共查询到20条相似文献,搜索用时 62 毫秒
1.
《New Astronomy Reviews》2002,46(2-7):203-205
With objectives to model star formation in radio galaxies, we present results of a starburst model, built by coupling the two codes PÉGASE and CLOUDY. Continuum and emission line data are used to derive the properties of a sample of local starbursts. Data are well reproduced with a new relation between the ionization parameter and the metallicity. Colors and Hα equivalent widths indicate that: (i) an underlying stellar population is needed, and (ii) burst ages span the range [0, 6] Myr. 相似文献
2.
L.M. Cairós B. GarcÍa-Lorenzo N. Caon J.M. VÍlchez P. Papaderos K. Noeske 《Astrophysics and Space Science》2003,284(2):611-614
Preliminary results from a detailed spectrophotometric analysis of the blue compact dwarf galaxy (BCD) Mrk 35 are presented.
We have performed deep UBVRI broad-band and Hα narrow-band optical observations, near-infrared (JHK
s) imaging and long-slit spectroscopy of the galaxy. Mrk 35 is composed of a very young starburst population distributed in
a bar-like structure, placed on top of an underlying, older stellar host galaxy. Using predictions of evolutionary synthesis
models, we estimate the ages of both the starburst regions and the underlying stellar component.
This revised version was published online in August 2006 with corrections to the Cover Date. 相似文献
3.
Qiu-Sheng Gu Lei Shi Shi-Jun Lei Wen-Hao Liu Jie-Hao Huang Department of Astronomy Nanjing University Nanjing qsgu@nju.edu.cn 《中国天文和天体物理学报》2003,3(3):203-211
We present spectrophotometric results of the Seyfert 2 galaxy NGC 2273. The presence of high-order Balmer absorption lines (H8, H9, H10) and weak equivalent widths of Call K A3933, CN A4200, G-band A4300 and MgIb 5173 clearly indicate recent star-forming activity in the nuclear region. Using a simple stellar population synthesis model, we find that for the best fit, the contributions of a power-law featureless continuum, an intermediate-age (~ 108 yr) and an old (> 109yr) stellar population to the total light at the reference normalization wavelength are 10.0%, 33.4% and 56.6%, respectively. The existence of recent starburst activity is also consistent with its high far-infrared luminosity (log LFIR/L = 9.9), its infrared color indexes [a(25,60) = -1.81 and a(60,100) = -0.79, typical values for Seyfert galaxies with circumnuclear starburst], and its q-value (2.23, ratio of infrared to radio flux, very similar to that of normal spirals and starburst galaxies). Byrd et al. have suggested that NGC 2273 mig 相似文献
4.
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
5.
We have investigated the stellar population properties in the central regions of a sample of lenticular galaxies with bars
and single-exponential outer stellar disks using the data from the SAURON integral-field spectrograph retrieved from the open
Isaac Newton Group Archive. We have detected chemically decoupled compact stellar nuclei with a metallicity twice that of
the stellar population in the bulges in seven of the eight galaxies. A starburst is currently going on at the center of the
eighth galaxy and we have failed to determine the stellar population properties from its spectrum. The mean stellar ages in
the chemically decoupled nuclei found range from 1 to 11 Gyr. The scenarios for the origin of both decoupled nuclei and lenticular
galaxies as a whole are discussed. 相似文献
6.
Using a sample of 57 VLT FORS spectra in the redshift range 1.37< z < 3.40 and a comparison sample with 36 IUE spectra of local (
) starburst galaxies we derive CIV equivalent width values and estimate metallicities of starburst galaxies as a function
of redshift. Assuming that a calibration of the CIV equivalent widths in terms of the metallicity based on the local sample
of starburst galaxies is applicable to high-z objects, we find a significant increase of the average metallicities from about 0.16 Z
⊙ at the cosmic epoch corresponding to z ≈ 3.2 to about 0.42 Z
⊙ at z ≈ 2.3. A significant further increase in metallicity during later epochs cannot be detected in our data. Compared to the
local starburst galaxies our high-redshift objects tend to be overluminous for a given metallicity.
