Early and Rapid Merging as a Formation Mechanism of Massive Galaxies: Empirical Constraints

Conselice, Christopher J.

doi:10.1086/499067

Cited by 196 publications

(408 citation statements)

References 106 publications

(230 reference statements)

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“…However, we note that our MASSIV data seem to indicate a flattening of the merger rate's evolution beyond z ∼ 1. Previous studies from morphological criteria (e.g., Conselice 2003;Conselice et al 2008) and from photometric pairs (Ryan et al 2008) suggest that the power-law parametrization is not longer valid at z 1.5, where a lower merger fraction than expected from the low-z evolution is measured, possibly indicating a maximum in the major merger rate at z ∼ 2 (e.g., Conselice 2006;Ryan et al 2008;López-Sanjuan et al 2009b). Our new measurements agree with this picture and measurements from spectroscopic close pairs beyond z ∼ 1.5 are needed to test the early evolution of the merger fraction.…”

Section: The Redshift Evolution Of the Gas-rich Major Merger Ratementioning

confidence: 97%

MASSIV: Mass Assembly Survey with SINFONI in VVDS

López-Sanjuán

Fèvre

Tasca

et al. 2013

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Context. The contribution of the merging process to the early phase of galaxy assembly at z > 1 and, in particular, to the build-up of the red sequence, still needs to be accurately assessed. Aims. We aim to measure the major merger rate of star-forming galaxies at 0.9 < z < 1.8, using close pairs identified from integral field spectroscopy (IFS). Methods. We use the velocity field maps obtained with SINFONI/VLT on the MASSIV sample, selected from the star-forming population in the VVDS. We identify physical pairs of galaxies from the measurement of the relative velocity and the projected separation (r p ) of the galaxies in the pair. Using the well constrained selection function of the MASSIV sample, we derive at a mean redshift up to z = 1.54 the gas-rich major merger fraction (luminosity ratio μ = L 2 /L 1 ≥ 1/4), and the gas-rich major merger rate using merger time scales from cosmological simulations. Results. We find a high gas-rich major merger fraction of 20.8 +15.2 −6.8 %, 20.1 +8.0 −5.1 %, and 22.0 +13.7 −7.3 % for close pairs with r p ≤ 20 h −1 kpc in redshift ranges z = [0.94, 1.06], [1.2, 1.5), and [1.5, 1.8), respectively. This translates into a gas-rich major merger rate of 0.116 +0.084 −0.038 Gyr −1 , 0.147 +0.058 −0.037 Gyr −1 , and 0.127 +0.079 −0.042 Gyr −1 at z = 1.03, 1.32, and 1.54, respectively. Combining our results with previous studies at z < 1, the gas-rich major merger rate evolves as (1 + z) n , with n = 3.95 ± 0.12, up to z = 1.5. From these results we infer that ∼35% of the star-forming galaxies with stellar masses M = 10 10 −10 10.5 M have undergone a major merger since z ∼ 1.5. We develop a simple model that shows that, assuming that all gas-rich major mergers lead to early-type galaxies, the combined effect of gas-rich and dry mergers is able to explain most of the evolution in the number density of massive early-type galaxies since z ∼ 1.5, with our measured gas-rich merger rate accounting for about two-thirds of this evolution. Conclusions. Merging of star-forming galaxies is frequent at around the peak in star formation activity. Our results show that gasrich mergers make an important contribution to the growth of massive galaxies since z ∼ 1.5, particularly on the build-up of the red sequence.

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Section: The Redshift Evolution Of the Gas-rich Major Merger Ratementioning

confidence: 97%

MASSIV: Mass Assembly Survey with SINFONI in VVDS

López-Sanjuán

Fèvre

Tasca

et al. 2013

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“…Although it is possible that in some high mass ratio mergers the low mass companion will become highly asymmetric while the high mass companion will not, we statistically correct the merger fraction to select only major mergers, so the assumption that fam = 1 is still reasonable. Following the definition in Conselice (2006), the fraction of galaxies in major mergers is given by…”

Section: Definitionsmentioning

confidence: 99%

“…Note that this is inverse of the notation used in Conselice (2006), but the same as Hopkins et al (2010b).…”

