* Astronomy

Members Login
Post Info TOPIC: NGC 253


L

Posts: 131433
Date:
RE: NGC 253
Permalink  
 


Title: Spectral analysis and interpretation of the -ray emission from the Starburst galaxy NGC 253
Authors: H.E.S.S. Collaboration, A. Abramowski, F. Acero, F. Aharonian, A. G. Akhperjanian, G. Anton, A. Balzer, A. Barnacka, Y. Becherini, J. Becker, K. Bernlöhr, E. Birsin, J. Biteau, A. Bochow, C. Boisson, J. Bolmont, P. Bordas, J. Brucker, F. Brun, P. Brun, T. Bulik, I. Büsching, S. Carrigan, S. Casanova, M. Cerruti, P. M. Chadwick, A. Charbonnier, R. C. G. Chaves, A. Cheesebrough, G. Cologna, J. Conrad, C. Couturier, M. Dalton, M. K. Daniel, I. D. Davids, B. Degrange, C. Deil, H. J. Dickinson, A. Djannati-Ataï, W. Domainko, L. O'C. Drury, G. Dubus, K. Dutson, J. Dyks, M. Dyrda, K. Egberts, P. Eger, P. Espigat, L. Fallon, S. Fegan, F. Feinstein, M. V. Fernandes, A. Fiasson, G. Fontaine, A. Förster, M. Fübling, M. Gajdus, Y. A. Gallant, T. Garrigoux, H. Gast, et al. (135 additional authors not shown)

Very-high-energy (VHE; E >100 GeV) and high-energy (HE; 100 MeV < E < 100 GeV) data from \gamma-ray observations performed with the H.E.S.S. telescope array and the Fermi-LAT instrument, respectively, are analysed in order to investigate the non-thermal processes in the starburst galaxy NGC 253. The VHE \gamma-ray data can be described by a power law in energy with differential photon index \Gamma=2.14 ± 0.18_stat ± 0.30_sys and differential flux normalisation at 1 TeV of F_0 = (9.6 ± 1.5_stat (+5.7,-2.9)_sys) x 10^{-14} TeV^{-1} cm^{-2} s^{-1}. A power-law fit to the differential HE \gamma-ray spectrum reveals a photon index of \Gamma=2.24 ± 0.14_stat ± 0.03_sys and an integral flux between 200 MeV and 200 GeV of F(0.2-200 GeV) = (4.9 ± 1.0_stat ± 0.3_sys) x 10^{-9} cm^{-2} s^{-1}. No evidence for a spectral break or turnover is found over the dynamic range of both the LAT instrument and the H.E.S.S. experiment: a combined fit of a power law to the HE and VHE \gamma-ray data results in a differential photon index \Gamma=2.34 ± 0.03 with a p-value of 30%. The \gamma-ray observations indicate that at least about 20% of the energy of the cosmic rays capable of producing hadronic interactions is channelled into pion production. The smooth alignment between the spectra in the HE and VHE \gamma-ray domain suggests that the same transport processes dominate in the entire energy range. Advection is most likely responsible for charged particle removal from the starburst nucleus from GeV to multiple TeV energies. In a hadronic scenario for the \gamma-ray production, the single overall power-law spectrum observed would therefore correspond to the mean energy spectrum produced by the ensemble of cosmic-ray sources in the starburst region.

Read more (202kb, PDF)



__________________


L

Posts: 131433
Date:
Permalink  
 

A spectacular new image of the Sculptor Galaxy (NGC 253) has been taken with the ESO VISTA telescope at the Paranal Observatory in Chile as part of one of its first major observational campaigns. By observing in infrared light VISTA's view is less affected by dust and reveals a myriad of cooler stars as well as a prominent bar of stars across the central region. The VISTA image provides much new information on the history and development of the galaxy.
The Sculptor Galaxy (NGC 253) lies in the constellation of the same name and is one of the brightest galaxies in the sky. It is prominent enough to be seen with good binoculars and was discovered by Caroline Herschel from England in 1783. NGC 253 is a spiral galaxy that lies about 13 million light-years away. It is the brightest member of a small collection of galaxies called the Sculptor Group, one of the closest such groupings to our own Local Group of galaxies. Part of its visual prominence comes from its status as a starburst galaxy, one in the throes of rapid star formation. NGC 253 is also very dusty, which obscures the view of many parts of the galaxy. Seen from Earth, the galaxy is almost edge on, with the spiral arms clearly visible in the outer parts, along with a bright core at its centre.

Read more

__________________


L

Posts: 131433
Date:
Permalink  
 

The H.E.S.S. telescope system detects high-energy rays from the starburst region of a galactic system outside the Milky Way
Quite a few distant galaxies turn out to be cosmic delivery rooms. Large numbers of massive stars are born in the hearts of these starburst galaxies, and later explode as supernovae. In the remnants they leave behind, particles are accelerated to very high energies. Astrophysicists have now used the H.E.S.S. telescopes to make detailed measurements of the gamma rays from the NGC 253 galaxy. As predicted, these high-energy rays originate from the region of maximum supernova activity close to the centre.


