28 research outputs found
Galaxie se slupkami: kinematika slupek, rozpad satelitní galaxie a dynamické tření
Název práce: Galaxie se slupkami: kinematika slupek, rozpad satelitní galaxie a dynamické tření Autor: Ivana Ebrová Katedra / Ústav: Astronomický ústav AV ČR, v.v.i. Vedoucí doktorské práce: RNDr. Bruno Jungwiert, Ph.D., Astronomický ústav AV ČR, v.v.i. Abstrakt: Slupky hvězdné povahy pozorované v mnoha eliptických a čočkových galaxiích, jakožto i v několika spirálních a trpasličích galaxiích jsou pravděpodobně pozůstatkem radiální galaktické srážky velké a malé galaxie. Ukazujeme, že distribuce rychlostí hvězd slupky ve směru zorného paprsku vykazuje čtyři jasná maxima. Našli jsme jednoduchý analytický předpis spojující polohy těchto maxim s tvarem potenciálu galaxie, jmenovitě s kruhovou rychlostí na poloměru slupky a rychlostí šíření slupky. Tento předpis s úspěchem aplikujeme na výsledky simulace radiální srážky galaxií s testovacími částicemi. Kinematika slupek se tedy může stát novým nezávislým nástrojem pro určení obsahu temné hmoty ve slupkových galaxiích až do vzdálenosti okolo 100 kpc od centra galaxie. Navíc zkoumáme dynamické tření a postupný rozpad kanibalizované galaxie během srážky produkující slupky v simulacích s testovacími částicemi. Kombinace těchto dvou efektů může značně přerozdělit polohy a jasnosti vzniklých slupek. Zanedbání těchto efektů může vést k závažným chybách při pokusu o...Title: Shell galaxies: kinematical signature of shells, satellite galaxy disruption and dynamical friction Author: Ivana Ebrová Department / Institute: Astronomical Institute of the Academy of Sciences of the Czech Republic Supervisor of the doctoral thesis: RNDr. Bruno Jungwiert, Ph.D., Astronomical Institute of the Academy of Sciences of the Czech Republic Abstract: Stellar shells observed in many giant elliptical and lenticular as well as a few spiral and dwarf galaxies presumably result from radial minor mergers of galaxies. We show that the line-of-sight velocity distribution of the shells has a quadruple-peaked shape. We found simple analytical expressions that connect the positions of the four peaks of the line profile with the mass distribution of the galaxy, namely, the circular velocity at the given shell radius and the propagation velocity of the shell. The analytical expressions were applied to a test-particle simulation of a radial minor merger, and the potential of the simulated host galaxy was successfully recovered. Shell kinematics can thus become an independent tool to determine the content and distribution of dark matter in shell galaxies up to ~100 kpc from the center of the host galaxy. Moreover we investigate the dynamical friction and gradual disruption of the cannibalized galaxy...Matematicko-fyzikální fakultaFaculty of Mathematics and Physic
N-body simulations of shell galaxies
Shell galaxies are ordinary elliptical galaxies that contain a fine structure in the form of concentric arcs with sharp edges in their luminous profile. This work contains a summary of our comprehensive study of the actual research and publications on this remarkable phenomenon, concerning both the observations as well as the numerical simulations. Along with it we present the results of our own simulations that broaden our view of the origin of the shells in a radial merger of a massive elliptical galaxy with a less massive one. We have introduced the dynamical friction into the simulation by semi-analytical means based on the Chandrasekhar formula. The main result is that the dynamical friction together with the gradual disintegration of the secondary galaxy that is also discussed can significantly affect the process of the shell formation and must be taken into consideration in their modelling. It turns out that the time scales on which the merger takes place are rather sensitive to the choice of the parameters. We present an estimate of their magnitude in different cases. The mass loss of the secondary galaxy during the merger mitigates the effect of the dynamical friction but does not make its role negligible.Astronomický ústav UKAstronomical Institute of Charles UniversityFaculty of Mathematics and PhysicsMatematicko-fyzikální fakult
Galaxie se slupkami
Název práce: Galaxie se slupkami Autor: Ivana Ebrová Katedra / Ústav: Astronomický ústav AV ČR, v.v.i. Vedoucí doktorské práce: RNDr. Bruno Jungwiert, Ph.D., Astronomický ústav AV ČR, v.v.i. Abstrakt: Slupky hvězdné povahy pozorované v mnoha eliptických a čočkových galaxiích, jakožto i v několika spirálních a trpasličích galaxiích jsou pravděpodobně pozůstatkem radiální galaktické srážky velké a malé galaxie. Ukazujeme, že distribuce rychlostí hvězd slupky ve směru zorného paprsku vykazuje čtyři jasná maxima. Našli jsme jednoduchý analytický předpis spojující polohy těchto maxim s tvarem potenciálu galaxie, jmenovitě s kruhovou rychlostí na poloměru slupky a rychlostí šíření slupky. Tento předpis s úspěchem aplikujeme na výsledky simulace radiální srážky galaxií s testovacími částicemi. Kinematika slupek se tedy může stát novým nezávislým nástrojem pro určení obsahu temné hmoty ve slupkových galaxiích až do vzdálenosti okolo 100 kpc od centra galaxie. Navíc zkoumáme dynamické tření a postupný rozpad kanibalizované galaxie během srážky produkující slupky v simulacích s testovacími částicemi. Kombinace těchto dvou efektů může značně přerozdělit polohy a jasnosti vzniklých slupek. Zanedbání těchto efektů může vést k závažným chybách při pokusu o datování srážky v pozorovaných slupkových galaxiích. Klíčová...Title: Shell galaxies