Transcript Mobasher

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)
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/coevolution?
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
Use near– and mid–IR to select high redshift and evolved galaxies?
The Balmer break is a prominent feature for stellar populations age t > 100 Myrs
z=7
no extinction
t = 50 Myr
t = 100 Myr
t = 300 Myr
t = 500 Myr
t = 600 Myr
t = 800 Myr
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
Model tracks from BC03
•z=5
•z=8
•z=5
•z=8
•z=5
•z=8
•z=5
•z=8
•z=2
•z=4
Post-starburst galaxies (age 0.2–1.0 Gyr)
Elliptical (age > 3 Gyr)
Dusty starburst galaxies
•z=2
•z=4
K-selected sample from GOODS-S
HST/ACS (BViz);
VLT/ISAAC (JHKs);
SST/IRAC (3.6, 4.5, 5.8, 8mm)
5754 sources
155 / 85 selected; 14/12 z > 5 (total 17)
~82% complete at KAB = 23.5
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
t = 0 - 1.0 Gyr
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
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
Pure AGN SEDs
AGN + dust
(NGC6240)
QSO (type 2)
Stellar Component
Pure Starburst SEDs
Pure starburst SEDs:
Arp220
M82
The template SEDs
contain significant
extinction
Obscured AGN+Starburst SED
Mkr231 SED:
Stellar+ AGN-heated dust
with an intense starburst
at the center.
Large Infrared luminosity
Stellar Component
Higher Redshift Counterparts
JD2 (J-dropout) in HUDF
(Mobasher et al. 2005)
z = 6.5
no current star formation
age ~ 0.65 – 1.0 Gyr
EB-V = 0.0
M* = 5 1011 Mo
Z ~ 0.2 – 1.0 Zo
z
EB-V
age
t
M*
= 5.6
= 0.025
= 0.8 Gyr
= 0.2 Gyr
= 1 1011 Mo
z
EB-V
age
t
M*
= 4.9
= 0.150
= 1.0 Gyr
= 0.3 Gyr
= 2 1011 Mo
zspec = 5.554
Vanzella et al. 2006
Stellar mass density
The stellar mass density
derived from M*~1011 Mo
at z~5.4 and z~4.5 appear
consistent with the observed
decrease with redshift
from Yan et al. 2006
(Yan et al. 2006)
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