共查询到20条相似文献,搜索用时 31 毫秒
1.
Peter M. Weilbacher U. Fritze-von Alvensleben P.-A. Duc 《Astrophysics and Space Science》2003,284(2):639-642
We analyzed a sample of 44 candidates for Tidal Dwarf Galaxies(TDGs) previously selected on optical imaging with low resolution spectroscopy. Most of the TDG candidates have the same redshift
as the interacting system, 3 of them very likely are low metallicity dwarf galaxies in projection, and 13 show signs of kinematics
decoupled from their hosting tidal tail. Subsequent NIR photometry in combination with evolutionary synthesis modeling allows
us to derive stellar masses, star formation rates, and the ratio of old to young stars within each TDG candidate.
This revised version was published online in August 2006 with corrections to the Cover Date. 相似文献
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We present a comparative analysis of 5 GHz VLA and 200 ks Chandra ACIS-I image. In the 5 GHz image the familiar jet and much weaker counterjet are seen, which bend as the jet propagates towards
the hotspots. Furthermore, where the lobe detected in 5 GHz emission starts to interact with the jet, we see that the jet
“threads”. In the 0.2–10 keV X-ray image we do not detect the jet, but do detect a relic of the counterjet. 相似文献
4.
Gerhard Hensler Daniel Tschöke Dominik Bomans Alessandro Boselli 《Astrophysics and Space Science》2003,284(2):467-470
Observations of the Virgo Cluster galaxy NGC 4569 in soft X-rays and in Hα reveal both an asymmetrically distributed hot gaseous
halo and a giant filament of diffuse emission, respectively, extending from the same side of the disk, the latter one to at
least 8.8 kpc. A deep longslit spectrum along the filament shows velocities systematically different from the systemic velocity
of NGC 4569. With the inclination of the disk one can determine the Hα spur as a giant outflow in NGC 4569.
This revised version was published online in August 2006 with corrections to the Cover Date. 相似文献
5.
L. Tanvuia W.W. Zeilinger P. Focardi B. Kelm R. Rampazzo 《Astrophysics and Space Science》2003,284(2):459-462
This is a study concerning the investigation of galaxy formation and evolution in small-scale structures and the influence
of the environment on the properties of galaxies. The environment plays a key role in the evolution of galaxies since it governs
the type of encounters. We present results from low-resolution spectroscopy and R-band surface photometry of multiplets of
galaxies found in low-density environments and compare them to cluster environments. Properties such as induced galaxy activity,
star formation enhancements, AGN activity and the connection between merging and galaxy morphology are investigated.
This revised version was published online in August 2006 with corrections to the Cover Date. 相似文献
6.
Andrei Lobanov 《Astrophysics and Space Science》2007,311(1-3):263-267
Compact relativistic jets in active galactic nuclei offer an effective tool for investigating the physics of nuclear regions
in galaxies. The emission properties, dynamics, and evolution of jets in AGN are closely connected to the characteristics
of the central supermassive black hole, accretion disk and broad-line region in active galaxies. Recent results from studies
of the nuclear regions in several active galaxies with prominent outflows are reviewed in this contribution. 相似文献
7.
K.G. Noeske P. Papaderos L.M. Cairós K.J. Fricke 《Astrophysics and Space Science》2003,284(2):615-618
We present deep Near-Infrared (NIR) imaging of Blue Compact Dwarf Galaxies (BCDs), allowing for the first time to derive and
systematize the NIR structural properties of their stellar low-surface brightness (LSB) host galaxies. Compared to optical
data, NIR images, being less contamined by the extended stellar and ionized gas emission from the starburst, permit to study
the LSB host galaxy closer to its center. We find that radial surface brightness profiles (SBPs) of the LSB hosts show at
large radii a mostly exponential intensity distribution, in agreement with previous optical studies. At small to intermediate
radii, however, the NIR data reveal an inwards flattening with respect to the outer exponential slope (`type V SBPs', Binggeli
and Cameron, 1991) in the LSB component of more than one half of the sample BCDs. This result may constitute an important
observational constraint to the dynamics and evolution of BCDs. We apply a modified exponential fitting function (Papaderos
et al., 1996a) to parametrize and systematically study type V profiles in BCDs. A Sérsic law is found to be less suitable
for studying the LSB component of BCDs, since it yields very uncertain solutions.
This revised version was published online in August 2006 with corrections to the Cover Date. 相似文献
8.
We study the spatial orientation of 5 169 galaxies that have radial velocity 3 000 to 5 000 km s−1. The ‘position angle–inclination’ method is used to find the spin vector and the projections of spin vector of the galaxy
rotation axes. The spatial isotropic distribution is assumed to examine the non-random effects. For this, we have performed
chi-square, Fourier, and auto-correlation tests. We found a random alignment of spin vectors of total galaxies with respect
to the equatorial coordinate system. The spin vector projections of total galaxies is found to be oriented tangentially with
respect to the equatorial center. The spiral galaxies show a similar orientation as shown by the total sample. Five subsamples
of barred spiral (late-type) galaxies show a preferred alignment. However, early-type barred spirals show a random orientation.
