共查询到20条相似文献，搜索用时 609 毫秒
1.
By using the SDSS spectra, we have studied the star formation properties of the nearby spiral galaxies selected from the Revised Bright Galaxy Sample, and tried to find the effect of bar structure on the star formation activity in the nuclear regions of nearby galaxies. The stellar population composition and the intensity of star formation activities of each sample galaxy are acquired by using the stellar population synthesis code—STARLIGHT, and the star formation properties of nuclear regions are compared with those of integral sample galaxies. We find that the star formation in barred spiral galaxies is more active than that of unbarred spirals, and that barred spirals have younger stellar populations. 相似文献
2.
利用SDSS光谱,研究了IRAS卫星亮红外源星表中的盘状星系中的恒星形成性质,并着重探讨了棒对星系核区恒星形成活动的影响.利用星族合成的方法得到了每个样本星系核区的恒星组成性质、恒星形成活动的强度等信息,并比较了星系整体和核区恒星形成性质的差异.得到的结论:除去相互作用,样本中的棒星系显示出比非棒旋星系更强的核区恒星形成活动和更多的年轻星族成分. 相似文献
3.
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
4.
D. M. Worrall 《Astronomy and Astrophysics Review》2009,17(1):1-46
Jet physics is again flourishing as a result of Chandra’s ability to resolve high-energy emission from the radio-emitting structures of active galaxies and separate it from the X-ray-emitting thermal environments of the jets. These enhanced capabilities have coincided with an increasing interest in the link between the growth of super-massive black holes and galaxies, and an appreciation of the likely importance of jets in feedback processes. I review the progress that has been made using Chandra and XMM-Newton observations of jets and the medium in which they propagate, addressing several important questions, including: Are the radio structures in a state of minimum energy? Do powerful large-scale jets have fast spinal speeds? What keeps jets collimated? Where and how does particle acceleration occur? What is jet plasma made of? What does X-ray emission tell us about the dynamics and energetics of radio plasma/gas interactions? Is a jet’s fate determined by the central engine? 相似文献
5.
H. Arp 《Astrophysics and Space Science》2006,301(1-4):117-126
The association of low redshift, active galaxies with high redshift quasars is here tested in two regions uniformly surveyed
for quasars to faint limits. Three active galaxies in these regions all show significant association with nearby quasars.
Radio, optical and X-ray data available for these galaxies give new information on the processes which accompany the proposed
ejection of the quasars. It is concluded that the quasars are originally relatively compact compared to the galactic medium
through which they exit but can be slowed. It is argued that effects of ejection can be seen on the galaxies and may be connected
with spiral structure. Evidence for periodicity of the redshifts is discussed. 相似文献
6.
Gennady Bisnovatyi-Kogan 《Astrophysics and Space Science》2007,311(1-3):287-292
Many quasars and active galactic nuclei (AGN) appear in radio, optical, and X-ray maps, as a bright nuclear sources from which
emerge single or double long, thin jets. When observed with high angular resolution these jets show structure with bright
knots separated by relatively dark regions. Nonthermal nature of a jet radiation is well explained as the synchrotron radiation
of the relativistic electrons in an ordered magnetic field. We consider magnetic collimation, connected with torsional oscillations
of a cylinder with elongated magnetic field, and periodically distributed initial rotation around the cylinder axis. The stabilizing
azimuthal magnetic field is created here by torsional oscillations, where charge separation is not necessary. Approximate
simplified model is developed. Ordinary differential equation is derived, and solved numerically, what gives a possibility
to estimate quantitatively the range of parameters where jets may be stabilized by torsional oscillations. 相似文献
7.
Summary The nuclear regions of many galaxies are not accessible at optical wavelengths and are devoid of HI, but contain large quantities of molecular gas and dust. With recent advances in instrumentation it is now possible to probe the kinematics and physical state of the cool dense interstellar medium, thus providing a new and important tool to investigate the circumnuclear gas in galaxies that are more active than our own. The scope of this review is to summarize results related to the subject with an emphasis on observational data. Sects. 1 and 2 present a general introduction, followed by a discussion of molecular mass estimates. In Sect. 3 correlations between nuclear and global galactic properties are discussed. Sects. 4 and 5 summarize observational results for nearby strongly interacting galaxies, properties of molecular bars and rings, and theoretical advances in modelling the data. The main part of the review (Sects. 6–8) describes the kinematics and the physical and chemical properties of the dense gas, including masers, and compares them with the nuclear region of the Galaxy. Molecular gas in distant galaxies and the evolution of active galaxies are discussed in Sect. 9. Some promising avenues for future research are outlined in Sect. 10. 相似文献
8.
