First Stars VI: abstract book
Universidad de Concepción01.03.2020

S1: Population III stars: formation, IMF, multiplicity
and evolution

Formation of First Star with Various Masses
Shingo Hirano (Invited Talk)
Kyushu University
hirano.shingo.821@m.kyushu-u.ac.jp

I will present the formation mechanism of first stars with different masses, in especially considering
dependence on the environmental properties of the star-forming region. Theoretically, previous studies
have well pictured the outline of the first star formation with considering dynamical, thermal, andradiative processes of the star-forming region from the cosmological large-scale to stellar small-scale.
However, it is still far from the theoretical derivation of the initial mass function of first stars, whichplays a vital role in the early Universe by determining the initial phase of the chemical evolution. The
formation mechanisms and final fates of first stars strongly depend on the physical conditions of thecircumstances; e.g. physical states of the star-forming cloud, fragmentation, magnetic effects, externalradiation sources, cosmological dynamics, and particle nature of dark matter. Because of dependenceof the typical mass and mass range of first stars, we must consider such “first star family” to construct
the initial mass function. Interestingly, recent observations suggest the existence of low- to high- mass
stars in the early Universe; e.g. relic abundances in extremely metal poor stars, close massive binary
blackholes detected by gravitational waves, and supermassive blackholes at high-z Universe. This talkwill summarize the current understandings of the first star formation in relationship to the observational
results and remaining issues for future studies.

The initial mass function of Population III stars: where do we stand?
Simon Glover
ITA/ZAH, University of Heidelberg
glover@uni-heidelberg.de

The formation of the first stars, the so-called Population III or Pop. III stars, was a key event in
the history of our Universe. These first stars had a profound effect on their surroundings in the form ofradiative, mechanical and chemical feedback, and understanding the details of Pop. III star formationis crucial for understanding the initial conditions for later generations of star formation. The form of
the Pop. III initial mass function (IMF) is of particular importance. Its upper mass limit and slope
help determine the amount of feedback produced by a given amount of Pop. III star formation, while
its lower mass limit determines whether it is possible for any Pop. III stars to survive until the presentday. In this talk, I will review our current state of knowledge of the Pop. III IMF, focussing on themost important open questions and our prospects for placing observational constraints on it in the near
future.

The influence of streaming velocities and Lyman-Werner radiation on theformation of Pop. III stars
Anna Schauer
UT Austinanna.schauer@utexas.edu

The first stars form in small galaxies, so-called minihaloes. In order to host Pop. III stars, they haveto cross a minimum mass threshold in the range of a few 105 M⊙ − 107 M⊙ , depending on the large
scale streaming velocity in their creation region. A second effect, Lyman-Werner radiation, influences theminimum and average halo mass for star formation as well. With hydrodynamical simulations, we tested
which of the two effects is dominant, and find streaming velocities to play a bigger role than LymanWerner radiation. In my talk, I will give an overview of my numerical results and provide a physicalexplanation thereof. Only by understanding the combination of these effects, observational signatures
like the 21-cm signal can be interpreted correctly.

Primordial & Extremely Metal-poor high-mass star formation in theearly universe
Takashi Hosokawa (Highlight Talk)
Kyoto Univ.
hosokawa@tap.scphys.kyoto-u.ac.jp.

I present our recent efforts toward understanding the high-mass star formation that occurs in theearly universe.
The disk fragmentation is a possible process leading to the formation of stellar multiple systems
including binaries. However, numerical simulations show diverse fates of the fragments; some evolve into
binaries and others merge away with a central star. I first show that the key physics behind such diversity
is well understood postulating that the orbital angular momentum is removed by (i) the gravitational
torque, and (ii) tidal disruption (Chon & Hosokawa 2019). I also show the binaries generally expand
while accreting the disk gas. I demonstrate that such features are also observed in our latest radiationhydro simulations using a AMR code, showing that massive primordial stellar multiple system appears
under the protostellar radiative feedback (Sugimura et al. in prep.).
Extremely metal-poor (EMP) environments are realized soon after massive primordial supernovae.
The subsequent star formation has been studied, but mostly focusing on the possible formation of lowmass (< 1 M⊙ ) EMP stars caused by the fragmentation. I also show our recent 2D simluations that
follow the formation of **massive** EMP stars under the protostellar radiative feedback (Fukushima
et al. in prep.). The results show that, even at Z = 10−2 Z⊙ , the star accretes the gas of ≃ 190 M⊙
until terminated by the stellar UV feedback as in the primordial cases. I argue that the massive starformation even in nearby metal-poor galaxies should occur under the radiative feedback which is similar
to that expected for the primordial star formation.

The impact of magnetic field strength on the primordial initial massfunction
Piyush Sharda
Australian National University
piyush.sharda@anu.edu.au

Magnetic fields have been long proposed to play a potentially vital role in setting the primordial initial
mass function. Using the AMR code FLASH with the primordial chemistry network from KROME, wecarry out 200 3D MHD simulations of turbulent magnetized primordial cloud collapse under the influenceof different randomly oriented magnetic field strengths that produce more than 1000 first stars. All thesimulations have sufficient resolution for the small-scale dynamo to operate and amplify the field beyond
flux-freezing. We show a clear tendency towards the formation of more massive first stars as stronger
magnetic fields are introduced even before the onset of radiation feedback, primarily due to the formationof magnetically-supported discs that suppress further fragmentation. Naturally, this completely changes
clustering and multiplicity properties of primordial clouds. Further, we analyze the density and velocity
power spectra and PDFs of the collapsing clouds and compare them to contemporary star formation
models as well as studies of isolated turbulence in a box simulations. These comparisons reveal that themagnetic field strength has a vital role in defining the low density characteristics of primordial clouds,
however, have no impact on the high density regions whose characteristics are governed by gravity.
Nonetheless, there is an apparent bimodality in the density PDF where the second peak changes position
with time as the disk around the first star expands. The driving force behind turbulence goes through asequence of episodes where it can either be driven by magnetic fields (solenoidal modes) or gravitational
collapse (compressive), with clear differences in the turbulent Mach numbers traced by the two. This
analysis provides an exciting new window to not only understand the physics of primordial star formation
but also test theories of contemporary star formation and magnetized turbulence in more realistic setups.

Radiation feedback in a high resolved Population III star formation
Ondrej Jaura
ITA ZAH, University of Heidelberg
ondrej.jaura@uni-heidelberg.de

First models of Population III star formation proposed that the radiation from the first stars caneasily escape molecular accretion disks and affect their surroundings through ionization and heatingof the gas. This feedback has an important effect on the resulting stellar initial mass function in theprimordial Universe. To address this problem, we employ detailed radiation-hydrodynamic simulations
and follow a collapse of isolated minihalos for 700−750 kyr until their central dense gas regions fragment
and form multiple stars. We model the subsequent star-disk system evolution by zooming in on theminihalos’ innermost 3.9 pc. Radiation produced by the new stars si performed using the innovative
radiation transfer code SPRAI. Our results show that future simulations should treat the onset of theionizing radiation near the first stars with special care. Low resolution and choice of the simple sub-gridmodels can lead to qualitatively different outcomes. In the talk, I will introduce our different simulation
setups and show their final IMFs. Furthermore, I will discuss how the accretion disk gas properties near
the most massive stars influence the escaping radiation and expanding HII regions.

Number of population III stars per minihalo
Hajime Susa
Konan University
susa@konan-u.ac.jp

The numerical studies on the mass accretion phase of pop. III star formation in the last decadesuggest that they could be < 1 M⊙ because of the disk fragmentation. In fact, those stars are formed asa member of a multiple system in a minihalo. In order to investigate the fragmentation process in detail,
we perform a set of numerical simulations on the collapse of the gas in the minihalo. We find that the
average number of stars is roughly proportional to t0.3 , where t is the elapsed time since the formationof the first protostar. In this talk I will show the latest results on this issue in which the elapsed time ismuch longer than the previous calculation (Susa 2019, ApJ 877:99).

S2: Transition to second-generation star formation
Is there significance to the critical metallicities?
Britton Smith
University of Edinburgh
britton.smith@ed.ac.uk

It is understood that the radiative cooling provided by heavy elements is crucial to the transition
from Pop. III to Pop. II star formation. Classically, two critical metallicities have been identified as
the minimum amount of metal required to allow collapsing gas to cool and fragment where metal-freegas cannot. For heavy elements in the gas phase, the critical metallicity is roughly 10−3.5 Z⊙ . However,for metals in dust grains, the critical abundance is 100 to 1000 times lower. Simulations have shownthat metals in excess of each of these critical abundances can lead to fragmentation in the respective
density/temperature regimes where they operate. This would suggest that the lower, dust-related critical
metallicity is the true value of importance for forming the first low mass stars. Yet, the vast majorityof metal-poor stars observed have total metallicities that exceed the higher critical metallicity. I will
present results from simulations that follow the enrichment, collapse, and fragmentation of star forminggas within a cosmological context. In these simulations, metal-enriched star formation occurs at various
metallicities and via different enrichment scenarios. I will characterize this diversity of star formation
outcomes and connect them with observed metal-poor stars in order to understand what role the critical
metallicities truly play.

The mass transition from Population III to Population II stars
Gen Chiaki (Invited Talk)
Georgia Institute of Technology
gen.chiaki@physics.gatech.edu

The standard Lambda-CDM model suggests that firstly smaller structures form and grow in theirmass through merger of dark matter halos. The first Population III stars form in the pristine gas without
elements heavier than Helium hosted by the least massive structures (minihalos). It is considered thatthe first stars are majorly massive (10−1000 M⊙ ) because the pristine gas clouds collapse stably against
fragmentation. Whereas, long-lived (∼ Hubble time) and low-mass (< 1 M⊙ ) metal-poor (PopulationII) stars have been observed in the Local Group. The critical condition for the transition of stellar massscale from massive Population III stars to low-mass Population II stars is still unknown. In this talk, I
review the efforts of researchers to disclose this problem.

Metal mixing in primordial minihaloes
Mattis Magg (Highlight Talk)
Center for Astronomy, University of Heidelberg
mattis.magg@stud.uni-heidelberg.de

The most metal-poor stars in the Milky Way are thought to have formed from the ejecta of one orof a few Population III stars. Comparing the modeled yields of primordial supernovae to the abundance
patterns of extremely metal-poor stars is one of the few currently available pathways to constrain theproperties of the first stars. However, this abundance fitting often only considers the abundance ratios,and does not consider how the expected outcome depends on the explosion energy and total yields ofthe supernovae. In this talk I will discuss recent advances in modeling the metal-mixing and fall-backoccurring after the first supernovae, with a particular focus on the dilution of metals and the expected
metallicities.

Metallicity Dependence of Massive Star Formation
Kei Tanaka
Osaka University / NAOJ
ktanaka@astro-osaka.jp

We are theoretically and observationally investigating massive star formation at various metallicities.
Massive stars play a lot of essential roles in a wide range of astrophysical settings throughout cosmic
history. Therefore, it is crucial to understand how the process of massive star formation depends on
galactic environmental conditions. We developed the first model of massive star formation, including
multiple feedback processes, i.e., MHD disk wind, radiation pressure, photo-ionization, and stellar winds(Tanaka et al. 2017; 2018). We find that the feedback does not set the upper mass limit of stellar birthmass at any metallicity. At the solar metallicity, unlike the conventional perspective, the MHD disk
wind is the dominant feedback to determine rather than radiative feedback even in the formation of very
massive stars with > 100 M⊙ (see also Staff, Tanaka et al. 2019). On the other hand, photo-evaporation
is found to be the dominant feedback at low metallicity of < 10−2 Z⊙ due to the lack of dust absorption,
decreasing the star formation efficiencies from prestellar cores. To test our theoretical model, we arealso conducting high-resolution ALMA observations of massive protostars in the Milky Way and theMagellanic Clouds (Zhang, Tanaka et al. 2019; Shimonishi+Tanaka et al., submitted; etc.). In the talk,we will also introduce our theoretical study, which predicted that the binary system formation is more
frequent at lower metallicity of 10−5 −10−3 Z⊙ (Tanaka & Omukai 2014). This prediction is consistent
with what suggested by recent observations (Moe et al. 2019). Our studies raise a question on thecommon assumption of the universal IMF with a truncated at 100 M⊙ .

Star-cluster formation in low-metallicity massive clouds under radiative
feedback
Hajime Fukushima
University of Tsukuba
fukushima@ccs.tsukuba.ac.jp

Star formation in star-forming clouds proceeds under UV feedback from massive stars. Recent observations of nearby galaxies showed that massive clouds were disrupted within dynamical time (∼ 10 Myr)
after star formation started (e.g., Kruijssen et al. 2019). They indicated that photoionization feedback
was responsible for inducing the disruption of clouds. However, it is still unclear how the photo-ionization
feedback regulates the star formation and destroy clouds in different physical properties, e.g., cloud mass,compactness, and metallicity. For example, the strength of photoionization feedback is likely to dependon the metallicity because dust grains absorb ionizing photons in HII regions. In this talk, using 3D
radiative hydrodynamics simulations of star-forming clouds at various metallicities, we study the metallicity dependence on star formation efficiencies (SFEs) and lifetimes of clouds. We use turbulent clouds
with masses of 104 −105 M⊙ and surface densities of 10−300 M⊙ pc−2 as the initial conditions. We
show that the dust makes the photo-ionization feedback less significant and the SFE decreases as themetallicity increases: 16 % for Z = Z⊙ and 7 % for Z = 0.01 Z⊙ at 80 M⊙ pc−2 . The duration time ofstar formation is regulated to the expansion time of HII regions, which nicely matches the observations.
In addition, we discuss the dependencies of cloud mass and compactness on SFEs.

S3: First supernovae and gamma-ray bursts; Pop. III
star fates; abundance patterns at high redshift
The First cosmic explosions
Daniel Whalen (Invited Talk)
ICG, Portsmouthdwhalen1999@gmail.com

Pop. III supernovae could be the ultimate cosmic lighthouses, some of which will be observable atcosmic dawn at z > 20. Detections of primordial transients could constrain the properties of the firststars, their formation rates, and even the channels of formation of the first quasars. I will review thefinal fates of Pop. III stars according to their masses, discuss the central engines of their explosions, andtheir prospects for detection in both deep, narrow surveys by JWST and ELTs on the ground and by
wide-field NIR surveys by Euclid and WFIRST in the coming decade.

