共查询到20条相似文献,搜索用时 31 毫秒
1.
P. Amram C. Mendes de Oliveira H. Plana C. Balkowski M. Bolte 《Astrophysics and Space Science》2002,281(1-2):397-400
We present kinematics and photometric evidence for the presence of seven candidate tidal dwarf galaxies in Stephan's Quintet.
The central regions of the two most probable parent galaxies, NGC 7319 and NGC 7318B, contain little or no gas whereas the
intragroup medium and, in particular, the optical tails that seem to be associated with NGC 7318B are rich in cold and ionized
gas. Two tidal dwarf candidates may be located at the edge of a tidal tail, another located within a tail, and for the four
others there is no obvious stellar/gaseous bridge between them and the parent galaxy. Two of the candidates are associated
with H I clouds, one of which is, in addition, associated with a CO cloud. All seven regions have low continuum fluxes and
high Hα luminosity densities [F(Hα) = (1-60) × 10-14 ergs s-1 cm-2]. Their magnitudes (MB = –16.1 to –12.6), sizes (∼ 3.5 h75
-1 kpc), colors (typically B – R = 0.7), and gas velocity gradients (∼ 8 –26 h75 km s-1 kpc-1) are typical for tidal dwarf galaxies. In addition, the ratios between their star formation rates determined from Hα and
from the B-band luminosity are typical of other tidal dwarf galaxies. The masses of the tidal dwarf galaxies in Stephan's
Quintet range from ∼ 2 × 108 to 1010 M⊙, and the median value for their inferred mass-to-light ratios is 7 (M/L)⊙. At least two of the systems may survive possible ‘fallbacks’ or disruption by the parent galaxies and may already be, or
turn into, self-gravitating dwarf galaxies, new members of the group.
This revised version was published online in September 2006 with corrections to the Cover Date. 相似文献
2.
Jonathan Braine P.-A. Duc U. Lisenfeld V. Charmandaris O. Vallejo S. Leon E. Brinks 《Astrophysics and Space Science》2002,281(1-2):407-408
We investigate the process of galaxy formation as can be observed in the only currently forming galaxies - the so-called Tidal
Dwarf Galaxies, hereafter TDGs - through observations of the molecular gas detected via its CO (Carbon Monoxide) emission.
These objects are formed of material torn off of the outer parts of a spiral disk due to tidal forces in a collision between
two massive galaxies. Molecular gas is a key element in the galaxy formation process, providing the link between a cloud of
gas and a bona fide galaxy. We have detected CO in 8 TDGs (Braine, Lisenfeld, Duc and Leon, 2000: Nature
403, 867; Braine, Duc, Lisenfeld, Charmandaris, Vallejo, Leon and Brinks: 2001, A&A
378, 51), with an overall detection rate of 80%, showing that molecular gas is abundant in TDGs, up to a few 108
M
⊙. The CO emission coincides both spatially and kinematically with the HI emission, indicating that the molecular gas forms
from the atomic hydrogen where the HI column density is high. A possible trend of more evolved TDGs having greater molecular
gas masses is observed, in accord with the transformation of HI into H2. Although TDGs share many of the properties of small irregulars, their CO luminosity is much greater (factor ∼ 100) than
that of standard dwarf galaxies of comparable luminosity. This is most likely a consequence of the higher metallicity (≳sim
1/3 solar) of TDGs which makes CO a good tracer of molecular gas. This allows us to study star formation in environments ordinarily
inaccessible due to the extreme difficulty of measuring the molecular gas mass. The star formation efficiency, measured by
the CO luminosity per Hα flux, is the same in TDGs and full-sized spirals. CO is likely the best tracer of the dynamics of
these objects because some fraction of the HI near the TDGs may be part of the tidal tail and not bound to the TDG. Although
uncertainties are large for individual objects, as the geometry is unknown, our sample is now of eight detected objects and
we find that the ‘dynamical’ masses of TDGs, estimated from the CO line widths, seem not to be greater than the ‘visible’
masses (HI + H2 + a stellar component). Although higher spatial resolution CO (and HI) observations would help reduce the uncertainties,
we find that TDGs require no dark matter, which would make them the only galaxy-sized systems where this is the case. Dark
matter in spirals should then be in a halo and not a rotating disk. Most dwarf galaxies are dark matter-rich, implying that
they are not of tidal origin. We provide strong evidence that TDGs are self-gravitating entities, implying that we are witnessing the
ensemble of processes in galaxy formation: concentration of large amounts of gas in a bound object, condensation of the gas,
which is atomic at this point, to form molecular gas and the subsequent star formation from the dense molecular component.
