THE STELLAR MASS STRUCTURE OF MASSIVE GALAXIES FROMz= 0 TOz= 2.5: SURFACE DENSITY PROFILES AND HALF-MASS RADII

ABSTRACT The galaxy size–stellar mass and central surface density–stellar mass relationships are fundamental observational constraints on galaxy formation models. However, inferring the physical size of a galaxy from observed stellar emission is non-trivial due to various observational effects, such as the mass-to-light ratio variations that can be caused by non-uniform stellar ages, metallicities, and dust attenuation. Consequently, forward-modelling light-based sizes from simulations is desirable. In this work, we use the skirt dust radiative transfer code to generate synthetic observations of massive galaxies ($M_{*}\sim 10^{11}\, \rm {M_{\odot }}$ at z = 2, hosted by haloes of mass $M_{\rm {halo}}\sim 10^{12.5}\, \rm {M_{\odot }}$) from high-resolution cosmological zoom-in simulations that form part of the Feedback In Realistic Environments project. The simulations used in this paper include explicit stellar feedback but no active galactic nucleus (AGN) feedback. From each mock observation, we infer the effective radius (Re), as well as the stellar mass surface density within this radius and within $1\, \rm {kpc}$ (Σe and Σ1, respectively). We first investigate how well the intrinsic half-mass radius and stellar mass surface density can be inferred from observables. The majority of predicted sizes and surface densities are within a factor of 2 of the intrinsic values. We then compare our predictions to the observed size–mass relationship and the Σ1−M⋆ and Σe−M⋆ relationships. At z ≳ 2, the simulated massive galaxies are in general agreement with observational scaling relations. At z ≲ 2, they evolve to become too compact but still star forming, in the stellar mass and redshift regime where many of them should be quenched. Our results suggest that some additional source of feedback, such as AGN-driven outflows, is necessary in order to decrease the central densities of the simulated massive galaxies to bring them into agreement with observations at z ≲ 2.

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High accuracy analytical solutions for the projected mass (counts) & surface density (brightness) of Einasto profiles

Monthly Notices of the Royal Astronomical Society ◽

10.1093/mnras/stab1029 ◽

2021 ◽

Author(s):

Barun K Dhar

Keyword(s):

Dark Matter ◽

Gravitational Lensing ◽

Surface Density ◽

Surface Brightness ◽

Analytical Approximation ◽

High Accuracy ◽

Density Profiles ◽

Massive Galaxies ◽

Multiple Components ◽

Number Counts

Abstract The Einasto profile has been successful in describing the density profiles of dark matter haloes in ΛCDM N-body simulations. It has also been able to describe multiple components in the surface brightness profiles of galaxies. However, analytically projecting it to calculate quantities under projection is challenging. In this paper, we will see the development of a highly accurate analytical approximation for the mass (or counts) enclosed in an infinitely long cylindrical column for Einasto profiles—also known as the projected mass (or counts)—using a novel methodology. We will then develop a self-consistent high accuracy model for the surface density from the expression for the projected mass. Both models are quite accurate for a broad family of functions, with a shape parameter α varying by a factor of 100 in the range 0.05 ≲ α ≲ 5.0, with fractional errors ∼10−6 for α ≲ 0.4. Profiles with α ≲ 0.4 have been shown to fit the density profiles of dark matter haloes in N-body simulations as well as the luminosity profiles of the outer components of massive galaxies. Since the projected mass and the surface density are used in gravitational lensing, I will illustrate how these models facilitate (for the first time) analytical computation of several quantities of interest in lensing due to Einasto profiles. The models, however, are not limited to lensing and apply to similar quantities under projection, such as the projected luminosity, the projected (columnar) number counts and the projected density or the surface brightness.

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A quantitative demonstration that stellar feedback locally regulates galaxy growth

Monthly Notices of the Royal Astronomical Society ◽

10.1093/mnras/staa2906 ◽

2020 ◽

Vol 499 (1) ◽

pp. 1172-1187

Author(s):

Javier Zaragoza-Cardiel ◽

Jacopo Fritz ◽

Itziar Aretxaga ◽

Yalia D Mayya ◽

Daniel Rosa-González ◽

...