Rotations of first stars: need of a theory anchored on present-day
observational constraints
Georges Meynet
Geneva University
georges.meynet@unige.ch

Transport processes in stars have a very important impact on the evolution of both single and multiple
stars. Indeed, these transport processes govern the distribution of the chemical elements in the interior,have an impact on the surface properties (surface rotation, surface abundances, luminosities, temperatures, gravities, mass loss rates, magnetic fields), determines the angular momentum content of the coreat the end of the evolution and thus have an impact on the physics of the core collapse and the outcomeof the possibly associated supernova event. In this talk, we shall first provide a brief description of thedifferent transport processes presently available and their advantages/disadvantages when confronted toobservational constraints. Then, we shall discuss the impact on Pop. III and very metal-poor stars ofdifferent treatments of these transport processes showing their impact on nucleosynthesis, possibly also
on their final outcome.

State-of-the-art of chemodynamical simulations: The origin of elements
and their evolution in galaxies
Chiaki kobayashi
University of Hertfordshirec.kobayashi@herts.ac.uk

State-of-the art of chemical evolution modeling has provided deeper understanding of the origin of elements as well as the evolution of galaxies. We have been running hydrodynamical simulations of galaxies
including detailed chemical enrichment from core-collapse supernovae, Type Ia supernovae, AGB stars,
super AGB stars, and neutron star mergers. Unlike classical ‘one-zone’ models, in chemodynamical simulations, chemical enrichment takes place inhomogeneously, which results in a significant contribution
from long time-delay sources (e.g., AGB stars) in metal-poor environments. Because of this inhomogeneous effect, the observed N/O-O/H relations in nearby star-forming galaxies can be well reproduced

without rotation of stars. However, even with this effect, it is not possible to explain the observed distribution of rapid-neutron capture elements with neutron star mergers only, and a significant contribution
from magneto-rotational supernovae is necessary. With recent observational techniques, the maps ofmetallicities and elemental abundances can be obtained also for external galaxies. These are in good
agreement with our predictions from cosmological simulations with feedback from super-massive black
holes that originate from the First Stars. We also predict the evolution of elements that can be exploredwith James Webb Space Telescope in near future.

Rotation, explosion and nucleosynthesis in early massive stars and theabundances of metal-poor stars
Arthur Choplin
Konan University
arthur.choplin@konan-u.ac.jp

During the hydrostatic burning phases of early massive stars, rotation is believed to boost the synthesis of light (especially nitrogen) and s-process elements through meridional circulation and shear mixing.
Fast rotation is also believed to trigger aspherical jet-like supernova explosions, inducing peculiar explosive nucleosynthesis. By combining 1D stellar models with 2D relativistic hydrodynamical simulations,
I will discuss the interplays between rotation, explosion and nucleosynthesis in the early massive stars
and investigate the implication on the early chemical enrichment by confronting the model yields withthe abundances of observed metal-poor stars.

Chemical abundances in metal-poor quasar absorbtion line systems
Trystyn BergESO Chile
Trystyn.Berg@eso.org

Quasar sightlines through intervening material provide insights into the evolution of gaseous reservoirs
within and surrounding galaxies across cosmic time. With the advent of high resolution spectrographs
on 8m class telescopes, quasar absorption line systems are excellent probes of the chemical evolution ofneutral gas, providing an orthogonal approach to detailed stellar abundances in the Local Group. In thistalk I will present recent work focusing on using both damped and sub-damped Lyman alpha systems tostudy the chemical enrichment of the Universe from the XQ-100 survey between redshifts 2 and 4. I will
highlight past and ongoing efforts to search for the chemical signatures of the first stars in these gas-rich
quasar absorbers to compliment chemical abundance studies at lower redshifts.

Searches for Population III pair-instability supernovae with upcoming
near-infrared transient surveys
Takashi Moriya (Highlight Talk)
National Astronomical Observatory of Japan
takashi.moriya@nao.ac.jp

Probing the high redshift Universe with Long Gamma-Ray Bursts
Emeric Le FlochCEA-Saclay (France)
emeric.lefloch@cea.fr

Because they can be detected up to very high redshift, Long Gamma-Ray Bursts (LGRBs) are seen
as a unique probe of structure formation in the early Universe. Yet, their apparent excess-rate beyondz ∼ 3 relative to standard predictions based on cosmic star formation challenges our understanding
between LGRBs and massive stars. I will report on recent progress toward the characterization of theenvironments where LGRBs take place, mostly based on new data obtained at long wavelengths (ALMA,
VLA, GMRT). In particular I will discuss the debated hypothesis on the physical origin of the bias thatexists between LGRB hosts and galaxies of the field at low redshifts (i.e., metallicity, stellar density, ...),and I will show that the current number of GRBs identified at z > 4 is however too low to investigate
the relevance of such a bias at high redshift. In this context, I will finally present future GRB-dedicatedprojects like SVOM and THESEUS, which will provide new insights into GRBs at cosmic dawn, andopen a new window on the early Universe complementary to that afforded by cosmological surveys.

Discrimination of heavy elements originating from Pop. III stars in z = 3
intergalactic medium
Takanobu Kirihara
Chiba University
tkirihara@chiba-u.jp

We investigate the distribution of metals in the cosmological volume at z = 3, in particular, provided
by massive population III (Pop. III) stars using a cosmological N-body simulation in which a model ofPop. III star formation is implemented. Owing to the simulation, we can choose minihalos where Pop.
III star formation occurs at z > 10 and obtain the spatial distribution of the metals at lower-redshifts.
To evaluate the amount of heavy elements provided by Pop. III stars, we consider metal yield of pairinstability or core-collapse supernovae (SNe) explosions of massive stars. By comparing our results to
the Illustris-1 simulation, we find that heavy elements originating in Pop. III stars can be discriminatedfrom galactic ones in low-density regions. The median value of the volume-averaged metallicity is log
Z/Z⊙ ∼ -4.5 − -2 at the regions. Spectroscopic observations with the next-generation telescopes are
expected to detect the metals imprinted on quasar spectra.

S4: Gravitational waves as a new probe of the high-z
Universe
Remnants of first stars for gravitational wave sources.
Tomoya Kinugawa (Invited Talk)
ICRR, University of Tokyokinugawa@astron.s.u-tokyo.ac.jp

We showed that the typical mass of binary black holes (BH-BHs) whose origin is the first star is
30Msun and mergers of Pop III BH-BH can have sufficiently long merger times to occur in the nearby
universe before GW150914 (Kinugawa et al. 2014). The detection rate of the coalescing Pop III BH-BHs
is 200 events/yr. This result predicted the gravitational wave events of massive BH-BHs like GW150914
and LIGO paper said ‘recently predicted BBH total masses agree astonishingly well with GW150914 andcan have sufficiently long merger times to occur in the nearby universe (Kinugawa et al. 2014)’ (Abbot
et al. ApJL 818,22 (2016)). Thus, there is a good chance to check indirectly the existence of Pop III
massive stars by gravitational waves. In this talk, I will summarise the Pop III binary evolutions andthe features of Pop III BH-BHs and the detectability of Pop III BH-BHs by the gravitational detectors
including future plans.

Exploring new frontiers with gravitational waves from massive black holes
Tilman Hartwig (Highlight Talk)
University of Tokyo
Tilman.Hartwig@ipmu.jp

Observations of black holes at high redshift are currently limited to the tip of the iceberg. Future spaceborne gravitational wave detectors will overcome this limitation by probing the black hole population tohigher redshifts and lower masses. This will provide unique probes of supermassive black hole seeding
and growth scenarios. I will summarise current model predictions for gravitational waves from massive
black holes and their main uncertainties. I will discuss the expected detection rate of binary black holemergers and how we can maximise the scientific information gain from the upcoming data.

Gravitational wave signals of Pop. III-seeded binary black holes formedby dynamical capture
Boyuan Liu
University of Texas at Austin
boyuan@utexas.edu

We use cosmological hydrodynamic simulations to study the gravitational wave (GW) signals fromhigh-redshift ex-situ binary blackholes (BBHs) formed by dynamical capture during mergers of their hosthaloes/galaxies. We particularly focus on BHs originated from the remnant of the first generation ofmassive metal-poor stars (so-called Pop. III stars). These BHs can also be born into binary systems fromPop. III binary stars (i.e., in-situ BBHs), whose GW signals have been intensely studied. Our fiducial
simulation produces a local intrinsic rate density of GW events for ex-situ BBHs as 0.01−0.1 per year
per cubic Gpc, and a all-sky occurrence rate of 1−570 per yer within z < 5, depending on the sub-gridmodel for the stellar environments of ex-situ BBHs. Our rates are comparable to or even higher than
the rates predicted for in-situ BBHs, showing that the ex-situ channel of binary BH formation is at least
as important as the in-situ channel for producing GWs. We also use the simulated BBHs to predict thedetectability of BH-BH merger events for future planned GW instruments such as the Einstein Telescopeand deci-hertz detectors.

S5: Stellar archeology as a powerful probe of thehigh-z Universe
The SkyMapper Extremely Metal-Poor Star Program
David Yong (Invited Talk)
Australian National University
david.yong@anu.edu.au

Chemical abundances in the oldest, most metal-poor stars provide an observational window into theearly Universe. Those data enable us to test and refine our understanding of the earliest chemical enrichment events (e.g., supernovae, AGB stars). I will present an update of our high-resolution spectroscopic
follow-up of halo metal-poor star candidates from the SkyMapper Telescope as well as the implications
and insights into their progenitors.

Looking for the first stars: back to the Lithium plateau.
David Aguado
University of Cambridge
daguado@ast.cam.ac.uk

In the past few decades an important effort has been made looking for the most metal-poor stars.
Those stars are invaluable fossil records and their chemical signatures provide crucial information about
the early Universe and the formation and evolution of the Milky Way. Finding these extremely rare
objects is challenging and multiple approaches have been attempted.
Spite et al. (1982), found that the lithium abundance in metal-poor stars exhibited an approximately
constant value, the so-called ”lithium plateau”, suggesting it corresponded to the primordial value.
This result was later confirmed by Rebolo et al. 1988. More recently and in the context of Λ-CDM
model, cosmological observations with the Wilkinson Microwave Anisotropy Probe (WMAP) indicateda primordial lithium abundance that is larger by a factor 3−4 compared with the observations of metalpoor stars (Spergel et al. 2003). This discrepancy is known as the “Cosmological Lithium Problem”.
The analysis of a few stars with even lower lithium abundance, the “meltdown” of the plateau, pointed
to an explanation that stars are depleting lithium. However, with the discovery of the unevolved star
J0023+0307 at [Fe/H] < -6.1 (Aguado et al. 2019a), lying on the plateau, the lithium problem is back.
In addition to it a brief description of both methodologies to find these stars with spectroscopic searches(Aguado et al 2016, 2017) and photometric ones (Starkenburg et al. 2017, Youakim et al. 2017) will
be discussed together with the main results of 3-years follow-up spectroscopic EMP candidates selectedfrom the Pristine survey, (Aguado et al. 2019c).

Interpreting spectroscopic survey data for metal-poor stars withsupernova yield models
Miho Ishigaki (Highlight Talk)
Tohoku University
miho@astr.tohoku.ac.jp

With the advent of recent large spectroscopic surveys of metal-poor stars in our Milky Way Galaxy,unprecedentedly large data sets of elemental abundances in the atmosphere of metal-poor stars are now
available. Statistical properties of the measured elemental abundances have put useful constraints on

nucleosynthetic yields of supernovae of different generations of stars as a function of cosmic time. I
would like to present highlight results from our studies of the systematic comparison between observed
elemental abundances in metal-poor stars and theoretical supernova yield models including those of thefirst (Pop. III) stars. Issues and prospects for planned future large spectroscopic surveys will also be
discussed.

A search for the oldest stars in the inner galaxy with the Pristine survey
Anke Arentsen
Leibniz-Institut für Astrophysik Potsdam (AIP)
aarentsen@aip.de

Old, metal-poor stars are not only expected to be present in the Milky Way halo and the dwarf
galaxies. Cosmological simulations predict that the fraction of stars that are both very old and metalpoor is highest towards the centers of galaxies: in their bulges. I will present the Pristine Inner Galaxy
Survey (PIGS), which is building towards an unprecedented large sample of very metal-poor stars in thebulge region using metallicity sensitive photometry followed by low-/intermediate resolution spectroscopy.
Specifically, I will present new results on the carbon-enhanced metal-poor (CEMP) fraction of thestars in this region. Previous work by the SkyMapper team found a much smaller CEMP fraction in
the inner Galaxy when compared to the halo. Our narrow-band photometric filter is narrower than the
SkyMapper filter and is less biased by the large amounts of carbon some of these stars have. Consequently,
we can provide a more unbiased estimate of the CEMP fraction. Comparing this fraction between thehalo and the inner Galaxy has interesting scientific implications for differences in the contributions ofboth binary stars and first stars ejecta to very metal-poor stars in these environments.

Accurate abundances at the lowest detected iron abundance: SMSS
1605-1443
Thomas Nordlander
Australian National University
Thomas.Nordlander@anu.edu.au

We recently announced the discovery of SMSS 1605-1443, a red giant star in the Milky Way’s halothat has the lowest detected iron abundance of any star at [Fe/H] = -6.2 (1D LTE) but is strongly carbon
enhanced with [C/Fe] = 4. Its chemical composition agrees well with predictions for Population III starsof just 10 solar masses exploding in low-energy fallback-and-mixing supernovae (from Heger & Woosley2010). Preliminary results from follow-up UVES spectroscopy as well as accurate 3D NLTE spectrum
synthesis calculations support these results.

