Browsing University of Hertfordshire by Author "Yi, S.K."

Now showing items 1-20 of 23

    • Anatomy of a post-starburst minor merger : A multi-wavelength WFC3 study of NGC 4150 

      Crockett, R.M.; Kaviraj, S.; Silk, J.I.; Whitmore, B.C.; Mutchler, M.; Bond, H.E.; O'Connell, R.W.; Balick, B.; Calzetti, D.; Carollo, C.M.; Disney, M.J.; Dopita, M.A.; Frogel, J.A.; Hall, D.N.B.; Holtzman, J. A.; Kimble, R.A.; McCarthy, P.J.; Paresce, F.; Saha, A.; Trauger, J.T.; Walker, A.R.; Windhorst, R.A.; Young, E.T.; Jeong, H.; Yi, S.K. (2011-02-01)
      We present a spatially resolved near-UV/optical study, using the Wide Field Camera 3 (WFC3) on board the Hubble Space Telescope, of NGC 4150, a sub-L , early-type galaxy (ETG) of around 6 × 10 M , which has been observed ...

    • Better age estimation using ultraviolet-optical colours : Breaking the age-metallicity degeneracy 

      Kaviraj, S.; Rey, S.-C.; Yoon, S.-J.; Yi, S.K.; Rich, R.M. (2007-10-01)
      We demonstrate that the combination of GALEX ultraviolet (UV) photometry in the far-UV (FUV; ~1530 Å) and near-UV (NUV; ~2310 Å) passbands with optical photometry in the standard U, B, V, R, I filters can efficiently break ...

    • Decoding the spectra of SDSS early-type galaxies : New indicators of age and recent star formation 

      Rogers, B.; Ferreras, I.; Lahav, O.; Bernardi, M.; Kaviraj, S.; Yi, S.K. (2007-12-01)
      We apply principal component analysis (PCA) to a sample of early-type galaxies from the Sloan Digital Sky Survey (SDSS) in order to infer differences in their star formation histories from their unresolved stellar populations. ...

    • Destruction of molecular gas reservoirs in early-type galaxies by active galactic nucleus feedback 

      Schawinski, K.; Lintott, C.J.; Kaviraj, S.; Silk, J.; Zuntz, J.; Bayet, E.; Thomas, D.; Maraston, C.; Viti, S.; Sarzi, M.; Yi, S.K.; Joo, S-J.; Daddi, E.; Bell, T. (2009)
      Residual star formation at late times in early-type galaxies and their progenitors must be suppressed in order to explain the population of red, passively evolving systems we see today. Likewise, residual or newly accreted ...

    • The effect of environment on the ultraviolet color-magnitude relation of early-type galaxies 

      Schawinski, K.; Kaviraj, S.; Khochfar, S.; Yoon, S.-J.; Yi, S.K.; Lee, Y.-W.; Deharveng, J.-M.; Boselli, A.; Donas, J.; Milliard, B.; Barlow, T.; Conrow, T.; Forster, K.; Friedman, P.G.; Martin, D.C.; Morrissey, P.; Seibert, M.; Small, T.; Wyder, T.; Neff, S.; Schiminovich, D.; Blanchi, L.; Heckman, T.; Szalay, A.; Madore, B.; Rich, R.M. (2007-12-01)
      We use GALEX near-UV (NUV ) photometry of a sample of early-type galaxies selected in the SDSS (Sloan Digital Sky Survey) to study the UV color-magnitude relation (CMR). NUV - r color is an excellent tracer of even small ...

    • The elliptical galaxy colour-magnitude relation as a discriminant between the monolithic and merger paradigms 

      Kaviraj, S.; Devriendt, J.E.G.; Ferreras, I.; Yi, S.K. (2005-06-11)
      The colour-magnitude relation (CMR) of cluster elliptical galaxies has been widely used to constrain their star formation histories (SFHs) and to discriminate between the monolithic collapse and merger paradigms of elliptical ...

    • Environment and the epochs of galaxy formation in the SDSS era 

      Thomas, D.; Maraston, C.; Schawinski, K.; Joo, S.-J.; Kaviraj, S.; Sarzi, M.; Yi, S.K. (2006-12-01)
      We analyse a sample of 1,652 elliptical galaxies morphologically selected from the SDSS DR4 with respect to their stellar population properties such as luminosity weighted ages, metallicities and /Fe element abundance ...

