Dry Mergers in GEMS: The Dynamical Evolution of Massive Early-Type Galaxies

By Eric F. Bell, Thorsten Naab, Daniel H. McIntosh, R. Somerville, J. A. R. Caldwell, M. Barden, Christian Wolf, Hans-Walter Rix, S. Beckwith, A. Borch and 9 more. 2005

250 citations recorded by the source corpus.

We have used the 28′ × 28′ Hubble Space Telescope image mosaic from the GEMS (Galaxy Evolution from Morphology and SEDs) survey in conjunction with the COMBO-17 photometric redshift survey to constrain the incidence of major mergers between spheroid-dominated galaxies with little cold gas (dry mergers) since z = 0.7. A set of N-body merger simulations was used to explore the morphological signatures of such interactions: they are recognizable either as <5 kpc separation close pairs or because of broad, low surface brightness tidal features and asymmetries. Data with the depth and resolution of GEMS are sensitive to dry mergers between galaxies with MV ≲ -20.5 for z ≲ 0.7; dry mergers at higher redshifts are not easily recovered in single-orbit HST imaging. Six dry mergers (12 galaxies) with luminosity ratios between 1 : 1 and 4 : 1 were found from a sample of 379 red early-type galaxies with MV < -20.5 and 0.1 < z < 0.7. The simulations suggest that the morphological signatures of dry merging are visible for ~150 Myr, and we use this timescale to convert the observed merger incidence into a rate. On this basis we find that present-day spheroidal galaxies with MV < -20.5 on average have undergone between 0.5 and 2 major dry mergers since z ~ 0.7. We have compared this result with the predictions of a cold dark matter-based semianalytic galaxy formation model. The model reproduces the observed declining major merger fraction of bright galaxies and the space density of luminous early-type galaxies reasonably well. The predicted dry merger fraction is consistent with our observational result. Hence, hierarchical models predict and observations now show that major dry mergers are an important driver of the evolution of massive early-type galaxies in recent epochs.

Subfields: Astronomy and Astrophysics, Atomic and Molecular Physics, and Optics, Instrumentation

View Paper: https://www.semanticscholar.org/paper/ec9cf269e4f46fee6b43e3c3a60276f175599ac2

