DISSIPATION AND EXTRA LIGHT IN GALACTIC NUCLEI. II. “CUSP” ELLIPTICALS

By P. Hopkins, Thomas J. Cox, S. Dutta, L. Hernquist, J. Kormendy, Tod R. Lauer. 2008

195 citations recorded by the source corpus.

We study the origin and properties of “extra” or “excess” central light in the surface brightness profiles of cusp or power-law elliptical galaxies. Dissipational mergers give rise to two-component profiles: an outer profile established by violent relaxation acting on stars already present in the progenitor galaxies prior to the final stages of the merger, and an inner stellar population comprising the extra light, formed in a compact central starburst. By combining a large set of hydrodynamical simulations with data that span a broad range of profiles at various masses, we show that observed cusp ellipticals appear consistent with the predicted “extra light” structure, and we use our simulations to motivate a two-component description of the observations that allows us to examine how the properties and mass of this component scale with, e.g., the mass, gas content, and other properties of the galaxies. We show how to robustly separate the physically meaningful extra light and outer, violently relaxed profile, and demonstrate that the observed cusps and “extra light” are reliable tracers of the degree of dissipation in the spheroid-forming merger. We show that the typical degree of dissipation is a strong function of stellar mass, roughly tracing the observed gas fractions of disks of the same mass over the redshift range z ∼ 0–2. We demonstrate a correlation between the strength of this component and effective radius at fixed mass, in the sense that systems with more dissipation are more compact, sufficient to explain the discrepancy in the maximum phase-space and mass densities of ellipticals and their progenitor spirals. We show that the outer shape of the light profile in simulated and observed systems (when fit to properly account for the central light) does not depend on mass, with a mean outer Sérsic index ∼2.5. We also explore how this relates to, e.g., the shapes, kinematic properties, and stellar population gradients of ellipticals. Extra light contributes to making remnants rounder and diskier, and imprints stellar population gradients. Simulations with the gas content needed to match observed surface brightness profiles reproduce the observed age, metallicity, and color gradients of cusp ellipticals, and we make predictions for how these can be used as tracers of the degree of dissipation in spheroid formation.

Subfields: Astronomy and Astrophysics, Instrumentation

View Paper: https://www.semanticscholar.org/paper/1992e177e126d9b80e2ede357e90360ac3e0a1c1

