The Structure of Classical Bulges and Pseudobulges: The Link Between Pseudobulges and Sérsic Index

Fisher, David B.; Drory, Niv

doi:10.1088/0004-6256/136/2/773

Cited by 354 publications

(586 citation statements)

References 73 publications

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“…The correlation between the intrinsic shape of bulges with n ≤ 2 and those in galaxies with B/T ≤ 0.3 and between bulges with n > 2 and those in galaxies with B/T > 0.3 agrees with the correlation between the bulge Sérsic index and bulge-to-total ratio of the host galaxy, as found by Drory & Fisher (2007) and Fisher & Drory (2008).…”

Section: Discussionsupporting

confidence: 85%

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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Section: Discussionsupporting

confidence: 85%

Structural properties of disk galaxies

Méndez-Abreu

Simonneau

Aguerri

et al. 2010

A&A

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“…A sersic index n = 4 corresponds to the de-Vaucouleurs profile, typical of spheroids and classical bulges. Pseudobulges, on the other hand, have less-concentrated profiles, typically with a low sersic index, n < 2 (Kormendy & Kennicutt 2004;Laurikainen et al 2007;Fisher & Drory 2008;Gadotti 2009). The sersic fitting of the profiles is done using a Monte Carlo, least-squared fitting that samples the parameter space randomly and uniformly, so the probability that the solution converges to wrong secondary minima is low.…”

Section: Stellar Surface Density Profiles and Sersic Fittingmentioning

confidence: 99%

Early formation of massive, compact, spheroidal galaxies with classical profiles by violent disc instability or mergers

Ceverino

Dekel

Tweed

et al. 2015

Monthly Notices of the Royal Astronomical Society

105

100

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We address the formation of massive stellar spheroids between redshifts z = 4 and 1 using a suite of AMR hydro-cosmological simulations. The spheroids form as bulges, and the spheroid mass growth is partly driven by violent disc instability (VDI) and partly by mergers. A kinematic decomposition to disc and spheroid yields that the mass fraction in the spheroid is between 50% and 90% and is roughly constant in time, consistent with a cosmological steady state of VDI discs that are continuously fed from the cosmic web. The density profile of the spheroid is typically "classical", with a Sersic index n = 4.5 ± 1, independent of whether it grew by mergers or VDI and independent of the feedback strength. The disc is characterized by n = 1.5±0.5, and the whole galaxy by n = 3±1. The high-redshift spheroids are compact due to the dissipative inflow of gas and the high universal density. The stellar surface density within the effective radius of each galaxy as it evolves remains roughly constant in time after its first growth. For galaxies of a fixed stellar mass, the surface density is higher at higher redshifts.

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“…In the model, this is closely related to the origin of galactic bulges. Most of the total stellar mass in bulges is in "classical" bulges, which a wide range of observational and theoretical constraints indicate formed in violent mergers (see references in § 4.2 above; for reviews, see Kormendy & Kennicutt 2004;Kormendy & Bender 2012;Fisher & Drory 2008;Balcells et al 2007;Gadotti 2009). However, even if most of the bulge is formed in such an event, it is primarily via the transformation of pre-existing stars from a disk to a bulge via violent relaxation.…”

Section: How Does This Relate To Star Formation?mentioning

confidence: 99%

“…Kormendy & Kennicutt 2004;Kormendy & Bender 2012;Fisher 2006;Fisher & Drory 2008;Balcells et al 2007;Gadotti 2009). Verifying that this holds for the AGN hosts themselves (rather than simply for their "relics" at z = 0, would represent a direct and very powerful confirmation of the models.…”

Section: Observational Predictionsmentioning

confidence: 99%

Do we expect most AGN to live in discs?

Hopkins¹,

Kocevski²,

Bundy³

2014

Monthly Notices of the Royal Astronomical Society

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Recent observations have indicated that a large fraction of the low to intermediate luminosity AGN population lives in disk-dominated hosts, while the more luminous quasars live in bulge-dominated hosts (that may or may not be major merger remnants), in conflict with some previous model predictions. We therefore build and compare a semi-empirical model for AGN fueling which accounts for both merger and non-merger "triggering." In particular, we show that the "stochastic accretion" model -in which fueling in disk galaxies is essentially a random process arising whenever dense gas clouds reach the nucleusprovides a good match to the present observations at low/intermediate luminosities. However it falls short of the high-luminosity population. We combine this with models for major merger-induced AGN fueling, which lead to rarer but more luminous events, and predict the resulting abundance of disk-dominated and bulge-dominated AGN host galaxies as a function of luminosity and redshift. We compile and compare observational constraints from z ∼ 0 − 2. The models and observations generically show a transition from disk to bulge dominance in hosts near the Seyfert-quasar transition, at all redshifts. "Stochastic" fueling dominates AGN by number (dominant at low luminosity), and dominates BH growth below the "knee" in the present-day BH mass function ( 10 7 M ). However it accounts for just ∼ 10% of BH mass growth at masses 10 8 M . In total, fueling in disky hosts accounts for ∼ 30% of the total AGN luminosity density/BH mass density. The combined model also accurately predicts the AGN luminosity function and clustering/bias as a function of luminosity and redshift; however, we argue that these are not sensitive probes of BH fueling mechanisms.

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The Structure of Classical Bulges and Pseudobulges: The Link Between Pseudobulges and Sérsic Index

Cited by 354 publications

References 73 publications

Structural properties of disk galaxies

Structural properties of disk galaxies

Early formation of massive, compact, spheroidal galaxies with classical profiles by violent disc instability or mergers

Do we expect most AGN to live in discs?

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