Andrei Mesinger Princeton University

Andrei Mesinger Princeton University
Investigating Radiative Feedback in the Early Universe with Numerical and Semi-Numerical Techniques Andrei Mesinger Princeton University UV radiative feedback Hubble Symposium, STScI march, 2009

Hubble Symposium, STScI 11. march, 2009
Outline Efficient “semi-numerical” simulations of structure and reionization Radiative feedback throughout reionization: advanced stages of reionization and Mmin early stages (fossil HII regions around massive stars) UV radiative feedback Hubble Symposium, STScI march, 2009

Challenges in Modeling Global Processes
Dynamic range required is enormous: single star --> Universe Complex small-scale astrophysics must be modeled Relevant scales (e.g. HII bubbles, X-ray m.f.p., QSOs…) can be > tens or hundreds of comoving Mpc. Simulation boxes of > hundreds of Mpc are required. Virtually nothing is well-known at high-z --> enormous parameter space to explore UV radiative feedback Hubble Symposium, STScI march, 2009

Philosophy Use the right tool for the job! Mesinger (2007) one size DOES NOT fit all! UV radiative feedback Hubble Symposium, STScI march, 2009

Philosophy scale Analytic Estimates Semi-Numerical Simulations
(independent; 3D realizations; e.g. PTHalos, Pinocchio for halo fields) scale Ok, so what do I mean by semi-numerical simulations Semi-numerical, since they are closer to numerical, and are independent Hydrodynamical Numerical Simulations (+RT) UV radiative feedback Hubble Symposium, STScI march, 2009

Deus ex Machina (DexM) Etymology: New Latin Literally: "God from a Machine", translation of Greek theos ek mechanes - a person or thing that appears unexpectedly and provides a contrived solution to an apparently insoluble difficulty ( 2 meanings: Absurdly conceited literal translation, But more appropriate is true literary definition UV radiative feedback Hubble Symposium, STScI march, 2009

Deus ex Machina (DexM) Halo fields (updated form of the independently developed “peak-patch” formalism of Bond & Myers 1996) create linear density and velocity fields (like N-body) filter halos from the linear density field using excursion-set formalism (e.g. Bond+ 1991) adjust halo locations using linear-order displacements (Zel’Dovich 1970) Ionization fields perturb linear density field using linear-order displacements (Zel’Dovich 1970) filter ionized regions from the halo and perturbed density fields using excursion-set formalism (Furlanetto+ 2004; Zahn+ 2007) UV radiative feedback Hubble Symposium, STScI march, 2009

Halo Filtering Mesinger & Furlanetto (2007) z=8.7 N-body halo field from McQuinn et al. (2007) UV radiative feedback Hubble Symposium, STScI march, 2009

Density Fields z=7 Numerical results from Trac+2008 UV radiative feedback Hubble Symposium, STScI march, 2009

Density Fields, cont. Mesinger (in preparation) UV radiative feedback Hubble Symposium, STScI march, 2009

HII Bubble Filtering Mesinger & Furlanetto (2007) RT ionization field from Zahn et al. (2007) UV radiative feedback Hubble Symposium, STScI march, 2009

Cool PR Movie DexM public release available at Why does it work so well? Some numbers for simulators… Runs on a desktop computer in a couple of hours! parallize Parameter space Are using our simulation to help MWA EoR team! UV radiative feedback Hubble Symposium, STScI march, 2009

Mmin? Ionizing UVB suppresses gas content of low-mass galaxies (e.g. Efstathiou 1992; Shapiro+1994; Thoul & Weinberg 1996; Hui & Gnedin 1997; Gnedin 2000) How important is this negative feedback during reionization? (we focus on atomically-cooled halos, Tvir>104 K) can extend reionization early work, z=2 halos with vcir<35km/s completely suppressed; vcir < 100km/s partially suppressed NOT THIS SIMPLE! Not instantaneous; high-z mediated by more compact profiles, increased cooling efficiencies, shorter exposure times (Kitayama & Ikeuchi 2000; Dijkstra+ 2004) Can we draw any general conclusions about this exceedingly complex problem? Complicated modeling… 35km/s = 45,000K 100km/s = 360,000K It became popular in the literature to use these values..instantaneous suppression Feedback depends on state of evolution when UVB on, and its duration UV radiative feedback Hubble Symposium, STScI march, 2009

