HYDRODYNAMICS OF HIGH-REDSHIFT GALAXY COLLISIONS: FROM GAS-RICH DISKS TO DISPERSION-DOMINATED MERGERS AND COMPACT SPHEROIDS

By Frédéric Bournaud, Damien Chapon, Romain Teyssier, Leila Powell, Bruce G. Elmegreen, D. Elmegreen, Pierre-Alain Duc, Thierry Contini, B. Epinat, K. Shapiro. 2010

208 citations recorded by the source corpus.

Disk galaxies at high redshift (z ∼ 2) are characterized by high fractions of cold gas, strong turbulence, and giant star-forming clumps. Major mergers of disk galaxies at high redshift should then generally involve such turbulent clumpy disks. Merger simulations, however, model the interstellar medium as a stable, homogeneous, and thermally pressurized medium. We present the first merger simulations with high fractions of cold, turbulent, and clumpy gas. We discuss the major new features of these models compared to models where the gas is artificially stabilized and warmed. Gas turbulence, which is already strong in high-redshift disks, is further enhanced in mergers. Some phases are dispersion dominated, with most of the gas kinetic energy in the form of velocity dispersion and very chaotic velocity fields, unlike merger models using a thermally stabilized gas. These mergers can reach very high star formation rates, and have multi-component gas spectra consistent with SubMillimeter Galaxies. Major mergers with high fractions of cold turbulent gas are also characterized by highly dissipative gas collapse to the center of mass, with the stellar component following in a global contraction. The final galaxies are early type with relatively small radii and high Sersic indices, like high-redshift compact spheroids. The mass fraction in a disk component that survives or re-forms after a merger is severely reduced compared to models with stabilized gas, and the formation of a massive disk component would require significant accretion of external baryons afterwards. Mergers thus appear to destroy extended disks even when the gas fraction is high, and this lends further support to smooth infall as the main formation mechanism for massive disk galaxies.

Subfields: Astronomy and Astrophysics, Instrumentation

View Paper: https://www.semanticscholar.org/paper/061e3e799162cd028895ae7851cbcc286ea7b912

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In Astronomy and Astrophysics

