اشترك بالحزمة الذهبية واحصل على وصول غير محدود شمرا أكاديميا
تسجيل مستخدم جديدThe effect of galaxy mass ratio on merger--driven starbursts
94
0
0.0
(
0
)
تأليف
T. J. Cox
اسأل ChatGPT حول البحث
ﻻ يوجد ملخص باللغة العربية
We employ numerical simulations of galaxy mergers to explore the effect of galaxy mass ratio on merger--driven starbursts. Our numerical simulations include radiative cooling of gas, star formation, and stellar feedback to follow the interaction and merger of four disk galaxies. The galaxy models span a factor of 23 in total mass and are designed to be representative of typical galaxies in the local Universe. We find that the merger--driven star formation is a strong function of merger mass ratio, with very little, if any, induced star formation for large mass ratio mergers. We define a burst efficiency that is useful to characterize the merger--driven star formation and test that it is insensitive to uncertainties in the feedback parameterization. In accord with previous work we find that the burst efficiency depends on the structure of the primary galaxy. In particular, the presence of a massive stellar bulge stabilizes the disk and suppresses merger--driven star formation for large mass ratio mergers. Direct, co--planar merging orbits produce the largest tidal disturbance and yield that most intense burst of star formation. Contrary to naive expectations, a more compact distribution of gas or an increased gas fraction both decrease the burst efficiency. Owing to the efficient feedback model and the newer version of SPH employed here, the burst efficiencies of the mergers presented here are smaller than in previous studies.
قيم البحث
اقرأ أيضاً
Extragalactic starbursts induced by gravitational interactions can now be studied from z = ~0 to ~2. The evidence that mergers of gas-rich galaxies tend to trigger galaxy-wide starbursts is strong, both statistically and in individual cases of major
disk-disk mergers. Star formation rates appear enhanced by factors of a few to ~10^3 above normal. Detailed studies of nearby mergers and ULIRGs suggest that the main trigger for starbursts is the rapidly mounting pressure of the ISM in extended shock regions, rather than high- velocity, ~50 - 100 km/s cloud-cloud collisions. Numerical simulations demonstrate that in colliding galaxies the star formation rate depends not only on the gas density, but crucially also on energy dissipation in shocks. An often overlooked characteristic of merger-induced starbursts is that the spatial distribution of the enhanced star formation extends over large scales (~10 - 20 kpc). Thus, although most such starbursts do peak near the galactic centers, young stellar populations pervade merger remnants and explain why (1) age gradients in descendent galaxies are mild and (2) resultant cluster systems are far-flung. This review presents an overview of interesting phenomena observed in galaxy-wide starbursts and emphasizes that such events continue to accompany the birth of elliptical galaxies to the present epoch.
The majority of galaxy mergers are expected to be minor mergers. The observational signatures of minor mergers are not well understood, thus there exist few constraints on the minor merger rate. This paper seeks to address this gap in our understandi
ng by determining if and when minor mergers exhibit disturbed morphologies and how they differ from the morphology of major mergers. We simulate a series of unequal-mass moderate gas-fraction disc galaxy mergers. With the resulting g-band images, we determine how the time-scale for identifying galaxy mergers via projected separation and quantitative morphology (the Gini coefficient G, asymmetry A, and the second-order moment of the brightest 20% of the light M20) depends on the merger mass ratio, relative orientations and orbital parameters. We find that G-M20 is as sensitive to 9:1 baryonic mass ratio mergers as 1:1 mergers, with observability time-scales ~ 0.2-0.4 Gyr. In contrast, asymmetry finds mergers with baryonic mass ratios between 4:1 and 1:1 (assuming local disc galaxy gas-fractions). Asymmetry time-scales for moderate gas-fraction major disc mergers are ~ 0.2-0.4 Gyr, and less than 0.06 Gyr for moderate gas-fraction minor mergers. The relative orientations and orbits have little effect on the time-scales for morphological disturbances. Observational studies of close pairs often select major mergers by choosing paired galaxies with similar luminosities and/or stellar masses. Therefore, the various ways of finding galaxy mergers (G-M20, A, close pairs) are sensitive to galaxy mergers of different mass ratios. By comparing the frequency of mergers selected by different techniques, one may place empirical constraints on the major and minor galaxy merger rates.
