Skywalking GEMS and UDF

The two large colour mosaics of the GEMS and UDF projects, both obtained with the Hubble Space Telescope and ACS, consist of large amounts of data. We present two web application pages (the GEMS and UDF "Skywalker") that allow to pan around in these mosaics with downloading only small parts at a time.Comment: 1 pag

Seeing the sky through Hubble's eye: The COSMOS SkyWalker

Large, high-resolution space-based imaging surveys produce a volume of data that is difficult to present to the public in a comprehensible way. While megapixel-sized images can still be printed out or downloaded via the World Wide Web, this is no longer feasible for images with 10^9 pixels (e.g., the Hubble Space Telescope Advanced Camera for Surveys [ACS] images of the Galaxy Evolution from Morphology and SEDs [GEMS] project) or even 10^10 pixels (for the ACS Cosmic Evolution Survey [COSMOS]). We present a Web-based utility called the COSMOS SkyWalker that allows viewing of the huge ACS image data set, even through slow Internet connections. Using standard HTML and JavaScript, the application successively loads only those portions of the image at a time that are currently being viewed on the screen. The user can move within the image by using the mouse or interacting with an overview image. Using an astrometrically registered image for the COSMOS SkyWalker allows the display of calibrated world coordinates for use in science. The SkyWalker "technique" can be applied to other data sets. This requires some customization, notably the slicing up of a data set into small (e.g., 256^2 pixel) subimages. An advantage of the SkyWalker is the use of standard Web browser components; thus, it requires no installation of any software and can therefore be viewed by anyone across many operating systems.Comment: 4 pages, 2 figures, accepted for publication in PAS

The properties of the extended warm ionised gas around low-redshift QSOs and the lack of extended high-velocity outflows

(Abridged) We present a detailed analysis of a large sample of 31 low-redshift, mostly radio-quiet type 1 QSOs observed with integral field spectroscopy to study their extended emission-line regions (EELRs). We focus on the ionisation state of the gas, size and luminosity of extended narrow line regions (ENLRs), which corresponds to those parts of the EELR dominated by ionisation from the QSO, as well as the kinematics of the ionised gas. We detect EELRs around 19 of our 31 QSOs (61%) after deblending the unresolved QSO emission and the extended host galaxy light in the integral field data. We identify 13 EELRs to be entirely ionised by the QSO radiation, 3 EELRs are composed of HII regions and 3 EELRs display signatures of both ionisation mechanisms at different locations. The typical size of the ENLR is 10kpc at a median nuclear [OIII] luminosity of log(L([OIII])/[erg/s])=42.7+-0.15. We show that the ENLR sizes are least a factor of 2 larger than determined with HST, but are consistent with those of recently reported type 2 QSOs at matching [OIII] luminosities. The ENLR of type 1 and type 2 QSOs appear to follow the same size-luminosity relation. Furthermore, we show for the first time that the ENLR size is much better correlated with the QSO continuum luminosity than with the total/nuclear [OIII] luminosity. We show that ENLR luminosity and radio luminosity are correlated, and argue that radio jets even in radio-quiet QSOs are important for shaping the properties of the ENLR. Strikingly, the kinematics of the ionised gas is quiescent and likely gravitationally driven in the majority of cases and we find only 3 objects with radial gas velocities exceeding 400km/s in specific regions of the EELR that can be associate with radio jets. In general, these are significantly lower outflow velocities and detection rates compared to starburst galaxies or radio-loud QSOs.Comment: 34 page, 22 figures (slightly degraded in resolution), 10 tables, accepted for publication in A&A, minor corrections to match with the publisher versio

The low-metallicity QSO HE 2158-0107: A massive galaxy growing by the accretion of nearly pristine gas from its environment?

