The Kinematic Structure of Merger Remnants

Cox, Thomas J.; Dutta, Sourish; Matteo, Tiziana Di; Hernquist, Lars; Hopkins, Philip F.; Robertson, Brant; Springel, Volker

doi:10.1086/507474

Cited by 371 publications

(565 citation statements)

References 99 publications

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“…Inflow on to the black hole requires further removal of angular momentum, which becomes efficient only after most of the gas has been consumed by star formation activity (Hopkins 2012), introducing a time lag between the onset of star formation and the triggering of the AGN. Realistic hydro-dynamical models appear to naturally produce a time lag that is qualitatively similar to what is observed in nearby ETGs (Hopkins 2012, see also Cox et al 2006.…”

Section: T I M E D E L Ay I N T H E O N S E T O F Ag N a N D I M P L supporting

confidence: 56%

The triggering of local AGN and their role in regulating star formation

Kaviraj

Shabala

Deller

et al. 2015

Mon. Not. R. Astron. Soc.

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We explore the processes that trigger local AGN and the role of these AGN in regulating star formation, using ∼550 nearby galaxies observed by the mJy Imaging VLBA Exploration at 20 cm (mJIVE) survey. The 10 7 K brightness temperature required for an mJIVE detection cannot be achieved via star formation alone, allowing us to unambiguously detect nearby radio AGN and study their role in galaxy evolution. Radio AGN are an order of magnitude more common in early-type galaxies (ETGs) than in their late-type counterparts. The VLBI-detected ETGs in this study have a similar stellar mass distribution to their undetected counterparts, are typically not the central galaxies of clusters and exhibit merger fractions that are significantly higher than in the average ETG. This suggests that these radio AGN (which have VLBI luminosities >10 22 W Hz −1 ) are primarily fuelled by mergers, and not by internal stellar mass-loss or cooling flows. Our radio AGN are a factor of ∼3 times more likely to reside in the UV-optical red sequence than the average ETG. Furthermore, typical AGN lifetimes (a few 10 7 yr) are much shorter than the transit times from blue cloud to red sequence (∼1.5 Gyr). This indicates that nearby (merger-triggered) AGN appear several dynamical time-scales into the associated star formation episode. This implies that such AGN typically couple only to residual gas, at a point where star formation has already declined significantly, and are, therefore, unlikely to play a significant role in regulating the star formation episode.

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Section: T I M E D E L Ay I N T H E O N S E T O F Ag N a N D I M P L supporting

confidence: 56%

The triggering of local AGN and their role in regulating star formation

Kaviraj

Shabala

Deller

et al. 2015

Mon. Not. R. Astron. Soc.

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“…Cox et al (2006) studied the structure of spheroidal remnants formed by major dissipationless and dissipational mergers of disk galaxies. Dissipationless remnants are triaxial with a tendency to be more prolate, whereas dissipational remnants are triaxial and tend to be much closer to oblate.…”

Section: Discussionmentioning

confidence: 99%

Structural properties of disk galaxies

Méndez-Abreu

Simonneau

Aguerri

et al. 2010

A&A

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Context. Knowledge of the intrinsic shapes of galaxy components provides crucial information when constraining phenomena driving their formation and evolution. Aims. We analize the structural parameters of a magnitude-limited sample of 148 unbarred S0-Sb galaxies to derive the intrinsic shape of their bulges. Methods. We developed a new method to derive the intrinsic shapes of bulges based on geometrical relationships between the apparent and intrinsic shapes of bulges and disks. Bulges were assumed to be triaxial ellipsoids sharing the same center and polar axis of their surrounding disks. Disks were assumed to be circular, infinitesimally thin, and to lie on the equatorial plane of bulges. The equatorial ellipticity and intrinsic flattening of bulges were obtained from the length of the apparent major and minor semi-axes of the bulge, the twist angle between the apparent major axis of the bulge and the galaxy line of nodes, and the galaxy inclination. Results. We find that the intrinsic shape is well constrained for a subsample of 115 bulges with favorable viewing angles. A large fraction of them are characterized by an elliptical section (B/A < 0.9). This fraction is 33%, 55%, and 43% if using their maximum, mean, or median equatorial ellipticity, respectively. Most are flattened along their polar axis (C < (A + B)/2). Only 18% of the observed bulges have a probability >50% and none has a probability >90% of being elongated along the polar axis. The distribution of triaxiality is strongly bimodal. This bimodality is driven by bulges with Sérsic index n > 2, or equivalently, by the bulges of galaxies with a bulge-to-total ratio B/T > 0.3. Bulges with n ≤ 2 and with B/T ≤ 0.3 follow a similar distribution, which differs from that of bulges with n > 2 and B/T > 0.3. In particular, bulges with n ≤ 2 and B/T ≤ 0.3 exhibit a larger fraction of oblate axisymmetric (or nearly axisymmetric) bulges, a smaller fraction of triaxial bulges, and fewer prolate axisymmetric (or nearly axisymmetric) bulges with respect to bulges with n > 2 and with B/T > 0.3, respectively. No correlation is found between the intrinsic shape and either the luminosity or velocity dispersion of bulges. Conclusions. According to predictions of the numerical simulations of bulge formation, bulges with n ≤ 2, which show a high fraction of oblate axisymmetric (or nearly axisymmetric) shapes and have B/T ≤ 0.3, may be the result of dissipational minor mergers. Both major dissipational and dissipationless mergers seem to be required to explain the variety of shapes found for bulges with n > 2 and B/T > 0.3.

