P. Katgert’s research while affiliated with Leiden University and other places

What is this page?


This page lists works of an author who doesn't have a ResearchGate profile or hasn't added the works to their profile yet. It is automatically generated from public (personal) data to further our legitimate goal of comprehensive and accurate scientific recordkeeping. If you are this author and want this page removed, please let us know.

Publications (113)


A WSRT search for HI at z=3.35
  • Article

August 2017

·

2 Reads

Symposium - International Astronomical Union

·

M.H. Wieringa

·

P. Katgert

·

R. Sancisi

The origin and evolution of the large-scale structures in the universe (from galaxies up to superclusters) forms one of the outstanding problems of present-day cosmology. Several attempts have been made to observe the precursors of the structures observed today, at epochs as early as possible. Results of a search for redshifted HI associated with “protoclusters” or “pancakes” were first reported by Davies et al. (1978). They used the Jodrell Bank Mark 1A-telescope at frequencies of 328 and 240 MHz (z=3.3 and 4.9 respectively). More recently Bebbington (1986) used the Cambridge 6C synthesis radio telescope for a search at 151 MHz (z=8.4). Both experiments gave negative results and raised the question whether the observations were matched to the “expected” properties of the structures that they looked for.



Fig. 2. Frame of the RM-synthesis cube at Faraday depth φ = −1 rad m −2 displaying the extended polarized emission. Grating rings can be seen around the bright point sources at (α, δ) J2000 ≈ (02 h 38 m , 59 • .1) (close to the edge of the image), and (α, δ) J2000 ≈ (03 h 06 m , 62 • .5). The drawn boxes are chosen to infer the noise behaviour (box 1) and derive the cross-correlation profile (box 2), see text.
Fig. 3. Example of Faraday dispersion spectrum with emission at a single Faraday depth along the line of sight, averaged over a beam-sized box region. The noise level is indicated by 1σ error bars.
Table 3 . Parameters of nearby pulsars located in the direction of the FAN region.
Fig. 4. Distribution of polarized intensity as a function of Faraday depth, above a threshold of 5 mJy. At |φ| ≥ 40 rad m −2 the residual signal from side lobes of Cyg A and Cas A are visible, while the Galactic emission occurs around −1 rad m −2 and has an asymmetric profile.
Fig. 5. Noise behaviour in the PI map derived from a region denoted by box 1 in figure 2 as a function of Faraday depth under the assumption of Rayleigh distribution statistics. The expected mean and variance values of the noise are indicated by the dashed and solid lines, while the measured values indicated by circles and stars refer to the noise mean and variance, respectively.

+7

Rotation measure synthesis at the 2 m wavelength of the FAN region: Unveiling screens and bubbles
  • Article
  • Full-text available

October 2012

·

68 Reads

·

41 Citations

Astronomy and Astrophysics

Rotation Measure synthesis (RM synthesis) of the Westerbork Synthesis Radio Telescope (WSRT) observations at 2 m wavelength of the FAN region at l=137deg, b=+7deg shows the morphology of structures in the ionized interstellar medium. We interpret the diffuse polarized synchrotron emission in terms of coherent structures in the interstellar medium and the properties of the interstellar magnetic field. For the first time, cross-correlation is applied to identify and characterize polarized structures in Faraday depth space. Complementary information about the medium are derived from Hα\alpha emission, properties of nearby pulsars, and optical polarized starlight measurements. Three morphological patterns are recognized, showing structures on scales from degrees down to the beam size. At low Faraday depth values, a low gradient across the imaged field is detected, almost aligned with the Galactic plane. Power spectra of polarized structures in Faraday depth space provide evidence of turbulence. A sign reversal in Faraday depth space indicates a reversal of the magnetic field component along the line of sight, from towards the observer and nearby to away from the observer at larger distances. The distance to the nearby, extended component is estimated to be lesser than 100 pc, which suggests that this structure corresponds to the Local Bubble wall. For the circular component, various physical interpretations are discussed. The most likely explanation is that the circular component seems to be the presence of a nearby (about 200 pc away) relic Stromgren sphere, associated with an old unidentified white dwarf star and expanding in a low-density environment.

