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Starburst Galaxy NGC (starburst + galaxy_ngc)

Distribution by Scientific Domains
Physics and Astronomy100%

Selected Abstracts

A high-resolution radio study of neutral gas in the starburst galaxy NGC 520

MONTHLY NOTICES OF THE ROYAL ASTRONOMICAL SOCIETY, Issue 2 2003
R. J. Beswick
ABSTRACT We present subarcsec angular resolution observations of the neutral gas in the nearby starburst galaxy NGC 520. The central kpc region of NGC 520 contains an area of significantly enhanced star formation. The radio continuum structure of this region resolves into ,10 continuum components. By comparing the flux densities of the brightest of these components at 1.4 GHz with published 15-GHz data we infer that these components detected at 1.4 and 1.6 GHz are related to the starburst and are most likely to be collections of several supernova remnants within the beam. None of these components is consistent with emission from an active galactic nuclei. Both neutral hydrogen (H i) and hydroxyl (OH) absorption lines are observed against the continuum emission, along with a weak OH maser feature probably related to the star formation activity in this galaxy. Strong H i absorption (NH, 1022 atoms cm,2) traces a velocity gradient of 0.5 km s,1 pc,1 across the central kpc of NGC 520. The H i absorption velocity structure is consistent with the velocity gradients observed in both the OH absorption and in CO emission observations. The neutral gas velocity structure observed within the central kpc of NGC 520 is attributed to a kpc-scale ring or disc. It is also noted that the velocity gradients observed for these neutral gas components appear to differ with the velocity gradients observed from optical ionized emission lines. This apparent disagreement is discussed and attributed to the extinction of the optical emission from the actual centre of this source hence implying that optical ionized emission lines are only detected from regions with significantly different radii to those sampled by the observations presented here. [source]

Metal enrichment of the intracluster medium: SN-driven galactic winds

ASTRONOMISCHE NACHRICHTEN, Issue 9-10 2009
V. Baumgartner
Abstract We investigate the role of supernova (SN)-driven galactic winds in the chemical enrichment of the intracluster medium (ICM). Such outflows on galactic scales have their origin in huge star forming regions and expel metal enriched material out ofthe galaxies into their surroundings as observed, for example, in the nearby starburst galaxy NGC 253. As massive stars in OB-associations explode sequentially, shock waves are driven into the interstellar medium (ISM) of a galaxy and merge, forming a superbubble (SB). These SBs expand in a direction perpendicular to the disk plane following the density gradient of the ISM. We use the 2D analytical approximation by Kompaneets (1960) to model the expansion of SBs in an exponentially stratified ISM. This is modified in order to describe the sequence of SN-explosions as a time-dependent process taking into account the main-sequence life-time of the SN-progenitors and using an initial mass function to get the number of massive stars per mass interval. The evolution of the bubble in space and time is calculated analytically, from which the onset of Rayleigh-Taylor instabilities in the shell can be determined. In its further evolution, the shell will break up and high-metallicity gas will be ejected into the halo ofthe galaxy and even into the ICM. We derive the number of stars needed for blow-out depending on the scale height and density ofthe ambient medium, as well as the fraction of alpha- and iron peak elements contained in the hot gas. Finally, the amount of metals injected by Milky Way-type galaxies to the ICM is calculated confirming the importance ofthis enrichment process (© 2009 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source]

Transport of cosmic rays in the nearby starburst galaxy NGC 253,

ASTRONOMISCHE NACHRICHTEN, Issue 9-10 2009
V. Heesen
Abstract Radio halos require the coexistence of extra-planar cosmic rays and magnetic fields. Because cosmic rays are injected and accelerated by processes related to star formation in the disk, they have to be transported from the disk into the halo. A vertical large-scale magnetic field can significantly enhance this transport. We observed NGC 253 using radio continuum polarimetry with the Effelsberg and VLA telescopes. The radio halo of NGC 253 has a dumbbell shape with the smallest vertical extension near the center. With an estimate for the electron lifetime, we measured the cosmic-ray bulk speed as 300 ± 30 km s,1 which is constant over the extent of the disk. This shows the presence of a "disk wind" in NGC 253. We propose that the large-scale magnetic field is the superposition of a disk (r, ,) and halo (r, z) component. The disk field is an inward-pointing spiral with even parity. The conical (even) halo field appears in projection as an X-shaped structure, as observed in other edge-on galaxies. Interaction by compression in the walls of the superbubbles may explain the observed alignment between the halo field and the lobes of hot H, and soft X-ray emitting gas. The disk wind is a good candidate for the transport of small-scale helical fields, required for efficient dynamo action, and as a source for the neutral hydrogen observed in the halo (© 2009 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source]

Extragalactic integral field spectroscopy on the Gemini telescopes

ASTRONOMISCHE NACHRICHTEN, Issue 2 2004
A. Bunker
Abstract We have been undertaking a programme on the Gemini 8-m telescopes to demonstrate the power of integral field spectroscopy, using the optical GMOS spectrograph, and the new CIRPASS instrument in the near-infrared. Here we present some preliminary results from 3D spectroscopy of extra-galactic objects, mapping the emission lines in a 3CR radio galaxy and in a gravitationally lensed arc, exploring dark matter sub-structure through observations of an Einstein Cross gravitational lens, and the star formation time-scales of young massive clusters in the starburst galaxy NGC 1140. (© 2004 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source]