Section: Definitionsmentioning

confidence: 99%

“…Studies which use N-body simulations and do not consider the effects of changing gas fraction (Conselice 2006;Lotz et al 2010a) find that the CAS system is most sensitive to mergers where the galaxies are of similar mass (mass ratios of <4:1). In these simulations minor mergers with greater mass ratios were generally not detected as mergers in CAS, or were for only a very short period of time compared to major mergers.…”

Section: Detection Of Minor Mergersmentioning

confidence: 99%

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Galaxy And Mass Assembly (GAMA): refining the local galaxy merger rate using morphological information

Casteels

Conselice

Bamford

et al. 2014

Monthly Notices of the Royal Astronomical Society

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We use the Galaxy And Mass Assembly (GAMA) survey to measure the local Universe mass dependent merger fraction and merger rate using galaxy pairs and the CAS structural method, which identifies highly asymmetric merger candidate galaxies. Our goals are to determine which types of mergers produce highly asymmetrical galaxies, and to provide a new measurement of the local galaxy major merger rate. We examine galaxy pairs at stellar mass limits down to M * = 10 8 M ⊙ with mass ratios of <100:1 and line of sight velocity differences of ∆V < 500 km s −1 . We find a significant increase in mean asymmetries for projected separations less than the sum of the individual galaxy's Petrosian 90 radii. For systems in major merger pairs with mass ratios of <4:1 both galaxies in the pair show a strong increase in asymmetry, while in minor merger systems (with mass ratios of >4:1) the lower mass companion becomes highly asymmetric, while the larger galaxy is much less affected. The fraction of highly asymmetric paired galaxies which have a major merger companion is highest for the most massive galaxies and drops progressively with decreasing mass. We calculate that the mass dependent major merger fraction is fairly constant at ∼ 1.3 − 2% between 10 9.5 < M * < 10 11.5 M ⊙ , and increases to ∼ 4% at lower masses. When the observability time scales are taken into consideration, the major merger rate is found to approximately triple over the mass range we consider. The total co-moving volume major merger rate over the range 10 8.0 < M * < 10 11.5 M ⊙ is (1.2 ± 0.5) × 10 −3 h 3 70 Mpc −3 Gyr −1 . Key words: galaxies: general -galaxies: evolution -galaxies: interactions -galaxies: statistics ⋆ E-mail: kcasteels@gmail.com (KRVC) 2 K. R. V. Casteels et al.

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“…These results notwithstanding, according to current formation scenarios, merging has played an important role in the mass assembly of most of the local massive elliptical galaxies. Observations and theory suggest that, first, violent mergers at high z have transformed most of the available gas into stars, and, later on, these systems might have evolved through gas-free (the so-called dry) mergers (Conselice 2006; see otherwise Scarlata et al 2007). …”

Section: Introductionmentioning

confidence: 99%

Shape and kinematics of elliptical galaxies: evolution due to merging at z ${<}$ 1.5

González-García¹,

Oñorbe²,

Domínguez-Tenreiro³

et al. 2009

A&A

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Aims. We investigate the evolution in the shape and kinematics of elliptical galaxies in a cosmological framework. Methods. We identified relaxed, elliptical-like objects (ELOs) at redshifts z = 0, z = 0.5, z = 1 and z = 1.5 within a set of hydrodynamic, self-consistent simulations completed for a concordance cosmological model. Results. The population of elliptical systems that we analysed evolve systematically with time becoming rounder in general by z = 0 and also more velocity dispersion supported. We found that this is due primarily to major dry mergers where only a modest amount of angular momentum is involved in the merger event. Despite the general trend, in a significant number of cases the merger event involves a relatively high amount of specific angular momentum, which causes the system in general to acquire higher rotational support and/or a more oblate shape. These evolutionary patterns persist when we study our systems in projection, in simulating true observations, and thus should be evident in future observations.

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Early and Rapid Merging as a Formation Mechanism of Massive Galaxies: Empirical Constraints

Cited by 196 publications

References 106 publications

MASSIV: Mass Assembly Survey with SINFONI in VVDS

MASSIV: Mass Assembly Survey with SINFONI in VVDS

Galaxy And Mass Assembly (GAMA): refining the local galaxy merger rate using morphological information

Shape and kinematics of elliptical galaxies: evolution due to merging at z ${<}$ 1.5

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