Browsing by Author "Gunawardhana, Madusha L. P."
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- ItemEvidence 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, IstvanWe 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.
- ItemGalaxy and Mass Assembly (GAMA): active galactic nuclei in pairs of galaxies(OXFORD UNIV PRESS, 2017) Gordon, Yjan A.; Owers, Matt S.; Pimbblet, Kevin A.; Croom, Scott M.; Alpaslan, Mehmet; Baldry, Ivan K.; Brough, Sarah; Brown, Michael J. I.; Cluver, Michelle E.; Conselice, Christopher J.; Davies, Luke J. M.; Holwerda, Benne W.; Hopkins, Andrew M.; Gunawardhana, Madusha L. P.; Loveday, Jonathan; Taylor, Edward N.; Wang, LingyuThere exist conflicting observations on whether or not the environment of broad-and narrowline active galatic nuclei (AGN) differ and this consequently questions the validity of the AGN unification model. The high spectroscopic completeness of the Galaxy and Mass Assembly (GAMA) survey makes it ideal for a comprehensive analysis of the close environment of galaxies. To exploit this, and conduct a comparative analysis of the environment of broad-and narrow-line AGN within GAMA, we use a double-Gaussian emission line fitting method to model the more complex line profiles associated with broad-line AGN. We select 209 type 1 (i.e. unobscured), 464 type 1.5-1.9 (partially obscured), and 281 type 2 (obscured) AGN within the GAMA II data base. Comparing the fractions of these with neighbouring galaxies out to a pair separation of 350 kpc h(-1) and triangle z < 0.012 shows no difference between AGN of different type, except at separations less than 20 kpc h(-1) where our observations suggest an excess of type 2 AGN in close pairs. We analyse the properties of the galaxies neighbouring our AGN and find no significant differences in colour or the star formation activity of these galaxies. Further to this, we find that Sigma(5) is also consistent between broad-and narrow-line AGN. We conclude that the observations presented here are consistent with AGN unification.