Stray–radiation correction as applied to the 
Leiden/Dwingeloo survey of Hi  in the Galaxy

Hartmann, D.; Kalberla, P. M. W.; Burton, W. B.; Mebold, U.

doi:10.1051/aas:1996233

Cited by 39 publications

(48 citation statements)

References 9 publications

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“…A related possibility is that N(HI) is actually lower than measured because the sidelobe contamination has been underestimated, an issue that is worst for the lowest columns (Hartmann et al, 1996;Murphy et al, 1996). With a mean column of 6-7×10 19 cm −2 , a spectral model does not require a soft excess component, but this value lies about 3σ below current measurement for the HI column in this direction.…”

Section: The Coma Clustermentioning

confidence: 85%

The Search for the Missing Baryons at Low Redshift

Bregman

2007

Annu. Rev. Astron. Astrophys.

351

345

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The baryon content of the universe is known from Big Bang nucleosynthesis and cosmic microwave background considerations, yet at low redshift, only about one-tenth of these baryons lie in galaxies or the hot gas seen in galaxy clusters and groups. Models posit that these "missing baryons" are in gaseous form in overdense filaments that connect the much denser virialized groups and clusters. About 30% of the baryons are cool (<10 5 K) and are detected in Lyα absorption studies, but about half the mass is predicted to lie in the 10 5 -10 7 K regime, where detection is very challenging. Material has been detected in the 2-5×10 5 K range through OVI absorption studies, indicating that this gas accounts for about 7% of the baryons. Hotter gas (0.5-2×106 K) has been detected at zero redshift by OVII and OVIII Kα absorption at X-ray energies. However, this appears to be correlated with the Galactic soft X-ray background, so it is probably Galactic Halo gas, rather than a cosmologically significant Local Group medium. There are no compelling detections of the intergalactic hot gas (0.5-10×10 6 K) either in absorption or in emission. Early claims of intergalactic X-ray absorption lines have not been confirmed, but this is consistent with theoretical models, which predited equivalent widths below current detection thresholds. There have been many investigations for emission from this gas, within and beyond the virial radius of clusters, but the positive signals for this soft emission are largely artifacts of background subtraction and field-flattening. We discuss the various techniques that can be used to detect the missing baryons and show that it should be detectable with moderate improvements in sensitivity.

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Section: The Coma Clustermentioning

confidence: 85%

The Search for the Missing Baryons at Low Redshift

Bregman

2007

Annu. Rev. Astron. Astrophys.

351

345

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“…More commonly, RFI produces extremely narrow spike signals, or a characteristic sin(x)/x ringing, and can be rather easily recognised by these and other properties as not being of an interstellar origin. But Hartmann (1994) and Hartmann & Burton (1997) show examples of RFI signals detected in the LDS which mimic the properties of spectral features of astronomical interest. In these examples, the interference was of short temporal duration, thereby disabling the common diagnostic tool of being on the look-out for features remaining at a constant frequency, or with an unusual telltale drift in frequency.…”

Section: Observationsmentioning

confidence: 99%

“…The nominal brightness-temperature sensitivity of the LDS is 0.07 K, although this value varies for individual spectra. Hartmann et al (1996) describe the corrections applied to the LDS material in order to remove contamination by stray radiation.…”

Section: Observationsmentioning

confidence: 99%

An automated search for compact high–velocity clouds in the Leiden/Dwingeloo Survey

