Modelling high redshift Lyman-alpha Emitters

We present a new model for high redshift Lyman-Alpha Emitters (LAEs) in the cosmological context which takes into account the resonant scattering of Ly-a photons through expanding gas. The GALICS semi-analytic model provides us with the physical properties of a large sample of high redshift galaxies. We implement a gas outflow model for each galaxy based on simple scaling arguments. The coupling with a library of numerical experiments of Ly-a transfer through expanding or static dusty shells of gas allows us to derive the Ly-a escape fractions and profiles. The predicted distribution of Ly-a photons escape fraction shows that galaxies with a low star formation rate have a f_esc of the order of unity, suggesting that, for those objects, Ly-a may be used to trace the star formation rate assuming a given conversion law. In galaxies forming stars intensely, the escape fraction spans the whole range from 0 to 1. The model is able to get a good match to the UV and Ly-a luminosity function (LF) data at 3 < z < 5. We find that we are in good agreement with both the bright Ly-a data and the faint population observed by Rauch et al. (2008) at z=3. Most of the Ly-a profiles of our LAEs are redshifted by the diffusion in the outflow which suppresses IGM absorption. The bulk of the observed Ly-a equivalent width (EW) distribution is recovered by our model, but we fail to obtain the very large values sometimes detected. Predictions for stellar masses and UV LFs of LAEs show a satisfactory agreement with observational estimates. The UV-brightest galaxies are found to show only low Ly-a EWs in our model, as it is reported by many observations of high redshift LAEs. We interpret this effect as the joint consequence of old stellar populations hosted by UV-bright galaxies, and high HI column densities that we predict for these objects, which quench preferentially resonant Ly-a photons via dust extinction.Comment: 17 pages, 12 figures, 3 tables, accepted for publication in MNRA

The FORS Deep Field Spectroscopic Survey

We present a catalogue and atlas of low-resolution spectra of a well defined sample of 341 objects in the FORS Deep Field. All spectra were obtained with the FORS instruments at the ESO VLT with essentially the same spectroscopic set-up. The observed extragalactic objects cover the redshift range 0.1 to 5.0. 98 objects are starburst galaxies and QSOs at z > 2. Using this data set we investigated the evolution of the characteristic spectral properties of bright starburst galaxies and their mutual relations as a function of the redshift. Significant evolutionary effects were found for redshifts 2 < z < 4. Most conspicuous are the increase of the average C IV absorption strength, of the dust reddening, and of the intrinsic UV luminosity, and the decrease of the average Ly alpha emission strength with decreasing redshift. In part the observed evolutionary effects can be attributed to an increase of the metallicity of the galaxies with cosmic age. Moreover, the increase of the total star-formation rates and the stronger obscuration of the starburst cores by dusty gas clouds suggest the occurrence of more massive starbursts at later cosmic epochs.Comment: 24 pages, 25 figures (35 PS files), 4 tables, accepted for publication in A&A. v2: minor typos corrected and references update

On the dependence between UV luminosity and Lyman-alpha equivalent width in high redshift galaxies

We show that with the simple assumption of no correlation between the Ly-alpha equivalent width and the UV luminosity of a galaxy, the observed distribution of high redshift galaxies in an equivalent width - absolute UV magnitude plane can be reproduced. We further show that there is no dependence between Ly-alpha equivalent width and Ly-alpha luminosity in a sample of Ly-alpha emitters. The test was expanded to Lyman-break galaxies and again no dependence was found. Simultaneously, we show that a recently proposed lack of large equivalent width, UV bright galaxies (Ando et al. 2006) can be explained by a simple observational effect, based on too small survey volumes.Comment: 7 pages, 3 figures, 2 tables, accepted in MNRA

Lyman-alpha emission galaxies at a redshift of z = 5.7 in the FORS Deep Field

We present the results of a search for Lyman-alpha emission galaxies at z~ 5.7 in the FORS Deep Field. The objective of this study is to improve the faint end of the luminosity function of high-redshift Lyman-alpha emitting galaxies and to derive properties of intrinsically faint Lyman-alpha emission galaxies in the young universe. Using FORS2 at the ESO VLT and a set of special interference filters, we identified candidates for high-redshift Lyman-alpha galaxies. We then used FORS2 in spectroscopic mode to verify the identifications and to study their spectral properties. The narrow-band photometry resulted in the detection of 15 likely Lyman-alpha emission galaxies. Spectra with an adequate exposure time could be obtained for eight galaxies. In all these cases the presence of Lyman-alpha emission at z = 5.7 was confirmed spectroscopically. The line fluxes of the 15 candidates range between 3 and 16 * 10^-21 Wm^-2, which corresponds to star-formation rates not corrected for dust between 1 and 5 Msun/yr. The luminosity function derived for our photometrically identified objects extends the published luminosity functions of intrinsically brighter Lyman-alpha galaxies. With this technique the study of high-redshift Lyman-alpha emission galaxies can be extended to low intrinsic luminosities.Comment: 9 pages, 17 figures. Accepted by A&A. PDF version with higher resolution figures here: http://www.lsw.uni-heidelberg.de/users/jheidt/fdf/pubs/fdflae5_7_110406.pd

