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Evoluzione delle galassie e loro dipendenza dall’ambiente
Marco Castellano
Universita' “(La) Sapienza”Dottorato in Fisica XXI ciclo
Roma
16.10.2008
Thesis Advisor
Prof D. Trevese
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Introduction: Short Summary of the History of the Universe
The Cosmic Microwave Background is not homogeneous: its fluctuations, that reflectsthe quantum fluctuations at the birth of the universe, will evolve in presentday galaxies and clusters.
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Structure Formation in 3D:
from the (nearly) homogeneous universe of the CMB to present day structures
From z=30 (0.1 Gyr after the Big Bang)
to z=0(today, ~14 Gyr after the BB)
T6group Los Alamos
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A huge variety of galaxies have formed in these 14 Gyr
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Observations show that their properties evolved with cosmic time
The formation of stars inside galaxies reached a maximum and then decreased
Through Star Formation the visible mass grew with time
Galaxies merged and increased their sizes
The activity of the central black holes also reached a maximum and then decreased, regulating the cooling of baryonic mass and star formation
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But they did not evolve in isolation!
They interacted, merged and built up groups and clusters:
T6group Los Alamos
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Clusters are among the most important astrophysical objects:
They are composed by hot gas (plasma) and hundreds of galaxies
Brehmsstraluhng emission (Xray) Stellar emission (visibleIR)
but their main component is dark matter!
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Zwicky was the first to hypothesize the existence of dark matter computing the mass of the Coma cluster (1933): clusters collapse because of the DM potential wells while the universe evolve
Today we can use the abundance of galaxy clusters to constrain the density of the different ingredients of the universe.
blue: dark matterdistribution inferredfrom galaxy lensing
red: Xray emission from hot plasma
lines: galaxy distribution
A merging between two clusters (“Bullet Cluster”):
Markevitch 2007
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Galaxy populations inside clusters are different
In general we have two populations (bimodality): blue/late type and red/early type galaxies,
1) In clusters there are mainly elliptical/red galaxies: i.e. galaxies with old stellar populations:
This is very evident in local clusters.
But at higher redshift thefraction of red galaxies inoverdensities decrease.
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2) Their brightest galaxies form a tight sequence: brighter galaxies are redder, i.e. they have more emission at longer opticalIR wavelenghts
It is evident also in distant massive clusters
log(
Flu
x(52
0 n
m)/
Flu
x(36
0 n
m))
log(Flux(520 nm))
Bower 1992
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1) Segregation of red galaxies:
Biased galaxy formation (“Nature” scenario)
Effects of the environment that transform blue/late galaxies in red/early galaxies (“Nurture” scenario)
Ram Pressure Stripping: removal of galactic gas by pressure exerted by the ICM (Gunn & Gott 1972).
Thermal Evaporation and Turbulent/Viscous Stripping of the galactic gas (Cowie & Songaila 1977; Nulsen 1982).
Pressure Triggered Star Formation (Evrard 1991).
Star formation rate increased by Tidal Compression of Galactic Gas (Byrd & Valtonen 1990)
Tidal Truncation of the outer galactic regions (Merritt 1983).
Mergers leading to bursts of star formation (Mihos 1995).
Harassment (Moore et al. 1996, 1998), i.e. high speed galaxy encounters removing galactic gas.
Theory
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2) Colour Magnitude relation ('red sequence') of early type galaxies:
Effects of Supernova Winds: the heating of the interstellar medium by supernovae in the initial starburst triggers the formation of a galactic wind when the thermal energy of the gas exceeds the gravitational binding energy:
Wind ejects the gas in
lowmass galaxies
More massive galaxies retain enriched supernova
ejecta
Stellar populations with higher metallicity
have redder colours
= MassMetallicity* relation
Met
alli
city
log(M/M_sun)
*[Fe/H] =log(N
Fe/N
H)
starlog(N
Fe/N
H)
sun
Arimoto&Yoshii 87
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The Goals of the Present Work
1) Find a way to detect distant, forming clusters:
To investigate all the astrophysical (and cosmological) problems involved in the evolution of clusters we have first to resolve the astronomical problem of detecting them!
What we have done: build an algorithm to detect clusters from multiwavelenght surveys, the redshift of the objects is determined with photometry, not with spectroscopy
2) Extend our knowledge on the evolution of galaxies in clusters
Building a self consistent scenario for the evolution of galaxies as a function of the environment is essential to individuate the role of different physical mechanisms in structure formation
What we have done: study of two deep multiwavelenght surveys (K20 and GOODS)
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Task one:
Detecting Galaxy Clusters with Photometric Redshifts
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A photometric estimate of the redshift of a galaxy can be obtained from multiwavelength data through a reconstruction of the galaxy SED (e.g. 2 fitting in redshiftcolour space using libraries of synthetic templates):
Photometric redshifts have been used to study Luminosity Functions, Mass Functions, the evolution of the Star Formation Rate through cosmic time etc.But these quantities only describe the average evolution of galaxy populations!