Download


The large-scale magnetic field in the fourth Galactic quadrant

April 2010

·

29 Reads

·

41 Citations

Astronomy and Astrophysics

Aims: We have re-examined the published rotation measures (RMs) of extragalactic point sources and pulsars with |b| < 3° to study the magnetic field in the fourth Galactic quadrant. Methods: We reduced the influence of structure in electron density as much as possible by excluding objects for which Hα-data indicate large fluctuations in ne somewhere along the line of sight. We also excluded objects for which the RM may have been significantly “corrupted” by an intervening supernova remnant. We modeled RM(l), the longitude dependence of RM of the unaffected extragalactic sources and pulsars. We assumed several geometries for the large-scale field. All but one of those are based on logarithmic spiral arms (with various pitch angles and widths), while one has circular symmetry. We also made different assumptions about the large-scale ne-distribution. Results: The data suggest the following generic behaviour of the large-scale field in the 4th Galactic quadrant. The field is most likely organized along logarithmic spiral arms and shows two significant reversals: from the Norma arm (CCW field) to the Norma-Crux interarm region (CW field), and from the Norma-Crux interarm region to the Crux arm (CCW field). The present data do not constrain the field in and beyond the Crux-Carina interarm region. Although the models give a good description of the global character of RM(l), individual RM-estimates deviate by typically 15 times their measurement errors. We argue that these large deviations are most likely due to the “small-scale” field that dominates on scales of up to several hundred pc. Conclusions: The picture that emerges is thus of a field that has significant structure on smaller scales, but for which the average values in arms and interarm regions are nevertheless well-defined. In addition, this smaller-amplitude large-scale field appears to reverse at each arm-interarm boundary that we can study with the present data. We briefly discuss the link between these results and theoretical predictions.


WSRT Faraday tomography of the Galactic ISM at lambda ~ 0.86 m. I. The GEMINI data set at (l, b) = (181°, 20°)

February 2009

·

17 Reads

·

62 Citations

Astronomy and Astrophysics

Aims: We investigate the properties of the Galactic ISM by applying Faraday tomography to a radio polarization data set in the direction of the Galactic anti-centre. Methods: We address the problem of missing large-scale structure in our data, and show that this does not play an important role for the results we present. Results: The main peak of the Faraday depth spectra in our data set is not measurably resolved for about 8% of the lines of sight. An unresolved peak indicates a separation between the regions with Faraday rotation and synchrotron emission. However, cosmic rays pervade the ISM, and synchrotron emission would therefore also be produced where there is Faraday rotation. We suggest that the orientation of the magnetic field can separate the two effects. By modelling the thermal electron contribution to the Faraday depth, we map the strength of the magnetic field component along the line of sight. Polarized point sources in our data set have rotation measures that are comparable to the Faraday depths of the diffuse emission in our data. Our Faraday depth maps show narrow canals of low polarized intensity. We conclude that depolarization over the telescope beam produces at least some of these canals. Finally, we investigate the properties of one conspicuous region in this data set and argue that it is created by a decrease in line-of-sight depolarization compared to its surroundings.


WSRT Faraday tomography of the Galactic ISM at λ ˜ 0.86 m. First results for a field at (l, b)~=~(181°,20°)

July 2007

·

19 Reads

·

27 Citations

Astronomy and Astrophysics

Aims:We investigate the distribution and properties of Faraday rotating and synchrotron emitting regions in the Galactic ISM in the direction of the Galactic anti-centre. Methods: We apply Faraday tomography to a radio polarization dataset that we obtained with the WSRT. We developed a new method to calculate a linear fit to periodic data, which we use to determine rotation measures from our polarization angle data. From simulations of a Faraday screen + noise we could determine how compatible the data are with Faraday screens. Results: An unexpectedly large fraction of 14% of the lines-of-sight in our dataset show an unresolved main component in the Faraday depth spectrum. For lines-of-sight with a single unresolved component we demonstrate that a Faraday screen in front of a synchrotron emitting region that contains a turbulent magnetic field component can explain the data.