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Citations in the corpus

The Evolving Luminosity Function of Red Galaxies (2006, background): “While there have been valiant attempts to measure the galaxymerger rate with redshift (e.g., Le Fèvre et al. 2000; Bell et al. 2006), there is debate about the selection function of merger candidates and the duration of observable galaxymergers.”
A Cosmological Framework for the Co-Evolution of Quasars, Supermassive Black Holes, and Elliptical Galaxies. II. Formation of Red Ellipticals (2007, result): “…we assume does not evolve with redshift (as suggested by a large number of observations at least to z 1:5, and by some to zk 3; Conselice et al. 2005; Flores et al. 2006; Bell et al. 2006b; Kassin et al. 2007; van Dokkum et al. 2004), but we have tried all three estimators and find similar results.”
Properties of Early-Type, Dry Galaxy Mergers and the Origin of Massive Elliptical Galaxies (2005, background): “Bell et al. (2006) and van Dokkum (2005) also find clear evidence for this process in the field.”
RED NUGGETS AT z ∼ 1.5: COMPACT PASSIVE GALAXIES AND THE FORMATION OF THE KORMENDY RELATION (2008, background): “Mergers, both gas-rich and dissipationless, are also thought to be important in the growth of the red sequence and evidence, both direct and indirect, supports that this is occuring at intermediate and low redshifts (e.g., Bell et al. 2006b, and the references therein).”
Formation of Early-Type Galaxies from Cosmological Initial Conditions (2005, background): “…plausible and popular idea that ‘‘dry merging’’ (i.e., merging of predominantly stellar systems) among elliptical systems (Tran et al. 2005; van Dokkum 2005; Bell et al. 2006a, 2006b) pushes more and more of the mass over the observational cutoff to provide an increased number of 0.5Y2 L galaxies.”
The Sloan Lens ACS Survey. II. Stellar Populations and Internal Structure of Early-Type Lens Galaxies (2005, background): “…the assembly of massive early-type galaxies (e.g. Khochfar & Burkert 2003) are the so-called “dry” mergers, i.e. mergers that do not involve a significant amount of cold gas and hence not associated with star formation (see Bell et al. 2006 and van Dokkum 2005 for recent results and discussions).”
The Redshift Evolution of Wet, Dry, and Mixed Galaxy Mergers from Close Galaxy Pairs in the DEEP2 Galaxy Redshift Survey (2008, background): “…1995; Neuschaefer et al. 1997; Patton et al. 1997; Carlberg et al. 2000; Le Fèvre et al. 2000; Patton et al. 2002; Conselice et al. 2003; Bundy et al. 2004; Lin et al. 2004; Cassata et al. 2005; Conselice 2006; Bell et al. 2006b; Lotz et al. 2008; Kampczyk et al. 2007; Kartaltepe et al. 2007).”
Discriminating Between the Physical Processes that Drive Spheroid Size Evolution (2009, background): “…models (Khochfar & Silk 2006; Hopkins et al. 2009d; Naab et al. 2009) or permitted by observational constraints implying ∼1– 2 major dry mergers (typical mass ratio ∼1:3) per system since z = 2 (van Dokkum 2005; Bell et al. 2006; Lin et al. 2008; Darg et al. 2009a,b; Bridge et al., in preparation).”
Structure and Star Formation in Galaxies out to z = 3: Evidence for Surface Density Dependent Evolution and Upsizing (2008, background): “…evidence presented here that the galaxies with surface density> 109 M⊙ kpc−2 were forming stars at higher redshift, the latter from theoretical predictions, and determinations of the merger rate (e.g., Bell et al. 2006, van Dokkum et al. 2005), which are still quite uncertain, however.”
The Evolution of the MBH-σ Relation (2005, background): “…evidence from the red sequence of the galaxy color bimodality (Strateva et al. 2001; Blanton et al. 2003; Baldry et al. 2004; Bell et al. 2004; Faber et al. 2005) suggests that the most massive galaxies are produced through the dry merging of spheroids at z < 1 (Bell et al. 2006; van Dokkum 2005).”
MINOR MERGERS AND THE SIZE EVOLUTION OF ELLIPTICAL GALAXIES (2009, background): “…events are the prime candidates for the strong mass and size evolution of stellar spheroids at z < 2 (Naab et al. 2006; Khochfar & Silk 2006; Bell et al. 2006a,b; Ruszkowski & Springel 2009; Hopkins et al. 2009; van der Wel et al. 2009) as the additional presence of a dissipative component…”
MERGERS AND BULGE FORMATION IN ΛCDM: WHICH MERGERS MATTER? (2009, background): “…be surprising, given the agreement with observed merger fractions demonstrated in § 4.2 above; Hopkins et al. (2007a, 2008b), Bundy et al. (2009), and Bell et al. (2006a) have demonstrated that observed major merger fractions are sufficient, within a factor∼ 2, to account for the observed growth…”
DISSIPATION AND EXTRA LIGHT IN GALACTIC NUCLEI. IV. EVOLUTION IN THE SCALING RELATIONS OF SPHEROIDS (2008, background): “…still relatively small, so this is consistent with the∼ 1 major dry merger sincez ∼ 1 which direct observations of dry merging pairs (van Dokkum 2005; Bell et al. 2006; Lin et al. 2008) and constraints from mass function evolution (Bundy et al. 2005; Borch et al. 2006; Pérez-González et al.…”
The Fundamental Scaling Relations of Elliptical Galaxies (2005, background): “The recent observations suggesting that elliptical galaxies undergo 0.5–1 such mergers at redshifts z < 1 (Bell et al. 2006; van Dokkum 2005) may require such behavior as the tight local FP relation observationally limits the possible importance of scenarios that substantially increase the FP…”
The effect of mass ratio on the morphology and time-scales of disc galaxy mergers: Effect of mass ratio on merger morphology (2009, background): “…have not explored the properties of mixed-morphology mergers (e.g. disc-spheroid: Johansson et al. 2009) or spheriod-spheroid mergers (e.g. Naab, Khochfar, & Burkert 2006; Bell et al. 2006; BoylanKolchin, Ma, & Quataert 2005), which are likely to give shorter morphological disturbance time-scales.”