Since autumn 2008 an L-band 7-Feed-Array is operated for astronomical science at the 100-m radio telescope at Effelsberg. This receiver is used to perform an unbiased, fully sampled HI survey of the whole northern hemisphere observing both the galactic and extragalactic sky in parallel - the Effelsberg-Bonn HI survey (EBHIS). We present first results based on the Milky Way data. Up to now two larger coherent regions were mapped each covering about 2000 square degrees. One of these fields covers the northern part of the high-velocity cloud complex GCN. With the better angular resolution of the EBHIS we resolve the previously detected clouds into isolated compact clumps and find a linewidth-radial velocity relation giving hints on an interaction of accreting material with the Milky Way halo.
The Effelsberg-Bonn HI Survey (EBHIS) covers the whole sky north of Dec(2000) = -5 deg. on a fully sampled angular grid. Using state-of-the-art FPGA-spectrometers we perform a Milky Way and an extragalactic HI survey in parallel. Moreover, the high dynamic range and short dump time of the HI spectra allow to overcome the vast majority of all radio-frequency-interference (RFI) events. The Milky Way data will be corrected for the stray-radiation bias which warrants a main-beam efficiency of 99%. Towards the whole survey area we exceed the sensitivity limit of HIPASS, while towards the Sloan-Digi…
The Effelsberg-Bonn HI survey (EBHIS) comprises an all-sky survey north of Dec = -5 degrees 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 HI 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 800…
Since autumn 2008 a new L-band 7-Feed-Array receiver is used for an HI 21-cm line survey performed with the 100-m Effelsberg telescope. The survey will cover the whole northern hemisphere comprising both, the galactic and extragalactic sky in parallel. Using state-of-the-art FPGA based digital Fast Fourier Transform spectrometers, superior in dynamic range and temporal resolution, allows to apply sophisticated radio frequency interferences (RFI) mitigation schemes to the survey data. The EBHIS data reduction software includes the RFI mitigation, gain-curve correction, intensity calibration, st…
The Effelsberg-Bonn HI 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 HI line emission from the Milky Way and the Local Volume. We aim to substitute the northern-hemisphere part of the Leiden/Argentine/Bonn Milky Way HI survey (LAB) with this first EBHIS data release, which presents the HI gas in the Milky Way regime. 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-…
We aim at analysing systematically the distribution and physical properties of neutral and mildly ionised gas in the Milky Way halo, based on a large absorption-selected data set. Multi-wavelength studies were performed combining optical absorption line data of CaII and NaI with follow-up HI 21-cm emission line observations along 408 sight lines towards low- and high-redshift QSOs. We made use of archival optical spectra obtained with UVES/VLT. HI data were extracted from the Effelsberg-Bonn HI survey and the Galactic All-Sky survey. For selected sight lines we obtained deeper follow-up observ…
Imaging of galaxies to study the interstellar medium on scales of a few pc is difficult. However, for the Milky Way galaxy two major Galactic all sky HI 21-cm line surveys will become available soon with unprecedented quality. We present the Galactic All Sky Survey (GASS) obtained with the Parkes 64-m telescope for the southern hemisphere with a resolution of 15 arcmin. The Effelsberg Bonn HI Survey (EBHIS) will complete the survey for the northern sky with 9 arcmin resolution and we describe this project. A combined All Sky Survey will become available in 2010/2011, early enough to serve as s…
We analyse the all-sky Leiden/Argentina/Bonn HI survey, where we identify shells belonging to the Milky Way. We used an identification method based on the search of continuous regions of a low brightness temperature that are compatible with given properties of HI shells. We found 333 shells in the whole Galaxy. The size distribution of shells in the outer Galaxy is fitted by a power law with the coefficient of 2.6 corresponding to the index 1.8 in the distribution of energy sources. Their surface density decreases exponentially with a scale length of 2.8 kpc. The surface density of shells with…
