A search for protocliisters atz = 3.3

We have used the Very Large Array to image a single field in a set of adjacent frequency bands around 333.0 MHz in an attempt to detect 21 cm emission from large scale H I inhomogeneities at a redshift of z = 3.3. Following the subtraction of continuum radio sources, the absence of any spectral signals apart from that expected due to the system thermal noise has been used to derive constraints on the evolutionary scenario leading to the formation of the present day clusters of galaxies. The observations rule out the existence of H I protoclusters atz = 3.3 with masses ≃3.5 × 10¹⁴ M _⊙ in H I gas and space density exceeding (74 Mpc)⁻³. This indicates that the present day rich clusters of galaxies either formed as gaseous protocluster condensates prior toz = 3.3 or else they formed through the clustering of their constituent galaxies.     

Studying the first galaxies with ALMA

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.     

The Basic Building Blocks of Galaxies

Current cold dark matter models of structure formation make a clear prediction for cosmic structures in the Dark Ages. We discuss the formation and nature of the first collapsed and first luminous objects in the universe arising in these theories. The first virialized objects are dark matter halos at the free streaming length which depends on the mass and nature of the assumed weakly interacting massive particle. The first objects that also contain significant fractions of gas have masses of the cosmological Jeans scale ∼ 10^4M _⊙ at the redshifts of interest (z ∼ 30). The first pre-galactic objects that host stars have masses of 10⁶ M _⊙. This mass scale is given by the requirement of a sufficiently high virial temperature to enable the chemical reactions necessary to form molecular hydrogen which subsequently allows the gas to dissipate its gravitational energy and to collapse to form a star. An individual massive star is formed per such object and explodes in a supernova within a few Myrs. All these stages of the formation of the first objects are illustrated by fully resolved three dimensional cosmological hydrodynamic simulations. This revised version was published online in September 2006 with corrections to the Cover Date.     

The Evolutionary Status of Early-type Galaxies in Abell 2390

We explore the evolution of the early-type galaxy population in the rich cluster Abell 2390 at z=0.23. For this purpose, we have obtained spectroscopic data of 51 elliptical and lenticular galaxies with MOSCA at the 3.5 m telescope on Calar Alto Observatory. As our investigation spans both a broad range in luminosity (–22.3≤M_B≤–:19.3)and a wide field of view (10′×10′), the environmental dependence of different formation scenarios can be analysed in detail as a function of radius from the cluster center. In this paper, we present first results on the Faber-Jackson relation and, for a subsample of 14 galaxies with morphological and structural parameters from HST, we also investigate the evolution of the Kormendy relation and the Fundamental Plane. We find a mild luminosity evolution of the early-type galaxies in Abell 2390: our objects are on average brighter by m _B∼0.4 mag. This revised version was published online in July 2006 with corrections to the Cover Date.     

New photometric models of galactic evolution applied to the HDF

We summarize our modelling of galaxy photometric evolution (the GRASIL code). By including the effects of dust grains and PAH molecules in a two-phase clumpy medium, where clumps are associated with star-forming regions, we reproduce the observed UV to radio SEDs of galaxies with star formation rates from zero to several hundred M _⊙ yr^-1.GRASIL is a powerful tool for investigating star formation, the initial mass function and the supernova rate in nearby starbursts and normal galaxies, as well as for predicting the evolution of luminosity functions of different types of galaxies at wavelengths covering six decades. It may be interfaced with any device to provide the star formation and metallicity histories of a galaxy. As an application, we have investigated the properties of early-type galaxies in the HDF, tracking the contribution of this population to the cosmic star formation history, which has a broad peak between z = 1.5 and 4.To explain the absence of objects at z ≳ 1.3, we suggest a sequence of dust-enshrouded merger-driven starbursts in the first few Gyr of galaxy lifetimes. We are at present working on a complementary sample of late-type objects selected in a similar way. This revised version was published online in July 2006 with corrections to the Cover Date.     

