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“Nature” and “nurture”
a theoretical perspective
Gabriella De Lucia
INAF – Astronomical Observatory of Trieste
The morphology-density relation
“There are some indications of a correlation between characteristic
type and compactness, the density of the cluster diminishing as the
most frequent type advances along the sequence of classification”
Hubble, “The Realm of the Nebulae”, 1936
Heredity or Nature
against
Nurture or Environment
Dressler 1980
R [Mpc]
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projected density
Gabriella De Lucia, November 5, Bologna
Outline
✔ Techniques we use to model galaxy formation in a cosmological
framework (limits & aims)
✔ Overview of the most relevant physical processes, and of their
relative importance at different masses, times, and environments
✔ Critical review of recent progress and open issues.
✔ The role of “heredity”
✔ A brief presentation of the project(s) ongoing in a new group
recently formed in Trieste
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Gabriella De Lucia, November 5, Bologna
A premise
✔ Theoretical (and observational) studies trying to assess the
influence of the environment on galaxy evolution have mostly
focused on galaxy clusters (“good laboratories”, “easy” to find, etc)
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Gabriella De Lucia, November 5, Bologna
A premise
✔ Theoretical (and observational) studies trying to assess the
influence of the environment on galaxy evolution have mostly
focused on galaxy clusters (“good laboratories”, “easy” to find, etc)
✔ Clusters are biased environments and represent rare objects. In
addition, in order to really establish if some cluster-dependent
physics is playing a role, one would need to establish a difference
between the evolution of galaxies in clusters and that of identical
galaxies in the field.
INAF – Astronomical Observatory of Trieste
Gabriella De Lucia, November 5, Bologna
A premise
✔ Theoretical (and observational) studies trying to assess the
influence of the environment on galaxy evolution have mostly
focused on galaxy clusters (“good laboratories”, “easy” to find, etc)
✔ Clusters are biased environments and represent rare objects. In
addition, in order to really establish if some cluster-dependent
physics is playing a role, one would need to establish a difference
between the evolution of galaxies in clusters and that of identical
galaxies in the field.
✔ If we live in a hierarchical Universe, then structure grows
hierarchically. In this framework, a simple distinction between
“nature” and “nurture” is difficult to accommodate and both are
likely playing a role in determining the observed environmental
dependences
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Gabriella De Lucia, November 5, Bologna
Star formation
Cooling
(metallicity, halo
structure, conductivity)
(threshold, efficiency,
initial mass function)
Dust
(formation,distribution,
heating and cooling)
GALAXY
FORMATION
SN Feedback
(IGM heating,
IGM enrichment,
efficiency, winds)
BHs and AGNs
(BH growth, quasar
winds, radio bubbles)
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Mergers and
Galaxy
interactions
(morphological
transformations,
induced star
formation)
Stellar evolution
(spectro-photometric
evolution,
yields,feedback)
Gabriella De Lucia, November 5, Bologna
Dark matter haloes & galaxies #1
✔ Halo occupation models
(bypass modeling of physical processes, provide a statistical
characterization of the link between DM and galaxies)
P(N|M) + spatial distribution
Berlind et al. 2002
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Gabriella De Lucia, November 5, Bologna
Dark matter haloes & galaxies #2
Roediger & Brueggen (2007)
✔ Hydrodynamical simulations
(explicit description of gas dynamics,
limited mass and spatial resolution,
computational time, “sub-grid” physics)
z = 0.8
Courtesy:
Volker Springel
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Gabriella De Lucia, November 5, Bologna
Dark matter haloes & galaxies #3
z=3.
✔ Semi-analytic models
(simple but physically and observationally
motivated prescriptions, large dynamic range,
fast)
Cold Gas
Croton et al. 2006
- AGN heating
Hot Gas
cooling
star formation
feedback
Ejected Gas
Stars
De Lucia et al. 2004, De Lucia & Blaizot 2007
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Kauffmann et al. 1999
re-incorporation
z=1.
z=0.
