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Register a new userEvolution of Starburst Galaxies in the Illustris Simulation
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Charlotte Wilkinson
Publication date
2018
fields
Physics
and research's language is
English
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There is a consensus in the literature that starburst galaxies are triggered by inter- action events. However, it remains an open question as to what extent both merging and non-merging interactions have in triggering starbursts? In this study, we make use of the Illustris simulation to test how different triggering mechanisms can effect starburst events. We examine star formation rate, colour and environment of starburst galaxies to determine if this could be why we witness a bimodality in post-starburst populations within observational studies. Further, we briefly test the extent of quenching due to AGN feedback. From Illustris, we select 196 starburst galaxies at z = 0.15 and split them into post-merger and pre-merger/harassment driven starburst samples. We find that 55% of this sample not undergone a merger in the past 2 Gyr. Both of our samples are located in low-density environments within the filament regions of the cosmic web, however we find that pre-merger/harassment driven starburst are in higher density environments than post-merger driven starbursts. We also find that pre-merger/harassment starbursts are redder than post-merger starbursts, this could be driven by environmental effects. Both however, produce nuclear starbursts of comparable strengths.
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We present the first study of evolution of galaxy groups in the Illustris simulation. We focus on dynamically relaxed and unrelaxed galaxy groups representing dynamically evolved and evolving galaxy systems, respectively. The evolutionary state of a group is probed from its luminosity gap and separation between the brightest group galaxy and the center of mass of the group members. We find that the Illustris simulation, over-produces large luminosity gap galaxy systems, known as fossil systems, in comparison to observations and the probed semi-analytical predictions. However, this simulation is equally successful in recovering the correlation between luminosity gap and luminosity centroid offset, in comparison to the probed semi-analytic model. We find evolutionary tracks based on luminosity gap which indicate that a large luminosity gap group is rooted in a small luminosity gap group, regardless of the position of the brightest group galaxy within the halo. This simulation helps, for the first time, to explore the black hole mass and its accretion rate in galaxy groups. For a given stellar mass of the brightest group galaxies, the black hole mass is larger in dynamically relaxed groups with a lower rate of mass accretion. We find this consistent with the latest observational studies of the radio activities in the brightest group galaxies in fossil groups. We also find that the IGM in dynamically evolved groups is hotter for a given halo mass than that in evolving groups, again consistent with earlier observational studies.
(Abridged) Any viable cosmological model in which galaxies interact predicts the existence of primordial and tidal dwarf galaxies (TDGs). In particular, in the standard model of cosmology ($Lambda$CDM), according to the dual dwarf galaxy theorem, there must exist both primordial dark matter-dominated and dark matter-free TDGs with different radii. We study the frequency, evolution, and properties of TDGs in a $Lambda$CDM cosmology. We use the hydrodynamical cosmological Illustris-1 simulation to identify tidal dwarf galaxy candidates (TDGCs) and study their present-day physical properties. We also present movies on the formation of a few galaxies lacking dark matter, confirming their tidal dwarf nature. TDGCs can however also be formed via other mechanisms, such as from ram-pressure-stripped material or, speculatively, from cold-accreted gas. We find 97 TDGCs with $M_{stellar} >5 times 10^7 M_odot$ at redshift $z = 0$, corresponding to a co-moving number density of $2.3 times 10^{-4} h^3 cMpc^{-3}$. The most massive TDGC has $M_{total} = 3.1 times 10^9 M_odot$, comparable to that of the Large Magellanic Cloud. TDGCs are phase-space-correlated, reach high metallicities, and are typically younger than dark matter-rich dwarf galaxies. We report for the first time the verification of the dual dwarf theorem in a self-consistent $Lambda$CDM cosmological simulation. Simulated TDGCs and dark matter-dominated galaxies populate different regions in the radius-mass diagram in disagreement with observations of early-type galaxies. The dark matter-poor galaxies formed in Illustris-1 have comparable radii to observed dwarf galaxies and to TDGs formed in other galaxy-encounter simulations. In Illustris-1, only 0.17% of all selected galaxies with $M_{stellar} = 5 times 10^7-10^9 M_odot$ are TDGCs or dark matter-poor dwarf galaxies. The occurrence of NGC 1052-DF2-type objects is discussed.