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“…In turn, this requires an analytical description of such processes to be implemented into existing semi-analytic models (see Baugh 2006 for an introduction) or as sub-grid physics in cosmological simulations. As for the IT scenario, multi-scale high-resolution hydrodynamical N-body simulations are now resolving scales ∼10 pc, showing that collisions efficiently cause most of the gas to flow to the centre on timescales of a few dynamical times (see Hopkins et al 2010 and references therein); analytical -though simplified -or phenomenological descriptions of the inflow determined by mergers have been developed by several authors (see, e.g., Makino & Hut 1997;Cavaliere & Vittorini 2000) and then calibrated and tested against binary hydrodynamic merger simulations (Robertson et al 2006a,b;Cox et al 2006;Hopkins et al 2007b); here the fraction of galactic gas which is able to lose angular momentum and flow to the centre is related to large relative variations ∆ j/ j of the gas specific angular momentum induced by the interactions, which is in turn connected to the mass ratio M /M of the merging partners.…”

Section: Introductionmentioning

confidence: 99%

Triggering active galactic nuclei in hierarchical galaxy formation: disk instability vs. interactions

Menci

Gatti

Fiore

et al. 2014

A&A

141

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Using a state-of-the-art semi analytic model for galaxy formation, we investigated in detail the effects of black hole (BH) accretion triggered by disk instabilities (DI) in isolated galaxies on the evolution of the AGN population. Specifically, we took on, developed, and expanded the Hopkins & Quataert (2011, MNRAS, 411, 1027 model for the mass inflow following disk perturbations, based on a physical description of nuclear inflows and tested against aimed N-body simulations. We compared the evolution of AGN due to such a DI accretion mode with that arising in a scenario where galaxy interactions (IT mode) produce the sudden destabilization of large quantities of gas feeding the AGN; this constitutes the standard AGN feeding mode implemented in the earliest versions of most semi-analytic models. To study the maximal contribution of DI to the evolution of the AGN population, we extended and developed the DI model to assess the effects of changing the assumed disk surface density profile, and to obtain lower limits for the nuclear star formation rates associated to the DI accretion mode. We obtained the following results: i) For AGN with luminosity M 1450 > ∼ −26, the DI mode can provide the BH accretion needed to match the observed AGN luminosity functions up to z ≈ 4.5. In such a luminosity range and redshift, it constitutes a viable candidate mechanism to fuel AGN, and can compete with the IT scenario as the main driver of cosmological evolution of the AGN population. ii) The DI scenario cannot provide the observed abundance of high-luminosity QSO with M 1450 ≤ −26 AGN, as well as the abundance of high-redhshift z > ∼ 4.5 QSO with M 1450 ≤ −24. As found in our earliest works, the IT scenario provides an acceptable match to the observed luminosity functions up to z ≈ 6. iii) The dispersion of the distributions of Eddington ratio λ for low-and intermediate-luminosity AGN (bolometric L AGN = 10 43 −10 45 erg s −1 ) is predicted to be much smaller in the DI scenario compared to the IT mode. iv) The above conclusions concerning the DI mode are robust with respect to the explored variants of the DI model. We discuss the physical origin of our findings. Finally, we discuss how it is possible to pin down the dominant fueling mechanism of AGN in the low-intermediate luminosity range M 1450 > ∼ −26 where the DI and the IT modes are both viable candidates as the main drivers of the AGN evolution. We show that an interesting discriminant could be provided by the fraction of AGN with high Eddington ratios λ ≥ 0.5, since it increases with luminosity in the IT case, while the opposite is true in the DI scenario.

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The Kinematic Structure of Merger Remnants

Cited by 371 publications

References 99 publications

The triggering of local AGN and their role in regulating star formation

The triggering of local AGN and their role in regulating star formation

Structural properties of disk galaxies

Triggering active galactic nuclei in hierarchical galaxy formation: disk instability vs. interactions

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