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Using the final Mapping Nearby Galaxies at Apache Point Observatory sample of 10K galaxies, we investigate the dark matter (DM) fraction f DM within one half-light radius R e for about 6K galaxies with good kinematics spanning a wide range of morphologies and stellar velocity dispersion. We employ two techniques to estimate f DM: (i) Jeans anisotropic modelling (JAM), which performs DM decomposition based on stellar kinematics and (ii) comparing the total dynamical mass-to-light ratios (M / L)JAM and (M */ L)SPS from stellar population synthesis (SPS). We find that both methods consistently show a significant trend of increasing f DM with decreasing σe and low f DM at larger σe. For 235 early-type galaxies with the best models, we explore the variation of stellar initial mass function (IMF) by comparing the stellar mass-to-light ratios from JAM and SPS. We confirm that the stellar mass excess factor αIMF increases with σe, consistent with previous studies that reported a transition from Chabrier-like to Salpeter IMF among galaxies. We show that the αIMF trend cannot be driven by M */ L or IMF gradients as it persists when allowing for radial gradients in our model. We find no evidence for the total M / L increasing toward the centre. We detect weak positive correlations between αIMF and age, but no correlations with metallicity. We stack galaxy spectra according to their αIMF to search for differences in IMF-sensitive spectral features (e.g. the |$\rm Na_{\rm I}$| doublet). We only find marginal evidence for such differences, which casts doubt on the validity of one or both methods to measure the IMF. [ABSTRACT FROM AUTHOR]

The effect of angular momentum on galaxy formation and evolution has been studied for several decades. Our recent two papers using IllustrisTNG-100 simulation have revealed the acquisition path of the angular momentum from large-scale environment (satellites within hundreds of kpc) through the circumgalactic medium (CGM) to the stellar discs, putting forward the co-rotation scenario across the three distance scales. In real observations, although the rotation signature for the CGM and environmental three-dimensional angular momentum are difficult to obtain, line-of-sight kinematics of group member galaxies and stellar disc kinematics of central galaxies are available utilizing existing group catalogue data and integral field unit (IFU) data. In this paper, we use (1) the group catalogue of SDSS DR7 and MaNGA IFU stellar kinematic maps and (2) the group catalogue of GAMA DR4 data and SAMI IFU stellar kinematic maps, to test if the prediction above can be seen in real data. We found the co-rotation pattern between stellar discs and satellites can be concluded with 99.7 per cent confidence level (∼3σ) when combining the two data sets. And the random tests show that the signal can be scarcely drawn from random distribution. [ABSTRACT FROM AUTHOR]

This is the second paper of the Mapping Nearby Galaxies at Apache Point Observatory (MaNGA) Dynamics and stellar Population (DynPop) series, which analyses the global stellar population, radial gradients, and non-parametric star-formation history of ∼10K galaxies from the MaNGA Survey final data release 17 and relates them with dynamical properties of galaxies. We confirm the correlation between the stellar population properties and the stellar velocity dispersion σe, but also find that younger galaxies are more metal-poor at fixed σe. Stellar age, metallicity, and mass-to-light ratio (M */ L) all decrease with increasing galaxy rotation, while their radial gradients become more negative (i.e. lower value at the outskirts). The exception is the slow rotators, which also appear to have significantly negative metallicity gradients, confirming the mass–metallicity gradient correlation. Massive disc galaxies in the green valley, on the |$(\sigma _{\rm e},\rm age)$| plane, show the most negative age and metallicity gradients, consistent with their old central bulges surrounded by young star-forming discs and metal-poor gas accretion. Galaxies with high σe, steep total mass-density slope, low dark matter fraction, high M */ L , and high metallicity have the highest star-formation rate at earlier times, and are currently quenched. We also discover a population of low-mass star-forming galaxies with low rotation but physically distinct from the massive slow rotators. A catalogue of these stellar population properties is provided publicly. [ABSTRACT FROM AUTHOR]