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

In Instrumentation

1. P. Hopkins
2. L. Hernquist
3. R. Dav'e
4. R. Somerville
5. A. Dekel
6. Thomas J. Cox
7. T. Naab
8. P. V. van Dokkum

Citations in the corpus

• Early type galaxies have been the predominant morphological class for massive galaxies since only z~1 (2011, methodology): “For massive galaxies this model predicts a rapid formation phase at 2<z<6 dominated by a dissipational in-situ star formation fed by cold flows (Oser et al. 2010; Dekel et al. 2009; Keres et al. 2005) and/or gas rich mergers (Ricciardelli et al. 2010; Wuyts et al. 2010; Bournaud et al. 2011).”
• THE LESSER ROLE OF STARBURSTS IN STAR FORMATION AT z = 2 (2011, background): “This is also much shorter than the expected duration of the SFRexcess phase in mergers based on numerical simulations (e.g. di Matteo et al. 2008, Martig et al. 2010), where the duration of the phase with SFR in excess of > 4 over the pre-merger SFR is of order of 200-300Myr (Bournaud et al. 2011).”
• Theoretical Challenges in Galaxy Formation (2016, background): “As the low angular momentum gas is efficiently converted into stars, some of the systems can be remarkably small (also supported by mergers, Bournaud et al. 2011a, Wuyts et al. 2010), very similar to the population of observed high-redshift compact galaxies (Oser et al. 2012, 2010, Sommer-Larsen &…”
• Star formation in galaxy mergers with realistic models of stellar feedback and the interstellar medium (2012, background): “Bournaud et al. (2011) argued that disc survival is very inefficient in their simulations, for similar reasons – the gas undergoes dramatic fragmentation and ‘clumps’ scatter off one another, providing new torques.”
• The Dark Matter Crisis: Falsification of the Current Standard Model of Cosmology (2012, methodology): “Therefore, mergers and encounters between galaxies are logically implied events that shape all larger galaxies (e.g. Bournaud et al. 2011; Martig et al. 2012) such that, by Implication 3 (Section 3.2), type B dwarfs appear in significant numbers.”
• THE COSMOLOGICAL SIZE AND VELOCITY DISPERSION EVOLUTION OF MASSIVE EARLY-TYPE GALAXIES (2011, background): “…& 2 - which has been suggested as a reasonable formation mechanism for compact high-redshift galaxies (Wuyts et al. 2010; Ricciardelli et al. 2010; Bournaud et al. 2011) - followed by passive evolution can be ruled out (Kriek et al. 2008; van Dokkum et al. 2008; Trujillo et al. 2009) unless the…”
• Wet Disc Contraction to Galactic Blue Nuggets and Quenching to Red Nuggets (2013, background): “There are already possible detections of such cases (Elmegreen, Elmegreen & Ferguson 2005; Bournaud et al. 2011a, Figure 9).”
• FIRE-2 simulations: physics versus numerics in galaxy formation (2017, background): “…true of models which invoke only energetic feedback (thermal injection) via supernovae (SNe), which typically found the energy was efficiently radiated away (Katz 1992; Guo et al. 2010; Powell et al. 2011; Brook et al. c© 0000 RAS, MNRAS 000, 000–000 2011; Nagamine 2010; Bournaud et al. 2011).”
• KILOPARSEC-SCALE DUST DISKS IN HIGH-REDSHIFT LUMINOUS SUBMILLIMETER GALAXIES (2016, background): “Theoretically, the profiles of merger remnants are expected to be relatively compact and strongly centrally peaked due to the violent and dissipative collapse expected in turbulent and clumpy gas (e.g., Bournaud et al. 2011).”
• How do minor mergers promote inside-out growth of ellipticals, transforming the size, density profile and dark matter fraction? (2012, background): “Even if the progenitor disks were gas-rich leading to a compact remnant (Ricciardelli et al. 2010; Wuyts et al. 2010; Bournaud et al. 2011) those would have to evolve further by a separate process (see e.g. Hopkins et al. 2009).”
• REGULARITY UNDERLYING COMPLEXITY: A REDSHIFT-INDEPENDENT DESCRIPTION OF THE CONTINUOUS VARIATION OF GALAXY-SCALE MOLECULAR GAS PROPERTIES IN THE MASS-STAR FORMATION RATE PLANE (2013, unknown): “Compared to the boost distribution in the simulations of major mergers in Di Matteo et al. (2008) it is indeed displaced to systematically lower SFR enhancements.”
• Compaction and quenching of high-z galaxies in cosmological simulations: blue and red nuggets (2014, background): “There are already possible observational detections of such cases (Elmegreen, Elmegreen & Ferguson 2005; Bournaud et al. 2011a; Genzel et al. 2014a).”
• Cusp-core transformations in dwarf galaxies: observational predictions (2012, methodology): “These recipes have all been implemented in the RAMSES code and used for many galaxy formation studies in the recent years (Agertz, Teyssier & Moore 2009; Teyssier, Chapon & Bournaud 2010; Bournaud et al. 2011; Agertz, Teyssier & Moore 2011; Scannapieco et al. 2012).”
• CANDELS: CONSTRAINING THE AGN–MERGER CONNECTION WITH HOST MORPHOLOGIES AT z ∼ 2 (2011, background): “…to the centers of galaxies on short timescales (a single disk rotation) and at high inflow rates (∼10 M yr−1; M. Cacciato et al. 2011, in preparation; Bournaud et al. 2011b), potentially fueling increased AGN activity in disk galaxies without the need for galaxy–galaxy mergers (Bournaud et al.…”
• Ionized gas outflows and global kinematics of low-z luminous star-forming galaxies (2014, background): “Indeed, there are models that expect the BH to be fed more efficiently in discs with higher turbulence, since the latter helps to remove angular momentum (e.g., Bournaud et al. 2011).”
• A general model for the CO–H2 conversion factor in galaxies with applications to the star formation law (2011, background): “…unstable even in the model disc galaxies at z ∼ 2, similar to both observations (e.g. Elmegreen, Bournaud & Elmegreen 2008; Elmegreen et al. 2009a,b; Genzel et al. 2011), and recent simulations with other codes (e.g. Bournaud et al. 2008, 2010, 2011; Dekel et al. 2009; Ceverino et al. 2010).”
• The VPOS: a vast polar structure of satellite galaxies, globular clusters and streams around the Milky Way (2012, background): “The rate of TDG formation could thus be higher at higher redshift (Kroupa et al. 2010), which seems to be supported by simulations of gas-rich galaxy mergers (Bournaud et al. 2011).”
• Structural and Star-forming Relations since z ∼ 3: Connecting Compact Star-forming and Quiescent Galaxies (2015, background): “…a mixture of weaker instabilities, which can still cause enhanced gas inflows or inward migration of stellar clumps (e.g., Dekel et al. 2009b; Bournaud et al. 2011; Genel et al. 2012), and secular processes (Kormendy & Kennicutt 2004) associated with torques and dynamical friction in the…”