Keyword(s):

Star Formation ◽

Surface Density ◽

Stellar Mass ◽

Stellar Structure ◽

Star Formation History ◽

Mass Loading ◽

Density Profiles ◽

Stellar Feedback ◽

Formation History ◽

Hydrodynamical Simulations

ABSTRACT We have applied stellar population synthesis to 500-pc-sized regions in a sample of 102 galaxy discs observed with the MUSE spectrograph. We derived the star formation history and analyse specifically the ‘recent’ ($20\,\rm {Myr}$) and ‘past’ ($570\,\rm {Myr}$) age bins. Using a star formation self-regulator model, we can derive local mass-loading factors, η for specific regions, and find that this factor depends on the local stellar mass surface density, Σ*, in agreement with the predictions form hydrodynamical simulations including supernova feedback. We integrate the local η–Σ* relation using the stellar mass surface density profiles from the Spitzer Survey of Stellar Structure in Galaxies (S4G) to derive global mass-loading factors, ηG, as a function of stellar mass, M*. The ηG–M* relation found is in very good agreement with hydrodynamical cosmological zoom-in galaxy simulations. The method developed here offers a powerful way of testing different implementations of stellar feedback, to check on how realistic are their predictions.

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Evolution of spatially resolved star formation main sequence and surface density profiles in massive disc galaxies at 0 ≲ z ≲ 1: inside–out stellar mass buildup and quenching

Monthly Notices of the Royal Astronomical Society ◽

10.1093/mnras/sty1771 ◽

2018 ◽

Vol 479 (4) ◽

pp. 5083-5100 ◽

Cited By ~ 15

Author(s):

Abdurro’uf ◽

Masayuki Akiyama

Keyword(s):

Star Formation ◽

Surface Density ◽

Main Sequence ◽

Stellar Mass ◽

Density Profiles ◽

Spatially Resolved ◽

Inside Out ◽

Disc Galaxies

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Analysis of the galaxy size versus stellar mass relation

Monthly Notices of the Royal Astronomical Society ◽

10.1093/mnras/staa1108 ◽

2020 ◽

Cited By ~ 1

Author(s):

J Sánchez Almeida

Keyword(s):

Surface Density ◽

Surface Brightness ◽

Stellar Mass ◽

Mass Relation ◽

Physical Reason ◽

Density Profiles ◽

Analytical Results ◽

The Galaxy ◽

Optimal Values ◽

Density Threshold

Abstract The scatter in the galaxy size versus stellar mass (M⋆) relation gets largely reduced when, rather than the half-mass radius Re, the size at a fixed surface density is used. Here we address why this happens. We show how a reduction is to be expected because any two galaxies with the same M⋆ have at least one radius with identical surface density, where the galaxies have identical size. However, the reason why the scatter is reduced to the observed level is not trivial, and we pin it down to the galaxy surface density profiles approximately following Sersic profiles with their Re and Sersic index (n) anti-correlated (i.e., given M⋆, n increases when Re decreases). Our analytical results describe very well the behavior of the observed galaxies as portrayed in the NASA Sloan Atlas (NSA), which contains more than half a million local objects with 7 < log (M⋆/M⊙) < 11.5. The comparison with NSA galaxies also allows us to find the optimal values for the mass surface density ($2.4_{-0.9}^{+1.3}\, M_\odot \, {\rm pc}^{-2}$) and surface brightness (r-band 24.7 ± 0.5 mag arcsec−2) that minimize the scatter, although the actual values depend somehow on the subset of NSA galaxies used for optimization. The physical reason for the existence of optimal values is unknown but, as Trujillo et al. (2020) point out, they are close to the gas surface density threshold to form stars and thus may trace the physical end of a galaxy. Our NSA-based size–mass relation agrees with theirs on the slope as well as on the magnitude of the scatter. As a by-product of the narrowness of the size–mass relation (only 0.06 dex), we propose to use the size of a galaxy to measure its stellar mass. In terms of observing time, it is not more demanding than the usual photometric techniques and may present practical advantages in particular cases.

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A study of stellar orbit fractions: simulated IllustrisTNG galaxies compared to CALIFA observations

Monthly Notices of the Royal Astronomical Society ◽

10.1093/mnras/stz2164 ◽

2019 ◽

Vol 489 (1) ◽

pp. 842-854 ◽

Cited By ~ 3

Author(s):

Dandan Xu ◽

Ling Zhu ◽

Robert Grand ◽

Volker Springel ◽

Shude Mao ◽

...

