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by: Bryon Mueller


Bryon Mueller
GPA 3.97


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Class Notes
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Popular in anthropology, evolution, sphr

This 27 page Class Notes was uploaded by Bryon Mueller on Saturday September 12, 2015. The Class Notes belongs to Anthro 10 at University of California - Irvine taught by Staff in Fall. Since its upload, it has received 21 views. For similar materials see /class/201908/anthro-10-university-of-california-irvine in anthropology, evolution, sphr at University of California - Irvine.




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Date Created: 09/12/15
Galaxy Formation in ACDM and Merger Histories of Milky Waysized Dark Matter Halos Kyle Stewart l Advancement to PhD I 71 la l L 239 l LVL39H L 1 FZl39 39l39 l 5 I IElW l 101 IJV39JI39 JL lu J39J i LEI I3939l Ill I I I I I 1 2 3 4 5 Outline Overview of ACDM cosmology Hierarchical Structure Formation Disk Formation amp Dark Matter Simulations Results Merger Rates of Milky Waysized Dark Matter Halos and Implications for Disk Survival Future Work MassEnergy Budget of the Universe Earth is here and so are we 73 DARK mane DarkrEnerg39y denoted A a er Einstein s cosmological constantquot causes universe s observed acceleration 85 ofthematter in the universe is dark matterquot Some Evidence for Dark Matter 1 Galactic Dynamics Use kinematics of visible matter to determine the enclosed mass Then compare with the visible mass Galactic rotation curves disk galaxies Velocity dispersions elliptical galaxies HST WFPCZ Galaxy Cluster Abell 2218 NASA A Fruchter and the EEO Team STSCIJ STSclPRCOOOS Velocity Distance A predicted rotation curve based on visible matter B observed rotation curve 2 Gravitational Lensing Relies on general relativity not dynamics to get mass estimates of clusters Why Cold Dark Matter Hotwanncold dark matter refers to ultrarelativistic relativistic non relativistic particle velocities at decoupling when the particles fall out of equilibrium with the hot dense plasma Faster moving particles will not clump together to form structure on small scales Lymancc forest also shows small scale structure at high redshi Current CDM particle candidates Selja etal 2006 g 731 A k l o m Large scales k km3w small scales axlon WIMPs eg Neutralin o Theo etical predictions and observations of Lya forest power spectrum Thick lines are CDM thin lines are WDM CDM is more consistent Inflation Inflation a phase of exponential expansion of the early universe driven by a negativepressure vacuum energy density mm 10quotquot wm m an wavelength Solves Flatness Problemquot 9 very close to QCHI requires arbitrary ne tuning at early times to accomplish Horizon Problemquot homogeneous amp isotropic universe even though distant parts that have had no causal contact Hierarchical Structure Formation in ACDM Sanctum begins with quantum 11mm au ng inflation creating panamath in the form of a Wainwrimt Wm madam uid 39 Linear EMS m ustuwmu KM I chm preferenmfoumailm to 1 quot quotquotquotquot quotI quotquotquotquotquotquotquotquotquotquotquotquotquotquotquot collapse rst 7 Thui small dumps of matter mime ta form luau ma Inger clumps of nmndlzsd by o39IGQRIB Mpclh tantrum animate 04193 Matthew amassO p1 claw Ilready calm 31 uleg may at Hierarchical Structure Formation in ACDM Structure forms bottom up with smaller clumps of matter forming first with each clump containing both dark matter amp baryonic matter Small dark matter halos then merge together over time to build up larger ones The baryonic mass within them galaxies also merge to form more massive galaxies Merger Trees show mass accretion hisc gories for a given dark matter halo at Z But What about the baryons emu Hierarchical Structure Formation in ACDM Dark matter halo properties to first order simply rely on the Mass to determine its behavior and are self lf baryons simply followed dark matter what might galaxies 00k like Similar across all mass scales Image from Kazantzidis et al 2007 Actual galaxy NGC 4414 But galaxies baryons are much more complicated Most big galaxies are disks not spheres Cloud formation and fragmentation AGN supernova feedback disk bulge components gas cooling heating star formation the list goes on Disk Formation and Dark Matter Simulations Attempts to simulate disk galaxies with prescriptions for all the baryon physics give results unlike observations Simulated disks tend to be Too small and thick Too centrally concentrated containing large bulges Require special merger histories to create In short we don t fully understand baryonic physics very well but ifwe did given the hierarchical mergerdriven model of ACDM even if a thindisk were to form somehow would it survive later mergers Disk Formation and Dark Matter Simulations Dark Matter mergers onto disk galaxies tend to Thicken the disk promote a central bar and create pronounced aring ringlike features and filamentary structure o o N E y a Q Q bl E m s x nkpc lt gt Disk Formation and Dark Matter Simulations 1 Determine dark matter halo merger histories 2 Assign likely galaxies to dark matter halos Statistically possible Statistically possible Only reasonable guesses possible at this stage 3 Understand how mergers affect galaxies In progress currently not veryA well understood and often NOT based on halo statistics given merger history 4 Determine galaxy type for any Disk Formation a Simulal Q How do we construct merger histories for a statistically