The most metal-poor stars in the Large Magellanic Cloud
Kevin Schlaufman
Johns Hopkins University
kschlaufman@jhu.edu

The chemical abundances of the most metal-poor stars in a galaxy can be used to investigate theearliest stages of its formation and chemical evolution. Differences between the abundances of the mostmetal-poor stars in the Milky Way and in its satellite dwarf galaxies have been noted and provide thestrongest available constraints on the earliest stages of general galactic chemical evolution models. However, the masses of the Milky Way and its satellite dwarf galaxies differ by four orders of magnitude,
leaving a gap in our knowledge of the early chemical evolution of intermediate mass galaxies like the
Magellanic Clouds. To close that gap, we have extended the Best & Brightest survey to the MagellanicClouds using the mid-infrared metal-poor star selection of Schlaufman & Casey (2014). We have discovered the three most metal-poor giant stars known in the Large Magellanic Cloud (LMC) and reobserved
the previous record holder. The stars have metallicities in the range -2.70 < [Fe/H] < -2.00 and threeshow r-process enhancement: one has [Eu II/Fe] = +1.65 and two others have [Eu II/Fe] = +0.65.
The probability that four randomly selected very metal-poor stars in the halo of the Milky Way are as
r-process enhanced is 0.0002. For that reason, the early chemical enrichment of the heaviest elementsin the LMC and Milky Way were qualitatively different. It is also suggestive of a possible chemical link
between the LMC and the ultra-faint dwarf galaxies nearby with evidence of r-process enhancement (e.g.,
Reticulum II and Tucana III). Like Reticulum II, the most metal-poor star in our LMC sample is the
only one not enhanced in r-process elements.

The Oldest Extremely Metal-poor Stars
Henrique Reggiani
Jhons Hopkins University
hreggiani@jhu.edu

It is tempting to assert that the most metal-poor stars in the Galaxy are the direct descendants ofthe first stars. This is not necessarily the case though, as metal-poor stars form over a range of redshift.
Other properties beyond metallicity are therefore necessary to separate the old from the genuinely ancient
metal-poor stars. The bulge is the oldest component of the Milky Way, and numerous groups have usedsimulations to predict that the oldest stars at a given metallicity are found on bulge-like orbits. Tightly
bound metal-poor stars have been impossible to find in the inner bulge though, as most metal-poor stars
have been discovered using short-wavelength data. These classical techniques fail in the inner bulge
due to extreme reddening and extinction. We have used the mid-infrared metal-poor star selection of
Schlaufman & Casey (2014) on Spitzer/GLIMPSE data to overcome these problems and discover the mostmetal-poor stars known in the inner bulge. A comprehensive orbit analysis using Gaia DR2 astrometry
and our measured radial velocities confirms that these stars are tightly bound to the Milky Way. We
have used high-resolution Magellan/MIKE optical spectra to determine the detailed abundances of eachstar, and we find a distinct abundance signature in the inner bulge that is not present in halo or dwarf
galaxy stars at a similar metallicity. We propose that the distinct abundance signature we detect is a
product of a high star-formation rate in the core of the proto-Milky Way that is not realized in dwarf
galaxies or the event that produced most of the inner halo.

The Ancient Bulge Globular Clusters
Doug Geisler
Universidad de Concepcion and Universidad de La Serena
dgeisler@astroudec.cl

Bulge globular clusters contain a wealth of information about the formation and evolution of thisoldest Galactic component. However, until lately they have been relatively neglected, for good reason:
most of the bulge GCs suffer from large and often variable reddening, making traditional optical studies
extremely difficult. Many of them have only very basic parameters measured based on crude optical data.
We present new results on a number of bulge GCs based on a variety of near-IR techniques, including
metallicities and velocities obtained from the VLT FORS2 instrument, deep CMDs from the GEMINI-S
GeMS MCAO imager and HST, and first results from CAPOS, a long-term project to investigate detailed
chemical abundances in bulge GCs using APOGEE-2S.

The age of Halo metal-poor stars
Marica Valentini
Leibniz Institut für Astrophysik Potsdam (AIP)
mvalentini@aip.de

The modern, sophisticated models of the chemo-dynamical evolution of the Milky Way need much
more stringent observational constraints. Our understanding on the formation and evolution of ourgalaxy strongly depends on the quality and precision of fundamental stellar properties as distances,kinematics, masses, ages, and chemical composition.
How we can reach such precision, especially in the metal-poor domain? How we can provide precise
ages for a big number of field metal-poor stars?
In this talk I will present a sample of 10 Halo metal-poor red giant stars with -3 < [Fe/H] < -1
dex, for which we derived precise element abundances, ages, and kinematics. Our technique combines
asteroseimology, high resolution spectroscopy, and Gaia satellite data. We used asteroseismology frompast and recent missions (such as CoRoT, Kepler/K2 and TESS) first for analyzing high resolution stellar
spectra using the very precise seismic surface gravity. We then combined the spectroscopically derived
atmospheric parameters and abundances with the seismic parameters in a Bayesian tool (PARAM) to
derive stellar mass, distance, and age. We finally derived stars kinematics using the very precise propermotions from Gaia DR2. The adopted technique has been first presented in Valentini et al. (2019), ourpilot study.
With our method we can obtain a precision of < 30 % on age, 15 % in distance, and <0.07 dex inchemical abundances. This sample will help probing the history of the galactic Halo. In particular we
will provide an unique insight into its major accretion relics, such as Sequoia and the Gaia-Sausage. We
provide not only an informative chemical profile up to Europium, but also precise ages, unveiling whenthese accretion events happened.

The extreme enhancement in carbon, nitrogen, and oxygen of theiron-poor star J0815+4729
Jonay I. González Hernández
Instituto de Astrofı́sica de Canarias
jonay@iac.es

Low-mass extremely metal-poor stars must have formed from a mixture of material from the primordial
nucleosynthesis and matter ejected from the first supernovae. The chemical composition of these stars,
especially those still on the main sequence, holds crucial information, such as the properties of the firststars and the early chemical enrichment of the Universe.
We identified the iron-poor dwarf star SDSS J0815+4729 (Aguado et al. 2018a) using the OSIRIS
spectrograph at the 10.4m-GTC telescope in La Palma (Canary Islands, Spain). The low-dispersion
OSIRIS spectrum revealed already the huge C enhancement in this primitive star with a million times
less iron than the Sun.
We have recently acquired high-resolution spectroscopy with HIRES at the 10m-Keck telescope,
uncovering the unique abundance pattern of this star (Gonzalez Hernandez et al. 2019, ApJL, in press).
We derive [Fe/H] = -5.5 and detect the near-IR OI triplet for the first time in an ultra metal-poor star,confirming the extreme CNO abundances of J0815+4729 with, ratios [X/Fe] > 4. We are unable todetect Li in this star, placing an upper-limit at A(Li)< 1.3 dex, about 0.7 dex below the detection,at the level of the lithium plateau, in J0023+0307 (Aguado et al. 2018b, 2019), and exacerbating thecosmological lithium problem.

Constraining nucleosynthesis in CEMP-s progenitors using Fluorine
Aldo Mura-Guzman
The Australian National University
aldo.muraguzman@anu.edu.au

Carbon-Enhanced Metal-Poor (CEMP) stars are among the most important objects for constraining
the formation and evolution of the first stellar populations in the Galaxy. CEMP stars with enhancements
in slow neutron-capture process (s-process) elements (CEMP-s stars, objects with [Fe/H] < -2, [C/Fe] >0.7 and [Ba/Fe] > 1) are a significant fraction (as high as 25 %) of all metal-poor stars. Of the proposed
formation channels for CEMP-s stars, mass transfer in a binary system from an AGB companion which is
now an unseen white dwarf is the most widely accepted scenario. Fluorine production at low metallicity
is extremely sensitive to the physical conditions where is produced and probably related to the same
nucleosynthetic process responsible for s-process element production in AGB stars during the thermalpulsating phase. Thus, Fluorine measurements in CEMP-s stars provide a direct test for CEMP-sformation scenarios, nucleosynthesis, and chemical enrichment mechanisms in the early beginnings ofthe Milky Way. At low-metallicity, [Fe/H] < −2, Fluorine have been detected and measured in just 2stars: HE 1305+0132 and HD 5223. A handful of upper limits also exist. We present Fluorine detectionsin 2 CEMP-s stars along with a careful comparison with state-of-the-art nucleosynthesis predictions
indicating some successes, and shortcomings, of the models.

Life on the fast lane: chemistry of Halo (?) stars on extreme orbits
Luca Sbordone
ESO - European Southern Observatorylsbordon@eso.org

One of the least studied population of stars in the Milky Way comprises objects on extremely highenergy orbits, barely (if at all) bound to our Galaxy, and reaching deep in the farthest outskirts of the
Halo. These objects are expected to include stars accelerated by close encounters in dense stellar systems,
remnants of high-energy substructure accretion, and unbound stars entering the MW from intergalactic
space. However interesting, until recently only very few of these elusive objects were known. We present
a chemical and kinematical analysis of 65 cool evolved stars selected from Gaia DR2 to have extreme
Halo (or unbound) orbits. These stars, observed with FORS, show heliocentric velocities in excess of
500 km s−1 , apogalactic distances exceeding in some cases 200 kpc, generally low metallicities (-2.5 <[Fe/H] < -1.0) and, at least in some cases, surprisingly young ages. We will present abundances for C,
Mg, Ca, Ti, Fe, and Ba, and discuss orbital solutions, integrals of motion and possible origins of these
extreme members of our System.

Clues on the lithium meltdown in dwarf stars using the red giant branch
stars
Lorenzo Monaco
Universidad Andres Bellolorenzo.monaco@unab.cl

The lithium abundance, A(Li), in the oldest stars is a key element in our understanding of the Big
Bang nucleosynthesis. A(Li) remains constant in dwarf stars down to [Fe/H] = -2.8 dex and, at lower
metallicity, drops by 0.3 dex. The origin of this lithium meltdown is still unclear: this drop could be
primordial (challenging the current models for the primordial nucleosynthesis) or due to (still unknown)
settling/diffusion mechanisms in the stellar atmosphere. Red giant branch (RGB) stars below the bumplevel (LRGB) are insensitive to diffusion effects occurring in dwarf stars. If the lithium drop observed in
dwarf stars is a birthmark, it should be observable in RGB stars as well. I will present the preliminary
results of the study of the lithium content in a sample of LRGB stars of in the same metallicity range ofthe lithium meltdown.

Near-field cosmology with metal-poor stars: Births and deaths of stars in
the Magellanic Clouds
Venu Kalari
Gemini Observatory/ Universidad de Chilevkalari@gemini.edu

Stars forming (and dying) in nearby metal-poor Galaxies can be studied to a level of detail not affordedin other observations. We summarize our results focusing on the metal-poor stellar populations in starforming regions of the nearby Magellanic Clouds. We attempt to place it in the context of near-fieldcosmology, to place constraints on the formation of the first stars and galaxies.

Heavy puzzle pieces: Learning about the i process from Pb abundances
Melanie Hampel
Monash University
Melanie.Hampel@monash.edu

Abundances of elements heavier than iron are observed in the photospheres of old stars and teachus about nucleosynthesis in the early Universe. The large majority of heavy-elements are formed by
the slow (s) and rapid (r) neutron capture processes. However, it has become clear that a neutroncapture process operating at neutron densities intermediate to the s and r process (i process) gives rise
to its own characteristic abundance pattern. This i-process pattern is successful at reproducing observed
heavy-element abundances that could not be explained previously, e.g. those of carbon-enhanced metalpoor stars that show enrichments of s- and r-process elements (CEMP-s/r, CEMP-i) or Pb-poor postasymptotic giant branch stars. The required high neutron densities of n ∼ 1015 cm−3 may occur as aresult of proton ingestion episodes in metal-poor and metal-free low-mass stars. However, the sites of
the i process in nature are as yet unknown.
Comparing theoretical predictions of i-process nucleosynthesis with the observed abundance patternsof CEMP stars and post-AGB stars in the Magellanic Clouds allows us to learn about the thermodynamic
properties of possible i-process sites. In this contribution I will present the results of my nuclear-network
calculations of i-process nucleosynthesis in comparison to observations.

Spectroscopic follow-up of metal poor candidates from the Pristine
survey with Narval at TBL.
Aroa del Mar Matas Pinto
Observatoire de Paris
Aroa.del-Mar-Matas-Pinto@obspm.fr

Metal-poor stars, thanks to their old ages are at the heart of near field cosmology. They are nevertheless very rare objects. The Pristine survey, using narrow band photometry centred on the CaII
H&K lines, conducted at the CFHT with the wide-field imager MegaCam, allows the determinationof the metallicity for a large number of stars, and among them it is possible to have a reliable selection of candidate metal-poor stars. In this talk I will describe the results of follow-up spectroscopy of
Pristine metal-poor candidates conducted at the 2m Telescope Bernard Lyot (Pic du Midi) with the
Narval Spectrograph. I will also show how the photometric metallicity estimate compares to the spectroscopic metallicity for this and other samples of stars observed in the Pristine spectroscopic follow-up
effort. Finally I will discuss how Pristine photometric metallicities can be used to study the metallicity
distribution function of metal-poor stars.

S6: From the first galaxies to the epoch of reionization
Probing cosmic dawn with the 21-cm signal
Anastasia Fialkov (Invited Talk)
Cambridge University
anastasia.fialkov@gmail.com

Cosmic dawn is one of the least-explored epochs in the history of the Universe illuminated by the very
first stars and black holes. One of the potentially powerful probes of cosmic dawn is the predicted 21-cm
signal of neutral intergalactic hydrogen. The 21-cm signal is tied to the intensity of radiation generated
by the first sources of light, and, thus, can be used to constrain process of primordial star and black holeformation as well as reionization. In my talk I will discuss the status of the field of 21-cm cosmology.

