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| Teaching - PHAS2521 - GALAXIES postgrad |
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| Pages to help me work - IDL help - Common spectral lines & wavelengths |
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Starbursts
Starbursts occur on large (galaxy-wide) or small (ring, tidal tail, etc.) scales, from the local Universe, out to the highest redshifts observable. The reasons why starbursts occur is still largely unknown, but often evidence indicates some kind of recent gravitational interaction or merger with another galaxy or large gas cloud. The starburst phenomenon encompasses a period of intense star-formation, followed by the formation of super-bubbles, where the hot winds and supernova ejecta expand out into the galaxies' ambient interstellar medium, sweeping up the ambient matter into a shell. If this expanding bubble gets big enough, it can 'burst' (break out), allowing the hot gas to escape into the galaxy's halo (or even the intergalactic medium). In cases where the energy input is constant over a long period of time, a steady-state galactic superwind can develop. It is thought that the majority of stars form in clusters, and clusters form a continuous spectrum in sizes and masses. However, starbursts appear to have a special ability to form hyper-luminous, ultra-compact clusters known as super-star clusters (SSCs). SSCs have typical sizes of 3-5 pc, masses of >105 M⊙, and radiate with luminosities of up to 100 million times that of the sun. Much recent work has been done to determine whether SSCs are likely to remain gravitationally bound after the massive stars have completed their evolution. If they do, they may represent the precursors of globular clusters. In the course of my research so far, I have looked in detail at two starburst
galaxies in particular, M82 and NGC 1569. Read on to find out more... All you want to know about M82 (by Divakara Mayya) HST/WIYN composite image (May 2004):
HST/ACS colour image (March 2007):
NGC 1569 NGC 1569 (distance 2.2 Mpc) is a small dwarf irregular galaxy (similar to the LMC) that underwent a burst of star forming activity that ended ~20Myr ago. This starburst event has formed a number of prominent super-star clusters (SSCs) near the galaxy centre, and a number of other young star clusters, all of which contribute energy and mass to the galactic outflow. This outflow appears to emanate from the whole disk, and can easily be seen in X-rays. HST/WIYN composite image (April 2007):
NGC 1140 NGC 1140 (distance 20 Mpc) is another dwarf irregular galaxy that is experiencing a starburst event. This is thought to have been triggered by an encounter with a small companion gas cloud. A number of young massive star clusters have formed near the galaxy centre which have begun to drive material out of the galaxy in a fairly chaotic manner. This outflowing gas is clearly seen in Hα. Below is an HST WFPC2 and ACS colour composite made from F300W (blue), F656N (red) and F814W (green).
WIYN Hα run (Mar 2009) Below are three colour-composite images made from deep B, R and Hα exposures taken with the MiniMo instrument on the WIYN telescope in March 2009. They have been stretched and colour coded to emphasise the faint, extended Hα-emitting outflows driven by the starbursts in each galaxy.
Together with Katrina Exter, we have founded the Integral Field Spectroscopy wiki, a project aiming to set up a central repository of information, tips, codes, tools, references, etc., regarding the whole subject of IFS which is accessible and editable by the whole community. We feel that many of the problems that arise when dealing with integral field data could easily be avoided by not having to 're-invent the wheel' and benefiting from the experience and knowledge of others.
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