Accurate estimation of the merger timescale of galaxy clusters is important to understand the cluster merger process and further the formation and evolution of the large-scale structure of the universe. In this paper, we explore a baryonic effect on
the merger timescale of galaxy clusters by using hydrodynamical simulations. We find that the baryons play an important role in accelerating the merger process. The merger timescale decreases with increasing the gas fraction of galaxy clusters. For example, the merger timescale is shortened by a factor of up to 3 for merging clusters with gas fractions 0.15, compared with the timescale obtained with zero gas fractions. The baryonic effect is significant for a wide range of merger parameters and especially more significant for nearly head-on mergers and high merging velocities. The baryonic effect on the merger timescale of galaxy clusters is expected to have impacts on the structure formation in the universe, such as the cluster mass function and massive substructures in galaxy clusters, and a bias of no-gas may exist in the results obtained from the dark matter-only cosmological simulations.
We present an evolutionary model for starbursts, quasars, and spheroidal galaxies in which mergers between gas-rich galaxies drive nuclear inflows of gas, producing intense starbursts and feeding the buried growth of supermassive black holes (BHs) un
til feedback expels gas and renders a briefly visible optical quasar. The quasar lifetime and obscuring column density depend on both the instantaneous and peak luminosity of the quasar, and we determine this dependence using a large set of simulations of galaxy mergers varying host galaxy properties, orbital geometry, and gas physics. We use these fits to deconvolve observed quasar luminosity functions (LFs) and obtain the evolution of the formation rate of quasars with a certain peak luminosity, n(L_peak,z). Quasars spend extended periods of time at luminosities well below peak, and so n(L_peak) has a maximum corresponding to the break in the observed LF, falling off at both brighter and fainter luminosities. From n(L_peak) and our simulation results, we obtain self-consistent fits to hard and soft X-ray and optical quasar LFs and predict many observables, including: column density distributions of optical and X-ray samples, the LF of broad-line quasars in X-ray samples and the broad-line fraction as a function of luminosity, active BH mass functions, the distribution of Eddington ratios at z~0-2, the z=0 mass function of relic BHs and total mass density of BHs, and the cosmic X-ray background. In every case, our predictions agree well with observed estimates, and unlike previous modeling attempts, we are able to reproduce them without invoking any ad hoc assumptions about source properties or distributions. We provide a library of Monte Carlo realizations of our models for comparison with observations. (Abridged)
We have tested the effect of spatial gradients in stellar mass-to-light ratio (Y) on measurements of black hole masses (MBH) derived from stellar orbit superposition models. Such models construct a static gravitational potential for a galaxy and its
central black hole, but typically assume spatially uniform Y. We have modeled three giant elliptical galaxies with gradients alpha = d(log Y)/d(log r) from -0.2 to +0.1. Color and line strength gradients suggest mildly negative alpha in these galaxies. Introducing a negative (positive) gradient in Y increases (decreases) the enclosed stellar mass near the center of the galaxy and leads to systematically smaller (larger) MBH measurements. For models with alpha = -0.2, the best-fit values of MBH are 28%, 27%, and 17% lower than the constant-Y case, in NGC 3842, NGC 6086, and NGC 7768, respectively. For alpha = +0.1, MBH are 14%, 22%, and 17% higher than the constant-Y case for the three respective galaxies. For NGC 3842 and NGC 6086, this bias is comparable to the statistical errors from individual modeling trials. At larger radii, negative (positive) gradients in Y cause the total stellar mass to decrease (increase) and the dark matter fraction within one effective radius to increase (decrease).
سجل دخول لتتمكن من نشر تعليقات
التعليقات
جاري جلب التعليقات
سجل دخول لتتمكن من متابعة معايير البحث التي قمت باختيارها
