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Observing Compact Sbbhs Observing Compact SBBHs! ! •" Evidence for SBBHs ! –" Indirect methods! •" Precession, periodic behaviors! •" Double optical lines! –" Direct Imaging with Very Long Baseline Interferometry ! •" The radio galaxy 0402+379! •" Searching for more SBBHs with the VLBA! Hydra A! P_precession ~ 300,000 y! P_orbital ~ 17 y! 10 kpc! Taylor et al. 1992! 1946+708! Precession! Period ~ 5700 y! 10 pc! Taylor & Vermeulen! Quasi Periodic Behaviours! OJ287 Maxima every ~11.9 years ! ! Similar behaviour seen sporadically in! 3C273, 3C345, BL Lac, etc.! Valtaoja et al. 2000! Radio Continuum Spectra ! ! In both hotspots of the source, N2 and S2, a steep spectrum was found.! ! For both central components, C1 and C2, the spectrum peaks at ~10 GHz. ! Spectral index distribution between 8 and# 22 GHz from the 2005 VLBA observations. ! Circular orbit! •" Small 7 pc separation and minimum energy leads to assumption of circular orbit! •" Inclination i of 75° from HI absorption model! •" Period P of 20,000 years from observed velocity of 0.007c.! •" Initial guess of semi-major axis a = 6.9 mas from our astrometry, I guessed by eye the initial ascending node $ and nodal passage epoch T0. ! •" Perform fit for $ and a T0! Inclination = 75° circular orbit! a=7.08 ± 0.71 mas! e=0.0! i=75°! ω=0.0°! Ω=100.27° ± 2.71°! P=7,305,000 days! T0 =2,194,481.1 (JD)! = 1296 AD Feb 29! ! "! Our 3 observed points ! shown with 10x error ! ellipses for visibility! Close-up view, observed # and predicted astrometry! Large error ellipses are our 3 ! Observed 8 GHz points. ! Bob’s 100th birthday, 2065! ! JD = 2035.0! Small error circles are ! JD = 2025.0! predicted future positions! ! Double Peaked Narrow Lines! SDSSJ104807+005543 [OIII]4959, 5007 Hβ, single- peaked Alternatives: Disks, bipolar outflows! Zhou et al 2005! Double Peaked Broad Lines! SDSSJ1536+0441 Boroson & Lauer 2009! Alternatives: Disks, bipolar outflows! Astronomy 422! Lecture 13: Galactic Evolution II! Announcements! !Outline for paper due on Tuesday, March 8! !Test #2 on Thursday, March 10! ! Key concepts:! ! !Galaxy formation scenarios! !!monolithic collapse (ELS model)! !!Hierarchical formation (SZ model)! !! !Jean’s Mass! !Mean molecular weight! ! ! !! ! !! ! !! !! ! Galaxy formation: classical models! ! • First models of galaxy formation based on observations of stellar populations in the Milky Way! •" Two main models:! –" Eggen, Lynden-Bell & Sandage (1962)! •" monolithic collapse# –" Searle & Zinn (1978)! •" aggregation of smaller protogalactic fragments! ! Recall structure of the Milky Way:! Models based on MW observations:! ! •" Halo stars old and metal poor! •" Disk stars are young and metal-rich ! •" High velocity stars near the Sun! –" Metal-poor! –" Eccentric orbits (most disk stars circular)! –" High kinetic energy perpendicular to disk! –" High angular momentum Lz! –" These correlate with metallicity! •" lower [Fe/H] implies higher eccentricity, higher Ez, lower Lz! Eggen, Lynden-Bell & Sandage (ELS)! ! •" Because of orbit eccentricity, and Ez, Lz are adiabatic invariants (if potential changes slowly, they should be conserved)! –" Metal-poor stars must have formed on eccentric orbits! –" or violent star formation history! •" Basic paradigm: MW formed from a ~spherical cloud of rotating, metal- poor gas.! –" Exceeds Jeans mass, free-fall collapse! –" Most metal-poor stars and halo glob. cluster stars form here! –" SN from this pop increased metallicity! –" Remaining gas collapses into metal-rich disk, subsequently forming younger disk stars and clusters.! !Milky Way formed from rapid collapse of a proto-galactic nebula in <109 yrs. This is a top-down process.! ! Homologous collapse! ! Virial Theorem: 2K + U = 0 is stable, but if U is too big cloud collapses! ! For a spherical cloud of constant density:! ! ! ! ! ! Thermal energy is just! ! ! where! ! ! ! And u is the molecular weight (typically about 0.6 for 90% H, 10% He) ! Homologous collapse! ! The condition that U > 2K leads to! ! ! ! Assuming constant density, R is given by:! ! ! ! So, if MJ > Mc we have collapse and the minimum mass that does this is the Jean’s mass:! ! ! ! ! Which has a radius:! Problems! ! •" Need high initial SFR 100-1000 M/yr! •" Doesn't explain! –" thin/thick disk components! –" stars of different ages in the bulge! –" Continued growth of the MW! –" retrograde motion of some halo stars! –" dynamical clumps of stars in halo (moving groups)! –" age differences and metallicity differences in globular clusters (age spread ~3Gyrs)! •" No treatment of dark matter (well, it was 1962…)! ! A more modern view! Larson 1969, Searle & Zinn 1978 etc (SZ)! ! •" Accounts for the fact that metallicities of halo GC spread over large range (not formed of same material)! •" Suggest MW formed from collapse of individual gas clouds! –" metallicity of those components depend on number of SN explosions occurring before gas blown away by kinetic energy of SNe.! •" Unclear how disk is formed! Basic SZ! ! 