Lyman alpha emission in high-redshift galaxies

A significant fraction of the high-redshift galaxies show strong Lyman emission lines. For redshifts z>5, most known galaxies belong to this class. However, so far not much is known about the physical structure and nature of these objects. Our aim is to analyse the Lyman alpha emission in a sample of high-redshift UV-continuum selected galaxies and to derive the physical conditions that determine the Lyman alpha profile and the line strength. VLT/FORS spectra with a resolution of R ~ 2000 of 16 galaxies in the redshift range of z = 2.7 to 5 are presented. The observed Lyman alpha profiles are compared with theoretical models. The Lyman alpha lines range from pure absorption (EW = -17 Angstroem) to strong emission (EW = 153 Angstroem). Most Lyman alpha emission lines show an asymmetric profile, and three galaxies have a double-peaked profile. Both types of profiles can be explained by a uniform model consisting of an expanding shell of neutral and ionised hydrogen around a compact starburst region. The broad, blueshifted, low-ionisation interstellar absorption lines indicate a galaxy-scale outflow of the ISM. The strengths of these lines are found to be determined in part by the velocity dispersion of the outflowing medium. We find star-formation rates of these galaxies ranging from SFR(UV) = 1.2 to 63.2 Msun uncorrected for dust absorption. The Lyman alpha emission strength of our target galaxies is found to be determined by the amount of dust and the kinematics of the outflowing material.Comment: 11 pages, 6 figures. A&A accepte

HyPLC: Hybrid Programmable Logic Controller Program Translation for Verification

Programmable Logic Controllers (PLCs) provide a prominent choice of implementation platform for safety-critical industrial control systems. Formal verification provides ways of establishing correctness guarantees, which can be quite important for such safety-critical applications. But since PLC code does not include an analytic model of the system plant, their verification is limited to discrete properties. In this paper, we, thus, start the other way around with hybrid programs that include continuous plant models in addition to discrete control algorithms. Even deep correctness properties of hybrid programs can be formally verified in the theorem prover KeYmaera X that implements differential dynamic logic, dL, for hybrid programs. After verifying the hybrid program, we now present an approach for translating hybrid programs into PLC code. The new tool, HyPLC, implements this translation of discrete control code of verified hybrid program models to PLC controller code and, vice versa, the translation of existing PLC code into the discrete control actions for a hybrid program given an additional input of the continuous dynamics of the system to be verified. This approach allows for the generation of real controller code while preserving, by compilation, the correctness of a valid and verified hybrid program. PLCs are common cyber-physical interfaces for safety-critical industrial control applications, and HyPLC serves as a pragmatic tool for bridging formal verification of complex cyber-physical systems at the algorithmic level of hybrid programs with the execution layer of concrete PLC implementations.Comment: 13 pages, 9 figures. ICCPS 201

The Great Observatories Origins Deep Survey. VLT/FORS2 Spectroscopy in the GOODS-South Field: Part III

Aims. We present the full data set of the spectroscopic campaign of the ESO/GOODS program in the GOODS-South field, obtained with the FORS2 spectrograph at the ESO/VLT. Method. Objects were selected as candidates for VLT/FORS2 observations primarily based on the expectation that the detection and measurement of their spectral features would benefit from the high throughput and spectral resolution of FORS2. The reliability of the redshift estimates is assessed using the redshift-magnitude and color-redshift diagrams, and comparing the results with public data. Results. Including the third part of the spectroscopic campaign (12 masks) to the previous work (26 masks, Vanzella et al. 2005, 2006), 1715 spectra of 1225 individual targets have been analyzed. The actual spectroscopic catalog provides 887 redshift determinations. The typical redshift uncertainty is estimated to be sigma(z) ~ 0.001. Galaxies have been selected adopting different color criteria and using photometric redshifts. The resulting redshift distribution typically spans two domains: from z=0.5 to 2 and z=3.5 to 6.3. The reduced spectra and the derived redshifts are released to the community through the ESO web page http://www.eso.org/science/goods/Comment: 11 pages, 11 figures; accepted for publication in Astronomy & Astrophysics. Data are available at http://www.eso.org/science/goods