Subscribe to the gold package and get unlimited access to Shamra Academy
Register a new userAbell 1451 and 1RXS J131423.6-251521: a multi-wavelength study of two dynamically perturbed clusters of galaxies
45
0
0.0
(
0
)
Authors
I.Valtchanov
Ask ChatGPT about the research
No Arabic abstract
We present results from optical, X-ray and radio observations of two X-ray bright (L_X ~ 10^{45} erg/s) galaxy clusters. A1451 is at redshift z=0.1989 and has line-of-sight velocity dispersion sigma_v = 1330 km/s as measured from 57 cluster galaxies. It has regular X-ray emission without signs of substructure, a Gaussian velocity distribution, lack of a cooling flow region and significant deviations from the observed scaling laws between luminosity, temperature and velocity dispersion, indicating a possible merging shock. There is only one spectroscopically confirmed cluster radio galaxy, which is close to the X-ray peak. 1RXS J131423.6-251521 has z=0.2474 and sigma_v = 1100 km/s from 37 galaxies. There are two distinct galaxy groups with a projected separation of ~700 kpc. The velocity histogram is bi-modal with a redshift-space separation of ~1700 km/s, and the X-ray emission is double peaked. Although there are no spectroscopically confirmed cluster radio galaxies, we have identified a plausible relic source candidate.
rate research
Read More
This paper analyzes a sample of 489 Spitzer/IRAC sources in the Extended Groth Strip whose spectral energy distributions fit a red power law from 3.6 to 8.0 micron. The median for sources with known redshift is <z>=1.6. Though all or nearly all of the sample are likely to be active galactic nuclei, only 33% were detected in the EGS X-ray survey (AEGIS-X) using 200 ks Chandra observations. The detected sources are X-ray luminous with L_X > 10^43 erg/s and moderately to heavily obscured with N_H > 10^22 cm^-2. Stacking the X-ray-undetected sample members yields a statistically significant X-ray signal, suggesting that they are on average more distant or more obscured than sources with X-ray detections. The ratio of X-ray to mid-infrared fluxes suggests that a substantial fraction of the sources undetected in X-rays are obscured at the Compton-thick level, in contrast to the X-ray-detected sources, all of which appear to be Compton-thin. For the X-ray-detected power-law sources with redshifts, an X-ray luminosity L_X ~ 10^44 erg/s marks a transition between low-luminosity, blue sources dominated by the host galaxy to high-luminosity, red power-law sources dominated by nuclear activity. X-ray-to-optical ratios, infrared variability, and 24 micron properties of the sample are consistent with the identification of infrared power-law sources as active nuclei, but a rough estimate is that only 22% of AGNs are selected by the power law criteria. Comparison of the power-law selection technique and various IRAC color criteria for identifying AGNs confirms that high-redshift samples selected via simple IRAC colors may be heavily contaminated by starlight-dominated objects.
We report on a multi-wavelength study of the relationship between young star clusters in the Antennae galaxies (NGC 4038/9) and their interstellar environment, with the goal of understanding the formation and feedback effects of star clusters in merging galaxies. This is possible for the first time because various new observations (from X-rays to radio wavelengths) have become available in the past several years. Quantitative comparisons are made between the positions of the star clusters (broken into three age groups) and the properties of the interstellar medium by calculating the two-point correlation functions. We find that young star clusters are distributed in a clustered fashion. The youngest star clusters are associated with molecular cloud complexes with characteristic radii of about 1 kpc. In addition, there is a weak tendency for them to be found in regions with higher HI velocity dispersions. No dominant triggering mechanism is identified for the majority of the clusters in the Antennae. Feedback from young bright cluster complexes show large H_alpha bubbles and H_alpha velocity gradients in shells around the complexes. We estimate the current star formation rate to be 20 solar mass/yr, and the gas consumption timescale to be 700 Myr. The latter is comparable to the merging time scale and indicates that star formation has been enchanced by the merger event. Finally, we find that the Schmidt law, with index N=-1.4, is also a good description of the cluster formation triggered by merging in the Antennae. There is some evidence that feedback effects may modify the Schmidt law at scales below 1 kpc.
