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The methods and techniques for the slitless spectroscopy software aXe, which was designed to reduce data from the various slitless spectroscopy modes of Hubble Space Telescope instruments, are described. aXe can treat slitless spectra from different instruments such as ACS, NICMOS and WFC3 through the use of a configuration file which contains all the instrument dependent parameters. The basis of the spectral extraction within aXe are the position, morphology and photometry of the objects on a companion direct image. Several aspects of slitless spectroscopy, such as the overlap of spectra, an extraction dependent on object shape and the provision of flat-field cubes, motivate a dedicated software package, and the solutions offered within aXe are discussed in detail. The effect of the mutual contamination of spectra can be quantitatively assessed in aXe, using spectral and morphological information from the companion direct image(s). A new method named 'aXedrizzle' for 2D rebinning and co-adding spectral data, taken with small shifts or dithers, is described. The extraction of slitless spectra with optimal weighting is outlined and the correction of spectra for detector fringing for the ACS CCD's is presented. Auxiliary software for simulating slitless data and for visualizing the results of an aXe extraction is outlined.

Abstract. The emission line survey within the Calar Alto Deep Imaging Survey (CADIS) detects emission line galaxies by a scan with an imaging Fabry-Perot interferometer. It covers 5 fields of >100 each in three wavelengths windows centered on λ 700, 820, and 920 nm, and reaches to a typical limiting line flux of 3× 10 −20 W m −2 . This is the deepest emission line survey covering a field of several 100 . Galaxies between z = 0.25 and z = 1.4 are detected by prominent emission lines (from Hα to [O ]372.7) falling into the FP scans. Additional observations with a dozen medium band filters allow to establish the line identification and thus the redshift of the galaxies to better than σ z = 0.001. On the basis of a total of more than 400 emission line galaxies detected in Hα (92 galaxies), [O ]500.7 (124 galaxies), or [O ]372.7 (222 galaxies) we measure the instantaneous star formation rate (SFR) in the range 0.24 < z < 1.21. With this purely emission line selected sample we are able to reach much fainter emission line galaxies than previous, continuum-selected samples. Thus completeness corrections are much less important. Although the relative [O ] emission line strength depends on excitation and metallicity and shows strong variation, the mean line ratios yield SFR[O ] values consistent with the SFR evolution. Our results substantiates the indications from previous studies (based on small galaxy samples) that the SFR decreases by a factor of ∼20 between z = 1.2 and today. In fact, for a Ω m = 0.3, Ω λ = 0.7 cosmology, we find an exponential declineρ SFR ∝ exp(−t lookback /2.6 Gyr). This decrease of the SFR with time follows an exponential law which is compatible with the decreasing galaxy merger rate as expected from model calculations. The inferred SF density is in perfect agreement with that deduced from the FIR emission of optically selected galaxies which is explained by a large overlap between both populations. We show that self-consistent extinction corrections of both our emission lines and the UV continua lead to consistent results for the SF density.

Future galaxy redshift surveys aim to measure cosmological quantities from the galaxy power spectrum. A prime example is the detection of baryonic acoustic oscillations, providing a standard ruler to measure the dark energy equation of state, w(z), to high precision. The strongest practical limitation for these experiments is how quickly accurate redshifts can be measured for sufficient galaxies to map the large-scale structure. A promising strategy is to target emission-line (i.e. star-forming) galaxies at high redshift (z ∼ 0.5-2); not only is the space density of this population increasing out to z ∼ 2, but also emission lines provide an efficient method of redshift determination. Motivated by the prospect of future dark energy surveys targeting Hα emitters at near-infrared wavelengths (i.e. z > 0.5), we use the latest empirical data to model the evolution of the Hα luminosity function out to z ∼ 2 and thus provide predictions for the abundance of Hα emitters for practical limiting fluxes. We caution that the estimates presented in this work must be tempered by an efficiency factor, , giving the redshift success rate from these potential targets. For a range of practical efficiencies and limiting fluxes, we provide an estimate ofnP 0.2 , wheren is the 3D galaxy number density and P 0.2 is the galaxy power spectrum evaluated at k = 0.2 h Mpc −1 . Ideal surveys must providē nP 0.2 > 1 in order to balance shot-noise and cosmic variance errors. We show that a realistic emission-line survey ( = 0.5) could achievenP 0.2 = 1 out to z ∼ 1.5 with a limiting flux of 10 −16 erg s −1 cm −2 . If the limiting flux is a factor of 5 brighter, then this goal can only be achieved out to z ∼ 0.5, highlighting the importance of survey depth and efficiency in cosmological redshift surveys.