Systematic approach -> Minimize Assumptions
Does UV radiative feedback impact the advanced stages of reionization? Does/How Mmin effectively increase in ionized regions? We do NOT attempt to self-consistently model reionization (we are humble mortals..) LARGE parameter space (small knowledge at high-z): z = 7, 10, 13 <xHI> ionization efficiency, fid (=1 to match z=6 LAE and LBG LFs) Our semi-numeric codes ideally suited Don’t trust anyone who tries to tell you x <--> z In cosmo sim… Remember, we are looking for gross trends, not detailed predictions UV radiative feedback Hubble Symposium, STScI march, 2009

Two Tier Approach Mesinger & Dijkstra (2008) 1D hydro simulations to model collapse of gas + dark matter under UVB: fg(Mhalo, z, J21, zon=14) Semi-numerical code to model halo, ionization and inhomogeneous flux fields: J21(x, z, <xH>, fid) UV radiative feedback Hubble Symposium, STScI march, 2009

Ionizing UV Flux Fields
Mesinger & Dijkstra (2008) Trivial to add stocasticity flux ∑ L(Mhalo)/r2 e-r/mfp UV radiative feedback Hubble Symposium, STScI march, 2009

Global impact Mesinger & Dijkstra (2008) Proportional to how much “fuel” is left to aid in progress of reionization Curves correspond to different luminosity values UV radiative feedback Hubble Symposium, STScI march, 2009

Mmin Factor of 10 increase in ionizing efficiency is required to extend suppression by only factor of 2 in mass. Solid curves are fully ionized boxes, so maximum suppression UV radiative feedback Hubble Symposium, STScI march, 2009

Being Conservative… No self-shielding mfp = 20 Mpc (the high-end of z<4 LLS extrapolations; Storrie-Lombardi+ 1994) zon = 14 (zre = /- 1.4; Dunkley+ 2008) biased halo formation No redshift evolution of J21 over zon --> z UV radiative feedback Hubble Symposium, STScI march, 2009

Relic HII Regions Short lived, massive Pop III stars carve out ionized bubbles, then turn off. Structure formation is highly biased at high-z; what happens inside these relic HII regions? ? ? Different regime… molecularly cooled halos UV radiative feedback Hubble Symposium, STScI march, 2009

UV Radiative Feedback in Relic HII Regions
Radiative feedback on subsequent star formation can be: positive (e- catalyzes H2 formation/cooling channel) negative (LW radiation disassociates H2; radiative heating can photoevaporate small halos or leave gas with tenacious excess entropy) Problem is very complex and can benefit from both semi-analytic (e.g. Haiman et al. 1996; Oh & Haiman 2003; MacIntyre et al. 2005), and numerical studies (e.g. Machacek+2003; Ricotti+2002; Kuhlen & Madau 2005; O’Shea+2005; Abel+2007; ; Ahn & Shapiro 2007; Whalen+2008) We attempt to quantify the feedback effects from a UVB consistent with that expected from an early Pop III star using the cosmological AMR code, Enzo. Fiducial runs: Can be regarded as spanning the likely range of J_UV JUV = 0 Flash JUV = 0.08 JUV = 0.8 Then add LWB of various strengths UV radiative feedback Hubble Symposium, STScI march, 2009

Pretty Pictures JUV = 0.08 z = 25 20 h-1 kpc 10 104 T(K) UV radiative feedback Hubble Symposium, STScI march, 2009

Pretty Pictures JUV = 0.08 z = 24.9 20 h-1 kpc 10 104 T(K) UV radiative feedback Hubble Symposium, STScI march, 2009

Pretty Pictures JUV = 0.08 z = 24.62 20 h-1 kpc 10 104 T(K) UV radiative feedback Hubble Symposium, STScI march, 2009