6 8 •" At time of galaxy formation, expect Jeans mass of 10 -10 M! •" 100s-1000s of dark-matter dominated fragments collided and merged to create each giant galaxy. ! –" Leftovers + smaller events created dwarfs.! –" recently plenty of observations of nearby dwarfs! •" Bottom-up process - small pieces merged together as stars form.! •" Early on, gas in some fragments collapse to form globular clusters.! –" Perhaps 1000s in the MW initially, now only ~150 left (the dense cores that could survive tidal disruption)! •" Collisions between fragments heat proto-galaxy, slowing the collapse! –" age spread of halo and thick disk! •" Collapse is fastest where the density is highest! -1/2! –" recall tff ∝ ρ –" ρ highest in inner region => central bulge! –" This is where chemical enrichment would be fastest! •" we do observe old, metal-rich stars in the central bulge! •" Also, massive fragments subject to dynamical friction, fed bulge.! –" Why massive? Recall ! •" Remaining gas eventually settled into rotating disk! •" Further accretion events => bulge and thick disk growth, age spread.! •" OR: thick disk formed when collapsing structure had 106 K, with scale height ~1-2 kpc, thin disk formed later as gas cooled (see C&O)! ! ! SZ pro's and con's:! ! •" Explains! –" retrograde halo stars and moving groups! –" different metallicities and ages of halo GC! •" Does not include dark matter! •" Does not explain formation of disk! •" Real evolution could be somewhat more complex! !! Ibata et al. 2003: Canis Major galaxy.! What about ellipticals?! ! Old, single age stellar population, not rotationally supported.! ! •" Complete star formation before disk could form?! –" does not agree so well with the hierarchical picture! •" OR, only disk systems formed, E's made by mergers (recall Toomre sequence).! –" evidence for a small 'frosting' of younger stars! –" counter-rotating cores! –" Butcher-Oemler effect: more blue galaxies in high redshift clusters than in low redshift clusters! –" Morphology-density relation ! ! ! Progress in the last # 10-15 years! •" ΛCDM paradigm shown to be consistent with broad range of observations (CMB, Ly-α forest, weak lensing, galaxy clustering, galaxy clusters)! •" galaxy surveys: ! –" large homogeneous samples at low z! –" huge progress in discovering & cataloging high-z galaxies! –" build-up of panchromatic view of the Universe! •" development of detailed simulations of dark matter and (to some extent) gas processes ! •" developments of (not totally im-)plausible picture for galaxy formation within this framework ! Putting it all together Numerical simulations are used to trace the gravitational collapse of matter (dark+luminous) across cosmic time Simulating the Universe! Growth of structure - The Cosmic Web! The “Missing Satellite Problem” ! •" Models/simulations predict large numbers of satellites => Logarithmic slope of the faint end of the CDM mass function ~ -1.8 (Press-Schechter value) •" Kauffmann et al. (1993) •" Klypin et al. (1999) •" But the current census does not count them (light not mass): •" Faint end slope of the optical LF •" Faint end slope of the HIMF The HI Mass Function •" Previous surveys N=1000 have included few (if any) objects with HI ? masses less than 108 M. •" At lowest masses, differ by 10X: Rosenberg & Schneider (2000) versus Zwaan et al. (1997) •" Statistics •" Systematics Parkes HIPASS survey: Zwaan et al. 2003 HIMF @ z=0 Challenges •" Need better statistics: larger, more sensitive surveys •" At the faint end, all the galaxies are nearby •" Redshift distances are highly unreliable •" Large Scale Structure affects accuracy of flow models Masters, H & G 2004, ApJ 607 L115 •" Need a “fair sample” to overcome (and allow study of) cosmic variance •" Σ(1/Vmax) corrections must account for Large Scale Structure •" Not just that space density varies with distance •" Fractional volume of space occupied by regions of a particular density do too Springob, H & G 2005, ApJ 621, 215 Cosmic variance Must sample enough volume to acquire a “fair sample” If we covered a similar slice in the opposite part of the sky (coming….) we would see a very DIFFERENT redshift distribution At these distances, 540 square degrees is not enough. Statistics, statistics, statistics N=2800 N= 265 Springob et al. 2005 (optically selected) Rosenberg & Schneider 2002 Environment & the HIMF Previous studies based only on Virgo have suggested that the HIMF in Virgo is flatter than in the field •" Only a single cluster •" Very small number statistics/systematics vs comparison Inconsistency: •" Is this just HI deficiency? Symptom of •"
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