Download HIERARCHICAL GALAXY ASSEMBLY AND ITS MANIFESTATIONS

Chiara Tonini, Sydney 2015
HIERARCHICAL GALAXY ASSEMBLY
AND ITS MANIFESTATIONS
star formation history & dynamical state
In collabora*on with: Darren Croton, Simon Mutch, Stuart Wyithe ASSEMBLY & MASS REDISTRIBUTION CHANNELS
Quiescent accretion of gas in undisturbed environment
DISK , with dynamical properties deriving from DM halo
Chaotic accretion, in dense environment / high z
Clumps & disk instabilities
Minor mergers and tidal interactions
Disk instabilities, streams
SECULAR BULGE + DISK
Major mergers
CLASSICAL BULGE
: Ellipticals
(low mass bulges in spirals)
A HIERACHICAL GALAXY FORMATION MODEL
MERGER TREES
DARK MATTER HALO
!
?
MORPHOLOGY
BARYONIC COOLING
?
STAR FORMATION
FEEDBACK
CHEMICAL ENRICHMENT
+
AGN
?
STAR FORMATION HISTORIES
Hierarchical model
SED fitting
single
burst
constant
tau model
PART ONE:
WHAT’S IN THESE GALAXIES?
STAR FORMATION RATE
REDSHIFT
Liu Liu et al. 2012 see Paola Oliva’s talk Total
Specific
CT et al. 2012
LUMINOSITY EVOLUTION
CT et al. 2012
Luminosity and colour evolution are indistinguishable from those of
single stellar populations of age > 3 Gyr…
Collins et al. 2009 PASSIVE EVOLUTION IN THE HIERARCHICAL SENSE
Age of a galaxy: minimum age of certain fraction of its stars
1: model BCGs are old at z=0
2: BCGs age a lot since z=1, but so does the Universe,
with the same speed
3: the SFRs are not large enough to offset this behaviour
The ageing of the BCG is dominated by its stellar populations
getting older, regardless of where they formed and when
they were accreted: ageing of the merger tree
CT et al. 2012
CT et al. in prep.
PART TWO:
WHERE IS ALL THIS STUFF?
… AND HOW DID IT GET THERE?
BULGES GROWN BY MERGERS : “CLASSICAL”
Ef inal

(Mstar1 + Mstar2 + Mstar
=G
Rf inal
new )
2
Ef inal = Einitial + Eorbital + Erad
Einitial

(Mstar1 + Mgas1 )2
(Mstar2 + Mgas2 )2
=G
+
R1
R2
Eorbital = G
(Mstar1 + Mgas1 )(Mstar2 + Mgas2 )
R1 + R2
Erad = Crad · Einitial ·
Mstar
✏ = ✏1:1
new
✓
Mgas1 + Mgas2
Mstar1 + Mgas1 + Mstar2 + Mgas2
= ✏(Mgas1 + Mgas2 )
Msat
Mcentral
◆
Rf inal = ↵Rclassical
“SECULAR” AND MIXED BULGES
when disk dominates the
stellar mass
Rsecular = 0.2 RD
FISHER Fisher & Drory 2008
Rbulge
Mclassical Rclassical + Msecular Rsecular
=
Mclassical + Msecular
SECULAR vs CLASSICAL
“BULGE”: stellar component (mostly)
not originating from direct cooling of
gas, which turns into stars
The formation mechanism is going to
be imprinted in the bulge distribution.
The distribution of bulge types seem
to indicate that secular and classical
channels are well separated.
BULGE GROWTH
STELLAR POPULATIONS IN BULGES
FABER – JACKSON
Auger + 2009; Newman + 2010
MASS – SIZE RELATION
Huertas-Company + 2012
CONCLUSIONS
Classic passive evolution does not exist: in the hierarchical
universe, galaxies are complex systems of stellar
populations. Central galaxies of halos (like BCGs) not only
have a complex assemby, but they can have intense star
formation at relatively low redshifts. When the specific star
formation rate cannot offset the galaxy mass-weighted age,
the galaxy is evolving passively in the hierarchical sense.
Classical and secular bulges form through 2 separate
channels (fast and merger-driven, and slow and
perturbation-driven), and mixed bulges are rare.
The incidence of secular/classical bulges is related to the
merger rate and the speed of disk growth.
The galaxy assembly history can be reconstructed through
the ratios between disk, secular and classical bulge, which
are also mirrored in the distribution of the galaxy stellar
populations.
STELLAR DENSITY PROFILES
Classical bulge : Sersic n = 4
Secular bulge : Sersic n =2
Disk: Sersic n=1
⇢(r) = ⇢0 Exp
" ✓
r
r0
◆1/n #
MASS PROFILES & LENSING
Mass + Deriva*ves Can we find the spot
in the mass
distribution of the
lens, where the
lensing signal
confusion goes below
an acceptable
threshold ?
Radius (arbitrary units) M (x) = Mtot

1
(3n, Dn x1/n )
(3n)
ALSO IN THE BOX
DYNAMICAL CHARACTERISATION
mass density profiles of all galaxy components,
rotation curves, angular momentum distributions
STAR-FORMATION HISTORIES
recorded with a non-uniform time grid, in look-back time at every output
redshift (every galaxy has the same age-grid), matching the age
resolution of the SSP model (to capture younger stellar generations)
PHOTOMETRY
galaxy spectra + mock galaxy catalogues with absolute/apparent
magnitudes and dust extinction, tailored on your preferred survey’s
specifications (filters, errors, cuts…)
“OBSERVED” PARAMETERS
Older then the Universe!
Maraston, Daddi, Renzini, et al. 2006
Different evolutionary population synthesis mostly agree at low z
Until recently, other discrepancies with data made this effect negligible
IS THIS PROBLEM REAL?
Is there something fundamentally wrong with hierarchical clustering (CDM)?
PROBABLY NOT.
Galaxy formation models
MASS
SFR, age, Z
LIGHT
- Hierarchical mass assembly
and star formation
- Synthetic spectra
associated
to stellar mass at each
timestep
Observations
LIGHT
MASS
SFR, age, Z
SED fitting with template synthetic
spectra
SFH toy models
+ K-corr + E-corr
STELLAR POPULATION MODELS
+
STAR FORMATION HISTORIES
STELLAR MASS FUNCTION: “OBSERVED”?
Optical to mid-infrared data
Goods – Giavalisco et al. 2004
Musyc – Gawiser et al. 2006
Marchesini et al. 2009
RED: ALIVE OR DEAD?
Colour-colour relations at z~2: star-forming vs passive galaxies
?
V-K
B-V
CT et al. 2010, MNRAS, 403, 1749 MASSIVE RED OLD GALAXIES ...?
BCGs are very luminous in K, and very red
Collins et al. 2009 With BC03 modeling, they are also
estimated to be the most massive
galaxies we observe. They evolve in
luminosity and colour like single
stellar population models, with
epoch of formation z~3-5: passive
evolution
Hierarchical semi-analytic models produce slower and more
prolonged evolution, and lower masses at high redshift,
OR: less luminous, bluer galaxies