Observing the Feedback Process?
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Observing the Feedback Process?
Peter Capak (SSC-Caltech)
Nick Scoville (Caltech)
Mara Salvato (MPIA- Garching)
Dan Masters (UC Riverside)
Tommy Wiklind (ESO-ALMA)
Bahram Mobasher (UC Riverside)
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Questions• What are the parameters affecting the
feedback process?
• What are the relative contributions of starburst and AGN to the feedback
process?
• What is the observational evidence for the starburst-AGN connection/co-
evolution?
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AIM• Find galaxies while undergoing the
feedback process- by star formation or AGN
• This needs selection of evolved galaxies with high stellar mass at relatively high
redshifts, hosting AGN• Select bright enough galaxies to allow
follow-up spectroscopy
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z = 7
no extinction
t = 50 Myrt = 100 Myrt = 300 Myrt = 500 Myrt = 600 Myrt = 800 Myr
The Balmer break is a prominent feature for stellar populations age t > 100 Myrs
Use near– and mid–IR to select high redshift and evolved galaxies?
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Source Selection• Construct a Spitzer/IRAC 4.5 micron
selected sample, using COSMOS data• This corresponds to a “mass-selected”
sample at z~2-5
• Select galaxies with zphot > 4 from this sample
• Select objects with bright IRAC ch1 and ch2 fluxes (high mass & evolved systems)
• Objects with marginal or no detection at optical bands
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• z = 5• z = 8
• z = 5• z = 8
• z = 2• z = 4
• z = 5• z = 8
• z = 5• z = 8
• z = 2• z = 4
K-selected sample from GOODS-S
HST/ACS (BViz);VLT/ISAAC (JHKs);
SST/IRAC (3.6, 4.5, 5.8, 8m) 5754 sources
155 / 85 selected; 14/12 z > 5 (total 17)
~82% complete at KAB = 23.5
Model tracks from BC03
Post-starburst galaxies (age 0.2–1.0 Gyr)Elliptical (age > 3 Gyr)
Dusty starburst galaxies
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Stellar Population Models
Population synthesis models (Bruzual & Charlot 2003):• Redshift range z = 0.2 - 8.6• Age range = 5 Myr - 2.4 Gyr• Calzetti attenuation law EB-V = 0.0 - 1.0• IGM absorption• Metallicities Z = 0.2, 0.4 1.0, 2.5 Zo
• Salpeter IMF: 0.1 – 100 Mo
• Star formation history: exponentially declining SFR = 0 - 1.0 Gyr
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Fit to the Stellar Component
Redshift 4.37
EB-V = 0.20
Age (Gyr) = 1.4
SF time-scale (Gyr) =0.6
Log(M*) = 11.10 Msun
Corrected for dust
Not corrected for dust
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Observations at longer Wavelengths
• The source is detected at 24 micron• At 4.5-24 microns the SED has a power-law
shape. • the galaxy is not detected at mm wavelengths with IRAM; at sub-mm (1.2 mm) with MAMBO;
at radio continuum (1.4 GHz) and X-ray.• The absence of sub-mm and mm flux implies
there is little or no cold dust => no on-going star formation activity
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Pure AGN SEDs
AGN + dust
(NGC6240)
QSO (type 2)
Stellar Component
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Pure Starburst SEDs
Pure starburst SEDs:
Arp220
M82
The template SEDs contain significant extinction
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Obscured AGN+Starburst SED
Mkr231 SED:
Stellar+ AGN-heated dust with an intense starburst at the center.
Large Infrared luminosity
Stellar Component
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Higher Redshift Counterparts
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JD2 (J-dropout) in HUDF(Mobasher et al. 2005)
z = 6.5no current star formationage ~ 0.65 – 1.0 GyrEB-V = 0.0M* = 5 1011 Mo
Z ~ 0.2 – 1.0 Zo
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z = 5.6EB-V = 0.025age = 0.8 Gyr = 0.2 GyrM* = 1 1011 Mo
z = 4.9EB-V = 0.150age = 1.0 Gyr = 0.3 GyrM* = 2 1011 Mo
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Vanzella et al. 2006
zspec = 5.554
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(Yan et al. 2006)
Stellar mass densityfrom Yan et al. 2006
The stellar mass densityderived from M*~1011 Mo
at z~5.4 and z~4.5 appearconsistent with the observeddecrease with redshift
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Conclusions• The discovered galaxy appears to be a lower redshift counterpart of the more distant (old and
evolved) systems• It has gone through intense star formation
activity (77 Msun/year)
• Given that there is an AGN at the core of the galaxy, the SF is not the only process responsible
for removal of gas• Number density of these galaxies strongly constrains the CDM models for formation of
galaxies