Physics of First Star and Galaxy Formation Conference

Conference (website) at University of Edinburgh

(Day 1) 10 June 2014

Clark – The formation of Pop III stars: first collapse and early fragmentation

  • (Greif+ 2011) Streaming velocities can delay Pop III star formation up to Δz ~ 4 and provide additional turbulence to the halo.
  • Review of H2 and HD cooling, where HD cooling is effective when electron fractions are elevated in a relic HII region.
  • (Clark+ 2011) Disk fragmentation that occurs in the spiral arms. Followed fragmentation up to 4 stars.
  • Greif+ (2011) followed up with Arepo simulations and found further fragmentation.
  • Problem 1: H2 line cooling through line transfer. There are differences between the CIE approximation (Ripamonti & Abel 2004), Sobolev length, and ray tracing (Greif 2014). He found that there was a 20-50% change in temperature.
  • Problem 2: DM annihilation. Spolyar+ (2008, 2009), Smith+ (2012), Stacy+ (2014).
  • Problem 3: Turbulent dynamo can amplify B-fields any small-scale field (Schleicher+ 2009, Schober+ 2012). Confirmed in simulations in (Sur+ 2010, Federrath+ 2011, Turk+ 2012). Generates randomly directed B-fields instead of coherent fields that have efficient magnetic braking (see present-day SF).
  • Problem 4: 3-body H2 formation rates are very uncertain (2 orders of magnitude). Can lead to very different morphologies (Turk+ 2011).
  • Problem 5: Numerical resolution, especially in MHD simulations (Turk+ 2012). Could this be caused by inaccuracies in the chemistry solver (Bovino+ 2012)?
  • Future directions: ejection from 3-body interactions from multiple systems; Are Pop III stars confined to the halo, leading to changes to the HII region morphology? With a flat IMF, what is the most massive star?

Hosokawa –  The endgame of the first star formation: protostellar evolution and radiative feedback

  • How massive do Pop III stars become? Radiative UV feedback is the key process, where McKee & Tan (2008) found in analytic work the mass to be ~150 solar masses.
  • On the upper end, could supermassive stars (~10^4 – 10^5 solar masses) form in H2-starved halos? More talks on massive black hole formation tomorrow.
  • (Hosokawa+ 2011, 2012) Used 2D rad-hydro simulations to understand when accretion stops. Includes a stellar evolution model coupled with the simulation. Found ~40 solar masses.
  • (Hirano+ 2014) Used the same model but for 100 cosmological halos to obtain more statistics for a Pop III IMF. Very rapid accretion changes the stellar evolution qualitatively, where the star reaches ZAMS at a higher mass.
  • (Hosokawa+ 2012, 2013) With >0.01 Msun/yr accretion, the stellar radius monolithically increases with mass because the accreted mass-energy is greater than the energy loss from radiation. Termed “supergiant protostar”, which has a low surface temperature that provides little UV feedback.
  • Diversity of the stellar masses originate from different accretion rates, which come from the different cosmological halos.
  • (Susa, in prep) Performing ~60 simulations similar to his 2014 paper. Finding a ~Gaussian IMF with a peak around 30 Msun, bounds at 3 and 300 Msun. There is one example with a stellar mass below 0.8 Msun.
  • (Hosokawa, in prep) 3D rad-hydro simulations. Found a final mass of ~35 Msun instead of a ~120 Msun star. Did not see a clear accretion stoppage, possibly caused by a lack of spatial resolution.

Norris – Near field cosmology with the most metal-poor stars

  • This talk is an overview of what I heard about in the Galactic Archaeology II Conference.
  • (Iben 1983) Original work on the metal pollution of a metal-free star as it moves through the ISM.
  • (Suda+ 2004) Metallicity enrichment from binary mass transfer and/or accretion from the ISM during main sequence.
  • (Gilmore+ 2013) Abundance study of Bootes I uFd galaxy. Found one CEMP-no star.
  • (Geha+ 2009; Simon+ 2011; Frebel+ 2014) Segue 1. M_v = -1.5, r_h = 29 pc, d = 23 kpc, [Fe/H] = -3.3, M_star = 600-1300 Msun. One CEMP-no star (Norris+ 2010). Four of seven stars are C-rich.

