1,287 research outputs found
The effects of ram-pressure stripping on the internal kinematics of simulated spiral galaxies
We investigate the influence of ram-pressure stripping on the internal gas
kinematics of simulated spiral galaxies. Additional emphasis is put on the
question of how the resulting distortions of the gaseous disc are visible in
the rotation curve and/or the full 2D velocity field of galaxies at different
redshifts. A Milky-Way type disc galaxy is modelled in combined
N-body/hydrodynamic simulations with prescriptions for cooling, star formation,
stellar feedback, and galactic winds. This model galaxy moves through a
constant density and temperature gas, which has parameters similar to the
intra-cluster medium (ICM). Rotation curves (RCs) and 2D velocity fields of the
gas are extracted from these simulations in a way that follows the procedure
applied to observations of distant, small, and faint galaxies as closely as
possible. We find that the appearance of distortions of the gaseous disc due to
ram-pressure stripping depends on the direction of the acting ram pressure. In
the case of face-on ram pressure, the distortions mainly appear in the outer
parts of the galaxy in a very symmetric way. In contrast, in the case of
edge-on ram pressure we find stronger distortions. The 2D velocity field also
shows signatures of the interaction in the inner part of the disc. At angles
smaller than 45 degrees between the ICM wind direction and the disc, the
velocity field asymmetry increases significantly compared to larger angles.
Compared to distortions caused by tidal interactions, the effects of
ram-pressure stripping on the velocity field are relatively low in all cases
and difficult to observe at intermediate redshift in seeing-limited
observations. (abridged)Comment: 9 pages, 11 figures, accepted for publication in A&
The narrow X-ray tail and double H-alpha tails of ESO 137-002 in Abell 3627
We present the analysis of a deep Chandra observation of a ~2L_* late-type
galaxy, ESO 137-002, in the closest rich cluster A3627. The Chandra data reveal
a long (>40 kpc) and narrow tail with a nearly constant width (~3 kpc) to the
southeast of the galaxy, and a leading edge ~1.5 kpc from the galaxy center on
the upstream side of the tail. The tail is most likely caused by the nearly
edge-on stripping of ESO 137-002's ISM by ram pressure, compared to the nearly
face-on stripping of ESO 137-001 discussed in our previous work. Spectral
analysis of individual regions along the tail shows that the gas throughout it
has a rather constant temperature, ~1 keV, very close to the temperature of the
tails of ESO 137-001, if the same atomic database is used. The derived gas
abundance is low (~0.2 solar with the single-kT model), an indication of the
multiphase nature of the gas in the tail. The mass of the X-ray tail is only a
small fraction (<5%) of the initial ISM mass of the galaxy, suggesting that the
stripping is most likely at an early stage. However, with any of the single-kT,
double-kT and multi-kT models we tried, the tail is always "over-pressured"
relative to the surrounding ICM, which could be due to the uncertainties in the
abundance, thermal vs. non-thermal X-ray emission, or magnetic support in the
ICM. The H-alpha data from SOAR show a ~21 kpc tail spatially coincident with
the X-ray tail, as well as a secondary tail (~12 kpc long) to the east of the
main tail diverging at an angle of ~23 degrees and starting at a distance of
~7.5 kpc from the nucleus. At the position of the secondary H-alpha tail, the
X-ray emission is also enhanced at the ~2 sigma level. We compare the tails of
ESO 137-001 and ESO 137-002, and also compare the tails to simulations. Both
the similarities and differences of the tails pose challenges to the
simulations. Several implications are briefly discussed.Comment: 15 pages, 6 figures, accepted for publication in Ap
The properties of the Malin 1 galaxy giant disk: A panchromatic view from the NGVS and GUViCS surveys
Low surface brightness galaxies (LSBGs) represent a significant percentage of
local galaxies but their formation and evolution remain elusive. They may hold
crucial information for our understanding of many key issues (i.e., census of
baryonic and dark matter, star formation in the low density regime, mass
function). The most massive examples - the so called giant LSBGs - can be as
massive as the Milky Way, but with this mass being distributed in a much larger
disk. Malin 1 is an iconic giant LSBG, perhaps the largest disk galaxy known.