We present deep unbiased spectroscopy of the Hubble Ultra Deep Field (UDF) carried out using the slitless grism spectroscopy mode of the Advance Camera for Surveys on the Hubble Space Telescope (HST). The GRIsm ACS Program for Extragalactic Science (GRAPES) achieves continuum detection as faint as z AB = 27.2 using 40 orbits (9.2 × 10 4 seconds) on HST. The data were taken at four orientation angles to correct for the overlap of spectra. GRAPES data provide a unique, uninterrupted, low resolution (R=100) spectral coverage for 5500Å < λ < 10500Å, and allow us to detect high redshift galaxies at 4 < z < 7 whether they have Lyα lines or just show the Lyman Break, as well as find

Abstract. We present Ulysses and NEAR data from the detection of the short or intermediate duration (2 s) gamma-ray burst GRB 000301C (2000 March 1.41 UT). The gamma-ray burst (GRB) was localised by the Inter Planetary Network (IPN) and RXTE to an area of ∼50 arcmin 2 . A fading optical counterpart was subsequently discovered with the Nordic Optical Telescope (NOT) about 42 h after the burst. The GRB lies at the border between the long-soft and the short-hard classes of GRBs. If GRB 000301C belongs to the latter class, this would be the first detection of an afterglow to a short-hard burst. We present UBRI photometry from the time of the discovery until 11 days after the burst. We also present JHK photometry obtained with UKIRT on 2000 March 4.5 UT (3.1 days after the burst). Finally, we present spectroscopic observations of the optical afterglow obtained with the ESO VLT Antu telescope 4 and 5 days after the burst. The optical light curve is consistent with being achromatic from 2 to 11 days after the burst and exhibits a break. A broken power-law fit yields a shallow pre-break decay power-law slope of α1 = −0.72 ± 0.06, a break time of t break = 4.39 ± 0.26 days after the burst, and a post-break slope of α2 = −2.29 ± 0.17. These properties of the light curve are best explained by a sideways expanding jet in an ambient medium of constant mean density. In the optical spectrum we find absorption features that are consistent with Fe ii, C iv, C ii, Si ii and Lyα at a redshift of 2.0404 ± 0.0008. We find evidence for a curved shape of the spectral energy distribution of the observed afterglow. It is best fitted with a power-law spectral distribution with index β ∼ −0.7 reddened by an SMC-like extinction law with AV ∼ 0.1 mag. Based on the Lyα absorption line we estimate the H i column density to be log(N(H i)) = 21.2 ± 0.5. This is the first direct indication of a connection between GRB host galaxies and Damped Lyα Absorbers.

Abstract. We present the B-band luminosity function and comoving space and luminosity densities for a sample of 2779 I-band selected field galaxies based on multi-color data from the CADIS survey. The sample is complete down to I815 = 22 without correction and with completeness correction extends to I815 = 23.0. By means of a new multi-color analysis the objects are classified according to their spectral energy distributions (SEDs) and their redshifts are determined with typical errors of δz ≤ 0.03. We have split our sample into four redshift bins between z = 0.1 and z = 1.04 and into three SED bins E-Sa, Sa-Sc and starbursting (emission line) galaxies. The evolution of the luminosity function is clearly differential with SED. The normalization φ * of the luminosity function for the E-Sa galaxies decreases towards higher redshift, and we find evidence that the comoving galaxy space density decreases with redshift as well. In contrast, we find φ * and the comoving space density increasing with redshift for the Sa-Sc galaxies. For the starburst galaxies we find a steepening of the luminosity function at the faint end and their comoving space density increases with redshift.

Galaxies selected on the basis of their emission line strength show low metallicities, regardless of their redshifts. We conclude this from a sample of faint galaxies at redshifts between 0.6 < z < 2.4, selected by their prominent emission lines in lowresolution grism spectra in the optical with the Advanced Camera for Surveys (ACS) on the Hubble Space Telescope (HST) and in the near-infrared using Wide-Field Camera 3 (WFC3). Using a sample of 11 emission line galaxies (ELGs) at 0.6 < z < 2.4 with luminosities of −22 M B −19 which have [OII], Hβ, and [OIII] line flux measurements from the combination of two grism spectral surveys, we use the R23 method to derive the gas-phase oxygen abundances: 7.5 <12+log(O/H)<8.5. The galaxy stellar masses are derived using Bayesian based Markov Chain Monte Carlo (πMC 2 ) fitting of their Spectral Energy Distribution (SED), and span the mass range 8.1 < log(M * /M ⊙ ) < 10.1. These galaxies show a mass-metallicity (M-L) and Luminosity-Metallicity (L-Z) relation, which is offset by -0.6 dex in metallicity at given absolute magnitude and stellar mass relative to the local SDSS galaxies, as well as continuum selected DEEP2 samples at similar redshifts. The emission-line selected galaxies most resemble the local "green peas" galaxies and Lyman-alpha galaxies at z ≃ 0.3 and z ≃ 2.3 in the M-Z and L-Z relations and their morphologies. The G − M 20 morphology analysis shows that 10 out of 11 show disturbed morphology, even as the star-forming regions are compact. These galaxies may be intrinsically metal poor, being at early stages of formation, or the low metallicities may be due to gas infall and accretion due to mergers.