark matter halo, bulge, and disk) do not yet allow any one of the models to be uniquely preferred. The NFW and Burkert models have the highest significance levels for two of the four galaxies and for the other two, respectively. At the same time, using the NFW model in the latter two cases leads to an estimate of the disk surface density close to the photometric one, which may suggest that these models are more realistic. The surface density estimates for the galactic disks based the criterion of their marginal gravitational stability have also been used. The disks of the galaxies under consideration may be overheated, because the modeling using these estimates gives larger deviations of the model rotation curves from the observed ones than in the case where the surface density is assumed to be a free parameter. Using the disk surface density estimates based on the criterion of marginal gravitational stability does not change the preference in choosing the shape of the dark matter density profile in the galaxies under consideration compared to the case with a “free disk.”  相似文献   

12.
Gamma‐ray bursts (GRBs) are the most powerful explosions since the formation of the Universe, associated with the death of massive stars or mergers of compact stellar objects. Several recent striking results strongly support the idea that host galaxies of GRBs are opening a new view on our understanding of galaxy formation and evolution, back to the very primordial universe at z ∼ 8. They form a unique sample of galaxies which cover a wide range of redshift, they are typically weak with low mass and unlike other methods they are not selected on luminosity. In recent years, thanks to the support of new generation instruments, multi‐band photometry and spectroscopy allow us to better investigate the properties of these host galaxies (e.g., stellar mass, age, SFR, metallicity), to study their possible evolution and to compare them with field galaxies and other classes of galaxies. GRB host spectroscopy is one of the main science drivers behind the X‐shooter spectrograph. In this paper, we present the first results of the program devoted to Italian‐French GTO multiband spectroscopy of GRB host galaxies with X‐shooter (© 2011 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)  相似文献   

13.
Compact object mergers are one of the currently favoured models for the origin of gamma-ray bursts (GRBs). The discovery of optical afterglows and identification of the nearest, presumably host, galaxies allow the analysis of the distribution of burst sites with respect to these galaxies. Using a model of stellar binary evolution we synthesize a population of compact binary systems which merge within the Hubble time. We include the kicks in the supernovae explosions and calculate orbits of these binaries in galactic gravitational potentials. We present the resulting distribution of merger sites and discuss the results in the framework of the observed GRB afterglows.  相似文献   

14.
The initial principles of a method for analyzing the spatial distribution of visible matter in the universe with structures on size scales of thousands of Mpc are discussed. This method is based on analyzing the distribution N(z) of the photometric redshifts of galaxies in deep fields using large bins Δ z=0.1–0.3. Fluctuations in the numbers of galaxies in these bins in terms of redshifts are caused by Poisson noise, correlated structures, and systematic errors in estimating photo-z. This method involves covering a sufficiently large region of the celestial sphere with a grid of deep multi-band surveys with a cell size on the order of 10o×10o, with deep fields of size ∼10'×10' observed with 3-10 meter telescopes at its nodes. The distribution of the photometric redshifts of the galaxies within each deep field will yield information on the radial extent of superlarge structures, while comparing the radial distributions in neighboring fields will yield information on the tangential extent of these structures. A necessary element of this method is an analysis of possible distortions in the radial distributions of the galaxies associated with the technique for evaluating the photometric redshifts.  相似文献   

15.
We present new models for the formation of disc galaxies that improve upon previous models by following the detailed accretion and cooling of the baryonic mass, and by using realistic distributions of specific angular momentum. Under the assumption of detailed angular momentum conservation, the discs that form have density distributions that are more centrally concentrated than an exponential. We examine the influence of star formation, bulge formation, and feedback on the outcome of the surface brightness distributions of the stars. Low angular momentum haloes yield disc galaxies with a significant bulge component and with a stellar disc that is close to exponential, in good agreement with observations. High angular momentum haloes, on the other hand, produce stellar discs that are much more concentrated than an exponential, in clear conflict with observations. At large radii, the models reveal distinct truncation radii in both the stars and the cold gas. The stellar truncation radii result from our implementation of star formation threshold densities, and are in excellent agreement with observations. The truncation radii in the density distribution of the cold gas reflect the maximum specific angular momentum of the gas that has cooled. We find that these truncation radii occur at H  i surface densities of roughly 1 M⊙ pc−2, in conflict with observations. We examine various modifications to our models, including feedback, viscosity, and dark matter haloes with constant-density cores, but show that the models consistently fail to produce bulge less discs with exponential surface brightness profiles. This signals a new problem for the standard model of disc formation: if the baryonic component of the protogalaxies out of which disc galaxies form has the same angular momentum distribution as the dark matter, discs are too compact.  相似文献   

