A textbook example of ram-pressure stripping in the Hydra A/A780 cluster

In the current epoch, one of the main mechanisms driving the growth of galaxy clusters is the continuous accretion of group-scale halos. In this process, the ram pressure applied by the hot intracluster medium on the gas content of the infalling group is responsible for stripping the gas from its dark-matter halo, which gradually leads to the virialization of the infalling gas in the potential well of the main cluster. Using deep wide-field observations of the poor cluster Hydra A/A780 with XMM-Newton and Suzaku, we report the discovery of an infalling galaxy group 1.1 Mpc south of the cluster core. The presence of a substructure is confirmed by a dynamical study of the galaxies in this region. A wake of stripped gas is trailing behind the group over a projected scale of 760 kpc. The temperature of the gas along the wake is constant at kT ~ 1.3 keV, which is about a factor of two less than the temperature of the surrounding plasma. We observe a cold front pointing westwards compared to the peak of the group, which indicates that the group is currently not moving in the direction of the main cluster, but is moving along an almost circular orbit. The overall morphology of the group bears remarkable similarities with high-resolution numerical simulations of such structures, which greatly strengthens our understanding of the ram-pressure stripping process

Galaxies undergoing ram-pressure stripping: the influence of the bulge on morphology and star formation rate

We investigate the influence of stellar bulges on the star formation and morphology of disc galaxies that suffer from ram pressure. Several tree-SPH (smoothed particle hydrodynamics) simulations have been carried out to study the dependence of the star formation rate on the mass and size of a stellar bulge. In addition, different strengths of ram pressure and different alignments of the disc with respect to the intra-cluster medium (ICM) are applied. As claimed in previous works, when ram pressure is acting on a galaxy, the star formation rate (SFR) is enhanced and rises up to four times with increasing ICM density compared to galaxies that evolve in isolation. However, a bulge suppresses the SFR when the same ram pressure is applied. Consequently, fewer new stars are formed because the SFR can be lowered by up to 2 M_sun/yr. Furthermore, the denser the surrounding gas, the more inter-stellar medium (ISM) is stripped. While at an ICM density of 10^-28 g/cm^3 about 30% of the ISM is stripped, the galaxy is almost completely (more than 90%) stripped when an ICM density of 10^-27 g/cm^3 is applied. But again, a bulge prevents the stripping of the ISM and reduces the amount being stripped by up to 10%. Thereby, fewer stars are formed in the wake if the galaxy contains a bulge. The dependence of the SFR on the disc tilt angle is not very pronounced. Hereby a slight trend of decreasing star formation with increasing inclination angle can be determined. Furthermore, with increasing disc tilt angles, less gas is stripped and therefore fewer stars are formed in the wake. Reducing the disc gas mass fraction results in a lower SFR when the galaxies evolve in vacuum. On the other hand, the enhancement of the SFR in case of acting ram pressure is less pronounced with increasing gas mass fraction. Moreover, the fractional amount of stripped gas does not depend on the gas mass fraction.Comment: 11 pages, 18 figure

Molecular gas dominated 50 kpc ram pressure stripped tail of the Coma galaxy D100

We have discovered large amounts of molecular gas, as traced by CO emission, in the ram pressure stripped gas tail of the Coma cluster galaxy D100 (GMP 2910), out to large distances of about 50 kpc. D100 has a 60 kpc long, strikingly narrow tail which is bright in X-rays and H{\alpha}. Our observations with the IRAM 30m telescope reveal in total ~ 10^9 M_sun of H_2 (assuming the standard CO-to-H_2 conversion) in several regions along the tail, thus indicating that molecular gas may dominate its mass. Along the tail we measure a smooth gradient in the radial velocity of the CO emission that is offset to lower values from the more diffuse H{\alpha} gas velocities. Such a dynamic separation of phases may be due to their differential acceleration by ram pressure. D100 is likely being stripped at a high orbital velocity >2200 km/s by (nearly) peak ram pressure. Combined effects of ICM viscosity and magnetic fields may be important for the evolution of the stripped ISM. We propose D100 has reached a continuous mode of stripping of dense gas remaining in its nuclear region. D100 is the second known case of an abundant molecular stripped-gas tail, suggesting that conditions in the ICM at the centers of galaxy clusters may be favorable for molecularization. From comparison with other galaxies, we find there is a good correlation between the CO flux and the H{\alpha} surface brightness in ram pressure stripped gas tails, over about 2 dex