This revised version was published online in September 2006 with corrections to the Cover Date. 相似文献
3.
Recent spectroscopic observations of galaxies in the Fornax-Cluster reveal nearly unresolved ‘star-like’ objects with red-shifts
appropriate to the Fornax-Cluster. These objects have intrinsic sizes of ≈ 100 pc and absolute B-band magnitudes in the range
- 14 < MB < -11.5 mag and lower limits for the central surface brightness μB ≥ 23 mag/arcsec2 (Phillipps et al., 2001, Hilker et al., 1999), and so appear to constitute a new population of ultra-compact dwarf galaxies
(UCDs). Such compact dwarfs were predicted to form from the amalgamation of stellar super-clusters (= clusters of star clusters;
not to confuse with super stellar clusters (SSC)) by P. Kroupa (1998), which are rich aggregates of young massive star clusters
(YMCs) that can form in collisions between gas-rich galaxies. Here we present the evolution of super-clusters in a tidal field.
The YMCs merge on a few super-cluster crossing times. Super-clusters that are initially as concentrated and massive as Knot
S in the interacting Antennae galaxies (Whitmore et al., 1999) evolve to merger objects that are long-lived and show properties
comparable to the newly discovered UCDs.
This revised version was published online in September 2006 with corrections to the Cover Date. 相似文献
4.
Daniel Thomas Ralf Bender Ulrich Hopp Claudia Maraston Laura Greggio 《Astrophysics and Space Science》2003,284(2):599-602
We present kinematics and stellar population properties of 17 dwarf early-type galaxies in the luminosity range -14 ≥ M
B ≥ -19. Our sample fills the gap between the intensively studied giant elliptical and Local Group dwarf spheroidal galaxies.
The dwarf ellipticals of the present sample have constant velocity dispersion profiles within their effective radii and do
not show significant rotation, hence are clearly anisotropic. The dwarf lenticulars, instead, rotate faster and are, at least
partially, supported by rotation. From optical Lick absorption indices, we derive metallicities and element abundances. Combining
our sample with literature data of the Local Group dwarf spheroidals and giant ellipticals, we find a surprisingly tight linear
correlation between metallicity and luminosity over a wide range: -8 ≥ M
B ≥ -22. The α/Fe ratios of our dwarf ellipticals are significantly lower than the ones of giant elliptical galaxies, which
is in agreement with spectroscopy of individual stars in Local Group dwarf spheroidals. Our results suggest the existence
of a clear kinematic and stellar population dichotomy between dwarf and giant elliptical galaxies. This result is important
for theories of galaxy formation, because it implies that present-day dwarf ellipticals are not the fossiled building blocks
of giant ellipticals.
This revised version was published online in August 2006 with corrections to the Cover Date. 相似文献
5.
We present the results of our analysis of the frequencies of galaxies with tidal tails and M51-type galaxies in several deep
fields of the Hubble Space Telescope (HDF-N, HDF-S, HUDF, GOODS, GEMS). In total, we have found about seven hundred interacting
galaxies at redshifts z ≤ 1.5 in these fields. At z ≤ 0.7, the observed space densities of galaxies with tidal structures and M51-type galaxies have been found to increase as
∝(1 + z)
m
, where m ≈ 2.6. According to our estimates, over the last 6–7 Gyr, i.e., at z ≤ 0.7, about a third of the galaxies with M(B) ≤ −18
m
must have undergone strong gravitational perturbations and mergers and ∼1/10−1/5 of the galaxies have swallowed relatively
low-mass nearby satellites typical of M51-type galaxies. The possible decrease in the time scale on which a distant galaxy
appears peculiar with growing z can increase considerably the estimated rate of mergers. 相似文献
6.