The evolution of disk galaxies in clusters

We are carrying out a programme to measure the evolution of the stellar and dynamical masses and M/L ratios for a sizeable sample of morphologically-classified disk galaxies in rich galaxy clusters at 0.2 < z < 0.9. Using FORS2 at the VLT we are obtaining rotation curves for the cluster spirals so that their Tully-Fisher relation can be studied as a function of redshift and compared with that of field spirals. We already have rotation curves for ∼ 10 cluster spirals at z = 0.83, and 25 field spirals at lower redshifts and we plan to increase this sample by one order of magnitude. We present here the first results of our study, and discuss the implications of our data in the context of current ideas and models of galaxy formation and evolution. This revised version was published online in September 2006 with corrections to the Cover Date.     

The observed structure of extremely distant galaxies

We have identified 22 galaxies with photometric redshifts z_ph=5–7 in the northern and southern Hubble Space Telescope deep fields. An analysis of the images of these objects shows that they are asymmetric and very compact (～1 kpc) structures with high surface brightness and absolute magnitudes of M_B≈?20^m. The average spectral energy distribution for these galaxies agrees with the distributions for galaxies with active star formation. The star formation rate in galaxies with z_ph=5–7 was estimated from their luminosity at λ=1500 Å to be ~30 M_⊙yr^?1. The spatial density of these objects is close to the current spatial density of bright galaxies. All the above properties of the distant galaxies considered are very similar to those of the so-called Lyman break galaxies (LBGs) with z ～ 3–4. The similarity between the objects considered and LBGs suggests that at z ～6, we observe the progenitors of present-day galaxies that form duringmergers of protogalactic objects and that undergo intense starbursts.     

Integral field observations of damped Lyman‐α galaxies

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 (z_abs = 3.15) and Q0151+045 (z_abs=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)     

A Research on the Evolution of Star Formation Activities of Early-type Galaxies

The observational investigation of the evolution of the star formation activities of early-type galaxies (ETGs) with redshifts helps us to understand the formation and evolution of this kind of galaxies. Combined with the highresolution images from HST/ACS (Hubble Space Telescope/Advanded Camera for Surveys) of the GEMS (Galaxy Evolution fromMorphology and SEDs) survey and the multi-band data from Spitzer, GALEX (Galaxy Evolution Explorer) and so on in the CDFS (Chandra Deep Field South) field, a complete sample including 456 ETGs with their redshifts in the range of 0.2 ≤ z ≤ 1.0 is selected on the basis of morphology, color and stellar mass. By using the stacking technique, the ultraviolet and infrared average luminosities of sample galaxies are measured, and the star formation rates of ETGs are estimated. The results indicate that the star formation rates of ETGs are relatively low (< 3 M yr⁻¹) and decrease with decreasing redshifts. The mass contributed by the star formation since z = 1 is less than 15%. The analyses of stellar populations also confirm that the bulk of the population of massive ETGs was formed in the early universe (z > 2).     

An X-ray hubble diagram for quasi-stellar objects

To form the Hubble diagram for quasi-stellar objects (QSOs),we have made use of the recently published data on X-ray fluxes of 159 QSOs observed from the Einstein Observatory. The scatter in the Hubble diagram and the lack of an obvious redshift-flux density correlation for these QSOs have been attributed to the observational selection effect that the intrinsically less luminous QSOs can be detected only in the nearby region of space. When the optical, radio and X-ray selection effects are removed, keeping only the intrinsically brighter sources, we obtain a sample of 16 QSOs having a small dispersion in X-ray luminosities (〈 logL _x〉) = 46.12 ± 0.28), a statistically significant linear correlation between (logf _x, logcz) pairs and a slopeA =-1.906 ± 0.061 of the linear regression oflog f _x on logcz. This slope is consistent, at a confidence level of 95 per cent or greater, with the slope of-2.0 expected theoretically based on the assumption that the redshifts of QSOs are cosmological in nature.     

Evidence for chemical evolution in spectra of high redshift galaxies

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.     

Constraints on big bang models from structure formation

I review the constraints on standard big bang model arising from considerations related to structure formation. I will focus on two specific series of models though similar analysis can be performed for a wider class of models. The first one is a Ω = 1 model with non-zero cosmological constant and the second one is a Ω < 1 model with zero cosmological constant. The observational constraints which I shall discuss include the measurement of the Hubble’s constant, the ages of globular clusters, the abundance of rich clusters, the baryon content of galaxy clusters and the abundance of high redshift objects. These constraints limit the allowed range of the cosmological parameters and allow. for only a small region to survive. In particular, the aesthetically pleasing model with Ω = 1 and zero cosmological constant is ruled out by the observations. It seems necessary to fine-tune the theoretical parameters if they have to fall within the available space. This talk is based on the work in Baglaet al. (1996).     

