共查询到20条相似文献，搜索用时 46 毫秒
1.
Sabine Richling 《Astrophysics and Space Science》2003,284(2):361-364
The Lyα line emission of high-redshift galaxies depends on the density and temperature distribution of the gas, the kinematics
and the dust content. We use a finite element method to model theLyα radiation of different 3D configurations considering
complete frequency redistribution and the influence of velocity fields. Our results show that the central absorption feature
of the double-peaked Lyα line profile observed in many radio galaxies with z=2-4 is probably the consequence of frequency redistribution rather than foreground absorption. The blue peak of the profile
is enhanced for models with in fall motion and the red peak for models with outflow motion. In particular, we attempt to model
the extendedLyα emission of high-redshift radio galaxies, where we consider results of corresponding hydrodynamical simulations
to select possible model configurations. We find that Lyα photons scattered outside a jet-influenced low-density region are
able to produce an extended Lyα halo.
This revised version was published online in August 2006 with corrections to the Cover Date. 相似文献
2.
A simple consistency argument for hypothesis of the galactic halo origin of the Lyα forest absorption lines is advanced, based
on the recent determination of column-density vs. impact parameter relation for the low-redshift gaseous galactic haloes.
It is shown that observations of neutral hydrogen absorption around luminous galaxies are consistent with the index of the
power-law column density distribution derived from statistical analyses of large samples of high-redshift Lyα forest lines.PACS: 98.62.Ra, 98.62.Gq, 98.80.Es
This revised version was published online in July 2006 with corrections to the Cover Date. 相似文献
3.
We present a study of the [α/Fe-peak] and [N/α] abundance ratios in Damped Lyα (DLA) systems. By using ratios of undepleted
elements ([S/Zn] and [N/S]) or when abundances of refractory elements are corrected by dust depletion ([Si/Fe]corr), the resulting ratios do not resemble those observed in the Galactic metal-poor stars, showing instead similarities with
those ratios observed in dwarf galaxies. These results challenge the idea that these absorbers are the progenitors of the
present-day spiral galaxies, and suggest an origin in low-mass galaxies for the systems up to now investigated.
This revised version was published online in July 2006 with corrections to the Cover Date. 相似文献
4.
Jesper Sommer-Larsen Sune Toft Jesper Rasmussen Kristian Pedersen Martin Götz Laura Portinari 《Astrophysics and Space Science》2003,284(2):693-696
The X-ray properties of the haloes of disk galaxies formed in fully cosmological, hydro/gravity simulations are discussed.
The results are found to be consistent with observational X-ray detections and upper limits. Disk galaxy haloes are predicted
to be about an order of magnitude brighter at z ∼ 1 than at z=0. The Lyα and Hα surface brightness of an edge-on, Milky Way like model galaxy has been determined. The emission is found
to be quite extended, with a scale height of about 600 pc, neglecting dust corrections.
This revised version was published online in August 2006 with corrections to the Cover Date. 相似文献
5.
Milan M. Ćirković 《Astrophysics and Space Science》1998,262(4):497-508
If a significant fraction of QSO absorption line systems arises in halos of normal galaxies, absorber statistical data will
tell us a lot about the structure of the gaseous envelopes of galaxies. Comparison of a class of density profile models for
the metal-absorbing halos of luminous galaxies with the recent Lyα empirical data is presented. Cosmological mass fraction
contained in such gas is also briefly discussed. It is shown that important constraints on the model parameters can be inferred
in this way.
This revised version was published online in August 2006 with corrections to the Cover Date. 相似文献
6.
The distribution of element abundances with redshift in Damped Lyα (DLA) systems can be adequately reproduced by the same
models reproducing the halo and disk components of the Milky Way Galaxy at different galactocentric distances. In this sense,
DLA systems are well represented by normal spiral galaxies in their early evolutionary stages.
This revised version was published online in July 2006 with corrections to the Cover Date. 相似文献
7.
In an earlier research the employment of a radiation transport model with angle-dependent partial frequency redistribution,
self-absorption by interplanetary hydrogen, realistic solar HLyαemission profile, and a time dependent `hot' hydrogen model to analyze 5 interplanetary HLyα glow spectra obtained with theHubble–Space–Telescope–GHRS spectrometer, has not resulted in unequivocal determination of
a set of thermodynamical parameters of the interstellar hydrogen The residual discrepancies between the model and the data
concern the observations performed within an interval of 1 year close to the solar minimum from very similar lines of sight.
