Detalles de publicación
PP 09046
Are Dry Mergers Dry, Moist, or Wet?
(1) Jeremiah Horrocks Insitute for Astrophisics & Supercomputing, UCLan, Preston, PR1 2HE, UK
(2) Instituto de Astrofisica de Canarias, c/Via Lactea s/n, 38205, La Laguna, Tenerife, Spain.
(3) Departamento de Astrofísica, Universidad de La Laguna, E-38205 La Laguna, Tenerife, Spain
(4) Mullard Space Science Laboratory, Holmbury St Mary, RH5 6NT, UK
(5) Departamento de Astrofisica y CC de la Atmosfera, Universidad Complutense de Madrid, Av Complutense s/n, 28040, Madrid, Spain
We present a spectral analysis of a sample of red-sequence galaxies identified by van~Dokkum (2005) as dry merger remnants and ongoing dry mergers. Kinematics, stellar population absorption features, and ionisation from emission lines, are derived. We find that approximately half of the sample showing strong tidal features have younger stellar populations than a control sample at a given velocity
dispersion. Conversely, galaxies with weak tidal tails and/or ongoing mergers -- with the exception of one galaxy -- do not show this young component. This seems to indicate that the young stellar populations observed in a significant fraction of ellipticals is the consequence of star formation triggered by mergers. This young component is consistent with a light ``frosting'' of young stars (<2% by mass) superimposed upon a dominant, old ($\sim$11~Gyr), stellar population. In terms of
stellar populations, these mergers are, in fact, fairly dry. We found, however, that merger remnants with young stellar populations are supported by rotation, contrary to the expectations of a major dry
merger. This suggests that the small amount of gas involved has been sufficient to produce a dynamically cold stellar component. Half of the galaxies with strong tidal distortion, however, are slow rotating and have stellar populations compatible with the control sample at a given velocity dispersion. Remarkably, none of the galaxies with velocity dispersions in excess of
250 km/s have a young stellar component, independent of the merger stage.
dispersion. Conversely, galaxies with weak tidal tails and/or ongoing mergers -- with the exception of one galaxy -- do not show this young component. This seems to indicate that the young stellar populations observed in a significant fraction of ellipticals is the consequence of star formation triggered by mergers. This young component is consistent with a light ``frosting'' of young stars (<2% by mass) superimposed upon a dominant, old ($\sim$11~Gyr), stellar population. In terms of
stellar populations, these mergers are, in fact, fairly dry. We found, however, that merger remnants with young stellar populations are supported by rotation, contrary to the expectations of a major dry
merger. This suggests that the small amount of gas involved has been sufficient to produce a dynamically cold stellar component. Half of the galaxies with strong tidal distortion, however, are slow rotating and have stellar populations compatible with the control sample at a given velocity dispersion. Remarkably, none of the galaxies with velocity dispersions in excess of
250 km/s have a young stellar component, independent of the merger stage.