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1.
We report preliminary results from a targeted investigation on quasars containing damped Lyman‐α absorption (DLA) lines as well strong metal absorption lines, carried out with the Potsdam Multi Aperture Spectrophotometer (PMAS). We search for line‐emitting objects at the same redshift as the absorption lines and close to the line of sight of the QSOs. We have observed and detected the already confirmed absorbing galaxies in Q2233+131 (zabs = 3.15) and Q0151+045 (zabs=0.168), while failing to find spectral signatures for the z = 0.091 absorber in Q0738+313. From the Q2233+131 DLA galaxy, we have detected extended Lyα emission from an area of 3″ ×5″. (© 2004 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)  相似文献   

2.
Models for the formation of galaxies and clusters of galaxies require strong feedback in order to explain the observed properties of these systems. We investigate whether such feedback has observational consequences for the intergalactic medium, as probed in absorption towards background quasars. A typical quasar sight-line intersects one protocluster per unit redshift, and significant feedback from forming galaxies or active galactic nuclei, heating the protocluster gas, will result in a large clearing of reduced absorption in the Ly α forest. Such a gap could be detected at redshift ≳3 when the mean opacity is high. Feedback from Lyman-break galaxies in protoclusters can be probed by the absorption lines produced in their winds. Strong feedback from galaxies has a major impact on the number and properties of absorption lines with column densities N H  i ∼1016 cm−2. This feedback can be probed with multiple sight-lines and by studying the unsaturated higher order lines of the Lyman series. Galactic winds from dwarf galaxies should break up into clouds, in order not to overproduce the number of absorption lines. These clouds can then coast to large distances.  相似文献   

3.
We investigate the properties of the Lα absorption lines in the high resolution spectra of nine quasars, B2 1225+31.7, PKS 2126-158, Q 0002-422, Q 1453-423, PHL 957, PKS 0528-250, PKS 0805+046, PKS 1448-232 and PKS 1442+101. Their emission line redshift range is 2.20 ? zem ? 3.54; a total of 350 Lα absorption lines cover the range 1.70 ? zabs ? 3.54. Our analysis support the following conclusions; 1) the number density of Lα absorption lines is not significantly different in different quasars. 2) The number density does not vary significantly with redshift. 3) Their equivalent width spectrum does not vary significantly with redshift. 4) Their properties are the same whether in the wing of the Lα emission or in the continuum. 5) Their two-point correlation function is flat within the limit of resolution, which is different from the behaviour of galaxies. These results show that the Lα absorption lines in high-redshift quasars are very probably produced by intergalactic hydrogen clouds uniformly distributed throughout space.  相似文献   

4.
GRB 100219A at z = 4.667 has been the highest redshift gamma‐ray burst observed with the X‐shooter spectrograph up to now. The spectrum covering the range from 5000 to 24000 Å and a large number of absorption lines allows to make a detailed study of the interstellar medium in a high redshift galaxy. The ISM in the low ionisation state and the kinematics of the absorption line components reveal a complex velocity field. The metallicity measured from different absorption lines is around 0.1 solar. Other GRB hosts at redshift beyond ∼3 have similar metallicities albeit with a large scatter in the metallicity distribution. X‐shooter will allow us to determine metallicities of a larger number of GRB hosts beyond redshift 5, to probe the early chemical enrichment of the Universe and to study its evolution from redshift 2 to beyond 10 (© 2011 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)  相似文献   

5.
Lyα radiation is an important diagnostic tool in a wide range of astrophysical environments. I will first describe here how measurements of the matter power spectrum on small scales from Lyα forest data constrain the mass of dark matter particles. I then will report on an ambitious program of searching for very faint spatially extended Lyα emission at z ∼ 3 which has led to the discovery of a new population of faint Lyα emitters which I will argue should be identified with the long searched for host galaxies of damped Lyα absorbers. Finally, I will discuss the possibility of measuring the redshift drift of Lyα absorption features and therefore the change of the expansion rate of the Universe in real time with the ultra‐stable high‐resolution spectrograph CODEX proposed for the E‐ELT (© 2010 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)  相似文献   