Keyword(s):

Observational Data ◽

Mass Range ◽

Stellar Mass ◽

Model Uncertainties ◽

Massive Galaxies ◽

Hubble Sequence ◽

Galaxy Sample ◽

The Mean ◽

Stellar Orbit

ABSTRACT Motivated by the recently discovered kinematic ‘Hubble sequence’ shown by the stellar orbit-circularity distribution of 260 CALIFA galaxies, we make use of a comparable galaxy sample at z = 0 with a stellar mass range of $M_{*}/\mathrm{M}_{\odot }\in [10^{9.7},\, 10^{11.4}]$ selected from the IllustrisTNG simulation and study their stellar orbit compositions in relation to a number of other fundamental galaxy properties. We find that the TNG100 simulation broadly reproduces the observed fractions of different orbital components and their stellar mass dependences. In particular, the mean mass dependences of the luminosity fractions for the kinematically warm and hot orbits are well reproduced within model uncertainties of the observed galaxies. The simulation also largely reproduces the observed peak and trough features at $M_{*}\approx 1\rm {-}2\times 10^{10}\, \mathrm{M}_{\odot }$ in the mean distributions of the cold- and hot-orbit fractions, respectively, indicating fewer cooler orbits and more hotter orbits in both more- and less-massive galaxies beyond such a mass range. Several marginal disagreements are seen between the simulation and observations: the average cold-orbit (counter-rotating) fractions of the simulated galaxies below (above) $M_{*}\approx 6\times 10^{10}\, \mathrm{M}_{\odot }$ are systematically higher than the observational data by $\lesssim 10{{\ \rm per\ cent}}$ (absolute orbital fraction); the simulation also seems to produce more scatter for the cold-orbit fraction and less so for the non-cold orbits at any given galaxy mass. Possible causes that stem from the adopted heating mechanisms are discussed.

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Emerge: Empirical predictions of galaxy merger rates since z ∼ 6

Monthly Notices of the Royal Astronomical Society ◽

10.1093/mnras/staa3746 ◽

2020 ◽

Author(s):

Joseph A O’Leary ◽

Benjamin P Moster ◽

Thorsten Naab ◽

Rachel S Somerville

Keyword(s):

Galaxy Formation ◽

Power Law ◽

Stellar Mass ◽

Direct Result ◽

Mass Relation ◽

Massive Galaxies ◽

The Galaxy ◽

Major Merger ◽

Low Mass ◽

Merger Rate

Abstract We explore the galaxy-galaxy merger rate with the empirical model for galaxy formation, emerge. On average, we find that between 2 per cent and 20 per cent of massive galaxies (log10(m*/M⊙) ≥ 10.3) will experience a major merger per Gyr. Our model predicts galaxy merger rates that do not scale as a power-law with redshift when selected by descendant stellar mass, and exhibit a clear stellar mass and mass-ratio dependence. Specifically, major mergers are more frequent at high masses and at low redshift. We show mergers are significant for the stellar mass growth of galaxies log10(m*/M⊙) ≳ 11.0. For the most massive galaxies major mergers dominate the accreted mass fraction, contributing as much as 90 per cent of the total accreted stellar mass. We reinforce that these phenomena are a direct result of the stellar-to-halo mass relation, which results in massive galaxies having a higher likelihood of experiencing major mergers than low mass galaxies. Our model produces a galaxy pair fraction consistent with recent observations, exhibiting a form best described by a power-law exponential function. Translating these pair fractions into merger rates results in an inaccurate prediction compared to the model intrinsic values when using published observation timescales. We find the pair fraction can be well mapped to the intrinsic merger rate by adopting an observation timescale that decreases linearly with redshift as Tobs = −0.36(1 + z) + 2.39 [Gyr], assuming all observed pairs merge by z = 0.

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Dynamical Evolution of Globular Clusters After Core Collapse

Symposium - International Astronomical Union ◽

10.1017/s0074180900147357 ◽

1985 ◽

Vol 113 ◽

pp. 139-160 ◽

Cited By ~ 4

Author(s):

Douglas C. Heggie

Keyword(s):

Surface Density ◽

Globular Clusters ◽

Stellar System ◽

Dynamical Evolution ◽

Theoretical Models ◽

Numerical Calculations ◽

Core Collapse ◽

Density Profiles ◽

The Core ◽

Fokker Planck

This review describes work on the evolution of a stellar system during the phase which starts at the end of core collapse. It begins with an account of the models of Hénon, Goodman, and Inagaki and Lynden-Bell, as well as evaporative models, and modifications to these models which are needed in the core. Next, these models are related to more detailed numerical calculations of gaseous models, Fokker-Planck models, N-body calculations, etc., and some problems for further work in these directions are outlined. The review concludes with a discussion of the relation between theoretical models and observations of the surface density profiles and statistics of actual globular clusters.

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