The WENSS & Dwingeloo surveys and the Galactic magnetic field

November 2006

·

18 Reads

·

18 Citations

Astronomy and Astrophysics

In this paper we use the diffuse Galactic synchrotron emission to study the properties of the Galactic magnetic field. We combined data from the low-frequency WENSS survey with single-dish observations carried out by Brouw and Spoelstra to (partially) fill in the central gap in the (u,v) plane that is missing from the interferometer data. The small bandwidth of the WENSS data meant that we could not determine rotation measures (RM) directly. Instead we interpreted the polarization angle gradients that we derived as gradients in RM, and to do this we found a new way to efficiently and reliably fit linear gradients to periodic data. RM are available for the single-dish observations, and we found that we have to rescale these single-dish RM to match the RM gradients that we derive from the combined WENSS/single-dish dataset with the single-dish only RM gradients. We tentatively show that the difference in beamsize between the datasets can be responsible for this. We interpret the scaled-up RM we find in terms of a simple toy model, and by combining our results with those by Haverkorn et al. (2004) we reconstruct the full 3D magnetic field vector along a number of lines-of-sight. For these lines-of-sight we derive the properties of the magnetic field component perpendicular to the Galactic plane.


Radio polarization and RM structure at high Galactic latitudes

June 2006

·

13 Reads

·

21 Citations

Astronomische Nachrichten

We present WSRT observations at low frequencies (315–388 MHz) of the diffuse polarized emission in an area of 6° × 6° at high Galactic latitude. Polarized emission is found to be ubiquitous with typical levels of about 3–5 K brightness temperature with a generally mottled structure. The Rotation Measure (RM) of the emission varies between values of –5 to +20 rad m–2. Most of the polarized emission appears Faraday thin with a single unresolved valued for the RM. The data suggest both inhomogeneous as well as dissimilar distribution functions of the synchrotron emitting and Faraday rotating media along the line of sight. The systematic patterns in the RM at this high Galactic latitude of +71° also provide evidence for significant variations in the vertical component of the local Galactic magnetic field at a level of 1 μ Gauss. The potential for Galactic polarimetry at even lower frequencies using LOFAR and SKA is briefly discussed. (© 2006 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim)


ENACS. VIII. Galaxies classification (Thomas+, 2006)

November 2005

·

6 Reads

This table gives the morphological, spectral and adopted classifications of 4879 galaxies in the ESO Nearby Cluster Survey (or ENACS); see 1996, Cat. and 1998, Cat. (with link to the original ENACS catalogue). All galaxies have at least a morphological or a spectral type; of the adopted types 2102 are based on morphological types, 2446 on spectral types and 331 on a combination of the two. (1 data file).


Citations (40)


... Verschuur (1969) associated it with the star HD 20336 (distance 246 ± 20 pc; Gaia Collaboration et al. 2023), suggesting that the B2(e) star had tunneled its way through a cloud of neutral hydrogen, disrupting it and ionizing a portion of the hydrogen gas. Haverkorn et al. (2003) detected this polarized circular object at 350 MHz, but considered HD 20336 an unlikely progenitor for the feature on account of the star's high proper motion of 18 mas yr −1 being too large to maintain a circular Strömgren sphere. Instead, they suggest that the structure would be elongated in the direction opposite to the motion of the star. ...

Reference:

Faraday Tomography with CHIME: The “Tadpole” Feature G137+7
Multi-frequency polarimetry of the Galactic radio background around 350�MHz
  • Citing Article
  • June 2003

Astronomy and Astrophysics

... However, linearly polarized intensity P and polarization angle ϕ show abundant small-scale structure. Other fields observed with the WSRT at a single frequency around 350 MHz also show small-scale structure in polarized intensity and polarization angle, but of very different topologies ( [6]). ...

Small-scale structure in the diffuse polarized radio background: WSRT observations at lambda80-90 CM
  • Citing Article
  • January 1999

... Utilizing polarization data over a wide range of wavelengths allows the creation of a (complex) Faraday depth cube of F ℓ b , , f( ) for Galactic coordinates (ℓ, b). The Faraday depth resolution, measured as the FWHM of the main lobe of R R f f = ( ) |˜( )|, can be approximated as (Schnitzeler et al. 2009) ...

