Lunch & Learn: On the Formation of Massive Galaxies

 All who lis­ten to Jerry Ostriker, Pro­fes­sor of Astro­phys­i­cal Sci­ences at Prince­ton Uni­ver­sity, come to know that we live in pro­foundly excit­ing times. We have learned only recently the age and com­po­si­tion of the uni­verse, and for the first time, we are com­ing to under­stand how the galac­tic struc­tures we observe through­out the sky came to be. Sim­ply put, where do they come from, and how could they form if the early uni­verse was rel­a­tively uni­form? And how can we use them as stan­dard objects unless we under­stand how and when they formed and how they evolved?

One of the key find­ings, said Ostriker at the Sep­tem­ber 29 Lunch ‘n Learn sem­i­nar, came from the WMAP satel­lite. Its obser­va­tions of the Cos­mic Back­ground Radi­a­tion show the begin­nings of struc­ture in the after­math of the Big Bang.

Armed with our best cos­mo­log­i­cal mod­els, asks Ostriker, “Can we start with those ini­tial con­di­tions and our under­stand­ing of the stan­dard model of cos­mol­ogy, add stan­dard physics, com­pute for­ward and end with galax­ies like those we see about us?”

From 50 years of obser­va­tions, he tells us, we know that giant ellip­ti­cal galax­ies, galax­ies that involve on the order of 100 mil­lion stars, form early and grow in size and mass with­out much late star-formation. He adds that major merg­ers are uncom­mon at later times or else disk galax­ies would have been destroyed.

Using high res­o­lu­tion sim­u­la­tions of mas­sive galaxy for­ma­tion, he has com­puted the for­ma­tion of cos­mic struc­tures. He begins by putting down par­ti­cles on a dense grid with slight per­tur­ba­tions of the posi­tions con­sis­tent with the early large scale struc­ture given by the CBR. He then gives the par­ti­cles small veloc­i­ties con­sis­tent with the den­sity struc­ture and the con­ti­nu­ity equa­tion. He then uses the super­com­put­ers at Prince­ton to cal­cu­late the accel­er­a­tions of all the par­ti­cles using Newton’s laws.

The sim­u­la­tion updates again and again the posi­tions and veloc­i­ties and accel­er­a­tions to find the new dis­tri­b­u­tion of par­ti­cles, all cul­mi­nat­ing with a video sim­u­la­tion of the evo­lu­tion of cos­mic structures.

Here are three videos from the presentation:

• video 1
• video 2
• video 3

Says Ostriker, “Look­ing back­wards we have been able to recon­struct from the detailed struc­ture of our own Galaxy and from the fos­sil evi­dence derived from the study of nearby galax­ies a plau­si­ble his­tory of how galax­ies formed over the last sev­eral bil­lion years. In addi­tion, now that we have a quite def­i­nite cos­mo­log­i­cal model, pro­vid­ing us with a quan­ti­ta­tive pic­ture of how per­tur­ba­tions grew from very low ampli­tude Gauss­ian fluc­tu­a­tions, we can per­form the for­ward mod­el­ing of rep­re­sen­ta­tive pieces of the uni­verse using stan­dard phys­i­cal processes to see how well we match our local knowl­edge and the time-reversed mod­el­ing based on the fos­sil evi­dence. Finally, we can employ large ground and space based tele­scopes to use the uni­verse as a time-machine – directly observ­ing the past his­tory of our light-cone. While none of these approaches can give us at the present time results accu­rate to more than roughly the 5% -> 10% level, a coher­ent and plau­si­ble pic­ture is emerging.”

“Mas­sive galax­ies form in two phases. In the first phase, which peaks at red­shift z = 6 and ends by red­shift z = 2, cold gas streams in mak­ing stars in a small (<1kpc) region, but as the stel­lar mass approaches 10,¹¹ M_solar, a hot bub­ble forms which sup­presses fur­ther inflow of cold gas. But from red­shift z = 3 to the present time, small stel­lar satel­lite sys­tems are accreted at typ­i­cally 10kpc from the cen­ter and the size of the total sys­tem grows by about a fac­tor of three as the mass dou­bles. This added, accreted com­po­nent is mainly com­prised of old and low metal­lic­ity stars. Energy release from grav­i­ta­tional infall in var­i­ous forms will ter­mi­nate star-formation leav­ing the galax­ies ‘red and dead’. Even in the absence of feed­back from SN or MBHs. This phys­i­cal pic­ture seems nat­u­rally to lead to the mass, size scale and epoch of galaxy for­ma­tion and, increas­ingly, to a first under­stand­ing of the detailed inter­nal struc­ture of these systems.”

A pod­cast and the speaker’s slides are avail­able.

About the speaker:

Jere­miah P. Ostriker has been an influ­en­tial researcher in one of the most excit­ing areas of mod­ern sci­ence, the­o­ret­i­cal astro­physics, with cur­rent pri­mary work in the area of cos­mol­ogy, par­tic­u­larly the aspects that can be approached best by large scale numer­i­cal calculations.

Ostriker has inves­ti­gated many areas of research, includ­ing the struc­ture and oscil­la­tions of rotat­ing stars, the sta­bil­ity of galax­ies, the evo­lu­tion of glob­u­lar clus­ters and other star sys­tems, pul­sars, X-ray binary stars, the dynam­ics of clus­ters of galax­ies, grav­i­ta­tional lens­ing, astro­phys­i­cal blast waves, active galac­tic nuclei, the cos­mic web, and galaxy formation.

Most sig­nif­i­cantly, Ostriker’s research focused on the the­o­ries of:

• Pul­sars
• Inter­stel­lar Medium
• Dark Mat­ter and Dark Energy
• The Warm-Hot Inter­galac­tic Medium (WHIM)
• The First Stars and Reion­iza­tion of the Universe
• Galaxy For­ma­tion
• Inter­ac­tion between Quasars and their surroundings

Ostriker has super­vised and col­lab­o­rated with many young researchers and grad­u­ates stu­dents. He is the author or co-author of more than 300 sci­en­tific publications.