共查询到20条相似文献,搜索用时 31 毫秒
1.
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
2.
Juan P. Madrid William B. Sparks D. E. Harris Eric S. Perlman Duccio Macchetto John Biretta 《Astrophysics and Space Science》2007,311(1-3):329-333
Near-ultraviolet imaging with HST offers the best possible spatial resolution currently available for optical/UV astronomical
imaging. The giant elliptical galaxy M87 hosts one of the most spectacular, best studied and nearest (d=16 Mpc) galactic-scale relativistic (synchrotron emitting plasma) jets. We have extracted from the HST archive all 220 nm
images of the jet of M87, taken with the STIS MAMA camera and co-added them to provide the deepest image ever at this wavelength.
The combination of highest spatial resolution and long integration time, 42500 seconds, reveals a wealth of complex structure,
knots, filaments and shocks. We compare this image with deep X-ray observations obtained with the Chandra X-ray telescope. 相似文献
3.
We report on the results of cross-correlation of a sample of 903 Utraluminous IRAS galaxies (ULIRGs) with the ROSAT-All Sky Survey Bright Source Catalogue and the ROSAT archived pointing observations. The sample of ULIRGs has been compiled from the recently released PSCz redshift survey. In total,35 ULIRGs are securely detected by the ROSAT All-Sky Survey and pointing observations, five of which are blazars. The statistical properties of these sources in the soft X-ray band are determined and compared with their properties on other wavebands. We find that the ratio of the soft X-ray to the far-infrared flux spans about five orders of magnitude and reaches values of about unity. This ratio is a good indicator of the main energy source of ULIRGs. Those with soft X-ray to far-infrared flux exceeding 0.01 are probably powered by accretion onto central supermassive black holes while those with ratios smaller than 0.001 are probably powered by starbursts or other heating processes, or are Compton thick sources. Some ULIRGs have energy contributions from both. This ratio is low for most ULIRGs and hyperluminous infrared galaxies, which explains their low detection rate by ROSAT and ASCA.We also find that some ULIRGs have a similar soft X-ray luminosity vs. temperature relation to that for groups of galaxies and elliptical galaxies,suggesting a common origin of these systems. Our study also reveals a tight correlation between the hardness ratio and the soft X-ray luminosity for Seyfert 1s/QSOs. 相似文献
4.
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
5.
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
6.
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
7.
We discuss the properties of the galaxies in about 60 rich, nearby clusters, using kinematic data from the ESO Nearby Abell
Cluster Survey, combined with new imaging data. The images were used to classify the galaxies, and to recalibrate the galaxy
types derived from the ENACS spectra; this yields galaxy-type estimates for about4800 galaxies. For about 1200 galaxies, a
bulge/disk decomposition could be made, which yields sizes and luminosities of bulges and disks. From the projected radial
distances and relative l.o.s.-velocities we derived the galaxy ensembles with significantly different phase-space distributions.
We find that galaxies in and outside substructure must be distinguished. The morphological composition of the substructures
appears to vary with projected radius. Outside substructures, 4 galaxy ensembles must be defined: viz. the brighest Es, the
other early-type galaxies, the early spirals(Sa-Sb), and the late spirals (including the emission-line galaxies). We also
study the morphology-density relation, and we find that the segregation of the late spirals is driven mostly by global factors,
while the segregation of Es, S0s and early spirals is driven mostly by local density. The properties of early spirals and
S0ssupport the picture in which early spirals transform into S0s, while the properties of the late spirals do not support
such a relation.
This revised version was published online in July 2006 with corrections to the Cover Date. 相似文献
8.
《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
9.
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
10.
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
11.
