STRUCTURE AND FORMATION OF ELLIPTICAL AND SPHEROIDAL GALAXIES

By J. Kormendy, D. Fisher, M. Cornell, R. Bender. 2008

764 citations recorded by the source corpus.

New surface photometry of all known elliptical galaxies in the Virgo cluster is combined with published data to derive composite profiles of brightness, ellipticity, position angle, isophote shape, and color over large radius ranges. These provide enough leverage to show that Sérsic log I ∝ r1/n functions fit the brightness profiles I(r) of nearly all ellipticals remarkably well over large dynamic ranges. Therefore, we can confidently identify departures from these profiles that are diagnostic of galaxy formation. Two kinds of departures are seen at small radii. All 10 of our ellipticals with total absolute magnitudes MVT ⩽ −21.66 have cuspy cores—“missing light”—at small radii. Cores are well known and naturally scoured by binary black holes (BHs) formed in dissipationless (“dry”) mergers. All 17 ellipticals with −21.54 ⩽ MVT ⩽ −15.53 do not have cores. We find a new distinct component in these galaxies: all coreless ellipticals in our sample have extra light at the center above the inward extrapolation of the outer Sérsic profile. In large ellipticals, the excess light is spatially resolved and resembles the central components predicted in numerical simulations of mergers of galaxies that contain gas. In the simulations, the gas dissipates, falls toward the center, undergoes a starburst, and builds a compact stellar component that, as in our observations, is distinct from the Sérsic-function main body of the elliptical. But ellipticals with extra light also contain supermassive BHs. We suggest that the starburst has swamped core scouring by binary BHs. That is, we interpret extra light components as a signature of formation in dissipative (“wet”) mergers. Besides extra light, we find three new aspects to the (“E–E”) dichotomy into two types of elliptical galaxies. Core galaxies are known to be slowly rotating, to have relatively anisotropic velocity distributions, and to have boxy isophotes. We show that they have Sérsic indices n > 4 uncorrelated with MVT. They also are α-element enhanced, implying short star-formation timescales. And their stellar populations have a variety of ages but mostly are very old. Extra light ellipticals generally rotate rapidly, are more isotropic than core Es, and have disky isophotes. We show that they have n ≃ 3 ± 1 almost uncorrelated with MVT and younger and less α-enhanced stellar populations. These are new clues to galaxy formation. We suggest that extra light ellipticals got their low Sérsic indices by forming in relatively few binary mergers, whereas giant ellipticals have n > 4 because they formed in larger numbers of mergers of more galaxies at once plus later heating during hierarchical clustering. We confirm that core Es contain X-ray-emitting gas whereas extra light Es generally do not. This leads us to suggest why the E–E dichotomy arose. If energy feedback from active galactic nuclei (AGNs) requires a “working surface” of hot gas, then this is present in core galaxies but absent in extra light galaxies. We suggest that AGN energy feedback is a strong function of galaxy mass: it is weak enough in small Es not to prevent merger starbursts but strong enough in giant Es and their progenitors to make dry mergers dry and to protect old stellar populations from late star formation. Finally, we verify that there is a strong dichotomy between elliptical and spheroidal galaxies. Their properties are consistent with our understanding of their different formation processes: mergers for ellipticals and conversion of late-type galaxies into spheroidals by environmental effects and by energy feedback from supernovae. In an appendix, we develop machinery to get realistic error estimates for Sérsic parameters even when they are strongly coupled. And we discuss photometric dynamic ranges necessary to get robust results from Sérsic fits.

Subfields: Astronomy and Astrophysics, Instrumentation

View Paper: https://www.semanticscholar.org/paper/7463a66b7392935ec6789433211c4a92021035c2