A global view on star formation: The GLOSTAR Galactic plane survey XII. Effelsberg's continuum view and data release
Max-Planck-Institut für Radioastronomie（马克斯·普朗克射电天文研究所）；Purple Mountain Observatory, Chinese Academy of Sciences（中国科学院紫金山天文台）；National Radio Astronomy Observatory（国家射电天文台）；Center for Astrophysics | Harvard & Smithsonian（哈佛史密森尼天体物理中心）
Using Milky Way data of the new Effelsberg-Bonn HI Survey (EBHIS) and the Galactic All-Sky Survey (GASS), we present a revised picture of the high-velocity cloud (HVC) complex Galactic Center Negative (GCN). Owing to the higher angular resolution of these surveys compared to previous studies (e.g., the Leiden Dwingeloo Survey), we resolve Complex GCN into lots of individual tiny clumps, that mostly have relatively broad line widths of more than 15 km/s. We do not detect a diffuse extended counterpart, which is unusual for an HVC complex. In total 243 clumps were identified and parameterized wh…
We present deep HI observations of three compact high-velocity clouds (CHVCs). The main goal is to study their diffuse warm gas and compact cold cores. We use both low- and high-resolution data obtained with the 100 m Effelsberg telescope and the Westerbork Synthesis Radio Telescope (WSRT). The combination is essential in order to study the morphological properties of the clouds since the single-dish telescope lacks a sufficient angular resolution while the interferometer misses a large portion of the diffuse gas. Here single-dish and interferometer data are combined in the image domain with a…
Aims: we studied the global distribution and kinematics of the extra-planar neutral gas in the Milky Way. Methods: we built 3D models for a series of Galactic HI layers, projected them for an inside view, and compared them with the Leiden-Argentina-Bonn 21-cm observations. Results: we show that the Milky Way disk is surrounded by an extended halo of neutral gas with a vertical scale-height of 1.6[+0.6/-0.4] kpc and an HI mass of 3.2[+1.0/-0.9]x10^8 solar masses, which is 5-10% of the total Galactic HI. This HI halo rotates more slowly than the disk with a vertical velocity gradient of -15[+/-4…
Measurement of the Galactic neutral atomic hydrogen (HI) column density, NHI, and brightness temperatures, Tb, is of high scientific value for a broad range of astrophysical disciplines. In the past two decades, one of the most-used legacy HI datasets has been the Leiden/Argentine/Bonn Survey (LAB). We release the HI 4$π$ survey (HI4PI), an all-sky database of Galactic HI, which supersedes the LAB survey. The HI4PI survey is based on data from the recently completed first coverage of the Effelsberg-Bonn HI Survey (EBHIS) and from the third revision of the Galactic All-Sky Survey (GASS). EBHIS …
We present a new face-on map of dense neutral atomic hydrogen (HI) gas in the outer Galaxy. Our map has been produced from the Leiden/Argentine/Bonn (LAB) HI 21-cm line all-sky survey by finding intensity maxima along every line of sight and then by projecting them on the Galactic plane. The resulting face-on map strikingly reveals the complex spiral structure beyond the solar circle, which is characterized by a mixture of distinct long arcs of HI concentrations and numerous 'interarm' features. The comparison with more conventional spiral tracers confirms the nature of those long arc structur…
There is mounting evidence for an extra-planar gas layer around the Milky Way disk, similar to the anomalous HI gas detected in a few other galaxies. As much as 10% of the gas may be in this phase. We analyze HI clouds located in the disk-halo interface outside the solar circle to probe the properties of the extra-planar HI gas, which is following Galactic rotation. We use the Leiden/Argentine/Bonn (LAB) 21-cm line survey to search for HI clouds which take part in the rotation of the Galactic plane, but are located above the disk layer. Selected regions are mapped with the Effelsberg 100-m tel…
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 $|v_{\rm LSR}| < 25 $ kms$^{-1}$ on angular scales of 11' to 16'. Unsharp masking (USM) is applied to extract small scale features. We find cold filaments that are aligned with polarized dust emission and conclude that the cold neutral medium (CNM) is mostly organized in sheets that are, because of projection effects, observed as filaments. These…