Jacobson – Searching for signatures of the first stars: news from the SkyMapper survey

  • Skymapper: 1.4m telescope (g ~ 23 mag limit), dedicated survey mode. Using photometry (with one narrow-band filter) to measure stellar properties and target EMP stars.
  • Use med-res and hi-res follow-ups to get accurate measurements of metallicity.
  • (Jacobson, in prep) 69 EMP stars; 20 stars between [Fe/H] = -3.5 and -3.0, 3 stars < -3.5, and one star with [Fe/H} ~ -4.
  • Discovered 1 “Fe-rich” EMP star, 1 highly enriched star in light n-capture elements, and 10 mildly r-enhanced EMP stars.

Stacy – The First Stars: A Low-Mass Formation Mode

  • (Stacy+ 2012) Studying disk fragmentation with protostellar feedback. Radiative feedback suppresses accretion, but the binary still forms.
  • (Stacy & Bromm 2013) Still find fragmentation with some ejected stars, but the total sink masses range between 20 and 120 Msun.
  • (Stacy 2014) Halos that have high rotational support in the inner SF-region have relatively low accretion rates, leading to a low-mass star formation event (3.2 Msun after 5000 yr).
  • LW background only has moderate effects on accretion rates. Most of the change is at large radii but is similar at small (~tens of AU) radii.

Glover – Chemistry and cooling in the first protogalaxies

  • (Glover+ 2006) Rate coefficient survey in the H- reaction in H2 formation.
  • (Kreckel+ 2011; Cizek; Gerlich+ 2012) Updated coefficients for H-, showing a peak around 100K.
  • Mutual neutralization (H+ + H- -> H + H) Also explored in Glover+ (2006). Updated coefficients in Stenrup+ (2009).
  • Three-body H2 formation: New rates established in (Forrey 2013). See application in Bovino+ (2014).
  • H- formation rates are consistent within 5-10% between 500-1000 K.
  • Optically-thick H2 line cooling: Ripamonti & Abel (2004), Sobolev (Yoshida+ 2006), Ray tracing (Greif 2014), Tree-col method (Clark+ 2012; Hartwig+ in prep).
  • Other problems: accretion luminosity heating – currently, assuming T_rad = T_gas; Dust cooling at very low Z (right values for dust-to-gas ratio; dust size distribution; accommodation coefficient).

Cooke – The transition from a metal-free to a metal-poor stellar generation

  • Mixing & fallback SN models (Umeda & Nomoto 2003; Tominaga+ 2007) explain the abundance patterns in the CEMP stars.
  • Two mechanisms (mass transfer and direct enrichment) for the differences in CEMP-no and CEMP-s stars, respectively.
  • (Cooke & Madau 2014) High [C/Fe] values originate from Faint SNe and more massive stars (i.e. flat IMF). As more stars form in the cluster, the chemical signature is washed out but can still be carbon-rich if a faint SN is assumed.
  • Super-CEMP stars could be caused by AGN mass transfer, pulsational-pair instability SNe, Rotationally enhanced mass loss, or a relic from their efficient mixing assumption.

