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The ISM and quenching channels of high-redshift quiescent galaxies - The habitability of galaxies through time

Raphael Gobat from Pontificia Universidad Catolica de Valparaiso

The ISM and quenching channels of high-redshift quiescent galaxies :
Massive early-type galaxies (ETG), typically used as a tracer of overdense structure, have been spectroscopically confirmed up to z 3-4. This, together with their ages and abundances at z>1.5, implies that their progenitors must have converted gas into stars on short timescales. Observational data at high-redshift further suggests that the timescale for the quenching of star formation in massive ETG does not depend on local environment but is mostly set by internal processes. This "mass quenching" can in principle occur through different, unrelated channels, which are expected to leave signatures in quenched galaxies, such as stellar population structure and non-negligible amounts of residual gas and/or dust. The latter in particular has been constrained via far-infrared stacking analyses, which revealed a much larger ISM content in z>1 ETGs with respect to their local counterparts.

The habitability of galaxies through time :
The idea of a plurality of worlds, in which the Universe is filled with a vast number of life-harboring planets similar to our own, has long fascinated philosophers and has more recently become part of popular culture. This idea was entirely speculative and remains unproven, as to this day no incontrovertibly habitable planet other than our own has been found. However, the rapid pace of exoplanet discoveries and the large amount of detected extrasolar planets has made the determination of true planetary distributions functions possible. Furthermore, our knowledge of the evolution of galaxies and their stellar populations is now mature enough that we can model their formation history from early times to the present day. Combining the two allows us to estimate the amount of potentially habitable planets in our galaxy and others.