Galaxy Formation and Galaxy Formation and Dark GalaxiesDark Galaxies

John SchreiberJohn Schreiber

OutlineOutline

Background info (formation/evolution of Background info (formation/evolution of galaxies)galaxies)

Implications of theoriesImplications of theories More dwarf galaxies should be observedMore dwarf galaxies should be observed These may exist as difficult-to-detect “dark galaxies”These may exist as difficult-to-detect “dark galaxies”

VIRGOHI21VIRGOHI21 Rotating H cloud in the Virgo clusterRotating H cloud in the Virgo cluster Possible dark galaxyPossible dark galaxy DiscrepanciesDiscrepancies

Background infoBackground info

What is a galaxy?What is a galaxy? Basic unit of Basic unit of

cosmologycosmology Can contain stars, Can contain stars,

gas, dust, dark mattergas, dust, dark matter

Formation of GalaxiesFormation of Galaxies BeforeBefore

As universe expands, density As universe expands, density enhancements either grew or enhancements either grew or dispersed. dispersed.

Smaller, more dense density Smaller, more dense density enhancements first to enhancements first to collapse. collapse.

These first “lumps” that broke These first “lumps” that broke free contained some H and free contained some H and He, but mostly dark matter. He, but mostly dark matter.

ProtogalaxiesProtogalaxies When this “lump” collapses When this “lump” collapses

under its own gravityunder its own gravity Appear abt. 14 mill. years b.p.Appear abt. 14 mill. years b.p. Should be detectable via their Should be detectable via their

heat signatureheat signature

Evolution of GalaxiesEvolution of Galaxies

Primeval galaxyPrimeval galaxy Collision creates a high Collision creates a high

density region where a star density region where a star cluster formscluster forms

Remaining gas heated by Remaining gas heated by stars (dissipates)stars (dissipates)

Initial rate of star formationInitial rate of star formation Slow—cons. ang. Slow—cons. ang.

momentum forces a spiral momentum forces a spiral diskdisk

Fast---elliptoidFast---elliptoid

Star FormationStar Formation Clouds of gas orbit in the Clouds of gas orbit in the

protogalaxyprotogalaxy Density of some of these Density of some of these

clouds increases as gas clouds increases as gas falls towards the core of the falls towards the core of the protogalaxyprotogalaxy

Clouds collide Clouds collide

Implications of Current TheoryImplications of Current Theory

More dwarf galaxies More dwarf galaxies should exist than should exist than currently observedcurrently observed

May exist as dark May exist as dark galaxiesgalaxies Starless clouds of H Starless clouds of H

and dark matterand dark matter Observed via radio Observed via radio

waves (w/ wavelength waves (w/ wavelength of ~ 21 cm)of ~ 21 cm)

No dark galaxies No dark galaxies have currently been have currently been discovereddiscovered

Other possibilitiesOther possibilities Galactic cannibalismGalactic cannibalism Unaccounted for Unaccounted for

environmental factorenvironmental factor Little empirical info Little empirical info

about “young galaxies”about “young galaxies”

VIRGOHI21-Dark Galaxy?VIRGOHI21-Dark Galaxy?

Possible dark galaxyPossible dark galaxy Rotating cloud in the Rotating cloud in the

Virgo clusterVirgo cluster Contains enough H to Contains enough H to

form 100 mill. Sun-form 100 mill. Sun-sized starssized stars

Recently located by a Recently located by a team led by Robert team led by Robert MinchinMinchin

Used the radio-Used the radio-telescope at the telescope at the University of University of ManchesterManchester

After examining it w/ After examining it w/ optical optical telescope“confident” it telescope“confident” it is a dark galaxyis a dark galaxy

VIRGOHI21-Other Possibilities?VIRGOHI21-Other Possibilities? May not be a dwarfMay not be a dwarf

Mass from dark matter prevents rotation from tearing Mass from dark matter prevents rotation from tearing galaxies apartgalaxies apart

Measured speed of rotation implies ~1/10 dark matter Measured speed of rotation implies ~1/10 dark matter of Milky Wayof Milky Way

This implies 100x more H should be presentThis implies 100x more H should be present May be two passing H cloudsMay be two passing H clouds

Would give illusion of rotationWould give illusion of rotation Counter-argumentsCounter-arguments

Few known H cloudsFew known H clouds If H gas ionized it would be “invisible to radio If H gas ionized it would be “invisible to radio

telescopes”telescopes”

SourcesSources http://www.newscientist.com/article.ns?id=dn7056http://www.newscientist.com/article.ns?id=dn7056 http://abyss.uoregon.edu/~js/ast123/lectures/lec25.htmlhttp://abyss.uoregon.edu/~js/ast123/lectures/lec25.html http://pinot.phys.uvic.ca/~jfn/mywebpage/gxform.htmlhttp://pinot.phys.uvic.ca/~jfn/mywebpage/gxform.html http://www.oarval.org/galaxfrm.htmhttp://www.oarval.org/galaxfrm.htm http://hermes.physics.ox.ac.uk/users/Astrophysics/http://hermes.physics.ox.ac.uk/users/Astrophysics/

guides/universe/galformation.shtmlguides/universe/galformation.shtml http://www.absoluteastronomy.com/encyclopedia/G/http://www.absoluteastronomy.com/encyclopedia/G/

Ga/Galaxy_formation_and_evolution.htmGa/Galaxy_formation_and_evolution.htm http://www.astro.cf.ac.uk/computing/parallel/gal2/http://www.astro.cf.ac.uk/computing/parallel/gal2/

Sbc.htmlSbc.html