Evans – New results from studies of massive stars

  • (Sana & Evans 2010, 2012) Multiplicity in massive stars in local stellar clusters. Average of ~40%, but there is some observational bias. Correcting for that, 75% of all O stars are born in binaries; 71% will interact during their lives. 37% of binaries are O+O binaries. 24% of their binaries merge → formation of very massive stars or GRBs?
  • Careful about simple stellar populations (e.g. STARBURST99) that don’t include binaries or stars with M > 100 Msun.
  • (Evans+ 2010) Runaway stars in 30 Dor. Traveling 100 km/s from star cluster R136. In a follow-up (in prep), they have now found ~20 runaways.
  • Binary interactions require a high stellar density, which occurs in the center of 30 Dor, or runaways that are fast rotators after a SN in a binary will produce an even larger runaway fraction.
  • (Campbell+ 2010; Crowther+ 2010) VLT observations of 30 Dor, visually showing multiplicity. Initial masses are 150-350 Msun and are currently 140-270 Msun. Similar but less massive (100-150 Msun) stars are forming in NGC 3603.
  • In R136, only the very massive (M > 100 Msun) stars show HeII emission.
  • (Evans+ 2010) Scaled-up R136 clusters at z ~ 2 with r ~ 100 pc and SFR ~ 1-10 Msun/yr; can probe the upper-end of the IMF.

Klessen – IMF Intro

  • Showing the Carina Nebula to demonstrate the complexity of star formation, leading to the IMF.
  • IMF depends on (1) turbulent initial conditions; (2) collapse and interaction of prestellar cores; (3) thermodynamics properties of the gas; (4) protostellar feedback terminates star formation.
  • Feedback processes: protostellar outflows, stellar winds, SNe, thermal and ionizing radiative feedback, chemical feedback, indirect (cosmic rays, global interstellar radiation field, chemical enrichment), AGN feedback.
  • IMF is sensitive to the EoS. γ < 1: number of fluctuations around M_jeans is large; otherwise, there is a narrow mass range for the fluctuations.
  • (Dopcke+ 2013) In the [Z/H] = -4 case, there is a turnover in the simulated IMF, but below, the IMF is hinted to be flat.
  • The Pop III IMF is still uncertain, but it’s expected to be wide with a typical mass of several of tens of solar masses.
  • Current frontier: protostellar feedback and magnetic fields.

Susa – The IMF of the First Stars

  • (Susa 2013) Idealized BE cloud with LW radiative feedback but not ionizing radiation because of limited resolution. With feedback a total of 150 Msun of stars form in a cluster of 5 massive stars with a maximum of 50 Msun.
  • (Susa+ 2014) Similar method as the 2013 paper but using cosmological simulations as initial conditions for the collapse. Find an IMF that peaks at ~30 Msun with bounds 1-300 Msun.
  • Between 1 and 6 stars form per minihalo. Single stars are >100 Msun, primary stars in multiple systems are >30 Msun, and massive secondaries are ~20 Msun. 60-70% of the minihalos host multiple systems, which is similar to present-day SF observations.

Suda – IMF of the First Stars Explored Using CEMP Star Statistics

  • (Komiya+ 2014) Surface pollution of metal-free stars from an enriched ISM. Results in a broad but small distribution of metal-poor stars between [Fe/H] = -3 and -7.
  • Origin of the most Fe-poor stars can come from binary mass transfer from AGB stars and pollution from the ISM, suggesting that the IMF of the first stars is top-heavy.

Skuladóttir – The first carbon enhanced star in the Sculptor dwarf spheroidal

  • [Fe/H] = -2.0; [C/Fe] = 0.5; [Ba/Fe] < 0.5; [Eu/Fe] < 0.5
  • Signatures of mixing: log L/Lsun = 3.1; log n(Li) = -0.12; [N/Fe] = 1.2
  • Original carbon abundance: [C/Fe] > 0.8 and lows from internal mixing.
  • Sculptor: MDF (Starkenburg+ 2010); SFH (Wylie de Boer+ 2012) dominated by stars with ages >10 Gyr.
  • All of the other EMP stars are C-normal or C-poor and have undergone mixing.
  • CEMP-no stars are rare at [Fe/H] = -2 (Norris+ 2012)
  • The star is enhanced in the neutron capture elements compared to the other Sculptor stars, and has an extremely high [Fe/H] compared to other CEMPs. Signs of primordial processes?

