Scientific report: Deconstructing Galaxies at Cosmic Noon: The Present and Future of Deep Spectroscopic Surveys at High Redshift

Alessandra Beifiori, Audrey Galametz, Trevor Mendel,  Arjen van der Wel, Marijn Franx, Joop Schaye  



Description and aims

The latest generation of ground- and space-based imaging surveys have shown that quiescent galaxies evolve dramatically from z = 3-4 to the present, both in absolute number as well as average properties.  While these surveys provide an unprecedented statistical view of the galaxy population, they raise a number of questions that are difficult to address using photometric data alone.  With the development of efficient, multi-object optical and near-infrared spectrographs, it is now possible to directly probe this evolution by studying detailed galaxy properties—e.g., stellar and dynamical masses, star-formation rates, ages, star-formation histories, etc.—out to the highest redshifts.



The schedule was organized so as to maximize interaction among participants, with small blocks of discussion time spread throughout each day to address immediate questions, and longer “curated” discussion sessions led by experts centered around 6 main topics: “Massive galaxies at high redshift”, “Massive galaxy progenitors”, “Galaxy assembly and growth”, “Kinematics/dynamics of galaxies”, “The impact of environment on galaxy evolution”, and “Modeling galaxy properties”.  This format helped to maintain a feeling of ongoing discussion throughout the week, while at the same time allowing all participants to present their work.  The majority of our participants were early-career researchers and PhD students, which helped to contribute to an extremely friendly, open, and productive atmosphere.


In addition to these pre-planned discussions, the schedule included two free-form “breakout” sessions, during which participants could work in small groups and delve more deeply into particular areas of interest.  A list of possible topics was collected at the start of the workshop; these topics were used as starting points for the various breakout discussions.  These sessions proved to be extremely productive, and we would recommend such breakout sessions to future workshop organizers as an excellent way to stimulate discussion.


Scientific developments and Aha-insights

This workshop brought together a diverse group of experts in order to discuss recent progress towards understanding the formation and evolution of massive, passive galaxies with a particular focus on the value added by spectroscopic data.


The main outcomes are summarized below:

·         It is important not to over-interpret galaxy properties derived from, for example, color-color diagrams which are specifically designed to hide certain “nuisance” parameters like dust content.  In nearly all cases, such analyses can be improved by including additional information such as the UV slopes, star-formation histories, etc.

·         Multi-wavelength data is critical to robustly constrain galaxy properties.  Especially at z > 3, where the majority of massive galaxies appear to be extremely dusty, independent estimates of the dust content and distribution from Balmer decrement, UV slope, and/or sub-mm data should be incorporated when possible.

·         It is time to move past “simple” estimates of galaxy dynamical mass as a means to test stellar mass/size measurements at high redshift.  It remains unclear how to self-consistently incorporate the most up-to-date information about the star-forming progenitor population into the analysis of passive galaxies.


The facilities provided by the Lorentz Center were excellent, and we would like to thank in particular Eline Pollaert, our workshop coordinator, for her support both before and during the workshop.  We have received very positive feedback from all participants, and would recommend the Lorentz Center to anyone else looking to organize a similar type of workshop.