Author: Ivana Ebrová Department / Institute: Astronomical Institute of the Academy of Sciences of the Czech Republic Supervisor of the doctoral thesis: RNDr. Bruno Jungwiert, Ph.D., Astronomical Institute of the Academy of Sciences of the Czech Republic Abstract: Stellar shells observed in many giant elliptical and lenticular as well as a few spiral and dwarf galaxies presumably result from radial minor mergers of galaxies. We show that the line-of- sight velocity distribution of the shells has a quadruple-peaked shape. We found simple analytical expressions that connect the positions of the four peaks of the line profile with the mass distribution of the galaxy, namely, the circular velocity at the given shell radius and the propagation velocity of the shell. The analytical expressions were applied to a test-particle simulation of a radial minor merger, and the potential of the simulated host galaxy was successfully recovered. Shell kinematics can thus become an independent tool to determine the content and distribution of dark matter in shell galaxies up to ~100 kpc from the center of the host galaxy. Moreover we investigate the dynamical friction and gradual disruption of the cannibalized galaxy during the shell formation in the framework of a simulation with test particles. The...Matematicko-fyzikální fakultaFaculty of Mathematics and Physic
Shell galaxies as laboratories for testing MOND
Tests of MOND in ellipticals are relatively rare because these galaxies often
lack kinematic tracers in the regions where the MOND effects are significant.
Stellar shells observed in many elliptical galaxies offer a promising way to
constrain their gravitational field. Shells appear as glowing arcs around their
host galaxy. They are observed up to ~100 kpc. The stars in axially symmetric
shell systems move in nearly radial orbits. The radial distributions of shell
locations and the spectra of stars in shells can be used to constrain the
gravitational potential of their host galaxy. The symmetrical shell systems,
being especially suitable for these studies, occur in approximately 3% of all
early-type galaxies. Hence the shells substantially increase the number of
ellipticals in which MOND can be tested up to large radii. In this paper, we
review our work on shell galaxies in MOND. We summarize the paper B\'{i}lek et
al. (2013), where we demonstrated the consistency of shell radii in an
elliptical NGC 3923 with MOND, and the work B\'{i}lek et al. (2014), in which
we predicted a giant (~200 kpc), as yet undiscovered shell of NGC 3923. We
explain the shell identification method, which was used in these two papers. We
further describe the expected shape of line profiles in shell spectra in MOND
which is very special due to the direct relation of the gravitational field and
baryonic matter distribution (B\'{i}lek et al., 2014, in preparation).Comment: 21 pages, 8 figures, 1 table, accepted for publication in the special
MOND issue of the Canadian Journal of Physic
Galaxies with kinematically distinct cores in Illustris
The growing amount of integral-field spectroscopic data creates an increased
demand for understanding kinematic peculiarities that carry valuable
information about the evolution of the host galaxies. For kinematically
distinct cores (KDCs), a number of formation mechanisms have been proposed, but
it is still unclear which of them commonly occur in the Universe. We aim to
address the KDC formation in the cosmological context. We used the publicly
available data of the large-scale hydrodynamic cosmological simulation
Illustris. We identify 134 KDCs, study their properties, and follow their
evolution back in time. Examples of four galaxies hosting KDCs are presented
and described in detail. The masses of the KDC hosts follow the general
distribution of the Illustris galaxies, with a possible slight preference
towards massive galaxies. KDCs can be long-lived features, with their formation
epochs roughly uniformly distributed in look-back times 0-11.4 Gyr, and they
can survive even major or multiple subsequent mergers. There is no single
channel of KDC formation, but mergers seem to be the formation mechanism for
about 60% of KDCs with a significant preference for major mergers and with the
percentage being higher among massive hosts. Other KDCs formed during a
pericentric passage or flyby of another galaxy, by precession of a previously
formed rapidly rotating core, or without an obvious external cause. The mean
mass-weighted stellar age inside the KDC radius is either about the same as the
look-back time of the KDC formation or older. Although the radii of our KDCs
are on average larger than observed, we find that younger stellar ages are
typically associated with smaller KDCs. A significant fraction of KDC hosts
possess stellar shells formed during mergers that led to KDCs within the last 5
Gyr, or double peaks in their velocity dispersion maps.Comment: 18 pages, 16 figures, 1 table; accepted for publication in A&
MOND implications for spectral line profiles of shell galaxies: shell formation history and mass-velocity scaling relations
Context. Many ellipticals are surrounded by round stellar shells probably
stemming from minor mergers. A new method for constraining gravitational
potential in elliptical galaxies has recently been suggested. It uses the
spectral line profiles of these shells to measure the circular velocity at the
edge of the shell and the expansion velocity of the shell itself. MOND is an
alternative to the dark matter framework aiming to solve the missing mass
problem.
