27 research outputs found
Formation of galaxies in {\Lambda}CDM cosmologies. I. The fine structure of disc galaxies
We present a detailed analysis of the global and fine structure of four
middle-mass disc galaxies obtained from simulations in a CDM scenario.
These objects have photometric D/T ratios in good agreement with those observed
for late-type spirals, as well as kinematic properties in agreement with the
observational Tully-Fisher relation. We identify the different dynamical
components at z=0 on the basis of both orbital parameters and the binding
energy of stars in the galaxy. In this way, we recognize a slowly rotating
centrally concentrated spheroid, and two disc components supported by rotation:
a thin disc with stars in nearly circular orbits, and a thick disc with orbital
parameters transitional between the thin disc and the spheroid. The spheroidal
component is composed mainly by old, metal-poor and {\alpha}-enhanced stars.
The distribution of metals in this component shows, however, a clear bimodality
with a low-metallicity peak, which could be related to a classical bulge, and a
high-metallicity peak, which could be related to a pseudo-bulge. The thin disc
appears in our simulations as the youngest and most metal-rich component. The
radial distribution of ages and colours in this component are U-shaped: the new
stars are forming in the inner regions, and then migrate through secular
processes. Finally, we also find a thick disc containing about 16% of the total
stellar mass and with properties that are intermediate between those of the
thin disc and the spheroid. Its low-metallicity stars are {\alpha}-enhanced
when compared to thin disc stars of the same metallicity. The structural
parameters (e.g., the scale height) of the simulated thick discs suggest that
such a component could result from the combination of different thickening
mechanisms that include merger-driven processes, but also long-lived internal
perturbations of the thin disc. [Abridged]Comment: 23 pages, 16 figures, accepted for publication in MNRAS, references
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The distribution of mass components in simulated disc galaxies
Using 22 hydrodynamical simulated galaxies in a LCDM cosmological context we
recover not only the observed baryonic Tully-Fisher relation, but also the
observed "mass discrepancy--acceleration" relation, which reflects the
distribution of the main components of the galaxies throughout their disks.
This implies that the simulations, which span the range 52 < V <
222 km/s where V is the circular velocity at the flat part of the
rotation curve, and match galaxy scaling relations, are able to recover the
observed relations between the distributions of stars, gas and dark matter over
the radial range for which we have observational rotation curve data.
Furthermore, we explicitly match the observed baryonic to halo mass relation
for the first time with simulated galaxies. We discuss our results in the
context of the baryon cycle that is inherent in these simulations, and with
regards to the effect of baryonic processes on the distribution of dark matter.Comment: 8 pages, 7 pdf figures. Accepted for publication in MNRAS on 2015
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The Origin of Kinematically Persistent Planes of Satellites as Driven by the Early Evolution of the Cosmic Web in ÎCDM
Kinematically persistent planes (KPPs) of satellites are fixed sets of satellites co-orbiting around their host galaxy, whose orbital poles are conserved and clustered across long cosmic time intervals. They play the role of âskeletons,â ensuring the long-term durability of positional planes. We explore the physical processes behind their formation in terms of the dynamics of the local cosmic web (CW), characterized via the so-called Lagrangian volumes (LVs) built up around two zoom-in, cosmological hydro-simulations of Milky Wayâmass disk galaxy + satellites systems, where three KPPs have been identified. By analyzing the LV deformations in terms of the reduced tensor of inertia (TOI), we find an outstanding alignment between the LV principal directions and the KPP satellitesâ orbital poles. The most compressive local mass flows (along the eË3 eigenvector) are strong at early times, feeding the so-called eË3 -structure, while the smallest TOI axis rapidly decreases. The eË3 -structure collapse marks the end of this regime and is the timescale for the establishment of satellite orbital pole clustering when the Universe is âČ4 Gyr old. KPP protosatellites aligned with eË3 are those whose orbital poles are either aligned from early times or have been successfully bent at eË3 -structure collapse. KPP satellites associated with eË1 tend to have early trajectories already parallel to eË3 . We show that KPPs can arise as a result of the ÎCDM-predicted large-scale dynamics acting on particular sets of protosatellites, the same dynamics that shape the local CW environment
NIHAO XIII: Clumpy discs or clumpy light in high redshift galaxies?
