the milky way galaxy · the milky way galaxy a.k.a. the galaxy (galaxias kyklos) nb this is a...

The Milky Way Galaxya.k.a. the Galaxy (galaxias kyklos)

NB this is a painting, not a photograph

Milky Way Galaxy

• Appearance, size, morphology– Disk, bulge, halo

• Constituents:– Stars of various populations– Gas (cold, warm, hot) and dust = ISM– Dark matter

• Dynamics• Evolution and recycling • Galactic centre

The local group, a photo montage

QuickTime och enTIFF (okomprimerat)-dekomprimerare

krävs för att kunna se bilden.

Artist’s impresseion

The Milky Way Galaxy

Galaxy = MWgalaxy = others

QuickTime och enTIFF (okomprimerat)-dekomprimerare

krävs för att kunna se bilden.

Milky way look alike

QuickTime och enTIFF (okomprimerat)-dekomprimerare

krävs för att kunna se bilden.

NGC 891

MW (COBE)

Equatorialvs

Galacticcoordinates

Extent of optical emission (starlight) vs 21cm (neutral gas)In Milky Way and other spiral galaxies

21 cm spin fliptransition of neutral Hydrogen (HI) (see box 1.3, page 30)

QuickTime och enTIFF (okomprimerat)-dekomprimerare

krävs för att kunna se bilden.

QuickTime och enTIFF (okomprimerat)-dekomprimerare

krävs för att kunna se bilden.

Nearest stars Brightest stars

Nearest stars dominated by low luminosity brighest stars dominated by highbecause these are most common lumionsity as we can see them far away

Pleiades youngstar cluster

Horsehead nebulain Orion

Pop I = youngStars in the disk

Globular cluster (population II) on the order of a million stars, gravitationally bound

X-ray binaries in globular cluster ”47 Tuc”

Colour distribution of halo and disk stars- Age vs Metallicity

Metal-richGlobularClusters(near the plane)

Metal-poorGlobularClusters(in the halo)

Vertical distribution of stars

I = I0 e−r / hDisks have exponential light distribution: I = surface brightness, h = scale length (height)

Thin (hz= 300 pc)

vs

Thick (hz= 1 kpc)

Disk

Thick disk older, hence no A-stars

Disks have exponential light distribution: I = surface brightness, intensity (flux per angular area) h = scale length (height)

I = I0 e−r / h

Surface photometry

NB surface brightness independent of distance- Flux per angular area - Luminosity per metric area

QuickTime och enTIFF (okomprimerat)-dekomprimerare

krävs för att kunna se bilden.

Radial distribution of neutral atomic (HI) and molecular (H2) gas in the Milky Way Galaxy

H2 has no ’dipole moment’ and therefore no suitably observabletransitions at typical ISM cloud temperatures, but the CO molecule can be used as tracer (see Box 1.4 on page 33 in JL)

Property Population I Intermediate Population IIOrbits Circular Elongated Very ellipticalShape spiral arms disk spherical/haloThickness(pc) 120 400 2000Metals (%) 3-4 0.4-2 0.4 or lessMass (Msun) 2x109 5x1010 2x1010

Age (yr) 108 109 1010

Typical objects Open clusters, Sun Globular clustersHII regions, RR Lyrae stars

Stellar populations in MW

Population III ? Zero metallicity

Chemical compositionof starclusters in MW

High latitude neutral hydrogen