[abridged] The metallicities of AGN are usually well above solar in their NLR, often reaching up to several times solar in their broad-line regions. Low-metallicity AGN are rare objects which have so far always been associated with low-mass galaxies hosting low-mass BHs (M_BH<10^6Msun). In this paper we present IFS data of the low-redshift QSO HE 2158-0107 for which we find strong evidence for sub-solar NLR metallicities associated with a massive BH (M_BH~3x10^8Msun). The QSO is surrounded by a large extended emission-line region reaching out to 30kpc from the QSO in a tail-like geometry. We present optical and near-IR images and investigate the properties of the host galaxy. The SED of the host is rather blue, indicative of a significant young age stellar population formed within the last 1Gyr. A 3sigma upper limit of L_bulge<4.5x10^10Lsun for the H band luminosity and a corresponding stellar mass upper limit of M_bulge<3.4x10^10Msun show that the host is offset from the local BH-bulge relations. This is independently supported by the kinematics of the gas. Although the stellar mass of the host galaxy is lower than expected, it cannot explain the exceptionally low metallicity of the gas. We suggest that the extended emission-line region and the galaxy growth are caused by the infall of nearly pristine gas from the environment of the QSO host. Minor mergers of dwarf galaxies or the theoretically predicted smooth accretion of cold gas are both potential drivers behind that process. Since the metallicity of the gas in the NLR is much lower than expected, we suspect that the external gas has already reached the galaxy centre and may even contribute to the current feeding of the BH. HE 2158-0107 appears to represent a particular phase of substantial BH and galaxy growth that can be observationally linked with the accretion of external material from its environment.Comment: 14 pages, 12 figures, accepted for publication in A&

Ultrafast pump-probe dynamics in ZnSe-based semiconductor quantum-wells

Pump-probe experiments are used as a controllable way to investigate the properties of photoexcited semiconductors, in particular, the absorption saturation. We present an experiment-theory comparison for ZnSe quantum wells, investigating the energy renormalization and bleaching of the excitonic resonances. Experiments were performed with spin-selective excitation and above-bandgap pumping. The model, based on the semiconductor Bloch equations in the screened Hartree-Fock approximation, takes various scattering processes into account phenomenologically. Comparing numerical results with available experimental data, we explain the experimental results and find that the electron spin-flip occurs on a time scale of 30 ps.Comment: 10 pages, 9 figures. Key words: nonlinear and ultrafast optics, modeling of femtosecond pump-probe experiments, electron spin-flip tim

The B band luminosities of QSO host galaxies

We report on the analysis of B band imaging data of 57 low-redshift QSOs and Seyfert 1 galaxies selected from the Hamburg/ESO-Survey, for which host galaxy dependent selection biases are greatly reduced compared to other optical surveys. Only one object in the sample is known to be radio-loud. We adopted a procedure to remove the AGN contribution by subtracting a scaled point spread functions from each QSO image. To reclaim the integrated host galaxy flux we correct for oversubtraction based on simulations. This method shows to be quite insensitive to the host galaxy morphological type, which we can unambiguously established for 15 of the 57 objects. The quasar host galaxies are detected in all cases. The hosts are very luminous, ranging in absolute magnitude M_B from -19.0 to -23.8, with an average of M_B,gal = -21.5, considerably above L* for field galaxies. For the luminous QSO subsample with M_B < -23 the average host absolute magnitude is M_B,gal = -23.0, while for the complementary low-luminosity AGN we get M_B,gal = -21.2, roughly equal to L*. The luminous host galaxies in the sample are typically approx. 1 mag brighter than expected when inferring B band luminosities from studies of similar objects at longer wavebands. We argue that this mismatch is not likely to be explained by selection effects, but favor host galaxy colours significanlty bluer than those of inactive galaxies. Although published B band data are scant, this result and the findings of other authors are in good agreement.Comment: 15 pages, 10 figures, accepted for publication in MNRA

FERENGI: Redshifting galaxies from SDSS to GEMS, STAGES and COSMOS

We describe the creation of a set of artificially "redshifted" galaxies in the range 0.1<z<1.1 using a set of ~100 SDSS low redshift (v<7000 km/s) images as input. The intention is to generate a training set of realistic images of galaxies of diverse morphologies and a large range of redshifts for the GEMS and COSMOS galaxy evolution projects. This training set allows other studies to investigate and quantify the effects of cosmological redshift on the determination of galaxy morphologies, distortions and other galaxy properties that are potentially sensitive to resolution, surface brightness and bandpass issues. We use galaxy images from the SDSS in the u, g, r, i, z filter bands as input, and computed new galaxy images from these data, resembling the same galaxies as located at redshifts 0.1<z<1.1 and viewed with the Hubble Space Telescope Advanced Camera for Surveys (HST ACS). In this process we take into account angular size change, cosmological surface brightness dimming, and spectral change. The latter is achieved by interpolating a spectral energy distribution that is fit to the input images on a pixel-to-pixel basis. The output images are created for the specific HST ACS point spread function and the filters used for GEMS (F606W and F850LP) and COSMOS (F814W). All images are binned onto the desired pixel grids (0.03" for GEMS and 0.05" for COSMOS) and corrected to an appropriate point spread function. Noise is added corresponding to the data quality of the two projects and the images are added onto empty sky pieces of real data images. We make these datasets available from our website, as well as the code - FERENGI: "Full and Efficient Redshifting of Ensembles of Nearby Galaxy Images" - to produce datasets for other redshifts and/or instruments.Comment: 11 pages, 10 figures, 3 table