Physical and observable properties of the first galaxies and black holes
John Wise (Highlight Talk)
Georgia Institute of Technology
jwise@physics.gatech.edu

I present results from a suite of cosmological radiation hydrodynamics simulations that focus on
massive metal-free stars and the first generations of galaxies. We find that low-luminosity galaxies have
UV escape fractions that can exceed 10 per cent during bursts of star formation but is highly variable inboth time and angle. We also find that the galaxy luminosity function flattens at absolute UV magnitudes
dimmer than -14, arising from internal radiative and supernova feedback. We also calculate the sizes,
colors, and typical stellar populations of these first generations of galaxies. We find that a rare set ofgalaxies form a massive black hole before any star formation, and I present observational predictions forthis population that can probe the seeding of supermassive black holes.

Galaxy formation in quasar fields during reionization
Huanqing Chen
University of Chicago
hqchen@uchicago.edu

Recent observations have found that many z ∼ 6 quasar fields lack galaxies. This unexpected lack ofgalaxies may potentially be explained by quasar radiation feedback. To accurately model this problem
requires both a large cosmological simulation volume and high spatial resolution to resolve galaxies,
as well as fully self-consistent radiative transfer (RT). Here I present a suite of 3D radiative transfer
cosmological simulations of quasar fields. We find that quasar radiation suppresses star formation in low
mass galaxies, mainly by photo-dissociating their molecular hydrogen. Photo-heating also plays a role,
but only after ∼100 Myr. However, galaxies which already have stellar mass above 105 M⊙ when thequasar turns on will not be suppressed significantly. Quasar radiative feedback suppresses the faint endof the galaxy luminosity function (LF) within 1 pMpc, but to a far lesser degree than the field-to-field
variation of the LF. My study also suggests that by using the number of bright galaxies (M 1500 < −16)around quasars, we can potentially recover the underlying mass overdensity, which allows us to put
reliable constraints on quasar environments.

A new formation channel for globular clusters
Yeou Chiou
University of California, Los Angelesyschiou@physics.ucla.edu

The puzzling origins of globular clusters have been greatly debated over the years. I will present a newformation channel for globular clusters, linking them to objects that formed without dark matter in theearly Universe in the presence of the stream velocity. This stream velocity (Tseliakhovich & Hirata 2010)
arises due to the drop in radiation pressure of baryons from matter-radiation decoupling and induces aphase shift/physical separation between dark matter and baryonic overdensity peaks (Naoz & Narayan
2014). This effect gives rise to gas dominant objects with little to no dark matter. These gas-rich
structures, called Supersonically Induced Gas Objects (SIGOs), form naturally outside of dark matter
halos as a consequence of the stream velocity. Running hydrodynamic AREPO simulations we find that
SIGOs density is high enough to allow stars to form. Then, we model the star formation process andestimate the luminosity of the first star clusters within a SIGO. We find that SIGOs occupy a different
part of the luminosity-mass parameter than classical, dark matter halos with gas. SIGOs are dimmer
and have globular cluster-like masses. We further adopt a simple model to evolve the SIGOs to current
day objects and show that their radius and luminosity is consistent with present-day (local) globularclusters. Since the relative velocity between the baryons and dark matter is coherent over a few Mpc
scales, we predict that if this is the dominant mechanism for globular clusters, their abundance should
vary significantly over these scales.

Modelling X-ray feedback from binaries at the early universe
Nina Sanches Sartorio
University of Cambridge
sartorio.nina@ast.cam.ac.uk

In the early universe XRBs are thought to play a key role in heating and ionizing the intergalactic
medium (IGM) . This is due to the fact that X-rays have larger mean free paths than the UV light emitted
by the first stars. Consequently, while the latter is responsible for the bulk of the Universe’s reionization,
the former would have started acting in the IGM at much earlier times, thus having important effects on
the 21-cm signal of neutral hydrogen. Despite their significance, the impact of XRBs at high redshifts isstill poorly constrained, both due to the uncertainty in their number as well as their SEDs. In my talk I
will present an effort to improve the modeling of high-redshift X-ray binaries. We use data from binaries
formed within different cosmological Arepo simulations alongside a binary evolution code, Binary c, toconstrain the number of XRBs we expect to be present at each redshift as a function of the underling
IMF. By taking this “bottom up” approach we can determine, for each simulation, the XRB number
density, the type of each of the binaries (low or high mass) and for how long each pair emits X-rays.
Aiming to get better estimates of the influence XRBs’ have both on their mother halo and on the IGM
we have designed a suitable SED model for each X-ray binary. This new feedback prescription will be
publicly available and can be used to improve the treatment of XRBs in future numerical simulations.

Understanding the physical conditions of high-redshift (z ∼ 6) metal
absorption lines
Teresita Suarez Noguez
University of Edinburgh
suarez@roe.ac.uk

Dense regions in the high-redshift intergalactic medium (IGM) might be metal enriched. Lowionization absorption lines can be observable in these regions, particularly during the last phase ofreionization. In this work we study these regions by modeling the absorption systems as individual gas
clouds heated and ionized by a radiation field to predict its physical conditions (temperature, density,
ionization state) and analyze their abundance measurements. We study the properties of these systems(such as column density ratios) to separate them into those where collisional ionization dominates (hightemperatures) and those where photoionization dominates (low temperatures). In this talk, I will present
the predicted systems by photoionization models and I will show how they compare to low- and highionization systems from observations.

Probing Cosmic Dawn : determining the age of the most distant galaxies
Nicolas Laporte (Highlight Talk)
Kavli Institute for Cosmology
nl408@cam.ac.uk

Determining the period when the first galaxies emerged from a dark intergalactic medium represents
a fundamental milestone in assembling a coherent picture of cosmic history. But the so-called ‘Cosmic
Dawn’ period is not accessible yet directly by current ground-based and space telescopes, but it canbe constrained following two different methods : simulations of the first population of galaxies or bymeasuring the age of the most distant galaxies. For the later, a multi-wavelength approach combining
photometric and spectroscopic data from the NIR to sub-mm is crucial. This technique allows to estimate the age of very high-redshift galaxies from either the shape of the 4000A break or the amountof dust formed. Our group is conducting deep NIR spectroscopic surveys using X-Shooter/VLT and
MOSFIRE/Keck combined with deep ALMA observations to probe the nature and properties (including
age, nature, stellar mass, and SFR) of z > 7 HST selected galaxies. In this talk, I will describe the latest
constraints we obtained on several of the most distant galaxies as well as what we can expect from futurefacilities.

S7: Dwarf galaxies as a potential probe of the early
Universe
Signatures of the First Stars in Relics of the First Galaxies
Alexander Ji (Invited Talk)
Carnegie Observatories
aji@carnegiescience.edu

Detection of a spatially extended population of extremely metal-poorstars in the Tucana II ultra-faint dwarf galaxy
Anirudh Chiti
MITachiti@mit.edu

Ultra-faint dwarf galaxies (UFDs) are some of the oldest (∼ 13 Gyr) and most chemically primitive([Fe/H] < -2.0) systems in the Milky Way halo. Therefore, the chemical abundances of their stars canplace strong constraints on early chemical enrichment and the merging and growth of the first galaxies.
However, studies of UFDs are limited since (1) generally less than ∼ 10−20 stars per UFD have beenchemically characterized due to their faintness and (2) prior work has largely not searched for member
stars outside of two half-light radii due to significant foreground stellar contamination.
Here we bypass the above issues and thereby show that the Tucana II UFD is chemically even moreprimitive and spatially much more extended than previously assumed. We implement a novel, highly
efficient membership selection technique by first deriving photometric metallicities and surface gravities
for every star within ∼ 10 half-light radii of Tucana II using deep (g ∼ 21) SkyMapper photometry.
We then identify likely members as metal-poor red giants with Gaia DR2 proper motions consistent
with that of Tucana II. By spectroscopically observing these stars, we identify a population of extremely
metal-poor ([Fe/H] < -3.0) members located out to ∼ 8 half-light radii of the Tucana II UFD, suggesting
Tucana II to be the product of one of the earliest galactic mergers. Our observations further show that
the Tucana II UFD is the first known extremely metal-poor dwarf galaxy ([Fe/H] < -3.0).
Our result demonstrates that UFDs may principally host spatially extended populations of stars thatwere missed by previous studies. Indeed, two additional UFDs, Bootes I and Segue 1, already have
known individual members at ∼ 4 half-light radii. Identifying such populations of stars would be crucial
in comprehensively modeling UFDs and plausibly discriminating whether UFDs have a merger history.
This, in turn, would be pivotal in understanding the nature of the building blocks of Milky Way sizedgalaxies.

What conditions shape the Eu abundances of stars in UFDs?
Yuta Tarumi
University of Tokyoy0u1t1a5.t@gmail.com

Two ultra-faint dwarf galaxies (UFDs) are known to be r-process rich. The abundances of europium(Eu) suggest that the origins are likely to be neutron-star mergers (NSMs). However, the diversity in theprogenitor system and the environment is not investigated in detail. For example, NSM can happen in theoutskirt of the galaxy, as the binary neutron-stars are expected to receive kick by the anisotropic explosionof two supernovae. We study how the star formation histories of the UFD progenitors and the positionsof the merger sites affect the stellar Eu abundance distributions. We use cosmological hydrodynamic
simulation to model the r-process enrichment of the UFDs. In this talk, I will demonstrate for the firsttime how the explosion site and the star formation history of the progenitors affect the observed stellar
Eu abundance. I will also discuss the implications of the UFD progenitors and the origin of the r-processelements.

Dwarf galaxies and their hidden treasures
Stefania Salvadori (Highlight Talk)
University of Florence
stefania.salvadori@unifi.it

Dwarf galaxies are the most common type of systems in the Local Universe and they were evenmore common at early times, since they were likely the building-blocks of present-day galaxies. After
reviewing the most recent observational and theoretical findings for present-day metal-poor stars andgalaxies, I will show that Local Group dwarf galaxies are key objects to study the properties of the firststars and the early processes of star-formation. I will demonstrate that these small systems are indeed
the best targets to unveil the hidden chemical signatures of the first stars along with their living fossils.
I will finally show how upcoming stellar surveys and next generation telescopes will allow us to tightly
constrain the first star mass distribution and to successfully link Near- and Far-Field Cosmology.

Constraining the low-mass end of the first stars
Martina Rossi
Università degli studi di Firenze (Florence,Italy)
rossi@arcetri.astro.it

The precise value of the lower-mass limit of Pop. III stars is important in predicting whether any
truly metal-free stars could have survived until present-day. Therefore, we investigate the frequency offirst stars relics in Ultra-faint dwarf galaxies to limit the low-mass end of the Initial Mass Function (IMF)of the first stars. To this end we develop a theoretical model that follows the formation and evolutionof isolated Ultra-Faint dwarf galaxy, particularly focusing on the best studied system: Boötes I. We
calibrate the model by comparing our results with available observations (galaxy Luminosity, Metallicity
Distribution Function, and Star Formation History) and we detailed studied how the incomplete samplingof the stellar IMF affects the chemical evolution of poorly star-forming Ultra-Fain dwarf galaxies. We
explore the impact of different Pop. III IMFs on the expected number of long-living first stars in Boötes
I and, by exploiting available data, we provide observational-driven constraints on the minimum mass
(Mmin ) of the first stars: we can exclude that Pop. III stars have Mmin ≤ 0.8 M⊙ independently fromthe shape of the IMF at 68 % confidence level.

Dynamical relics of the ancient galactic halo
Zhen Yuan
Shanghai Astronomical Observatorysala.yuan@gmail.com

We search for dynamical substructures in the LAMOST DR3 very metal-poor (VMP) star catalog
cross matched with Gaia DR2. From 3300 VMP stars with halo kinematics, we are able to recover
all the existing substructures such as Gaia-Sausage, Sequoia, and the Helmi Stream. There are alsoa few new substructures discovered. More interestingly, we found one VMP dominated substructureRg5 is dynamically associated with two highly r-process-enhanced stars with [Fe/H] ∼ −3. This finding
indicates that its progenitor might be an ultra-faint dwarf galaxy that has experienced r-process enrichment from neutron star mergers. This study has taken the first steps in finding dynamical associations
between disrupted dwarf galaxies and r-process-enhanced stars, which is crucial for studying their birthenvironments. This helps us understand the star forming activities, nucleosynthetic events, and chemical
evolution in UFDs and other dwarf galaxies in the early universe. The great advantage of studying debris
in the nearby halo is that high-resolution spectroscopic observations are much more readily obtainable,
so we expect this field of activity to have a rich future in the coming decades.

The stellar populations of high-redshift dwarf galaxies
Viola Gelli
Università degli Studi di Firenze (Florence, Italy)gelli@arcetri.inaf.it(V.Gelli, S.Salvadori, A. Pallottini, A. Ferrara)
We use state-of-art cosmological zoom-in simulations of a typical z ∼ 6 Lyman Break Galaxy (LBG)
to investigate the stellar properties of its dwarf satellite galaxies. We find six of them residing in thehost galaxy halo, their stellar masses ranging from M⋆ ≃ 106 M⊙ to ≃ 109 M⊙. All the dwarf satellites
properties show no dependence on the distance from the central massive LBG. These systems are mostly
spherical, and old and metal-poor stars are located in the inner regions. The SFH and chemical evolution
reveal that high-mass dwarf galaxies (M⋆ ≃ 5 × 108 M⊙) form preferably from a pristine gas, experiencing
a long history of star formation, characterized by many merger events. Low-mass systems (M⋆ ≃ 5 ×
108 M⊙) are instead born from an already chemically enriched gas and have much shorter formation
histories due to the strong influence of SN feedback and of the dissociating radiation from the nearby starforming LBG. All satellites are characterised by high SFRs (typically > 5 M⊙ yr−1 ) and by estimating
their emission we found that such high rates make them luminous enough to be detected by upcoming
next-generation facilities like James Webb Space Telescope.

S8: Formation, growth and observational constraints
on the first supermassive black holesLife and death of supermassive stars
Lionel Haemmerle
University of Geneva
lionel.haemmerle@unige.ch

Supermassive stars (SMSs) are candidates for being the progenitors of the most massive quasars at
redshift z > 6. The viability of this formation channel (direct collapse) depends on the properties of theprogenitor, whose evolution is dominated by rapid accretion. I will present the most recent models of
SMSs, that include accretion and rotation, and discuss their implications regarding the direct collapse
scenario and the possible observational signatures of these extreme objects.

