Statistical Properties of Collisionless Equal- and Unequal-Mass Merger Remnants of Disk Galaxies

By T. Naab, A. Burkert. 2001

355 citations recorded by the source corpus.

We perform a large parameter survey of collisionless N-body simulations of binary mergers of disk galaxies with mass ratios of 1 : 1, 2 : 1, 3 : 1, and 4 : 1, using the special-purpose hardware GRAPE. A set of 112 merger simulations is used to investigate the fundamental statistical properties of merger remnants as a function of the initial orientation and mass ratio of the progenitor disks. The photometric and kinematical properties of the simulated merger remnants are analyzed. The methods used to determine the characteristic properties are equivalent to the methods used for observations of giant elliptical galaxies. We take projection effects into account and analyze the remnant properties in a statistical way for comparison with observations. The basic properties of the remnants correlate with the mass ratio of the progenitor disks. We find that about 80% of the equal-mass merger simulations lead to slowly rotating merger remnants having * < 0.4. Observers would interpret those objects as being supported by anisotropic velocity dispersions. All 1 : 1 remnants show significant minor-axis rotation. Half of all projected 1 : 1 remnants show boxy (a4 < 0) isophotes, and the other half show disky (a4 > 0) isophotes. A distinct subclass of 4 out of 12 initial orientations leads to purely boxy remnants independent of orientation. The 1 : 1 mergers with other initial orientations show disky or boxy isophotes, depending on the viewing angle. Remnants with mass ratios of 3 : 1 and 4 : 1 have more homogeneous properties. They all rotate rapidly (maximum value of v/σ = 1.2) and show a small amount of minor-axis rotation, consistent with models of isotropic or slightly anisotropic oblate rotators. If observed in projection, they would be interpreted as being supported by rotation. About 90% of the projected 3 : 1 and 4 : 1 remnants show disky isophotes. The 2 : 1 remnants show intermediate properties. Projection effects lead to a large spread in the data, in good agreement with observations. They do not change the fundamental kinematical differences between equal- and unequal-mass merger remnants. The correlation between isophotal twist and apparent ellipticity of every single merger remnant is in good agreement with observations. The amount of twisting strongly depends on the orientation of the remnant but is only weakly dependent on the mass ratio of the merger. The results of this study weaken the disk merger scenario as the possible formation mechanism of massive boxy giant ellipticals, as only equal-mass mergers with special initial orientations can produce purely boxy anisotropic merger remnants. Some orientations of 1 : 1 mergers can even lead to disky and anisotropic remnants that are either not observed or would be classified as S0 galaxies based on their morphology. In general, the properties of equal-mass (and 2 : 1) merger remnants are consistent with those of the observed population of giant ellipticals in the intermediate-mass regime between low-mass, fast-rotating, disky and bright, massive, boxy giant ellipticals. The 3 : 1 and 4 : 1 merger remnants, however, are in very good agreement with the class of low-luminosity, fast-rotating giant elliptical galaxies. Binary mergers of disk galaxies are therefore still very good candidates for being the main formation mechanism for intermediate- and low-mass giant ellipticals. The homogeneous class of massive boxy ellipticals most likely formed by a different process.

Subfields: Astronomy and Astrophysics, Instrumentation

View Paper: https://www.semanticscholar.org/paper/94c2314198e34d34d0f37653c321df16d76b24e5

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In Astronomy and Astrophysics

1. P. Hopkins
2. L. Hernquist
3. Thomas J. Cox
4. Volker Springel
5. R. Somerville
6. T. Naab
7. R. Dav'e
8. M. Cappellari