Hirano – Population III Initial Mass Function: Effect of a Large Fraction of Population III.2 Stars Formed from Photo-Dissociated Clouds

  • Using 2D rad-hydro simulations of Pop III.2 stars, very similar to their work on Pop III.1 stars.
  • Star formation in low-mass (~2 x 10^5 Msun) halos are more likely at high (z = 20-30) redshifts.
  • dM/dt distribution: bi-modal. At the lower end, HD-cooling contributes to the lower dM/dt peak. The peak accretion rate decreases with decreasing redshift.
  • Pop III.2_DIS stars: in photo-dissociation regions that decrease the H2 fraction and increase dM/dt, creating more massive stars. They explore 5 different constant LW intensities J_21 = (0, 0.1, 0.316, 1, 10). Going from J_21 = 0.1 to 1 increases the stellar mass from 30 to ~500 Msun.
  • Self-shielding prevents the photo-dissociation for the collapsed region, and the later collapse depends only on the cloud’s dynamics, dM/dt.
  • At high-z, Pop III.1 and Pop III.2_DIS. At lower z, Pop III.1 and Pop III.2. They have typical stellar masses of 25, 250, and 400 Msun.

Chiaki –  Hydrodynamic simulations of collapsing gas clouds with low metallicities

  • Critical metallicity: one-zone dust model in the local universe results in [Z/H] = -5.5.
  • With a model of grain growth, the critical metallicity reduces to somewhere between [Z/H] = -6.2 and -4.5, producing a fragmentation event at ~10^15 cm^-3.
  • Now applying the model to Gadget-3 simulations; taking abundance pattern and 8 grain species abundances and size distributions from Nozawa+ (2007).
  • NEQ implicit chemical model with 27 species. Calculates the chemical evolution, finding a CO core, C, and C+ shells.
  • Dust-induced fragmentation at high densities starting at 10^14 cm^-3. Followed the fragments to 0.04 solar masses.

(Day 2) 11 June 2014

Ritter – Outflows and Chemical Enrichment from Clustered Supernovae in the First Galaxies

  • Following the formation of one Pop III star and its supernova. Then the ejecta is tracked until it enriches the formation of the first metal-enriched star, using cosmological FLASH simulations.
  • (Ritter+ 2013) A significant fraction of the ejecta is confined to the halo environment, returning after 5 Myr. The enrichment is highly inhomogeneous.
  • (Ritter, in prep) Same setup but 7 stars (80, 63, 50, 40, 32, 25, 20 Msun) with all stars producing 10^51 erg SNe. The halo recollapses after ~200 Myr, enriched to ~5 x 10^-5 Zsun. At this time, the halo has grown from 10^6 to 4 x 10^7 Msun.
  • The SN tracer particles are confined to sheets (converging flows) while falling back into the halo and then mixes through turbulence in the inner ~50 pc.

Davis – The Effect of Feedback on Baryons and Dark Matter in the First Galaxies

  • Impact of reionization on the gas fraction: halos below 1.5 x 10^9 Msun have their fractions decreased from 8 to 4%.
  • DM density enhancement fraction (mass difference between DM-only and FiBY runs inside 100 pc): Low-mass halos are unchanged, but the halos with M > 1.5 x 10^9 Msun are enhanced up to a factor of 3.
  • The DM cusp is repeatedly destroyed by the changing potential from stellar feedback (see Pontzen & Governato 2011). The cusp is well described by adiabatic contraction (Gnedin+ 2004).
  • The model of Lackner & Ostriker (2010) of DM mass loss (destroying the cusp) from dynamical friction does not work because the halo brings gas along with it.
  • The DM density profile is best fit by the Dehnen profile because the inner slope is a free parameter.
  • The core profile is between -1.5 and -2.0 in most halos, but there are some halos with intense SF that have cored profiles. But at any halo mass, there is a mix of both cored and cusped profiles.

