2018 Topics in the Evolution of the Universe

Overview

The course will examine different aspects of the formation and evolution of galaxies in the Universe. The course will start with a general introduction about how we can directly observe the evolution of the Universe, and what is actually observed. This introduction will also give the broad outlines of the relatively simple formation of dark matter structures in the Universe. Following this introduction, we will then look in more detail at several aspects of the more complex evolution of the "baryonic" component of the Universe, the formation of stars and black holes in galaxies, the inflows and outflows of gas and so on. In each of these topics there will be a short lecture introducing the topic, a longer presentation by a student based on a few key papers or concepts, followed by a discussion of the issues raised. Students will previously meet with the instructor(s) to help them prepare their individual presentations.

The first goal is to give students an overall understanding of the most important processes observed in the evolving universe. However, another very important goal for this course concerns more the nature of scientific research. By focusing on practical questions at the forefront of our knowledge, the course will also expose students to the challenges that are encountered in carrying out research using "passive" investigations, in this case astronomical observations. These include the challenges of inferring causal relations from data, the meaning of probability when describing classical phenomena, the difficulties of dealing with an evolving population, and the importance of the prevailing paradigm in formulating what are the most interesting scientific questions to be asked. Many of these issues will therefore be of general interest for other emerging areas of science in which large datasets are passively queried.

Lecturer: Prof. Dr. Simon Lilly

Substitute Lecturer: Dr. Bruno Henriques

Schedule

Wednesday, HIT F 31.1, 09.45 - 11.30 h

Program

A    Introduction

The first three double lectures will be presented by S. Lilly as an introduction to the course. Topics to be covered will be:

1.   Baryonic matter
      • Introduction to Big Bang cosmology.
      • Evidence for dark matter as dominant matter component of Universe.
      • Observations of galaxies at all epochs and introduction to the basic
        phenomenology of galaxies and galaxy evolution.
      • Why is it difficult theoretically? Timescales and spatial scales.
      • Why is it difficult observationally? Astronomical methodology
        (c.f. data science).
      • Focus on explaining most basic effects: reverse engineering
        philosophy.
      • Point of the course: real world research challenges, critical thinking
        etc. in context of data science.

2.   The easy part: Dark matter structure formation
      • Origin and linear growth of dark matter density perturbations.
      • Non-linear growth of dark matter density perturbations:
        dark matter haloes.
      • The mass function of haloes as f(t).
      • The cosmic web of dark matter and baryons.

B The evolution of galaxies

Each double-lecture will consist of
     • a short 20 minute introduction by S. Lilly to the issue, highlighting key
       question(s) etc.
     • two roughly 20 minute presentations by students,
     • a roughly 20 minute discussion involving everybody.

DETAILED PLAN FOR FIRST FIVE WEEKS OF TALKS

3. The star-formation rate of the Universe (part 1): Low redshift z < 2
     • Introduction:
        o The SFRD after z ~ 2
        o sSFR and the Main Sequence of galaxies
        o Star-bursts above the MS (mergers)
        o Evolution of the Main Sequence
     • Talk 1:
        o The m_star-m_halo relation
        o Supernova energy injection and galactic winds and the M_halo-m_star
           relation (at M < M*)
        o Feedback within SF regions: Why is star-formation in galaxies so
           inefficient, i.e. 𝜏_gas >> 𝜏_ff?
     • Talk 2:
        o What causes the evolution of the Main Sequence specific
           star-formation rate? Comparison of sSFR and sMIR?
        o Gas regulation models.
        o Why is the sSFR > sMIR?
        o The additional role of "quenching" in producing the SFRD evolution.

4. The star-formation rate of the Universe (part 2): High redshift z > 2
     • Introduction:
        o SFRD at z > 2
        o How we find high redshift galaxies
        o Looking ahead: JWST
     • Talk 1:
        o Build up of haloes in the Universe in Press-Schechter
        o Accretion growth vs. merging growth for DM haloes at m > m* and
           m < m*
        o At what redshift does the halo M* match the quenching mass?
     • Talk 2:
        o Reionization: evidence for the phase transition
        o Reionization: what causes it: counting ionizing photons
        o What effects might reionization have on forming galaxies?

5. Quenching (part 1): so-called mass-quenching
     • Introduction
        o Constancy of M*_SF
        o m_halo-m_star relation again at high masses
        o Difficulty: which mass is important - they are all correlated - debate
           in community.
        o Pengic rates of quenching etc. - most quenching galaxies at high z.
     • Talk 1:
        o Possible physical processes (a) suppression of star-formation
           (e.g. structure), (b) internal expulsion (e.g. BH feedback) or external
           starvation (e.g. halo)
        o Physics of gas cooling and difficulty of simple cooling arguments
        o AGN feedback as plausible energy source to counter cooling
     • Talk 2:
        o The m_star-m_halo relation and "the Birrer et al coincidence".
        o Henriques et al paper (+Bower et al)

6. Quenching (part 2): so-called environment quenching
     • Introduction
        o Halo growth through merging
        o Galaxy evolution in clusters
        o Peng et al separability
        o Other clues: conformity
     • Talk 1:
        o Halo growth and origin of satellites
        o Age-mass links for haloes
        o Characteristics of satellites, crossing times, splash-back etc,
        o Physics of stripping through ram-pressure and tidal effects
        o Other possibilities: strangulation, harrassment?
     • Talk 2:
        o What does the apparent "separability" of fQ actually tell us ?
        o What does so-called "conformity" tell us?
        o Probability and hidden variables (Knobel et al, Sin et al).
        o One and two halo effects

7. Size and structure
     • Introduction
        o Overall links between star-formation and structure
        o Omand et al plot
     • Talk 1
        o Why is star-forming gas always in a disk?
        o Two mechanisms for making spheroids
        o Include later disk regeneration?
        o Rotation vs dispersion support for early-type galaxies
     • Talk 2:
        o How does the size of disks evolve with time, and why?
        o General problem: How progenitor effects in the population can
           mimic evolutionary effects?
        o Related to this, the difficulty of establishing causality from f_q(xi)
           plots.
        o The example of the Lilly & Carollo paper.
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LESS DETAILED PLAN FOR REMAINING TALKS

8. Quasars and AGN
     • What are AGN?
     • Black hole - stellar scaling relations in galaxies.
     • Evolution of the AGN luminosity function and evidence for
       "co-evolution"
     • Caplar+ 2015 analyses of the distribution functions.

9. Links between star-formation and black-hole accretion
     • "AGN feedback" and the failure of SN feedback: Henriques et al.
     • Caplar+ 2018 model(s).

10. Accretion, cooling and heating
     • Theoretical cooling curve(s)
     • Shock heating of incoming gas, cold flows
     • Cooling and the feeding of galaxies
     • Energy injection and the heating of the circumgalactic medium.

11. Chemical evolution of galaxies
     • Closed box
     • modified closed box
     • Different interpretation: Flow through

12. The first galaxies
     • Population III
     • Issues with cooling without metals.
     • Searches for Pop III and/or first light
     • Pop III enrichment signatures