6.
The conventional interpretation of the cosmic background radiation (CBR) as a relic of the Big Bang assumes that the intergalactic medium is highly transparent to radio frequency radiation. Previous work (Lerner, 1990) used the well-known correlation of IR and radio luminosities of spiral galaxies to test this assumption. That analysis, using 237 Shapley-Ames galaxies showed that radio luminosity (L R ) for a given IR-luminosity, declines with distance, implying that the IGM strongly absorbs radio frequency radiation. That absorption has now been confirmed using a sample of 301 IR-bright galaxies. Using two independent methods of determining the correlation of IR and radio luminosities of spiral and interacting galaxies, the sample shows that for a givenL IR ,L R D –0.32±0.04 over a range of distances from 0.7-300 Mpc. (H 0 = 75 km s–1 Mpc–1). The correlation is significant at the 8 or 10–14 level. Absorption by the IGM is the only reasonable explanation for this correlation. The existence of such absorption implies that neither the isotropy nor the spectrum of the CBR are primordial and that neither is evidence for a Big Bang.  相似文献   

7.
The spectra of the host galaxies of gamma‐ray bursts at low redshift generally show strong hydrogen lines of the Balmer, Paschen and Brackett series, in addition to strong nebular metal lines. In special cases the hosts can be resolved in separate star forming regions, and spatially resolved spectroscopy can be obtained. Generally, the three strongest Balmer lines are used to derive the reddening experienced by the emission lines of the host gas, assuming a Milky Way extinction curve, case B recombination and a fixed electron temperature. We demonstrate how the wide wavelength range of X‐shooter, in combination with a rigorous calibration strategy, can be used to fit explicitly for RV, Te, and AV simultaneously using a large number of H and He I recombination lines, explicitly corrected for stellar atmosphere absorption. This increases our understanding of extinction and absorption in starforming regions in GRB hosts. We use two GRB hosts as examples of the methods, outlining the advantages of using X‐shooter over other instruments (© 2011 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)  相似文献   

8.
At high redshift the ubiquity of outflows and winds in strongly star‐forming galaxies has been demonstrated using rest frame UV absorption lines. In the cases with optical emission lines, the studies mostly had to rely on low and intermediate dispersion spectra. This implies that for detailed studies of galactic wind physics we have to use local objects. In particular, dwarf galaxies are well suited to extrapolation to high redshift protogalaxies. Several kinematic studies of strongly starforming dwarf galaxies using Fabry‐Pérot and IFU spectrographs exist. Unfortunately, similar as for high redshift galaxies the employed spectral resolution is often significantly higher that the thermal line width. As a result faint high velocity features and details of the turbulent motion are hidden or unresolved. Here we will present an analysis of the ionized gas kinematics of the prototypical star‐forming irregular galaxy NGC 4449 using long‐slit, high‐dispersion échelle spectra. (© 2014 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)  相似文献   

9.
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10.
We present results of an investigation of clustering evolution of field galaxies between a redshift of z ∼ 1 and the present epoch. The current analysis relies on a sample of ∼ 14000 galaxies in two fields of the COMBO 17 survey. The redshift distribution extends to z ∼ 1. The amplitude of the three-dimensional correlation function can be estimated by means of the projected correlation function w(r p ). The validity of the deprojection was tested on the Las Campanas Redshift Survey (LCRS). In a flat cosmology with non-zero cosmological constant for bright galaxies (M B ≤-18) the clustering growth is proportional to (1+z) -2. However, the measured clustering evolution clearly depends on Hubble type. While locally the clustering strength of early type galaxies is equal to that of the bright galaxies, at high redshifts they are much stronger clustered, and thus the clustering has to evolve much more slowly. This revised version was published online in August 2006 with corrections to the Cover Date.  相似文献   

11.
We have made a Monte Carlo simulation of the intergalactic absorption in order to model the Lyman continuum absorption, which is required to estimate the escape fraction of the Lyman continuum from distant galaxies. To input into the simulation, we derive an empirical distribution function of the intergalactic absorbers which reproduces recent observational statistics of the Lyman α forest, Lyman limit systems (LLSs) and damped Lyman α systems (DLAs) simultaneously. In particular, we assume a common functional form of the number evolution along the redshift for all types of absorbers. The Lyman series transmissions in our simulation reproduce the observed redshift evolution of the transmissions excellently, and the Lyman continuum transmission also agrees with an observed estimation which is still quite rare in the literature. The probability distribution of the Lyman α opacity in our simulation is lognormal with a tail towards a large opacity. This tail is produced by DLAs. The probability distribution of the Lyman continuum opacity in our simulation also shows a broad tail towards a large opacity. This tail is produced by LLSs. Because of the rarity of LLSs, we have a chance to have a clean line of sight in the Lyman continuum even for   z ∼ 4  with a probability of about 20 per cent. Our simulation expects a good correlation between the Lyman continuum opacity and the Lyman α opacity, which may be useful to estimate the former from the latter for an individual line of sight.  相似文献   

