Clues for satellite galaxy formation and accretion from
self­consistent hydrodynamical simulations
M.A. Gómez­Flechoso , H. Artal , R. Domínguez­Tenreiro , J. Oñorbe
(1)
(2)
(2)
(2)
(1) Universidad Europea de Madrid
(2) Universidad Autónoma de Madrid
ARE DWARFS IMPORTANT BUILDING­BLOCKS OF MASSIVE GALAXIES?
What we now from observations :
It is unlikely that present­day dwarfs are the major building blocks of massive galaxies (Milky­Way or early­type like; Tossi 2003)
Region 2
­ Early­type galaxies contain on average older stars than present­day dwarfs
­ On average, the star formation period is more time­concentrated in ellipticals than in dwarfs.
However, minor merger events could be very frequent at low z (z < 1.5) :
­ Blue cores in a morphologically selected sample of field spheroidal galaxies taken from HST ACS ERO program of UGC 10214 (Menanteau et al. 2004) (= recent star formation).
­ Evolution of re and M* (=baryon accretion) and no signs of major mergers (Dickinson et al. 2003 ; Bundy et al. 2003 ; Conselice et al. 2003,2004 ; Trujillo et al, 2004).
Region 1
390 Kpc
Aim of this poster :
y
Where and when do satellite galaxies form.
Fate of satellites of massive galaxies.
Role of satellites in massive galaxy star formation history.
z
How could we analyse the accretion of dwarfs ?
Using cosmological self­consistent simulations
Satellite 12
Our simulations :
Satellite 5
Satellite 11
Satellite 12
y
Cosmolgical self­consistent simulation (obtained using DEVA (Serna et al. 2003) and analysed with IRHYS (Artal et al. S1 poster Satellite 4
Satellite 4
Satellite 6
Satellite 7
Satellite 5
z
Satellite 3
Satellite 10
Satellite 7
session)).
Satellite 8
Satellite 2
Satellite 6 ( tidally disrupted )
We get a sample of elliptical­like objects (ELOs) consistent with observations:
Satellite 1
Satellite 10
Satellite 9
Fig. 1
­ Structure and dynamics (Saíz et al 2004).
­ Trends of the age distributions of their stellar populations (Domínguez­Tenreiro et al. 2004).
Satellite 2
­ Formation scenario (Oñorbe et al, S1 poster session).
In this poster, we select a region for analysing the joint satellite and main galaxy evolution:
475 Kpc
430 Kpc
Fig. 2a
­ The main galaxy is an ELO field galaxy ; we want to “isolate” the effect of the dwarfs. Fig. 2b
­ The selected dwarfs are the satellites of the main galaxy within a sphere of 215 kpc at z=1 (Fig. 2a) inside 215 kpc : we want to “analyse” the importance of minor mergers at low redshifts.
­ We study the formation and the fate of the selected dwarfs: snapshots at several redshifts are plotted (Fig. 3).
y
x
492 Kpc
525 Kpc
600 Kpc
649 Kpc
718 Kpc
687 Kpc
510 Kpc
1020 Kpc
492 Kpc
525 Kpc
600 Kpc
649 Kpc
718 Kpc
687 Kpc
510 Kpc
1020 Kpc
z
x
Fig. 3
RESULTS
DISCUSSION
The previous results could explain:
(1) The satellites in Fig. 2a are mainly formed within two regions (R1 and R2, dashed grid in Fig. 1).
The main formation region, R1, gives rise to number 1,2,5 and 7 satellites (Fig. 2a ).
(1) The existence of regions of satellite formation could explain the existence of satellite galaxies that seem to orbit in the same plane.
At high z, R1 is a piece of the celullar structure of the mass density (walls, filaments, nodes) and constitutes an attraction basin (Sierra Glez de Buitrago et al. 2003). Mass gets adhered to filaments (Fig. 3, from z ~ 6 to z ~ 2.5) while the basin contracts. Filaments finally fragment, giving rise to the satellites orbiting the main galaxy at z=1 (Fig 3 from z ~ 2.5 to z ~ 1). (2) The main galaxy has already formed stars before the assembly of the satellite dwarfs (see Fig. 3 at z=4).
(3) Some satellites present at z=1 have been accreted at z=0 (Fig2a and 2b):
(a) Part of the satellite gas forms stars at the center of the main galaxy (blue dots at z=0 Fig. 3, see also Fig. 4).
(b) The stars of the accreted satellites end up at the core of the main galaxy, however some of them are difused into the “halo” of the main galaxy (see Fig. 2b, white dots)
(3) The satellite accretion modifies the size and mass of the main galaxy
(a) The new stars formed from the satellite gas explain the blue cores of the early­type galaxies.
(b) The accreted or newly formed stars explain why the stellar mass of the main galaxy increases at low redshift.
(4) The survival satellites represent the present satellite population observed in numerous galaxies
Magents dots: constituent gaseous particles of the satellites selected at z = 1.
White dots: constituent stellar particles of the satellites selected at z = 1.
Blue dots: stars formed between z = 1 and z = 0 out of gaseous particles belonging to the satellites at z = 1.
Yellow dots: stars not in the selected satellites.
(2) It explains that early­type galaxies contain on average an older stellar population than present dwarfs. Unlikely present­day dawrfs are the major building­blocks of massive galaxies.
(4) Some satellites survive at z=0 (see Fig 2b).
(5) Some satellites are disrupted forming tidal tails (see satellite 6 at z=0 in Fig. 2b).
Colors Code for Snapshots
(5) The gaseous tidal tails observed in some galaxies can be explained as part of the accretion process of the satellite population.
z=1
Fig. 4
Now