In this paper we investigate by calculating interplanetary HLyα lines with the use of a one hydrogen distribution and several solar HLyα line profiles whether this residual may be caused by possible variations in time of the shape of the solar HLyα emission line profile which cause variable illuminations of the interplanetary gas. These variations of illuminations cause
variations in Doppler shift of the resonant interplanetary HLyα line that can amount to ≃ 4 km s-1in the line peak. Consequently we conclude that without adequate knowledge of the solar HLyα emission line profile during spectral observations of the interplanetary hydrogen gas it is impossible to obtain an agreement
between models and observations better than by this value.
This revised version was published online in July 2006 with corrections to the Cover Date. 相似文献
8.
Jesper Sommer-Larsen 《Astrophysics and Space Science》2001,276(2-4):999-1006
The hypothesis that damped Lyα systems (DLAs) are large galactic discs (Milky Way sized) is tested by confronting predictions
of models of the formation and evolution of (large) disc galaxies with observations, in particular the zinc abundance distribution
with neutral hydrogen column density found for DLAs. A pronounced mismatch is found, strongly hinting that the majority of
DLAs may not be large galactic discs.
This revised version was published online in July 2006 with corrections to the Cover Date. 相似文献
9.
Ly α and Ly β line profiles in a solar prominence were observed with high spatial and spectral resolution with SOHO/SUMER.
Within a 60-arcsec scan, we measure a very large variety of profiles: not only reversed and nonreversed profiles but also
red-peaked and blue-peaked ones in both lines. Such a spatial variability is probably related to both the fine structure in
prominences and the different orientations of mass motions. The usage of integrated-intensity cuts along the SUMER slit allowed
us to categorize the prominence in three regions. We computed average profiles and integrated intensities in these lines in
the range 2.36 – 42.3 W m−2 sr−1 for Ly α and 0.027 – 0.237 W m−2 sr−1 for Ly β. As shown by theoretical modeling, the Ly α/Ly β ratio is very sensitive to geometrical and thermodynamic properties
of fine structure in prominences. For some pixels, and in both lines, we found agreement between observed intensities and
those predicted by one-dimensional models. But a close examination of the profiles indicated a rather systematic disagreement
concerning their detailed shapes. The disagreement between observations and thread models (with ambipolar diffusion) leads
us to speculate about the importance of the temperature gradient between the cool and coronal regions. This gradient could
depend on the orientation of field lines as proposed by Heinzel, Anzer, and Gunár (Astron. Astrophys.
442, 331, 2005). 相似文献
10.
A. Vourlidas B. Sanchez Andrade-Nu?o E. Landi S. Patsourakos L. Teriaca U. Schühle C. M. Korendyke I. Nestoras 《Solar physics》2010,261(1):53-75
The Very high Angular resolution ULtraviolet Telescope (VAULT) is a sounding rocket payload built to study the crucial interface
between the solar chromosphere and the corona by observing the strongest line in the solar spectrum, the Ly α line at 1216 ?.
In two flights, VAULT succeeded in obtaining the first ever subarcsecond (
$0.5\hbox{$0.5\hbox{
) images of this region with high sensitivity and cadence. Detailed analyses of those observations contributed significantly
to new ideas about the nature of the transition region. Here, we present a broad overview of the Ly α atmosphere as revealed
by the VAULT observations and bring together past results and new analyses from the second VAULT flight to create a synthesis
of our current knowledge of the high-resolution Ly α Sun. We hope that this work will serve as a good reference for the design
of upcoming Ly α telescopes and observing plans. 相似文献
11.
Saumyadip Samui Raghunathan Srianand Kandaswamy Subramanian 《Monthly notices of the Royal Astronomical Society》2009,398(4):2061-2068
We present a semi-analytical model of star formation which explains simultaneously the observed ultraviolet (UV) luminosity function (LF) of high-redshift Lyman break galaxies (LBGs) and LFs of Lyman α emitters. We consider both models that use the Press–Schechter (PS) and Sheth–Tormen (ST) halo mass functions to calculate the abundances of dark matter haloes. The Lyman α LFs at z ≲ 4 are well reproduced with only ≲10 per cent of the LBGs emitting Lyman α lines with rest equivalent width greater than the limiting equivalent width of the narrow band surveys. However, the observed LF at z > 5 can be reproduced only when we assume that nearly all LBGs are Lyman α emitters. Thus, it appears that 4 < z < 5 marks the epoch when a clear change occurs in the physical properties of the high-redshift galaxies. As Lyman α escape depends on dust and gas kinematics of the interstellar medium (ISM), this could mean that on an average the ISM at z > 5 could be less dusty, more clumpy and having more complex velocity field. All of these will enable easier escape of the Lyman α photons. At z > 5 , the observed Lyman α LF are well reproduced with the evolution in the halo mass function along with very minor evolution in the physical properties of high-redshift galaxies. In particular, up to z = 6.5 , we do not see the effect of evolving intergalactic medium opacity on the Lyman α escape from these galaxies. 相似文献
12.