Deep Chandra observations of the stripped galaxy group falling into Abell 2142

In the local Universe, the growth of massive galaxy clusters mainly operates through the continuous accretion of group-scale systems. The infalling group in Abell 2142 is the poster child of such an accreting group, and as such, it is an ideal target to study the astrophysical processes induced by structure formation. We present the results of a deep (200 ks) observation of this structure with Chandra, which highlights the complexity of this system in exquisite detail. In the core of the group, the spatial resolution of Chandra reveals the presence of a leading edge and a complex AGN-induced activity. The morphology of the stripped gas tail appears straight in the innermost 250 kpc, suggesting that magnetic draping efficiently shields the gas from its surroundings. However, beyond $\sim300$ kpc from the core, the tail flares and the morphology becomes strongly irregular, which could be explained by a breaking of the drape, e.g. because of turbulent motions. The power spectrum of surface-brightness fluctuations is relatively flat ($P_{2D}\propto k^{-2.3}$), which indicates that thermal conduction is strongly inhibited even beyond the region where magnetic draping is effective. The amplitude of density fluctuations in the tail is consistent with a mild level of turbulence with a Mach number $M_{3D}\sim0.1-0.25$. Overall, our results show that the processes leading to the thermalization and mixing of the infalling gas are slow and relatively inefficient.Comment: Accepted for publication in A&

Deep Chandra observations of the stripped galaxy group falling into Abell 2142

In the local Universe, the growth of massive galaxy clusters mainly operates through the continuous accretion of group-scale systems. The infalling group in Abell 2142 is the poster child of such an accreting group, and as such, it is an ideal target to study the astrophysical processes induced by structure formation. We present the results of a deep (200 ks) observation of this structure with Chandra that highlights the complexity of this system in exquisite detail. In the core of the group, the spatial resolution of Chandra reveals a leading edge and complex AGN-induced activity. The morphology of the stripped gas tail appears straight in the innermost 250 kpc, suggesting that magnetic draping efficiently shields the gas from its surroundings. However, beyond ~ 300 kpc from the core, the tail flares and the morphology becomes strongly irregular, which could be explained by a breaking of the drape, for example, caused by turbulent motions. The power spectrum of surface-brightness fluctuations is relatively flat (P2D ∝ k⁻²∙³ which indicates that thermal conduction is strongly inhibited even beyond the region where magnetic draping is effective. The amplitude of density fluctuations in the tail is consistent with a mild level of turbulence with a Mach number M3D ~ 0:1 -0:25. Overall, our results show that the processes leading to the thermalization and mixing of the infalling gas are slow and relatively inefficient

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

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

Expanding retrieval practice promotes short-term retention, but equally spaced retrieval enhances long-term retention.

for promoting long-term retention relative to equally spaced retrieval practice. In Experiments 1 and 2, the authors found that expanding retrieval practice of vocabulary word pairs produced short-term benefits 10 min after learning, conceptually replicating Landauer and Bjork’s results. However, equally spaced retrieval produced superior retention 2 days later. This pattern occurred both with and without feedback after test trials. In Experiment 3, the 1st test occurred immediately or after a brief delay, and repeated tests were expanding or equally spaced. Delaying the first test improved long-term retention, regardless of how the repeated tests were spaced. The important factor for promoting long-term retention is delaying initial retrieval to make it more difficult, as is done in equally spaced retrieval but not in expanding retrieval. Expanding the interval between repeated tests had little effect on long-term retention in 3 experiments