    • Galaxy evolution explorer ultraviolet color-magnitude relations and evidence of recent star formation in early-type galaxies 

      Yi, S.K.; Yoon, S.-J.; Lee, Y.-W.; Ree, C.H.; Sohn, Y.-J.; Rey, S.-C.; Rhee, J.; Byun, Y.-I.; Kim, S.-W.; Kaviraj, S.; Deharveng, J.-M.; Boselli, A.; Donas, J.; Malina, R.; Milliard, B.; Rich, R.M.; Salim, S.; Friedman, P.G.; Martin, D.C.; Morrissey, P.; Small, T.; Barlow, T.; Forster, K.; Wyder, T.K.; Lee, J.-W.; Bianchi, L.; Heckman, T.M.; Szalay, A.S.; Jee, M.J.; Jelinsky, P.; Siegmund, O.; Welsh, B.; Madore, B.F.; Neff, S.; Schiminovich, D. (2005-01-20)
      We have used the Galaxy Evolution Explorer UV photometric data to construct a first near-UV (NUV) color-magnitude relation (CMR) for the galaxies preclassified as early-type by Sloan Digital Sky Survey studies. The NUV CMR ...

    • Galaxy Zoo: a sample of blue early-type galaxies at low redshift 

      Schawinski, K.; Lintott, C.; Kaviraj, S.; Khochfar, S.; Land, K.; Thomas, D.; Bamford, S. P.; Nichol, R.C.; Sarzi, M.; Andreescu, D.; Murray, P.; Raddick, M.J.; Szalay, A.; Vandenberg, J.; Slosar, A.; Yi, S.K. (2009)
      We report the discovery of a population of nearby, blue early-type galaxies with high star formation rates (0.5 < SFR < 50 M⊙ yr−1) . They are identified by their visual morphology as provided by Galaxy Zoo for Sloan Digital ...

    • Galex-derived residual star formation history of elliptical galaxies 

      Yi, S.K.; Kaviraj, S.; Schawinski, K.; Khochfar, S. (EDP Sciences, 2007)
      Bright early-type galaxies are still forming stars at low-level residual star formation (RSF) mode. The GALEX UV satellite has detected excessive UV flux in > 30% of our volume-limited sample of ∼10 galaxies. The RSF galaxy ...

    • Globular clusters as probes of galaxy evolution : NGC 5128 

      Yi, S.K.; Kaviraj, S.; Yoon, S.-J.; Peng, E.; Ford, H. (2004-04-21)
      We present the results of our analysis of the photometric data of globular clusters in the elliptical galaxy NGC 5128 (Cen A). We show that the integrated colour U - B can be an effective metallicity indicator for simple ...

    • Identifying the progenitor set of present-day early-type galaxies : A view from the standard model 

      Kaviraj, S.; Ferreras, I.; Devriendt, J.E.G.; Silk, J.; Yi, S.K. (2009-08-01)
      We present a comprehensive theoretical study, using a semi-analytical model within the standard LCDM framework, of the photometric properties of the progenitors of present-day early-type galaxies in the redshift range 0 ...

    • The look-back time evolution of far-ultraviolet flux from the brightest cluster elliptical galaxies at z <0.2 

      Ree, C.H.; Lee, Y.-W.; Yi, S.K.; Yoon, S.-J.; Sohn, Y.-J.; Rhee, J.; Sheen, Y.-K.; Rich, R.M.; Deharveng, J.-M.; Boselli, A.; Donas, J.; Milliard, B.; Kaviraj, S.; Schawinski, K.; Rey, S.-C.; Seibert, M.; Wyder, T.K.; Barlow, T.A.; Forster, K.; Friedman, P.G.; Martin, D.C.; Morrissey, P.; Small, T.; Bianchi, L.; Heckman, T.M.; Szalay, A.S.; Madore, B.F.; Neff, S.G.; Schiminovich, D.; Welsh, B.Y. (2007-12-01)
      We present the GALEXUV photometry of the elliptical galaxies in Abell clusters at moderate redshifts (z <0.2) for the study of the look-back time evolution of the UV upturn phenomenon. The brightest elliptical galaxies (M ...