Gabriella De Lucia, November 5, Bologna
Physical mechanisms
Galaxy mergers:
WHERE : field + low velocity dispersion groups
e.g. Negroponte & White ‘82,
Barnes & Hernquist ‘91, ‘96
Mihos & Hernquist ‘94, ‘96,
WHAT : strong internal dynamical response
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Gabriella De Lucia, November 5, Bologna
Galaxy mergers
Toomre & Toomre,
1972
Springel, PhD Thesis, 1999
M51
Mihos 2004
Barnes & Hernquist, 1996
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Cox, PhD thesis, 2004
Gabriella De Lucia, November 5, Bologna
Galaxy mergers in SAMs
Effective # of mergers
fraction
formation
time
assembly
time
redshift
Mstar [M h-1]
De Lucia et al. 2006
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Observational evidence for
dry mergers (e.g. van Dokkum
2005) but mergers rates are
not accurately measured
Gabriella De Lucia, November 5, Bologna
Physical mechanisms
Galaxy mergers:
WHERE : field + low velocity dispersion groups
e.g. Negroponte & White ‘82,
Barnes & Hernquist ‘91, ‘96
Mihos & Hernquist ‘94, ‘96,
WHAT : strong internal dynamical response
Harassment:
WHERE : in massive clusters
e.g. Spitzer & Baade ‘51,
Richstone ‘76, Farouky &
Shapiro ‘81, Moore et al.
‘96, Moore et al. ‘98
WHAT : some damage but less than mergers –
at least on luminous members
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Gabriella De Lucia, November 5, Bologna
Harassment
Mastropietro et al, 2005
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Gabriella De Lucia, November 5, Bologna
Physical mechanisms
Galaxy mergers:
WHERE : field + low velocity dispersion groups
e.g. Negroponte & White ‘82,
Barnes & Hernquist ‘91, ‘96
Mihos & Hernquist ‘94, ‘96,
WHAT : strong internal dynamical response
Harassment:
WHERE : in massive clusters
e.g. Spitzer & Baade ‘51,
Richstone ‘76, Farouky &
Shapiro ‘81, Moore et al.
‘96, Moore et al. ‘98
WHAT : some damage but less than mergers –
at least on luminous members
Gas stripping:
WHERE : in the central regions of clusters
e.g. Gunn & Gott ‘72, Cowie
& Songaila ‘77, Nulsen ‘82,
Quilis et al. ‘00
WHAT : suppression of star formation and
indirect effect on morphology
INAF – Astronomical Observatory of Trieste
Gabriella De Lucia, November 5, Bologna
Ram-pressure in SAMs
“we find that ram-pressure stripping
is not important for colours and star
formation rates of galaxies in the
cluster core”
Okamoto & Nagashima 2003
B-V
Lanzoni et al. 2005
“including or neglecting ram-pressure
stripping in the model, galaxy
properties only show mild variations”
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r/R200
Gabriella De Lucia, November 5, Bologna
Physical mechanisms
Galaxy mergers:
WHERE : field + low velocity dispersion groups
e.g. Negroponte & White ‘82,
Barnes & Hernquist ‘91, ‘96
Mihos & Hernquist ‘94, ‘96,
WHAT : strong internal dynamical response
Harassment:
WHERE : in massive clusters
e.g. Spitzer & Baade ‘51,
Richstone ‘76, Farouky &
Shapiro ‘81, Moore et al.
‘96, Moore et al. ‘98
WHAT : some damage but less than mergers –
at least on luminous members
Gas stripping:
WHERE : in the central regions of clusters
e.g. Gunn & Gott ‘72, Cowie
& Songaila ‘77, Nulsen ‘82,
Quilis et al. ‘00
WHAT : suppression of star formation and
indirect effect on morphology
Strangulation:
WHERE : anytime the galaxy falls in a larger
system
WHAT : suppression of star formation and
indirect effect on morphology
e.g. Larson, Tinsley &
Caldwell ’80, Balogh,
Navarro & Morris ‘00
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The colour-magnitude bimodality
✔ Tail of blue
bright object
(despite a “strong”
AGN feedback – a
“dust” problem?)
✔ Excess of faint
red satellites
✔ Transition
region not as well
populated as in the
observational data
Quantitatively, the CM bimodality is not well reproduced
(see discussion in De Lucia 2007)
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Gabriella De Lucia, November 5, Bologna
The stripping of the hot reservoir
Strangulation is usually assumed to
be instantaneous.
