L. Flöer

The Effelsberg Bonn H I Survey (EBHIS)

The Effelsberg-Bonn H I survey (EBHIS) comprises an all-sky survey north of Dec = –5° of the Milky Way and the local volume out to a red-shift of z ≃ 0.07. Using state of the art Field Programmable Gate Array (FPGA) spectrometers it is feasible to cover the 100 MHz bandwidth with 16.384 spectral channels. High speed storage of H I spectra allows us to minimize the degradation by Radio Frequency Interference (RFI) signals. Regular EBHIS survey observations started during the winter season 2008/2009 after extensive system evaluation and verification tests. Until today, we surveyed about 8000 square degrees, focusing during the first all-sky coverage of the Sloan-Digital Sky Survey (SDSS) area and the northern extension of the Magellanic stream. The first whole sky coverage will be finished in 2011. Already this first coverage will reach the same sensitivity level as the Parkes Milky Way (GASS) and extragalactic surveys (HIPASS). EBHIS data will be calibrated, stray-radiation corrected and freely accessible for the scientific community via a webinterface. In this paper we demonstrate the scientific data quality and explore the expected harvest of this new all-sky survey (© 2011 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim)

The Effelsberg-Bonn H i Survey: Milky Way gas - First data release

Context. The Effelsberg–Bonn H i Survey (EBHIS) is a new 21-cm survey performed with the 100-m telescope at Effelsberg. It covers the whole northern sky out to a redshift of z ∼ 0.07 and comprises H i line emission from the Milky Way and the Local Volume. Aims. We aim to substitute the northern-hemisphere part of the Leiden/Argentine/Bonn Milky Way H i survey (LAB) with this first EBHIS data release∗, which presents the H i gas in the Milky Way regime. Methods. The use of a seven-beam L-band array made it feasible to perform this all-sky survey with a 100-m class telescope in a reasonable amount of observing time. State-of-the-art fast-Fourier-transform spectrometers provide the necessary data read-out speed, dynamic range, and spectral resolution to apply software radio-frequency interference mitigation. EBHIS is corrected for stray radiation and employs frequency-dependent flux-density calibration and sophisticated baseline-removal techniques to ensure the highest possible data quality. Results. Detailed analyses of the resulting data products show that EBHIS is not only outperforming LAB in terms of sensitivity and angular resolution, but also matches the intensity-scale of LAB extremely well, allowing EBHIS to be used as a drop-in replacement for LAB. Data products are made available to the public in a variety of forms. Most important, we provide a properly gridded Milky Way H i column density map in HEALPix representation. To maximize the usefulness of EBHIS data, we estimate uncertainties in the H i column density and brightness temperature distributions, accounting for systematic effects.

The Effelsberg–Bonn H I Survey: Data Reduction

Starting in winter 2008/2009 an L-band seven-feed-array receiver is used for a 21 cm line survey performed with the 100 m telescope, the Effelsberg-Bonn H I survey (EBHIS). The EBHIS will cover the whole northern hemisphere for decl. > – 5° comprising both the galactic and extragalactic sky out to a distance of about 230 Mpc. Using state-of-the-art FPGA-based digital fast Fourier transform spectrometers, superior in dynamic range and temporal resolution to conventional correlators, allows us to apply sophisticated radio frequency interference (RFI) mitigation schemes. In this paper, the EBHIS data reduction package and first results are presented. The reduction software consists of RFI detection schemes, flux and gain-curve calibration, stray-radiation removal, baseline fitting, and finally the gridding to produce data cubes. The whole software chain is successfully tested using multi-feed data toward many smaller test fields (1-100 deg2) and recently applied for the first time to data of two large sky areas, each covering about 2000 deg2. The first large area is toward the northern galactic pole and the second one toward the northern tip of the Magellanic Leading Arm. Here, we demonstrate the data quality of EBHIS Milky Way data and give a first impression on the first data release in 2011.

Comparison of potential ASKAP Hi survey source finders

The large size of the ASKAP Hi surveys DINGO and WALLABY necessitates automated 3D source finding. A performance difference of a few percent corresponds to a significant number of galaxies being detected or undetected. As such, the performance of the automated source finding is of paramount importance to both of these surveys. We have analysed the performance of various source finders to determine which will allow us to meet our survey goals during the DINGO and WALLABY design studies. Here we present a comparison of the performance of five different methods of automated source finding. These source finders are duchamp, gamma-finder, a cnhi finder, a 2d–1d wavelet reconstruction finder and a sigma clipping method (s+c finder). Each source finder was applied to the same three-dimensional data cubes containing (a) point sources with a Gaussian velocity profile and (b) spatially extended model-galaxies with inclinations and rotation profiles. We focus on the completeness and reliability of each algorithm when comparing the performance of the different source finders.

SOFIA: A flexible source finder for 3D spectral line data

We introduce SOFIA, a flexible software application for the detection and parametrization of sources in 3D spectral line data sets. SOFIA combines for the first time in a single piece of software a set of new source-finding and parametrization algorithms developed on the way to future H I surveys with ASKAP (WALLABY, DINGO) and APERTIF. It is designed to enable the general use of these new algorithms by the community on a broad range of data sets. The key advantages of SOFIA are the ability to: search for line emission on multiple scales to detect 3D sources in a complete and reliable way, taking into account noise level variations and the presence of artefacts in a data cube; estimate the reliability of individual detections; look for signal in arbitrarily large data cubes using a catalogue of 3D coordinates as a prior; provide a wide range of source parameters and output products which facilitate further analysis by the user. We highlight the modularity of SOFIA, which makes it a flexible package allowing users to select and apply only the algorithms useful for their data and science questions. This modularity makes it also possible to easily expand SOFIA in order to include additional methods as they become available. The full SOFIA distribution, including a dedicated graphical user interface, is publicly available for download.

HI4PI: a full-sky H i survey based on EBHIS and GASS

Deutsche Forschungsgemeinschaft (DFG) [KA1265/5-1, KA1265/5-2, KE757/71, KE757/7-2, KE757/7-3, KE757/11-1.]; International Max Planck Research School for Astronomy and Astrophysics at the Universities of Bonn and Cologne (IMPRS Bonn/Cologne); Estonian Research Council [IUT26-2]; European Regional Development Fund [TK133]; Australian Research Council Future Fellowship [FT150100024]; NSF CAREER grant [AST-1149491]

COLD MILKY WAY H i GAS IN FILAMENTS

We investigate data from the Galactic Effelsberg--Bonn HI Survey (EBHIS), supplemented with data from the third release of the Galactic All Sky Survey (GASS III) observed at Parkes. We explore the all sky distribution of the local Galactic HI gas with

Using Negative Detections to Estimate Source-Finder Reliability

|v_{\rm LSR}| 20^\circ

The high-velocity cloud complex Galactic center negative as seen by EBHIS and GASS I. Cloud catalog and global properties

is described by a log-normal distribution, with a median Doppler temperature

2D–1D Wavelet Reconstruction as a Tool for Source Finding in Spectroscopic Imaging Surveys

T_{\rm D} = 223