    • Minor-merger-driven growth of early-type galaxies over the last 8 billion years 

      Kaviraj, S.; Crockett, R.M.; Silk, J.; Ellis, R.S.; Yi, S.K.; O'Connell, R.W.; Windhorst, R.; Whitmore, B.C. (Cambridge University Press, 2011-09)
      We summarise recent progress in understanding the star formation activity in early-type galaxies (ETGs), using recent studies that leverage photometry in the rest-frame ultraviolet (UV) wavelengths. While classically thought ...

    • Observational evidence for AGN feedback in early-type galaxies 

      Schawinski, K.; Thomas, D.; Sarzi, M.; Maraston, C.; Kaviraj, S.; Silk, J.; Joo, S-J.; Yi, S.K. (2007)
      A major amendment in recent models of hierarchical galaxy formation is the inclusion of so-called active galactic nucleus (AGN) feedback. The energy input from an active central massive black hole is invoked to suppress ...

    • On the globular cluster formation history of NGC 5128 

      Kaviraj, S.; Ferreras, I.; Yoon, S.-J.; Yi, S.K. (2005-09-01)
      We deduce the globular cluster formation history of the nearby elliptical galaxy, NGC 5128, by using a chemical enrichment model to accurately reproduce its observed metallicity distribution function (MDF). We derive the ...

    • Recent star formation in high-redshift early-type galaxies : Insights from the rest-frame UV 

      Kaviraj, S.; Khochfar, S.; Schawinski, K.; Silk, J.; Yi, S.K.; Gawiser, E.; Van Dokkum, P.G. (2007-06)
      We combine deep UBV RIzJK photometry from the MUSYC survey with redshifts from the COMBO-17 survey to study the rest-frame ultraviolet (UV) properties of 674 high-redshift (0.5 <z <1) early-type galaxies, drawn from the ...

    • The SAURON project – XIII. SAURON–GALEX study of early-type galaxies: the ultraviolet colour–magnitude relations and Fundamental Planes 

      Jeong, H.J.; Yi, S.K.; Bureau, M.; Davies, R.L.; Falcon-Barroso, J.; van de Ven, G.; Peletier, R.F.; Bacon, R.; Cappellari, M.; de Zeeuw, T.; Emsellem, E.; Krajnovic, D.; Kuntschner, H.; McDermid, R.M.; Sarzi, M.; van den Bosch, R.C.E. (2009)
      We present Galaxy Evolution Explorer far-ultraviolet (FUV) and near-ultraviolet (NUV) imaging of 34 nearby early-type galaxies from the SAURON representative sample of 48 E/S0 galaxies, all of which have ground-based optical ...

    • The SAURON project – XVI : On the sources of ionization for the gas in elliptical and lenticular galaxies 

      Sarzi, M.; Shields, J.C.; Schawinski, K.; Jeong, H.J.; Shapiro, K.; Bacon, R.; Bureau, M.; Capellari, M.; Davies, R.L.; de Zeeuw, P.T.; Emsellem, E.; Falcon-Barroso, J.; Krajnovic, D.; Kuntschner, H.; McDermid, R.M.; Peletier, R.F.; van den Bosch, R.C.E.; van de Ven, G.; Yi, S.K. (2010)
      Following our study on the incidence, morphology and kinematics of the ionized gas in early-type galaxies, we now address the question of what is powering the observed nebular emission. To constrain the likely sources of ...

    • Suppression of star formation in early-type galaxies by feedback from supermassive black holes 

      Schawinski, K.; Khochfar, S.; Kaviraj, S.; Yi, S.K.; Lee, Y.-W.; Boselli, A.; Donas, J.; Milliard, B.; Barlow, T.; Conrow, T.; Forster, K.; Friedman, P.G.; Martin, D.C.; Morrissey, P.; Seibert, M.; Small, T.; Wyder, T.K.; Neff, S.; Schiminovich, D.; Bianchi, L.; Heckman, T.; Szalay, A.; Madore, B.; Rich, R.M. (2006-08-24)
      Detailed high-resolution observations of the innermost regions of nearby galaxies have revealed the presence of supermassive black holes. These black holes may interact with their host galaxies by means of 'feedback' in ...