H.-J. Roser

Supernova Shock Breakout from a Red Supergiant

Massive stars undergo a violent death when the supply of nuclear fuel in their cores is exhausted, resulting in a catastrophic “core-collapse” supernova. Such events are usually only detected at least a few days after the star has exploded. Observations of the supernova SNLS-04D2dc with the Galaxy Evolution Explorer space telescope reveal a radiative precursor from the supernova shock before the shock reached the surface of the star and show the initial expansion of the star at the beginning of the explosion. Theoretical models of the ultraviolet light curve confirm that the progenitor was a red supergiant, as expected for this type of supernova. These observations provide a way to probe the physics of core-collapse supernovae and the internal structures of their progenitor stars.

Object classification in astronomical multi-color surveys

We present a photometric method for identifying stars, galaxies and quasars in multi-color surveys, which uses a library of > 65000 color templates for comparison with observed objects. The method aims for extracting the information content of object colors in a statistically correct way, and performs a classication as well as a redshift estimation for galaxies and quasars in a unied approach based on the same probability density functions. For the redshift estimation, we employ an advanced version of the Minimum Error Variance estimator which determines the redshift error from the redshift dependent probability density function itself. The method was originally developed for the Calar Alto Deep Imaging Survey (CADIS), but is now used in a wide variety of survey projects. We checked its performance by spectroscopy of CADIS objects, where the method provides high reliability (6 errors among 151 objects with R< 24), especially for the quasar selection, and redshifts accurate within z 0:03 for galaxies and z 0:1 for quasars. For an optimization of future survey eorts, a few model surveys are compared, which are designed to use the same total amount of telescope time but dierent sets of broad-band and medium-band lters. Their performance is investigated by Monte-Carlo simulations as well as by analytic evaluation in terms of classication and redshift estimation. If photon noise were the only error source, broad-band surveys and medium-band surveys should perform equally well, as long as they provide the same spectral coverage. In practice, medium-band surveys show superior performance due to their higher tolerance for calibration errors and cosmic variance. Finally, we discuss the relevance of color calibration and derive important conclusions for the issues of library design and choice of lters. The calibration accuracy poses strong constraints on an accurate classication, which are most critical for surveys with few, broad and deeply exposed lters, but less severe for surveys with many, narrow and less deep lters.

HST optical spectral index map of the jet of 3C 273

We present HST images at 622 nm and 300 nm of the jet in 3C 273 and determine the run of the optical spectral index at 0: 00 2 along the jet. The smoothness of spectral index changes shows that the physical conditions are varying smoothly across the jet. There is no correlation between the optical flux and spectral index, as would be expected for relativistic electrons suering strong cooling due to synchrotron emission. We nd no evidence for localized acceleration or loss sites. This suggests that the spectral shape is not changing much throughout the jet. We show that relativistic beaming and/or sub-equipartition magnetic elds cannot remove the discrepancy between light-travel time along the jet and the lifetime of electrons emitting optical synchrotron radiation. We consider this further evidence in favour of a distributed electron acceleration process.

Multi-color classification in the calar alto deep imaging survey

We use a multi-color classification method introduced by Wolf et al. ([CITE]) to reliably identify stars, galaxies and quasars in the up to 16-dimensional color space provided by the filter set of the Calar Alto Deep Imaging Survey (CADIS). The samples of stars, galaxies and quasars obtained this way have been used for dedicated studies which are published in separate papers. The classification is good enough to detect quasars rather completely and efficiently without confirmative spectroscopy. The multi-color redshifts are accurate enough for most statistical applications, e.g. evolutionary studies of the galaxy luminosity function. Also, the separation between stars and galaxies reaches deeper than with morphological criteria, so that studies of the stellar population can be extended to fainter levels. We characterize the dataset presently available on the CADIS 1 h-, 9 h- and 16 h-fields. Using Monte-Carlo simulations we model the classification performance expected for CADIS. We present a summary of the classification results on the CADIS database and discuss unclassified objects. More than 99% of the whole catalog sample at R < 22 (more than 95% at R < 23) are successfully classified matching the expectations derived from the simulations. A small number of peculiar objects challenging the classification is discussed in detail. Spectroscopic observations are used to check the reliability of the multi-color classification (6 mistakes among 151 objects with R < 24). From these, we also determine the accuracy of the multi-color redshifts which are rather good for galaxies (σ_z ≈ 0.03) and useful for quasars. We find that the classification performance derived from the simulations compares well with results from the real survey. Finally, we locate areas for potential improvement of the classification.

The radio-ultraviolet spectral energy distribution of the jet in 3C 273

We present deep VLA and HST observations of the large-scale jet in 3C 273 matched to 0. �� 3 resolution. The observed spectra show a significant flattening in the infrared-ultraviolet wavelength range. The jets emission cannot therefore be assumed to arise from a single electron population and requires the presence of an additional emission component. The observed smooth variations of the spectral indices along the jet imply that the physical conditions vary correspondingly smoothly. We determine the maximum particle energy for the optical jet using synchrotron spectral fits. The slow decline of the maximum energy along the jet implies particle reacceleration acting along the entire jet. In addition to the already established global anti-correlation between maximum particle energy and surface brightness, we find a weak positive correlation between small-scale variations in maximum particle energy and surface brightness. The origin of these conflicting global and local correlations is unclear, but they provide tight constraints for reacceleration models.

The Calar Alto Deep Imaging Survey:

We present K-band number counts for the faint galaxies in the Calar Alto Deep Imaging Survey (CADIS). We covered 4 CADIS fields, a total area of 0.2 deg^2, in the broad band filters B, R and K. We detect about 4000 galaxies in the K-band images, with a completeness limit of K = 19.75 mag, and derive the K-band galaxy number counts in the range of 14.25 18 mag. We also find that most of the K = 18 – 20 mag galaxies have a B - K color bluer than the prediction of a no-evolution model for an L⋆ Sbc galaxy, implying either significant evolution, even for massive galaxies, or the existence of an extra population of small galaxies.

K

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

-band Galaxy number counts

I_{815} = 22

The luminosity function of field galaxies and its evolution since

without correction and with completeness correction extends to

\vec{z=1}

I_{815}=23.0