In Instrumentation

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

Citations in the corpus

• How do minor mergers promote inside-out growth of ellipticals, transforming the size, density profile and dark matter fraction? (2012, background): “The observations also rule out the formation of ellipticals in a single ’disk merger’ event, a scenario for massive ellipticals which might also suffer from other problems (Ostriker 1980; Naab & Burkert 2003; Burkert et al. 2008; Naab & Ostriker 2009).”
• The Effect of Environment on the Ultraviolet Color-Magnitude Relation of Early-Type Galaxies (2006, background): “However, we know since the simulations of (Toomre&Toomre 1972) that the product of a spiral-spiral merger can be an elliptical galaxy (Negroponte &White 1983; Barnes 1988; Hernquist 1992; Naab & Burkert 2003).”
• Orbital parameters of merging dark matter halos (2003, neutral): “As many characteristic properties of elliptical galaxies as e.g. the amount of rotation are determined by the mass ratio (Naab & Burkert 2003) the cosmological models would predict that massive and low-mass ellipticals should have similar properties which is not in agreement with observations.”
• Moving mesh cosmology: numerical techniques and global statistics (2011, methodology): “These properties have made the method also popular for applications other than cosmic structure growth, e.g. for isolated merger simulations (Barnes & Hernquist 1991, 1992, 1996; Mihos & Hernquist 1994, 1996; Naab & Burkert 2003; Cox et al. 2006).”
• Merger Histories of Galaxy Halos and Implications for Disk Survival (2007, background): “Major mergers are believed to play an important role in shaping the Hubble sequence (Toomre & Toomre 1972; Barnes 1988; Hernquist 1993; Naab & Burkert 2003; Khochfar & Burkert 2005; Cox et al. 2006a; Robertson et al. 2006a,b,c; Maller et al. 2006; Jesseit et al. 2007; Bournaud et al. 2007) and…”
• Formation of Early-Type Galaxies from Cosmological Initial Conditions (2005, methodology): “…major mergers of disk galaxies (Robertson et al. 2006; Hopkins et al. 2006), which cannot reproduce the properties the most massive ellipticals (Naab & Burkert 2003; Cox et al. 2006), whose evolution could be driven by mergers of evolved ellipticals (Ostriker & Hausman 1977; Khochfar & Burkert…”
• Dynamical modelling of luminous and dark matter in 17 Coma early-type galaxies (2007, background): “…assembly epoch (Navarro, Frenk & White 1996; Jing & Suto 2000; Wechsler et al. 2002), the orbital state contains imprints of the assembly mechanism of ellipticals (e.g. van Albada 1982; Hernquist 1992, 1993; Weil & Hernquist 1996; Dubinski 1998; Naab & Burkert 2003; Jesseit, Naab & Burkert 2005).”
• Star formation and AGN activity in SDSS cluster galaxies (2009, background): “…to transform spiral galaxies into ellipticals (e.g. Toomre 1977; Farouki & Shapiro 1982; Negroponte & White 1983; Barnes & Hernquist 1992, 1996; Naab & Burkert 2003; Cox et al. 2006), they are unlikely to occur frequently in galaxy clusters due to the high relative velocities of cluster…”
• The evolution of massive black holes and their spins in their galactic hosts (2012, background): “We also recall that numerical simulations (Walker, Mihos, & Hernquist 1996; Naab & Burkert 2003; Bournaud, Jog, & Combes 2005) suggest that mergers where the mass ratio between the total baryonic masses is larger than ∼ 0.25 − 0.3 (“major mergers”) disrupt the galactic disks and give rise to a…”
• Dynamical Properties of Ultraluminous Infrared Galaxies. I. Mass Ratio Conditions for ULIRG Activity in Interacting Pairs (2005, methodology): “In this paper we analyzed mergers with 16 different initial disk orientations and mass ratios 1:1 and 3:1 (geometries 1–16 in Naab & Burkert 2003; geometries 17–32 for the 3:1 mergers did not change the results presented here).”
• THE DRIVING MECHANISM OF STARBURSTS IN GALAXY MERGERS (2010, background): “In general, merger-induced SF is assumed to be centrally concentrated and to fuel the formation of bulges and compact spheroids rather than extended disks (Naab & Burkert 2003; Bournaud et al. 2004).”
• The Kinematic Structure of Merger Remnants (2006, methodology): “A similar result has been found for mergers of dissipationless remnants by Naab et al. (2006) and we note that other work has also shown that multiple merger remnants can remain on the fundamental plane (Capelato et al. 1995; Nipoti et al. 2003; González-Garćıa & van Albada 2003; Boylan-Kolchin et”
• The effects of gas on morphological transformation in mergers: implications for bulge and disc demographics (2009, result): “…because the efficiency of bulge formation as calibrated in simulations is nearly linear in mass ratio, they give indistinguishable results for our purposes here, so long as they all occur within a short time-scale (see e.g. Naab & Burkert 2003; Bournaud, Jog & Combes 2005; Cox et al. 2008; H09).”
• Feedback in simulations of disc-galaxy major mergers (2005, methodology): “…et al. 1993; Mihos & Hernquist 1994a; Barnes & Hernquist 1996; Springel 2000; Naab & Trujillo 2005), the kinematic structure of merger remnants (Naab & Burkert 2003; González-Garćıa & van Albada 2005a,b; Cox et al. 2006), or if the merger remnants fall on the fundamental plane (Bekki &…”
• MERGERS IN ΛCDM: UNCERTAINTIES IN THEORETICAL PREDICTIONS AND INTERPRETATIONS OF THE MERGER RATE (2010, result): “We also see a continuum of behavior in between, as has been noted in many numerical studies (Hernquist 1989; Hernquist & Mihos 1995; Naab & Burkert 2003; Cox et al. 2008; Younger et al. 2008; Bournaud et al. 2005; Hopkins et al. 2009a; Johansson et al. 2009b,a).”
• Erratum: From dwarf spheroidals to cD galaxies: simulating the galaxy population in a ΛCDM cosmology (2010, result): “Many aspects of these recipes are quite crude but they nevertheless represent reasonably well the results of recent simulations of both gas-poor and gas-rich galaxy mergers (e.g. Naab & Burkert 2003; Cox et al. 2008).”
• HOW DO DISKS SURVIVE MERGERS? (2008, background): “Simulations (Quinn 1984; Quinn & Goodman 1986; Quinn et al. 1993; Hernquist & Mihos 1995; Walker et al. 1996; Velazquez & White 1999; Naab & Burkert 2003; Bournaud et al. 2005; Younger et al. 2007, 2008) and analytic arguments (Ostriker & Tremaine 1975; Toth & Ostriker 1992; Sellwood et al. 1998)…”
• Properties of Early-Type, Dry Galaxy Mergers and the Origin of Massive Elliptical Galaxies (2005, background): “While the properties of low-luminosity elliptical galaxies are consistent with their being remnants of early-type spiral mergers (Naab & Burkert 2003, hereafter NB03; Naab & Trujillo 2005), it is, for several reasons, unlikely that high-luminosity elliptical galaxies formed in a similar way: (1)…”
• A DIVERSITY OF PROGENITORS AND HISTORIES FOR ISOLATED SPIRAL GALAXIES (2012, background): “In particular, major mergers can transform disks into ellipticals (Toomre & Toomre 1972; Barnes 1992; Naab et al. 1999; Naab & Burkert 2003; Cox et al. 2006), especially when they involve two relatively gaspoor galaxies, which can often be the case at low redshift.”