Thermal evaporation,
AGN feedback
and quenched star formation
in massive galaxies
Carlo Nipoti
Dipartimento di Astronomia
Università di Bologna
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Chandra NGC 4649 (Randall et al.)
Carlo Nipoti - Vulcano, May 2008
OUTLINE
 Why are L>L* galaxies red and dead?
 The role of AGN feedback & thermal evaporation
 What happens at L<L*?
 The origin of the core/cusp dichotomy of ellipticals
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Carlo Nipoti - Vulcano, May 2008
BLUE CLOUD & RED SEQUENCE GALAXIES
<- Truncation of the blue cloud
Red sequence
Colour
Blue cloud
SDSS
Baldry et al 2004
L≈L*
<- Luminosity
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Carlo Nipoti - Vulcano, May 2008
Why are L>L* galaxies red and dead?
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Carlo Nipoti - Vulcano, May 2008
A critical halo mass
Mcrit = 1012 Msun
(Mcrit L* )
Shock heating
Mshock > Mshock ~ Mcrit
(Binney 1977; Dekel & Birnboim 2003, Keres+ 2005)
Trapping SN-heated gas
Mhalo > MSN ~ Mcrit
(Dekel & Silk 1986)
Halos with Mhalo>Mcrit accumulate dense hot (Tvir) gas
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Carlo Nipoti - Vulcano, May 2008
The role of (radio) AGN feedback
Hot gas remains hot and does not form stars
because:
- it can cool only in the centre
- in the centre it is re-heated by radio-AGN feedback
From observations of cooling flows (e.g. Birzan et al. 2004; Binney 2004)
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The role of thermal evaporation
in Mhalo>Mcrit halos:
In principle cosmic infall and gas-rich merging might restart star formation
BUT
Cool gas can be eliminated via ablation and thermal evaporation by hot gas
(Nipoti & Binney 2007)
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MODELING OF THERMAL EVAPORATION IN
GALAXIES
(Nipoti & Binney 2007)
- Cool (T≈104 K) clouds infalling in hot (Tvir≈106-107 K) ISM
- Minimum rate of ablation
- The fate of a cool clouds depends on its mass
(Cowie & McKee 1977)
Mcloud < Mmin => evaporation
Mcloud > Mmin => star formation
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Carlo Nipoti - Vulcano, May 2008
TWO MODEL GALAXIES
HIGH-MASS (HM)
T=107 K Mgal=3x1011 Msun
Mhalo>Mcrit
LOW-MASS (LM)
T=2.5x106 K Mgal=3x1010 Msun
Mhalo <≈ Mcrit
(Nipoti & Binney 2007)
Model can be applied to any galaxy with known T(r) and ne(r) of ISM
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MINIMUM CLOUD MASS TO SURVIVE EVAPORATION
Mhalo>Mcrit ---->
Mhalo <≈ Mcrit ---->
(Nipoti & Binney 2007)
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Carlo Nipoti - Vulcano, May 2008
MINIMUM MASS NORMALIZED TO GALAXY MASS
HIGH-MASS
Mhalo>Mcrit
Mmin/Mgal
LOW-MASS
Mhalo <≈ Mcrit
(Nipoti & Binney 2007)
CLOUD ELLIPTICITY
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Carlo Nipoti - Vulcano, May 2008
WHY ARE L>L* GALAXIES RED AND DEAD?
(summary)
Quenching of star-formation
Lack of cold gas
Galaxies with Mhalo>1012Msun accumulate hot (Tvir) gas
Tvir gas is kept hot
Accreted cold gas is heated
by
by
radio-mode AGN feedback
(+ other mechanisms?)
ablation & thermal evaporation
(+ other mechanisms?)
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What happens at L<L*?
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AT L<L* ENVIRONMENT IS IMPORTANT
Galaxies with Mhalo<1012Msun have lower-n, lower-T atmosphere
Thermal evaporation by the ISM is not efficient
Cold gas available in
prmary haloes
(field galaxies)
Blue cloud
Lack of cold gas in
secondary haloes
(cluster galaxies)
Red sequence
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The cusp/core dichotomy within the red sequence
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A DICHOTOMY WITHIN THE RED SEQUENCE
Truncation of the blue cloud
Core galaxies
Power-law galaxies (cuspy)
Red sequence
Colour
SDSS
Baldry et al 2004
Blue cloud
L≈L*
<- Luminosity
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Carlo Nipoti - Vulcano, May 2008
CENTRAL SB PROFILE OF RED SEQUENCE
GALAXIES
Core galaxies (<0.3)
Power-law galaxies (>0.5)
Graham et al (2003)
- Power law <=> dissipation Larson (1974)
- Cores <=> dissipationless dynamics (binary BHs?)
Begelman+ (1980)
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CORE
GALAXIES
POWER-LAW GALAXIES
Higher LB
Lower LB
High LX/LB
Low LX/LB
NO stellar nuclei
Stellar nuclei
Faber et al. (1997)
Pellergini (2005)
Coté et al. (2006)
NO central disks
Central disks
Lauer et al. (2005)
Radio-loud AGN
Radio-quiet AGN
De Reuter et al. (2005)
Lower L/LEdd AGN
Higher L/LEdd AGN
Capetti & Balmaverde (2006)
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OPEN QUESTIONS
1) Why are CGs luminous and PLGs fainter?
(no characteristic mass in purely stellar dynamical processes!)
2) Why does the central slope correlate with diffuse LX?
3) Why does the central slope correlate with AGN properties?
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A SCENARIO FOR THE ORIGIN OF THE DICHOTOMY
Nipoti & Binney (2007)
§ All Es at some stage of evolution have central cores
§ All Es accrete cold gas
§ In hot-gas poor Es cold gas can form stars in the centre
(=> core refilled => PLGs)
§ In hot-gas rich Es cold gas is evaporated
(=> core preserved => CGs)
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Support from observations: new correlation for Es
CENTRAL SLOPE vs CENTRAL AGE OF STARS
CGs
Nipoti & Binney (2007)
PLGs
data from Lauer et al. (2007), McDermid et al. (2006, SAURON)
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LOW-MASS
ELLIPTICALS
Mgal<1011Msun (Mhalo<1012Msun)
HIGH-MASS ELLIPTICALS
Mgal>1011Msun (Mhalo>1012Msun)
X-ray faint
X-ray bright
no evaporation
cold gas available
central
starbursts
core refilled
(PLG)
cold mode AGN
“higher” L/LEdd
evaporation
no cold gas available
no central
starbursts
hot-mode AGN
core preserved
(GC)
“lower” L/LEdd
radio quiet AGN
stellar nucleus/disk
radio loud AGN
no stellar nucleus/disk
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CONCLUSIONS
1) L>L*: Radio-mode feedback + thermal evaporation => “red and dead”
2) L<L*: primary halo => cold gas available => blue cloud
secondary halo => lack of cold => red sequence
3) Thermal evaporation can explain the core/cusp dichotomy of Ellipticals
Ultimately the energy for quenching star-formation comes from black holes,
which act as thermostats for Tvir gas
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