This revised version was published online in August 2006 with corrections to the Cover Date. 相似文献
7.
Matteo Correnti Francesco Paresce Rossella Aversa Giacomo Beccari Guido De Marchi Marcella Di Criscienzo Xiaoying Pang Loredana Spezzi Elena Valenti Paolo Ventura 《Astrophysics and Space Science》2012,340(2):263-279
We have used new, deep, visible and near infrared observations of the compact starburst cluster in the giant HII region NGC 3603 and its surroundings with the WFC3 on HST and HAWK-I on the VLT to study in detail the physical properties of its intermediate mass (∼1–3 M⊙) stellar population. We show that after correction for differential extinction and actively accreting stars, and the study of field star contamination, strong evidence remains for a continuous spread in the ages of pre-main sequence stars in the range ∼2 to ∼30 Myr within the temporal resolution available. Existing differences among presently available theoretical models account for the largest possible variation in shape of the measured age histograms within these limits. We also find that this isochronal age spread in the near infrared and visible Colour-Magnitude Diagrams cannot be reproduced by any other presently known source of astrophysical or instrumental scatter that could mimic the luminosity spread seen in our observations except, possibly, episodic accretion. The measured age spread and the stellar spatial distribution in the cluster are consistent with the hypothesis that star formation started at least 20–30 Myrs ago progressing slowly but continuously up to at least a few million years ago. All the stars in the considered mass range are distributed in a flattened oblate spheroidal pattern with the major axis oriented in an approximate South-East–North-West direction, and with the length of the equatorial axis decreasing with increasing age. This asymmetry is most likely due to the fact that star formation occurred along a filament of gas and dust in the natal molecular cloud oriented locally in this direction. 相似文献
8.
The formation and evolution of elliptical galaxies (EGs) are still an open question. In particular, recent observations suggest that EGs are not only simple spheroidal systems of old stars. In this paper, we analyse a sample of EGs selected from the Sloan Digital Sky Survey in order to study the star-forming activity in local EGs. Among these 487 ellipticals, we find that 13 EGs show unambiguous evidence of recent star formation activity betrayed by conspicuous nebular emission lines. Using the evolutionary stellar population synthesis models and Lick absorption line indices, we derive stellar ages, metallicities and α-element abundances, and thus reconstruct the star formation and chemical evolution history of the star-forming elliptical galaxies (SFEGs) in our sample.
We find that SFEGs have relative younger stellar population age, higher metallicity and lower stellar mass, and that their star formation history can be well described by a recent minor and short starburst superimposed on old stellar component. We also detect 11 E+A galaxies whose stellar population properties are closer to those of quiescent (normal) ellipticals than to star-forming ones. However, from the analysis of their absorption line indices, we note that our E+A galaxies show a significant fraction of intermediate-age stellar populations, remarkably different from the quiescent galaxies. This might suggest an evolutionary link between E+As and star-forming ellipticals. Finally, we confirm the relations between age, metallicity, α-element abundance and stellar mass for local EGs. 相似文献
We find that SFEGs have relative younger stellar population age, higher metallicity and lower stellar mass, and that their star formation history can be well described by a recent minor and short starburst superimposed on old stellar component. We also detect 11 E+A galaxies whose stellar population properties are closer to those of quiescent (normal) ellipticals than to star-forming ones. However, from the analysis of their absorption line indices, we note that our E+A galaxies show a significant fraction of intermediate-age stellar populations, remarkably different from the quiescent galaxies. This might suggest an evolutionary link between E+As and star-forming ellipticals. Finally, we confirm the relations between age, metallicity, α-element abundance and stellar mass for local EGs. 相似文献
9.
星暴星系是一类内部正在发生极为剧烈恒星形成的天体。介绍了星暴星系的研究历史及星暴星系的定义。综述了从射电波段到X射线波段星暴星系的光度光谱观察特征及其研究的最新进展。列出了星暴星系研究中存在的一些热点问题,包括星暴的触发机制,星暴时标,星族组分,恒星形成率,内红化以及星暴星系与活动星系核之间的关系等。最后,简述了可能有助于解决这些问题的观测手和理论方法。 相似文献
10.