C. Tadhunter T. G. Robinson R. M. González Delgado K. Wills R. Morganti 《Monthly notices of the Royal Astronomical Society》2005,356(2):480-494
We present high-quality long-slit spectra for three nearby powerful radio galaxies – 3C 293, 3C 305 and PKS 1345+12. These were taken with the aim of characterizing the young stellar populations (YSP), and thereby investigating the evolution of the host galaxies, as well as the events that triggered the activity. Isochrone spectral synthesis modelling of the wide wavelength coverage spectra of nuclear and off-nuclear continuum-emitting regions have been used to estimate the ages, masses and luminosities of the YSP component, taking full account of reddening effects and potential contamination by activity-related components. We find that the YSP make a substantial contribution to the continuum flux in the off-nuclear regions on a radial scale of 1–20 kpc in all three objects. Moreover, in two objects we find evidence for reddened post-starburst stellar populations in the near-nuclear regions of the host galaxies. The YSP are relatively old (0.1–2 Gyr), massive (109 < M YSP < 2 × 1010 M⊙ ) and make up a large proportion (∼1–50 per cent) of the total stellar mass in the regions of the galaxies sampled by the observations. Overall, these results are consistent with the idea that the nuclear activity of active galactic nuclei in some radio galaxies is triggered by major gas-rich mergers. Therefore, these radio galaxies form part of the subset of early-type galaxies that is evolving most rapidly in the local Universe. Intriguingly, the results also suggest that the radio jets are triggered relatively late in the merger sequence, and that there is an evolutionary link between radio galaxies and luminous/ultraluminous infrared galaxies. 相似文献
9.
Susanne Aalto 《Astrophysics and Space Science》2008,313(1-3):273-278
Molecular line emission is a useful tool for probing the highly obscured inner kpc of starburst galaxies and buried AGNs.
Molecular line ratios serve as diagnostic tools of the physical conditions of the gas—but also of its chemical properties.
Both provide important clues to the type and evolutionary stage of the nuclear activity. While CO emission remains the main
tracer for molecular distribution and dynamics, molecules such as HCN, HNC, HCO+, CN and HC3N are useful for probing the properties of the denser (n≳104 cm−3), star-forming gas. Here I discuss current views on how line emission from these species can be interpreted in luminous galaxies.
HNC, HCO+ and CN are all species that can be associated both with photon dominated regions (PDRs) in starbursts—as well as X-ray dominated
regions (XDRs) associated with AGN activity. HC3N line emission may identify galaxies where the starburst is in the early stage of its evolution. 相似文献
10.
Research on two-dimensional (2-D) properties of galaxies is a significant component of the study of galaxy formation and evolution.
Through the spatial distribution of physical properties (derived from integrated luminosity and spectroscopy) of galaxies,
we are allowed to realize the inner environment and evolution history of each individual galaxy and finally answer how galaxies
were assembled. In this paper, with reviewing previous work, we present a proposal for study on 2-D properties of nearby galaxies.
In our prospective work, we will make use of multi-wavelength data covering a range from ultraviolet to far-infrared to determine
the distributions of properties such as age, metallicity and dust-reddening in nearby galaxies, and try to remove the degeneracy
among them. Combining with surface photometry and spectroscopy, we will also analyze the distribution of HII regions and star
formation properties in galaxies. In our future plan, the World Space Observatory for Ultraviolet (WSO/UV) will be applied to our research and allow detail diagnosis of nearby galaxies at ultraviolet band. 相似文献
11.
Galactic winds are important in recycling energy and metals in galaxies. They are also suspected to be the primary mechanism
in the enrichment of the intergalactic medium. New observations are revealing the ubiquity of galactic winds, particularly
at high redshift. We review the observational evidence for them in nearby star-forming and active galaxies and in the high-redshift
universe. 相似文献
12.
OASIS observations obtained at the Canada–France–Hawaii Telescope for the spiral galaxies NGC 4900 and NGC 5430 produce one spectrum for each 0.41″ element of the 11″ × 15″ field of view. This allows for the spatial characterisation of the different stellar populations. From these observations we study the young (10 Myr) and older stellar populations using evolutionary synthesis codes. Based on the gas emission lines, we find that the young populations are located in relatively small regions and dominate the integrated flux. In NGC 4900, the young populations are distributed in a bar-like structure featuring a hole near the position of the galaxy’s centre. The young stellar populations of NGC 5430 form a nuclear ring and two patches at the base of the spiral arms. Based on Mg2 and FeI absorption lines, we find that in both galaxies, the young stars are superimposed on a relatively homogenous population of a few Gyr. 相似文献
13.
