1	Astr 5460 Wed. Sep. 1, 2004 Today: Classification and Morphology (following ch. 1 of the textbook) Unless noted, all figs and equations from Combes et al. or Longair.
2	Chapter 1: The Classification and Morphology of Galaxies Observational Basics – more to come Classifications Luminosity Distributions Stellar Populations, Color Some Statistical Properties
3	A Brief History Initially just a type of nebula Hubble resolved stars in M31 (1920s) Many mixed catalogs already existed Messier (M – “fuzzy non-comets”), 39 of 109 New General Catalog (NGC), 3200 of 7840 Today there are many surveys/catalogs (see NED entries while doing homework) SDSS and 2dF (more later this semester)
4	“Tuning Fork” Diagram
5	Spiral types The nuclear bulge is population II (old stars) So the Sa – Sc sequence is consistent with little gas Þ more gas
6	Elliptical Galaxy: M87
7	cD Galaxies M87 is a cD galaxy, technically. Kormendy (1982) distinguishes these from being merely giant ellipticals. Extensive stellar envelope up to 100 kpc Only in regions of enhanced galaxy density (a factor of 100 denser than the average) Multiple nuclei in 25-50% of cDs (a very rare thing) Regular cD clusters are systems that have relaxed into dynamical equilibrium.
8	The Local Group of Galaxies Galaxies live in clusters Rich clusters: thousands of galaxies Poor clusters: Fewer than a thousand
9	The Coma Cluster
10	Irregular Galaxies: Magellanic Clouds
11	Interacting Galaxies: The Antennae
12	Interacting Galaxies: Cartwheel
13	Interacting Galaxies: Cartwheel
14	De Vaucouleur’s Revised Scheme
15	De Vaucouleur’s Revised Scheme
16	van den Bergh Luminosity Classes
17	Luminosity Distributions -- Bulges Elliptical galaxies have an apparently simple structure, can be characterized by their luminosity distribution. Maximum in center, and falls off: Hubble’s Law: I/I₀ = [(r/a) + 1] ^-2 De Vaucouleur’s r^1/4Law: Log (I/I_e) = -3.33[(r/r_e)^1/4 – 1]
18	Luminosity Distributions -- Bulges
19	Luminosity Distributions -- Spirals
20	Luminosity Distributions -- Spirals
21	Stellar Populations, colors, models
22	Stellar Populations, colors, models
23	Stellar Populations, colors, models
24	Stellar Populations, colors, models
25	Stellar Populations, colors, models
26	Stellar Populations, colors, models
27	Luminosity Functions The frequency with which galaxies of a particular luminosity are found in space. Note that luminosities can be expressed in magnitudes:
28	Luminosity Functions
29	Luminosity Functions Felton (1977):
30	Luminosity Functions Solid line is the best fit SCHECHTER (1976) function:
31	Luminosity Functions Exact parameters depend on sample. SDSS and 2dF provide the best estimates. Typically slopes around a = -1, M_B = -20 (note for reference that quasars by definition more luminous than -23).
32	Luminosity Functions Features to note Morphology matters, also field vs. cluster. L* or M* in rich clusters isn’t a bad “standard candle” cD galaxies in cluster centers are special cases; they are like massive ellipticals but have extra stellar envelopes. They do not fit extrapolations of ellipitical LFs. Low luminosity end of LFs not well determined (Irr and dwarf ellipticals). Again SDSS will probably be the best word on this (if it goes faint enough).
33	Frequency of Galaxy Types
34	Frequency of Galaxy Types
35	Frequency of Galaxy Types: As a function of clustering
36	Trends along Hubble Sequence
37	Trends along Hubble Sequence Roberts & Haynes 1994:
38	Trends along Hubble Sequence Roberts & Haynes 1994: Masses from S0 to Scd roughly constant, then decrease, and M/L roughly the same – more next chapter H I not significant in ellipticals (< 1 in 10000), but is in spirals (0.01 to 0.15 from Sa to Sm) Total surface density decreases, H I surface density increases Ellipticals are red, spirals are blue… H II regions frequency increases monotonically along the sequence (Kennicutt et al. 1989) Star formation rates appear key to these relations
39	Cosmic Star Formation History From Hopkins et al. (2001)