Richard De Grijs Robert W. O'Connell John S. Gallagher III 《Astrophysics and Space Science》2001,276(2-4):397-404
We present high-resolution optical and near-infrared HST observations of two adjacent regions in the fossil starburst region
inM82, M82 B1 and B2. The presence of both the active and the fossil starburst in M82 provides a unique physical environment
to study the stellar and dynamical evolution of star cluster systems. The cluster population in B2 is more heavily affected
by internal extinction than that in B1, amounting to an excess extinction in B2 of AV,excess≃1.1±0.3 mag. Preliminary age estimates date the cluster population in the fossil starburst between ∼2× 108 and ∼ 109 years. The radial luminosity profiles of the brightest clusters are more closely approximated by power laws than by a Gaussian
model, in particular in their wings, which favours a slow star formation scenario.
This revised version was published online in July 2006 with corrections to the Cover Date. 相似文献
11.
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
12.
《New Astronomy Reviews》2000,44(4-6):257-262
Infrared observations of starburst galaxies provide fundamental information on their stellar content and interstellar medium also in the innermost central regions. Many interesting absorption features due to the red stellar populations and nebular emission lines are present in their spectra. By comparing observations and theoretical predictions based on evolutionary synthesis models, a few crucial features as potential tracers of the galaxy evolution will be analyzed, highlighting the major results and caveats. 相似文献
13.
Olga K. Sil’chenko 《Astrophysics and Space Science》2011,335(1):171-176
I review the origin of UV-radiation in galaxies of different morphological types. UV-excess in spectra of massive elliptical
galaxies which have predominantly old stellar populations is traditionally explained by the contribution of low-mass stars
at very late, poorly known stages of evolution—by so called ‘AGB-manqué’ stars or by the population of extended horizontal
branch. However recent results from the GALEX survey of a large sample of nearby ellipticals have also demonstrated probable
traces of recent star formation in a third of all ellipticals observed. In spiral galaxies extended UV-disks have been discovered
by the GALEX; they are certainly illuminated by the current star formation, but what has provoked star formation in the areas
of very low gas density, beyond the distribution of older stars, is a puzzle yet. The UV-spectra of starburst galaxies or
starforming galactic nuclei are characterized by weak emission lines, if any, quite dissimilar to their optical spectra. 相似文献
14.
Integral spectroscopy data for the nebula GM 1-29 and the source star PV Cep obtained on the 2.6-m telescope at the Byurakan
Observatory are presented. The structure and kinematics of a collimated emission outflow directed along the axis of the nebula
are studied. Changes in the radial velocity and intensity of the absorption component of the nebular Hα line are observed
and studied; these are interpreted as a result of an anisotropy in the stellar wind at distances on the order of several stellar
radii, where this absorption is formed.
__________
Translated from Astrofizika, Vol. 51, No. 3, pp. 461–468 (August 2008). 相似文献
15.
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
16.
S. Lourenso A. Vazdekis R.F. Peletier J.E. Beckman 《Astrophysics and Space Science》2001,276(2-4):651-658
As part of an ongoing project aimed at studying the age and metallicity gradients of the stellar populations along the bars
of a sample of barred spirals of different morphological types, we present our first results on NGC 4314 (SBa). We have obtained
optical and NIR colours and spectral indices along the bar and we interpret some of these results here and discuss their uncertainties
on the basis of single stellar population models. In a preliminary analysis, we constrain the limits for the age and metallicity
of the nucleus and two selected regions in the star formation ring of NGC 4314, characterizing both as metal rich (Z<Z
solar) stellar populations, and finding a difference in the mean luminosity-weighted age of at least ∼ 3–4 Gyr.
This revised version was published online in July 2006 with corrections to the Cover Date. 相似文献
17.