The first quasars in cosmological hydrodynamic simulations
Tiziana DiMatteo (Invited Talk)
Carnegie Mellon University
tiziana@phys.cmu.edu

Stellar black holes at cosmic dawn

Felix Mirabel (Highlight Talk)
IAFE-UBA-Argentina
felix.mirabel@cea.fr

Theoretical models and observations suggest that large fractions of Pop. III stars end as black holes(BHs) in High-Mass-X-ray Binaries (BH-HMXBs), which are sources of hard X-rays and synchrotron
relativistic jets (Microquasars1: MQs). The hard X-rays from these accreting BHs of Pop III have long
free paths, pre-heat the Intergalactic Medium (IGM), and produce a smooth end of the re-ionization
epoch 2. I will show that the relativistic jets from BH-HMXB-MQs of Pop. III produce a cosmic radio
background (CRB) that can account for the excess amplitude and bottom flat absorption of atomic
hydrogen at z ∼ 17 (78 MHz) reported by EDGES3. I will conclude that the Cosmic Radio Backgroundfrom BH-HMXB-MQs of Pop. III is the smoking gun of Pop. III stars4.

Ezequiel Treister (Highlight Talk)-

Super-Eddington gas accretion onto intermediate-mass seed black holes
Daisuke Toyouchi
Kyoto University
toyouchi@tap.scphys.kyoto-u.ac.jp

Super-Eddington gas accretion onto seed black holes is an essential formation mechanism of supermassive black holes (SMBHs) with about one billion solar mass discovered at z ∼ 7. Wada et al. (2016)
investigated the detailed gas structure around SMBHs at the scale of dusty tori or circumnuclear disks(CNDs) based on three-dimensional radiation hydrodynamics (RHD) simulations. However, they justsupposed local-AGNs, assuming the solar-abundance gas and constant sub-Eddington accretion. In thisstudy, we, for the first time, explore the feasibility of the super-Eddington growth of intermediate-mass
seed BHs in the low-metallicity environments, Z < 0.1 Z⊙ , with 3D RHD simulations, which solve thehydrodynamics, radiative transfer of ionizing photons and thermal emissions from dust grains, and nonequilibrium chemistry self-consistently. Our simulations show that higher gas density and metallicity
leads to colder and thinner CNDs, which consequently weakens the photoevaporation of the accretinggas. As a result, we find that the super-Eddington accretion occurs when the metal-enriched gas with Z> 0.01 Z⊙ goes into the CND regions with the inflow rate of 100 times higher than Eddington. In thistalk, based on these results, we will discuss the sites of SMBH formation in the early universe.

Long- and Short-distance relationships with massive black holes
Aycin Aykutalp
Los Alamos National Laboratory
aycina@lanl.gov

In the last decade, growth of supermassive black holes in the centers of galaxies and their rolein shaping the evolution of galaxies and their star formation histories has become a central topic incosmology. However, the underlying physics of how a black hole affects the evolution of its host galaxy
as well as nearby halos around its vicinity are still not well understood. I will talk about how an
accreting black hole can affect the thermodynamics of the interstellar (short-distance) and intergalactic(long-distance) medium and induce/inhibit formation of objects through radiation. I will further provide
observational diagnostics for finding the fingerprints of massive black holes in the early universe withforthcoming telescopes such as James Webb Space Telescope.

Formation of massive black hole seeds following collapse andfragmentation of atomic cooling halos
Bastian Reinoso
Universidad de Concepciónbreinoso@udec.cl

The observational evidence of Super Massive Black Holes at high redshift (z ∼ 7) has lead to thedevelopment of models for the rapid formation and growth of massive black hole seeds from pristinegas clouds collapsing inside atomic cooling halos ∼ 108 M⊙ . The most promising model in terms of
the final mass of the black hole seed is the direct collapse of gas clouds in atomic cooling halos yielding
products with ∼ 105 − 106 M⊙ if fragmentation can be efficiently suppressed, however recent numericalsimulations show that fragmentation cannot be avoided but still a massive object (∼ 105 M⊙ ) can beformed if the fragments are able to merge afterwards. In this work we present a model that considers
fragmentation during the collapse of the gas clouds by performing direct Nbody + SPH simulations tomodel a dense cluster of accreting protostars still embedded in their natal gas cloud in order to better
understand how the amount of fragmentation affects the final mass of the black hole seed.

Highlights of direct collapse black holes from the past decade
Muhammad Latif (Highlight Talk)
UAE University
latifne@gmail.com

More than 300 quasars have been observed observed at z¿ 6, they unveil the existence of supermassive
black holes of a billion solar mass which pose a challenge for theories of structure formation. How comethese monsters grow to such high masses in a very short time is still a mystery. In this talk, I will discuss
our current understanding and challenges of forming supermassive black holes. Also show some recent
results which suggest that some of them will form in binaries or even multiple systems. In the end I will
results from radiation hydrodynamical simulations about the growth of DCBHs.

Formation of the massive seed BHs in the low-metallicity environment
Sunmyon Chon
Tohoku University
sunmyon.chon@astr.tohoku.ac.jp

Recent observation reveals that many SMBHs reside in the early universe, z > 7. Direct collapse (DC)model is one of the promising path to form such SMBHs. Massive seed BHs with 105 M⊙ forms out of theclouds with special condition (DC clouds), i.e. very close to a luminous galaxy, which will grow into thehigh-z SMBHs. In the DC model, the cloud is usually assumed to be completely primordial. The critical
metallicity for the massive BH formation is still no consensus so far. Omukai et al. (2008) have foundthat once a cloud is polluted by heavy elements, the cloud temperature suddenly decreases at the densitywith n > 1010 cm−3 , which can induce the violent fragmentation. Whether the fragmentation reduces
the final mass of the seed BH or not, should be further investigated by the numerical simulation. We
have performed the hydrodynamical simulation, which follows the dynamical evolution of the DC clouds
with low-metallicity environment. What we have found is that the existence of the heavy element does
not prevent the massive seed BH formation when the cloud metallicity is smaller than 10−4 Z⊙ . During
the initial 104 years, the mass of the central star reaches 6000−8000 M⊙ even in the low-metallicity
environment. The dust cooling does induce the strong fragmentation, but the central star efficiently
grows in mass by the gas accretion and the stellar mergers. In this presentation, I will summarize theresults of our calculation and discuss implication for the SMBH formation.

Pulsational instability of very massive stars with various metallicities
Daisuke Nakauchi
Tohoku University
nakauchi@astr.tohoku.ac.jp

The recent discovery of high-redshift (z > 6) supermassive black holes (SMBH) of 1010 M⊙ poses thequestion of their origin. They require both the formation of massive seed BHs and the subsequent rapid
mass accretion within < 1 Gyr after the Big Bang. One plausible scenario for a massive seed BH formationis the so-called stellar merger scenario. In metal-enriched star-forming clouds within a protogalaxy,efficient cooling via metal-line and dust-continuum emission would lead to vigorous fragmentation of thecloud, enabling the formation of dense stellar clusters. Massive seed BHs can be formed, if very massive
stars are born through runaway collision in the dense stellar clusters. By combining the cosmologicalsimulation with the N-body simulation, previous studies have shown that very massive stars of 400−1900
M⊙ can be formed in this scenario. It is generally believed, however, that very massive stars are unstableto pulsational instability, which could prohibit massive BH formation, if significant mass-loss is driven
by the instability. So far, stability analysis was performed only for zero metallicity and solar metallicity
cases, and the stability of slightly metal-enriched stars is not well understood. Here, we study pulsational
instability of very massive stars with various metallicities and examine how much fraction of mass is lost
during their lifetime.

Making a supermassive star by stellar bombardment
Hiromichi Tagawa
Eotvos University
htagawa@caesar.elte.hu

Approximately two hundred supermassive black holes (SMBHs) have been discovered within thefirst ∼ Gyr after the Big Bang. One pathway for the formation of SMBHs is through the collapse of
supermassive stars (SMSs). A possible obstacle to this scenario is that the collapsing gas fragments
and forms a cluster of main sequence stars. Here we raise the possibility that stellar collisions may besufficiently frequent and energetic to inhibit the contraction of the massive protostar, avoiding strong UVradiation driven outflows, and allowing it to continue growing into a SMS. We investigate this scenario
with semi-analytic models incorporating star formation, gas accretion, dynamical friction from stars andgas, stellar collisions, and gas ejection. We find that when the collapsing gas fragments at a density of< 3 ×1010 cm−3 , the central protostar contracts due to infrequent stellar mergers, and in turn photoevaporates the remaining collapsing gas, resulting in the formation of < 104 M⊙ object. On the other
hand, when the collapsing gas fragments at higher densities (expected for a metal-poor cloud with Z <10−5 Z⊙ with suppressed H2 abundance) the central protostar avoids contraction and keeps growing via
frequent stellar mergers, reaching masses as high as ∼ 105 −106 M⊙ . We conclude that frequent stellar
mergers represent a possible pathway to form massive BHs in the early universe.

S9: Current and future surveys and observational
facilities

The R-Process Alliance – Progress and Preview
Timothy Beers
University of Notre Dametbeers@msu.edu

I report on the progress to date on the R-Process Alliance (RPA), an effort to more than quadruple
the number of known highly r-process-enhanced stars (r-II) stars in the Galaxy. These stars are being
used to constrain the nature and site(s) of the astrophysical r-process. I also provide a description of how
we are dramatically increasing the pace of discovery, using a pre-survey for likely r-I and r-II candidates
from MRS spectra obtained by LAMOST, and follow-up of dynamically tagged groups known to haveat least one or more r-I and r-II stars.

Big data in Galactic archeology: the future surveys
Elisabetta Caffau (Invited Talk)
Observatoire de Paris
Elisabetta.Caffau@obspm.fr

A main concern in the stellar community is to complete the information that will be provided by
the Gaia mission. Gyes was conceived in 2010 to complete this information, but, unfortunately, theCFHT board decided not to pursue it. Nevertheless the experience of Gyes was instrumental to spin
off subsequent projects like MOONS, 4MOST, and WEAVE. High multiplex (from several hundreds toseveral thousands spectra per exposure), high resolution spectrographs are going to play a major role inthe development of astrophysical knowledge in the next decades.
I will give a biased oversight of the current status of the Gaia follow-up.

Else Starkenberg (Invited Talk)
Leibniz Institute for Astrophysics Potsdam
estarkenburg@aip.de

Characterizing the origin and properties of the halo r-process star
population with data collected by the R-Process Alliance
Anna Frebel
MIT
afrebel@mit.edu

Over the last several years, the R-Process Alliance has collected high-resolution spectra of metalpoor giants to systematically identify rare r-process enhanced stars. The combined sample of 380 stars
analyzed so far suggests a fraction of 7enhanced stars and 40the Milky Way’s halo (Sakari et al. 2018,
Hansen et al. 2018, Ezzeddine et al. 2020). Considering the formation history of Milky Way’s halo andkinematics of halo stars, it can be expected that these stars did not form in situ but were accreted alongwith their birth host galaxies as part of the Milky Way’s growth over time.
The discovery of the r-process galaxy Reticulum II certainly has shown that small galaxy can experience a neutron star merger or another prolific r-process event that gives rise to a local population of
r-process stars (Ji et al . 2016). This provides a this new type of chemical tagging in which the existenceof stellar r-process signatures can be used to trace the merger history of the halo. Recent simulations
make use of this idea that the frequency of r-process galaxies drives the number of r-process stars ultimately brought into the Milky Way. The majority of the halo r-process star population can indeed be
explained as having originated in small dwarf galaxies similar to Reticulum II (Brauer et al. 2018).
This picture is further supported by the kinematics signatures of halo r-process stars which show
clustering effects. This shows that is likely that groups of r-process enhanced stars entered the Milkyhalo together as part of the dissolution of their host galaxies (Roederer et al. 2019)

A global 21-cm Chilean experiment: MIST
Ricardo Bustos
U. Católica de la Santı́sima Concepciónrbustos@ucsc.cl

Different experiments around the world are trying to detect the global 21-cm signal from neutralhydrogen in the intergalactic medium during the Dark Ages, the Cosmic Dawn, and the Epoch of Reionization. The EDGES experiment in 2018 was the first to report an absorption feature that departs fromtheoretical models. Here, we present a Chilean experiment MIST (Mapper of the IGM Spin Temperature)aiming to independently detect the global 21-cm signal that can confirm or discard the EDGES detectionin the 50-120 MHz range from the MARI site in northern Chile.

Searching for the first generations of stars at high redshift with JWST
Andrew Bunker (Highlight Talk)
University of Oxford
Andy.Bunker@physics.ox.ac.uk

I will describe future searches for galaxies in the early Universe with the James Webb Space Telescope(JWST). The NIRSpec near-infrared spectrograph on JWST is sensitive out to 5microns, probing therest-frame optical emission of galaxies out to z = 7, and potentially lines such as Lyman-alpha, HeII
and [OII] at z >> 10. With my colleagues on the ESA NIRSpec Instrument Science Team, we areplanning a large GTO survey of galaxies in the high redshift universe, taking advantage of the multiplex
available with the microshutter array of NIRSpec to target hundreds of Lyman break galaxies at z > 5.
By studying line ratios, we can chart the evolution of metallicity, dust extinction and AGN contribution,and coupling with SED fits to the continuum we can determine stellar masses and potentially look forsignatures of a different initial mass function (IMF). In particular, the HeII 1640 Ang line might be
the signature of a hard ionizing spectrum expected from a top-heavy IMF expected from Population III
stars. We will also address the build-up of stellar mass in galaxies at high redshift, and will estimate
for the first time the escape fraction of ionizing photons for galaxies at z > 6 through comparison of theBalmer lines with the rest-UV continuum. The escape fraction is a critical and unknown quantity in thequest for which sources reionized the Universe at z ∼ 6−9. JWST will push to even earlier epochs, using
the Lyman break to potentially detect the first massive galaxies to form at z > 10, and I will present
our expected parameter space and sensitivities for our survey.

