Quantifying the impact of mergers on the angular momentum of simulated galaxies

Lagos, Claudia del P.; Stevens, Adam; Bower, Richard G.; Davis, Timothy A.; Contreras, Sergio; Padilla, Nelson; Obreschkow, Danail; Croton, Darren J.; Trayford, James W.; Welker, Charlotte; Theuns, Tom

doi:10.1093/mnras/stx2667

Cited by 145 publications

(130 citation statements)

References 100 publications

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“…As has been shown in previous work (e.g. Lotz et al 2010;Naab et al 2014;Lagos et al 2018;Martin et al 2018), gas-rich mergers will 'spin up' merger remnants, as the gas creates a new rotationally-supported stellar component. As shown graphically in Figure 2 (top row, left-hand column), these gas-rich recent mergers produce an uptick in V /σ, that moves the system from the spheroid to the disc regime.…”

Section: The Dominant Channel Of Massive Disc Formation: Disc Rejuvensupporting

confidence: 58%

Why do extremely massive disc galaxies exist today?

Jackson

Martin

Kaviraj

et al. 2020

Monthly Notices of the Royal Astronomical Society

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Galaxy merger histories correlate strongly with stellar mass, largely regardless of morphology. Thus, at fixed stellar mass, spheroids and discs share similar assembly histories, both in terms of the frequency of mergers and the distribution of their mass ratios. Since mergers are the principal drivers of disc-to-spheroid morphological transformation, and the most massive galaxies typically have the richest merger histories, it is surprising that discs exist at all at the highest stellar masses (e.g. beyond the knee of the mass function). Using Horizon-AGN, a cosmological hydro-dynamical simulation, we show that extremely massive (M * > 10 11.4 M ) discs are created via two channels. In the primary channel (accounting for 70% of these systems and 8% of massive galaxies) the most recent, significant merger (stellar mass ratio > 1:10) between a massive spheroid and a gas-rich satellite 'spins up' the spheroid by creating a new rotational stellar component, leaving a massive disc as the remnant. In the secondary channel (accounting for 30% of these systems and 3% of massive galaxies), a system maintains a disc throughout its lifetime, due to an anomalously quiet merger history. Not unexpectedly, the fraction of massive discs is larger at higher redshift, due to the Universe being more gas-rich. The morphological mix of galaxies at the highest stellar masses is, therefore, a strong function of the gas fraction of the Universe. Finally, these massive discs have similar black-hole masses and accretion rates to massive spheroids, providing a natural explanation for why a minority of powerful AGN are surprisingly found in disc galaxies.

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Section: The Dominant Channel Of Massive Disc Formation: Disc Rejuvensupporting

confidence: 58%

Why do extremely massive disc galaxies exist today?

Jackson

Martin

Kaviraj

et al. 2020

Monthly Notices of the Royal Astronomical Society

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“…Darg et al (2010) studied merging galaxies with tidal features identified through the Galaxy Zoo project and concluded that the effects of mergers on spiral galaxies were much more dramatic (eroding their gas and angular momentum supplies and strongly enhancing their SFRs), so disturbed spiral galaxies were more easily observable than disturbed ellipticals. This result may also reflect the fact that modest gas fractions are expected to lead to more spheroidal remnant morphologies (Naab et al 2006;Duc & Renaud 2013), while gas-rich mergers should yield diskdominated remnants (Lotz et al 2008;Hopkins et al 2009;Lagos et al 2018).…”