large number of dark matter halos A N Body Simulations NBody simulations in a nutshell Only consider dark matter in the universe 85 of all matter Begin with the Gaussian random eld uctuations and ACDM parameters Allow dark matter to clump by gravity See what happens over the age ofthe universe Dark matterhalo mergertree from such a Simulatlun fora Milky Way SlZed system l5 shown ere NBody Simulation Kravtsov et al 2001 What results does the simulation yield One last point about disk galaxies For the sake of comparison to the Milky Way focus on Milky Way sized halos 1012 M9 2 Assign likely galaxies to dark matter halos Although late type galaxy is vaguely defined there seems a consensus that 70 of Milky Way sized halos are disk galaxies Late Types Early Types Intermediate Types itllllLilllll Hulk it lllu sAll Galaxies 777 il hlg 0395 1 7774719520 A swim l 721722 E 06f I filveel7231 5 5047 e e 02 JAM 21quot v E Ollllllllllllllllll39lllllllllllllllll39llllllllllllllllll 12 13 1 13 14 15 1 13 14 10gM hquotMa Figure 2 Thu fraction of late type galaxies early y galaxies and uttermcdlaco typo galaxies as a function of l d P up mass Dlll39aml lme styles denote different allsolute magnitude bins as indict Review Halos form by mergers Roughly 70 of Galaxy sized halos contain disk dominated galaxies Large DM mergers turn disks into thick puffy more bulgy systems How worried should we be Look at merger statistics from NBody simulations eg Weinmann et al 2006 Choi et al 2007 Park et al 2007 llbert et al 2006 emu Simulation DM only ACDM N Body sim 32 80 h Mpo Box 0509 512 particles 31 mp316x10a h1 M 9 better resolution m than Millennium 31 Adaptive Refinement Tree oode 512 oells refined to max of 8 levels hPeak 1 2h1kpo Kravtsov et al 1997 5 Focus on Z0 host masses ranging 53 from 1011 10 h1MG 3333 gt 15000 host halos in this range 22 Complete to 101 WM 0 22 Example merger tree shown I for a Mn 1012h391 Mquot nqsn dark matter halo which experiences a 1011 merger w How do we characterize mergers 1 Merger Ratio mMz Doesn t quantify the actual mass without knowing Mz MP mass varies with z completeness issues Significant accretion afterwards on average 2 Absolute merging halo mass m Little subsequent accretion No completeness issues Normalized by MD for host mass trends Our Goals Provide robust halo merger statistics for General understanding of expectations Groundwork for future merger models We define an infalling halo to be merged once it falls within vir We are mainly concerned with mergers with m gt 1011h391MO which are typically 15 merger events at the time of accretion Such large mergers have short dynamical friction times 3 Gyrs Adding a disk potential would only shorten it Without baryon physics more detailed merger statistics would be incomplete and our goal is to present accurate results After comparing the following results to the case where we only considered mergers that are destroyed by zO we found nearly identical results Where does a halo s mass come from I 39f I 39 to quot 39EPS quot 39 39 39 close to N Body considering mass definitions M O1M0 Largest contribution to nal halo mass comes from mergers with mMo 10 A E 01 10 hr Mohalos buIlt up from a 1012 MM mergers 3 1O12 hr Mohalos built up from quotquot 1011 hVWI mergers A 1011 hr1Mohalos built up from 101 WM mergers 39 01 39 0001 0010 0100 1000 mMo How often do mergers occur in 1012h1M3halos Redshift 016 05 055 1 DB LEE 414 10 r u u I u r u I u a u I u l u I w u v u u l u n E f a I Ma 10quot 1 39Me 1 By StFICt mass cut H m gt 005 M r m 03 am a I In last 10 Gyrs a gt 3443 n a gt I I u a Egg 70 of halos a gt gt 11 E 15 I m 1 0X10 2quot U U E 50 of halos E a m gt 15x1011 wquot 34 hquot a 39 E c I x g quot 30 of halos U I u J in 11 D r 39 v39 m gt 25x10 i 392 39 x Li 39 39 x assw 0 39 lquotquot3939f n A v u u 39 39 39 39 39 39 39 39 39 39 39 39 39 39 Lookback Time It Gyr Is there a trend with mass from 1011 1013 1 word answer Nope 2 word answer Only slightly Fraction with merger since 1 Gyr P on P a 0 b I Could a disk have formed afterwards Mass accretion since last major merger Li Given a halo with mass Mn a 20 which we know has experienced at least 1 merger ofmass gt m What fraction 0an was accreted AFTER the most recent merger gt m At most only 30 These systems probably cannot subsequently regrow a sizeable disk from newly accreted material Conclus on 3E 70 of Milky Way sized halos have 222 had a gt 1011 h1Mo merger in the past 10 Grs and accreted little mass since Since we presume that most Milky Way size halos are disk dominated these results imply that A 1011 h1M Gfiark matter halo merger can not destroy a typical Galactic disk or we have a serious problem Gas rich mergers Robertson et al 06 Other Work Common lore Cluster galaxies are preprocessed in Groups before they fill into the Cluster Simulation results suggest that for smaller Clusters M 1014101475 this is not true Most halos fell in alone 1 101400 Mclul 101475 101400 ngu 10kle E 01 3 H 301Eliiiinlniiiliiiiliiii liliiiiliiiiz z 101411 Mcm 101425 Mcm 1014quot I 7 L 0391 l E I W 39139 In I W ill I jL Ll ll W L39 n I ll gel l 001illumin imrimwillwillimriml 0 o 10 20 30 40 Number of companions when halo fell into a cluster Future Work Major Merger rates starting from z t 0 Fitting functions Varying host mass redshift Future Work Accretion rates in general Pmt Mhost Statistics of halo futures look forward instead of backwards Jeff Cooke detection of massive galaxy galaxies at z3 possible protocluster


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