Read more

__________________


L

Posts: 131433
Date:
Permalink  
 

HESS détecte le rayonnement gamma d'une galaxie à flambée d'étoiles
Les régions de formation stellaire dans les galaxies à flambée d'étoiles sont le berceau de nombreuses étoiles massives de faible durée de vie. Leur explosion en supernovae est propice à l'accélération de particules à des énergies élevées. Les télescopes internationaux de la collaboration HESS, qui inclut des chercheurs du CNRS (IN2P3 et INSU) et du CEA, ont permis pour la première fois la détection de l'émission d'une telle galaxie, NGC 253, ainsi que son étude détaillée. Ces observations confirment les prévisions : ce rayonnement provient effectivement de la région la plus active en supernovae de cette galaxie. Cette découverte fait l'objet d'un article qui vient d'être publié dans Science.

Read more (French)

__________________


L

Posts: 131433
Date:
Permalink  
 

Title: Evidence of a pure starburst nature of the nuclear region of NGC 253
Authors: A. Brunthaler (1), P. Castangia (1,2), A. Tarchi (2,3), C. Henkel (1), M. J. Reid (4), H. Falcke (5,6) K. M. Menten (1) ((1) Max-Planck-Institut fuer Radioastronomie, (2) INAF-Osservatorio Astronomico di Cagliari, (3) INAF - Istituto di Radioastronomia Bologna, (4) Harvard-Smithsonian Center for Astrophysics, (5) Radboud Universiteit Nijmegen, (6) ASTRON)

We present high-resolution spectral line and continuum VLBI and VLA observations of the nuclear region of NGC 253 at 22 GHz. While the water vapour masers in this region were detected on arcsecond and milliarcsecond scales, we could not detect any compact continuum emission with a 5 sigma upper limit of ~ 1 mJy. The observations reveal that the water maser emission is not related to a possible low-luminosity active galactic nucleus but is almost certainly associated with star-formation activity. Not detecting any compact continuum source on milliarcsecond scales also questions the presence of a - previously assumed - active nucleus in NGC 253.

Read more  (55kb, PDF)

__________________


L

Posts: 131433
Date:
Permalink  
 

Astronomers from the Instituto de Astrofísica de Canarias in Spain used NACO, an adaptive optics instrument on the European Southern Observatory's Very Large Telescope (located in Atacama desert in northern Chile), to study NGC 253 in finer detail in the near-infrared.
Adaptive optics corrects for the blurring effect that Earth's atmosphere can have on images taken by ground-based telescopes. Sensors and deformable mirrors correct distortions of incoming light, producing images as clear as if the telescope were in space.
With its adaptive optics system, NACO revealed features of NGC 253 that were only 11 light-years across.


Read more 

__________________


L

Posts: 131433
Date:
Permalink  
 

L'activité frénétique d'usines stellaires poussiéreuses
Grâce à l'oeil perçant en proche infrarouge (Le rayonnement infrarouge (IR) est un rayonnement électromagnétique d'une longueur d'onde supérieure à celle de la...) du VLT (Very Large Telescope), des astronomes ont découvert une multitude de nouvelles jeunes et massives pépinières stellaires dans la galaxie voisine NGC 253. Le centre de cette galaxie semble héberger un jumeau du trou noir supermassif (En astrophysique, un trou noir supermassif est un trou noir dont la masse est d'environ un million à un milliard de...) de notre Voie lactée ( Anciennement, la Voie lactée ne désignait que la bande blanchâtre traversant le ciel nocturne. Il existe plusieurs...).

Read more (French)

__________________


L

Posts: 131433
Date:
Permalink  
 



__________________


L

Posts: 131433
Date:
Permalink  
 

Frantic activity revealed in dusty stellar factories
Thanks to the Very Large Telescope's acute and powerful near-infrared eye, astronomers have uncovered a host of new young, massive and dusty stellar nurseries in nearby galaxy NGC 253. The centre of this galaxy appears to harbour a twin of our own Milky Way's supermassive black hole.
Astronomers from the Instituto de Astrofísica de Canarias (Spain) used NACO, a sharp-eyed adaptive optics instrument on ESO's Very Large Telescope (VLT), to study the fine detail in NGC 253, one of the brightest and dustiest spiral galaxies in the sky. Adaptive Optics (AO) corrects for the blurring effect introduced by the Earth's atmosphere. This turbulence causes the stars to twinkle in a way that delights poets, but frustrates astronomers, since it smears out the images. With AO in action the telescope can produce images that are as sharp as is theoretically possible, as if the telescope were in space.
NACO revealed features in the galaxy that were only 11 light-years across.

"Our observations provide us with so much spatially resolved detail that we can, for the first time, compare them with the finest radio maps for this galaxy - maps that have existed for more than a decade" - Juan Antonio Fernández-Ontiveros, the lead author of the paper reporting the results

Read more

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

Please log in to post quick replies.



Create your own FREE Forum
Report Abuse
Powered by ActiveBoard