Yasuhiro Shioya Kenji Bekki Alexandre Vazdekis 《Astrophysics and Space Science》2001,276(2-4):823-829
We investigate a one-zone chemo-photometric evolutionary model of truncated spiral galaxies with and without starbursts in
order to explore the origin of the spectrophotometric properties of S0s. First, we show that 1) the tight U-V colour–magnitude (CM) relation cannot reject the model with a starburst and 2) the model with a starburst can explain the
difference in the I-K colour–magnitude relation between S0 galaxies and spiral galaxies. Next, we demonstrate how we can distinguish the truncated
spirals with a starburst from those without a starburst by using the CaII–Hδ/λ4045 diagram (proposed by Leonardi and Rose,
1996) and the 1550-V colour.
This revised version was published online in July 2006 with corrections to the Cover Date. 相似文献
18.
N. D. Melikian V. S. Tamazian J. A. Docobo A. A. Karapetian R. Sh. Natsvlishvili 《Astrophysics》2006,49(4):488-496
Spectral observations of the flare star EV Lac made on the 2.6-m telescope at the Byurakan Observatory in 2000–2002 are reported.
A powerful flare was detected and it was possible to follow the variation in the equivalent widths of the Hα and Hβ lines,
both during the flare and during the quiescent phase of the star. It is shown that the profiles and equivalent widths of the
lines underwent substantial changes. The equivalent widths of these emission lines reached a maximum roughly 40 min after
the flare maximum.
__________
Translated from Astrofizika, Vol. 49, No. 4, pp. 573–583 (November 2006). 相似文献
19.
A composite sample of NIR-selected galaxies having extended multicolor coverage has been used to probe the cosmological evolution
of the blue luminosity function and of the stellar mass function. The bright fraction of the sample has spectroscopic redshifts,
and the remaining fraction well-calibrated photometric redshifts. The resulting blue luminosity function shows an increasing
brightening with redshift respect to the local luminosity function. Hierarchical CDM models predictions are in agreement only
at low and intermediate redshifts but fail to reproduce the observed brightening at high redshifts (z ∼ 2–3). This brightening marks the epoch where starburst activity triggered by galaxy interactions could be an important
physical mechanism for the galaxy evolution. At the same time the NIR galaxy sample has been used to trace the evolution of
the cosmological stellar mass density up to ∼3. A clear decrease of the average mass density is apparent with a fraction ∼15%
of the local value at z ∼ 3. UV bright star-forming galaxies are substancial contributors to the evolution of the stellar mass density. Although
these results are globally consistent with Λ–CDM scenarios, they tend to underestimate the mass density produced by more massive
galaxies present at z > 2. 相似文献
20.
Javier Alcolea Valentín Bujarrabal Roberto Neri 《Astrophysics and Space Science》2008,313(1-3):235-239
M 1–92 is a very well studied bipolar pPN that can be considered an archetype of this type of sources; it shows a clear axial
symmetry, along with the kinematics characteristic of this class of envelopes around post-AGB stars. We performed sub-arcsecond
resolution observations of the J=2–1 rotational line of 13CO in M 1–92 with the new extended configurations of the IRAM Plateau de Bure interferometer, for studying the morphology
and velocity field of the molecular gas better in the nebula, particularly in its central parts. We found that the equatorial
structure dividing the two lobes is a thin flat disk, which expands radially with a velocity proportional to the distance
to the central stellar system. The kinetic age of this equatorial flow is very similar to that measured in the two lobes,
suggesting that the whole structure was formed as a result of a single event some 1200 yr ago, after which the nebula reached
an expansion velocity field with axial symmetry. The small widths and velocity dispersion in the gas forming the lobe walls
confirm that the acceleration responsible for the nebular shape could not last more than 100–120 yr. In view of the similarity
to η Car, we speculate on the possibility that the whole nebula was formed as a result of a magneto-rotational explosion in a
common-envelope system. The study of the possible importance of this mechanism in the context of global PNe and pPNe reshaping
should be one on the fields in which future ALMA observations will make a crucial contribution.
Based on observations carried out with the IRAM Plateau de Bure Interferometer. IRAM is supported by INSU/CNRS (France), MPG
(Germany) and IGN (Spain). 相似文献