The Eridanus galaxies follow the well-known radio—FIR correlation. The majority (70%) of these galaxies have their star formation
rates below that of the Milky Way. The galaxies that have a significant excess of radio emission are identified as low luminosity
AGNs based on their radio morphologies obtained from the GMRT observations. There are no powerful AGNs (L
20cm > 1023 W Hz−1) in the group. The two most far-infrared and radio luminous galaxies in the group have optical and HI morphologies suggestive
of recent tidal interactions. The Eridanus group also has two far-infrared luminous but radio-deficient galaxies. It is believed
that these galaxies are observed within a few Myr of the onset of an intense star formation episode after being quiescent
for at least a 100 Myr. The upper end of the radio luminosity distribution of the Eridanus galaxies (L
20cm ∼ 1022 W Hz−1) is consistent with that of the field galaxies, other groups, and late-type galaxies in nearby clusters. 相似文献
7.
DDO 68 (UGC 5340) is the second most metal-poor star-forming galaxy (12 + log(O/H) = 7.14). Its peculiar optical morphology
and its HI distribution and kinematics are indicative of a merger origin. We use the u, g, r, and i photometry based on the SDSS images of DDO 68 to estimate its stellar population ages. The Hα images of DDO 68 were used to select several representative regions without nebular emission. The derived colors were analyzed
by comparison with the PEGASE2 evolutionary tracks for various star formation (SF) scenarios, including the two extreme cases:
(i) an instantaneous starburst and (ii) continuous SF with a constant rate. The (u − g) and (g − r) colors for all of the selected regions are consistent with the scenario of several “instantaneous” SF episodes with ages
between ∼0.05 and ∼1 Gyr. The total mass of the visible stars in DDO 68 was estimated by comparing the colors and fluxes of
the observed stellar subsystems with PEGASE2 models to be ∼2.4 × 107
M
⊙. This accounts for ∼6% of the total baryonic mass of the galaxy. All of the available data are consistent with the fact that
DDO 68 is a very rare candidate for young galaxies. The bulk of its stars were formed during the recent (with the first encounter
∼1 Gyr ago) merger of two very gas-rich disks. DDO 68 is closest in its properties to cosmologically young low-mass galaxies.
This article was submitted by the authors in English. 相似文献
8.
A new orbital period analysis for U Geminorum is made by means of the standard O–C technique based on 187 times of light minima
including the three newest CCD data from our observation. Although there are large scatter near 70,000 cycles in its O–C diagram,
there is strong evidence (>99.9% confidence level) to show the secular increase of orbital period with a rate
s−1. Using the physical parameters recently derived by Echevarría et al. (Astron. J. 134:262, 2007), the range of mass transfer rate for U Geminorum is estimated as from −3.5(5)×10−9 M
⊙ yr−1 to −1.30(6)×10−8 M
⊙ yr−1. Moreover, the data before 60,000 cycles shows the obvious quasi-period variations. The least square estimation of a ∼17.4 yr
quasi-periodic variation superimposed on secular orbital period increase is derived. Considering the possibility that solar-type
magnetic activity cycles in the secondary star of U Geminorum may produce the quasi-period variations of the orbital period,
Applegate’s mechanism is discussed and the results indicate such mechanism has difficulty explaining the quasi-period variation
for U Geminorum. Hence, we attempted to apply the light-travel time effect to interpret the quasi-period variation and found
the perturbation of ∼17.4 yr quasi-period may result from a brown dwarf. If the orbital inclination is assumed as i∼15°, corresponding to the upper limit of mass of a brown dwarf, then its orbital radii is ∼7.7 AU. 相似文献
9.
The GMRTHI 21 cm-line observations of galaxies in the Eridanus group are presented. The Eridanus group, at a distance of ≈ 23 Mpc, is
a loose group of ≈200 galaxies. The group extends to more than 10 Mpc in projection. The velocity dispersion of the galaxies
in the group is ≈240 km s−1. The galaxies are clustered into different sub-groups. The overall population mix of the group is 30% (E + S0) and 70% (Sp
+ Irr). The observations of 57 Eridanus galaxies were carried out with the GMRT for ≈ 200 h. HI emission was detected from
31 galaxies. The channel rms of ≈ 1 mJy beam−1 was achieved for most of the image-cubes made with 4 h of data. The corresponding HI column density sensitivity (3σ) is ≈
1 × 1020 cm−2 for a velocity-width of ≈ 13.4 km s−1. The 3σ detection limit of HI mass is ≈ 1.2 X 107 Mpd for a line-width of 50 km s−1. Total HI images, HI velocity fields, global HI line profiles, HI mass surface densities, HI disk parameters and HI rotation
curves are presented. The velocity fields are analysed separately for the approaching and the receding sides of the galaxies.
