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Galactic & Extragalactic Astrophysics - ASTC22. Lecture 2 Stars Hubble sequence Galaxy classification Photometry. The role of star formation. Most star formation occurs in dense star clusters surrounded by H II regions. About 6 new stars per year are born in our Galaxy. - PowerPoint PPT Presentation
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Lecture 2
Stars Hubble sequenceGalaxy classificationPhotometry
The role of star formation
About 6 new stars per year are born in our Galaxy
Oph V380 Ori + NGC1999
GMCs contain: dark clouds, cores, Bok globulesGMC mass / solar mass ~ 105
Dark clouds
L57 Barnard 68
Oph Giant Molecular Cloud, 160 pc awaycontains numerous dark clouds
H II regions
Bright ionized hydrogen clouds,illuminated by type O,B stars
IRAS all sky survey in the infrared
8.5 kpc
Can you findthe sun?
Earlier ideasMore recent findings
V = GM(r)/r2
From BT
From Ch.1 BT
Other galaxies M 31 Andromeda galaxy (Sb)companions: M 32 (E2) (foreground object) & M 110 (E6p)
(below M31)
M-object namesare from a catalogueby Charles Messier1740s)
Hubble sequence (tuning fork diagram)
Similar classification applies to other bandpasses(near-IR, in this case)but there’s no guarantee thatthe morphological type willbe the same in the visible (here Hubble sequence is defined) and the otherwavelengths. On the contrary, there are sometimes bars and rings which are revealed only in theUV, IR, or radio wavelengths.
Hubble sequence (tuning fork diagram)
De Vaucouleurs galaxy classification extends the Hubblescheme in orthogonal directions, adding more criteria
De Vaucouleurs galaxy classification
(cross-section at Hubble type Sb)
Bulk Properties of Galaxies
Galaxy Type
Spiral /Barred Spiral M=109 to 1011 Msun, L=108 to 1010 Lsun, Diameter=5-250 kpc
disk: Population I halo:Population II f=77%(f=Percentage of Observed Galaxies)
Elliptical 105 to 1013 105 to 1011 1-205 kpc Population II f=20%
Irregular 108 to 1010 107 to 109 1-10 kpc Population I f=3%
a bright supernova
Some objects in/around galaxies are tinybut almost as bright: supernovae, Active Galactic Nuclei, Quasars (extreme AGNs)
M 104(Sa)
M81 (Sb)
M 51 (Sc) + NGC 5195 (peculiar SBb?)
Are these colliding or is it just projection effect?Can you say what type they are?
Criteria for distinguishing spirals along the sequence of ‘early-type’ to ‘late-type’: Sa--Sb--Sc
1. Bulge-to-disk light (mass) ratio, size of the bulge (decreases)
2. Prominence of spiral arms, arm-interarm contrast (increases)
3. Visibility and number of population I objects such as: H II regions, OB associations, dark lanes of dust
(increases)
4. Pitch angle (openness) of spiral arms (increases)