Scientific rationale

This focus meeting builds on a small conference held in September 2013 in Spain “Galaxies meet GRBs at Cabo de Gata” which brought together people from the GRB and starburst communities. It proved to be a great success and made clear the need for further interactions between these two branches of astronomy. In this meeting we want to persue this fruitfull mixture of communities and make it accessible to a wider audience.
From an observational perspective, this meeting will profit from a number of facilities that are being commissioned now and that will deliver the first important results in the near future. Large IFU surveys are currently ongoing (e.g., CALIFA) or in planning (e.g., MANGA and SAMI) together with facilities in the optical and IR such as KMOS/MUSE at the VLT. Narrow-band tunable filters allow studies at imaging resolutions which are available, e.g., at GTC and planned in the IR for JWST. ALMA will have completed cycle 2 observations by the time of the GA. With its interferometric capabilites and high sensitivity it will give us new resolved information on cold gas in star-forming galaxies. On the other end of the spectrum, X-ray facilities such as XMM observe and resolve the hot gas and signatures of outflows in star-forming galaxies. We want to bring together all these different observations to obtain a complete picture of star-forming galaxies which we then can extend to higher redshifts where resolution is limited.

Massive stellar explosions

The explosion of massive stars as GRBs and SNe are among the most powerful events in the Universe. Their progenitors require special conditions to form and upon their explosive death, they release energy and heavy elements back into their environment and a new cycle of star-formation begins with different initial conditions. These stellar explosions play an important role in the general evolution of galaxies across the entire history of the Universe.
Long GRBs are usually accompanied by a broad-line Type Ic supernova and are thought to originate from metal poor massive stars found in young star-forming regions. Those conditions are primarily met in dwarf galaxies in the local Universe, but the exact requirements to be a GRB progenitor, in terms of metallicity, angular momentum, binarity etc. are unknown. Short GRBs are the product of the coalescence of two compact stellar remnants and tend on average to occur in older populations. Different sub-populations exist and it remains an open question whether this maps to distinct progenitors. Similarly, SN classification has diversified in the last decade. Untargeted surveys like PTF or PanSTARRS allow us to discover completely new types such as superluminous supernovae (SLSNe) that might require particular conditions to form.

Which galaxy types are capable of hosting the different kinds of explosions? How well are they represented by the different starburst galaxy populations in the nearby Universe? Are the hosts of stellar explosions any way special in terms of star-formation history, their ability to form new stars, their chemical composition or their environment? Do we need large star-formation triggers to produce the star-formation necessary that leads to those stellar explosions?

Resolving the environment

Spatially resolved observations of the environment of stellar explosions outside the local group have only been done in the past few years. Studies at different wavelengths are now able to resolve individual star-forming regions, gas in- and outflows from starburst galaxies, ionized regions and abundances in great detail. This can give some important clues on the composition of the progenitor star, especially when the progenitor is too distant to be detected. The crucial question to answer is, whether we will be able to conclusively relate the properties of the environment to those of the progenitor and which observations do we need for this.

How different is the evolution of the progenitor under different initial conditions? Are there clear criteria for different progenitors and their end states? How different can the conditions be throughout a galaxy and what role does spatial resolution play in our conclusions? What can we learn from high-resolution observations in the local Universe for applications at high redshift?

Impact on the environment

Massive explosions surely do not leave their environments and host galaxies unaltered. Stellar explosions can both inhibit and give rise to new (massive) star formation in their surroundings and hosts. SNe and GRBs are responsible for the creation of most heavy elements, released or first created during the explosion. This enriches the host galaxy with metals that will influence the composition of the next generation of stars. And finally, the metal rich material can even leave the galaxy via galactic winds and deplete the intergalactic medium.

How would a GRB remnant look like and are there any examples of them in the local Universe? To which degree do stellar explosions influence the star-formation in their surroundings and in their hosts in general? What is their role in the feedback of energy and metals into the intergalactic medium? How do they influence the formation of new massive stars and their properties? Which influence do they have on the evolution of their hosts in general?

Stellar explosions as tracers of star-formation

Last but not least, stellar explosions, in particular GRBs, allow us to trace star-formation across the entire history of the universe out to the very first galaxies. GRBs in particular have the great advantage to trace any massively star-forming galaxy whereas high-redshift galaxy surveys are flux-limited and currently can only detect the most massive galaxies. As they are found at any redshift, they are also an excellent tool to study the evolution of (star-forming) galaxies and their composition from the first stars until today.

Which role do galaxies hosting stellar explosions play in the general star-formation history of the Universe? How well do they trace global star-formation? How have the conditions in star-forming galaxies changed over time?