Towards a new galaxy template library for multi-colour classification

The COMBO-17 survey cite(Wolf et al., 2002) contains ≈ 40000 galaxies down to R=24 mag on an area of one square degree, obtained with the wide field imager at the 2.2 m telescope at La Silla. A multi-colour classification on the basis of 5 broadband and 12 medium band filters (=17 bands) yields accurate redshifts (σ _z ≤ 0.01 at the bright end up to σ _z ≈ 0.1 at the faint end) and spectral energy distribution types (SEDs) when using observed galaxy templates from (Kinney et al.,1996). However, there is an obvious weakness in this classification scheme: The relation between star formation history and SED remains unclear. It is therefore impossible to draw firm conclusions about the age of the underlying stellar population and the expected aging between z ≈ 1 and z ≈ 0 can not be quantified. We will present first results of our attempt to replace the observed templates with model spectra from the PEGASE code (Fioc and Rocca-Volmerange, 1997), in order to get a better handle on the star formation history. This revised version was published online in August 2006 with corrections to the Cover Date.     

Scaling Properties of X-ray Clusters: The Chandra View

The study of X-ray clusters of galaxies, started 30 years ago, has revealed an increasing complexity in the thermodynamics of the X-ray emitting intracluster medium (ICM) as long as the sensitivity and the resolution of the X-ray satellites increased. At the same time, deep surveysdetected several, unexpected, high-z clusters. Here we focus on the Chandra observations of the most distant X-ray selected clusters (0.3 < z < 1.3), in order to constrain their thermodynamic evolution. The X-ray scaling properties show hints of negative evolution in the luminosity–temperature and M _gas–temperature relations, and a positive evolution in the entropy–temperature relation. We find that the mean iron abundance at 〈z〉 = 0.8 is Z _Fe = 0.25^+0.04 _−0.06 Z _⊙, and at 〈z〉 ∼ 1.2 is Z _Fe = 0.35^+0.06 _−0.05 Z _⊙, both measures consistent with no evolution with respect to the local value Z _Fe≃ 0.3 Z _⊙. These results can provide interesting constraints on the thermodynamics of the ICM at large look back times, pointing towards a redshift z ≳ 2 for the onset of non-gravitational processes.     

Clustering evolution between z=1 and today

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.     

Magnetic field of the young star RW Aur

Results of ourmeasurements of the longitudinal magnetic field B _z for the young star RWAur A are presented. B _z measured from the so-called narrow component of the He I 5876 line varies in the range from −1.47 ± 0.15 to +1.10 ± 0.15 kG. Our data are consistent with a stellar rotation period of }~5.6 days and the model of two hot spots with opposite magnetic field polarities spaced about 180° apart in longitude. Relative to the Earth, the spot with B _z < 0 lies in the hemisphere above the midplane of the accretion disk, while the spot with B _z > 0 is below the midplane. The upper limit for B _z (at the 3σ level) obtained by averaging all observations is 180 G for the photosphere and 220 and 230 G for the Hα and [OI] 6300 line formation regions, respectively. We have also failed to detect a field in the formation region of broad emission line components: the upper limit for B _z is 600 G. In two of 11 cases, we have detected a magnetic field in the formation region of the blue absorption wing of the Na I D doublet lines, i.e., in the wind from RW Aur A: B _z = −180 ± 50 and −810 ± 80 G. The radial velocity of the photospheric lines in RW Aur A averaged over all our observations is }~+10.5 km s⁻¹, i.e., a value lower than that obtained by Petrov et al. (2001) ten years earlier by 5.5 km s⁻¹. Therefore, we discuss the possibility that RW Aur is not a binary but a triple system.     