Aims. We study how the circular and expansion velocities behave in MOND for
large shells.
Methods. The asymptotic behavior for infinitely large shells is derived
analytically. The applicability of the asymptotic results for finitely sized
shells is studied numerically on a grid of galaxies modeled with S\'ersic
spheres.
Results. Circular velocity settles asymptotically at a value determined by
the baryonic mass of the galaxy forming the baryonic Tully-Fisher relation
known for disk galaxies. Shell expansion velocity also becomes asymptotically
constant. The expansion velocities of large shells form a multibranched analogy
to the baryonic Tully-Fisher relation, together with the galactic baryonic
masses. For many - but not all - shell galaxies, the asymptotic values of these
two types of velocities are reached under the effective radius. If MOND is
assumed to work in ellipticals, then the shell spectra allow many details of
the history to be revealed about the formation of the shell system, including
its age. The results pertaining to circular velocities apply to all elliptical
galaxies, not only those with shells.Comment: 8 pages, 7 figures, 1 table, accepted for publication in A&
Deep imaging of the shell elliptical galaxy NGC3923 with MegaCam
Context. The elliptical galaxy NGC 3923 is known to be surrounded by a number
of stellar shells, probable remnants of an accreted galaxy. Despite its
uniqueness, the deepest images of its outskirts come from the 1980s. On the
basis of the modified Newtonian dynamics (MOND), it has recently been predicted
that a new shell lies in this region.
Aims. We obtain the deepest image ever of the galaxy, map the tidal features
in it, and search for the predicted shell.
Methods. The image of the galaxy was taken by the MegaCam camera at the
Canada-France-Hawaii Telescope in the g' band. It reached the
surface-brightness limit of 29 mag/arcsec2. In addition, we reanalyzed an
archival HST image of the galaxy.
Results. We detected up to 42 shells in NGC 3923. This is by far the highest
number among all shell galaxies. We present the description of the shells and
other tidal features in the galaxy. A probable progenitor of some of these
features was discovered. The shell system likely originates from two or more
progenitors. The predicted shell was not detected, but the new image revealed
that the prediction was based on incorrect assumptions and poor data.Comment: 14 pages, 2 tables, 19 figures, accepted for publication in A&
FRAM telescopes and their measurements of aerosol content at the Pierre Auger Observatory and at future sites of the Cherenkov Telescope Array
A FRAM (F/(Ph)otometric Robotic Atmospheric Monitor) telescope is a system of
a robotic mount, a large-format CCD camera and a fast telephoto lens that can
be used for atmospheric monitoring at any site when information about the
atmospheric transparency is required with high spatial or temporal resolution
and where continuous use of laser-based methods for this purpose would
interfere with other observations. The original FRAM has been operated at the
Pierre Auger Observatory in Argentina for more than a decade, while three more
FRAMs are foreseen to be used by the Cherenkov Telescope Array (CTA). The CTA
FRAMs are being deployed ahead of time to characterize the properties of the
sites prior to the operation of the CTA telescopes; one FRAM has been running
on the planned future CTA site in Chile for a year while two others are
expected to become operational before the end of 2018. We report on the
hardware and current status of operation and/or deployment of all the FRAM
instruments in question as well as on some of the preliminary results of
integral aerosol measurements by the FRAMs in Argentina and ChileComment: Proceedings of AtmoHEAD 201