arXiv subjects

R. Gastaud

Publications and source records attributed to R. Gastaud.

24 records · Page 2Linked to original sources

arXiv2010

The Herschel view of star formation in the Rosette molecular cloud under the influence of NGC 2244

The Rosette molecular cloud is promoted as the archetype of a triggered star-formation site. This is mainly due to its morphology, because the central OB cluster NGC 2244 has blown a circular-shaped cavity into the cloud and the expanding HII-region now interacts with the cloud. Studying the spatial distribution of the different evolutionary states of all star-forming sites in Rosette and investigating possible gradients of the dust temperature will help to test the 'triggered star-formation' scenario in Rosette. We use continuum data obtained with the PACS (70 and 160 micron) and SPIRE instruments (250, 350, 500 micron) of the Herschel telescope during the Science Demonstration Phase of HOBYS. Three-color images of Rosette impressively show how the molecular gas is heated by the radiative impact of the NGC 2244 cluster. A clear negative temperature gradient and a positive density gradient (running from the HII-region/molecular cloud interface into the cloud) are detected. Studying the spatial distribution of the most massive dense cores (size scale 0.05 to 0.3 pc), we find an age-sequence (from more evolved to younger) with increasing distance to the cluster NGC 2244. No clear gradient is found for the clump (size-scale up to 1 pc) distribution. The existence of temperature and density gradients and the observed age-sequence imply that star formation in Rosette may indeed be influenced by the radiative impact of the central NGC 2244 cluster. A more complete overview of the prestellar and protostellar population in Rosette is required to obtain a firmer result.

astro-ph.GA↗

arXiv2001

Comparison of source detection procedures for XMM-Newton images

Procedures based on current methods to detect sources in X-ray images are applied to simulated XMM images. All significant instrumental effects are taken into account, and two kinds of sources are considered -- unresolved sources represented by the telescope PSF and extended ones represented by a b-profile model. Different sets of test cases with controlled and realistic input configurations are constructed in order to analyze the influence of confusion on the source analysis and also to choose the best methods and strategies to resolve the difficulties. In the general case of point-like and extended objects the mixed approach of multiresolution (wavelet) filtering and subsequent detection by SExtractor gives the best results. In ideal cases of isolated sources, flux errors are within 15-20%. The maximum likelihood technique outperforms the others for point-like sources when the PSF model used in the fit is the same as in the images. However, the number of spurious detections is quite large. The classification using the half-light radius and SExtractor stellarity index is succesful in more than 98% of the cases. This suggests that average luminosity clusters of galaxies (L_[2-10] ~ 3x10^{44} erg/s) can be detected at redshifts greater than 1.5 for moderate exposure times in the energy band below 5 keV, provided that there is no confusion or blending by nearby sources. We find also that with the best current available packages, confusion and completeness problems start to appear at fluxes around 6x10^{-16} erg/s/cm^2 in [0.5-2] keV band for XMM deep surveys.

astro-ph↗

arXiv2000

Measuring Cluster Temperature Profiles with XMM/EPIC

Using the PV observation of A1795, we illustrate the capability of XMM-EPIC to measure cluster temperature profiles, a key ingredient for the determination of cluster mass profiles through the equation of hydrostatic equilibrium. We develop a methodology for spatially resolved spectroscopy of extended sources, adapted to XMM background and vignetting characteristics. The effect of the particle induced background is discussed. A simple unbiased method is proposed to correct for vignetting effects, in which every photon is weighted according to its energy and location on the detector. We were able to derive the temperature profile of A1795 up to 0.4 times the virial radius. A significant and spatially resolved drop in temperature towards the center (r<200 kpc) is observed, which corresponds to the cooling flow region of the cluster. Beyond that region, the temperature is constant with no indication of a fall-off at large radii out to 1.2 Mpc.

astro-ph↗

arXiv2000

XMM- Newton Observation of the Coma Galaxy Cluster: The temperature structure in the central region

We present a temperature map and a temperature profile of the central part (r < 20' or 1/4 virial radius) of the Coma cluster. We combined 5 overlapping pointings made with XMM/EPIC/MOS and extracted spectra in boxes of 3.5' X 3.5'. The temperature distribution around the two central galaxies is remarkably homogeneous (r<10'), contrary to previous ASCA results, suggesting that the core is actually in a relaxed state. At larger distance from the cluster center we do see evidence for recent matter accretion. We confirm the cool area in the direction of NGC 4921, probably due to gas stripped from an infalling group. We find indications of a hot front in the South West, in the direction of NGC4839, probably due to an adiabatic compression.

astro-ph↗

arXiv2000

The NGC4839 group falling into the Coma cluster observed by XMM-Newton

We present here the first analysis of the XMM Newton EPIC-MOS data of the galaxy group around NGC4839, which lies at a projected distance to the Coma cluster center of 1.6Mpc. In our analysis, which includes imaging, spectro-imaging and spectroscopy we find compelling evidence for the sub group being on its first infall onto the Coma cluster. The complex temperature structure around NGC 4839 is consistent with simulations of galaxies falling into a cluster environment. We see indications of a bow shock and of ram pressure stripping around NGC4839. Furthermore our data reveal a displacement between NGC4839 and the center of the hot gas in the group of about 300kpc. With a simple approximation we can explain this displacement by the pressure force originating from the infall, which acts much stronger on the group gas than on the galaxies.

astro-ph↗

arXiv1999

An XMM pre-view of the cosmic network: galaxy groups and filaments

A large fraction of the baryons today are predicted to be in hot, filamentary gas, which has yet to be detected. In this paper, we use numerical simulations of dark matter and gas to determine if these filaments and groups of galaxy will be observable be XMM. The simulated maps include free-free and line emission, galactic absorption, the XMM response function, photon noise, the extragalactic source distribution, and vignetting. A number of cosmological models are examined as well as a range of very simple prescriptions to account for the effect of supernovae feedback (preheating). We show that XMM has a good chance of observing emission from strong filaments at z~0.1. This becomes much more difficult by z~0.5. The primary difficulties lie in detecting such a large, diffuse object and in selecting an appropriate field. We also describe the range of group sizes that XMM should be sensitive to (both for detection and spectral analysis), although this is more dependent on the unknown nature of the feedback. Such observations will greatly improve our understanding of feedback and should also provide stronger cosmological constraints.

astro-ph↗