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Citations in the corpus

A model for cosmological simulations of galaxy formation physics: multi-epoch validation (2013, background): “Such an approach for simulations with an unresolved ISM structure is very common (e.g., Ascasibar et al. 2002; Springel & Hernquist 2003a; Springel et al. 2005a; Robertson et al. 2006; Schaye & Dalla Vecchia 2008; Dubois & Teyssier 2008; Hopkins et al. 2008, 2009a,b; Few et al. 2012).”
The ATLAS3D project – III. A census of the stellar angular momentum within the effective radius of early‐type galaxies: unveiling the distribution of fast and slow rotators (2011, background): “As the orbital angular momentum for a (binary) merger event is often the main contributor (Khochfar & Burkert 2006), major mergers can form FRs (Paper VI; see also Springel & Hernquist 2005) even from slowly rotating galaxy progenitors (Di Matteo et al. 2009), the outer structure being generally mor”
How do massive black holes get their gas (2009, methodology): “This process has been described in detail in e.g. Hopkins et al. (2009c) and references therein, but for completeness we briefly summarize the important physics.”
THE METALLICITY EVOLUTION OF INTERACTING GALAXIES (2011, background): “These increases in stellar metallicity are relics from the merger-driven starbursts that leave behind central stellar cusps in merger remnants (Mihos & Hernquist 1994a; Hopkins et al. 2008) and elliptical galaxies (Hopkins et al. 2009a,c).”
An analytic model of angular momentum transport by gravitational torques: from galaxies to massive black holes (2010, background): “We find reasonable consistency with our simulation results and the profiles of observed cusp ellipticals by taking ηb ≈ ηd ≈ 1/2 over this radial range (see e.g. Lauer et al. 2007; Hopkins et al. 2009a).”
The SAURON project – XVII. Stellar population analysis of the absorption line strength maps of 48 early-type galaxies (2010, background): “The metallicity gradients are predicted to be strongly correlated with the efficiency of the dissipative process, and to only weakly depend on the remnant mass (Kobayashi 2004; Hopkins et al. 2009a, b).”
ANGULAR MOMENTUM AND GALAXY FORMATION REVISITED (2012, methodology): “…Sérsic fits, and we take the (ae, n) values according to the following priority: detailed photometric analysis in individual galaxy papers (e.g., Napolitano et al. 2009); the Kormendy et al. (2009) tabulation for Virgo galaxies; Hopkins et al. (2009a); Hopkins et al. (2009b); D’Onofrio (2001).”
Compact high-redshift galaxies are the cores of the most massive present-day spheroids (2009, background): “This is a relatively efficient channel for size–mass evolution, yielding a factor of several size evolution with only a factor of 1.5–2 increase in stellar mass (Hopkins et al. 2009d).”
ON SIZES, KINEMATICS, M/L GRADIENTS, AND LIGHT PROFILES OF MASSIVE COMPACT GALAXIES AT z ∼ 2 (2010, methodology): “…later times, they find that minor and gas-poor merging forms an efficient means to build up an envelope around this core (see also Section 6.3 of this paper, and Hopkins et al. 2009a).4 In the scenario investigated in this paper, the initial dissipational event occurs in the form of a major merger.”
Theoretical Challenges in Galaxy Formation (2016, methodology): “…infrared galaxies (ULIRGS) and explain observations of ’extra light’ in the centers of low mass early-type galaxies (Hayward et al. 2014; Hopkins et al. 2009a, 2013, 2009c; Kormendy 1999; Kormendy et al. 2009; Mihos & Hernquist 1994a,c, 1996; Springel 2000; Teyssier, Chapon & Bournaud…”
The SLUGGS Survey: kinematics for over 2500 globular clusters in 12 early-type galaxies (2012, background): “In contrast, beyond this radius (Reff > 1), the halo of the galaxy contains precious dynamical signatures of early merging or early collapse events that might have eventually built up the galaxy (Hopkins et al. 2009, 2010; Hoffman et al. 2010; Oser et al. 2010).”
THE GROWTH OF MASSIVE GALAXIES SINCE z = 2 (2009, background): “As noted by Franx et al. (2008); Hopkins et al. (2009c); Bezanson et al. (2009); Cenarro & Trujillo (2009) and others, a proper comparison would consider all progenitors, not just the quiescent galaxies, and explicitly take mass evolutioninto account.”
BULGE n AND B/T IN HIGH-MASS GALAXIES: CONSTRAINTS ON THE ORIGIN OF BULGES IN HIERARCHICAL MODELS (2008, methodology): “Due to the reduced stellar mass that ends up in the bulge after a major merger, the Hopkins et al. (2009) models tend to yield lower B/T after such a merger.”
How Stellar Feedback Simultaneously Regulates Star Formation and Drives Outflows (2015, background): “We not that suppression of starbursts is especially undesirable becaus they are critical for making realistic bulges (Hopkins et al. 2008, 2009a,c).”
MERGERS AND BULGE FORMATION IN ΛCDM: WHICH MERGERS MATTER? (2009, methodology): “A much more detailed investigation of e.g. differences in predicted merger rates between semi-empirical models, semi-analytic models, and simulations will be the subject of a companion paper (Hopkins et al. 2009f).”
The formation of massive, compact galaxies at z = 2 in the Illustris simulation (2014, background): “…of galaxies and puff up the existing system are one way to achieve this physical size growth (Naab et al. 2007; Naab, Johansson & Ostriker 2009; Hopkins et al. 2009b, 2010; Bezanson et al. 2009; Oser et al. 2010, 2012; Johansson, Naab & Ostriker 2012; Hilz, Naab & Ostriker 2013; Feldmann &…”
WHAT TURNS GALAXIES OFF? THE DIFFERENT MORPHOLOGIES OF STAR-FORMING AND QUIESCENT GALAXIES SINCE z ∼ 2 FROM CANDELS (2011, unknown): “2006, Hopkins et al. 2009, Hoffman et al. 2010).”
A REVISED PARALLEL-SEQUENCE MORPHOLOGICAL CLASSIFICATION OF GALAXIES: STRUCTURE AND FORMATION OF S0 AND SPHEROIDAL GALAXIES (2011, background): “And simulations of major galaxy mergers reproduce the elliptical-galaxy fundamental plane, not a parameter correlation that is almost perpendicular to it (e. g., Robertson et al. 2006; Hopkins et al. 2008, 2009b).”