galactic structure and formation szydagis 03.13.2015 1 / 14

GALACTIC STRUCTURE AND FORMATION SZYDAGIS 03.13.2015 1 / 14

CLICKER-STYLE QUESTIONS 1. What is one of the key ingredients needed for galaxy formation? a. dark energy b. clumps of gas c. supernovae d. neutron stars 2. Which explanation is currently best based on our observations? a. Top-down: big galaxies broke up b. Bottom-up: small galaxies combined c. Combination, but bottom-up favored d. Black holes eating dark matter 2 / 14

3 / 14 (not the same galaxies of course)

THE ORIGIN OF GALAXIES Most galaxies are very old. The very first began forming around 12-13 billion years ago, not long after the first stars formed Study of their formation from inner to outer portions and continuing evolution is still an area of active research to this day Models fall under one of two umbrellas: 1. top-down, 2. bottom-up 1. Galaxies began as clouds of gas bigger than galaxy 2. They started out as smaller fragments merging together In either case, black holes (super-massive ones) are involved, with galaxies building up around them as cores (in -> out) These came from the collapse of the first, largest stars Local over-density caused slower expansion (0.5% at 500,000 years after BB, 5% at 15e6, 200% at 1.2e9): runaway effect We will learn about this and more with the new James Webb Space Telescope, Hubbles successor, launching in three years 4 / 14

THE TOP-DOWN APPROACH Gravitational collapse will overcome gas pressure If cloud rotating slowly, stars form before collapse into disk can occur, resulting in elliptical galaxy If rotating faster, disk formed, so spiral galaxy (think of bulging earth) Star formation rate determines type of galaxy that will form, or perhaps it is other way around Variant: gas cloud fragmentation, each clump becoming small galaxy. Clusters form first Problem: takes too long, though explains clusters? I Zwicky 18 is a nearby dwarf galaxy that started forming stars only 500 million to one billion years ago. It may be an example of what the galaxies were like over 12 billion years ago. How this galaxy remained in an embryonic state for almost the entire history of the universe is unknown. Is it an example of a "dark galaxy"---a dark matter clump with cold primeval hydrogen and helium gas---in which the gas only now got compressed enough to form stars? -http://www.astronomynotes.com/galaxy/s10.htm A Baby Galaxy in a Grown-Up Universe! (High-density sheets of galaxies with large voids in between are easy to predict.) 5 / 14

http://abyss.uoregon.edu/~js/ast123/lectures/lec24.html 6 / 14

THE BOTTOM-UP APPROACH Little pieces merge Fragments could have already started collapsing very early on during the history of the universe Cluster hierarchically through mutual gravitational forces Predicts more smaller galaxies: check! Clusters should still be forming: check!! Variant: dark matter galaxies (hard to see). Cold DM favors bottom-up scenario Combining theories The radio galaxy MRC 1138-262, also called the "Spiderweb Galaxy" is a large galaxy in the making. At 10.6 billion light years away, we see it in the process of forming only 3 billion years after the Big Bang. Note the small, thin "tadpole" and "chain" galaxies that are merging together to create a giant galaxy. -astronomynotes.com 7 / 14

http://abyss.uoregon.edu/~js/ast123/lectures/lec24.html 8 / 14 WINNER

THE STRUCTURE OF A GALAXY Example, our own Milky Way Halo mostly dark matter. Not perfectly spherical. Modeled as spheroid / ellipsoidal profile Why sphere, while galaxy (if spiral) is a very flat disk Dust-rich: spiral (flat) Dust-poor: elliptical Sensitive to rotational degrees of freedom, initial conditions, particle interaction probability. Also, thinner->faster rotation Center of course black hole(s) thousands, millions, billions times more massive than sun So, BHs = birth & death North arbitrary: right-hand R.J. Hall http://www.cosmotography.com/images/s upermassive_blackholes_drive_galaxy_e volution_2.htmlhttp://www.cosmotography.com/images/s upermassive_blackholes_drive_galaxy_e volution_2.html (Journey to the Center) 9 / 14

A FEW VIDEOS Credit: Matthias Steinmetz The formation of a "galactic fountain" in a forming disk galaxy. The simulation includes a model for star formation and galactic winds. In this particular galaxy, the winds generated by ongoing star formation are confined by the gravitational potential of the dark matter halo, giving rise to a "galactic fountain. Credit: Volker Springel This movie shows two colliding and merging spiral galaxies. The simulation follows dark matter, gas, and a stellar component, but only the baryonic component is visualized. Credit: Volker Springel http://www.mpa-garching.mpg.de/galform/data_vis/galaxy.mpg http://www.mpa-garching.mpg.de/galform/data_vis/f10.mpg Links to a couple of extra videos that I had trouble embedding into the slides. The Max Planck Institute for Astrophysics (z is redshift. Now z = 0. Beginning z~20) 10 / 14

PARDON MY (HOT) GAS Chandra X-ray Observatory | NASA X-rays are in left pane and optical at right. What is binding all the gases in place to make those x-rays, considerably outside of the visible elliptical galaxy? Best answer we have so far: dark matter 11 / 14

USING HYDROGEN: SEE FARTHER http://upload.wikimedia.org/wi kipedia/commons/e/ec/M33_r otation_curve_HI.gif That is the wavelength. Frequency=1,420 MHz 12 / 14 Lets do it again: Back to slide 2, same question

HOMEWORK OVER BREAK Types and Classification of Galaxies http://www.astro.cornell.edu /academics/courses/astro2 01/galaxies/types.htm (plus sub-link:) http://www.astro.cornell.edu /academics/courses/astro2 01/galaxies/types.htm Also tuning fork A Rippled Milky Way May Be Much Larger Than Previously Estimated (from Anthony. Thanks!) http://scitechdaily.com/rippl ed-milky-way-may-much- larger-previously-estimated/ http://scitechdaily.com/rippl ed-milky-way-may-much- larger-previously-estimated/ Black Holes, Quasars and Active Galaxies | Hubble & European Space Agency http://www.spacetelescope. org/science/black_holes/ http://www.spacetelescope. org/science/black_holes/ 13 / 14 Terrifying information found on the first few pages of the childrens book First Space Encyclopedia (owned by a friend)

14 / 14 Image Credit: Sergey V. Pilipenko (LPI, MIPT)LPI, MIPT) A Redshift Lookup Table for our Universe