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Abstract Scaling relationships, both integrated and spatially resolved, arise owing to the physical processes that govern galaxy evolution and are frequently measured in both observed and simulated data. However, the accuracy and comparability of these measurements are hindered by various differences between studies such as spatial resolution, sample selection criteria, and fitting technique. In this Letter, we compare variations of standard least-squares techniques to the ridge line method for identifying spatially resolved scaling relations (Σ_*−Σ_SFR, Σ_*−Σ_gas, and Σ_gas−Σ_SFR) for TNG100 galaxies. We find that using the ridge line technique to fit these scaling relations with a double linear function (in logarithmic space) results in significantly better fits than fitting with ordinary least squares. We further illustrate the utility of the ridge line technique with an investigation into the dependence of resolved star formation main-sequence (rSFMS) measurements on spatial resolution and smoothing scale. Specifically, we find that the slope of the rSFMS at low Σ_*is independent (within 2σ) of spatial resolution and smoothing scale. Finally, we discuss the need for a consistent reanalysis of resolved scaling relations in the literature and physically motivate adoption of the ridge line technique over other fitting methods. 

Abstract We present radial density profiles, as traced by luminous galaxies and dark matter particles, for voids in 11 snapshots of theTNG 300simulation. The snapshots span 11.65 Gyr of cosmic time, corresponding to the redshift range 0 ≤z≤ 3. Using the comoving galaxy fields, voids were identified via a well-tested, watershed transformation-based algorithm. Voids were defined to be underdense regions that are unlikely to have arisen from Poisson noise, resulting in the selection of ∼100–200 of the largest underdense regions in each snapshot. At all redshifts, the radial density profiles as traced by both the galaxies and the dark matter resemble inverse top-hat functions. However, details of the functions (particularly the underdensities of the innermost regions and the overdensities of the ridges) evolve considerably more for the dark matter density profiles than for the galaxy density profiles. At all redshifts, a linear relationship between the galaxy and dark matter density profiles exists, and the slope of the relationship is similar to the bias estimates forTNG 300snapshots. Lastly, we identify distinct environments in which voids can exist, defining “void-in-void” and “void-in-cloud” populations (i.e., voids that reside in larger underdense or overdense regions, respectively), and we investigate ways in which the relative densities of dark matter and galaxies in the interiors and ridges of these structures vary as a function of void environment. 

Abstract We present radial profiles of luminosity-weighted age (age_L) and ΔΣ_SFRfor various populations of high- and low-mass central and satellite galaxies in the TNG100 cosmological simulation. Using these profiles, we investigate the impact of intrinsic and environmental factors on the radial distribution of star formation. For both central galaxies and satellites, we investigate the effects of black hole mass, cumulative active galactic nucleus (AGN) feedback energy, morphology, halo mass, and local galaxy overdensity on the profiles. In addition, we investigate the dependence of radial profiles of the satellite galaxies as a function of the redshifts at which they joined their hosts, as well as the net change in star-forming gas mass since the satellites joined their host. We find that high-mass (M_*> 10^10.5M_⊙) central and satellite galaxies show evidence of inside-out quenching driven by AGN feedback. Effects from environmental processes only become apparent in averaged profiles at extreme halo masses and local overdensities. We find that the dominant quenching process for low-mass galaxies (M_*< 10¹⁰M_⊙) is environmental, generally occurring at low halo mass and high local galaxy overdensity for low-mass central galaxies and at high host halo masses for low-mass satellite galaxies. Overall, we find that environmental processes generally drive quenching from the outside-in. 

Abstract Studies of isolated central galaxies and their satellites have shown that the spatial distributions of the satellites are distinctly “lopsided” with respect to the locations of the central galaxies. Here we extend this type of analysis to larger systems by analyzing the lopsidedness of 280 massive galaxy clusters in the IllustrisTNG300 Λ Cold Dark Matter simulation. Using a pairwise clustering statistic, we compute the probability that pairs of cluster galaxies are separated by a given polar angle difference, Δϕ, in the plane of the sky. Relative to the location of the central cluster galaxy, we find a statistically significant excess of galaxy pairs that are located on the same side of the cluster. The lopsidedness of the galaxy distribution is most pronounced for large clusters and for pairs of intrinsically red galaxies. The results summarized here were presented at the 243rd meeting of the American Astronomical Society. 