These data will be used to study the HI and the radio continuum properties, the Tully-Fisher relations, the dark matter halos,
and the kinematical and HI lopsidedness in galaxies. 相似文献
10.
The Devasthal Fast Optical Telescope (DFOT) is a 1.3 meter aperture optical telescope, recently installed at Devasthal, Nainital. We present here the first results using an Hα filter with this telescope on a Wolf–Rayet dwarf galaxy Mrk 996. The instrumental response and the Hα sensitivity obtained with the telescope are (3.3 ± 0.3) × 10???15 erg s?1 cm?2/counts s?1 and 7.5 × 10???17 erg s?1 cm?2 arcsec?2 respectively. The Hα flux and the equivalent width for Mrk 996 are estimated as (132 ± 37) × 10?14 erg s?1 cm?2 and ~96 Å respectively. The star formation rate is estimated as 0.4 ± 0.1M ⊙ yr?1. Mrk 996 deviates from the radio-FIR correlation known for normal star forming galaxies with a deficiency in its radio continuum. The ionized gas as traced by Hα emission is found in a disk shape which is misaligned with respect to the old stellar disk. This misalignment is indicative of a recent tidal interaction in the galaxy. We believe that galaxy–galaxy tidal interaction is the main cause of the WR phase in Mrk 996. 相似文献
11.
R. Guzmán 《Astrophysics and Space Science》1998,263(1-4):127-130
We study the nature of faint blue compact galaxies (BCGs) at redshifts z ∼ 0.2 - 1.3 using Keck and HST. Despite being very
luminous (LB ∼ L*), most distant BCGs have masses M ∼ 1010M⊙, i.e., they are dwarf stellar systems. The majority of these galaxies have colors, sizes, surface brightnesses, luminosities,
velocity widths, excitations, star formation rates (SFR), and mass-to-light ratios characteristic of the most luminous nearby
HII galaxies. The more massive BCGs form a more heterogeneous class of evolved starburst, similar to local disk starburst
galaxies. Without additional star formation, HII-like BCGs will most likely fade to resemble today's spheroidal galaxies such
as NGC 205.
This revised version was published online in July 2006 with corrections to the Cover Date. 相似文献
12.
We present the results of our stellar photometry and spectroscopy for the new Local Group galaxy VV124 (UGC4879) obtainedwith
the 6-m BTAtelescope. The presence of a fewbright supergiants in the galaxy indicates that the current star formation process
is weak. The apparent distribution of stars with different ages in VV 124 does not differ from the analogous distributions
of stars in irregular galaxies, but the ratio of the numbers of young and old stars indicates that VV 124 belongs to the rare
Irr/Sph type of galaxies. The old stars (red giants) form the most extended structure, a thick disk with an exponential decrease
in the star number density to the edge. Definitely, the young population unresolvable in images makes a great contribution
to the background emission from the central galactic regions. The presence of young stars is also confirmed by the [OIII]
emission line visible in the spectra that belongs to extensive diffuse galactic regions. The mean radial velocity of several
components (two bright supergiants, the unresolvable stellar population, and the diffuse gas) is υ
h = −70 ± 15 km s−1 and the velocity with which VV 124 falls into the Local Group is υ
LG = −12 ± 15 km s−1. We confirm the distance to the galaxy (D = 1.1 ± 0.1 Mpc) and the metallicity of red giants ([Fe/H] = −1.37) found by Kopylov et al. (2008). VV 124 is located on
the periphery of the Local Group approximately at the same distance from M31 and our Galaxy and is isolated from other galaxies.
The galaxy LeoA nearest to it is 0.5 Mpc away. 相似文献
13.
Edo Berger 《New Astronomy Reviews》2011,55(1-2):1-22
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
14.
Stellar abundance pattern of n-capture elements such as barium is used as a powerful tool to infer how the star formation proceeded in dwarf spheroidal
(dSph) galaxies. It is found that the abundance correlation of barium with iron in stars belonging to dSph galaxies orbiting
the Milky Way, i.e., Draco, Sextans, and Ursa Minor have a feature similar to that in Galactic metal-poor stars. The common
feature of these two correlations can be realized by our in homogeneous chemical evolution model based on the supernova-driven
star formation scenario if dSph stars formed from gas with a velocity dispersion of ∼ 26 km s-1. This velocity dispersion together with the stellar luminosities strongly suggest that dark matter dominated dSph galaxies.