The LAGER survey: Studying Reionization with Ly-alpha emitters
Jorge Gonzalez Lopez
Las Campanas Observatory
jgonzalez@carnegiescience.edu

Reionization of hydrogen in the intergalactic medium (IGM) is a landmark in structure formation.
Resonant scattering of Ly-alpha photons is sensitive to neutral hydrogen in the IGM, making Ly-alphaemitters a sensitive, practical, and powerful probe of the central phase of reionization. Redshift z ∼ 7 isthe frontier in Ly-alpha and reionization studies and appears to be in the middle of Reionization.
In the “LAGER” project (Lyman-Alpha Galaxies in the Epoch of reionization), we take deep narrowband images with DECam (3 deg2 field-of-view) and an optimally designed narrow-band filter to identify
Ly-alpha emission at z ∼ 7. We are conducting a program to observe an area of 24 deg2 in 8 fields with
DECam to select 600 LAEs and study reionization with the clustering properties of these Ly-alphasources.
In this talk I will present the first results from the LAGER survey and the posterior spectroscopic
campaign. Up to now, we have observed five DECam fields to full depth. Using instruments in Las
Campanas Observatory, we have confirmed 23 Ly-alpha galaxies in the first two fields (COSMOS and
CDFS). Based on the spectroscopically confirmed LAEs, we find a significant difference in the brightend of the luminosity functions for the COSMOS and CDFS fields, that could be explained by different
local ionization bubbles.
I will describe what we can learn about galaxy evolution and the process of reionization by studying
the field to field variation of the Ly-alpha luminosity function at z ∼ 7, the campaign to test theReionization bubbles scenario and the tentative detection of a proto-cluster of galaxies at z ∼ 7.

The 4MOST Milky Way Halo High-Resolution Survey
Norbert Christlieb
University of Heidelberg, Germany
N.Christlieb@lsw.uni-heidelberg.de

4MOST is a wide-field multi-object spectrograph that will start its operations at ESO’s 4m VISTA
telescope in 2022. With its 2.6 degree diameter field of view and 2400 fibres feeding two low-resolution
and one high-resolution spectrographs, it will be able to acquire more than 20 million spectra during thefirst 5 years of its operation.
The Milky Way Halo High-Resolution Survey is one of the ten 4MOST consortium surveys that will
be conducted simultaneously. In this survey, we will study the formation history of the Milky Way, andthe earliest phases of its chemical enrichment, with a sample 1.5 million stars at high galactic latitude.
Elemental abundances of up to 20 elements with a precision of better than 0.2 dex will be derived for thesestars. The sample will include members of kinematically-coherent substructures, which we will associatewith their possible birthplaces by means of their abundance signatures and kinematics, allowing us totest models of galaxy formation. Our target catalog will also contain 30,000 stars at a metallicity of lessthan one hundredth of that of the Sun. This sample will therefore be almost a factor of 100 larger thancurrently-existing samples of metal-poor stars for which precise elemental abundances determined fromhigh-resolution spectroscopy are available, hence enabling us to study the early chemical evolution of the
Milky Way in unprecedented detail.
In my talk, I will give an overview of the characteristics of the 4MOST instrument. I will then present
the consortium survey program, focusing in particular on the Milky Way Halo High-Resolution Survey.

POSTERS
Chemodynamical tracers for the formation of dSph - Leo I vs Simulations
Alex Alarcon
Universidad de Concepciónalexralarconj@udec.cl

We present a chemo-kinematic analysis of the Leo I satellite of the Milky Way. We are applying the
BEACON software to find chemo-kinematic patterns among stars of different stellar populations using
their metallicity and radial velocity along the line of sight. We present the detection of 13 possible
stream motions with angular momentum distributed randomly in the galaxy. We compare these resultswith different formation scenarios proposed for the formation of dwarf spheroidal galaxies, speciallythe dissolving star cluster model which predicts these rotating patterns, showing that this model is inagreement with this observational results.

Investigating Neutral Hydrogen Structures During The Epoch ofReionization using Fractal Dimension
Bidisha Bandyopadhyay
Universidad de Concepciónbidisharia@gmail.com

The clustering and lacunarities in density distributions can be chracterized using fractal dimensions.
The generalized fractal dimensions is used to study the neutral hydrogen distribution (HI) during theepoch of reionization. The analysis is done on a simulated data of HI field which is created using
a semi-numeric model of the ionized bubbles. We calculate the fractal dimensions for length scales
10h−1 cMpc. We find that the HI field displays significant multifractal behaviour and is not consistent
with homogeneity at these scales when the mass averaged fraction of neutral hydrogen <= 0.5. This
multifractal nature is completely driven by the shapes and distribution of the ionized regions. The factthat the fractal dimension is sensitive to the neutral fraction implies that it can be used for constraining
the reionization history. We also observe that the fractal dimension is relatively less sensitive to thevalue of the minimum mass of ionizing halos when it is in the range 109 − 1010 h−1 M⊙ . Interestingly,
the fractal dimension is very different when the reionization proceeds inside-out compared to when it isoutside-in. Thus the multifractal nature of HI density field at high redshifts can be used to study thenature of reionization.

Detection of the thermonuclear X-ray bursts and dips from the X-ray
binary 4U 1323-62
Yashpal Bhulla
Pacific University, Udaipur
yash.pkn@gmail.com

The results are obtained with the LAXPCs instrument on-board AstroSat satellite by observing the
Low Mass X-ray Binary neutron star 4U 1323-62. The observations of 4U 1323-62 observed during theperformance verification phase of AstroSat showed six thermonuclear X-ray bursts in a total effective
exposure of ∼ 49.5 ks over a period of about two consecutive days. Recurrence time of the detected
thermonuclear bursts is in accordance with the orbital period of the source ∼ 9400 seconds. Moreover,the light curve of 4U 1323-62 revealed the presence of two dips. We analyzing the individual burst dataof AstroSat/LAXPC from the neutron star LMXB 4U 1323−62 in the soft state and present the resultsfrom time-resolved spectroscopy performed during all of the six X-ray bursts. In addition, an alreadyknown Quasi-periodic oscillation (QPO) at ∼ 1 Hz has been detected. However, any evidence of kHz
QPO was not found. We have shown the burst profile at different energy ranges. Assuming a distanceof 10 kpc, we observed a mean flux ∼ 1.8 × 10−9 erg cm2 s−1 . The radius of the blackbody is found tobe highly consistent with the blackbody temperature and the blackbody flux of the bursts.

Investigating the 21 cm signal from the reionization epoch
Claudio Bravo
Universidad de Concepcion
clbravoc@udec.cl

Due to the formation of a enormous amount of neutral hydrogen during the pre-reionization epoch of
Universe, the intergalactic medium (IGM) can be characterized by using the 21-cm line. This powerfultool might allow us to learn about the end of ”Dark ages” when the formation of first structures and thefirst galaxies began. Once the first galaxies emerged the IGM was affected by the associated radiative
backgrounds. These objects start emitting ultraviolet radiation that carves out ionized regions aroundthem until hydrogen becomes fully ionized, giving pass to the Reionization era. We calculate the shapeof spin temperature and the brightness temperature considering radiative heating. A particular focus of
this project will be to consider the contributions from X-ray photons produced by the first massive black
holes.

Children of the first star: birth from a Pop III supernova
Corey Brummel-Smith
Georgia Institute of Technology
cdbs3@gatech.edu

The typical timescale for metal-rich outflows to recollapse in dwarf galaxies is tens of millions ofyears. As massive Pop III stars can have much shorter lifetimes, it is sensible that multiple Pop III stars
could enrich a single cluster of metal-poor stars. This poses a problem when trying to observationally
extract the masses of their progenitors. Using a suite of magneto-radiation-hydrodynamic simulations
to study cloud crushing by a nearby Pop III supernova, we investigate a star formation mechanism that
could provide a direct link between individual Pop III stars and metal-poor stellar clusters. Once theblast wave induces gravitational collapse, stars will form on a timescale on the order of millions of years,
so the cloud is less likely to be enriched by multiple Pop III supernovae. By varying the density of
the cloud, the separation between the cloud and progenitor, the magnetic field, and the mass of theprogenitor, we determine the conditions for triggered star formation to occur in the early universe. We
model metal transport from the blast wave into the cloud and study how the resultant metallicity of thesecond generation stars depends on their formation environment and progenitor mass. Depending on themetal mixing efficiency, this may provide a formation mechanism for a subset of Group II or Group III
CEMP-no stars.

Interpreting the abundance patterns of metal-poor stars with A-SLOTH
Li-Hsin Chen
ITA/ZAH University of Heidelberg
Li-Hsin.Chen@uni-heidelberg.de

With current observational technology, the best way to pin down the initial mass function of thefirst stars is perhaps to look at the abundance patterns of the second generation stars. We implementa modified Population II star formation recipe in the semi-analytical model A-SLOTH. Our approachtakes into account star formation in concert with the radiative, mechanical, and chemical feedback fromthe first and second generation of stars on a star-by-star basis. We utilize A-SLOTH to model thetransition from metal-free to metal-enriched star formation and to study the physical properties of theirbirth clouds inside satellite galaxies of Milky Way-like halos from simulated dark matter merger trees.
We compare our results with the observed abundance patterns of metal-poor stars in the Local Group.

Population III Supernovae in The First Galaxies. I. Gas, Metals, andStars
Li-Hsin Chen
ITA/ZAH University of Heidelberg
Li-Hsin.Chen@uni-heidelberg.de

Modern cosmological simulations successfully demonstrate that the hierarchical assembly of dark
matter halos provided the gravitational wells that nurse the primordial gases to form the first stars andgalaxies inside them. One of the most significant objects in the universe, the first galaxies, are naturally
regarded as the foundation of early Universe. To examine the effect of Pop III supernova remnants(SNRs) to the first galaxy formation, we perform high-resolution hydro simulations by considering initial
Pop III SNRs from different Pop III initial mass functions (IMFs). We follow the mergers of Pop III
SNRs with the primordial gas and study the consequent star formation in the first galaxies. We construct
18 models with different halo properties and Pop III SNR compositions. Our results suggest that it isstill possible to form Pop III stars inside the first galaxies after the first supernovae, which inject extra
metals and change the subsequent Pop II star formation history. We also find that Pop II stellar massfunction in our simulated galaxies can be described by power-laws, dN/dMstar proportional to M −α ,where the exponent α falls in a wide range of 1.46 - 4.76 (α = 2.35 for the Salpeter IMF). The mass star
distribution are highly sensitive to the previous Pop III supernovae and the properties of the host halos.
Our study can provide a channel to correlate the populations of the first stars and supernovae to starformation inside these first galaxies which may be soon observed by the James Webb Space Telescope.

Numerical simulation of astrochemical problems
Igor Chernykh
Institute of Computational Mathematics and Mathematical Geophysics SB RAS
chernykh@ssd.sscc.ru

Numerical simulation plays a key role in modern astrophysical researches because the characteristic
time scale for most of the processes begins from split seconds for some chemical processes and goes up
to hundreds of millions of years for galaxies collision processes. In our presentation, we provide a new
approach for the numerical simulation of astrophysical and astrochemical processes. This approach isbased on combining of both distributed and parallel computing techniques with advanced code vectorization for modern processors architectures such as Skylake-SP/Cascade Lake-SP. Our astrochemical solver
is based on a chemical kinetics approach. In our presentation, we will show the result of the numericalsimulation of some astrochemical processes in supernovas. This research was supported by the RSCF
grant 18-11-00044.

Star formation History in the Outskirt of the SMC
Patricio Correa

University of Edinburgh
pama@roe.ac.uk

We present the spatially resolved SFH of a shell-like structure located along the northeast part of the
SMC using deep optical photometry from the SMASH survey. We find that the recent activity in theshell-like structure is correlated with the global star formation peak at young ages in the SMC likely due
to tidal forces with the LMC and MW.

Stellar collisions in flattened and rotating Pop. III systems
Marcelo Cortes Vergara
Universidad de Concepcion
marccortes@udec.cl

In the early Universe was found that at low metallicity the fragmentation often occurs in disk-likestructures. Stellar collisions may have been a fundamental mechanism in the formation of massive stars
and their remnants. Here we investigate the impact of rotation and flattening of dense protostellar clusters
on the rate of formation of massive stars through collisions, which will later evolve into massive black
holes. We use the Miyamoto-Nagai distribution to represent our model and employ N-body simulations
to show, in detail, how flattening and rotation affects the number of collisions and the formation of amore massive object. Our preliminary results suggest that rotation keeps more stars in the system andpromotes collisions, i.e. less stars escape and more massive stars are generated by collisions.

Luminosity Functions of Supermassive Black Holes at high redshifts
Arpan Das
University of Western Ontario
adas45@uwo.ca

Observations found that supermassive black holes weighing up to ∼ 109 M⊙ are already in placeby z∼7, when the universe was . 1 Gyr old. Such high masses cannot be easily reached in standard
accretion scenarios. One possible explanation of the existence of these supermassive black holes is that
there was an earlier phase of very rapid accretion onto direct collapse black holes (DCBH) that started
their lives with masses ∼ 105 M⊙ . Basu & Das (2019) showed that the mass function of SMBHs in this
scenario would be a tapered power law function. Here we use simulation data for the number density andformation rate of DCBH along with models for the growth of the SMBH even after their rapid growthera. These are used to calculate synthetic observable quasar luminosity functions for various redshiftsz ∼ 3 − 7. We show how models can be constrained by observations, and also how the models can allow
physical interpretations of the quasar Luminosity functions at higher redshifts that will be observed with
future telescopes e.g., JWST.