A weak morphological dependence is noticed in the subsamples of late type barred spirals. A comparison with the previous works
and the possible explanation of the results will be presented. 相似文献
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Sebastian L. Hidalgo Antonio Aparicio David MartÍnez-Delgado 《Astrophysics and Space Science》2003,284(2):595-598
The surface brightness profile in the V band of the Phoenix dwarf galaxy shows two stellar components: an inner one, which
contains all the young stars of the galaxy, and an outer one predominantly populated by red stars. Deep color-magnitude diagrams
(CMDs), based on Hubble Space Telescope (HST) observations and reaching the oldest turn-offs, are used to analyze the inner
and outer stellar components. Results show that, together with an old stellar population, the outer field contains also an
intermediate-age population. These results are compatible with a scenario in which star forming regions are shrinking with
time (the shrinking scenario). It seems more difficult to support a halo-disk scenario, which would require extended structures
populated only by really old stars.
This revised version was published online in August 2006 with corrections to the Cover Date. 相似文献
11.
K. I. Kellermann R. C. Vermeulen J. A. Zensus M. H. Cohen A. West 《New Astronomy Reviews》1999,43(8-10)
The VLBA has been used over a period of four years to study the internal motions within a sample of quasars and AGN. In most sources, features appear to propagate away from the central engine along a well collimated radio jet with apparent transverse velocities between zero and 10c, with some evidence for apparent accelerations and decelerations. The distribution of apparent velocity is not consistent with any simple ballistic model and appears to require either a spread in intrinsic velocity or a difference between the bulk velocity and pattern velocity. The dependence of apparent angular velocity with redshift is consistent with standard Friedmann world models. Further observations of a larger source sample, especially at large redshift may lead to meaningful constraints on world models. 相似文献
12.
S. Boissier D. Monnier Ragaigne W. van Driel C. Balkowski N. Prantzos 《Astrophysics and Space Science》2003,284(2):913-916
We show that simple models of the chemical and spectrophotometric evolution of galaxies can be used to explore the properties
of present-day galaxies and especially the causes of the observed variety among disc galaxies. We focus on the link between
`classical' spirals and Low Surface Brightness galaxies.
This revised version was published online in August 2006 with corrections to the Cover Date. 相似文献
13.
P. Papaderos Y.I. Izotov K.G. Noeske L.M. Cairós N.G. Guseva T.X. Thuan K.J. Fricke 《Astrophysics and Space Science》2003,284(2):619-622
Using HST and ground-based optical and NIR imaging data, we investigate whether the blue compact dwarf (BCD) galaxy I Zw 18
possesses an extended low-surface brightness (LSB) old stellar population underlying its star-forming (SF) regions. We show
that the exponential intensity decrease observed in the filamentary LSB envelope of the BCD out to 18″ (1.3 kpc at the adopted
distance of 15 Mpc) is not due to an evolved stellar disc, but rather due to extended ionized gas emission. Broad-band images
reveal, after subtraction of nebular line emission, a compact stellar LSB component extending slightly beyond the SF regions.
This stellar host, being blue over a radius range of 5 exponential scale lengths and showing little colour contrast to the
SF component, differs strikingly from the red LSB host of standard BCDs. This fact, in connection with the blue colours of
component I Zw 18 C (see discussion in Papaderos et al. 2002), suggests that most of the stellar mass in I Zw 18 has formed
within the last 0.5 Gyr. Furthermore, we show that the exponential intensity fall-off in the filamentary ionized envelope
of I Zw 18 is not particular to this system but a common property of the ionized halo of many SF dwarf galaxies on galactocentric
distances of several kpc. In the absence of an appreciable underlying stellar background, extended ionized gas emission dominates
in the periphery of I Zw 18, superficially resembling an exponential stellar disc on optical surface brightness profiles.
The case of I Zw 18 suggests caution in the search of more distant young galaxy candidates. Intense SF activity in the early
phase of dwarf galaxy formation may result in an extended ionized gas halo which can be mistaken for an evolved stellar disc
by studying only its exponential surface brightness profile.
This revised version was published online in August 2006 with corrections to the Cover Date. 相似文献
14.
New observations show that most of the flattened diffuse elliptical (dE) galaxies are essentially isotropic rotators. This
supports the idea that dEs have evolved from fast rotating dIrr systems or late-type spirals after their gas was expelled
by SN-driven winds and stripped by ram pressure against the intergalactic medium.
This revised version was published online in August 2006 with corrections to the Cover Date. 相似文献
15.
The probabilistic nature of the IMF in stellar systems implies that clusters of the same mass and age do not present the same
unique values of their observed parameters. Instead they follow a distribution. We address the study of such distributions
in terms of their confidence limits that can be obtained by evolutionary synthesis models. These confidence limits can be
understood as the inherent uncertainties of synthesis models. We will compare such confidence limits arising from the discreteness
of the number of stars obtained with Monte Carlo simulations with the dispersion resulting from an analytical formalism. We
give some examples of the effects on the kinetic energy, V–K, EW(Hβ) and multiwavelength continuum.
