Galaxy evolution studies at 0<z<2 with PFS
1 – statistical nature of galaxy properties
2 – science cases from the white paper

Masayuki Tanaka

Statistical nature of galaxy properties
I know this is just like preaching the Buddha...

Galaxies form from density fluctuations

Galaxy formation takes place at peaks ofdensity fluctuations – galaxy formation is astatistical event!
Not surprisingly, each galaxy form andevolve in different ways and the only way
to characterize the galaxy evolution is tostudy galaxies in a statistical way.

How do we characterize the galaxy evolution?
SFR= f (time, environment, mass, merger, AGN, etc)

Stellar mass = g (time, environment, mass, SFR, merger, etc)
Metallicity = h (time, environment, mass, SFR, etc)
We need a statistical sample of galaxies with least possible selection biases
AGN rate=(time,environment,mass, SFR, merger, etc)
to isolve
thesegalaxy equations.
Merger rate = j (time, environment, mass, etc)
How does PFS compare to the on­going surveys?
Morphology = k (time, environment, mass, SFR, merger, etc)
Size= l (time, environment, mass, merger, etc)

etc..
The galaxy evolution is not a single equation. We have a set of parameters and wehave to solve all the equations simultaneously. Only when we find a parameter set
that satisfies all the equations, we can say 'we understand the galaxy evolution'.

zCOSMOS – a flux­limited survey to i=22.5

Primary features
down to m*

Secondary features
down to m*

Primary/secondaryfeatures for thebrightest galaxies(m*­1.5)

zCOSMOS – a flux­limited survey to i=22.5
Red symbols : quiescent galaxies

Blue symbols: star forming galaxies

Primary features : spectral features that provide well­calibrated
measurements.
Secondary features: spectral features that provide 'reasonable'measurements.

We model the evolution of m* (characteristic magnitude of theSchechter function) to quantify up to what redshfit we canstudy typical galaxies.
Primary features
down to m*

Secondary features
down to m*

Primary/secondaryfeatures for thebrightest galaxies(m*­1.5)

zCOSMOS – a flux­limited survey to i=22.5

Primary features
down to m* (SDSS­
like survey)

Secondary features
down to m*Primary/secondaryfeatures for thebrightest galaxies(m*­1.5)

PFS (with NIR) – a flux­limited survey to z=22.5

Primary features
down to m* (SDSS­like survey)

Secondary features
down to m*

Primary/secondaryfeatures for thebrightest galaxies(m*­1.5)

PFS (no NIR) – a flux­limited survey to z=22.5

Primary features
down to m* (SDSS­
like survey)

Secondary features
down to m*

Primary/secondaryfeatures for thebrightest galaxies(m*­1.5)

Comparison of the surveys
zCOSMOS down to i=22.5
To solve the galaxy equations, we needgood measurements of galaxy properties
over a wide redshift range.
Which one gives us good measurementsof all the properties over the widest
redshift range?
PFS with nearIR down to z=22.5

PFS with no nearIR down to z=22.5

So, the best one is PFS with NIR

The existing surveys do not allow us to solve all the galaxy equations
simultaneously. A large survey with PFS with nearIR arm will be the first
one to deliver a data set to do this job at z>0.
PFS delivers:
0<z<1 : a perfect data set to study the galaxy evolution
1<z<1.5: the first statistical sample of bright galaxies
1.5<z<2: the first statistical sample of bright, star­forming galaxies

Science cases from the white paper
I'm going to discuss galaxy properties as functions ofenvironment, mass and time. This is very complicated.
But, don't panic! The message here is that the current
galaxy studies are sort of 'patch work' and we do not havea big picture of galaxy evolution yet.

Star formation histories

Colors (approx. SFRs) depend on environment
and mass. The most massive galaxies show little
dependence on environment, while low­massgalaxies do.
Make this plot at 0<z<1.5 in fine redshift bins
(and replace colors with SFRs)!

Peng et al. 2010

Star formation histories
At z=1.2, we still observe the clear red
sequence in clusters, while the sequence issharply truncated at Ks=22 in groups.

The fraction of quiescent galaxies is higher
at >10^11 M_sun. The fraction is similar atlower mass.

In the last slide, we saw that the most
massive galaxies do not depend onenvironment. But, massive galaxies at z>1
depend more strongly on environment thanlower mass galaxies.
Tanaka et al. 2007

Star formation histories
At z=1.2, we still observe the clear red
sequence in clusters, while the sequence issharply truncated at Ks=22 in groups.

The fraction of quiescent galaxies is higher
at >10^11 M_sun. The fraction is similar atlower mass.

Tanaka et al. in prep.

In the last slide, we saw that the most
massive galaxies do not depend onenvironment. But, massive galaxies at z>1
depend more strongly on environment thanlower mass galaxies.

Stellar mass assembly histories

Stellar mass functions in thefield at 0<z<1.5 are fairly wellconstrained except for the most
massive end.
But, how does the stellar massassembly depend onenvironment?

Ilbert et al. 2009

Metal enrichment histories
z=00.2 < z < 1.2Peres­Montero et al. 2009

Tremonti et al 2004

Very poor statistics. I'm sure that PFS will
dramatically improves the situation.

AGN evolution (see Imanishi­san's talk)Kauffmann et al. 2003

We don't know how the AGN fraction depends on mass and environment at highredshift. Some work on X­ray AGNs has been made, but X­rays find a small fractionof the overall AGN populations. PFS allows us to study emission line AGNs in all
the environments up to z=1.

How do we characterize the galaxy evolution?
SFR= f (time, mass, environment, merger, AGN, etc)

Stellar mass = g (time, mass, environment, SFR, merger, etc)
Metallicity= h (time, mass, environment, SFR, etc)

AGN rate= i (time, mass, environment, SFR, merger, etc)

Merger rate = j (time, mass, environment, etc)
Morphology = k (time, mass, environment, SFR, merger, etc)
Size= l (time, mass, environment, merger, etc)

etc...
So far, galaxy evolution studies at z>0 are sort of 'patch work' and we are still far
from understanding the whole set of equations. SDSS provided an excellent data
set to study many of the equations at z=0. PFS will deliver a data set that allows us
to extend the SDSS up to z=1.5 for the first time.

Summary– Galaxies are statistical objects. Their properties can be studied only statistically.
– The galaxy evolution is multi­parameter equations.
Need to solve them simultaneously with least biased statistical galaxy sample.
– The on­going surveys do not deliver good enough data sets for us.
– PFS survey will be the one to solve the equations up to z=1.5.

Summary– Galaxies are statistical objects. Their properties can be studied only statistically.
– The galaxy evolution is multi­parameter equations.
Need to solve them simultaneously with least biased statistical galaxy sample.
– The on­going surveys do not deliver good enough data sets for us.
– PFS survey will be the one to solve the equations up to z=1.5.

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