Impact of radiation backgrounds on the formation of massive black holes
Vanesa Diaz
Universidad de Concepciónvdiazd@udec.cl

The presence of supermassive black holes (SMBHs) of a few billion solar masses at very high redshift
has motivated us to study how these massive objects formed during the first billion years after the Big
Bang. A promising model that has been proposed to explain this is the direct collapse of protogalactic
gas clouds. In this scenario, very high accretion rates are needed to form massive objects early on
and the suppression of H2 cooling is important in regulating the fragmentation. Recent studies haveshown that if we use a strong radiation background, the hydrogen molecules are destroyed, favoring highaccretion rates and therefore producing objects of very high mass. In this work, we study the impact of
UV radiation fields in a primordial gas cloud using the recently coupled code GRADSPH-KROME forthe modeling of gravitational collapse including primordial chemistry to explore the formation of first
SMBHs. We found that to suppress the formation of H2 a very high value of J21 is required, J21 105 .
As shown in previous work, such strong radiation backgrounds are very rare, so that the direct collapse
may be difficult to achieve and therefore this scenario could hardly explain the formation of the first
SMBH.

First stars and reionization on ULDM models
Mariano Dominguez
IATE
mariano.dominguez@unc.edu.ar

We present results of a semi numerical computation of the process of reionizacion in an ultra lightdark matter scenario. Our modelization include standard reionization by population III stars and it’sremaining black holes. The predictions of our models are relevant to the interpretation of the EDGES
signal.

The Role of Gas Fragmentation During the Formation of Supermassive
Black Holes
Andres Escala
Universidad de Chile
aescala@das.uchile.cl

We perform cosmological hydrodynamic simulations to study the effect of gas fragmentation on theformation of supermassive black hole seeds in the context of Direct Collapse. Our setup considers different
UV background intensities, host halo spins, and halo merger histories. We observe that our low-spin
halos are consistent with the Direct Collapse model when they are irradiated by a UV background of
J21 = 10000. In these cases, a single massive object 105M⊙ is formed in the center of the halo. On theother hand, in our simulations irradiated by a UV background of J21 = 10, we see fragmentation andthe formation of various less massive seeds. These fragments have masses of 103 − 104M⊙. These values
are still significant if we consider the potential mergers between them and the fact that these minor
objects are formed earlier in cosmic time compared to the massive single seeds. Moreover, in one of oursimulations, we observe gas fragmentation even in the presence of a strong UV intensity. This structurearises in a dark matter halo that forms after various merger episodes, becoming the structure with thehighest spin value. The final black hole seed mass is 105M⊙ for this run. From these results, we conclude
that fragmentation produces less massive objects; however, they are still prone to merge. In simulations
that form many fragments, they all approach the most massive one as the simulations evolve. We see nouniqueness in the strength of the UV intensity value required to form a DCBH since it depends on otherfactors like the system dynamics in our cases.

Applying Deep Learning to Super Luminous Supernovae
Amanda Ibsen
amanda.ibsen@gmail.com

Deep Learning has gained great popularity in the last decade due to its success analyzing both images
and sequential data, which makes it a powerful tool for time domain astronomy. There are several articles
investigating the possibility of using Super Luminous Supernovae (SLSNe) as cosmological beacons tostudy the high red shift universe. A better understanding of these objects is necessary to determine
whether this exciting prospect is indeed possible. Upcoming surveys such as LSST will provide many
more examples of SLSNe, which we will need to catch early on and classify. We present a light curveclassifier that uses a deep learning technique called attention and that is capable of distinguishing SLSNe
and other rare objects.

Evolution of Accretion Disk around Pop III Star : comparisons between
models and simulationsk
Kazutaka Kimura
Kyoto University
kazutaka.kimura@yukawa.kyoto-u.ac.jp

In numerical simulations following Population III (Pop III) star formation, it is broadly observedthat the circumstellar disk fragments to form binary and multiple stars. The disk fragmentation isimportant process because it may change the IMF dramatically and massive tight binaries may evolve
into gravitational wave sources. The structure of the Pop III circumstellar disk has been also investigatedby semi-analytical models (e.g., Tanaka & Omukai 2014; Matsukoba et al. 2019). In such models,
however, steady accretion is assumed and thorough comparisons with numerical results have not been
provided. In this work, we develop a non-steady one-dimensional disk model considering the effect ofmass supply from the surrounding envelope onto the disk (e.g., Takahashi et al. 2013). We are also able
to investigate the structure of the innermost part of the disk, which is often masked in three-dimensional
simulations. Our models suggest that the most unstable part of the disk (i.e., radii) changes with varying
the angular momentum of the accretion flow onto the disk. Moreover, the validity of the modeling is
also confirmed by comparing the results with our latest three-dimensional radiation-hydro simulations(Sugimura et al. in prep.)

Lagrangian coordinates in an Eulerian framework
Daegene Koh
Stanford/KIPAC
kdaegene@stanford.edu

We introduce a novel method to follow Lagrangian fluid flows within an Eulerian framework, by
creating passive scalar fields which represent each Lagrangian coordinate that are then advected withthe fluid. These fields are effectively a coordinate transformation from the Lagrangian to the Eulerianframe. The information from these fields can be combined at any given time to match specific fluid
elements across different time outputs and thus, providing a mechanism to reconstruct fluid flows. The
accuracy of this method is only limited by that of the underlying the hydrodynamics method governing
the fluid itself as the Lagrangian coordinate fields are advected in the same manner as the densities
and therefore, provides a natural Eulerian analogue to tracer particles. We implement this method in
the AMR magneto-hydrodynamics code Enzo, and demonstrate it’s function for select test problems in
1-D, 2-D, and 3-D. Particularly in the 3-D case, we show that the Lagrangian coordinate fields provide
additional information about the behavior of the fluid elements, specifically with respect to mixing.

A critical mass for Pop. III stars: dependence on Lyman-Wernerradiation, baryon/dark-matter streaming, and redshift
Mihir Kulkarni
Columbia University
mihir@astro.columbia.edu

A critical mass (Mcrit ) for Pop. III stars can be defined as the minimum halo mass which can hostsufficient cold dense gas that can lead to the formation of the first stars. The presence of LymanWerner radiation that can dissociate molecular hydrogen and baryon-dark matter streaming can delay
the formation of Pop. III stars by increasing Mcrit . Although the delays from both of these effects havebeen studied individually, their combined effect has not been investigated previously using numericalsimulations. In this work, we aim to constrain Mcrit as a function of FLW , vstreaming and z using
cosmological simulations with a large sample of halos using the AMR code Enzo. This function would beparticularly useful for semi-analytical and analytical models of early galaxy formation. We have measured
the z-dependence of Mcrit and find that it differs from either scaling with the virial temperature or thevirial mass of the halo, as sometimes assumed in the past. The measured z-dependence also varies with
FLW and vstreaming . The redshift evolution of Mcrit has been predicted in many analytical calculations,but not seen previously with numerical simulations with a large number of halos.

The numerical simulation of supernovae Ia by means a new AVX-512
optimizes hydrodynamic code
Igor Kulikov
ICMMG SB RAS
kulikov@ssd.sscc.ru

The talk presents a new result of numerical modeling of the supernova explosion process of Ia typeon massively parallel supercomputers on-base AVX-512-support processors. A hydrodynamic model ofwhite dwarfs closed by the stellar equation of state and supplemented by the Poisson equation for thegravitational potential is constructed. For numerical modeling of the explosion of supernova Ia has used
a sub-real physics, where carbon burning is a full numerical simulation. The numerical modeling showed,that burning and explosion of a supernova Ia is nonstandard.

Chemical properties of Blue Compact Dwarf Galaxies: local analogues ofhigh-redshift galaxies
Nimisha KumariSpace Telescope Science Institutekumari@stsci.edu

Blue compact dwarf galaxies (BCDs) are low-metallicity star-forming galaxies found in the nearby
Universe, as such they are thought to be excellent local analogues/proxies of high redshift galaxies. By
studying the properties of the interstellar medium of these less-evolved local systems, we can probe andpredict the properties of the primordial faint galaxies, which are not readily accessible using present
technology. This is one of the reasons why BCDs have been the focus of many imaging, spectroscopic
and integral field spectroscopic (IFS) studies for over two decades. IFS is the best available techniqueto study these galaxies hosting star-forming regions, because it not only allows us to access information
encoded in the emission lines from the star-forming regions but also enables us to map their distribution
and varying properties throughout each system. I use IFS observations from the Gemini North MultiObject Spectrograph (GMOS-N) to study the H II regions in a sample of BCDs, combine them withlarge samples of star-forming galaxies from previous studies including BCDs, green peas and low-mass
SDSS galaxies, and further explore the observed properties with chemical evolution models. Such studies
are imperative to enhance our understanding of the chemical abundance patterns not only in the local
Universe but also in the distant Universe, and hence shed light on several secrets of the chemical evolutionof the Universe.

Large Scale Dynamo in a Primordial Accretion Flow – An Interpretationfrom Hydrodynamic Simulation

Wei-Ting Liao
University of Illinois at Urbana-Champaign
wliao10@illinois.edu

Without an existing large scale coherent magnetic field in the early Universe, Population III (Pop.
III) stars would likely rotate at or near break-up speed. In this work, focusing on the accretion phase ofPop. III stars, we investigate the possibility of generating a coherent magnetic field through large scale
dynamo processes, as well as the corresponding field saturation level. Using results from hydrodynamic
simulations, we demonstrate that primordial accretion disks are turbulent with a Shakura-Sunyaev disk
parameter αss > 10−3 , and evidence helical turbulence with a dynamo number |DαΩ| ≫ 10. The presenceof helical turbulence at these levels allows large scale dynamo modes to grow, and the saturation level isdetermined by the amount of net helicity remaining in the dynamo-active regions (a.k.a. the quenchingproblem). We demonstrate that, if the accretion could successfully alleviate the quenching problem, themagnetic field can reach approximate equipartition with B/Beq ∼ 3.

Public Release of A Sloth: Ancient Star formation and Local Observable
by Tracing Haloes
Mattis Magg
Center for Astronomy, University of Heidelberg
mattis.magg@stud.uni-heidelberg.de

We will publicly release a semi-analytical model to simulate high-redshift star formation in a cosmological context: Understanding the formation of the first stars, their feedback, and the various observableconsequences of their properties is intrinsically a multi-scale problem that exceeds the capability of current numerical simulations. Semi-analytical models are suited to fill this gap and explore the parameter
space of these processes. In this poster, we present A SLOTH (Ancient Star formation and Local Observables by Tracing Haloes), our state-of-the-art semi-analytical model. The code runs on dark mattermerger trees and includes self-consistent chemical, radiative, and mechanical feedback. We demonstratethat A SLOTH reproduces various independent observables. This model has already been used to investigate the possibility of surviving metal-free stars, gravitational waves from the first stars, the nature of
the Lyman-alpha emitter CR7, and to study metal-poor stars in the Milky Way. The versatile A SLOTH
code can be used by the community for making various predictions, such as star formation rates, blackhole seeding scenarios, or high-z galaxy formation. The code will be made available to the communitysoon.

Disk fragmentation and intermittent accretion onto supermassive stars
Ryoki Matsukoba
Tohoku University
r.matsukoba@astr.tohoku.ac.jp

Supermassive stars, which are hypothesized to form by very rapid gas accretion with its rate exceeding 0.1 M⊙ yr−1 , are promising candidates for the progenitors of supermassive black holes. They are
considered to grow by the accretion via the circumstellar disk, but its fragmentation due to gravitational instability can result in intermittent accretion with quiescent period. If such a period is longer
than the stellar KH timescale, the forming protostar contracts toward the main sequence star and startemitting copious amount of ionizing photons, shutting off the accretion. Here, we study the formationof supermassive stars by accretion by way of two-dimensional hydrodynamical simulation and examine
the time evolution of the accretion rate. Its circumstellar disk fragments vigorously and the accretion
rate fluctuates significantly as a result of the clump accretion. The timescale of quiescent phase can besimilar to the KH timescale when the central star reaches 10000 M⊙ , and the ionization feedback can beimportant at this moment.

Ionization evolution in low-metallicity star-forming clouds
Kazu Omukai
Tohoku University
omukai@gmail.com

Magnetic fields play such roles in star formation as the angular momentum transport in star-forming
clouds, thereby controlling circumstellar disc formation and even binary star formation efficiency. The
coupling between the magnetic field and gas is determined by the temperature and ionization degreeof the gas. Here, we construct the thermal and chemical evolution model for thelow metallicity gas bysolving chemical reaction network where (i) all the reactions are reversed and (ii) molecule formation
via dust surface reactions are considered for all the molecules. (The results for the primordial has been
published as Nakauchi, Omukai and Susa 2019). We find that at > 1016 cm−3 , the ionization degree
becomes > 1000 times higher than the previous results due to the ionization of alkali metals, which has
been omitted so far. Among dust surface reactions, only H2 formation is important in controlling thegas temperature and ionization degree, and those for the other molecules has no such effect. We havealso invented minimal reaction network which can treat ionization degree and thus magnetic diffusivity
correctly.

Impact of small-scale structure on the cosmic reionization
Hyunbae Park
Kavli IPMU, U of Tokyohyunbae.park@ipmu.jp

Density inhomogeneity in the intergalactic medium (IGM) can boost the recombination rate of ionized gas substantially, affecting the growth of HII regions during reionization. We show that Small-scaledensity structures hugely boosts the recombination rate until the structures are disrupted by the hydrodynamic feedback after 10−100 Myr. Also, the streaming velocity between baryon and dark matterdamps down the recombination boost by suppressing small-scale structures. Given the fluctuations inthe streaming velocity at ∼100 Mpc scale, we may see a signature of this effect at the late-stage ofreionization from 21-cm surveys.

Initial Mass Function (IMF) under the processes of fragmentation andaccretion
Rafeel Riaz
University of Concepcion
rriaz@astro-udec.cl

We investigate the stellar Initial Mass Function (IMF) in the primordial universe where molecularhydrogen cooling is less efficient and the gas temperature can be higher by a factor of 30. Under
such conditions, the gas temperature can be influenced by the environment, metallicity and radiation
background. Here we explore if the latter affects the IMF of the stars considering fragmentation andaccretion. The fragmentation behavior depends mostly on the Jeans mass and we show that the Jeansmass at the transition point (isothermal to adiabatic phase of collapse) in the equation of state isindependent of the initial temperature, and hence the initial mass of the fragments is very similar.
Accretion on the other hand is strongly temperature dependent. We show that the latter becomes thedominant process for star formation efficiencies above 5−7 % leading to on average more massive stars.

