D. B. Wijesinghe

Publications (5)0 Total impact

• Article: Galaxy And Mass Assembly (GAMA): Spectroscopic analysis

  A. M. Hopkins, S. P. Driver, S. Brough, M. S. Owers, A. E. Bauer, M. L. P. Gunawardhana, M. E. Cluver, M. Colless, C. Foster, M. A. Lara-Lopez, [......], M. Seibert, L. Staveley-Smith, W. Sutherland, E. Taylor, L. Van Waerbeke, J. A. Vazquez-Mata, S. Warren, D. B. Wijesinghe, V. Wild, S. Wilkins
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  ABSTRACT: The Galaxy And Mass Assembly (GAMA) survey is a multiwavelength photometric and spectroscopic survey, using the AAOmega spectrograph on the Anglo-Australian Telescope to obtain spectra for up to ~300000 galaxies over 280 square degrees, to a limiting magnitude of r_pet < 19.8 mag. The target galaxies are distributed over 0<z<0.5 with a median redshift of z~0.2, although the redshift distribution includes a small number of systems, primarily quasars, at higher redshifts, up to and beyond z=1. The redshift accuracy ranges from sigma_v~50km/s to sigma_v~100km/s depending on the signal-to-noise of the spectrum. Here we describe the GAMA spectroscopic reduction and analysis pipeline. We present the steps involved in taking the raw two-dimensional spectroscopic images through to flux-calibrated one-dimensional spectra. The resulting GAMA spectra cover an observed wavelength range of 3750<lambda<8850 A at a resolution of R~1300. The final flux calibration is typically accurate to 10-20%, although the reliability is worse at the extreme wavelength ends, and poorer in the blue than the red. We present details of the measurement of emission and absorption features in the GAMA spectra. These measurements are characterised through a variety of quality control analyses detailing the robustness and reliability of the measurements. We illustrate the quality of the measurements with a brief exploration of elementary emission line properties of the galaxies in the GAMA sample. We demonstrate the luminosity dependence of the Balmer decrement, consistent with previously published results, and explore further how Balmer decrement varies with galaxy mass and redshift. We also investigate the mass and redshift dependencies of the [NII]/Halpha vs [OIII]/Hbeta spectral diagnostic diagram, commonly used to discriminate between star forming and nuclear activity in galaxies.
  01/2013;
• Article: Galaxy And Mass Assembly (GAMA): Galaxy environments and star formation rate variations

  D. B. Wijesinghe, A. M. Hopkins, S. Brough, E. N. Taylor, P. Norberg, A. Bauer, M. J. I. Brown, E. Cameron, C. J. Conselice, S. Croom, [......], C. C. Popescu, M. Prescott, R. Sharp, I. Baldry, E. M. Sadler, J. Liske, A. S. G. Robotham, S. Bamford, J. Bland-Hawthorn, M. Gunawardhana
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  ABSTRACT: We present a detailed investigation into the effects of galaxy environment on their star formation rates (SFR) using galaxies observed in the Galaxy and Mass Assembly Survey (GAMA). We use three independent volume-limited samples of galaxies within z < 0.2 and Mr < -17.8. We investigate the known SFR-density relationship and explore in detail the dependence of SFR on stellar mass and density. We show that the SFR-density trend is only visible when we include the passive galaxy population along with the star-forming population. This SFR-density relation is absent when we consider only the star-forming population of galaxies, consistent with previous work. While there is a strong dependence of the EWH?a on density we find, as in previous studies, that these trends are largely due to the passive galaxy population and this relationship is absent when considering a "star-forming" sample of galaxies. We find that stellar mass has the strongest influence on SFR and EWH?a with the environment having no significant effect on the star-formation properties of the star forming population. We also show that the SFR-density relationship is absent for both early and late-type star-forming galaxies. We conclude that the stellar mass has the largest impact on the current SFR of a galaxy, and any environmental effect is not detectable. The observation that the trends with density are due to the changing morphology fraction with density implies that the timescales must be very short for any quenching of the SFR in infalling galaxies. Alternatively galaxies may in fact undergo predominantly in-situ evolution where the infall and quenching of galaxies from the field into dense environments is not the dominant evolutionary mode.
  05/2012;
• Source

  Available from: Simon P. Driver

  Article: Galaxy and Mass Assembly (GAMA): Dust obscuration in galaxies and their recent star formation histories

