| Today: Classification and Morphology | |
| (following ch. 1 of the textbook) | |
| Unless noted, all figs and equations from Combes et al. or Longair. | |
Chapter 1: The Classification and Morphology of Galaxies
| Observational Basics – more to come | ||
| Classifications | ||
| Luminosity Distributions | ||
| Stellar Populations, Color | ||
| Some Statistical Properties | ||
| 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) | ||
| The nuclear bulge is population II (old stars) | |
| So the Sa – Sc sequence is consistent
with little gas Þ more gas |
| 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. | ||
| Galaxies live in clusters | ||
| Rich clusters: thousands of galaxies | ||
| Poor clusters: Fewer than a thousand | ||
Irregular Galaxies: Magellanic Clouds
Interacting Galaxies: The Antennae
Interacting Galaxies: Cartwheel
Interacting Galaxies: Cartwheel
De Vaucouleur’s Revised Scheme
De Vaucouleur’s Revised Scheme
van den Bergh Luminosity Classes
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 r1/4 Law: | ||
| Log (I/Ie) = -3.33[(r/re)1/4 – 1] | ||
Luminosity Distributions -- Bulges
Luminosity Distributions -- Spirals
Luminosity Distributions -- Spirals
Stellar Populations, colors, models
Stellar Populations, colors, models
Stellar Populations, colors, models
Stellar Populations, colors, models
Stellar Populations, colors, models
Stellar Populations, colors, models
| The frequency with which galaxies of a particular luminosity are found in space. Note that luminosities can be expressed in magnitudes: |
| Felton (1977): |
| Solid line is the best fit SCHECHTER (1976) function: |
| Exact parameters depend on sample. SDSS and 2dF provide the best estimates. Typically slopes around a = -1, MB = -20 (note for reference that quasars by definition more luminous than -23). |
| 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). | ||
Frequency of Galaxy
Types:
As a function of clustering
| Roberts & Haynes 1994: | |
| 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 | ||
| From Hopkins et al. (2001) |