WSRT Faraday tomography of the Galactic ISM at lambda ~ 0.86 m. I. The GEMINI data set at (l, b) = (181°, 20°)
  • Citing Article
  • February 2009

Astronomy and Astrophysics

... Multiwavelength observations of galaxy clusters provide a wealth of information about the physics of the intracluster medium (ICM) and its relationship with cluster galaxies. The optical and X-ray bands have historically been used to identify merger activity via optical substructure (Carter & Metcalfe 1980;Geller & Beers 1982;Rhee & Katgert 1987;Dressler & Shectman 1988;Rhee, van Haarlem & Katgert 1991;Wen & Han 2013) and morphological parameters determined from X-ray images (Mohr, Fabricant & Geller 1993;Jeltema et al. 2005;O'Hara et al. 2006;Santos et al. 2008). In the last decade, a link has been found between a cluster's merger status and the presence of large-scale diffuse synchrotron emission (see Brunetti & Jones 2014, and references therein). ...

A study of the elongation of Abell clusters. I - A sample of 37 clusters studied earlier by Binggeli and Struble and Peebles
  • Citing Article
  • August 1987

Astronomy and Astrophysics

... only 0.001% size change per °F). Van Haarlem et al. (1992) have also shown that film copy material on a similar substrate can achieve essentially the same astrometric fidelity as original glass plates. However, unlike copy film, original film exposures are subjected to deformations at the UKST's 3 m radius focal surface and changes in humidity and temperature during exposure. ...

High-fidelity copying of large-area astronomical plates - Principles and some practical results
  • Citing Article
  • February 1992

Monthly Notices of the Royal Astronomical Society

... As mentioned above, the shape of the counts demonstrates that these objects undergo a strong cosmological evolution. But when radio surveys reached sub-mJy flux density levels (Windhorst et al., 1984;Condon & Mitchell, 1984), the Euclidean normalized counts showed a flattening or an upturn, indicating the emergence of a new population (for updated counts at 1.4 GHz see Padovani, 2016). Windhorst et al. (1985), based on optical identifications available for less than half of the sample, suggested that "for 1 < S 1.4 < 10 mJy a blue radio galaxy population becomes increasingly important; these often have peculiar optical morphology indicative of interacting or merging galaxies". ...

A deep Westerbork survey of areas with multicolor Mayall 4 M plates. I - The 1412 MHz catalogue, source counts and angular size statistics
  • Citing Article
  • September 1984

Astronomy and Astrophysics Supplement Series

... Useful λ 2 coverage typically implies low frequencies and wide bandwidths (ideally octave or more). The use of Faraday synthesis, 24 a form of Faraday tomography (Takahashi 2023), enables studies of the large-scale structure of the magnetic field (Dickey et al. , 2022Erceg et al. 2022), and also of individual objects and small regions (e.g., Schnitzeler et al. 2007;Van Eck et al. 2017Thomson et al. 2019Thomson et al. , 2021. Direct modeling of the spectra of Stokes parameters Q and U (QU fitting) has proven able to detect multiple Faraday depth components in Faraday complex spectra more reliably than Faraday synthesis, but with the drawbacks of needing considerably longer computational time for each line of sight and requiring us to assume a Faraday rotation model (Farnsworth et al. 2011;O'Sullivan et al. 2012;Ideguchi et al. 2014;Sun et al. 2015). ...

WSRT Faraday tomography of the Galactic ISM at λ ˜ 0.86 m. First results for a field at (l, b)~=~(181°,20°)
  • Citing Article
  • July 2007

Astronomy and Astrophysics

... Such techniques oftentimes assume that roughness lengths are constants that are functions of the underlying surface types. For dense low buildings the experimental values of urban roughness lie between 0.4 and 0.7 m and for regularly built urban regions, the values lie between 0.7 to 1.5 m (Wieringa et al., 1993). The experiments indicate that the urban roughness is 1 10 of the average building height. ...

Small scale polarization structure in the diffuse galactic emission at 325 MHz

Astronomy and Astrophysics

M. H. Wieringa

·

·

D. Jansen

·

[...]

·

P. Katgert