Browsing by Author "Kovacs, Andras"

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    Evidence against a supervoid causing the CMB Cold Spot
    (OXFORD UNIV PRESS, 2017) Mackenzie, Ruari; Shanks, Tom; Bremer, Malcolm N.; Cai, Yan Chuan; Gunawardhana, Madusha L. P.; Kovacs, Andras; Norberg, Peder; Szapudi, Istvan
    We report the results of the 2dF-VST ATLAS Cold Spot galaxy redshift survey (2CSz) based on imaging from VST ATLAS and spectroscopy from 2dF AAOmega over the core of the CMB Cold Spot. We sparsely surveyed the inner 5 degrees. radius of the Cold Spot to a limit of i(AB) = 19.2, sampling similar to 7000 galaxies at z < 0.4. We have found voids at z = 0.14, 0.26 and 0.30 but they are interspersed with small overdensities, and the scale of these voids is insufficient to explain the Cold Spot through the Lambda CDM ISW effect. Combining with previous data out to z similar to 1, we conclude that the CMB Cold Spot could not have been imprinted by a void confined to the inner core of the Cold Spot. Additionally, we find that our 'control' field GAMA G23 shows a similarity in its galaxy redshift distribution to the Cold Spot. Since the GAMA G23 line of sight shows no evidence of a CMB temperature decrement, we conclude that the Cold Spot may have a primordial origin rather than being due to line-of-sight effects.
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    The VST ATLAS quasar survey I: Catalogue of photometrically selected quasar candidates
    (2023) Eltvedt, Alice M.; Shanks, T.; Metcalfe, N.; Ansarinejad, B.; Barrientos, L. F.; Sharp, R.; Malik, U.; Murphy, D. N. A.; Irwin, M.; Wilson, M.; Alexander, D. M.; Kovacs, Andras; Garcia-Bellido, Juan; Ahlen, Steven; Brooks, David; de la Macorra, Axel; Font-Ribera, Andreu; Gontcho, Satya Gontcho a; Honscheid, Klaus; Meisner, Aaron; Miquel, Ramon; Nie, Jundan; Tarle, Gregory; Vargas-Magana, Mariana; Zhou, Zhimin
    We present the VST ATLAS Quasar Survey, consisting of similar to 1229 000 quasar (QSO) candidates with 16 < g < 22.5 over similar to 4700 deg(2). The catalogue is based on VST ATLAS+NEOWISE imaging surveys and aims to reach a QSO sky density of 130 deg-2 for z < 2.2 and similar to 30 deg(-2) for z > 2.2. To guide our selection, we use X-ray/UV/optical/MIR data in the extended William Herschel Deep Field (WHDF) where we find a g < 22.5 broad-line QSO density of 269 +/- 67 deg(-2), roughly consistent with the expected similar to 196 deg(-2). We find that similar to 25 per cent of our QSOs are morphologically classed as optically extended. Overall, we find that in these deep data, MIR, UV, and X-ray selections are similar to 70-90 per cent complete while X-ray suffers less contamination than MIR and UV. MIR is however more sensitive than X-ray or UV to z > 2.2 QSOs at g < 22.5 and the S-X (0.5 - 10 keV) > 1 x10(-14) ergs cm(-2) s(-1) limit of eROSITA. We adjust the selection criteria from our previous 2QDES pilot survey and prioritize VST ATLAS candidates that show both UV and MIR excess, also selecting candidates initially classified as extended. We test our selections using data from DESI (which will be released in DR1) and 2dF to estimate the efficiency and completeness, and we use ANNz2 to determine photometric redshifts. Applying over the similar to 4700 deg(2) ATLAS area gives us similar to 917 000 z < 2.2 QSO candidates of which 472 000 are likely to be z < 2.2 QSOs, implying a sky density of similar to 100 deg(-2), which our WHDF analysis suggests will rise to at least 130 deg(-2) when eROSITA X-ray candidates are included. At z > 2.2, we find similar to 310() 000 candidates, of which 169 000 are likely to be QSOs for a sky density of similar to 36 deg(-2).