We determine the mass profile of a synthetic cluster built from the combination of 59 nearby clusters observed in the ESO
Nearby Abell Cluster Survey (ENACS). We use ellipticals and S0s as tracers of the cluster potential, and solve the Jeans equation
assuming isotropic orbits. Such an assumption is justified by the analysis of the shape of the velocity distribution of ellipticals
and S0s. We find that the cluster mass profile is consistent with the Navarro, Frenk and White(NFW) model. We use this cluster
mass profile to search for equilibrium solutions for the other cluster galaxy populations: very bright ellipticals (M
R
≤–22+5 log h),early-type spirals (Sa-Sb), and late-type spirals and irregulars (Sbc-Ir), together with emission-line galaxies. We find
equilibrium solutions for both the early- and the late-spirals, but not for the very bright ellipticals. The dynamics of very
bright ellipticals is probably affected by dissipative processes which invalidate the use of the collisionless Jeans equation.
The equilibrium solution found for the early-spirals implies them to move on nearly-isotropic orbits. Late-spirals are instead
found to be on mildly radial orbits, with the radial anisotropy increasing outwards. We discuss the implications of these
results for the evolutionary histories of the different populations of cluster galaxies.
This revised version was published online in July 2006 with corrections to the Cover Date. 相似文献
12.
13.
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
14.
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
15.
Javier Graciá-Carpio Santiago García-Burillo Pere Planesas 《Astrophysics and Space Science》2008,313(1-3):331-335
The sample of nearby LIRGs and ULIRGs for which dense molecular gas tracers have been measured is building up, allowing for
the study of the physical and chemical properties of the gas in the variety of objects in which the most intense star formation
and/or AGN activity in the local universe is taking place. This characterisation is essential to understand the processes
involved, discard others and help to interpret the powerful starbursts and AGNs at high redshift that are currently being
discovered and that will routinely be mapped by ALMA. We have studied the properties of the dense molecular gas in a sample
of 17 nearby LIRGs and ULIRGs through millimeter observations of several molecules (HCO+, HCN, CN, HNC and CS) that trace different physical and chemical conditions of the dense gas in these extreme objects. In
this paper we present the results of our HCO+ and HCN observations. We conclude that the very large range of measured line luminosity ratios for these two molecules severely
questions the use of a unique molecular tracer to derive the dense gas mass in these galaxies. 相似文献
16.
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
17.
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
18.
P. Augusto J. I. Gonzalez-Serrano A. C. Edge N. A. B. Gizani P. N. Wilkinson I. Perez-Fournon 《New Astronomy Reviews》1999,43(8-10)
We are conducting a multi-wavelength (radio, optical, and X-ray) observational campaign to classify, morphologically and physically, a sample of 55 flat-spectrum radio sources dominated by structure on kpc-scales. This sample contains 22 compact-/medium-sized symmetric object candidates, a class of objects thought to be in the early stages of the evolution of radio galaxies. The vast majority of the remaining objects have core-plus-one-sided-jet structures, half of which show sharply bent jets, probably due to strong interactions with the interstellar medium of the host galaxies. Once the observational campaign is completed, we will constrain evolutionary theories of radio galaxies at their intermediate stages and possibly understand the physics of the hypothesised narrow-line region in active galactic nuclei, given our advantageous statistical position. 相似文献
19.
We present density profiles, that are solutions of the spherical Jeans equation, derived under the following two assumptions: (i) the coarse grained phase-density follows a power-law of radius, ρ/σ3 ∝ r−, and (ii) the velocity anisotropy parameter is given by the relation βa(r)=β1+2β2 (r/r*)/[1+(r/r*)2] where β1, β2 are parameters and r* equals twice the virial radius, rvir, of the system. These assumptions are well motivated by the results of N-body simulations. Density profiles have increasing logarithmic slopes γ, defined by γ=−d ln ρ/d ln r. The values of γ at r=10−2.5rvir, a distance where the systems could be resolved by large N-body simulations, lie in the range 1.0–1.6. These inner values of γ increase for increasing β1 and for increasing concentration of the system. On the other hand, slopes at r=rvir lie in the range 2.42–3.82. A model density profile that fits well the results at radial distances between 10−3rvir and rvir and connects kinematic and structural characteristics of spherical systems is described. 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