16.
The initial principles of a method for analyzing the spatial distribution of visible matter in the universe with structures on size scales of thousands of Mpc are discussed. This method is based on analyzing the distribution N(z) of the photometric redshifts of galaxies in deep fields using large bins Δ z=0.1–0.3. Fluctuations in the numbers of galaxies in these bins in terms of redshifts are caused by Poisson noise, correlated structures, and systematic errors in estimating photo-z. This method involves covering a sufficiently large region of the celestial sphere with a grid of deep multi-band surveys with a cell size on the order of 10º×10º, with deep fields of size ～10'×10' observed with 3-10 meter telescopes at its nodes. The distribution of the photometric redshifts of the galaxies within each deep field will yield information on the radial extent of superlarge structures, while comparing the radial distributions in neighboring fields will yield information on the tangential extent of these structures. A necessary element of this method is an analysis of possible distortions in the radial distributions of the galaxies associated with the technique for evaluating the photometric redshifts.  相似文献   

17.
We investigate statistical distributions of differences in gravitational-lensing deflections between two light rays, the so-called lensing excursion angles. A probability distribution function of the lensing excursion angles, which plays a key role in estimates of lensing effects on angular clustering of objects (such as galaxies, quasi-stellar objects and also the cosmic microwave background temperature map), is known to consist of two components: a Gaussian core and an exponential tail. We use numerical gravitational-lensing experiments in a ΛCDM cosmology for quantifying these two components. We especially focus on the physical processes responsible for generating these two components. We develop a simple empirical model for the exponential tail which allows us to explore its origin. We find that the tail is generated by the coherent lensing scatter by massive haloes with   M > 1014  h −1 M⊙  at   z < 1  and that its exponential shape arises due to the exponential cut-off of the halo mass function at that mass range. On scales larger than 1 arcmin, the tail does not have a practical influence on the lensing effects on the angular clustering. Our model predicts that the coherent scatter may have non-negligible effects on angular clustering at subarcminute scales.  相似文献   

18.
The third EGRET catalog contains a large number of unidentified sources. This subset of objects is expected to include known gamma-ray emitters of Galactic origin such as pulsars and supernova remnants, in addition to an extragalactic population of blazars. However, current data allows the intriguing possibility that some of these objects may represent a new class of yet undiscovered gamma-ray sources. Many theoretically motivated candidate emitters (e.g. clumps of annihilating dark matter particles) have been suggested to account for these detections. We take a new approach to determine to what extent this population is Galactic and to investigate the nature of the possible Galactic component. By assuming that galaxies similar to the Milky Way should host comparable populations of objects, we constrain the allowed Galactic abundance and distribution of various classes of gamma-ray sources using the EGRET data set. We find it is highly improbable that a large number of the unidentified sources are members of a Galactic halo population, but that a distribution of the sources entirely in the disk and bulge is plausible. Finally, we discuss the additional constraints and new insights that GLAST will provide.  相似文献   

19.
It has been verified that the analytical results derived in a previous article for elliptical galaxies may also be used to describe spiral galaxies. Exploration of the model for small values of the principal parameter yields surface mass density distributions as functions of radius which, while always displaying the exponential disk, describe both of the subcategories of spiral galaxies. Within the constraints of the model, the two main questions concerning spirals posed some years ago by Freeman appear to be successfully addressed.An intrinsic model mechanism has been identified that could account for the extended state of elliptical galaxies, as opposed to the flat disks of spirals. In general, the model correctly describes the relative sizes of the various types of galaxies.  相似文献   

20.
Using detailed mock galaxy redshift surveys (MGRSs) we investigate the abundance and radial distribution of satellite galaxies. The mock surveys are constructed using large numerical simulations and the conditional luminosity function (CLF), and are compared against data from the Two Degree Field Galaxy Redshift Survey (2dFGRS). We use Monte Carlo Markov chains to explore the full posterior distribution of the CLF parameter space, and show that the average relation between light and mass is tightly constrained and in excellent agreement with our previous models and with that of Vale & Ostriker. The radial number density distribution of satellite galaxies in the 2dFGRS reveals a pronounced absence of satellites at small projected separations from their host galaxies. This is (at least partly) owing to the overlap and merging of galaxy images in the 2dFGRS parent catalogue. Owing to the resulting close-pair incompleteness we are unfortunately unable to put meaningful constraints on the radial distribution of satellite galaxies; the data are consistent with a radial number density distribution that follows that of the dark matter particles, but we cannot rule out alternatives with a constant number density core. Marginalizing over the full CLF parameter space, we show that in a ΛCDM concordance cosmology the observed abundances of host and satellite galaxies in the 2dFGRS indicate a power spectrum normalization of  σ8≃ 0.7  . The same cosmology but with  σ8= 0.9  is unable to match simultaneously the abundances of host and satellite galaxies. This confirms our previous conclusions based on the pairwise peculiar velocity dispersions and the group multiplicity function.  相似文献   

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