A key feature of a large population of low-mass, late-type disc galaxies are star-forming discs with exponential light distributions. They are typically also associated with thin and flat morphologies, blue colours, and dynamically cold stars moving along circular orbits within co-planar thin gas discs. However, the latter features do not necessarily always imply the former, in fact, a variety of different kinematic configurations do exist. In this work, we use the cosmological hydrodynamical IllustrisTNG simulation to study the nature and origin of dynamically hot, sometimes even counter-rotating, star-forming disc galaxies in the lower stellar mass range (between |$5\times 10^9\, \mathrm{M_{\odot }}$| and |$2\times 10^{10}\, \mathrm{M_{\odot }}$|⁠). We find that being dynamically hot arises in most cases as an induced transient state, for example due to galaxy interactions and merger activities, rather than as an age-dependent evolutionary phase of star-forming disc galaxies. The dynamically hot but still actively star-forming discs show a common feature of hosting kinematically misaligned gas and stellar discs, and centrally concentrated on-going star formation. The former is often accompanied by disturbed gas morphologies, while the latter is reflected in low gas and stellar spins in comparison to their dynamically cold, normal disc counterparts. Interestingly, observed galaxies from MaNGA with kinematic misalignment between gas and stars show remarkably similar general properties as the IllustrisTNG galaxies, and therefore are plausible real-world counterparts. In turn, this allows us to make predictions for the stellar orbits and gas properties of these misaligned galaxies. [ABSTRACT FROM AUTHOR]

We investigate the Fundamental Plane (FP) evolution of early-type galaxies in the IllustrisTNG-100 simulation (TNG100) from redshift z  = 0 to z  = 2. We find that a tight plane relation already exists as early as z  = 2. Its scatter stays as low as ∼0.08 dex across this redshift range. Both slope parameters b and c (where R  ∝ σ b I c with R , σ, and I being the typical size, velocity dispersion, and surface brightness) of the plane evolve mildly since z  = 2, roughly consistent with observations. The FP residual |$\rm Res$| (⁠|$\equiv \, a\, +\, b\log \sigma \, +\, c\log I\, -\, \log R$|⁠ , where a is the zero-point of the FP) is found to strongly correlate with stellar age, indicating that stellar age can be used as a crucial fourth parameter of the FP. However, we find that 4 c + b + 2 = δ, where δ ∼ 0.8 for FPs in TNG, rather than zero as is typically inferred from observations. This implies that a tight power-law relation between the dynamical mass-to-light ratio M dyn/ L and the dynamical mass M dyn (where M dyn ≡ 5σ2 R / G , with G being the gravitational constant) is not present in the TNG100 simulation. Recovering such a relation requires proper mixing between dark matter and baryons, as well as star formation occurring with correct efficiencies at the right mass scales. This represents a powerful constraint on the numerical models, which has to be satisfied in future hydrodynamical simulations. [ABSTRACT FROM AUTHOR]

We explore the isothermal total density profiles of early-type galaxies (ETGs) in the IllustrisTNG simulation. For the selected 559 ETGs at z  = 0 with stellar masses |$10^{10.7}\, \mathrm{M}_{\odot } \leqslant M_{\ast } \leqslant 10^{11.9}\, \mathrm{M}_{\odot }$|⁠ , the total power-law slope has a mean of 〈γ′〉 = 2.011 ± 0.007 and a scatter of |$\sigma _{\gamma ^{\prime }} = 0.171$| over the radial range 0.4–4 times the stellar half-mass radius. Several correlations between γ′ and galactic properties including stellar mass, effective radius, stellar surface density, central velocity dispersion, central dark matter fraction, and in situ -formed stellar mass ratio are compared to observations and other simulations, revealing that IllustrisTNG reproduces many correlation trends, and in particular, γ′ is almost constant with redshift below z  = 2. Through analysing IllustrisTNG model variations, we show that black hole kinetic winds are crucial to lowering γ′ and matching observed galaxy correlations. The effects of stellar winds on γ′ are subdominant compared to active galactic nucleus (AGN) feedback, and differ due to the presence of AGN feedback from previous works. The density profiles of the ETG dark matter haloes are well described by steeper than NFW profiles, and they are steeper in the full physics (FP) run than their counterparts in the dark matter-only (DMO) run. Their inner density slopes anticorrelate (remain constant) with the halo mass in the FP (DMO) run, and anticorrelate with the halo concentration parameter c 200 in both the types of runs. The dark matter haloes of low-mass ETGs are contracted whereas high-mass ETGs are expanded, suggesting that variations in the total density profile occur through the different halo responses to baryons. [ABSTRACT FROM AUTHOR]

