AY16 March 20, 2008 Galaxies

Galaxies A modern topic: 1920 Shapley-Curtis Debate Evidence against galaxies as external 1. Proper motion of M31 (van Maanen) 2. Shapley’s GC Distances 3. “Nova” 1885a in M31 Killer evidence for: 1. Hubble’s discovery of Cepheids in 3 galaxies and their distance determinations.

What Are Galaxies? 1.Artifacts of the Formation Process 2.Tracers of Test Particles of Larger Dynamics 3.Froth on an Ocean of Dark Matter 4.Objects Deserving Detailed Study in Their Own Right

Galaxies have a broad range of properties There exist connections between these properties and other parameters (location, location, location ---- formation + evolution) We must understand these connections to use galaxies to understand the cosmological model. We hold these truths …

Morphology Hubble’s Tuning Fork E0 E6 Sa Sb Sc Sd S0 SB0 SBa SBb SBc SBd Ellipticity = 10(a-b)/a < ~ 7 observationally Irr

Irregular Galaxies LMC = IBm M82 = Irr II = I0

Morphological classification is just taking the grossest, simplest observational properties and moving the bins around until they make sense. Relate form to physics. Regarding S0 galaxies, Hubble said “at present, the suggestion of cataclysmic action at this critical point in the evolutional development of nebulae is rather pronounced.” Hubble thought his diagram was an evolutionary sequence!

Hubble Types are now (1) Not considered to be “evolutionary” (2) Considerably Embellished! by Sandage, deVaucouleurs, van den Bergh, ++ (1)Irr  Im plus I0 (2)Sub classes added Sa, Sab, Sb, Sbc, Sc, Scd, Sd, Sdm, Sm, Im and S0/a = slight signs of structure in the disk (3) S0 class well established + rings, mixed types and peculiarities

e.g. SAbc(r) p = open Sbc galaxy with an inner ring and some peculiarities SX(rs)0 = mixed S0 galaxy with mixed ring morphology SBdm = barred very late type spiral galaxy

deVaucouleurs Expansion

Other Embellishments S. Van den Bergh introduced luminosity classes in the 1960’s  for spirals, L is a function of appearance. I = giant ---- V = dwarf this was used for a while to estimate H 0. (ugh!) in the 1970’s he introduced the Anemic sequence: very low surface brightness disks which is probably connected to the “stripping” of spirals in the field

Discovery of Anemic spirals and other effects (e.g. the morphology-density relation) spawned the “Nature” vs “Nurture” debate: Are S0’s born or made? Do field S0’s exist? Morgan in the 1950’s introduced spectral types for galaxies a, af, f, fg, g, gk, k which never caught on (but E+A galaxies are now a hot topic – emission + A type)

Finally, in the 1960’s the search for active galaxies and radio galaxies caused Morgan to introduce another classification scheme D galaxies --- E galaxies with apparently extended envelopes. cD galaxies --- Centrally located D’s N galaxies --- Compact Nuclei Plus other types like Seyferts + LINERS (both specroscopic) and Zwicky’s compact and “post-eruptive” galaxies…

M81 3.6μ

M81 Spitzer 3.6, μ

M87

M87 Deep AAT USM

2 μ

M101 W. Keel Optical

M101 UIT

R. Gendler

Ring galaxy

Crashing galaxies = The Antennae

Arp Introduced Peculiar Galaxies (1966) Atlas of Peculiar Galaxies, mostly interacting. Some 30% of al NGC objects are in the Arp or Vorontsov-Velyaminov catalogs. (Arp vs Sandage.) Arp also introduced us to our limitations sue to surface brightness considerations: We can’t see galaxies that are too small or that are too big (low Surface brightness)  THE LAMPPOST SYNDROME

By the numbers: In a blue selected, magnitude limited, z=0 sample, 1/3 are E + S0, 2/3 are S + I 20% 15% 60% < 10% For Spirals ~ 1/2 A ~ 1/4 X ~ 1/4 B per unit volume is something else again.

T Types -6 = cE 2 = Sab A = Unbarred -5 = E 3 = Sb X = Mixed -4 = E+ 4 = Sbc B = Barred -3 = S0- 5 = Sc -2 = S0 6 = Scd -1 = S0+ 7 = Sd 0 = S0/a 8 = Sdm etc. 1 = Sa 9 = Sm 10 = Im

Quantitative Morphology Elliptical Galaxy Surface Brightness Profiles What is the shape of the galaxy? What is its integrated light? (A) Hubble Law (one of 4) I(r) = I 0 (1 + r/r 0 ) -2 I 0 = Central Surface Brightness r 0 = Core radius Problem(!) 4π ∫ I(r) r dr diverges.

(B) deVaucouleurs r 1/4 Law I(r) = I e e -7.67((r/r e ) 1/4 - 1) a.k.a r e = effective radius = ½ light radius I e = surface brightness at r e Roughly, I 0 = e 7.67 I e ~ I e ~ 2100 I e r e ~ 11 r 0 This function is integrable.