In weakly ionized astrophysical plasmas, shear flow induced plasma - neutral gas friction yields self-generated magnetic fields
of seed-field order. This process is of cosmological importance and relevant for protogalactic systems like Lyα-clouds. In
our contribution we illustrate this mechanism by the help of 3-dimensional 2-fluid simulations of primordial rotating gas
clumps in Lyα-clouds showing that plasma - neutral gas interactions cause large scale magnetic fields of the order of 10−15G on time scales of the order of 106yrs.
This revised version was published online in July 2006 with corrections to the Cover Date. 相似文献
13.
Ultra-high resolution hydrodynamic simulations using 10243 grid points are performed of early supernova burst in a forming galaxy, with properties similar to those inferred for Lyman
α emitters (LAEs) and Lyman Break Galaxies (LBGs). We show that, at the earliest stages of less than 300 Myr, continual supernova
explosions produce multitudinous hot bubbles and cooled H(I) shells in-between. The H(I) shells radiate intense Lyman α (Lyα) emission like LAEs. We found that the bubbly structures produced are quite similar to the observed features in the Lyα surface brightness distribution of the extended LAEs. After 1 Gyr, the galaxies are dominated by stellar continuum radiation
and then resemble the LBGs. At this point, the abundance of heavy elements appears to be solar. After 13 Gyr, these galaxies
resemble present-day ellipticals. 相似文献
14.
C. L. Carilli F. Walter R. Wang A. Wootten K. Menten F. Bertoldi E. Schinnerer P. Cox A. Beelen A. Omont 《Astrophysics and Space Science》2008,313(1-3):307-311
We discuss observations of the first galaxies, within cosmic reionization, at centimeter and millimeter wavelengths. We present
a summary of current observations of the host galaxies of the most distant QSOs (z∼6). These observations reveal the gas, dust, and star formation in the host galaxies on kpc-scales. These data imply an enriched
ISM in the QSO host galaxies within 1 Gyr of the big bang, and are consistent with models of coeval supermassive black hole
and spheroidal galaxy formation in major mergers at high redshift. Current instruments are limited to studying truly pathologic
objects at these redshifts, meaning hyper-luminous infrared galaxies (L
FIR
∼1013
L
⊙). ALMA will provide the one to two orders of magnitude improvement in millimeter astronomy required to study normal star
forming galaxies (i.e. Ly-α emitters) at z∼6. ALMA will reveal, at sub-kpc spatial resolution, the thermal gas and dust—the fundamental fuel for star formation—in galaxies
into cosmic reionization. 相似文献
15.
Morphological and spectral studies of the galaxies Kaz 69 and Kaz 460 are reported. The observations were made on the 2.6-m
telescope at the Byurakan Observatory using the VAGR multiaperture spectrograph. Isophotes of monochromatic images of the
Hα, [NII] λ6584, and [SII] λ6717 lines are constructed. Densifications I and II are found to rotate with north-south oriented
axes of rotation. The two densifications (“knots”) have all the kinematic and spectral properties of individual galaxies.
It is assumed that Kaz 139 and the densifications I and II were ejected from the nucleus of Kaz 460 at different times, with
Kaz 139 probably having been ejected first, although they may all have been ejected simultaneously with different velocities.
Along with Kaz 460, these objects form a physical group of galaxies and, at the same time, are a consequence of the activity
of the nucleus of Kaz 460.
__________
Translated from Astrofizika, Vol. 50, No. 3, pp. 415–426 (August 2007). 相似文献
16.
Andrea Ferrara 《Astrophysics and Space Science》2003,284(2):415-424
I review recent results concerning the metal enrichment of the intergalactic medium and give arguments which allow to conclude
that the heavy elements detected in the Lyα forest absorbers must have been produced and injected by a population of protogalaxies
with typical mass ≈ 108 M⊙ at redshift z ≈ 10. In addition, I will discuss the existence of a metallicity-induced shift in the Initial Mass Function of first stars
from an extrely top-heavy distribution to a `normal' one and bring observational support to this idea.
