* Astronomy

Members Login
Username 
 
Password 
    Remember Me  
Home -> Astronomy News -> Stars/galaxy News -> Galactic Center
Post Info TOPIC: Galactic Center
Blobrana


L

Posts: 131433
Date:
RE: Galactic Center
Permalink  
 

Title: Planck Intermediate Results. IX. Detection of the Galactic haze with Planck
Authors: Planck Collaboration: P. A. R. Ade, N. Aghanim, M. Arnaud, M. Ashdown, F. Atrio-Barandela, J. Aumont, C. Baccigalupi, A. Balbi, A. J. Banday, R. B. Barreiro, J. G. Bartlett, E. Battaner, K. Benabed, A. Benoît, J.-P. Bernard, M. Bersanelli, A. Bonaldi, J. R. Bond, J. Borrill, F. R. Bouchet, C. Burigana, P. Cabella, J.-F. Cardoso, A. Catalano, L. Cayón, R.-R. Chary, L.-Y Chiang, P. R. Christensen, D. L. Clements, L. P. L. Colombo, A. Coulais, B. P. Crill, F. Cuttaia, L. Danese, O. D'Arcangelo, R. J. Davis, P. de Bernardis, G. de Gasperis, A. de Rosa, G. de Zotti, J. Delabrouille, C. Dickinson, J. M. Diego, G. Dobler, H. Dole, S. Donzelli, O. Doré, U. Dörl, M. Douspis, X. Dupac, G. Efstathiou, T. A. Enslin, H. K. Eriksen, F. Finelli, O. Forni, M. Frailis, E. Franceschi, et al. (126 additional authors not shown)

Using precise full-sky observations from Planck, and applying several methods of component separation, we identify and characterise the emission from the Galactic "haze" at microwave wavelengths. The haze is a distinct component of diffuse Galactic emission, roughly centered on the Galactic centre, and extends to |b| ~35 deg in Galactic latitude and |l| ~15 deg in longitude. By combining the Planck data with observations from the WMAP we are able to determine the spectrum of this emission to high accuracy, unhindered by the large systematic biases present in previous analyses. The derived spectrum is consistent with power-law emission with a spectral index of -2.55 ± 0.05, thus excluding free-free emission as the source and instead favouring hard-spectrum synchrotron radiation from an electron population with a spectrum (number density per energy) dN/dE ~ E^-2.1. At Galactic latitudes |b|<30 deg, the microwave haze morphology is consistent with that of the Fermi gamma-ray "haze" or "bubbles," indicating that we have a multi-wavelength view of a distinct component of our Galaxy. Given both the very hard spectrum and the extended nature of the emission, it is highly unlikely that the haze electrons result from supernova shocks in the Galactic disk. Instead, a new mechanism for cosmic-ray acceleration in the centre of our Galaxy is implied.

Read more (4631kb, PDF)



__________________
Blobrana


L

Posts: 131433
Date:
Permalink  
 

Title: Disentangling Confused Stars at the Galactic Center with Long Baseline Infrared Interferometry
Authors: Jordan M. Stone, J. A. Eisner, J. D. Monnier, J. Woillez, P. Wizinowich, J.-U. Pott, A. M. Ghez

We present simulations of Keck Interferometer ASTRA and VLTI GRAVITY observations of mock star fields in orbit within ~50 milliarcseconds of Sgr A*. Dual-field phase referencing techniques, as implemented on ASTRA and planned for GRAVITY, will provide the sensitivity to observe Sgr A* with infrared interferometers. Our results show an improvement in the confusion noise limit over current astrometric surveys, opening a window to study stellar sources in the region. Since the Keck Interferometer has only a single baseline, the improvement in the confusion limit depends on source position angles. The GRAVITY instrument will yield a more compact and symmetric PSF, providing an improvement in confusion noise which will not depend as strongly on position angle. Our Keck results show the ability to characterize the star field as containing zero, few, or many bright stellar sources. We are also able to detect and track a source down to mK~18 through the least confused regions of our field of view at a precision of ~200 microarcseconds along the baseline direction. This level of precision improves with source brightness. Our GRAVITY results show the potential to detect and track multiple sources in the field. GRAVITY will perform ~10 microarcsecond astrometry on a mK=16.3 source and ~200 microarcsecond astrometry on a mK=18.8 source in six hours of monitoring a crowded field. Monitoring the orbits of several stars will provide the ability to distinguish between multiple post-Newtonian orbital effects, including those due to an extended mass distribution around Sgr A* and to low-order General Relativistic effects. Early characterizations of the field by ASTRA including the possibility of a precise source detection, could provide valuable information for future GRAVITY implementation and observation.

Read more (1928kb, PDF)



__________________
Blobrana


L

Posts: 131433
Date:
Permalink  
 

Title: Can a Satellite Galaxy Merger Explain the Active Past of the Galactic Center?
Authors: Meagan Lang, Kelly Holley-Bockelmann, Tamara Bogdanovic, Pau Amaro-Seoane, Alberto Sesana

Observations of the Galactic Center (GC) have accumulated a multitude of "forensic" evidence indicating that several million years ago the center of the Milky Way galaxy was teaming with starforming and accretion-powered activity -- this paints a rather different picture from the GC as we understand it today. We examine a possibility that this epoch of activity could have been triggered by the infall of a satellite galaxy into the Milky Way which began at the redshift of 10 and ended few million years ago with a merger of the Galactic supermassive black hole with an intermediate mass black hole brought in by the inspiralling satellite.

Read more (36kb, PDF)



__________________
«First  <  1 2 | Page of 2  sorted by
Quick Reply

Please log in to post quick replies.
Home -> Astronomy News -> Stars/galaxy News -> Galactic Center


Create your own FREE Forum
Report Abuse 		Powered by ActiveBoard