The tidal force of the Milky Way links this velocity dispersion with the currently observed value ≲ 10 km s-1 by stripping the dark matter in dSph galaxies. As a result, the total mass of each dSph galaxy is found to have been originally
∼ 25 times larger than at present. In this model, supernovae immediately after the end of the star formation can expel the
remaining gas over the gravitational potential of the dSph galaxy.
This revised version was published online in August 2006 with corrections to the Cover Date. 相似文献
15.
L. Makarova E. Grebel I. Karachentsev A. Dolphin V. Karachentseva M. Sharina D. Geisler P. Guhathakurta P. Hodge A. Sarajedini P. Seitzer 《Astrophysics and Space Science》2003,285(1):107-111
We present a quantitative star formation history derivation of the four suspected tidal dwarf galaxies in the M 81 group:
Holmberg IX, BK3N,Arp-loop (A0952+69) and Garland using HST/WFPC2 images of these galaxies. We construct a library of synthetic
Colour-Magnitude Diagrams(CMDs) based on theoretical isochrones and data-derived determinations of photometric errors. These
synthetic CMDs were combined linearly andχ2-compared to observed photometry. All the galaxies show continuous star formation between about 20 and 200 Myr ago with star
formation rates between 7.5⋅10-3 M⊙/yr and 7.67⋅10-4 M⊙/yr. The metallicity of the detected stars is spanning rather a wide range, being lower than solar abundance. We suppose,
that all the galaxies were formed out of material from metal-poor outer part of the giant spiral galaxy M81after tidal interaction
about 200 Myr ago. However, this suggestion requires significantly more deep color-magnitude diagrams to be sure with the
scenario of the galaxy evolution.
This revised version was published online in July 2006 with corrections to the Cover Date. 相似文献
16.
V. A. Yakovleva O. A. Merkulova G. M. Karataeva L. V. Shalyapina N. V. Yablokova A. N. Burenkov 《Astronomy Letters》2016,42(4):215-227
We analyze new optical spectroscopic observations obtained at the 6-m telescope of the Special Astrophysical Observatory of the Russian Academy of Sciences with the SCORPIO focal reducer (in the modes of a Fabry–Perot interferometer (FPI) and long-slit spectroscopy) and the Multi-Pupil Fiber Spectrograph for the galaxy IC 883. We have confirmed that the main body of the galaxy rotates around its minor axis. The positions of the dynamical axes of the stellar and gaseous components have been found to differ by ~10°. The velocities in the SE tail do not correspond to the circular rotation around the galaxy’s minor axis. This structure is probably a fragment of an unwound curved spiral arm. Regions with high velocity dispersions and peculiarities in the velocity fields have been found along the minor axis. Our study of the age and metallicity of the galaxy’s stellar population has shown that the mean values of these parameters in the stellar disk, except for the central region (r ≤ 5?), are ≈1 Gyr and ≈?0.4 dex, respectively. Both young (2?5 × 108 yr) and old (5?10 × 109 yr) stellar populations are present in the circumnuclear region. Our analysis of the spectroscopic data for the bright feature 8? south of the nucleus coincident in position with a compact X-ray source has shown that this is apparently a dwarf galaxy or a remnant of a companion galaxy. Our FPI observations in the Hα emission line and direct images have revealed a region of ionized gas that together with the already known structures along the minor axis forms a clumpy tidal structure of ionized gas pulled from the companion galaxy. The results of our study confirm the previously proposed hypothesis that the observed peculiar structures were formed by the merger of two galaxies. However, it can be said that IC 883 does not belong to the class of polar-ring galaxies. 相似文献
17.
