1 - Introduction to galaxies Flashcards
Define a galaxy
A large collection of starts, hot/cold gas and dust held together by mutual gravitation
What is the range of mass and size of all galaxies?
Mass - 10^6 - 10^13 solar masses
Size - 1-200+ kpc
What are the 5 types of galaxies?
Spirals, ellipticals, lenticulars, irregulars and peculiars
What size is an elliptical galaxy?
1-250 kpc
What size is a spiral galaxy?
1-100 kpc
What types of small galaxies are there?
- Dwarf ellipticals (dE), 1-3kpc
- Dwarf spheroidals (dSph), 0.1-0.5kpc
- Dwarf irregulars (dI), <3kpc
What is the largest type of galaxy?
- Giant ellipticals (cD), found in centre of clusters, absorb other galaxies, large diffused haloes
Define extrinsic and intrinsic properties
- Extrinsic - properties that are observer-dependent or otherwise determined by external factors
- Intrinsic - properties that are an integral property of the galaxy
Give examples of extrinsic properties of galaxies
- Position in the sky
- Apparent magnitude
- Inclination angle
- Distance
Give examples of intrinsic properties of galaxies
- Physical size
- Absolute magnitude
- Rotation rate
- Mass
- Luminosity
- Spatial characteristics
What are the two main catalogues of galaxies?
1780 Messier ~100 objects
New General Catalogue - 7800 objects
How have modern-day galaxy surveys improved?
- Improved technology e.g - CCD detectors
- Modern-day computing power allows us to sift and analyse vast amount of data
What is the SDSS?
Sloan digital sky survey:
- Surveying 1/4 of sky
- 10^6 galaxies
- ~1000Mpc
What is the dark energy survey?
DES:
Used 4m optical telescope equipped with 570 mega-pixel camera to survey ~300 million galaxies in 5 optical filters
Name 2 radio surveys
- FIRST - ~9000 deg^2, 800
000 sources - NVSS - ~34000 deg^2 (82% of
sky), 1.8 million sources
Name 3 infrared surveys
- IRAS - 350000, ~11000 galaxies
- 2MASS - near-IR, all sky
- SPITZER - SWIPE survey
covering 50 deg^2, ~2 million
galaxies
What are 2 future galaxy survey projects?
- Vera Rubin Telescope - 10 million
galaxies surveyed over full
hemisphere of sky every 3 nights,
sensitive to transient sources - SKA - array of linked dishes and
antennae across 1000s of km, will
map hydrogen emission from over
a billion galaxies
What data issues do galaxy surveys produce?
Generate petabyte levels of data, in huge archives such as NASA Extragalactic Database (NED), suitable currently but datasets rapidly growing
What is citizen science?
Solution to data issues, Example was galaxy zoo - public sift through and classify galaxies from SDSS
Distributed computing clients such as BOINC - allows PC users to analyse data with screensaver programs
What is the Hubble Deep Field?
- Unique survey
- Several degrees away from any
bright star, field devoid of amy
a nearby bright objects/sources - Field has low IR cirrus flux from
dust - Low extinction (from dust), low
hydrogen column density