Cygnus A was the first hyper-active galaxy discovered, and it
remains by far the closest of the ultra-luminous radio galaxies. As
such, Cygnus A has played a fundamental role in the study of virtually
all aspects of extreme activity in galaxies. We present a review of jet
theory for powering the double-lobed radio emitting structures in
powerful radio galaxies, followed by a review of observations of Cygnus
A in the radio, optical, and X-ray relevant to testing various aspects
of jet theory. Issues addressed include: jet structure from pc- to
kpc-scales, jet stability, confinement, composition, and velocity, the
double shock structure for the jet terminus and the origin of multiple
radio hotspots, the nature of the filamentary structure in the radio
lobes, and the hydrodynamic evolution of the radio lobes within a dense
cluster atmosphere, including an analysis of pressure balance between
the various gaseous components. Also discussed are relativistic
particle acceleration and loss mechanisms in Cygnus A, as well as
magnetic field strengths and geometries both within the radio source,
and in the intracluster medium. We subsequently review the
classification, cluster membership, and the emission components of the
Cygnus A galaxy. The origin of the activity is discussed.
Concentrating on the nuclear regions of the galaxy, we review the
evidence for an obscured QSO, also given the constraints on the
orientation of the radio source axis with respect to the sky plane. We
present an overview of models of central engines in AGN and observations
of Cygnus A which may be relevant to testing such models. We conclude
with a brief section concerning the question of whether Cygnus A is
representative of powerful high redshift radio galaxies.
Received October 10, 1995 相似文献
14.
15.
利用星团谱样本的星族合成方法,研究了邻近巨椭圆星系NGC5018中的星族成分和其内部的恒星形成历史,给出了星系中不同年龄和金属丰度星族的成分占有比.星族合成结果表明,NGC5018中不仅存在大量金属丰度低的年老恒星成分,而且较年轻的星族成分(T=5×108yr)对星系光度贡献也很重要.星系吞并和相互作用过程可能是触发这些较年轻星族形成的物理原因,椭圆星系内部的恒星形成历史可能是2次爆发或者多次爆发过程.这些结果可以很好地解释NGC5018颜色偏蓝、Mg2谱指数强度偏弱等观测特征. 相似文献
16.
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
17.
We have used ESO’s new NIR IFS SINFONI during its Science Verification period to observe the central regions of local starburst galaxies. Being Science Verification observations, the aim was 2-fold: to demonstrate SINFONI’s capabilities while obtaining information on the nature of starclusters in starburst galaxies. The targets chosen include a number of the brighter clusters in NGC1808 and NGC253. Here we present first results. 相似文献
18.
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
19.
Active galactic nuclei (AGNs) form two distinct sequences on the radio-loudness–Eddington ratio plane. The ‘upper’ sequence contains radio selected AGNs, the ‘lower’ sequence is composed mainly of optically selected AGNs. The sequences mark the upper bounds for the radio-loudness of two distinct populations of AGNs, hosted, respectively, by elliptical and disk galaxies. Both sequences show the same dependence of the radio-loudness on the Eddington ratio (an increase with decreasing Eddington ratio), which suggests that another parameter in addition to the accretion rate must play a role in determining the efficiency of jet production in AGNs. We speculate that this additional parameter is the spin of the black hole, assuming that black holes in giant elliptical galaxies have (on average) much larger spins than black holes in disc galaxies. Possible evolutionary scenarios leading to such a spin dichotomy are discussed. The galaxy-morphology related radio dichotomy breaks down at high accretion rates where the dominant fraction of luminous quasars being hosted by giant ellipticals is radio-quiet. This indicates that the production of powerful jets at high accretion rates is in most cases suppressed and, in analogy to X-ray binary systems (XRB) during high and very high states, may be intermittent. Such intermittency can be caused by switches between two different accretion modes, assuming that only during one of them an outflow from the central engine is sufficiently collimated to form a relativistic jet. 相似文献
20.
G. Hasinger J.-U. Fischer A. D. Schwope T. Boller J. Trümper W. Voges 《Astronomische Nachrichten》1997,318(6):329-334
We have selected a complete, flux-limited sample of bright point-like sources with absorbed X-ray spectra from the ROSAT All-Sky survey, the ROSAT Hard Survey (RHS). The sample is drawn from the high-galactic latitude sky, |bII| > ±30°, and avoids the general direction of the Magellanic Clouds and the Virgo Cluster. It comprises a total of 182 objects of which 118 were previosly catalogued objects and 64 were new AGN candidates. Through optical follow-up studies at La Silla, Calar Alto and the 6m Zelentchuk telescope we could identify 56 of the new objects, thus achieving a spectrscopic completeness of 96% of the sample. The selection strategy turned out to be extremely useful. Out of the new identifications, 84% are indeed active galaxies or emission line galaxies. While 14 objects are new BL Lac candidates 33 of the new AGN are Seyfert galaxies with a redshift distribution in the range 0.021–0.63, peaking at around 0.06, i.e. relatively local. Surprisingly, about 40% of the X-ray selected Seyfert galaxies seem to reside in interacting systems. With smaller selection uncertainties this fraction exceeds the number of paired galaxies in optically selected samples and therefore gives strong support to the idea that AGN activity is triggered by interaction. 相似文献