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Citations in the corpus

The ATLAS3D project – XX. Mass–size and mass–σ distributions of early-type galaxies: bulge fraction drives kinematics, mass-to-light ratio, molecular gas fraction and stellar initial mass function (2012, background): “A caveat is that significant biases may still exist in the high-redshift photometry (Mancini et al. 2010), considering that systematic differences of up to a factor of 2 exist even on well-observed ETGs in the nearby Universe (Kormendy et al. 2009; Chen et al. 2010; Paper I).”
How do minor mergers promote inside-out growth of ellipticals, transforming the size, density profile and dark matter fraction? (2012, methodology): “…the light profiles of elliptical galaxies is an important parameter as it correlates with other observed properties of elliptical galaxies, such as the effective radius re, the total luminosity and the stellar mass (Caon et al. 1993; Nipoti et al. 2003; Naab & Trujillo 2006; Kormendy et al. 2009).”
MERGERS AND BULGE FORMATION IN ΛCDM: WHICH MERGERS MATTER? (2009, methodology): “…et al. (2009a,e, 2008a) develop and test an empirical method to estimate the dissipational mass fraction in observed local el- lipticals, and apply this to a wide range of observed ellipticals with a combination of HST and ground-based data from Kormendy et al. (2009) and Lauer et al. (2007).”
Kinematic properties of early-type galaxy haloes using planetary nebulae (2008, methodology): “We used the extended ground-based photometry given by Kormendy et al. (2009), which shows a very good agreement between stellar surface brightness and PNe number density.”
STELLAR KINEMATICS OF z ∼ 2 GALAXIES AND THE INSIDE-OUT GROWTH OF QUIESCENT GALAXIES, (2012, background): “Even though galaxies at low redshift are well-fitted by single Sérsic profiles (e.g.,Kormendy et al. 2009), this does not necessarily have to be true for galaxies atz ∼ 2.”
THE COSMOLOGICAL SIZE AND VELOCITY DISPERSION EVOLUTION OF MASSIVE EARLY-TYPE GALAXIES (2011, background): “…and the subsequent growth by stellar mergers is in agreement with predictions from semianalytical models (Kauffmann 1996; Khochfar & Silk 2006a; De Lucia et al. 2006; De Lucia & Blaizot 2007; Guo & White 2008; Shankar et al. 2010a,b) and the assembly scenario discussed in Kormendy et al. (2009).”
ANGULAR MOMENTUM AND GALAXY FORMATION REVISITED (2012, methodology): “Examining several galaxies in common between the samples, we find that the discrepancy persists for cases where we have made use of high-quality photometric analyses (Kormendy et al. 2009).”
On the correlations between galaxy properties and supermassive black hole mass (2011, methodology): “The model decompositions for few elliptical galaxies (NGC 4473, 4636, 4649) were significantly improved by including a disc component, as found in a few other elliptical galaxies (Kormendy et al. 2009; McDonald, Courteau & Tully 2009).”
The Evolution of Galaxy Structure Over Cosmic Time (2014, methodology): “While there is a large amount of work done on the structures and morphologies of galaxies in the nearby universe (e.g., see Kormendy et al. 2009; Buta 2013), it is difficult to investigate more than the very basics of structure and morphology when studying distant galaxies.”
Physical properties and environments of nearby galaxies (2009, methodology): “For elliptical galaxies, we refer the reader to multiple other reviews examining their more detailed properties, including their stellar populations (Renzini 2006), their structure and classification (Kormendy et al. 2009), and their hot gas content (Mathews & Brighenti 2003).”
Nuclear star clusters (2009, background): “This is especially true in more massive ellipticals and bulge-dominated early-type spirals with steep light profiles (e.g., Carollo et al. 2002; Côté et al. 2007; Kormendy et al. 2009).”
WHAT DOES A SUBMILLIMETER GALAXY SELECTION ACTUALLY SELECT? THE DEPENDENCE OF SUBMILLIMETER FLUX DENSITY ON STAR FORMATION RATE AND DUST MASS (2010, background): “All of these objects exhibit evidence of “excess” central light (Rothberg & Joseph 2004; Kormendy et al. 2009), indicative of relic starbursts (Mihos & Hernquist 1994, 1996) caused by merger-driven inflows of gas (Barnes & Hernquist 1991, 1996).”
THE MBH–LSPHEROID RELATION AT HIGH AND LOW MASSES, THE QUADRATIC GROWTH OF BLACK HOLES, AND INTERMEDIATE-MASS BLACK HOLE CANDIDATES (2012, background): “1–2) between dwarf and ordinary elliptical galaxies (Kormendy 1985; Kormendy et al. 2009).”
Galaxy Masses: A Review (2013, background): “It is thus common to retrieve specific radii values differing by factors of two or more for the same well-studied systems (e.g. Kormendy et al. 2009; Chen et al. 2010).”
THE BLACK HOLE MASS IN M87 FROM GEMINI/NIFS ADAPTIVE OPTICS OBSERVATIONS (2011, methodology): “Kinematic Fits To align the data with the kinematic axis at large radius from the fit of Kormendy et al. (2009), we take a position angle of -25◦ (E of N) for the major axis.”
BULGES OF NEARBY GALAXIES WITH SPITZER: SCALING RELATIONS IN PSEUDOBULGES AND CLASSICAL BULGES (2010, methodology): “We use the elliptical galaxy sample and data from Kormendy et al. (2009).”