Presupernova evolution, explosion and nucleosynthesis of zero and very
low metallicity massive stars

Lorenzo Roberti
INAF Osservatorio Astronomico di Roma
lorenzo.roberti@inaf.it

In the last years observations of Fe-poor stars have made possible to have detailed measurementsof their surface chemical composition. These objects are the perfect laboratories in which is possible
to investigate the differences among the disparate astrophysical sites of element production, from thelightest ones to the neutron capture elements. In fact, iron poor stars probably formed during the very
early epochs of the evolution of the Universe, hence the study of their abundance patterns may help toconstrain the nucleosynthetic yields of the
rst supernova explosions. Observations allow to divide iron poor stars in a multitude of subclasses.
A number of them shows not negligible abundances of neutron capture elements relative to iron (e.g. Sr,
Ba, Pb), which are supposed to be produced through the s-process nucleosynthesis. Since the efficiencyof this process scales with the initial metallicity, no production of elements heavier than Zn is obtainedin classical models of zero and very low metallicity massive stars. This unexpected high presence ofs-process nuclei in extremely iron poor stars may be the result of a mass transfer event from an AGB
star companion in a binary system, in which is expected an efficient s-process nucleosynthesis even atvery low metallicity. On the other hand, iron poor stars may also formed out from gas clouds that were
polluted by the supernova yields of rotating massive progenitors. Rotation at low metallicity, in fact,
can considerably boost the s-process nucleosynthesis in massive stars through a larger production ofneutrons, which is due to additional mixing processes inside the star. The aim of my work is to study ofthe evolution, nucleosynthesis and explosion of zero and very low metallicity massive stars. In particular,
I am focusing on the study of the efficiency of the s-process nucleosynthesis as a function of the initialrotational velocity and of the initial metallicity.

Magnetohydrodynamic effects on first star formation
Kenji Eric Sadanari
Tohoku university
k.sadanari@astr.tohoku.ac.jp

We perform three-dimensional MHD simulations of the first star formation ,starting from a dense
core until the formation of a protostar ,consistently solving the energy equation with detailed coolingprocesses and non-equilibrium chemistry. Previous MHD simulations (e.g., Machida et al.2008) haveshown magnetic fields can play important roles such as magnetic braking and MHD jet launching also in
first star formation, but they adopted a barotropic equation of state obtained from one-zone calculation
instead of solving energy equation. Here, I present our simulation results and compare them with thecases with barotropic EoS. In particular, I examine the effect of changes in thermal evolution due toshock heating as well as of delayed collapse by magnetic pressure, and discuss how those effects can alter
the nature of forming first stars.

The Pop III disk fragmentation: disentangling the numerical andphysical effects
Kazuhiro Shima
Kyoto University
kazuhiro shima@tap.scphys.kyoto-u.ac.jp

Pop III stars are likely formed in multiple systems via disk fragmentation. However, numericalsimulations show diverse results, and we have no consensus on what the typical multiplicity and binarity
of Pop III stars were. In order to disentangle possible physical and numerical effects that may cause thedivergent results, we perform a suite of 3D simulations focusing on the disk fragmentation process by using
the publicly-available AMR code ENZO. We follow the long-term evolution (t ¿ 1000 yr) after the birth

of the embryo protostar with the sink particle technique. We show that the number of protostars (i.e.,
sink particles) can substantially differ by an order of magnitude depending on different implementationof the sink particles. Nevertheless Susa (2019) recently shows that simulations by different authors may
suggest the similar trend that the number of protostars gradually increases with time as n ∝ t0 .3. We
investigate how such scaling may be modified in a variety of situations with different parameters such as
angular momentum and EOS of the accreting gas.

Lyman Werner background and Pop. III formation
Danielle Skinner
Georgia Institute of Technology
drenniks@gatech.edu

The formation of Population III (Pop III) stars is a critical step in the evolution of the early universe.
To understand how these stars affected their metal-enriched descendants, the details of how, why andwhere Pop III formation takes place needs to be determined. One of the processes that is assumed togreatly affect the formation of Pop III stars is the presence of a Lyman-Werner (LW) radiation background, that destroys H2, a necessary coolant in the creation of Pop III stars. Self-shielding can alleviate
the effect the LW background has on the H2 within halos. In this work, we perform a cosmologicalsimulation to study the birthplaces of Pop III stars, using the adaptive mesh refinement code Enzo. We
investigate the distribution of host halo masses and its relationship to the LW background intensity.
Compared to previous work, halos form Pop III stars at much lower masses, up to a factor of a few,
due to the inclusion of H2 self-shielding. We see no relationship between the LW intensity and host halo
mass. Most halos form multiple Pop III stars, with a median number of four, up to a maximum of 16, at
the instance of Pop III formation. Our results suggest that Pop III star formation may be less affectedby LW radiation feedback than previously thought and that Pop III multiple systems are common.

Compact Starburst Dwarf Galaxies at 150 MHz: Strong Magnetic Fields
in Proxies for Proto-Galaxies
Francisca Soto Bravo
Astronomical Institute Bochum Ruhr University Bochum
bravo@astro.ruhr-uni-bochum.deCompact Starburst Dwarf Galaxies at 150 MHz: Strong Magnetic fields in Proxies for Proto-Galaxies
Francisca SOTO-BRAVO(1), Dominik J. BOMANS(1) (1)Astronomical Institute, Ruhr University Bochum,
Germany In order to perform a detailed analysis of first galaxies and thus understand the formation andevolutionary process of galaxies in the very early universe, we need the sensitivity and resolution of thenext generation telescopes like JWST, E-ELT, and SKA. To overcome this technical barrier now, one
can use proxies of these galaxies in the local universe, like compact, strongly starforming dwarf galaxies.
Using data from the LOFAR 150MHz LoTSS Survey we probed the radio continuum emission of a sample
of 6 compact dwarf starburst galaxies and 10 Green Pea galaxies and derived their magnetic fields (using
three different approaches). The analysis of our sample suggests that that magnetic fields may play amajor role for the evolution of the low mass early galaxies (e.g. for the structure and evolution of theirgalactic outflows/winds). It also implies that these galaxies main contributors for the magnetization of
the intergalactic medium.

First detection obtained with the ALMA of the [N II]122 µm Line
Detection in a QSO−SMG Pair BRI 1202−0725 at z = 4.69
Paulina Troncoso

Universdiad Autonoma de Chile
p.troncoso.iribarren@gmail.com

I report the first detection obtained with the ALMA of the [N II] 122 µm line emission from a galaxygroup BRI 1202-0725 at z = 4.69 consisting of a quasi-stellar object (QSO) and a submillimeter-brightgalaxy (SMG). Combining this with the detection of [N II] 205 µm line in both galaxies, we constrain
the electron densities of the ionized gas based on the line ratio of [N II] 122/205. The derived electron
densities are 26-11+12 and 134-39+50 cm−3 for the SMG and the QSO, respectively. The electron densityof the SMG is similar to that of the Galactic Plane and to the average of the local spirals. However,higher electron densities (by up to a factor of three) could be possible for systematic uncertainties of theline flux estimates. The electron density of the QSO is comparable to high-z star-forming galaxies at z =1.5−2.3, obtained using rest-frame optical lines and with the lower limits suggested from stacking analysis
on lensed starbursts at z = 1−3.6 using the same tracer of [N II]. Our results suggest a large scatterof electron densities on a global scale at fixed star formation rates for extreme starbursts. The successof the [N II] 122 µm and 205 µm detections at z = 4.69 demonstrates the power of future systematicsurveys of extreme starbursts at z > 4 for probing the interstellar medium conditions and the effects on
surrounding environments.

The formation of Compact Ellipticals in the merger star cluster Scenario
Fernanda Urrutia Zapata
Universidad de Concepciónfeurrutia@udec.cl

In the last decades, extended old stellar clusters have been observed. They are like globular clusters(GCs) but with larger sizes (a limit of effective radius Ref f ) of 10 pc is currently seen as reasonable).
These extended objects (EOs) cover a huge range of mass. Objects at the low mass end with masses
comparable to normal globular clusters are called extended clusters or faint fuzzies (Larsen & Brodie(2000)) and objects at the high-mass end are called ultra compact dwarf galaxies (UCDs). Ultra compact
dwarf galaxies are compact object with luminositys above the brigtest known GCs. UCDs are morecompact than typical dwarf galaxies but with comparable luminosities. Usually, a lower mass limit of
2 × 106 M⊙ applied. Fellhauer & Kroupa (2002a,b) demostrated that object like ECs, FFs and UCDs
can be the remnants of the merger of star clusters complexes, this scenario is called the Merging Star
Cluster Scenario. A more concise study was performed by Bruns et al. (2009, 2011). Our work tries to
explain the formation of compact elliptical(cE). These objects are a comparatively rare class of spheroidal
galaxies, possessing very small Ref f and high central surface brightnesses (Faber 1973). cEs have thesame parameters as extended objects but they are slightly larger than 100 pc and the luminosities arein the range of -11 to -12 Mag. The standard formation scenario of these systems proposes a galaxy
origin. cEs are the result of tidal stripping and truncation of nucleated larger systems. Or they could
be a natural extension of the class of elliptical galaxies to lower luminosities and smaller sizes. We wantto propose a completely new formation scenario for cEs. In our project we try to model cEs in a similar
way that UCDs using the merging star cluster scenario extended to much higher masses and sizes. We
think that in the early Universe we might have produced sufficiently strong star bursts to form clustercomplexes which merge into cEs. So far it is observationally unknown if cEs are dark matter dominatedobjects. If our scenario is true, then they would be dark matter free very extended and massive ’star
clusters’.

Conditions for detecting Population III galaxies with next-generation
telescopes
Anton Vikaeus
Uppsala University, Department of Physics and Astronomy.
anton.vikaeus@physics.uu.seDark matter halos that manage to reach the HI-cooling mass without prior star formation or external
metal pollution represent potential formation sites for Population III star clusters (a.k.a. Population III
galaxies) and/or direct collapse black holes (e.g. Regan et al. 2019, arXiv:1908.02823). Since Pop. III
galaxies are expected to attain total stellar masses of at most 1e6 Msolar (e.g. Visbal et al. MNRAS,
469, 1456), finding such objects in blind surveys of the high-redshift Universe will be very challenging.
Which telescope that is most suitable for this endeavour depends on a combination of parameters; thecomoving number density of suitable halos, the stellar initial mass function of the Pop. III starburst
and the total stellar mass formed in this starburst. While JWST will be unbeatable when it comesto photometric and spectroscopic depth, smaller wide-field survey telescopes like Euclid and WFIRST
cover much larger volumes and could in principle beat JWST by picking up rare cases of gravitationallylensed objects. Here, we model the spectral properties and gravitational lensing probabilities of Pop. III
galaxies at z = 6−15 and identify the parameter regions required for detection with JWST, Euclid andWFIRST separately. The parameter combinations that would allow for detections are also compared to
the Pop. III galaxy comoving number densities and total stellar mass predictions favoured by current
simulations. We find that there are regions in the Pop. III galaxy parameter space for which WFIRST
would indeed allow for detections and JWST would not, Euclid is ruled unable to provide competitive
detection prospects.

Heating of Coronal Loops on Low-mass Pop III Stars
Haruka Washinoue
The University of Tokyo
washi@ea.c.u-tokyo.ac.jp

Recent cosmological simulations suggest the existence of low-mass Pop III stars in the current universe,
although they have not been detected. In this study, we focus on the radiation from coronae of those stars.
To understand the property of stellar atmosphere with low-metallicity, we performed one-dimensional
magnetohydrodynamics simulations for the heating of coronal loops with various metallicities. All thesimulated loops are heated up to around 106 K by the dissipation of Alfven waves, however, the behaviorof dynamical evolution and the physical properties of loops are quite different for different metallicity
cases. We find that lower-metal stars have hotter and denser corona because of the inefficient radiative
cooling. In particular, the density of metal-free corona is more than an order of magnitude higher thanthat of the solar-metallicity case. As a result, the UV and X-ray luminosities from the metal-free corona
are larger than those of the solar-metal corona, which indicates that the radiation from metal-free corona
could contribute to the structure formation in the early universe.

Galactic chemical evolution
Benjamin Wehmeyer
Konkoly Observatory, Hungary & Univ of Hertfordshire, UK
benjamin.wehmeyer@csfk.mta.hu

Galactic chemical evolution (“GCE”) is a great tool to probe the influence of various astrophysicalsites on the observed abundances of stars. We use the high resolution ((20 pc)3 /cell) inhomogeneous
GCE simulation tool “ICE” to to answer the most burning question of the GCE of r-process elements:
Why do some low-metallicity stars show (high) r-process abundances?

NEI evolution in SNRs
Gao-Yuan Zhang
Universidad de Concepcion
zgy0106@gmail.com

Mixed morphology supernova remnants (MMSNRs) comprise a substantial fraction of observed remnants, but their origin remains puzzling. Recently, a clue to their nature arose from X-ray evidence ofrecombining plasmas in some MMSNRs. Recent calculations of remnant evolution in a cloudy interstellar medium that included thermal conduction but not non-equilibrium ionization (NEI) showed promise
in explaining observed surface brightness distributions but could not determine if recombining plasmas
were present. We present numerical hydrodynamical models of MMSNRs in 2D and 3D, including explicit calculation of NEI effects done via an efficient eigenvalue method. Both the spatial ionization
distribution and temperature-density diagrams from the simulations show recombining plasmas createdboth by adiabatic expansion and thermal conduction, albeit in different regions. Features created by the
adiabatic expansion stand out in the spatial and temperature-density diagrams, but thermal conduction
also plays a role. Simulated observations from XRISM, Athena, and Lynx with both spatial and spectral
input from various regions will also be presented along with initial results on how well the underlying
physics can be uncovered from spectral analyses. With the KROME package, we are going to calculate
the chemistry and some microphysics in the SNR evolution.