Subscribe to the gold package and get unlimited access to Shamra Academy
Register a new userQuenched, bulge-dominated, but dynamically cold galaxies in IllustrisTNG and their real-world counterparts
73
0
0.0
(
0
)
Ask ChatGPT about the research
No Arabic abstract
Galaxy morphologies, kinematics, and stellar populations are thought to link to each other. However, both simulations and observations have pointed out mismatches therein. In this work, we study the nature and origin of the present-day quenched, bulge-dominated, but dynamically cold galaxies within a stellar mass range of $10.3<log,M_{ast}/mathrm{M_{odot}}<11.2$ in the IllustrisTNG-100 Simulation, as a companion paper of Lu et al.(2021), which aimed at the star-forming but dynamically hot disc galaxies within a lower stellar mass range of $9.7<log,M_{ast}/mathrm{M_{odot}}<10.3$. We compare cold quenched population with a population of normal star-forming dynamically cold disc galaxies and a population of normal quenched dynamically hot elliptical galaxies within the same mass range. The populations of the present-day quenched and bulge-dominated galaxies (both being dynamically cold and hot) used to have significantly higher star-formation rates and thinner morphologies at redshifts of z~2. They have experienced more frequent larger mass-ratio mergers below z~0.7 in comparison to their star-forming disc counterparts, which is responsible for the formation of their bulge-dominated morphologies. The dynamically cold populations (both being star-forming and quenched) have experienced more frequent prograde and tangential mergers especially below z~1, in contrast to the dynamically hot ellipticals, which have had more retrograde and radial mergers. Such different merging histories can well explain the differences on the cold and hot dynamical status among these galaxies. We point out that the real-world counterparts of these dynamically cold and hot bulge-dominated quenched populations are the fast- and slow-rotating early-type galaxies, respectively, as seen in observations and hence reveal the different evolution paths of these two distinct populations of early-type galaxies.
rate research
Read More
A key feature of a large population of low-mass, late-type disk galaxies are star-forming disks with exponential light distributions. They are typically also associated with thin and flat morphologies, blue colors, and dynamically cold stars moving along circular orbits within co-planar thin gas disks. 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 disk galaxies in the lower stellar mass range (between $5times 10^9,mathrm{M_{odot}}$ and $2times 10^{10},mathrm{M_{odot}}$). 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 disk galaxies. The dynamically hot but still actively star-forming disks show a common feature of hosting kinematically misaligned gas and stellar disks, 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 disk 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.
To break the degeneracy among galactic stellar components, we extract kinematic structures using the framework described in Du et al. (2019, 2020). For example, the concept of stellar halos is generalized to weakly-rotating structures that are composed of loosely bound stars, which can hence be associated to both disk and elliptical type morphologies. By applying this method to central galaxies with stellar mass $10^{10-11.5} M_odot$ from the TNG50 simulation, we identify three broadly-defined types of galaxies: ones dominated by disk, by bulge, or by stellar halo structures. We then use the simulation to infer the underlying connection between the growth of structures and physical processes over cosmic time. Tracing galaxies back in time, we recognize three fundamental regimes: an early phase of evolution ($zgtrsim2$), and internal and external (mainly mergers) processes that act at later times. We find that disk- and bulge-dominated galaxies are not significantly affected by mergers since $zsim2$; the difference in their present-day structures originates from two distinct evolutionary pathways, extended vs. compact, that are likely determined by their parent dark matter halos; i.e., nature. On the other hand, slow rotator elliptical galaxies are typically halo-dominated, forming by external processes (e.g. mergers) in the later phase, i.e., nurture. This picture challenges the general idea that elliptical galaxies are the same objects as classical bulges. In observations, both bulge- and halo-dominated galaxies are likely to be classified as early-type galaxies with compact morphology and quiescent star formation. However, here we find them to have very different evolutionary histories.