12.
H  ii regions surrounding supermassive black holes (SMBHs) in an otherwise still neutral intergalactic medium (IGM) are likely to be the most easily detectable sources by future 21-cm experiments like LOFAR. We have made predictions for the size distribution of such H  ii regions for several physically motivated models for BH growth at high redshift and compared this to the expected LOFAR sensitivity to these sources. The number of potentially detectable H  ii regions does not only depend on the ionization state of the IGM and the decoupling of the spin temperature of the neutral hydrogen from the cosmic microwave background temperature, but is also strongly sensitive to the rate of growth of BHs at high redshift. If the SMBHs at redshift 6 were built up via continuous Eddington-limited accretion from low mass seed BHs at high redshift, then LOFAR is not expected to detect isolated QSO H  ii regions at redshifts much larger than 6, and only if the IGM is still significantly neutral. If the high-redshift growth of BHs starts with massive seed BHs and is driven by short-lived accretion events following the merging of BH hosting galaxies then the detection of H  ii regions surrounding SMBHs may extend to redshifts as large as 8–9 but is still very sensitive to the redshift to which the IGM remains significantly neutral. The most optimistic predictions are for a model where the SMBHs at z > 6 have grown slowly. H  ii regions around SMBHs may then be detected to significantly larger redshifts.  相似文献   

13.
In this article we discuss the importance of high‐resolution absorption spectroscopy for our understanding of the distribution and physical nature of the gaseous circumgalactic medium (CGM) that surrounds the Milky Way. Observational and theoretical studies indicate a high complexity of the gas kinematics and an extreme multi‐phase nature of the CGM in low‐redshift galaxies. High‐precision absorption‐line measurements of the Milky Way's gas environment thus are essential to explore fundamental parameters of circumgalactic gas in the local Universe, such as mass, chemical composition, and spatial distribution. We shortly review important characteristics of the Milky Way's CGM and discuss recent results from our multi‐wavelength observations of the Magellanic Stream. Finally, we discuss the potential of studying the warm‐hot phase of the Milky Way's CGM by searching for extremely weak [Fe X] λ 6374.5 Å and [Fe XIV] λ 5302.9 Å absorption in optical QSO spectra. (© 2014 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)  相似文献   

14.
I demonstrate by means of high-resolution cosmological simulations, which include modelling of a two-phase interstellar medium, that the dominant mechanism for transporting heavy elements from protogalaxies into the intergalactic medium (IGM) is the merger mechanism as discovered by Gnedin & Ostriker. Direct ejection of the interstellar gas by supernovae plays only a minor role in transporting metals into the IGM: for a realistic cosmological scenario only a small fraction of all metals in the IGM is delivered by the supernova-driven winds, while most of the metals in the IGM are transported by the merger mechanism. As a result, the metallicity distribution in the IGM is highly inhomogeneous, in agreement with studies of the QSO metal absorption systems, and the predicted metallicity distribution of Lyman alpha absorbers as a function of their column density is in excellent agreement with the observational data.  相似文献   

15.
In recent years, the Lyman-α forest in quasar spectra has been used, together with N-body simulations, to determine the underlying matter distribution in the intergalactic medium (IGM). One of the key parameters to be known in order to compare observations and numerical simulations is the mean HI absorption in the IGM. To derive the latter, one has first to fit the quasar continuum. We have observed 20 high redshift and highly luminous QSOs (m V ≤ 17.5 and 2.40 ≤ z em ≤ 3.91) at intermediate spectral resolution, with either EMMI (ESO Multi-Mode Instrument) on the ESO-NTT telescope or CARELEC at the OHP (Observatoire de Haute-Provence), and applied different methods of determining the QSO continuum to this QSO sample. We have measured the amount of absorption, known as the flux decrement, DA, in the Lyman-α forest for these different methods and compared the results. In addition, we have compared DA values measured along the same lines of sight observed at high and intermediate spectral resolutions. We discuss the systematics resulting from the use of automatic continuum fitting methods.  相似文献   

16.
In the last couple of decades hundreds of studies have explored the nature of star‐forming galaxies at different redshifts. This contribution focuses on X‐shooter observations of star‐burst galaxies at 0 < z < 6 from commissioning runs, science verification, and regular observations, and demonstrates the capability of the new instrument in this competitive field. Observations of gravitationally lensed galaxies show that X‐shooter has no limitation in the redshift desert (1.4 < z < 2) where the strong optical emission lines are shifted to the near‐IR region. Physical properties of galaxies, such as masses, metallicities, abundance ratios, and star formation rates can be derived from observations with relatively short integration times for faint galaxies. The simultaneous UV to near‐IR spectral coverage makes derivation of physical quantities more reliable because there are no differential slit losses as may occur when observations from different optical and near‐IR instruments are used. Over the entire redshift range, spectra of faint galaxies will allow us to better measure stellar ages and dominating ionisation sources compared to broad band spectral energy distribution measurements (© 2011 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)  相似文献   

