21-cm Tomography

Background:
A 189 MHz, 2400 square degree Polarization Survey with the Murchison Widefield Array 32-element Prototype: Low-frequency Observations of the Moon with the Murchison Widefield Array: Low Frequency Imaging of Fields at High Galactic Latitude with the Murchison Widefield Array 32-Element Prototype:
    The Murchison Widefield Array (MWA) is a new low-frequency, wide field-of-view radio interferometer under development at the Murchison Radio-astronomy Observatory (MRO) in Western Australia. We have used a 32-element MWA prototype interferometer (MWA-32T) to observe two 50-degree diameter fields in the southern sky in the 110 MHz to 200 MHz band in order to evaluate the performance of the MWA-32T, to develop techniques for epoch of reionization experiments, and to make measurements of astronomical foregrounds. We developed a calibration and imaging pipeline for the MWA-32T, and used it to produce ~15' angular resolution maps of the two fields. We perform a blind source extraction using these confusion-limited images, and detect 655 sources at high significance with an additional 871 lower significance source candidates. We compare these sources with existing low-frequency radio surveys in order to assess the MWA-32T system performance, wide field analysis algorithms, and catalog quality. Our source catalog is found to agree well with existing low-frequency surveys in these regions of the sky and with statistical distributions of point sources derived from Northern Hemisphere surveys; it represents one of the deepest surveys to date of this sky field in the 110 MHz to 200 MHz band. Details can be found in Williams et al. (2012).
Clustering of Extragalactic Sources from 151 MHz to 232 MHz:
    In order to construct accurate point sources simulations at the frequencies relevant to 21-cm experiments, the angular correlation of radio sources must be taken into account. This paper presents a measurement of angular two-point correlation function, w(&theta), at 232 MHz from the MIYUN survey - tentative measurements of w(&theta) are also performed at 151 MHz. It is found that double power law with shape w(&theta) = A &theta^{-&gamma} fits the 232 MHz data well. For the angular lenght of 0.2 degrees < &theta < 0.6 degrees, &gamma ~ -1.12, and this value of slope is independent of the flux-density threshold; while for angular lenghts much greater than 0.6 degrees, &gamma has a shallower value of about -0.16. By comparing the results of this paper with previous measurements of w(&theta), it is discussed how w(&theta) changes with the change of frequency and completness limit. Details can be found in de Oliveira-Costa & Lazio (2010).
The Murchison Widefield Array:
    It is shown that the excellent Murchison Radio-astronomy Observatory site allows the Murchison Widefield Array to employ a simple RFI blanking scheme and still calibrate visibilities and form images in the FM radio band. The techniques described are running autonomously in our calibration and imaging software, which is currently being used to process an FM-band survey of the entire southern sky. Details can be found in Mitchell et al. (2010).
Clustering at 74MHz:
    In order to construct accurate point sources simulations at the frequencies relevant to 21-cm experiments, the angular correlation of radio sources must be taken into account. Using the 74 MHz VLSS survey, we measured the angular 2-point correlation function, w(&theta). We obtain the first measurement of clustering at the low frequencies relevant to 21 cm tomography. We find that a single power law with shape w(&theta) = A &theta^{-&gamma} fits well the data. For a galactic cut of 10 degrees, with a data cut of &delta less than -10 degrees, and a flux limit of S = 770 mJy, we obtain a slope of &gamma = (-1.2 +/- 0.35). This value of &gamma is consistent with that measured from other radio catalogues at the millimeter wavelengths. The amplitude of clustering has a length of 0.2 degrees - 0.6 degrees, and it is independent of the flux-density threshold. Details can be found in de Oliveira-Costa & Capodilupo (2010).

My papers on this subject:
  1. "A 189 MHz, 2400 square degree Polarization Survey with the Murchison Widefield Array 32-element Prototype" Bernardi et al. 2013, ApJ 771:105
  2. "Low-frequency Observations of the Moon with the Murchison Widefield Array" McKinley et al. 2013, AJ 145:23
  3. "Low-frequency Imaging of Fields at High Galactic Latitude with the Murchison Widefield Array 32 Element Prototype" Williams et al. 2012, ApJ 755:47
  4. "Probing the Universe with the CMB and 21-cm tomography" de Oliveira-Costa 2010, Online proceedings of "ADA 6 - Sixth Conference on Astronomical Data Analysis, in honor of Albert Bijaoui'', Monastir, Tunisia, May 3-7 May.
  5. "Clustering of Extragalactic Sources from 151 MHz to 232 MHz: Implications for Cosmological 21-cm Observations" de Oliveira-Costa & Lazio 2010, submitted.
  6. "The Murchison Widefield Array" Mitchell & the MWA Collaboration 2010, Review to be published in the proceedings of "RFI Mitigation Workshop'', Groningen, the Netherlands, March 29-31.
  7. "Clustering at 74MHz" de Oliveira-Costa & Capodilupo 2010, MNRAS 404:1962
  8. "A model of diffuse Galactic radio emission from 10 MHz to 100 GHz" de Oliveira-Costa, Tegmark, Gaensler, Jonas, Landecker & Reich 2008, MNRAS 388:247

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Last modified: Jan 4, 2014.