paper

Feeding compact bulges and supermassive black holes with low angular-momentum cosmic gas at high redshift

arXiv:1112.2479 · doi:10.1111/j.1365-2966.2012.21160.x

Abstract

We use cosmological hydrodynamical simulations to show that a significant fraction of the gas in high redshift rare massive halos falls nearly radially to their very centre on extremely short timescales. This process results in the formation of very compact bulges with specific angular momentum a factor 5-30 $s ma l l er t han t h e a v er a g e an g u l a r m o m e n t u m o f t h e ba r y o n s in t h e w h o l e ha l o . S u c h l o w an g u l a r m o m e n t u m or i g ina t es b o t h f r o m se g r e g a t i o nan d e f f ec t i v ec an ce l l a t i o n w h e n t h e g a s f l o w s t o t h ece n t r eo f t h e ha l o a l o n g w e l l d e f in e d co l df i l am e n t a r y s t r e am s . T h ese f i l am e n t s p e n e t r a t e d ee p in s i d e t h e ha l o an d co nn ec tt o t h e b u l g e f r o mm u l t i pl er a p i d l y c han g in g d i r ec t i o n s . S t r u c t u r es f a l l in g ina l o n g t h e f i l am e n t s (s a t e l l i t e g a l a x i es) or f or m e d b y g r a v i t a t i o na l in s t abi l i t i es t r i g g er e d b y t h e in f l o w (s t a r c l u s t er s) f u r t h er r e d u ce t h e an g u l a r m o m e n t u m o f t h e g a s in t h e b u l g e . F ina l l y, t h e f r a c t i o n o f g a sr a d ia l l y f a l l in g t o t h ece n t r e a pp e a r s t o in cr e a se w i t h t h e ma sso f t h e ha l o; w e a r g u e t ha tt hi s i s m os tl ik e l y d u e t o an e nhan ce d c an ce l l a t i o n o f an g u l a r m o m e n t u min r a r er ha l os w hi c ha r e f e d b y m or e i so t r o p i c a l l y d i s t r ib u t e d co l d s t r e am s . S u c hanin cr e a s in g l y e f f i c i e n t f u nn e l l in g o f l o w - an g u l a r m o m e n t u m g a s t o t h ece n t r eo f v er y ma ss i v e ha l os a t hi g h r e d s hi f t ma y a cco u n t f or t h er a p i d p a ce a tw hi c h t h e m os t ma ss i v es u p er ma ss i v e b l a c k h o l es g r o w t or e a c h o b ser v e d ma sses a r o u n d$ 10^9 $M$ _\odot$ at an epoch when the Universe is barely 1 Gyr old.

17 pages, 13 figures, MNRAS accepted