17.
We estimate the evolution of the contribution of galaxies to the cosmic background flux at 912 Å by means of a semi-analytic model of galaxy formation and evolution. Such modelling has been quite successful in reproducing the optical properties of galaxies. We assume that high-redshift damped Lyman α systems are the progenitors of present-day galaxies, and we design a series of models that are consistent with the evolution of cosmic comoving emissivities in the available near-infrared, optical, ultraviolet and far-infrared bands along with the evolution of the neutral hydrogen content and average metallicity of damped Lyman α systems. We use these models to compute the galactic contribution to the Lyman-limit emissivity and background flux for 0 ≃  z  ≤ 4. We take into account the absorption of Lyman-limit photons by H  I and dust in the interstellar medium of the galaxies. We find that the background Lyman-limit flux due to galaxies might dominate (or be comparable to) the contribution from quasars at almost all redshifts if the absorption by H  I in the interstellar medium is neglected. Such H  I absorption would result in a severe diminishing of this flux — by almost three orders of magnitude at high redshifts and by one to two orders at z  ≃ 0. Though the resulting galaxy flux is completely negligible at high redshifts, it is comparable to the quasar flux at z  ≃ 0.  相似文献   

18.
We have carried out targeted submillimetre observations as part of a programme to explore the connection between the rest-frame ultraviolet and far-infrared properties of star-forming galaxies at high redshift, which is currently poorly understood. On the one hand, the Lyman break technique is very effective at selecting     galaxies. On the other, 'blank-field' imaging in the submillimetre seems to turn up sources routinely, amongst which some are star-forming galaxies at similar redshifts. Already much work has been done searching for optical identifications of objects detected using the SCUBA instrument. Here we have taken the opposite approach, performing submillimetre photometry for a sample of Lyman break galaxies, the ultraviolet properties of which imply high star formation rates. The total signal from our Lyman break sample is undetected in the submillimetre, at an rms level of ∼0.5 mJy, which implies that the population of Lyman break galaxies does not constitute a large part of the recently detected blank-field submillimetre sources. However, our one detection suggests that with reasonable SCUBA integrations we might expect to detect those few Lyman break galaxies that are far-infrared brightest.  相似文献   

19.
Environment plays an important role in the evolution of the gas contents of galaxies. Gas deficiency of cluster spirals and the role of the hot intracluster medium in stripping gas from these galaxies is a well-studied subject. Loose groups with diffuse X-ray emission from the intragroup medium (IGM) offer an intermediate environment between clusters and groups without a hot IGM. These X-ray bright groups have smaller velocity dispersion and lower temperature than clusters, but higher IGM density than loose groups without diffuse X-ray emission. A single-dish comparative study of loose groups with and without diffuse X-ray emission from the IGM, showed that the galaxies in X-ray bright groups have lost more gas on average than the galaxies in non X-ray bright groups. In this paper we present GMRT H  i observations of 13 galaxies from four X-ray bright groups: NGC 5044, 720, 1550 and IC1459. The aim of this work is to study the morphology of H  i in these galaxies and to see if the hot IGM has in any way affected their H  i content or distribution. In addition to disturbed H  i morphology, we find that most galaxies have shrunken H  i discs compared to the field spirals. This indicates that IGM-assisted stripping processes like ram pressure may have stripped gas from the outer edges of the galaxies.  相似文献   

20.
本文对16个高红移类星体的L_α森林吸收线密度N(z_(abs))统计分析的结果,表明它明显地依赖于类星体自身的发射红移z_(em)。这不仅表现在z(em)越大的类星体其全部L_α吸收线的平均数密度N(z_(abs))也越大;更重要的是,对于相同的吸收红移值z_(abs),而言,N(z_(abs))在统计意义上明显地随着类星体z_(em)的增大而增大。另一方面,本文也在“吸收体源自类星体抛射”的框架下作了统计,结果仍表明z_(em)对L_α森林吸收线密度有显著影响,但抛射速度却对被抛射体的数目无显著影响。最后,对所得的结果以及可能影响N(z_(abs))的若干因素作了讨论。  相似文献   

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