Investigation of galaxy and quasar luminosity evolution in the model of standard cosmology

It is shown that the Hubble curvem(z) for galaxies and quasars averaged over a large volume of data forms in the first approximation a single continuous curve in the interval of red shifts 10^–2.5z4.5, which is satisfactorily described by the dependence .A large deviation of the observed mean dependence from the theoretical one predicted by the standard cosmology is explained by the evolution of the galaxy and especially quasar luminosity. The corresponding mid-statistical function of the absolute luminosity variation for the last 4/5 times of existence in the Universe is equal toM(z)–M(z ₀)=logz/z ₀+2z–0.4z ².The luminosity of the most far distant from the observed quasars on the average by 5–6 stellar magnitudes high than the luminosity of near galaxies and quasars. It is obtained that even the most far distant quasars atz5 are in the maximum of luminosity, or their extinction has just began, thus the quasar formation should be expected forz>(5–6). The relative rate of the luminosity decrease of galaxies and near quasars is rather accurately amounts in the recent epoch 7% per 10⁹ years. The obtained average Hubble curve of galaxies and quasars is evidently the main cause of their evolution in the Universe.     

Statistics of interacting galaxies at <Emphasis Type="Italic">z</Emphasis> ∼ 0.7

We present the results of our analysis of the frequencies of galaxies with tidal tails and M51-type galaxies in several deep fields of the Hubble Space Telescope (HDF-N, HDF-S, HUDF, GOODS, GEMS). In total, we have found about seven hundred interacting galaxies at redshifts z ≤ 1.5 in these fields. At z ≤ 0.7, the observed space densities of galaxies with tidal structures and M51-type galaxies have been found to increase as ∝(1 + z) ^m , where m ≈ 2.6. According to our estimates, over the last 6–7 Gyr, i.e., at z ≤ 0.7, about a third of the galaxies with M(B) ≤ −18 ^m must have undergone strong gravitational perturbations and mergers and ∼1/10−1/5 of the galaxies have swallowed relatively low-mass nearby satellites typical of M51-type galaxies. The possible decrease in the time scale on which a distant galaxy appears peculiar with growing z can increase considerably the estimated rate of mergers.     

Stability of motion in the Sitnikov 3-body problem

We study the stability of motion in the 3-body Sitnikov problem, with the two equal mass primaries (m ₁ = m ₂ = 0.5) rotating in the x, y plane and vary the mass of the third particle, 0 ≤ m ₃ < 10⁻³, placed initially on the z-axis. We begin by finding for the restricted problem (with m ₃ = 0) an apparently infinite sequence of stability intervals on the z-axis, whose width grows and tends to a fixed non-zero value, as we move away from z = 0. We then estimate the extent of “islands” of bounded motion in x, y, z space about these intervals and show that it also increases as |z| grows. Turning to the so-called extended Sitnikov problem, where the third particle moves only along the z-axis, we find that, as m ₃ increases, the domain of allowed motion grows significantly and chaotic regions in phase space appear through a series of saddle-node bifurcations. Finally, we concentrate on the general 3-body problem and demonstrate that, for very small masses, m ₃ ≈ 10⁻⁶, the “islands” of bounded motion about the z-axis stability intervals are larger than the ones for m ₃ = 0. Furthermore, as m ₃ increases, it is the regions of bounded motion closest to z = 0 that disappear first, while the ones further away “disperse” at larger m ₃ values, thus providing further evidence of an increasing stability of the motion away from the plane of the two primaries, as observed in the m ₃ = 0 case.     

Cosmological scalar fields that mimic the ΛCDM cosmological model

We look for cosmologies with a scalar field (dark energy without cosmological constant), which mimic the standard ΛCDM cosmological model yielding exactly the same large-scale geometry described by the evolution of the Hubble parameter (i.e. photometric distance and angular diameter distance as functions on z). Asymptotic behavior of the field solutions is studied in the case of spatially flat Universe with pressureless matter and separable scalar field Lagrangians; the cases of power-law kinetic term and power-law potential are considered. Exact analytic solutions are found in some special cases. A number of models have the field solutions with infinite behavior in the past or even singular behavior at finite redshifts. We point out that introduction of the cosmological scalar field involves some degeneracy leading to lower precision in determination of Ω _m . To remove this degeneracy additional information is needed besides the data on large-scale geometry. The article is published in the original.