Section: Introductionmentioning

confidence: 99%

The Origin of Faint Tidal Features around Galaxies in the RESOLVE Survey

Hood

Kannappan

Stark

et al. 2018

ApJ

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We study tidal features around galaxies in the REsolved Spectroscopy Of a Local VolumE (RESOLVE) survey. Our sample consists of 1048 RESOLVE galaxies that overlap with the DECam Legacy Survey, which reaches an r-band 3σ depth of ∼27.9 mag arcsec −2 for a 100 arcsec 2 feature. Images were masked, smoothed, and inspected for tidal features such as streams, shells, or tails/arms. We find tidal features in 17 ±2 % of our galaxies, setting a lower limit on the true frequency. The frequency of tidal features in the gas-poor (gas-to-stellar mass ratio <0.1) subsample is lower than in the gas-rich subsample (13 ±3 % versus 19 ±2 %). Within the gas-poor subsample, galaxies with tidal features have higher stellar and halo masses, ∼3× closer distances to nearest neighbors (in the same group), and possibly fewer group members at fixed halo mass than galaxies without tidal features, but similar specific star formation rates. These results suggest tidal features in gas-poor galaxies are typically streams/shells from dry mergers or satellite disruption. In contrast, the presence of tidal features around gas-rich galaxies does not correlate with stellar or halo mass, suggesting these tidal features are often tails/arms from resonant interactions. Similar to tidal features in gas-poor galaxies, tidal features in gas-rich galaxies imply 1.7× closer nearest neighbors in the same group; however, they are associated with diskier morphologies, higher star formation rates, and higher gas content. In addition to interactions with known neighbors, we suggest that tidal features in gas-rich galaxies may arise from accretion of cosmic gas and/or gas-rich satellites below the survey limit.

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“…with comparable values of xi) have much stronger ramifications than minor ones in terms of restructuring the dark matter (Ludlow et al 2012;Klypin et al 2016) and transforming the dynamics and kinematics of galaxies (e.g. Conselice 2014; Lagos et al 2018a). Translated to our problem, this means that more similar values {xi} should lead to higher values of s than more diverse sets.…”

Section: Self-similar Treesmentioning

confidence: 99%

“…In the CDM framework of structure formation, the stellar content of galaxies grows via two processes: internally by gas cooling and star formation in the host halo; and externally by accretion of other galaxies (Guo & White 2008;Zolotov et al 2009;Oser et al 2010;Pillepich et al 2015). The balance between these two processes affects a number of key observables, such as the morphology (Kormendy et al 2009), the amount of kinematic support (Lagos et al 2018a) and the structure of the stellar halo (Helmi et al 2018). Since the coalescence of galaxies is normally triggered by an earlier merger of their haloes, the hierarchical assembly of haloes is pivotal to understanding the evolution of galaxies (Toomre & Toomre 1972;White & Frenk 1991;Conselice 2014).…”

Section: Introductionmentioning

confidence: 99%

Characterizing the structure of halo merger trees using a single parameter: the tree entropy

Obreschkow

Elahi

Lagos

et al. 2020

Monthly Notices of the Royal Astronomical Society

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Linking the properties of galaxies to the assembly history of their dark matter haloes is a central aim of galaxy evolution theory. This paper introduces a dimensionless parameter s ∈ [0, 1], the 'tree entropy', to parametrise the geometry of a halo's entire mass assembly hierarchy, building on a generalisation of Shannon's information entropy. By construction, the minimum entropy (s = 0) corresponds to smoothly assembled haloes without any mergers. In contrast, the highest entropy (s = 1) represents haloes grown purely by equal-mass binary mergers. Using simulated merger trees extracted from the cosmological N -body simulation SURFS, we compute the natural distribution of s, a skewed bell curve peaking near s = 0.4. This distribution exhibits weak dependences on halo mass M and redshift z, which can be reduced to a single dependence on the relative peak height δ c /σ(M, z) in the matter perturbation field. By exploring the correlations between s and global galaxy properties generated by the SHARK semianalytic model, we find that s contains a significant amount of information on the morphology of galaxies -in fact more information than the spin, concentration and assembly time of the halo. Therefore, the tree entropy provides an information-rich link between galaxies and their dark matter haloes.

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Quantifying the impact of mergers on the angular momentum of simulated galaxies

Cited by 145 publications

References 100 publications

Why do extremely massive disc galaxies exist today?

Why do extremely massive disc galaxies exist today?

The Origin of Faint Tidal Features around Galaxies in the RESOLVE Survey

Characterizing the structure of halo merger trees using a single parameter: the tree entropy

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