اشترك بالحزمة الذهبية واحصل على وصول غير محدود شمرا أكاديميا
تسجيل مستخدم جديدA minor merger origin for stellar inner discs and rings in spiral galaxies
148
0
0.0
(
0
)
اسأل ChatGPT حول البحث
ﻻ يوجد ملخص باللغة العربية
Recent observations show that inner discs and rings (IDs and IRs, henceforth) are not preferably found in barred galaxies, a fact that points to the relevance of formation mechanisms different to the traditional bar-origin scenario. In contrast, the role of minor mergers in the formation of these inner components (ICs), while often invoked, is still poorly understood. We have investigated the capability of minor mergers to trigger the formation of IDs and IRs in spiral galaxies through collisionless N-body simulations. We have run a battery of minor mergers in which both primary and secondary are modelled as disc-bulge-halo galaxies with realistic density ratios. A detailed analysis of the morphology, structure, and kinematics of the ICs resulting from the minor merger has been carried out. All the simulated minor mergers develop thin ICs out of satellite material, supported by rotation. A wide morphological zoo of ICs has been obtained (including IDs, IRs, pseudo-rings, nested IDs, spiral patterns, and combinations of them), but all with structural and kinematical properties similar to observations. The existence of the resulting ICs can be deduced through the features that they imprint in the isophotal profiles and kinemetric maps of the final remnant, as in many real galaxies. The realistic density ratios used in the present models make the satellites to experience more efficient orbital circularization and disruption than in previous studies. Combined with the disc resonances induced by the encounter, these processes give place to highly aligned co- and counter-rotating ICs in the remnant centre. Therefore, minor mergers are an efficient mechanism to form rotationally-supported stellar ICs in spiral galaxies, neither requiring strong dissipation nor the development of noticeable bars (abridged).
قيم البحث
اقرأ أيضاً
Minor merger of galaxies are common during the evolutionary phase of galaxies. Here, we investigate the dynamical impact of a minor merger (mass ratio 1:10) event on the final fate of a stellar bar in the merger remnant. To achieve that, we choose a
set of minor merger models from the publicly available GalMer library of galaxy merger simulations. The models differ in terms of their orbital energy, orientation of the orbital spin vector, and morphology of the satellite galaxy (discy/spheroidal). We demonstrate that the central stellar bar, initially present in the host galaxy, undergoes a transient bar amplification phase after each pericentre passage of the satellite; in concordance with past studies of bar excitation due to tidal encounter. However, once the merger happens, the central stellar bar weakens substantially in the post-merger remnants. The accumulation of satellites stars in the central region of merger remnant plays a key role in the bar weakening process; causing a net increase in the central mass concentration as well as in the specific angular momentum content. We find that the efficiency of mass accumulation from the satellite in the central parts of merger remnants depends on the orbital parameters as well as on the satellites morphology. Consequently, different minor merger models display different degrees of bar weakening event. This demonstrates that minor merger of galaxies is a plausible avenue for bar weakening in disc galaxies.
We study the effect of dissipational gas physics on the vertical heating and thickening of disc galaxies during minor mergers. We produce a suite of minor merger simulations for Milky Way-like galaxies. This suite consists of collisionless simulation
s as well as hydrodynamical runs including a gaseous component in the galactic disc. We find that in dissipationless simulations minor mergers cause the scale height of the disc to increase by up to a factor of ~2. When the presence of gas in the disc is taken into account this thickening is reduced by 25% (50%) for an initial disc gas fraction of 20% (40%), leading to a final scale height z0 between 0.6 and 0.7 kpc, regardless of the initial scale height. We argue that the presence of gas reduces disc heating via two mechanisms: absorption of kinetic impact energy by the gas and/or formation of a new thin stellar disc that can cause heated stars to recontract towards the disc plane. We show that in our simulations most of the gas is consumed during the merger and thus the regrowth of a new thin disc has a negligible impact on the z0 of the post merger galaxy. Final disc scale heights found in our simulations are in good agreement with studies of the vertical structure of spiral galaxies where the majority of the systems are found to have scale heights of 0.4 kpc < z0 < 0.8 kpc. We also found no tension between recent measurements of the scale height of the Milky Way thin disc and results coming from our hydrodynamical simulations. We conclude that the existence of a thin disc in the Milky Way and in external galaxies is not in obvious conflict with the predictions of the CDM model.