Elliott – Populating long gamma-ray bursts in the First Billion Years simulations at z > 5

  • Use the GRB rate as a proxy of SFR, and to use them to pinpoint high-z galaxy for deep follow-ups.
  • (Krühler+ 2011) Most of the GRBs come from the brightest galaxies with M_UV > -18.
  • There are many difficulties with connecting GRBs to SF. Free parameters: LGRB luminosity function, function of redshift, function of progenitor? There is a growing evidence of super-solar host galaxies.
  • Populate the FiBY simulation with GRBs based on stellar models from the Heger & Woosley models.
  • There is a large dispersion of metallicity in the host galaxies, where it is hard to disentangle the metallicity of the host environment (i.e. star forming region) and the galaxy.
  • LGRBs can occur in a vast range of environments, but could be biased by the dispersion of host galaxy properties.

Smith – Metal-Enriched Star Formation in the Wake of the First Supernovae

  • (Meece+ 2014) Investigated the effects of turbulence, rotation, and metallicity on the fragmentation in an idealized halo collapse.
  • No notes because I’m a co-author!

Yoshida – SMBH Introduction

  • How to grow a 10^9 Msun SMBH by z=6 from a Pop III BH seed or massive BH seed?
  • (Tanikawa & Umemura 2011) BH mergers take about a Hubble time (500 Myr) to occur after the halo merger.
  • (Ohkubo+ 2009; Hirano+ 2014) 30% of the stars collapse into BHs from their IMF. Supermassive stars can form BHs around 1000 Msun from GR instabilities.
  • (Hosokawa+ 2012) JWST could detect supermassive (10^5 Msun) stars after 10 hours of exposure.
  • (Naoz+ 2011, 2013; Tanaka & Li 2014) For the first objects, supersonic baryonic streaming motion from recombination can delay collapses and thus BH seed formation.

Johnson – The effect of reionization on the formation of massive black hole seeds

  • Nearby radiation sources are necessary to suppress H2 formation in a halo to form a massive BH seed. These will also form X-rays, cosmic rays, and ionizing radiation (also see Inayoshi & Omukai 2011).
  • Investigated the effect of a UVB (with self-shielding) on the MBH seed formation. Delays the collapse by 25 Myr. Elevated e-fraction from reionization can catalyze H2 formation.
  • With ionizing radiation, the halo has a lower gas fraction.
  • (Noh & McQuinn 2014) The gas is often self-shielded to the ionization at high-redshift.
  • Only a fraction of DCBH formation is prevented from reionization.

Inayoshi – Formation of an embryo supermassive star in the first galaxy

  • Suppression of H2 cooling: either by LW radiation or H2+H collisions.
  • (Inayoshi & Omukai 2011) “Zone of no return” (no fragmentation) above 8000 K and 10^4 cm^-3.
  • (Inayoshi+ 2014) Can gas cool from the warm quasi-isothermal collapse to the H2-dominated cooling regime? What are the protostellar properties (M, R, dM/dt)?
  • Used an isolated turbulent halo as a testbed. Isothermal turbulent collapse to contain 1 Msun with 1 AU without fragmentation.
  • Above 10^12 cm^-3, three-body reactions create H2 up to a fraction of 1%.
  • (Inayoshi, in prep) Does the disk fragment around the SMS? Use a toy disk model (e.g. Levin 2007) with R_f = 0.1 pc, M_clump > 20 Msun, n_f = 10^8 cm^-3.
  • The clumps rapidly migrate and merge with the central protostar before forming stars, thus they conclude that disk fragmentation cannot prevent SMS formation.

Agarwal – Formation of massive black holes under time and spatial varying Lyman-Werner background

  • (Agarwal+ 2012) Find a few DCBH formation sites per 100 Mpc^3 in a semi-analytic model. Orders of magnitude above the observational expectation.
  • (Agarwal+ 2014) The DCBH formation sites are always above the critical J21 value to suppress H2 formation, and they remain pristine.
  • (Agarwal+ 2013) New class of objects with M_BH > M_star? Termed Obese BH Galaxies (OBGs). Possibly detectable with JWST.