V. M. Chechetkin S. S. Gershtein V. S. Imshennik L. N. Ivanova M. Yu. Khlopov 《Astrophysics and Space Science》1980,67(1):61-97
The present work studies the hydrodynamic process of thermonuclear explosion of hydrostatic equilibrium, degenerate carbon-oxygen
cores withM
C=1.40M
⊙ with different values of central densityϱ
c
within the interval 2 × 109 <ϱ
c
< 3 × 1010 g cm−3. The initial temperature distribution has been determined by the preceding thermal stage of explosion. The calculations successively
include the kinetics of thermonuclear burning, the kinetics of β-processes, and neutrino energy losses. By considering the
neutrino mechanism of heating and carbon ignition we obtained in our numerical hydrodynamic calculations two characteristic
versions of the development of an explosion: (a) at 2 × 109 <ϱ
c
< 9 × 109 g cm−3 there is disruption of the whole star with either complete or partial burning of the carbon and a 1050–1051 erg kinetic energy; and (b) at 9 × 109 <ϱ
c
< 3 × 1010 g cm−3 the stellar core collapses into a neutron star with partial outburst of the outer envelope with a smaller kinetic energy
of 1049–1050 erg. The paper proposes and details a hypothesis (the scenario of supernovae and the formation of neutron stars) on the first
version of explosion, corresponding to SNII, and on the second, supplemented by some mechanism of slow energy release into
the envelope expelled from the newly formed neutron star, corresponding to SNI. On the basis of the proposed hypothesis a
satisfactory agreement with the observed masses and energies of the supernovae envelope, their light curves and spectra, as
well as with the data on their chemical composition has been obtained. For this agreement we must assume that type I pre-supernovae
are almost bare compact carbon-oxygen stellar cores, and that type II presupernovae are red supergiants. It is most probable
that the evolution of type I pre-supernovae occurs in close binaries while the evolution of type II pre-supernovae seems to
be very similar to the evolution of a single star. 相似文献
18.
Jesper Sommer-Larsen Martin Götz Laura Portinari 《Astrophysics and Space Science》2002,281(1-2):519-524
We have performed TreeSPH simulations of galaxy formation in a standard ΛCDM cosmology, including effects of star formation,
energetic stellar feedback processes and a meta-galactic UV field, and obtain a mix of disk, lenticular and elliptical galaxies.
The disk galaxies are deficient in angular momentum by only about a factor of two compared to observed disk galaxies. The
stellar disks have approximately exponential surface density profiles, and those of the bulges range from exponential to r
1/4, as observed. The bulge-to-disk ratios of the disk galaxies are consistent with observations and likewise are their integrated
B-V colours, which have been calculated using stellar population synthesis techniques. Furthermore, we can match the observed
I-band Tully-Fisher (TF) relation, provided that the mass-to-light ratio of disk galaxies is (M/L
I) ≃ 0.6–0.7. The ellipticals and lenticulars have approximately r
1/4 stellar surface density profiles, are dominated by non-disklike kinematics and flattened due to non-isotropic stellar velocity
distributions, again consistent with observations.
This revised version was published online in September 2006 with corrections to the Cover Date. 相似文献
19.
M. Fellhauer H. Baumgardt P. Kroupa R. Spurzem 《Celestial Mechanics and Dynamical Astronomy》2002,82(2):113-131
Interacting galaxies like the famous Antennae (NGC 4038/4039) or Stephan's Quintet (HCG 92) show considerable star forming activity in their tidal arms. High resolution images (e.g. from HST-observations) indicate that these regions consist of up to hundreds of massive stellar clusters or tidal dwarf galaxies (TDG). In this paper we want to investigate the future fate of these clusters of massive star clusters (in this work called super-clusters). We simulate compact super-clusters in the tidal field of a host-galaxy and investigate the influence of orbital and internal parameters on the rate and timescale of the merging process. We show that it is possible that such configurations merge and build a dwarf galaxy, which could be an important mechanism of how long-lived dwarf satellite galaxies form. A detailed study of the merger object will appear in a follow-up paper.This revised version was published online in October 2005 with corrections to the Cover Date. 相似文献
20.
If massive sterile neutrinos exist, their decays into photons and/or electron-positron pairs may give rise to observable consequences.
We consider the possibility that MeV sterile neutrino decays lead to the diffuse positron annihilation line in the Milky Way
center, and we thus obtain bounds on the sterile neutrino decay rate Γ
e
≥10−28 s−1 from relevant astrophysical/cosmological data. Also, we expect a soft gamma flux of 1.2×10−4–9.7×10−4 ph cm−2 s−1 from the Milky Way center which shows up as a small MeV bump in the background photon spectrum. Furthermore, we estimate
the flux of active neutrinos produced by sterile neutrino decays to be 0.02–0.1 cm−2 s−1 passing through the earth. 相似文献