We attempt to bring new insights on its structure and evolution on the basis of
new images covering a wide range in wavelength. We have computed surface
brightness profiles (and average surface brightnesses in 16 regions of
interest), in six photometric bands (FUV, NUV, u, g, i, z). We compared these
data to various models, testing a variety of assumptions concerning the
formation and evolution of Malin 1. We find that the surface brightness and
color profiles can be reproduced by a long and quiet star-formation history due
to the low surface density; no significant event, such as a collision, is
necessary. Such quiet star formation across the giant disk is obtained in a
disk model calibrated for the Milky Way, but with an angular momentum
approximately 20 times larger. Signs of small variations of the star-formation
history are indicated by the diversity of ages found when different regions
within the galaxy are intercompared.For the first time, panchromatic images of
Malin 1 are used to constrain the stellar populations and the history of this
iconic example among giant LSBGs. Based on our model, the extreme disk of Malin
1 is found to have a long history of relatively low star formation (about 2
Msun/yr). Our model allows us to make predictions on its stellar mass and
metallicity.Comment: Accepted in Astronomy and Astrophysic
Deese-roediger-McDermott paradigm: Effect of previous recall and type of memory task
Pretendeu-se averiguar se a activação dos itens críticos no paradigma de Deese-Roediger-McDermott também ocorreria numa tarefa de completamento. Para analisar a contaminação explícita explorámos a existência de resultados dissociados em função da manipulação do nível de processamento. Na tarefa de completamento, a primação semântica foi estatisticamente superior à primação directa. A ausência do efeito do nível de processamento demonstra que o teste foi de memória implícita. Também avaliámos o impacto de uma tarefa de evocação numa tarefa de memória posterior. Verificámos que a evocação prévia anulou o efeito do nível de processamento na tarefa de reconhecimento. Na tarefa de completamento de inícios de palavras, o incremento de inícios de palavras completados com associados só foi expressivo quando as palavras foram codificadas superficialmente.This study aimed to verifj whether lhe activation ofcritical items in the Deese-Roediger-McDermott paradigm ofproducing false memories could also occur in the word stem completion task. The finding that lhe levei ofprocessing did not seem to have any effect on the word stem completion task supported lhe conclusion that the stem completion task was in fact an irnplicit memory test. The impact of a previous recali in a followng memory task was also evaluated. The results indicated that lhe previous recall inhibited the effect ofthe processing levei in lhe recognition task. In the word stem completion task lhe increase ofstems completed with associates was only relevam when words were encoded superficialiy.(undefined
Pinning down the ram-pressure-induced halt of star formation in the Virgo cluster spiral galaxy NGC 4388. A joint inversion of spectroscopic and photometric data
In a galaxy cluster, the evolution of spiral galaxies depends on their
cluster environment. Ram pressure due to the rapid motion of a spiral galaxy
within the hot intracluster medium removes the galaxy's interstellar medium
from the outer disk. Once the gas has left the disk, star formation stops. The
passive evolution of the stellar populations should be detectable in optical
spectroscopy and multi-wavelength photometry. The goal of our study is to
recover the stripping age of the Virgo spiral galaxy NGC 4388, i.e. the time
elapsed since the halt of star formation in the outer galactic disk using a
combined analysis of optical spectra and photometry. We performed VLT FORS2
long-slit spectroscopy of the inner star-forming and outer gas-free disk of NGC
4388. We developed a non-parametric inversion tool that allows us to
reconstruct the star formation history of a galaxy from spectroscopy and
photometry. The tool was tested on a series of mock data using Monte Carlo
simulations. The results from the non-parametric inversion were refined by
applying a parametric inversion method. The star formation history of the
unperturbed galactic disk is flat. The non-parametric method yields a rapid
decline of star formation < 200 Myr ago in the outer disk. The parametric
method is not able to distinguish between an instantaneous and a long-lasting
star formation truncation. The time since the star formation has dropped by a
factor of two from its pre-stripping value is 190 +- 30 Myr. We are able to
give a precise stripping age that is consistent with revised dynamical models.Comment: 12 pages, 10 figures, accepted for publication in A&
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