Observing Compact SBBHs • Evidence for SBBHs – Indirect methods • Precession, periodic behaviors • Double optical lines – Direct Imaging with Very Long Baseline Interferometry • The radio 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 Ω and nodal passage epoch T0. • Perform fit for Ω 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 Ω 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

• 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

• 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 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, 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 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 • Watch out for morphological biases inadequate volume?

Kovač, Oosterloo & van der Hulst (2005): CanVen • Similar to Virgo (low mass slow flatter)

BUT……..

Zwaan et al. (2005): HIPASS • Higher density regions => more low masses

HI and the “missing satellite” problem

 HIPASS result: no cosmologically significant population of HI- 8 rich dark galaxies: ALFALFA agrees… but HIPASS MHI > 10 M

 ALFALFA is specifically designed (wide area, high velocity 7.5 resolution) to detect hundreds of objects with MHI < 10 M • Low HI mass • Narrow HI line width + exclude face-on objects • Will only be detected nearby => need to sample cosmologically significant volume

 Future studies will focus on extending • Deeper in HI Mass than ALFALFA in Local • Much larger volume than AGES Lowest HI mass objects

log MHI < 7.2

ALFALFA has already detected more objects with log MHI < 7.5 than all other previous blind HI surveys combined Voids and

Gregory & Thompson (1978) Luminosity function of galaxies

• Void LF has a faint M* but a similar faint-end slope, compared to the overall LF

• Void galaxies are blue, disk-like and have high Hα equivalent width => good HI targets

Void galaxies in the SDSS: Hoyle et al (2005)

1000 galaxies in lowest density cells of total 155,000 galaxies (SDSS 2005) How and when do galaxies acquire their gas?

Kereš et al. (2005) How and when do galaxies acquire their gas?

Kereš et al. (2005) Highest mass objects: Challenge for SKA

ALFALFA has already detected more than twice as many

objects with log MHI > 10.4 than all other previous blind HI surveys combined Practice Problem! Assuming a uniform protogalactic cloud with a virial temperature of 106 K and a density of 0.05 cm-3 (a) estimate the upper mass limit that could collapse, (b) what is the velocity dispersion in such a cloud, and (c) what would be its Jean’s radius? Next time: The extragalactic distance scale Read chapter 27.1