The high abundance of disk galaxies without a large central bulge challenges predictions of current hydrodynamic simulations of galaxy formation. We aim to shed light on the formation of these objects by studying the redshift and mass dependence of their 3D shape distribution in the COSMOS galaxy survey. This distribution is inferred from the observed distribution of 2D shapes, using a reconstruction method which we test using hydrodynamic simulations. We find a moderate bias for the inferred average disk circularity and relative thickness with respect to the disk radius, but a large bias on the dispersion of these quantities. Applying the 3D shape reconstruction method on COSMOS data, we find no significant dependence of the inferred 3D shape distribution on redshift. The relative disk thickness shows a significant mass dependence which can be accounted for by the scaling of disk radius with galaxy mass. We conclude that the shapes of disk dominated galaxies are overall not subject to disruptive merging or feedback events below redshift $z=1.0$. This favours a scenario where these disks form early and subsequently undergo a tranquil evolution in isolation. In addition, our study shows that the observed 2D shapes of disk dominated galaxies can be well fitted using an ellipsoidal model for the galaxy 3D morphology combined with a Gaussian model for the 3D axes ratio distribution, confirming findings from similar work reported in the literature. Such an approach allows to build realistic mock catalogs with intrinsic galaxy shapes that will be essential for the study of intrinsic galaxy alignment as a contaminant of weak lensing surveys.
We study structural properties of spectroscopically confirmed massive quiescent galaxies at $zapprox 3$ with one of the first sizeable samples of such sources, made of ten $10.8<log(M_{star}/M_{odot})<11.3$ galaxies at $2.4 < z < 3.2$ in the COSMOS field whose redshifts and quiescence are confirmed by HST grism spectroscopy. Although affected by a weak bias toward younger stellar populations, this sample is deemed to be largely representative of the majority of the most massive and thus intrinsically rarest quiescent sources at this cosmic time. We rely on targeted HST/WFC3 observations and fit Sersic profiles to the galaxy surface brightness distributions at $approx 4000$ angstrom restframe. We find typically high Sersic indices and axis ratios (medians $approx 4.5$ and $0.73$, respectively) suggesting that, at odds with some previous results, the first massive quiescent galaxies may largely be already bulge-dominated systems. We measure compact galaxy sizes with an average of $approx 1.4$kpc at $log(M_{star}/M_{odot})approx 11.2$, in good agreement with the extrapolation at the highest masses of previous determinations of the stellar mass - size relation of quiescent galaxies, and of its redshift evolution, from photometrically selected samples at lower and similar redshifts. This work confirms the existence of a population of compact, bulge dominated, massive, quiescent sources at $zapprox 3$, providing one of the first statistical estimates of their structural properties, and further constraining the early formation and evolution of the first quiescent galaxies.
We present the analysis of medium-resolution spectra obtained at the Southern African Large Telescope (SALT) for nuclear globular clusters (GCs) in two dwarf spheroidal galaxies (dSphs). The galaxies have similar star formation histories, but they are situated in completely different environments. ESO269-66 is a close neighbour of the giant S0 NGC5128. KKs3 is one of the few truly isolated dSphs within 10 Mpc. We estimate the helium abundance $Y=0.3$, $rm age=12.6pm1$ Gyr, $[Fe/H]=-1.5,-1.55pm0.2$ dex, and abundances of C, N, Mg, Ca, Ti, and Cr for the nuclei of ESO269-66 and KKs3. Our surface photometry results using HST images yield the half-light radius of the cluster in KKs3, $rm r_h=4.8pm0.2$ pc. We demonstrate the similarities of medium-resolution spectra, ages, chemical compositions, and structure for GCs in ESO269-66 and KKs3 and for several massive Galactic GCs with $[Fe/H]sim-1.6$ dex. All Galactic GCs posses Extended Blue Horizontal Branches and multiple stellar populations. Five of the selected Galactic objects are iron-complex GCs. Our results indicate that the sample GCs observed now in different environments had similar conditions of their formation $sim$1 Gyr after the Big Bang.
Log in to be able to interact and post comments
comments
Fetching comments
Sign in to be able to follow your search criteria