McCarthy et al. 2008
Transition from blue cloud to red
sequence occurs on very short
time-scales (because there is also
an efficient feedback from
supernovae)
Recent numerical studies suggest
that the stripping of hot gas
occurs on longer time-scales. This
can potentially help keeping
satellite galaxies active for longer
times
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dark matter
gas
Gabriella De Lucia, November 5, Bologna
The colours of satellites
Assume a noninstantaneous stripping
of hot material + this
material can cool on
satellite galaxies
Central galaxies are
basically unaffected but
a larger fraction of
satellites become now
bluer (qualitative
agreement with obs.
data)
See also Kang et al. 2008
Font et al. 2008
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Gabriella De Lucia, November 5, Bologna
Physical mechanisms - continued
WHERE : centre of massive groups/clusters
e.g. Tabor & Binney 1993,
Churazov et al. ‘01, Brueggen
et al. ’02, Sijacki & Springel
’06, +++++++
WHAT : suppression of “cooling flows”
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Bower et al. 2006
McNamara et al. 2005
Croton et al. 2006
AGN heating:
Gabriella De Lucia, November 5, Bologna
Physical mechanisms - continued
AGN heating:
WHERE : centre of massive groups/clusters
e.g. Tabor & Binney 1993,
Churazov et al. ‘01, Brueggen
et al. ’02, Sijacki & Springel
’06, +++++++
WHAT : suppression of “cooling flows”
Cannibalism:
WHERE : groups and clusters
e.g. Ostriker & Tremaine ‘75,
White, ‘76, Makumuth &
Richstone ‘84, Merritt ‘85
WHAT : formation of BCGs?
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Gabriella De Lucia, November 5, Bologna
The merger tree of a BCG
De Lucia & Blaizot 2007
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Gabriella De Lucia, November 5, Bologna
The role of “heredity”
Halo properties do depend on the “environment”:
✔ Present day haloes in clusters are on average more concentrated,
more spherical, and rotate slower than haloes in the field (e.g. AvilaReese et al. 2005, Wechsler et al. 2006)
✔ Haloes in high-density environments form earlier and a higher
fraction of their mass is assembled during major mergers, compared
to haloes in low density environments (e.g. Sheth & Tormen 2004,
Maulbetsch et al. 2007)
This is bound to leave an “imprint” on galaxies that
inhabit different regions today
INAF – Astronomical Observatory of Trieste
Gabriella De Lucia, November 5, Bologna
The role of “heredity”
Gao et al. 2004
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De Lucia et al. 2006
Gabriella De Lucia, November 5, Bologna
The role of “heredity”
Symbols: objects with
M > 1010 M
M = 1.3x1011 M
MV = -22.11
B - V = 0.79
Cluster
M = 1.4x1011 M
MV = -22.15
B - V = 0.77
“Field”
Color-coding: B - V
INAF – Astronomical Observatory of Trieste
Gabriella De Lucia, November 5, Bologna
1 VVDS mock
Masses from SED fitting
The agreement with the
observed mass functions
is quite good. No
significant deficit rather an excess of faint
and intermediate mass
galaxies
Courtesy: Lucia Pozzetti
(see also Stringer et al.
2008)
INAF – Astronomical Observatory of Trieste
Gabriella De Lucia, November 5, Bologna
Conclusions
✔ Unsurprisingly, both heredity and environment affect galaxy
evolution, but what is their relative importance?
✔ Little attention has been devoted so far in “quantifying explicitly
the importance of conditions at formation (nature rather than
nurture). Not surprising either… this is difficult…
✔ We need to have gain a better understanding about physical
processes at the group scale. This is the most common galaxy
environment
✔ We also need to improve (and better understand) our definitions
of environment
INAF – Astronomical Observatory of Trieste
Gabriella De Lucia, November 5, Bologna
Tidal stripping of stars
Stellar Mass [1010 Msun/h]
Saro et al. submitted
Tidal stripping of stars
(stellar halo, intracluster light)
Obs measurements are,
unfortunately, very
uncertain (from few %
to more than 50%!!!)
Lookback time [Gyr]
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Tidal stripping is not
the main channel for the
production of ICL
(Rudick et al. 2006,
Murante et al. 2007).
Unfortunately, results
do not converge.
Gabriella De Lucia, November 5, Bologna