2)
1) 2)
U360nm
B420nm
V520nm
R650nm
I800nm
J1250nm
K2200nm
1)
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To better exploit multiwavelength data (e.g. the GOODS field) we developed a method to detect overdensities using photometric redshifts (Trevese et al. 2007 A&A 463; Castellano et al. 2006 MSAIS 9).
Given the large uncertainties we divide the survey volume in cells whoseextension in different directions depends on the relevant positional accuracy, and thus are elongated in the radial direction.
For each cell we count neighbouring objects of increasing distance, until a number n of objects is reached and define an associated density:
=Vn
We take into account the increase of limiting luminosity with increasing redshift assigning a weight w(z) to each object:
1w z
=∫−∞
Ml im z
M dM
∫−∞
Mc
MdM
On the basis of our knowledge of the LF we assume a reference redshift zc below which
we detect all objects brighter than the relevant Mc M≡
lim(zc)
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But there is still the possibility to statistically individuate overdensities.
The drawback is that the uncertainties are much larger than in the case of spectroscopic observations! A typical relative redshift uncertainty: z = |zΔ
spec − z
phot|/(1 + z) 0.05 ≈
The uncertainty on the recession velocity of a galaxy is bigger than the velocity dispersion of a rich cluster!
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Task two:
Analysis of Deep Photometric Surveys
The K20 Survey
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In a first application on the field of the K20 survey we detected two overdensities (Trevese et al. 2007, A&A 463). One is a known extended Xray source at z~0.73 and the other is a group at z~1.04 The density maps projected on the plane of the sky:
From a statistical background/foreground subtraction we estimated that they are poor clusters (richness class 0 in the Abell classification). From the distribution of photometric redshifts a third clump appears at z~1.55 – 1.6
Trevese et al. 2007
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Result: we confirm that the slope of the colour magnitude relation is constant up to z ~ 1Sl
op
e
Age of the UniverseTrevese et al. 2007
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Result: we find that at z ~ 1 the fraction of red galaxies at high density is lower than at lower z. Something has changed in less than 2.0 Gyr !
z ~ 0.7 z ~ 1.0
Density
Fraction of Red
Galaxies
Trevese et al. 2007
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Task two:
Analysis of Deep Photometric Surveys
The GOODS Survey
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The Great Observatories Origins Deep Survey covers all the Chandra Deep Field South.
The GOODSMUSIC catalogue (Grazian et al. 2006, A&A 449) uses 14 bands photometry of 14847 extragalactic objects, selected either in the z
850 or in the K
s band. E.g. limiting magnitude z
850 ~ 26
(AB).The average dispersion of its photoz is very good : <|z/(1 + z)|> = 0.03 up to redshift z = 2.
Image at ~ 0.8
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We built a comprehensive catalogue of structures in the GOODSSouth field up to z ~ 2.5 (Salimbeni et al. 2008 in preparation; preliminary results : Castellano et al. 2008 arXiv:0801.3557)
We generate 3d density maps in FITS format, here is an example (up to z~2) :
We find overdensities at z ~ 0.7 at z ~ 1, at z ~ 1.6 and (under scrutiny!) at z ~ 2.3
Density map at
increasing redshift
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Salimbeni et al. 08
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We can perform a study of single structures:
Masses for clusters at z=0.73 (top)and at z=1.61 (bottom):
M~3x10^(14) M_sun (===> ~ 5x10^44 Kg !)
Red sequence for galaxies in different overdensities: slope seems constant up to the highest redshifts!
Cluster Radius
Mas
s
z~0.7
z~1.6
Salimbeni et al. 08
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Result: we find that the color segregation progressively disappears at high redshift;
Our analysis confirms and extend previous studies limited at z~1.5 (e.g. Cucciati et al. 2007, Cooper et al. 2007):
Density
Fraction of
Red/Blue Galaxies
Lum
ino
sity
Age of the Universe
Salimbeni et al. 08
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Result: we find that galaxies at high densities have a distribution that peaks at higher masses
FieldGalaxies
ClusterGalaxies
log(Mass)
frac
tio
n
Salimbeni et al. 08
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We analysed in depth the forming cluster at z~1.6 (RA=03h 32m 29.28s, DEC=−27˚ 42' 35.99'') (Castellano et al. 2007, ApJ 671).
It is embedded in a diffuse structure at z~1.61 already known from spectroscopic observations (e.g. Vanzella et al. 2005, 2006).