Abstract We investigate the properties of voids and void galaxies in theTNG300simulation. Using a luminous galaxy catalog and a spherical void-finding algorithm, we identify 5078 voids at redshiftz= 0. The voids cover 83% of the simulation volume and have a median radius of 4.4h⁻¹Mpc. We identify two populations of field galaxies based on whether the galaxies reside within a void (“void galaxies”; 75,220 objects) or outside a void (“nonvoid galaxies”; 527,454 objects). Within the voids, mass does not directly trace light. Instead, the mean radial underdensity profile as defined by the locations of void galaxies is systematically lower than the mean radial underdensity profile as defined by the dark matter (i.e., the voids are more “devoid” of galaxies than they are of mass). Within the voids, the integrated underdensity profiles of the dark matter and the galaxies are independent of the local background density (i.e., voids-in-voids versus voids-in-clouds). Beyond the void radii, however, the integrated underdensity profiles of both the dark matter and the galaxies exhibit strong dependencies on the local background density. Compared to nonvoid galaxies, void galaxies are on average younger, less massive, bluer in color, less metal enriched, and have smaller radii. In addition, the specific star formation rates of void galaxies are ∼20% higher than nonvoid galaxies and, in the case of galaxies with central supermassive black holes withM_BH≳ 3 × 10⁶h⁻¹M_⊙, the fraction of active void galaxies is ∼25% higher than active nonvoid galaxies. 

Abstract Recent cosmological hydrodynamical simulations have produced populations of numerical galaxies whose global star-forming properties are in good agreement with those of observed galaxies. Proper modeling of energetic feedback from supernovae and active galactic nuclei is critical to the ability of simulations to reproduce observed galaxy properties, and historically, such modeling has proven to be a challenge. Here, we analyze the local properties of central and satellite galaxies in thez= 0 snapshot of the TNG100 simulation as a test of feedback models. We generate a face-on projection of stellar particles in TNG100 galaxies, from which we demonstrate the existence of a resolved star-forming main sequence (Σ_SFR–Σ_*relation) with a slope and normalization that is in reasonable agreement with previous studies. We also present radial profiles of various galaxy populations for two parameters: the distance from the resolved main-sequence line (ΔΣ_SFR) and the luminosity-weighted stellar age (Age_L). We find that, on average, high-mass central and satellite galaxies quench from the inside out, while low-mass central and satellite galaxies have similar, flatter profiles. Overall, we find that, with the exception of the starburst population, the TNG100 feedback models yield simulated galaxies whose radial distributions of Age_Land ΔΣ_SFRagree with those of observed galaxies. 

Abstract A recent observational study found that the projected spatial distributions of the satellites of bright, isolated host galaxies tend to be lopsided with respect to the locations of the hosts. Here, we examine the spatial distributions of the satellites of a large number of bright, isolated host galaxies that were obtained from mock redshift surveys of a Λ-cold dark matter (ΛCDM) simulation. Host galaxies and their satellites were identified using selection criteria that are identical to those used in the observational study, allowing for a direct comparison of the results for the simulated and observed systems. To characterize the spatial distribution of the satellites, we adopt two statistics: (1) the pairwise clustering of the satellites and (2) the mean resultant length. In agreement with the observational study, we find a strong tendency for satellites in the simulation to be located on the same side of their host, and the signal is most pronounced for the satellites of blue hosts. These lopsided satellite distributions are not solely attributable to incompleteness of the observed satellite catalog or the presence of objects that have been falsely identified as satellites. In addition, satellites that joined their hosts’ halos in the distant past (≳8 Gyr) show a pronounced lopsidedness in their spatial distributions and, therefore, the lopsidedness is not solely attributable to the late-time accretion of satellites. 

Abstract We investigate the spatial distribution of the satellites of isolated host galaxies in the IllustrisTNG100 simulation. In agreement with a previous, similar analysis of the Illustris-1 simulation, the satellites are typically poor tracers of the mean host mass density. Unlike the Illustris-1 satellites, here the spatial distribution of the complete satellite sample is well fitted by an NFW profile; however, the concentration is a factor of ∼2 lower than that of the mean host mass density. The spatial distributions of the brightest 50% and faintest 50% of the satellites are also well fitted by NFW profiles, but the concentrations differ by a factor of ∼2. When the sample is subdivided by host color and luminosity, the number density profiles for blue satellites generally fall below the mean host mass density profiles, while the number density profiles for red satellites generally rise above the mean host mass density profiles. These opposite, systematic offsets combine to yield a moderately good agreement between the mean mass density profile of the brightest blue hosts and the corresponding number density profile of their satellites. Lastly, we subdivide the satellites according to the redshifts at which they joined their hosts. From this, we find that neither the oldest one-third of the satellites nor the youngest one-third of the satellites faithfully trace the mean host mass density.