Ministerio de Economía y Competitividad Gobierno de Canarias Universidad de La Laguna CSIC Centro de Excelencia Severo Ochoa

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The cosmic assembly of stellar haloes in massive early-type Galaxies

Author/s: F. Buitrago, I. Trujillo, E. Curtis-Lake, M. Montes, A. P. Cooper, V. A. Bruce, P. G. Pérez-González, M. Cirasuolo

Reference: MNRAS 2017, 466, 4888 | Link

			Near-infrared image from the 6 massive galaxies that were analysed in the present study. The exceptional depth of the Hubble Ultra Deep Field image allow us not only to observe the stellar haloes surrounding the central objects, but many diffuse features and a plethora of satellite galaxies which will be eventually “cannibalised” by the massive galaxies.
Near-infrared image from the 6 massive galaxies that were analysed in the present study. The exceptional depth of the Hubble Ultra Deep Field image allow us not only to observe the stellar haloes surrounding the central objects, but many diffuse features and a plethora of satellite galaxies which will be eventually “cannibalised” by the massive galaxies.
Using the deepest observations of the Hubble Space Telescope (the HUDF12 program), we explore the ongoing assembly (i.e., the progressive creation) of the outermost regions of the most massive galaxies (those galaxies containing the largest number of stars). We remarkably achieve their analysis reaching as far as for nearby galaxies but this time when the Universe 8 billion years younger. The outskirts of massive galaxies, particularly for early-type / spheroidal galaxies, are expected to suffer a dramatic transformation across cosmic time due to the continuous “cannibalization” of small galaxies. HUDF imaging allows us to study this process individually for 6 massive galaxies, finding that 5-20% of the total stellar mass for these galaxies is contained in their stellar haloes. These values are in close agreement with state-of-the-art computer simulations, and higher than those reported for local late-type / disk galaxies (< 5%). The fraction of stellar mass stored in the haloes of Massive Early-Type Galaxies increases with cosmic time, being 28.7% in the local Universe but only 3.5% when the Universe was one fifth of its present age. The fraction of mass in diffuse features linked with ongoing galaxy merger events is > 1-2%, very similar to predictions based on other indirect methods. Therefore, our study reveals that that the size and mass growth of the most massive galaxies have been solely driven by galaxy merging in the last half of our Universe’s life.

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