Formazione ed evoluzione delle galassie

Bianca M. Poggianti - Febbraio 2007 - Padova

Presentazioni

anno, tesi, con chi

corsi seguiti su ev. Galassie durante corso di laurea

chi al corso di Dressler? Riprendero’ i concetti principali

Verifica: account?

astro-ph?

scelta argomento e metodo

calendario

LEZIONE DEL 14, e di domani

Cercheremo di fare due cose:

dare un quadro delle conoscenze attuali

imparare alcune delle tecniche piu’ utilizzate, per essere in grado di essere “operativi” e soprattutto per comprendere meglio i risultati e le loro incertezze

Non completo…..

RICORDA….

Il quadro cosmologico attuale

Il framework teorico

Evoluzione cosmica della formazione stellare

L’evoluzione della struttura, delle popolazioni stellari e delle masse

La connessione galassie-AGNs

Gruppi e ammassi di galassie, environment ed effetti ambientali

Le galassie a piu’ alto redshift

FORMAZIONE ED EVOLUZIONE DELLE GALASSIE

Alan Dressler’s lectures

Richard Ellis, in First light in the Universe, SAAS-FEE Advanced Course n.36, astro-ph 0701024

Shardha Jogee, 2006, Chapter 6, "Physics of Active Galactic Nuclei at all Scales", Lecture Notes in Physics, Vol. 693, (Eds: Alloin, D.,

Johnson, R., and Lira, P.), astro-ph 0408383

Laura Greggio’s lectures in Pd powerpoint

Guido Barbaro, dispense

BASED ON…

Role of Observations

Many of the key features which define our current view of the Universe came through surprising observations:

• Cosmic expansion (Slipher/Hubble 1917-1925): Einstein preferred a static Universe and disregarded the early observations

• Big Bang (Penzias & Wilson 1965, cosmic microwave background): Hoyle and others considered the Steady State theory to be the `natural’ solution

• Dark Matter (Zwicky 1933, Rubin & others 1976): Dominant role in structure formation followed the observational evidence

4. Dark Energy (Perlmutter et al, Riess et al 1998-1999,cosmic acceleration): Although was invoked many times in the past, cosmic acceleration was an unpredicted result

5. More surprises in store??

Cosmic ExpansionDetermination of Hubble’s Constant H0: HST Key Project

Primary Cepheid calibration of distances to nearby spirals (affected by galaxy peculiar velocities & Cepheid metallicities)

Secondary Tully-Fisher (luminosity and rotational velocity) distances for distant spirals in the smooth Hubble flow

Final result (Freedman et al Ap J 553, 47, 2001):

H0=72 ± 8 kms s-1 Mpc-1

Cosmic Microwave Background: thermal origin and fluctuations

2.73K

BOOMERANG

Blackbody spectrum of CMB corresponds to decoupling of matter & radiation at redshift z =1088 1 when t = 372 14 kyr

Progress in measuring CMB Fluctuations

Flat m = 0.3 (vacuum dominated)

Open m = 0.3 (no vacuum)

WMAP 3 year data

Spergel et al (2006)

Angular power spectrum – primary peak at a multiple moment ~200 (physical scale 1 degree) constrains total energy density Omega_tot, hence space curvature (flat within 1%)

Galaxies are best tracers of tapestry of structure -- large scale galaxy distributions, power spectrum -- from Max Tegmark’s website

2dFGRS Power Spectrum

Cole et al MNRAS 362, 505 (2005)

Power spectrum (fluctuations over the mean) of local galaxy distribution can be reconciled with models of LSS that fit CMB angular fluctuations

Early SNe Ia data indicated Cosmic AccelerationEarly SNe Ia data indicated Cosmic Acceleration

Perlmutter et al Ap J 517, 565 ( 1999)

In generalized Friedmann models q0 = M/2 –3/2 Negative q0 is acceleration and implies 0

How flat is space?

flat

closedopen

How flat is space?

How flat is space? Somewhat.

tot=1.003How flat is space?

“Precision Cosmology?”

• DM 0.24 0.03 (dark matter)

• B 0.042 0.004 (baryons)

• 0.73 0.04 (dark energy)

(Bennett et al 2003,

Spergel et al 2006)

All 3 ingredients comparable in magnitude but only one component physically understood!

Concordance CosmologyConcordance Cosmology

Amazing…..

