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HI4PI: A new all-sky survey of neutral hydrogen

Using data from the Galactic All-Sky Survey (GASS) and the Effelsberg-Bonn HI Survey (EBHIS) we constructed a full 4-PI data set of the neutral atomic hydrogen in the Milky Way. Its main aim is to replace the Leiden/Argentine/Bonn Survey (LAB). HI4PI has much better angular resolution and sensitivity than LAB, and it features full angular sampling.

Data can be downloaded from CDS, the Strasbourg data center.

Our team

N. Ben Bekhti
L. Flöer
R. Keller
J. Kerp (PI, EBHIS)
D. Lenz
B. Winkel
J. Bailin
M. R. Calabretta
L. Dedes
H. A. Ford
B. K. Gibson
U. Haud
S. Janowiecki
P. M. W. Kalberla
F. J. Lockman
N. M. McClure-Griffiths (PI, GASS)
T. Murphy
H. Nakanishi
D. J. Pisano
L. Staveley-Smith

Survey properties

Area: 4π
Angular resolution: 16.2 arcmin (Nyquist-sampled)
Number of spectral channels: 933
Bandwidth: 10 MHz
Velocity range: -600..+600 km/s (-470..+470 km/s for southern hemisphere)
Channel separation: 1.29 km/s
Velocity resolution: 1.45 km/s
RMS: ~43 mK

Related publications

T. Westmeier, A new all-sky map of Galactic high-velocity clouds from the 21-cm HI4PI survey, MNRAS 474, 289, 2017

D. Lenz, B. S. Hensley, O. Doré, A New, Large-scale Map of Interstellar Reddening Derived from H I Emission, ApJ 846, 38, 2017

T. Röhser, J. Kerp, D. Lenz et al., An all-sky census of Galactic high-latitude molecular intermediate-velocity clouds, A&A 596, 94, 2016

HI4PI Collaboration et al. (corresponding authors: B. Winkel and P. Kalberla), HI4PI: A full-sky HI survey based on EBHIS and GASS, A&A 594, A116, 2016, press release

Public outreach material

The Effelsberg-Bonn HI Survey (EBHIS)

In autumn 2008 we started a 21-cm line survey with 100-m Effelsberg telescope to map the neutral atomic hydrogen (HI) on the northern hemisphere. Using a new L-band 7-Feed-Array receiver and state-of-the-art FPGA based digital fast Fourier transform spectrometers (FFTS) allowed us to observe both, the galactic and extragalactic sky, in parallel. The FFTS - superior in dynamic range and providing high-speed recording - offers the possibility to apply sophisticated radio frequency interferences (RFI) mitigation schemes.

Data can be downloaded from CDS, the Strasbourg data center.

Our team

Jürgen Kerp (PI)
Benjamin Winkel
Lars Flöer
Peter M. W. Kalberla
Nadya Ben Bekhti
Daniel Lenz

Survey properties

Area: 20600 deg² (Declination > -5 deg)
Angular resolution: 10.8 arcmin (Nyquist-sampled)
Number of spectral channels: 16,384
Bandwidth: 100 MHz
Redshift range: ~0.07
Channel separation: 1.29 km/s
Velocity resolution: 1.45 km/s
RMS: ~90 mK

Related publications

B. Winkel, J. Kerp, L. Flöer, et al., The Effelsberg-Bonn HI Survey: Milky Way gas. First data release , A&A 585, A41, 2016, press release

D. Lenz, et al., Far-infrared excess emission as a tracer of disk-halo interaction , A&A 573, 83, 2015

Planck collaboration, Planck 2013 results. XXX. Cosmic infrared background measurements and implications for star formation , A&A 571, 30, 2014

L. Flöer, B. Winkel, and J. Kerp, Source finding, parametrization and classification for the extragalactic Effelsberg-Bonn HI Survey , A&A 569, 101, 2014

T. Röhser, J. Kerp, B. Winkel et al., A dynamical transition from atomic to molecular intermediate-velocity clouds , A&A, 564, 71, 2014

A. K. Hernandez et al., A Low Metallicity Molecular Cloud In The Lower Galactic Halo , ApJ, 777, 19, 2013

B. Winkel, L. Flöer, A. Kraus, Efficient least-squares basket-weaving , A&A, 547, A119, 2012

B. Winkel, A. Kraus, U. Bach, Unbiased flux calibration methods for spectral-line radio observations , A&A, 540, A140, 2012

L. Flöer and B. Winkel, 2D-1D Wavelet Reconstruction As A Tool For Source Finding In Spectroscopic Imaging Surveys , PASA, 29, 244, 2012

B. Winkel, N. Ben Bekhti, V. Darmstädter et al., The high-velocity cloud complex Galactic center negative as seen by EBHIS and GASS. I. Cloud catalog and global properties , A&A (highlight), 533, 105, 2011

J. Kerp, B. Winkel, N. Ben Bekhti et al., The Effelsberg-Bonn HI Survey (EBHIS) , AN, 332, 637, 2011

L. Flöer, B. Winkel, J. Kerp, RFI mitigation for the Effelsberg-Bonn HI Survey (EBHIS) , Conference proceedings of "RFI2010 - RFI Mitigation Workshop", Groningen, March 2010

B. Winkel, P. Kalberla, J. Kerp et al., The Effelsberg-Bonn HI Survey: Data reduction , ApJS, 188, 488W, 2010

Single-dish spectroscopy: next-generation data reduction

In recent years radioastronomical receiving systems have seen huge improvements in terms of bandwidth and back-end processing capabilities. As an example, the new K-band receiver that is currently under test at the Effelsberg 100-m radio telescope provides 8-GHz of instantaneous bandwidth and, using stacked FPGA-based FFT spectrometers, a total of more than 1 million spectral channels per polarization. While such new devices offer great potential to the modern observatory facilities, they also demand completely new data reduction software. On the one hand, the sheer amount of data produced needs sophisticated programming techniques to make use of parallel/distributed computing. One the other hand, for an accurate calibration, it must be taken into account that quantities like system temperature, Tsys, the intensity, Tcal, of calibration normals (noise diodes), and receiver and antenna gains are not constant over the large recorded bandwidth.

In Winkel, Kraus, & Bach (2012, A&A 540, 140) we introduced methods to incorporate frequency dependence into the flux calibration scheme for the widely used position- and frequency-switching techniques. They are based on modeling the quantity Tsys / Tcal using the raw input data. Primary calibration uses astronomical sources (calibrators) to initially infer a value for Tcal. While this works completely fine for many cases, we realized, that bad weather conditions, which cause changes of Tsys on rather short time scales, make the resulting Tcal value subject to unacceptably high scatter.

We are developing new procedures to improve on this shortcoming. Applying different observing schemes, like cross-scanning (in spectroscopy mode) allows to keep track of total-power changes and leads to a greatly improved determination of Tcal from primary calibrators. Compared to position switching, this is much less efficient with respect to observing time. However, it turns out that the target sources can still be observed using position switching using the calibration scheme proposed in Winkel, Kraus, & Bach. Building up a database of high-quality Tcal spectra as averaged from many different measurements and observing sessions would be beneficial.