(C) King Profile derived to fit isothermal spheres to globular star clusters, includes a tidal cutoff term with r c ~ r 0, and r t = tidal radius I(r) = I K [(1+r 2 /r c 2 ) – 1/2 - (1 + r t 2 /r c 2 ) -1/2 ] 2 (D) Oemler Truncated Hubble Law I(r) = I 0 (1 + r/r 0 ) -2 e –(r/b) 2 (pre computers)

Typical Numbers I 0 ~ 15 – 19 magnitudes /sq arcsec in B ~ 17 m/sq” for Giant Elliptical Galaxies, r 0 ~ 1 kpc r c ~ 10 kpc

N4494

King Profiles

Spiral Galaxies Profiles are on average (over the spiral arms) Exponential Disks I(r) = I S e -r/r s Freeman (1970) found I S ~ mag/sq” B for 28 of 36 galaxies r S ~ 1 – 5 kpc, function of Luminosity

Spirals are Composite Spirals have both bulges (like E galaxies) and disks. From the deVaucouleurs Law L Bulge = 2 ∫ I(r) πr dr = 7.22 π r e 2 I e L Disk = 2π ∫ I S e -r/r s r dr  D/B = 0.28 (r s /r e ) 2 I S /I e Disk to Bulge Ratio 0 ∞

Sombrero (M104) HST

Sombrero Spitzer

Spiral Galaxy Structure What gives Spiral Galaxies their appearance? There are 2 main components (plus others less visible) Disk --- rotationally supported --- thickness is a function of the local vertical “pressure” vs gravity Spiral Pattern --- Three models Density Wave Tidal Interactions SPSF = self propagating star formation

Density Waves  Lin’s “Grand Design” spirals (M81, M83) Interaction Induced Spirals  Good Looking spirals with Friends (M51) Self Propagating Star Formation --- detonation waves, SF driven by SF,  “Flocculent” Spirals

M81 Classic Grand Design Spiral

Another GD Spiral

M51 Interacting System Optical Molecular Gas -CO

M33 A Flocculent System

NGC4414 another Flocculent S

Spiral Structure Some Definitions: Number of Arms = m, most spirals have m=2, i.e. twofold symmetry Arm Orientation: Leading rotation Trailing

Density Wave Theory Developed over many years by first Bertil Lindblad, then C.C. Lin, then Frank Shu: Quasi-stationary Spiral Structure Hypothesis (spiral pattern changes only slowly w. time) + Density Wave Hypothesis Pattern is a SF pattern driven by density change

Follow the Mass Gravitational Field due to Stars & Gas = TOTAL RESPONSE + || Density Response of Stellar Disk Density Response of Gaseous Disk Total material needed to maintain the field

Density Wave Models + Bar Potential

Toomre 2 model for the Antennae

Galaxy Magnitudes!!! Galaxy magnitudes are measured many different ways!!! Isophotal (to a limiting radius in mag/sq” Metric (to a fixed size in kpc) Integrated Total (very hard!) Petrosian (to a fixed SB relative to the center) Kron (similar)

Properties vs Morphology Type vs Color  driven by star formation rates and histories Color Gradients  most galaxies get bluer with increasing radius (combination of SFR + [Fe/H]) Color vs Magnitude  mostly for E’s Morphology Density

Color vs Type (Optical) Type B-V U-B SB. E S Sa Sb Sc Sd Im

S/T = L Bulge /L tot which correlates with type.

Dressler Morphology- Density

Gas Content (HI) versus type Type M H /M E to S Sa 0.03 Sb 0.05 Sc 0.1 Im 0.2 to1.0

Luminosity versus Internal Motions L versus σ for E’s = Faber –Jackson L versus rotation for S’s = Tully-Fisher L α σ α, ΔV α ; Α ~ 2.5 to 4 Diameter versus Luminosity L α D 2 Surface Brightness versus Luminosity (and central SB vs Luminosity) 

The Fundamental Plane There exists a plane in several observable dimensions on which most E galaxies and similar objects lie. R e = f (σ,L) or f (σ, L, [Fe/H]) Ditto for Spirals TF relation implies that the mean global M/L for spirals varies by at most x2 over x100 in luminosity

For Spirals, Tully-Fisher Relation if L ~ M and rotation curves flat and galaxies similar in surf B =  M ~ v 2 R R~ M/v 2 L ~ 4  R 2 R ~ (L/4  ) 1/2 L ~ v 4 /4 

Summary 1.Galaxies come in many forms (morphology) 2.Properties of galaxies correlate with type 3.Generally brightness falls with R in a predictable way 4.Galaxy types correlate with density 5.Spiral structure can form several ways 6.Gravity rules! FP and TF relations show that the properties of galaxies are governed by M