Regan – High resolution simulations of direct collapse and the impact of anisotropic sources

  • (Regan+ 2014) Formation of Jeans-unstable clumps in disk fragmentation, which are 10-20 Msun.
  • (Regan, in prep) Anisotropic LW radiation source to dissociate H2 with ray tracing. Experimented with several LW luminosities, and found that all cases, including the J21 = 10^6 could self-shield the LW radiation.

Latif – The formation of supermassive black holes in the early Universe

  • (Latif+ 2013) Subgrid turbulence models can suppress fragmentation.
  • Also followed accretion onto sink particles that represented SMS, which grow to ~10^5 Msun.
  • (Latif+ 2014) Higher UVB (including ionizing radiation) decreases fragmentation, starting around J21 = 500.

Yajima – Formation of massive black holes in star clusters

  • Merging of stars and BHs to form SMBHs. Loss-cone depletion quickly occurs, which can inhibit the further infall of stars (Freitag+ 2002; Zwart+ 2004; Devechhi+ 2012, 2014).
  • To avoid this problem, there is the process of resonant relaxation (Rauch & Tremaine 1996; Hopman & Alexander 2006; Chen & Liu 2011).
  • Model assumptions: Mestel disk, gas inflow driven by bar instabilities, core-collapse timescales, stellar growth timescales, Salpeter IMF, resonant relaxation, BH growth timescales, Sheth-Tormen merger trees.
  • BH mass function at z=6 peaks at 10^4 Msun with bounds ranging an order of magnitude on each side.
  • Using this initial mass function in a merger tree, a mass function at z=6 is obtained and the value at M_BH = 10^9 Msun matches observations.
  • With Pop III seeds, SMBHs only reach 10^7 Msun by z=6. The decrease is caused by the lower seed mass.
  • Globular cluster initial mass function peaks at 10^6 Msun (log M/Msun = 5-7).

Katz – Formation of intermediate mass black holes in high redshift, metal poor, star clusters

  • (Glebbeek+ 2009) Found that the effect of stellar winds in solar supermassive stars can produce great mass loss.
  • Using direct N-body (GPU) simulations, taking cosmological simulations as ICs. Using RAMSES simulations with 2048^3 effective resolution (1 Mpc^3 box).
  • From clump to cluster simulations: (knowns) initial density profile, dM/dt, metallicity; (unknowns) IMF, final density profile, star formation efficiency, and distribution function.
  • Include single & binary stellar evolutions, mass loss from stellar winds, mass loss from collisions, and gas accretion and explusion.
  • They find a runaway collapse from stellar collisions, producing a BH of ~1500 Msun. They are initiated by the most massive stars ~100 Msun.
  • LW backgrounds and mergers create larger gas clumps, which could produce very massive stars, leading to MBH seeds.

Meiksin – Reionization introduction

  • Reionization observational signatures: Thomson scattering optical depth in the CMB, Gunn-Peterson troughs, high-l kSZ measurements in the CMB, ionization rate in Ly-α forest.

Becker – New Constraints on Reionization from Quasar Absorption Lines

  • Is there observational evidence for reionization at z = 6? Almost all of QSO QALs show that reionization has completed by z=6, but there are a few GP troughs that extend to z ~ 5.5.
  • No single mean free path fits all of the data. Fluctuations in the UVB required. The uniform UVB model works well at z < 5.
  • Lyman-limit systems require more time to be reionized. The time between z=6 and z=5 is the post-overlap regime of reionization.
  • Damping wing suggests that the IGM is >10% neutral at z>7. The evidence is tenous because z ~ 2 QSOs show decrements in the blueward Lyα wing.