We study the evolutionary trend of the total density profile of early-type galaxies (ETGs) in IllustrisTNG. To this end, we trace ETGs from z  = 0 to 4 and measure the power-law slope γ′ of the total density profile for their main progenitors. We find that their slopes γ′ steepen on average during z ∼ 4–2, then becoming shallower until z  = 1, after which they remain almost constant, aside from a residual trend of becoming shallower towards z  = 0. We also compare to a statistical sample of ETGs at different redshifts, selected based on their luminosity profiles and stellar masses. Due to different selection effects, the average slopes of the statistical samples follow a modified evolutionary trend. They monotonically decrease since z  = 3, and after z ≈ 1, they remain nearly invariant with a mild increase towards z  = 0. These evolutionary trends are mass dependent for both samples, with low-mass galaxies having in general steeper slopes than their more massive counterparts. Galaxies that transitioned to ETGs more recently have steeper mean slopes as they tend to be smaller and more compact at any given redshift. By analysing the impact of mergers and AGN feedback on the progenitors' evolution, we conjecture a multiphase path leading to isothermality in ETGs: dissipation associated with rapid wet mergers tends to steepen γ′ from z  = 4 to 2, whereas subsequent AGN feedback (especially in the kinetic mode) makes γ′ shallower again from z  = 2 to 1. Afterwards, passive evolution from z  = 1 to 0, mainly through gas-poor mergers, mildly decreases γ′ and maintains the overall mass distribution close to isothermal. [ABSTRACT FROM AUTHOR]

We compare galaxy morphology predicted by the Illustris hydrodynamical simulation and a semi-analytic model (SAM) grafted in the halo merger trees from the Illustris-Dark matter simulation. Morphology is classified according to the luminous profile and the kinematic bulge-to-total ratio for Illustris galaxy, and the bulge-to-total stellar mass ratio for SAM galaxy. For late-type galaxies in the Illustris catalogue, most of their counterparts in the SAM model have the same type, and the consistency between two models is higher for lower mass galaxies. For early-type (ET) galaxies in Illustris, the consistency is quite low for the counterparts except for most massive galaxies. By comparing in detail the growth histories of some matched galaxy pairs of Milky Way mass in Illustris and the SAM model, we notice two aspects of differences in determining galaxy morphology between the two galaxy formation implementations. First, in the SAM, major merger and frequent minor mergers result in the growth of bulges and turn the galaxy into ET, while bulge formation is not connected to mergers as tightly as in SAM for the Illustris galaxies. In addition, the satellite stellar mass can decrease significantly due to tidal stripping before merging into the central galaxy in Illustris, while it does not decrease in the SAM model. This results in less mergers with large (stellar) mass ratios in the Illustris simulation, and less effect of mergers on shaping galaxy morphology. [ABSTRACT FROM AUTHOR]

We explore orbit properties of 35 prolate-triaxial galaxies selected from the Illustris cosmological hydrodynamic simulation. We present a detailed study of their orbit families, and also analyse relations between the relative abundance of the orbit families and the spin parameter, triaxiality, the ratio of the angular momentum, and the baryon fraction. We find that box orbits dominate the orbit structure for most prolate-triaxial galaxies, especially in the central region. The fraction of irregular orbits in the prolate-triaxial galaxies is small, and it increases with galaxy radius. Both the x -tube and z -tube orbits are important in prolate-triaxial galaxies, especially in the outer regions. The fraction of box orbits for prolate-triaxial galaxies (0.7 < T < 1) decreases with the triaxiality of the stars, while the fraction of x -tube orbits increases with the triaxiality for a given axis ratio. The fraction of box orbits increases and the fractions of x -tube and z -tube orbits weakly decrease with increasing baryon fraction. These results help to understand the structure of prolate-triaxial galaxies and provide cross-checks for constructing dynamical models of prolate-triaxial galaxies by using the Schwarzschild or the made-to-measure methods. [ABSTRACT FROM AUTHOR]

The galaxy Malin 1 contains the largest stellar disc known but the formation mechanism of this structure has been elusive. In this paper, we report a Malin 1 analogue in the 100 Mpc IllustrisTNG simulation and describe its formation history. At redshift zero, this massive galaxy, having a maximum circular velocity V max of 430 km s−1, contains a 100 kpc gas/stellar disc with morphology similar to Malin 1. The simulated galaxy reproduces well many observed features of Malin 1's vast disc, including its stellar ages, metallicities, and gas rotation curve. We trace the extended disc back in time and find that a large fraction of the cold gas at redshift zero originated from the cooling of hot halo gas, triggered by the merger of a pair of intruding galaxies. Our finding provides a novel way to form large galaxy discs as extreme as Malin 1 within the current galaxy formation framework. [ABSTRACT FROM AUTHOR]