1 carlo nipoti dipartimento di astronomia università di bologna thermal evaporation, agn feedback...
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Carlo Nipoti
Dipartimento di Astronomia Università di Bologna
Thermal evaporation, AGN feedback
and quenched star formation in massive galaxies
Chandra NGC 4649 (Randall et al.) Carlo Nipoti - Vulcano, May 2008
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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
Carlo Nipoti - Vulcano, May 2008
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BLUE CLOUD & RED SEQUENCE GALAXIES
Colour
<- Luminosity
<- Truncation of the blue cloud
Red sequence
Blue cloudSDSSBaldry et al 2004
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L≈L*
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Why are L>L* galaxies red and dead?
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A critical halo mass
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
Mcrit = 1012 Msun
(Mcrit L* )
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The role of (radio) AGN feedback
Hot gas remains hot and does not form stars
because:
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- 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 principle cosmic infall and gas-rich merging might restart star formation
BUT
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Cool gas can be eliminated via ablation and thermal evaporation by hot gas (Nipoti & Binney 2007)
in Mhalo>Mcrit halos:
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MODELING OF THERMAL EVAPORATION IN GALAXIES
(Nipoti & Binney 2007)
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- 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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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
Model can be applied to any galaxy with known T(r) and ne(r) of ISM
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(Nipoti & Binney 2007)
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MINIMUM CLOUD MASS TO SURVIVE EVAPORATION
Mhalo>Mcrit ---->
Mhalo <≈ Mcrit ---->
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(Nipoti & Binney 2007)
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MINIMUM MASS NORMALIZED TO GALAXY MASS
Mmin/Mgal
HIGH-MASS
LOW-MASS
CLOUD ELLIPTICITY
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(Nipoti & Binney 2007)
Mhalo>Mcrit
Mhalo <≈ Mcrit
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WHY ARE L>L* GALAXIES RED AND DEAD?(summary)
Galaxies with Mhalo>1012Msun accumulate hot (Tvir) gas
Tvir gas is kept hot
Quenching of star-formation Lack of cold gas
Accreted cold gas is heated
by
radio-mode AGN feedback (+ other mechanisms?)
by
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)
Lack of cold gas in secondary haloes(cluster galaxies)
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Red sequenceBlue cloud
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The cusp/core dichotomy within the red sequence
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A DICHOTOMY WITHIN THE RED SEQUENCE
Colour
<- Luminosity
Core galaxies Power-law galaxies (cuspy)
SDSSBaldry et al 2004
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Truncation of the blue cloud
Red sequence
Blue cloud
L≈L*
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CENTRAL SB PROFILE OF RED SEQUENCE GALAXIES
Core galaxies (<0.3)
Graham et al (2003)
Power-law galaxies (>0.5)
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- Power law <=> dissipation - Cores <=> dissipationless dynamics (binary BHs?)
Larson (1974)
Begelman+ (1980)
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Higher LB
High LX/LB
NO stellar nuclei
NO central disks
Radio-loud AGN
Lower L/LEdd AGN
Lower LB
Stellar nuclei
Central disks
POWER-LAW GALAXIES
Radio-quiet AGN
Higher L/LEdd AGN
Low LX/LB
Faber et al. (1997)
Pellergini (2005)
Coté et al. (2006)
Lauer et al. (2005)
Capetti & Balmaverde (2006)
De Reuter et al. (2005)
CORE GALAXIES
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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
§ 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)
Nipoti & Binney (2007)
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CENTRAL SLOPE vs CENTRAL AGE OF STARS
data from Lauer et al. (2007), McDermid et al. (2006, SAURON)
CGs
PLGs
Support from observations: new correlation for Es
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Nipoti & Binney (2007)
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Mgal<1011Msun (Mhalo<1012Msun)
X-ray faint
no evaporation
central starbursts
cold gas available
core refilled (PLG)
stellar nucleus/disk
cold mode AGN
“higher” L/LEdd
radio quiet AGN
HIGH-MASS ELLIPTICALS
Mgal>1011Msun (Mhalo>1012Msun)
X-ray bright
evaporation
no central starbursts
no cold gas available
core preserved (GC)
no stellar nucleus/disk
hot-mode AGN
“lower” L/LEdd
radio loud AGN
LOW-MASS ELLIPTICALS
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CONCLUSIONS1) 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
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Ultimately the energy for quenching star-formation comes from black holes, which act as thermostats for Tvir gas