Until a few years ago we could not associate an AGE, DISTANCE and a VOLUME at a given REDSHIFT

“Today a precise measure of the form and energy of the Universe, and a detailed physical understanding of how structures grow and evolve” (RSE)

Numerical simulations The Millennium simulation

• 10 billion particles

• 500 h-1 Mpc box

• mp = 8108 h-1 Mo

• =1;m=0.25;b=0.045; h=0.73; n=1; 8 =0.9

• 20 106 gals brighter than LMC

Springel et al Nature 435, 629 (2005)

ΛCDM is now standard model

MOVIES millennium_sim

MOVIES lcdm

Observed

CDMbias #1

SCDMbias #1

SCDMbias #2

CDMbias #2

Beauty Contest

Reproduces Clustering of Local Galaxies

Dark matter only

2dFRS

NB: Requires input physics - semi-analytical modeling

The Development of DM StructureThe Development of DM Structure

The ability to follow the distribution of dark matter in simulations is fairly well advanced.

The same cannot be said of our understanding of how galaxies that we can detect are “painted on” to the large scale matter distribution.

100 Mpc

The CDM power spectrum seems to be holding up down to smaller and smaller scales (ground-based, balloon-borne measurements -- much noisier so far), so it would appear to look good for extending these successes to the properties of galaxies themselves.

Galaxy Formation in Cold Dark Matter ModelsGalaxy Formation in Cold Dark Matter Models

Semi-analytical models:

Numerical recipe for introducing baryons into DM n-body simulations and predicting observations using prescriptive methods for star formation, feedback & morphological assembly

Classic papers:

• Kauffmann et al 1993 MNRAS 264, 201

• Somerville & Primack 1999 MNRAS 310, 1087

• Cole et al 2000 MNRAS 319, 168

Semi-analytic prescription for galaxy formation Semi-analytic prescription for galaxy formation in CDM modelsin CDM models

Key issues: rate of cooling of baryons into DM halos, feedback from hot stars, supernovae and AGN

• Why CDM must be correct -- mostly

• Why CDM must be wrong -- partly

• Evidence that the evolution of galaxy spheroids (ellipticals and bulges) is not hierarchical

• The evolution of disks galaxies -- has the mode of star formation changed from starburst to continuous in “modern times?”

Benson et al. 2003 ApJ 599, 38

“What shapes the luminosity function of galaxies?”

The CDM power spectrum (halos) does not at all match the luminosity function of galaxies. To make it fit requires emptying the baryons out of small halos and suppressing star formation for massive systems, by feedback from massive black holes, for example.

1010 Msun109 Msun

CDM

But, right from the start, it seems something is fundamentally wrong:

Monolithic CollapseHierarchical Assembly

How

Did

Galaxies

Form?

Nature NurtureShort course:

The big problem for hierarchical models like CDM: For the biggest galaxies, the halos continue to merge until late times, z~1 or even z~0.5. This is why a picture in which ellipticals were made by merging spirals at late times seemed the “perfect fit.”

However, the stars of elliptical galaxies (and all big spheroids = bulges) really are old, and they are enhanced in alpha-elements compared to spirals. The stars in spheroids seem to be uniformly old, very few, or none of them, are young.

Dressler’s new “theory”

• An elliptical is an elliptical because lots of dark-matter halos brought their baryons together early (DM merged last), because it has a large mass of DM and baryons, and formed (all) its stars rapidly and long ago. It has a lots of noisy neighbors -- all this goes together. An elliptical is an urban creature.

• A spiral is a spiral because it forms from shallower DM halos, and grows slowly by accretion and star formation. It has only a few pesky neighbors -- this all goes together, too.

• S0 galaxies are “tweeners” -- the most massive of them are much more like E’s, and the least are more like spirals, again a strong correlation with mass. At what epoch are you looking?

• Dwarf galaxies are too complicated to talk about.

• The building blocks of galaxy formation may have had the same masses as today’s dwarf galaxies, but they were not today’s dwarf galaxies! They were dense blobs of early stars and gas, very dynamic, intense. They are all gone.

Observational Tests of Standard CDM Model

• Non-baryonic DM: what is it? little progress to date

• Distribution of DM on galactic and cluster scales:problems claimed on small scales

• Verification of basic galaxy properties, e.g. luminosity functions, dynamical masses etc: much fiddling required to account for baryon physics

• Detailed mass assembly history of galaxies: limited data available emphasizing baryon physics

• Dark energy: Dominant required (as observed)

Given reliance on standard model how we can be sure it’s correct other than via reproduction of large scale structure?