The question, whether the stellar populations in the Milky Way take part in flaring of the scale heights as observed for the HI gas is a matter of debate. Standard mass models for the Milky Way assume a constant scale height for each of the different stellar distributions. However, there is mounting evidence that at least some of the stellar distributions reach at large galactocentric distances high altitudes that are incompatible with a constant scale height. We discuss recent observational evidence for stellar flaring and compare it with HI data from the Leiden/Argentine/Bonn (LAB) survey. W…
One of the most robust observations of the stellar initial mass function (IMF) is its near-universality in the Milky Way and neighboring galaxies. But recent observations of early-type galaxies can be interpreted to imply a bottom-heavy IMF, while others of ultra-faint dwarfs could imply a top-heavy IMF. This would impose powerful constraints on star formation models. We explore what sort of cloud-scale IMF models could possibly satisfy these constraints. We utilize simulated galaxies which reproduce (broadly) the observed galaxy properties, while they also provide the detailed star formation …
The subsequent coalescence of low--mass halos over cosmic time is thought to be the major formation channel of massive spiral galaxies like the Milky Way and the Andromeda Galaxy (M31). The gaseous halo of a massive galaxy is considered to be the reservoir of baryonic matter persistently fueling the star formation in the disk. Because of its proximity, M31 is the ideal object for studying the structure of the halo gas in great detail. Using the latest neutral atomic hydrogen (HI) data of the Effelsberg-Bonn HI Survey (EBHIS) allows comprising a comprehensive inventory of gas associated with M3…
To explore the origin of high-velocity gas in the direction of the Large Magellanic Cloud (LMC) we analyze absorption lines in the ultraviolet spectrum of a Galactic halo star that is located in front of the LMC at d=9.2 kpc distance. We study the velocity-component structure of low and intermediate metal ions in the spectrum of RXJ0439.8-6809, as obtained with the Cosmic Origins Spectrograph (COS) onboard HST, and measure equivalent widths and column densities for these ions. We supplement our COS data with a Far-Ultraviolet Spectroscopic Explorer spectrum of the nearby LMC star Sk-69 59 and …
The HI halo clouds of the Milky Way, and in particular the intermediate-velocity clouds (IVCs), are thought to be connected to Galactic fountain processes. Observations of fountain clouds are important for understanding the role of matter recycling and accretion onto the Galactic disk and subsequent star formation. Here, we quantify the amount of molecular gas in the Galactic halo. We focus on the rare class of molecular IVCs (MIVCs) and search for new objects. The HI-FIR correlation was studied across the entire northern and southern Galactic hemispheres at Galactic latitudes $|b|>20^\circ$ t…
Because isolated high-velocity clouds (HVCs) are found at great distances from the Galactic radiation field and because they have subsolar metallicities, there have been no detections of dust in these structures. A key problem in this search is the removal of foreground dust emission. Using the Effelsberg-Bonn HI Survey and the Planck far-infrared data, we investigate a bright, cold, and clumpy HVC. This cloud apparently undergoes an interaction with the ambient medium and thus has great potential to form dust. To remove the local foreground dust emission we used a regularised, generalised lin…
The primary source of systematic uncertainty in the quest for the B-mode polarization of the Cosmic Microwave Background (CMB) introduced by primordial gravitational waves is polarized thermal emission from Galactic dust. Therefore, accurate characterization and separation of the polarized thermal dust emission is an essential step in distinguishing such a faint CMB B-mode signal. We provide a modelling framework to simulate polarized thermal dust emission based on the model described in Ghosh et al. (2017), making use of both the Planck dust and Effelsberg-Bonn HI surveys over the northern Ga…
A 5$^{\circ}$ $\times$ 7$^{\circ}$ sky area containing two large radio structures of G203.1+6.6 and G206.7+5.9 with a size of about 2.5$^{\circ}$ and 3.5$^{\circ}$ respectively is scanned by using the L-band 19-beam receiver of the Five-hundred-meter Aperture Spherical radio Telescope (FAST). The FAST L-band receiver covers a frequency range of 1.0-1.5 GHz. Commissioning of the receiving system, including the measurements of the half-power beam width, gain, and main-beam efficiency is made by observing the calibrators. The multi-channel spectroscopy backend mounted to the receiver allows an in…