The evolution of the Milky Way disk, which contains most of the stars in the Galaxy, is affected by several phenomena. For example, the bar and the spiral arms of the Milky Way induce radial migration of stars and can trap or scatter stars close to orbital resonances. External perturbations from satellite galaxies can also have a role, causing dynamical heating of the Galaxy, ring-like structures in the disk and correlations between different components of the stellar velocity. These perturbations can also cause phase wrapping signatures in the disk, such as arched velocity structures in the motions of stars in the Galactic plane. Some manifestations of these dynamical processes have already been detected, including kinematic substructure in samples of nearby stars, density asymmetries and velocities across the Galactic disk that differ from the axisymmetric and equilibrium expectations, especially in the vertical direction, and signatures of incomplete phase mixing in the disk. Here we report an analysis of the motions of six million stars in the Milky Way disk. We show that the phase-space distribution contains different substructures with various morphologies, such as snail shells and ridges, when spatial and velocity coordinates are combined. We infer that the disk must have been perturbed between 300 million and 900 million years ago, consistent with estimates of the previous pericentric passage of the Sagittarius dwarf galaxy. Our findings show that the Galactic disk is dynamically young and that modelling it as time-independent and axisymmetric is incorrect.
The current paradigm of cosmic formation and evolution of galaxy clusters foresees growth mostly through merging. Galaxies in the infall region or in the core of a cluster undergo transformations owing to different environmental stresses. For two X-ray luminous clusters at redshift z ~ 0.3 with opposite X-ray morphologies, RXCJ0014.3-3022 and RXCJ2308.3-0211, we assess differences in galaxy populations as a function of cluster topography. Cluster large-scale structure and substructure are determined from the combined photometry in the B, V, and R bands, and from multi-object optical spectroscopy at low resolution. A spectral index analysis is performed, based on the [OII] and Hdelta features, and the D4000 break, available for more than 100 member galaxies per cluster. Combination of spectral indices and FUV-optical colours provides a picture of the star formation history in galaxies. In spite of the potential presence of a small fraction of galaxies with obscured star formation activity, the average star-formation history of cluster members is found to depend on cluster-centric distance and on substructure. There is a sharp increase in star formation activity along two well-defined filamentary structures of the merging cluster RXCJ0014.3-3022, out to its virial radius and beyond, produced by luminous (L ~ L*) and sub-L* galaxies. Conversely, the regular cool-core cluster RXCJ2308.3-0211 mostly hosts galaxies which either populate the red sequence or are becoming passive. These results suggest the existence of a correspondence between assembly state and overall age of the stellar populations of galaxies inside the virialized region and in the surrounding large scale structure of massive clusters at z ~ 0.3. (Abridged)
We present a multi-wavelength analysis of three compact galaxy groups, HCGs 16, 22, and 42, which describe a sequence in terms of gas richness, from space- (Swift, HST, Spitzer) and ground-based (LCO, CTIO) imaging and spectroscopy. We study various signs of past interactions including a faint, dusty tidal feature about HCG 16A, which we tentatively age-date at <1 Gyr. This represents the possible detection of a tidal feature at the end of its phase of optical observability. Our HST images also resolve what were thought to be double nuclei in HCG 16C and D into multiple, distinct sources, likely to be star clusters. Beyond our phenomenological treatment, we focus primarily on contrasting the stellar populations across these three groups. The star clusters show a remarkable intermediate-age population in HCG 22, and identify the time at which star formation was quenched in HCG 42. We also search for dwarf galaxies at accordant redshifts. The inclusion of 33 members and 27 associates (possible members) radically changes group dynamical masses, which in turn may affect previous evolutionary classifications. The extended membership paints a picture of relative isolation in HCGs 16 and 22, but shows HCG 42 to be part of a larger structure, following a dichotomy expected from recent studies. We conclude that (a) star cluster populations provide an excellent metric of evolutionary state, as they can age-date the past epochs of star formation; and (b) the extended dwarf galaxy population must be considered in assessing the dynamical state of a compact group.
Log in to be able to interact and post comments
comments
Fetching comments
Sign in to be able to follow your search criteria