This revised version was published online in September 2006 with corrections to the Cover Date. 相似文献
16.
《New Astronomy》2015
Using the potential-density phase shift approach developed by the present authors in earlier publications, we estimate the magnitude of radial mass accretion/excretion rates across the disks of six nearby spiral galaxies (NGC 628, NGC 3351, NGC 3627, NGC 4321, NGC 4736, and NGC 5194) having a range of Hubble types. Our goal is to examine these rates in the context of bulge building and secular morphological evolution along the Hubble sequence. Stellar surface density maps of the sample galaxies are derived from SINGS 3.6 μm and SDSS i-band images using colors as an indicator of mass-to-light ratios. Corresponding molecular and atomic gas surface densities are derived from published CO (1-0) and HI interferometric observations of the BIMA SONG, THINGS, and VIVA surveys. The mass flow rate calculations utilize a volume-type torque integral to calculate the angular momentum exchange rate between the basic state disk matter and what we assume to be density wave modes in the observed galaxies. This volume-type integral contains the contributions from both the gravitational surface torque couple and the advective surface torque couple at the nonlinear, quasi-steady state of the wave modes, in sharp contrast to its behavior in the linear regime, where it contains only the contribution from the gravitational surface torque couple used by Lynden-Bell & Kalnajs in 1972. The potential-density phase shift approach yields angular momentum transport rates several times higher than those estimated using the Lynden-Bell and Kalnajs approach. And unlike Lynden-Bell and Kalnajs, whose approach predicts zero mass redistribution across the majority of the disk surface (apart from the isolated locations of wave-particle resonances) for quasi-steady waves, the current approach leads to predictions of significant mass redistribution induced by the quasi-steady density wave modes, enough for the morphological types of disks to evolve substantially within its lifetime. This difference with the earlier conclusions of Lynden-Bell and Kalnajs reflects the dominant role played by collisionless shocks in the secular evolution of galaxies containing extremely non-linear, quasi-steady density wave modes, thus enabling significant morphological transformation along the Hubble sequence during a Hubble time. We show for the first time also, using observational data, that stellar mass accretion/excretion is just as important, and oftentimes much more important, than the corresponding accretion/excretion processes in the gaseous component, with the latter being what had been emphasized in most of the previous secular evolution studies. 相似文献
17.
Sukyoung K. Yi 《Astrophysics and Space Science》2002,281(1-2):203-206
This paper investigates the uncertainties in the synthetic integrated colours of simple stellar populations, currently the most popular method of estimating the ages of unresolved stellar systems. Three types of uncertainties studied
here originate from the stellar models, the population synthesis techniques, and from the stellar spectral libraries. Despite
some skepticism, synthetic colours appear to be reliable age indicators as long as they are used for select age ranges.
This revised version was published online in September 2006 with corrections to the Cover Date. 相似文献
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19.
S. Baes-Fischlmair W.W. Zeilinger J.-C. Vega-Beltran J.E. Beckman 《Astrophysics and Space Science》2003,284(2):735-738
It is assumed that the two-fold disc-wide symmetry of spirals is caused by density waves, but also the potential of a bar
component may have a significant influence on structural properties. The strength of the bar component appears to be anti-correlated
with the degree of symmetry of star-forming regions in the spiral arms (Rozas et al., 1998). We present new results of R and
Hα surface photometry of a sample of bright barred spirals. A photometric decompositon of the galaxy components is carried
out in order to make a more accurate measurement of the strength of the bar and its interrelation to gas and stars in the
disc.
This revised version was published online in August 2006 with corrections to the Cover Date. 相似文献
20.
We present a statistical analysis of the big blue bump (BBB) feature for a large heterogeneous sample of 95 optically selected and soft X-ray bright, low redshift active galactic nuclei (AGNs). This sample covers a sufficiently broad luminosity range, allowing us to test the luminosity dependence of the spectral energy distribution in the BBB region. Following the works of Zheng et al., Laor et al. and Kriss et al., we introduce the broad band spectral index from 1050 Å to0.5 keV (α UV-SX ), compare its distribution with that of the soft X-ray spectral index (α SX ) obtained by ROSAT PSPC, and find that the two indices have equal average-values within 1 ~ 2σuncertainties, whether in the whole sample, in luminosity divisions or in subsamples. These equalities also have no obvious luminosity dependence. This indicates that a single power law can describe the overall UV toX-ray spectrum in a statistical sense, or the broad band UV to soft X-ray spectrum is the soft X-ray spectral extension on an average. Thus, our results support Laor et al.'s conjecture about the BBB peak aroundFUV 1050 Å from a statistical viewpoint. As we further test whether the equality holds for individual objects within measure errors, χ2 test refuse to accept it. In addition, our statistical results, from the luminosity divisions and on the correlation of spectral indices with luminosity (M B), imply that the luminosity dependence of α UV and α UV-SX is mainly due to absorption in low luminosity AGNs. 相似文献