  D. B. Wijesinghe, A. M. Hopkins, R. Sharp, M. Gunawardhana, S. Brough, E. M. Sadler, S. Driver, I. Baldry, S. Bamford, J. Liske, [......], B. Nichol, H. Parkinson, K. A. Pimbblet, M. Prescott, A. S. G. Robotham, M. Seibert, E. Simmat, W. Sutherland, E. Taylor, D Thomas
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  ABSTRACT: We present self-consistent star formation rates derived through pan-spectral analysis of galaxies drawn from the Galaxy and Mass Assembly (GAMA) survey. We determine the most appropriate form of dust obscuration correction via application of a range of extinction laws drawn from the literature as applied to Halpha, [O{II}] and UV luminosities. These corrections are applied to a sample of 31,508 galaxies from the GAMA survey at z < 0.35. We consider several different obscuration curves, including those of Milky Way, Calzetti (2001) and Fischera and Dopita (2005) curves and their effects on the observed luminosities. At the core of this technique is the observed Balmer decrement, and we provide a prescription to apply optimal obscuration corrections using the Balmer decrement. We carry out an analysis of the star formation history (SFH) using stellar population synthesis tools to investigate the evolutionary history of our sample of galaxies as well as to understand the effects of variation in the Initial Mass Function (IMF) and the effects this has on the evolutionary history of galaxies. We find that the Fischera and Dopita (2005) obscuration curve with an R_{v} value of 4.5 gives the best agreement between the different SFR indicators. The 2200A feature needed to be removed from this curve to obtain complete consistency between all SFR indicators suggesting that this feature may not be common in the average integrated attenuation of galaxy emission. We also find that the UV dust obscuration is strongly dependent on the SFR. Comment: Accepted by MNRAS. 13 pages. 8 figures
  09/2010;
• Source

  Available from: ArXiv

  Article: Morphological classification of galaxies and its relation to physical properties

  D. B. Wijesinghe, A. M. Hopkins, B. C. Kelly, N. Welikala, A. J. Connolly
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  ABSTRACT: We extend a recently developed galaxy morphology classification method, Quantitative Multiwavelength Morphology (QMM), to connect galaxy morphologies to their underlying physical properties. The traditional classification of galaxies approaches the problem separately through either morphological classification or, in more recent times, through analysis of physical properties. A combined approach has significant potential in producing a consistent and accurate classification scheme as well as shedding light on the origin and evolution of galaxy morphology. Here we present an analysis of a volume limited sample of 31703 galaxies from the fourth data release of the Sloan Digital Sky Survey. We use an image analysis method called Pixel-z to extract the underlying physical properties of the galaxies, which is then quantified using the concentration, asymmetry and clumpiness (CAS) parameters. The galaxies also have their multiwavelength morphologies quantified using QMM, and these results are then related to the distributed physical properties through a regression analysis. We show that this method can be used to relate the spatial distribution of physical properties with the morphological properties of galaxies. Comment: Accepted for publication by MNRAS. 11 pages, 16 figures
  01/2010;
• Source

  Available from: Steve Maddox

  Article: GAMA/H-ATLAS: The ultraviolet spectral slope and obscuration in galaxies

  D B Wijesinghe, E Da Cunha, A M Hopkins, L Dunne, R Sharp, M Gunawardhana, S Brough, E M Sadler, S Driver, I Baldry, [......], A S G Robotham, E E Rigby, M Seibert, S Serjeant, D J B Smith, P Temi, W Sutherland, E Taylor, D Thomas, P Van Der Werf
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  ABSTRACT: We use multiwavelength data from the Galaxy And Mass Assembly (GAMA) and Herschel ATLAS (H-ATLAS) surveys to compare the relationship between various dust obscuration measures in galaxies. We explore the connections between the ultraviolet (UV) spectral slope, β, the Balmer decrement, and the far infrared (IR) to 150 nm far ultraviolet (FUV) luminosity ratio. We explore trends with galaxy mass, star formation rate (SFR) and redshift in order to identify possible systematics in these various measures. We reiterate the finding of other authors that there is a large scatter between the Balmer decrement and the β parameter, and that β may be poorly constrained when derived from only two broad passbands in the UV. We also emphasise that FUV derived SFRs, corrected for dust obscuration using β, will be overestimated unless a modified relation between β and the attenuation factor is used. Even in the optimum case, the resulting SFRs have a significant scatter, well over an order of mag-nitude. While there is a stronger correlation between the IR to FUV luminosity ratio and β parameter than with the Balmer decrement, neither of these correlations are particularly tight, and dust corrections based on β for high redshift galaxy SFRs must be treated with caution. We conclude with a description of the extent to which the different obscuration measures are consistent with each other as well as the effects of including other galactic properties on these correlations.
  Mon. Not. R. Astron. Soc. C. Frenk J. Fritz. 01/2010; 00020(25):1-12.