Dixon – Using reionization to distinguish early galaxy formation

  • RAMSES Rad-hydro simulations (INCITE project). Voids are hotter than filaments because the recombination times are shorter.
  • Explored four different models of galaxy suppression (HMACHs suppressed, LMACHs suppressed, LMACHs gradually suppressed, and no suppression).

Salvadori – Dwarf galaxies: metal polluters and reionization sources

  • What is the connection between the local dwarf galaxies and reionization sources?
  • Using semi-analytic models (GAMETE) to follow 100 possible merger histories of a MW-like galaxy.
  • (Salvadori & Ferrara 2012) uFd galaxies represent the oldest galaxies in the MW system which assembled at z > 8.5 and have typical masses of <10^8 Msun. Can reproduce the [Fe/H] values for such galaxies.
  • (Salvadori+ 2014) Observations of SFHs in local dwarfs at reionization is between 5e-5 and 3e-3 Msun/yr.
  • Reionization models with f_esc = 0.1 for Pop II and III stars. Reionization starts around z=10 and the dwarf galaxies can produce up to 80% of the ionizing budget. Most of the metals in the MW are produced by high-z dwarf galaxies.

Dayal – Cosmic reionization: sources and constraints

  • (Hutter+ 2014) How can we use LAEs to constrain reionization?
  • Lya transfer simulations on top of cosmological galaxy simulations, assuming that f_alpha / f_cont = 0.7.
  • Model results in constraints of f_esc between 5 and 50%, f_alpha / f_cont is 0.7-1.8 with homogeneous and clumpy dust models.
  • Maximum star formation efficiency so that the gas is unbound from the galaxy from its feedback, which is a power law around 3% at 2 x 10^9 Msun (Dayal+ 2014).
  • Also reproduces the galaxy LF at z=5-8, using f_star = 3% and f_wind = 10%.

Paardekooper – The First Billion Years Project: The contribution of the first galaxies to cosmic reionisation

  • (Siana+ 2010) Redshift ~1 galaxies have average escape fractions below 2%
  • (JPP+ 2013) Producing over 100 photons per baryon in all simulated galaxies at z = 6, completing reionization at z ~ 11.
  • (JPP in prep) Finding that only the 10^7 – 10^8 halos have high f_esc, whereas the larger halos have f_esc nearly 1%. There is a huge scatter, even for two halos with very similar properties. The location of the SF regions is very important.

(Day 3) 12 June 2014

No notes for the first three talks because I was speaking in this session.

Riechers – Physical Conditions for Star Formation in Typical Galaxies and Extreme Starbursts back to the First Giga-Year of Cosmic Time

  • Use ALMA to measure the cold gas history of the universe to understand the SF history.
  • (Magdis+ 2012; Carilli & Walter 2013) Use the L_CO vs. L_FIR as a proxy for M_gas vs SFR. Many subtleties, but generally, high-z galaxies are higher in both relations, and there is a distinction between quiescent and starburst galaxies.
  • About a 1/3 of the AGN hosts have SFR > 1000 Msun/yr (bright in FIR). All of the FIR luminous QSOs are detected in CO, inferring M_gas > 10^10 Msun.
  • (Walter+ 2009; Riecher+ 2014) Maximum starburst at z=6.4, detected in [CII].
  • (Wang+ 2013; Willott+ 2013) [CII] luminosity of ~3 x 10^9 Lsun, M_dust = 10^8 Msun, M_dyn ~ 5 x 10^10 Msun, f_gas ~ 60%. Average SFR surface density ~300 Msun/yr/kpc^2.
  • (Riechers+ 2013) Followup with ALMA that confirmed a galaxy at z=6.34, detecting tens of emission lines. Highly enriched. Originally detected by searching for “red” Herschel sources at 500 microns.
  • More normal galaxies show stronger [CII] lines in comparison with the continuum. Traces the WNM, WIM, and star-forming gas.
  • No detection of [CII] in Himiko (z ~ 6.6) with ALMA. Is it poor in dust and metals or a selection effect?
  • (Riechers+ 2014) [CII] mapping of a z=5.3 protoclusters, detecting 4 out of 11(?) galaxies with ALMA. There is a triplet of LBGs that ~8 kpc apart, which are “normal” galaxies at z=5. M_dyn = 5 x 10^10 Msun, not an extreme starburst and not dusty.
  • (Capak+ 2014) In a sample of z=5-6 Keck galaxies, they detect all (10) of the galaxies in [CII] that have a FWMH of 200-450 km/s.