Heij

Braun²,

Burton

2002

A&A

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Abstract.We describe an automated search through the Leiden/Dwingeloo H  Survey (LDS) for high-velocity clouds north of δ = −28• . From the general catalog we extract a sample of relatively small (less than about 8• ) and isolated high-velocity clouds, CHVCs: anomalous-velocity H  clouds which are sharply bounded in angular extent with no kinematic or spatial connection to other H  features down to a limiting column density of 1.5 × 10 18 cm −2 . This column density is an order of magnitude lower than the critical H  column density, ∼2 × 10 19 cm −2 , (e.g. Maloney 1993) where the ionized fraction is thought to increase dramatically due to the extragalactic radiation field. As such, these objects are likely to provide their own shielding to ionizing radiation. Their small angular size, of less than about 1• FWHM, might then imply substantial distances, since the partially ionized H  skin in a power-law ionizing photon field has a typical exponential scale-length of 1 kpc (e.g. Corbelli & Salpeter 1993). The automated search algorithm has been applied to the HIPASS and to the Leiden/Dwingeloo data sets. The results from the LDS are described here; Putman et al. (2002) describe application of this algorithm to the HIPASS material. We identify 67 CHVCs in the LDS which satisfy stringent requirements on isolation, and an additional 49 objects which satisfy somewhat less stringent requirements. Independent confirmation is available for all of these objects, either from earlier data in the literature or from new observations made with the Westerbork Synthesis Radio Telescope and reported here. The catalog includes 54 of the 65 CHVCs listed by on the basis of a visual search of the LDS data.

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“…The point is that a large-scale H I structure at nearly zero radial velocities that is commonly called ridges is known to exist at high latitudes. Fejes and Wesselius (1973) gave parameters for 13 such ridges; most of them (11) are almost perpendicular to the Galactic plane, and some of them reach latitudes of ±40 • . Note also that, in contrast to the background gas, many of them have positive radial velocities, and five ridges fall within the region of our survey precisely where the peaks at positive velocities are observed.…”

Section: Resultsmentioning

confidence: 99%

“…An example of a profile that clearly shows the first and the third components is given in our previous paper . Eliminating the stray diffuse background is a serious problem, and special methods were developed for its solution (see, e.g., Heiles et al 1981; McGee and Newton 1986; Hartmann et al 1996). However, as we showed previously, this radiation may be ignored in the formulated problem, because the pattern of the diffuse background of the antenna cannot give smallscale features in the intensity distribution.…”

Section: Instrumentation and Techniquesmentioning

confidence: 99%

The structure of Galactic gas at high latitudes: The southern polar cap

2004

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Abstract-We analyze the angular structure of the 21-cm interstellar neutral hydrogen emission at six and seven declinations in the northern (published previously) and southern polar caps of the Galaxy (Galactic latitudes from −40• to −90 • ), respectively, with an extent of 90 • in right ascension. The RATAN-600 radio telescope has a beam width averaged over these regions of 2 .0 × 30 . One-dimensional power spectra for the angular distribution of interstellar neutral hydrogen emission were computed in each 6.3-km s −1 -wide spectral channel by using the standard fast Fourier transform (FFT) code and were smoothed over 1 h in right ascension. The Galactic latitude dependence of the mean parameters for the sky distribution of H I line emission at high latitudes was found to correspond to the distribution of gas in the form of a flat layer only in the northern region, while in the southern cap, the gas distribution is much less regular. In addition, the mean H I radial velocities are negative everywhere (−3.7 ± 3.0 km s −1 in the north and −6.0 ± 2.4 km sin the south). The power spectra of the angular fluctuations in the range of angular periods from 10 to 6• appear as power laws. However, the spectral indices change greatly over the sky: from −3 to −1.2; on average, as the Galactic latitude increases and the H I column density decreases, the fluctuation spectrum of the interstellar gas emission becomes flatter. In the northern polar region, this behavior is much more pronounced, which probably stems from the fact that the gas column density in the south is generally a factor of 2 or 3 higher than that in the north. Therefore, the spectra are, on average, also steeper in the south, but the dependence on Galactic latitude is weaker. Using simulations, we show that the observed power-law spectrum of the H I emission distribution can be obtained in terms of not only a turbulent, but also a cloud model of interstellar gas if we use our previous spectra of the diameters and masses of H I clouds. c 2004 MAIK "Nauka/Interperiodica".

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Stray–radiation correction as applied to the Leiden/Dwingeloo survey of Hi in the Galaxy

Cited by 39 publications

References 9 publications

The Search for the Missing Baryons at Low Redshift

The Search for the Missing Baryons at Low Redshift

An automated search for compact high–velocity clouds in the Leiden/Dwingeloo Survey

The structure of Galactic gas at high latitudes: The southern polar cap

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