1. Observing the formation and evolution of massive galaxies
Andrea Cimatti
University of Bologna – Department of Astronomy
“Towards the science case for E-ELT HIRES” – IoA, Cambridge, September 2012

2. Why ? Physical processes of mass assembly
Pozzetti et al. 2010
50%
mass
built
Physical processes of
mass assembly
Crucial test for mass assembly
history in ΛCDM cosmology
Cosmological applications
with passive ellipticals
Why ?

3. Early-Type Galaxies (ETGs): solid results at z<1
Oldest, passive, most massive
Downsizing evolution
Nearly constant number density

4. (I) (II) (III) sSFR Schematic Evolution of Massive Galaxies Redshift
(SFR/M*)
Star-forming
(I)
AGN
Post Starburst
(II)
E/S0
Quiescent
/Passive
(III)
Redshift

5. Phase I – The star-forming precursors at z ≥ 2 ?
Daddi et al. 2004
Halliday et al. 2008
Tecza et al. 2004
Shapiro et al. 2009
Dusty EROs, sBzK, DRGs, SMGs, ULIRGs…
SFR up to ~ 200+ Msun/yr
SFR – M* correlation
M* up to ~ 1011 Msun
High sSFR
Nearly solar gas metallicity for most massive ones
Massive disks or mergers
M(cold gas) ~ Msun (from CO)
Higher gas fraction than at z=0
M(dust) ~ Msun
SMGs : compact and dense (size : 1-2 kpc)
Fraction of AGN increases with mass
Strongly clustered (r0 ~ 8-11 h-1 Mpc)
Tacconi
et al. 2008

6. Phase II and III – From Post-starburst to Passive
Gobat et al. 2012
z=2.99
HST+WFC3
z=2.04 (Toft et al. 2012, VLT+X-shooter)
z(spec)max ~ 3
Low sSFR to passive
Ages >1- 3 Gyr, Z ≈ ZSun ?
zform>2–4
τ ≈ 0.1 – 0.3 Gyr
M* up to ~ M⊙
3x smaller (10x denser)
HST+ACS
Cimatti et al. 2008
Whitaker et al. 2011
Cimatti et al. 2008, VLT+FORS2
1.4<z<2 (Onodera et al. 2012, Subaru+MOIRCS)

7. Passive galaxies at even higher redshifts ?
z J H K μm μm μm μm μm
dusty
passive?
Rodighiero et al. 2007
Dominguez-Sanchez et al. 2011
Photometric candidates
3 < z < 6(?!)
10.8 < log M* < 11.5 M⊙
Ages ~ 0.2 – 0.8 Gyr
AV ~ 0 – 1
IRAC 3 -8 μm
K(AB) ~ => EELT + JWST !
Dunlop et al. 2006, Brammer et al. 2006, Wiklind et al. 2007, Mancini et al. 2008, Fontana et al. 2009, Marchesini et al. 2010

8. Main Open Questions Precursors ? Formation mechanism(s) ?
Size Growth ?
Mass growth ?
Mode(s) and suppression of star formation ?
Role of AGN ?
Fit into ΛCDM scenario of structure formation ?

9. Current limitations - Generally faint targets
K ≈ (AB)
Current limitations
- Generally faint targets
- Passive: red continuum, no emission lines
- Optical and NIR spectra needed
- R> ,000: challenging or impossible
Passive ETG
VLT + FORS2
~30h integration
K ~ 21.5 (AB)
I~ 25
z=2.04 (Toft et al. 2012, VLT+X-shooter)
VLT + X-shooter
K ~ 20.2 (AB)
J ~ 20.9
R~ 23.5
B ~ 24.8

10. Requirement Why ? Main Science Spectral Coverage Spectral Resolution
Simultaneous
Optical (λmin ~0.35 μm for Lyα at z=2) + YJHK
Several science cases
Stellar populations, emission line ratios, extinction, metallicity, star formation, SFH, AGN…
Spectral Resolution
(~1000 ?) – 10,000
R~1000: identification and characterization of faint rare targets from wide-field surveys (e.g. Euclid)
Mergers, scaling relations, kinematics, feedback, stellar & ISM absorption lines (e.g. metallicity, cold flows, …)
Multiplexing
FoV ~ 30”+ (diameter)
N ~ 10+
BzK galaxies in the field:
sBzK: arcmin-2 to K~ (AB)
pBzK: 0.1 arcmin-2 to K~ (AB)
Densities up to 10x in densest environments
Protoclusters
High-density fields around AGNs
Galaxy gaseous halos connection with IGM AO
Moderate (at most)
Galaxy sizes ~0.1” - 1”
S/N for small targets
Fiber vs Slit
Narrow slits (e.g. 0.3”)
IFU
Desirable
Internal properties
Kinematics, gradients
Sensitivity
K(AB)=22, seeing limited,
0.8” seeing, 0.8” slit, point source, R=10,000, R(S/N)=0,4” S/N~10 in 4h (ETC V2.14)
K(AB)=24.0
R=1000(0)
4(40)h to reach S/N=5

11. Wide spectral range needed Example of JHK spectrum
Submm-selected starburst galaxy at z=2.56
VLT+SPIFFI
K ~20 (AB)
Example of JHK spectrum
Wide spectral
range needed
Tecza et al. 2004
Example of optical + JHK spectrum
Compact quiescent galaxy at z=1.8
VLT+ X-shooter
van de Sande et al. 2011

12. Intermediate spectral resolution needed
Example of optical spectroscopy of star-forming galaxies at z≈ 2
VLT + FORS2 + grism 300V
equivalent to 800 hours integration !
Intermediate spectral resolution needed
GMASS; Halliday et al. 2008

13. Examples of MOS benefits (I)
Overdensity around radio galaxy at z = 2.2
(Miley et al. 2006)
Protocluster at z = 2.07 (Gobat et al. 2011)
Kurk et al. 2009
passive ETG triplet in a
protocluster at z=1.61
1.4’
21”

14. Examples of MOS benefits (II)
Giavalisco
et al. 2011
15”
Cold (T~104 K), chemically young
gas seen in absorption in an
overdensity of galaxies at z=1.6
using spectra of background
LBGs at z>3
The gas does not belong to
galaxies,but it is diffuse
Large scale infall motion ?
Accretion of cold gas onto galaxies ?
Feeding star formation ?
GMASS

15. Conclusions EELT+HIRES VLT Key and broad science case
Wide range of galaxy properties
=> Multi-purpose instrument
VLT
EELT+HIRES
R ~ 10,000 (1000?)
Simultaneous Optical + YJHK
MOS
Moderate AO + slit