On-axis spectroscopy of the host galaxies of 20 optically luminous quasars at z~0.3

We present the analysis of a sample of 20 bright low-redshift quasars (M_B<-23 and z < 0.35) observed spectroscopically with the VLT. The FORS1 spectra, obtained in Multi Object Spectroscopy (MOS) mode, allow to observe simultaneously the quasars and several reference stars used to spatially deconvolve the data. Applying the MCS deconvolution method, we are able to separate the individual spectra of the quasar and of the underlying host galaxy. Contrary to some previous claims, we find that luminous quasars are not exclusively hosted by massive ellipticals. Most quasar host galaxies harbour large amounts of gas, irrespective of their morphological type. Moreover, the stellar content of half of the hosts is a young Sc-like population, associated with a rather low metallicity interstellar medium. A significant fraction of the galaxies contain gas ionized at large distances by the quasar radiation. This large distance ionization is always associated with signs of gravitational interactions (as detected from images or disturbed rotation curves). The spectra of the quasars themselves provide evidence that gravitational interactions bring dust and gas in the immediate surrounding of the super massive black hole, allowing to feed it. The quasar activity might thus be triggered (1) in young gas-rich spiral galaxies by local events and (2) in more evolved galaxies by gravitational interactions or collisions. The latter mechanism gives rises to the most powerful quasars. Finally, we derive mass models for the isolated spiral host galaxies and we show that the most reliable estimators of the systemic redshift in the quasar spectrum are the tips of the Ha and Hb lines.Comment: 30 pages, 19 figures, 9 tables, accepted for publication in MNRAS, major revisio

Long-range Energy Transfer and Ionization in Extended Quantum Systems Driven by Ultrashort Spatially Shaped Laser Pulses

The processes of ionization and energy transfer in a quantum system composed of two distant H atoms with an initial internuclear separation of 100 atomic units (5.29 nm) have been studied by the numerical solution of the time-dependent Schr\"odinger equation beyond the Born-Oppenheimer approximation. Thereby it has been assumed that only one of the two H atoms was excited by temporally and spatially shaped laser pulses at various laser carrier frequencies. The quantum dynamics of the extended H-H system, which was taken to be initially either in an unentangled or an entangled ground state, has been explored within a linear three-dimensional model, including two z coordinates of the electrons and the internuclear distance R. An efficient energy transfer from the laser-excited H atom (atom A) to the other H atom (atom B) and the ionization of the latter have been found. It has been shown that the physical mechanisms of the energy transfer as well as of the ionization of atom B are the Coulomb attraction of the laser driven electron of atom A by the proton of atom B and a short-range Coulomb repulsion of the two electrons when their wave functions strongly overlap in the domain of atom B.Comment: 11 pages, 7 figure

Decomposition of AGN host galaxy images

We describe an algorithm to decompose deep images of Active Galactic Nuclei into host galaxy and nuclear components. Currently supported are three galaxy models: A de-Vaucouleurs spheroidal, an exponential disc, and a two-component disc+bulge model. Key features of the method are: (semi-)analytic representation of a possibly spatially variable point-spread function; full two-dimensional convolution of the model galaxy using gradient-controlled adaptive subpixelling; multiple iteration scheme. The code is computationally efficient and versatile for a wide range of applications. The quantitative performance is measured by analysing simulated imaging data. We also present examples of the application of the method to small test samples of nearby Seyfert 1 galaxies and quasars at redshifts z < 0.35.Comment: 12 pages, 15 figures, accepted for publication in MNRA