This revised version was published online in August 2006 with corrections to the Cover Date. 相似文献
17.
Guillermo Tenorio-Tagle Sergey A. Silich Daniel Kunth Elena Terlevich Roberto Terlevich † 《Monthly notices of the Royal Astronomical Society》1999,309(2):332-342
The detection of Ly α emission in star-forming galaxies in different shapes and intensities (always smaller than predicted for case B recombination) has puzzled the astronomical community for more than a decade. Here we use two-dimensional calculations to follow the evolution of superbubbles and of the H ii regions generated by the output of UV photons from massive stars. We show the impact caused by massive star formation in the ISM of different galaxies and we look at the conditions required to detect Ly α emission from a nuclear H ii region, and the variety of profiles that may be expected as a function of time. 相似文献
18.
Eric Quémerais Bill R. Sandel J.L. Bertaux R. Lallement 《Astrophysics and Space Science》2000,274(1-2):123-132
We present the Lyman α sky background data obtained by the UV spectrometers on the Voyager 1 and 2 spacecraft between 1993
and early 1998. These data which consist of special maneuvers dedicated to the study of the Lyα pattern in the outer heliosphere
represent a unique opportunity to constrain the hydrogen distribution in the outer heliosphere.A first analysis of the data
is presented. This consists of a comparison with a Hot Model of the hydrogen distribution combined with a radiative transfer
calculation in the hypothesis of Complete Frequency Redistribution. We confirm previous measurements showing the existence
of an excess in Lyα background in the upwind direction. The radial variation of the upwind intensity measurements found from
the two Voyager data sets are different. The Voyager 1 data show a radial decrease following r
-1.4 whereas the Voyager 2 data yield r
-0.79. These values have been derived after correction for solar flux variations using the SOLSTICE/UARS data set.
This revised version was published online in July 2006 with corrections to the Cover Date. 相似文献
19.
We have obtained Hα fluxes and luminosities for a sample of 95 galaxies from observations of 31 Hickson Compact Groups (HCGs) in the northern
hemisphere. This sample is the largest Hα selected catalogue of galaxies having Hα calibrated fluxes so far. The results obtained from a preliminary analysis of a subsample of66 galaxies show that the Hα luminosity of the galaxies is correlated with velocity dispersion and compactness of groups. These correlations would point
towards a scenario in which the brightest Hα galaxies reside in compact groups having higher probability of galaxy interaction, i.e. lower values of velocity dispersion.
Moreover, such relations seem to depend on the environment in which HCGs themselves are embedded.
This revised version was published online in July 2006 with corrections to the Cover Date. 相似文献
20.
Associated with one of the most important forms of active galactic nucleus (AGN) feedback, and showing a strong preference for giant elliptical host galaxies, radio AGN (\(L_{1.4\,\mathrm{GHz}} > 10^{24}\) W \(\hbox {Hz}^{-1}\)) are a key sub-class of the overall AGN population. Recently their study has benefitted dramatically from the availability of high-quality data covering the X-ray to far-IR wavelength range obtained with the current generation of ground- and space-based telescope facilities. Reflecting this progress, here I review our current state of understanding of the population of radio AGN at low and intermediate redshifts (\(z < 0.7\)), concentrating on their nuclear AGN and host galaxy properties, and covering three interlocking themes: the classification of radio AGN and its interpretation; the triggering and fuelling of the jet and AGN activity; and the evolution of the host galaxies. I show that much of the observed diversity in the AGN properties of radio AGN can be explained in terms of a combination of orientation/anisotropy, mass accretion rate, and variability effects. The detailed morphologies of the host galaxies are consistent with the triggering of strong-line radio galaxies (SLRG) in galaxy mergers. However, the star formation properties and cool ISM contents suggest that the triggering mergers are relatively minor in terms of their gas masses in most cases, and would not lead to major growth of the supermassive black holes and stellar bulges; therefore, apart from a minority (<20 %) that show evidence for higher star formation rates and more massive cool ISM reservoirs, the SLRG represent late-time re-triggering of activity in mature giant elliptical galaxies. In contrast, the host and environmental properties of weak-line radio galaxies (WLRG) with Fanaroff–Riley class I radio morphologies are consistent with more gradual fuelling of the activity via gas accretion at low rates onto the supermassive black holes. 相似文献