The presence of hot gaseous coronae around present-day massive spiral galaxies is a fundamental prediction of galaxy formation models. However, our observational knowledge remains scarce, since to date only four gaseous coronae were detected around spirals with massive stellar bodies ($gtrsim2times10^{11} rm{M_{odot}}$). To explore the hot coronae around lower mass spiral galaxies, we utilized Chandra X-ray observations of a sample of eight normal spiral galaxies with stellar masses of $(0.7-2.0)times10^{11} rm{M_{odot}}$. Although statistically significant diffuse X-ray emission is not detected beyond the optical radii ($sim20$ kpc) of the galaxies, we derive $3sigma$ limits on the characteristics of the coronae. These limits, complemented with previous detections of NGC 1961 and NGC 6753, are used to probe the Illustris Simulation. The observed $3sigma$ upper limits on the X-ray luminosities and gas masses exceed or are at the upper end of the model predictions. For NGC 1961 and NGC 6753 the observed gas temperatures, metal abundances, and electron density profiles broadly agree with those predicted by Illustris. These results hint that the physics modules of Illustris are broadly consistent with the observed properties of hot coronae around spiral galaxies. However, a shortcoming of Illustris is that massive black holes, mostly residing in giant ellipticals, give rise to powerful radio-mode AGN feedback, which results in under luminous coronae for ellipticals.
Quenching is a key topic in exploring the formation and evolution of galaxies. In this work, we study the quenching rate, i.e., the variation in the fraction of quenched galaxies per unit time, of the Illustris-1 simulation. By building the quenched fraction function $f(m,rho, t)$ of each snapshot in the simulation, we derive an accurate form of quenching rate as $Re_q=df(m,rho,t)/dt$. According to the analytic expression of the quenching rate $Re_q$, we split it into four components: mass quenching, environmental quenching, intrinsic mass quenching and intrinsic environmental quenching. The precise value and evolutions can be given via the formula of $Re_q$. With this method, we analyze the Illustris-1 simulation. We find that quenched galaxies concentrate around $M_*simeq10^{11}h^{-1}M_odot$ and $delta+1simeq10^{3.5}$ at earlier times, and that the quenching galaxy population slowly shifts to lower stellar mass and lower overdensity regions with time. We also find that mass quenching dominates the quenching process in this simulation, in agreement with some previous analytical models. Intrinsic quenching is the second most important component. Environmental quenching is very weak, because it is possible that the pre- or postprocessing of environments disguises environmental quenching as intrinsic quenching. We find that our method roughly predict the actual quenching rate. It could well predict the actual amount of galaxies quenched by intrinsic quenching. However, it overestimates the amount of mass quenching galaxies and underestimates the amount of environmental quenching. We suggest that the reason is the nonlinearity of the environmental overdensity change and mass growth of the galaxy.
Surveying dark matter deficient galaxies (those with dark matter mass to stellar mass ratio $M_{rm dm}/M_{rm star}<1$) in the Illustris simulation of structure formation in the flat-$Lambda$CDM cosmogony, we find $M_{rm star} approx 2 times 10^8, M_sun$ galaxies that have properties similar to those ascribed by citet{vanDokkumetal2018a} to the ultra-diffuse galaxy NGC1052-DF2. The Illustris simulation also contains more luminous dark matter deficient galaxies. Illustris galaxy subhalo 476171 is a particularly interesting outlier, a massive and very compact galaxy with $M_{rm star} approx 9 times 10^{10}, M_sun$ and $M_{rm dm}/M_{rm star} approx 0.1$ and a half-stellar-mass radius of $approx 2$ kpc. If the Illustris simulation and the $Lambda$CDM model are accurate, there are a significant number of dark matter deficient galaxies, including massive luminous compact ones. It will be interesting to observationally discover these galaxies, and to also more clearly understand how they formed, as they are likely to provide new insight into and constraints on models of structure formation and the nature of dark matter.
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