Schober – On the Role of the Turbulent Dynamo in Young Galaxies

  • Seed B-fields for small-scale dynamo from a QCD phase transition with B ~ 10^-20 G on 10 comoving Mpc scales (Sigl+ 1997) or Biermann battery with B ~ 10^-18 G (Xu+ 2008).
  • Kinematic (exponential growth) phase -> Non-linear phase -> Saturation
  • (Kazantsev 1968) Description of small-scale dynamo
  • At saturation, 1-40% of the kinetic energy is converted into magnetic energy. Dynamically important magnetic fields can be generated within 10 Myr.

Curtis – Stellar populations and morphological evolution of LBGs

  • (Huang+ 2013) If the effective radius of a galaxy is proportional to the spin parameter * virial radius, then the size is not expected to be that dependent on redshift. Measured in Curtis-Lake (in prep), r_50 ~ 1 kpc with a very shallow negative slope (r_50 vs. z).
  • Key questions to focus on now: Does the constant-UV selection most closely resemble a section at constant halo mass or constant circular velocity? Are we sure that the rest of the LBGs are relaxed disks? What mechanisms affect galaxy morphology at high-z? See Law+ (2009) for z=2-3 examples.
  • (Sales+ 2012) Does the accreted gas have a coherent alignment, i.e. angular momentum vectors, as galaxies grows?

Livermore – The Final Frontier: Galaxies in the First Billion Years

  • Spectroscopically confirmed four z>7 galaxies with MOSFIRE on Keck.
  • Frontier fields: 6 new fields. Simultaneous WFC3 (IR) and ACS (optical; 5′ away) fields.
  • Not many highly magnified galaxies found around Abel 18xx. Why? Probably from the containment of the cluster light.
  • When the light is removed through wavelet subtraction, then the light is recovered and in some cases, improved in faint sources!

Bowler – The bright end of the galaxy luminosity function at z ~ 7

  • (Bowler+ 2012, 2014) Found 34 bright high-z galaxies that resulted in a higher LF than the HUDF Schechter fits. A broken power law fits the data well instead of a Schechter fit.
  • (Bian+ 2013) found that QSOs contribute at z~3 to the bright-end of the LF. Could this be happening at z = 7?
  • Astrophysical interpretation: Feedback in fain galaxies already active at z= 7. But are they yet to become efficient in bright galaxies?

Song – Probing the Faint-End of the Galaxy Stellar Mass Function at z=7 with CANDELS and S-CANDELS

  • To get the halo mass function, usually one takes the luminosity function and the observed (inferred?) M/L ratios.
  • (Song+ 2013) Stellar mass versus UV luminosity at z=6 and 7. Detection limit is just below 10^8 Msun in stellar mass. The slope is -0.58 and -0.59 at z=6 and z=7, respectively, with a scatter of ~0.4 dex.
  • Can correct for the mass incompleteness in flux limited observations.
  • Can we trust the low-mass end slope? Yes, there is no bias in the M/L slope. On the other hand, there is some mass dependent scatter in M/L, which could lead to an artificially flattened slope. What is the intrinsic scatter w.r.t. M_UV.

Mármol – Impact of nebular emission in the derived properties of high-redshift galaxies

  • Motivation: Expected increase of 10x in sSFR in galaxies of fixed stellar mass between z = 2-7 (Gonzalez+ 2010, 2014; Stark+ 2013).
  • Find that sSFR is proportional to 1/(1+z) above z = 2-3.

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