We analyse a high-resolution, fully cosmological, hydrodynamical disc galaxy simulation, to study the source of the double-exponential light profiles seen in many stellar discs, and the effects of stellar radial migration upon the spatio-temporal evo
lution of both the disc age and metallicity distributions. We find a break in the pure exponential stellar surface brightness profile, and trace its origin to a sharp decrease in the star formation per unit surface area, itself produced by a decrease in the gas volume density due to a warping of the gas disc. Star formation in the disc continues well beyond the break. We find that the break is more pronounced in bluer wavebands. By contrast, we find little or no break in the mass density profile. This is, in part, due to the net radial migration of stars towards the external parts of the disc. Beyond the break radius, we find that ~60% of the resident stars migrated from the inner disc, while ~25% formed in situ. Our simulated galaxy also has a minimum in the age profile at the break radius but, in disagreement with some previous studies, migration is not the main mechanism producing this shape. In our simulation, the disc metallicity gradient flattens with time, consistent with an inside-out formation scenario. We do not find any difference in the intensity or the position of the break with inclination, suggesting that perhaps the differences found in empirical studies are driven by dust extinction.
We present an analysis of the structures and dynamics of the merging cluster Abell~1201, which has two sloshing cold fronts around a cooling core, and an offset gas core approximately 500kpc northwest of the center. New Chandra and XMM-Newton data re
veal a region of enhanced brightness east of the offset core, with breaks in surface brightness along its boundary to the north and east. This is interpreted as a tail of gas stripped from the offset core. Gas in the offset core and the tail is distinguished from other gas at the same distance from the cluster center chiefly by having higher density, hence lower entropy. In addition, the offset core shows marginally lower temperature and metallicity than the surrounding area. The metallicity in the cool core is high and there is an abrupt drop in metallicity across the southern cold front. We interpret the observed properties of the system, including the placement of the cold fronts, the offset core and its tail in terms of a simple merger scenario. The offset core is the remnant of a merging subcluster, which first passed pericenter southeast of the center of the primary cluster and is now close to its second pericenter passage, moving at ~1000 km/s. Sloshing excited by the merger gave rise to the two cold fronts and the disposition of the cold fronts reveals that we view the merger from close to the plane of the orbit of the offset core.
An $m=1$ lopsided asymmetry is common in disc galaxies. Here, we investigate the excitation of an $m=1$ lopsidedness in host galaxies during minor mergers (mass ratio 1:10) while choosing a set of minor merger models (with varying orbital configurati
ons, morphology of the host galaxy) from the GalMer library of galaxy merger simulations. We show that a minor merger triggers a prominent $m=1$ lopsidedness in the stars of the host galaxy. The strength of the $m=1$ lopsidedness undergoes a transient amplification phase after each pericentre passage of the satellite, in concordance with past findings of excitation of an $m=1$ lopsidedness due to tidal encounters. However, once the merger happens, and the post-merger remnant readjusts itself, the lopsidedness fades away in short time-scale ($sim 500-850$ Myr). Furthermore, a delayed merger can drive a prolonged ($sim 2$ Gyr) lopsidedness in the host galaxy. We demonstrate that the $m=1$ lopsidedness rotates with a well-defined pattern speed. The measured pattern speed is much slower than the $m=2$ bar pattern speed, and is retrograde with respect to the bar. This gives rise to a dynamical scenario where the Inner Linblad resonance (ILR) of the $m=1$ lopsidedness falls in between the corotation (CR) and the Outer Linblad resonance (OLR) of the $m=2$ bar mode. A kinematic lopsidedness also arises in the host galaxy, and the resulting temporal variation closely follows that of the density lopsidedness. The minor merger also triggers a transient off-centred stellar disc-dark matter halo configuration due to the tidal encounter with the satellite.
سجل دخول لتتمكن من نشر تعليقات
التعليقات
جاري جلب التعليقات
سجل دخول لتتمكن من متابعة معايير البحث التي قمت باختيارها
