MINOR MERGERS AND THE SIZE EVOLUTION OF ELLIPTICAL GALAXIES

By T. Naab, Peter H. Johansson, Jeremiah P. Ostriker. 2009

656 citations recorded by the source corpus.

Using a high-resolution hydrodynamical cosmological simulation of the formation of a massive spheroidal galaxy we show that elliptical galaxies can be very compact and massive at high redshift in agreement with recent observations. Accretion of stripped infalling stellar material increases the size of the system with time and the central concentration is reduced by dynamical friction of the surviving stellar cores. In a specific case of a spheroidal galaxy with a final stellar mass of 1.5 × 1011 M☉ we find that the effective radius re increases from 0.7 ± 0.2 kpc at z = 3 to re = 2.4 ± 0.4 kpc at z = 0 with a concomitant decrease in the effective density of an order of magnitude and a decrease of the central velocity dispersion by approximately 20% over this time interval. A simple argument based on the virial theorem shows that during the accretion of weakly bound material (minor mergers) the radius can increase as the square of the mass in contrast to the usual linear rate of increase for major mergers. By undergoing minor mergers compact high-redshift spheroids can evolve into present-day systems with sizes and concentrations similar to observed local ellipticals. This indicates that minor mergers may be the main driver for the late evolution of sizes and densities of early-type galaxies.

Subfields: Astronomy and Astrophysics, Instrumentation

View Paper: https://www.semanticscholar.org/paper/d2cf1fbf09f5da2a8620c47500e86e035ce60b4e

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In Astronomy and Astrophysics

1. P. Hopkins
2. L. Hernquist
3. M. Cappellari
4. T. Naab
5. R. Somerville
6. Volker Springel
7. C. Conroy
8. A. Dekel

In Instrumentation

1. P. Hopkins
2. L. Hernquist
3. M. Cappellari
4. P. V. van Dokkum
5. C. Conroy
6. A. Dekel
7. T. Naab
8. R. Somerville

Citations in the corpus

• Cool Gas in High-Redshift Galaxies (2013, background): “Subsequent dry (gas–poor) mergers at z < 2 lead to continued total mass build up, and morphological evolution, but little star formation in such models (Hopkins et al. 2010; Naab et al. 2009, Kereš et al. 2009).”
• The size evolution of star-forming and quenched galaxies in the IllustrisTNG simulation (2017, background): “Such individual size growth has most commonly been attributed to (in particular, minor) mergers (Naab et al. 2009; Oser et al. 2012; Oogi & Habe 2013; but see Nipoti et al. 2012), however also expansion due to mass loss has been suggested (driven by feedback as well as stellar evolution; Fan et al.…”
• CANDELS: THE COSMIC ASSEMBLY NEAR-INFRARED DEEP EXTRAGALACTIC LEGACY SURVEY (2011, neutral): “If these sizes are correct, the implication is that massive spheroids must have accreted considerable stellar mass after z ≈ 2 and that their extended stellar envelopes grew by dry minor mergers (Naab et al. 2009; van Dokkum et al. 2010).”
• Galactic accretion and the outer structure of galaxies in the CDM model (2013, background): “Like many recent numerical studies of the size evolution of massive quiescent galaxies (Meza et al. 2003; Naab et al. 2009; Oser et al. 2010) and Milky Way-like galaxies (Abadi, Navarro & Steinmetz 2006; Cooper et al. 2010; Font et al. 2011; Sales et al. 2012) we emphasize the difference between in…”
• Early type galaxies have been the predominant morphological class for massive galaxies since only z~1 (2011, background): “E-mail: fernando.buitrago@roe.ac.uk † Scottish Universities Physics Alliance than their lower redshift massive counterparts (Naab et al. 2009).”
• Structure and Kinematics of Early-Type Galaxies from Integral Field Spectroscopy (2016, background): “…simulations (e.g. Robertson et al. 2006; Boylan-Kolchin et al. 2006; Oser et al. 2012; Porter et al. 2014); and (ii) due to the fact that scaling parameters are actually expected to evolve very differently depending on the galaxy formation mechanism (e.g. Naab et al. 2009; Hopkins et al. 2010).”
• GRAVITATIONAL HEATING HELPS MAKE MASSIVE GALAXIES RED AND DEAD (2009, background): “Finally, the accretion of minor mergers can potentially explain the strong size evolution observed in elliptical galaxies between z = 2−0 (van Dokkum 2008; Naab et al. 2009).”
• HYDRODYNAMICS OF HIGH-REDSHIFT GALAXY COLLISIONS: FROM GAS-RICH DISKS TO DISPERSION-DOMINATED MERGERS AND COMPACT SPHEROIDS (2010, background): “The role of mergers in forming these ETGs has been questioned: while their evolution into modern, more extended elliptical galaxies can be explained through continuous hierarchical merging (Naab et al. 2009), the emergence of compact ellipticals at high redshift remains more mysterious.”
• Dissecting the size evolution of elliptical galaxies since z∼ 1: puffing-up versus minor-merging scenarios (2011, background): “Another possible scenario for elliptical galaxy growth involves minor mergers on parabolic orbits (e.g. Khochfar & Burkert 2006; Maller et al. 2006; Hopkins et al. 2009b; Naab et al. 2009) .”
• Evolution of density profiles in high-z galaxies: compaction and quenching inside-out (2015, background): “Often, this trend has been entirely ascribed to the physical growth of individual galaxies, where massive quiescent galaxies grow through accretion of smaller galaxies in minor gas-poor mergers (e.g. Naab et al. 2009; Hopkins et al. 2009; Nipoti et al. 2009; Feldmann et al. 2010; Oser et al. 2012).”
• THE TWO PHASES OF GALAXY FORMATION (2010, methodology): “We give, in Naab et al. (2009) a simple argument based on the virial theorem showing how late accretion of low mass satellites (’minor mergers’) will lead to the rapid growth in galactic size.”
• MERGERS AND BULGE FORMATION IN ΛCDM: WHICH MERGERS MATTER? (2009, background): “…very different structural properties in the remnants, including rotation and higher-order kinematics, flattening and isophotal shapes, profile shapes, central densities, effective radii, and triaxialities (Weil & Hernquist1994, 1996; Burkert et al. 2008; Naab et al. 2009; Hoffman et al. 2009).”