Physics Outline When the UVB turns on, gas gets ionized and heated to T~104 K. The temperature increase sets-off an outward moving pressure shock in the cores of halos, where density profiles have already steepened. This pressure shock smoothes out the gas distribution and leads to a decrease in gas density in the cores of halos. Once the UVB is turned off, the gas rapidly cools to T~103 K through a combination of atomic, molecular hydrogen and Compton cooling. This temperature approximately corresponds to the gas temperature at the virial radius of such a proto-galactic, molecularly-cooled halo, thus effectively neutralizing the impact of temperature change on feedback. A large amount of molecular hydrogen is produced, xH2 ~ few x 10-3, irrespective of the gas density and temperature. The pressure-shock begins to dissipate and gas with a newly enhanced H2 abundance starts falling back onto the partially evacuated halo. The enhanced H2 abundance allows the infalling gas to cool faster. - + Caveat: no RT ---> overestimate the strength of feedback UV radiative feedback Hubble Symposium, STScI march, 2009

Radial Profiles JUV = 0.8 JUV = 0 UV radiative feedback Hubble Symposium, STScI march, 2009

Transient Feedback _ Flash JUV = 0.08 JUV = 0.8 Another way to look at the net effect: delta 2 studies… Interesting rise! Mesinger+ (2006) Mesinger+ (2008) UV radiative feedback Hubble Symposium, STScI march, 2009

Physics Outline (halo embryos)
When the UVB turns on, gas gets ionized and heated to T~104 K. The temperature increase sets-off an outward moving pressure shock in the cores of halos, where density profiles have already steepened. This pressure shock smoothes out the gas distribution and leads to a decrease in gas density in the cores of halos. Once the UVB is turned off, the gas rapidly cools to T~103 K through a combination of atomic, molecular hydrogen and Compton cooling. This temperature approximately corresponds to the gas temperature at the virial radius of such a proto-galactic, molecularly-cooled halo, thus effectively neutralizing the impact of temperature change on feedback. A large amount of molecular hydrogen is produced, xH2 ~ few x 10-3, irrespective of the gas density and temperature. The pressure-shock begins to dissipate and gas with a newly enhanced H2 abundance starts falling back onto the partially evacuated halo. The enhanced H2 abundance allows the infalling gas to cool faster. - + Optically thin, so lack of RT doesn’t have an impact UV radiative feedback Hubble Symposium, STScI march, 2009

Eventual Positive Feedback
JUV=0.8, JLW=10-3 JUV = 0.8 JUV = 0 Lower redshift, since region wasn’t developed enough to be flagged by our halo finder However, very sensitive to a LWB UV radiative feedback Hubble Symposium, STScI march, 2009

Conclusions Our semi-numeric simulation can be a very useful scientific tool: density and velocity biases, ionization topology, but also radiative and chemical feedback, LAE studies, training ground for bubble detection algorithms and other 21-cm software, allows for wide parameter studies… Preserves 3D information --> higher order statistics Easy to fold-in smaller scale physics calibrated from numerical simulations. UV radiative feedback Hubble Symposium, STScI march, 2009

UV Feedback Conclusions
UV feedback on T>104 K halos NOT strong enough to notably affect bulk of reionization (requires factor of ~100 increase in ionizing efficiencies) Effectively Mmin ~ 108 Msun throughout most of reionization when minihalos go away (consistent with claims that faint galaxies dominate photon budget at z>6; Yan & Windhorst 2004a,b; Bouwens+ 2006) In early relic HII regions, feedback can be both + and -, but is transient; eventual + feedback is interesting, but can be supressed with modest values of LWB Natural timescale for bulk of reionization is the growth of the collapsed fraction in T>104 K halos, with small filling factor tail extending to higher z due to T<104 K halos, likely regulated by LWB Dynamic range is important in modeling reionization! This actually simplifies things. UV radiative feedback Hubble Symposium, STScI march, 2009

Andrei Mesinger Princeton University

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