We discuss physical conditions in Galactic neutral hydrogen based on deep, high velocity resolution interferometric HI 21 cm absorption spectroscopy towards 33 compact extra-galactic radio sources. The HI 21 cm optical depth spectra have root-mean-square noise values \lesssim 10^{-3} per 1 km/s velocity channel, i.e., sufficiently sensitive to detect HI 21 cm absorption by the warm neutral medium (WNM). Comparing these spectra with HI 21 cm emission spectra from the Leiden-Argentine-Bonn (LAB) survey, we show that some of the absorption detected on most sightlines must arise in gas with temper…
We present a detailed analysis comparing the velocity fields in molecular clouds and the atomic gas that surrounds them in order to address the origin of the gradients. To that end, we present first-moment intensity-weighted velocity maps of the molecular clouds and surrounding atomic gas. The maps are made from high-resolution 13CO observations and 21-cm observations from the Leiden/Argentine/Bonn Galactic HI Survey. We find that (i) the atomic gas associated with each molecular cloud has a substantial velocity gradient---ranging within 0.02 to 0.07 km/s/pc---whether or not the molecular clou…
Towards the high galactic latitude sky, the far-infrared (FIR) intensity is tightly correlated to the total hydrogen column density which is made up of atomic (HI) and molecular hydrogen (H$_{2})$. Above a certain column density threshold, atomic hydrogen turns molecular. We analyse gas and dust properties of intermediate-velocity clouds (IVCs) in the lower galactic halo to explore their transition from the atomic to the molecular phase. Driven by observations, we investigate the physical processes that transform a purely atomic IVC into a molecular one. Data from the Effelsberg-Bonn HI-Survey…
Given the current and past star-formation in the Milky Way in combination with the limited gas supply, the re-fuelling of the reservoir of cool gas is an important aspect of Galactic astrophysics. The infall of \ion{H}{i} halo clouds can, among other mechanisms, contribute to solving this problem. We study the intermediate-velocity cloud IVC135+54 and its spatially associated high-velocity counterpart to look for signs of a past or ongoing interaction. Using the Effelsberg-Bonn \ion{H}{i} Survey data, we investigated the interplay of gas at different velocities. In combination with far-infrare…
One of the key observations regarding the stellar initial mass function (IMF) is its near-universality in the Milky Way (MW), which provides a powerful way to constrain different star formation models that predict the IMF. However, those models are almost universally "cloud-scale" or smaller -- they take as input or simulate single molecular clouds (GMCs), clumps, or cores, and predict the resulting IMF as a function of the cloud properties. Without a model for the progenitor properties of all clouds which formed the stars at different locations in the MW (including ancient stellar populations…
We have carried out deep, high velocity resolution, interferometric Galactic HI 21 cm absorption spectroscopy towards 32 compact extra-galactic radio sources with the Giant Metrewave Radio Telescope (GMRT) and the Westerbork Synthesis Radio Telescope (WSRT). The optical depth spectra for most sources have root mean square noise values \lesssim 10^{-3} per 1 km/s velocity channel and are thus sufficiently sensitive to detect absorption by warm neutral hydrogen with HI column densities N_HI \gtrsim 10^{20} cm^{-2}, spin temperatures T_s \leq 5000 K, and line widths equal to the thermal width (20…
Surveys of the Milky Way at various wavelengths have changed our view of star formation in our Galaxy considerably in recent years. In this paper we give an overview of the GLOSTAR survey, a new survey covering large parts (145 square degrees) of the northern Galactic plane using the Karl G. Jansky Very Large Array (JVLA) in the frequency range 4-8 GHz and the Effelsberg 100-m telescope. This provides for the first time a radio survey covering all angular scales down to 1.5 arcsecond, similar to complementary near-IR and mid-IR galactic plane surveys. We outline the main goals of the survey an…