Many massive star forming disc galaxies in the redshift range 3 to 0.5 are
observed to have a clumpy morphology showing giant clumps of size 1 kpc
and masses of about to . The nature and fate
of these giant clumps is still under debate. In this work we use 19
high-resolution simulations of disc galaxies from the NIHAO sample to study the
formation and the evolution of clumps in the discs of high redshift galaxies.
We use mock HST - CANDELS observations created with the radiative transfer code
GRASIL-3D to carry out, for the first time, a quantitative comparison of the
observed fraction of clumpy galaxies and its evolution with redshift with
simulations. We find a good agreement between the observed clumpy fraction and
the one of the NIHAO galaxies. We find that dust attenuation can suppress
intrinsically bright clumps and enhance less luminous ones. In our galaxy
sample we only find clumps in light (u-band) from young stars but not in
stellar mass surface density maps. This means that the NIHAO sample does not
show clumpy stellar discs but rather a clumpy light distribution originating
from clumpy star formation events. The clumps found in the NIHAO sample match
observed age/color gradients as a function of distance from the galaxy center
but they show no sign of inward migration. Clumps in our simulations disperse
on timescales of a about a hundred Myr and their contribution to bulge growth
is negligible
Planes of satellites around simulated disk galaxies I: finding high-quality planar configurations from positional information and their comparison to MW/M31 data
We address the âplane of satellites problemâ by studying planar configurations around two disk galaxies with no late major mergers, formed in zoom-in hydro-simulations. Due to the current lack of good-quality kinematic data for M31 satellites, we use only positional information. So far, positional analyses of simulations are unable to find planes as thin and populated as the observed ones. We follow a novel systematic and detailed plane searching technique to study the properties and quality of planes of satellites, in both simulations or real data. In particular, (i) we extend the four-galaxy-normal density plot method (Pawlowski et al. 2013) in a way designed to efficiently identify high-quality planes (i.e., thin and populated) without imposing extra constraints on their properties, and (ii), we apply it for the first time to simulations. Using zoom-in simulations allows us to mimic Milky Way/M31- like systems regarding the number of satellites involved as well as galactic disk effects. In both simulations, we find satellite planar configurations that are compatible, along given time intervals, with all of the spatial characteristics of observed planes identified using the same methodology. During most of these periods, planes are approximately perpendicular to the galactic disk. However, the fraction of co-orbiting satellites within them is, in general, low, suggesting time-varying satellite membership. We conclude that high-quality positional planes of satellites could be not infrequent in ÎCDM-formed disk galaxies with a quiet assembly history. Detecting kinematically coherent, time-persistent planes demands considering the full six-dimensional phase-space information of satellites
A two-phase scenario for bulge assembly in ÎcDM cosmologies
The Astrophysical Journal 763.1 (2013): 26 reproduced by permission of the AASWe analyze and compare the bulges of a sample of L* spiral galaxies in hydrodynamical simulations in a cosmological context, using two different codes, P-DEVA and GASOLINE. The codes regulate star formation in very different ways, with P-DEVA simulations inputting low star formation efficiency under the assumption that feedback occurs on subgrid scales, while the GASOLINE simulations have feedback that drives large-scale outflows. In all cases, the marked knee shape in mass aggregation tracks, corresponding to the transition from an early phase of rapid mass assembly to a later slower one, separates the properties of two populations within the simulated bulges. The bulges analyzed show an important early starburst resulting from the collapse-like fast phase of mass assembly, followed by a second phase with lower star formation, driven by a variety of processes such as disk instabilities and/or mergers. Classifying bulge stellar particles identified at z = 0 into old and young according to these two phases, we found bulge stellar sub-populations with distinct kinematics, shapes, stellar ages, and metal contents. The young components are more oblate, generally smaller, more rotationally supported, with higher metallicity and less alpha-element enhanced than the old ones. These results are consistent with the current observational status of bulges, and provide an explanation for some apparently paradoxical observations, such as bulge rejuvenation and metal-content gradients observed. Our results suggest that bulges of L* galaxies will generically have two bulge populations that can be likened to classical and pseudo-bulges, with differences being in the relative proportions of the two, which may vary due to galaxy mass and specific mass accretion and merger histories.This work was partially supported by the MICINN (Spain) through the grants AYA2009-12792-C03-02 and AYA2009-12792-C03-03 from the PNAyA, as well as by the regional Madrid V PRICIT program through the ASTROMADRID network (CAM S2009/ESP-1496) and the âSupercomputaciĂłn y e-Cienciaâ Consolider-Ingenio CSD2007-0050 project