Density isosurfaces at z~1.6 (average, average+1 to average+6) superimposedon the ACS z
850 band image
Castellano et al. 08
Properties: we estimate an M200
mass
in the interval 1.3 × 1014 − 5.7 × 1014 Msun
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Galaxies are, on average, redder, more massive and more luminous than 'field' galaxies at the same redshift.
Castellano et al. 08
9 of its galaxies form a nascent red sequence
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It has interesting Xray features: emission is detected within the core and it is divided in three different clumps. Assuming a thermal spectrum with T=3 keV and Z=0.2 Z
sun we estimate an
emission of ~ 0.5 x 1043 erg/s (210 KeV)
Xray contours in the 0.43 keV interval (black lines), and galaxyisodensity curves (white lines)
The irregular morphology and the low total luminosity suggest that the structure has not yet reached its virial equilibrium.
X rayemission
GalaxyIsodensitySurfaces
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The cluster has been later spectroscopically confirmed in the context of the GMASS survey (Kurk et al. 2008, on astroph). A velocity dispersion of ~ 400 Km/s has been found.
Galaxy densityfrom spectroscopic
data
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Near the galaxy density peak:
A big and complex star forming galaxy with various 'blobs' of star forming regions around a redder core: we may be witnessing the formation of a cD galaxy...
V (0.52 ) I (0.8 ) J (1.24) 4.5
5 arcsec
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CONCLUSIONS
It is possible to study high redshift galaxy environment with photometric redshifts
We found that color segregation with density is higher at lower redshift and brighter magnitudes. It seems to disappear, also for the brightest galaxies, between z~1.5 and z~2.0
We found new evidence in favour of constant slope of the CM relation in clusters,implying a constant massmetallicity relation up to high redshift.
We built a comprehensive catalogue of structures in the GOODSSouth field. 'Sheets' of diffuse overdensities, with embedded groups/clusters, appear up to the highest redshifts probed.
We detected an high redshift small cluster later confirmed with spectroscopy. It shows the characteristics of a forming cluster: color, mass and luminosity segregation, clumpy and faint Xray emission
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QUALITATIVE AGREEMENT WITH
“HIERARCHICAL CLUSTERING” SCENARIO
CONCLUSIONS
It is possible to study high redshift galaxy environment with photometric redshifts
We found that color segregation with density is higher at lower redshift and brighter magnitudes. It seems to disappear, also for the brightest galaxies, between z~1.5 and z~2.0
We found new evidence in favour of constant slope of the CM relation in clusters,implying a constant massmetallicity relation up to high redshift.
We built a comprehensive catalogue of structures in the GOODSSouth field. 'Sheets' of diffuse overdensities, with embedded groups/clusters, appear up to the highest redshifts probed.
We detected an high redshift small cluster later confirmed with spectroscopy. It shows the characteristics of a forming cluster: color, mass and luminosity segregation, clumpy and faint Xray emission
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FUTURE APPLICATIONS?
Deep optical/near IR surveys with facilites like LBT, WFC3(@HST), VISTA(@VLT), EELT, JWST
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Collaborations for this work:
A. Fontana, E. Giallongo, S. Salimbeni, A. Grazian, L. Pentericci
at the “OAR” Osservatorio Astronomico di Roma (Monte Porzio Catone)
my contact: [email protected]
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StarFormation
Rate
(Sun masses per year
per Mpc^3)
Age of the Universe
Back
Hopkins & Beacom (2006)
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Back
Age of the Universe
MassAssembled
in Stars
(Sun masses per Mpc^3)
Elsner et al. (2008)
40
Back
Age of the Universe
Fractionof
InteractingGalaxies
Ryan et al. (2008)
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NumberDensity
ofClusters
Age of the Universe
Universewith
BaryonicMatter ~ 4%
Cold DarkMatter ~26%
Dark Energy ~70%
Back
Rosati et al. (2002)
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Back
Age of the Universe
AGNdensity
( Mpc^3)
Hopkins et al. (2007)
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Back
DensityDressler 1980
Fractionof galaxies
Ellipticals
Lenticulars
Spirals
44
Back
Fractionof red
galaxies
Age of the Universe
Clusters
Field
Back 2
Cooper 2007
45
Fractionof galaxies
log( Flux(520 nm)/Flux(360 nm))
Early type/EllipticalGalaxies
Late type/SpiralGalaxies
Back
Giallongo et al. 2005
46
Back
log(Flux(850 nm))
log(
Flu
x(85
0 n
m)/
Flu
x(77
5 n
m))
DeMarco 2007
Back 2
47
If we evolve the colors of of the 9 reddest galaxies we find a good agreement with the red sequence of a spectroscopically detected massive cluster at z =1.24 (e.g. De Marco et al. 2007).
Observed Relation
Galaxy Models Evolved
Co
lou
rs
Magnitudes
Back
Castellano 08
48
Back
