Subscribe to the gold package and get unlimited access to Shamra Academy
Register a new userOn the Formation of Elliptical Rings in Disk Galaxies
139
0
0.0
(
0
)
Ask ChatGPT about the research
No Arabic abstract
N-body simulations of galactic collisions are employed to investigate the formation of elliptical rings in disk galaxies. The relative inclination between disk and dwarf galaxies is studied with a fine step of five degrees. It is confirmed that the eccentricity of elliptical ring is linearly proportional to the inclination angle. Deriving from the simulational results, an analytic formula which expresses the eccentricity as a function of time and inclination angle is obtained. This formula shall be useful for the interpretations of the observations of ring systems, and therefore reveals the merging histories of galaxies.
rate research
Read More
In order to investigate the formation mechanisms of the rare compact elliptical galaxies (cE) we have compiled a sample of 25 cEs with good SDSS spectra, covering a range of stellar masses, sizes and environments. They have been visually classified according to the interaction with their host, representing different evolutionary stages. We have included clearly disrupted galaxies, galaxies that despite not showing signs of interaction are located close to a massive neighbor (thus are good candidates for a stripping process), and cEs with no host nearby. For the latter, tidal stripping is less likely to have happened and instead they could simply represent the very low-mass, faint end of the ellipticals. We study a set of properties (structural parameters, stellar populations, star formation histories and mass ratios) that can be used to discriminate between an intrinsic or stripped origin. We find that one diagnostic tool alone is inconclusive for the majority of objects. However, if we combine all the tools a clear picture emerges. The most plausible origin, as well as the evolutionary stage and progenitor type, can be then determined. Our results favor the stripping mechanism for those galaxies in groups and clusters that have a plausible host nearby, but favors an intrinsic origin for those rare cEs without a plausible host and that are located in looser environments.
We have searched for presence of current star formation in outer stellar rings of early-type disk (S0-Sb) galaxies by inspecting a representative sample of nearby galaxies with rings from the recent Spitzer catalog ARRAKIS (Comeron et al. 2014). We have found that regular rings (of R-type) reveal young stellar population with the age of less than 200~Myr in about half of all the cases, while in the pseudorings (open rings, R), which inhabit only spiral galaxies, current star formation proceeds almost always.
We investigate the formation history of massive disk galaxies in hydro-dynamical simulation--the IllustrisTNG, to study why massive disk galaxies survive through cosmic time. 83 galaxies in the simulation are selected with M$_{*,z=0}$ $>8times10^{10}$ M$_odot$ and kinematic bulge-to-total ratio less than $0.3$. We find that 8.4 percent of these massive disk galaxies have quiet merger histories and preserve disk morphology since formed. 54.2 percent have a significant increase in bulge components in history, then become disks again till present time. The rest 37.3 percent experience prominent mergers but survive to remain disky. While mergers and even major mergers do not always turn disk galaxies into ellipticals, we study the relations between various properties of mergers and the morphology of merger remnants. We find a strong dependence of remnant morphology on the orbit type of major mergers. Specifically, major mergers with a spiral-in falling orbit mostly lead to disk-dominant remnants, and major mergers of head-on galaxy-galaxy collision mostly form ellipticals. This dependence of remnant morphology on orbit type is much stronger than the dependence on cold gas fraction or orbital configuration of merger system as previously studied.
The level of star formation in elliptical galaxies is poorly constrained, due to difficulties in quantifying the contamination of flux-based estimates of star formation from unrelated phenomena, such as AGN and old stellar populations. We here utilise core-collapse supernovae (CCSNe) as unambiguous tracers of recent star formation in ellipticals within a cosmic volume. We firstly isolate a sample of 421 z < 0.2, r < 21.8 mag CCSNe from the SDSS-II Supernova Survey. We then introduce a Bayesian method of identifying ellipticals via their colours and morphologies in a manner unbiased by redshift and yet consistent with manual classification from Galaxy Zoo 1. We find ~ 25 % of z < 0.2 r < 20 mag galaxies in the Stripe 82 region are ellipticals (~ 28000 galaxies). In total, 36 CCSNe are found to reside in ellipticals. We demonstrate that such early-types contribute a non-negligible fraction of star formation to the present-day cosmic budget, at 11.2 $pm$ 3.1 (stat) $^{+3.0}_{-4.2}$ (sys) %. Coupling this result with the galaxy stellar mass function of ellipticals, the mean specific star formation rate (SSFR; $overline{S}$) of these systems is derived. The best-fit slope is given by log ($overline{S}(M)$/yr) = - (0.80 $pm$ 0.59) log ($M/10^{10.5}rm{M}_{odot}$) - 10.83 $pm$ 0.18. The mean SSFR for all log ($M/rm{M}_{odot}$) > 10.0 ellipticals is found to be $overline{S} = 9.2 pm 2.4$ (stat) $^{+2.7}_{-2.3}$ (sys) $times 10^{-12}$ yr$^{-1}$, which is consistent with recent estimates via SED-fitting, and is 11.8 $pm$ 3.7 (stat) $^{+3.5}_{-2.9}$ (sys) % of the mean SSFR level on the main sequence as also derived from CCSNe. We find the median optical spectrum of elliptical CCSN hosts is statistically consistent with that of a control sample of ellipticals that do not host CCSNe, implying that these SN-derived results are well-representative of the total low-z elliptical population.
In this paper we compare the predictions of a detailed multi-zone chemical evolution model for elliptical galaxies with the very recent observations of the galaxy NGC 4697. As a consequence of the earlier development of the wind in the outer regions with respect to the inner ones, we predict an increase of the mean stellar [<Mg/Fe>] ratio with radius, in very good agreement with the data for NGC4697. This finding strongly supports the proposed outside-in formation scenario for ellipticals. We show that, in spite of the good agreement found for the [<Mg/Fe>] ratio, the predicted slope of the mass-weighted metallicity gradient does not reproduce the one derived from observations, once a calibration to convert indices into abundances is applied. This is explained as the consequence of the different behaviour with metallicity of the line-strength indices as predicted by a Single Stellar Population (SSP) and those derived by averaging over a Composite Stellar Population (CSP). In order to better address this issue, we calculate the theoretical ``G-dwarf distributions of stars as functions of both metallicity ([Z/H]) and [Fe/H], showing that they are broad and asymmetric that a SSP cannot correctly mimick the mixture of stellar populations at any given radius. We find that these distributions differ from the ``G-dwarf distributions especially at large radii,except for the one as a function of [Mg/Fe]. Therefore, we conclude that in ellipticals the [Mg/Fe] ratio is the most reliable quantity to be compared with observations and is the best estimator of the star formation timescale at each radius.(abridged)
Log in to be able to interact and post comments
comments
Fetching comments
Sign in to be able to follow your search criteria
