Chris ChurchillNew Mexico State

- Galaxies form in the cosmic web- They accrete IGM gas, form stars, and deposit energy/metals back into IGM- Extended metal enriched “halos” are observed from z=0 to z=4

Observational data of these “halos” are underutilized for constraining galaxy formation physics in cosmological simulations… -how to do it?

QSO Absorption Lines and Cosmological Simulations: The Quest to Understand Galaxies

June 20, 1011

The universe is about 13.6 billion years old

The universe is expanding and its geometric curvature is “flat”

The universe comprises (add to 100%) 70% dark energy 26% dark matter 4% baryonic matter (normal stuff)

How do we know there is dark energy?

About 6 billion yrs ago, the expansion rate of the universe changed from deceleration to acceleration; dark energy acts like a “negative pressure” and it began to dominate later in the life of the universe

How do we know there is dark matter?

If we add up all the mass in stars within any random galaxy and measure the velocities of the stars, we would deduce that the galaxies should fly apart (become unbound); star must contribute only 10% to the galaxy’s mass

Getting acquainted with the universe…

dark matter is 85% of all matter baryonic matter is 15% of all matter

How do we know any of this?

“Astronomers are a breed of historian with lots of extra hubris.” – Sandra Faber

“Studying the history of the universe is something like trying to piece together the history of the earth’s climate by placing dixie cups out in the rain and then studying the few water drops collected” – Paul Hodge

Astronomers are handicapped experimental physicists, called “observers”.

We collect light in huge light buckets, try and organize the light by color, intensity, etc, apply the laws of atomic and gravitational physics- and…

ka-chow(!) … we have a little understanding of 4% of the the universe

… AND, FOLKS… WHAT A 4% IT IS!

Tips of the ice bergs

Galactic Pathology is a transient train wreck phenomena…

These galaxies started their lives as gaseous halos before any stars ever form!

The gas (4% of the universe) gravitationally follows the formation of dark matter halos (85% of matter), which formed due to localized gravitational instabilities as the universe expands

These instabilities were seeded by quantum fluctuations created in the first fraction of a second of the Big Bang; the distribution of galaxies in the universe and the fluctuations in the cosmic microwave background provide the mass spectrum of the fluctuations (we know it well!)

All sky CMB fluctuations Cosmic web distribution of galaxies

How do galaxies actually form…

We put the dark matter fluctuation spectrum in as the initial condition in a cosmological simulations code, with which we model gravitational forces, star formation, stellar feedback from supernovae explosions, and the build up of chemical species heavier than helium, and model the expansion of the universe and… let ‘er rip… we also put in the “trace” baryonic (normal) matter and let it follow the dark matter and we get- galaxies

… and yes, we get out disk/spiral galaxies that rotate and elliptical galaxies, and al the train wrecks you could ask for

… and we can track the baryonic gas that is otherwise invisible in that it does not radiate enough light for us to detect the gaseous structures

SO.. HERE IS A LITTLE DIDDY DESCRIBING OUR CURRENT VIEW OF THE LARGE SCALE STRCUTURE OF MATTER N THE UNIVERSE AND ON GALAXIES…

Building galaxies the only way we know how…

Click inside the box to start movie

Just as simulations suggest, galaxies are observed to be surrounded by lots of gas

Images alone do NOT provide detailed physics required to fully exploit the simulations (or improve them!)

Also, galaxies that are farther away appear dimmer and we become photon starved (crummy data)

We need an observational technique that yields the physics (chemical composition, temperatures, kinematics, and ionization conditions) AND is equally sensitive for both close and far galaxies…

As powerful as simulations are they are far from complete and require observational constraints and direct comparison testing with the real universe…

… since light interacts with matter (the 4%!) in very specific ways, the pattern of light intensity as a function of wavelength (spectrum) can be decoded and then atomic physics can be applied to deduce the very highly detailed physical state of the matter

A Spectrum is Worth a Thousand Pictures…

Absorption lines!

Star spectra, galaxy spectra, QSO spectra all sport them.

When a continuous spectrum passes through a “cloud” of gas, almost all the light passes through unimpeded…. but…

each type of atom/ion in the gas cloud interacts with photons of precisely well defined wavelengths that are specific to that atom/ion- the atoms absorb the light energy and become excited or ionized

There is a unique pattern of absorption lines for each atom/ion!

We are the FBI and absorption lines are atomic fingerprints

Astronomer’s Periodic TableH, He, metals!

Neutral hydrogen (HI) has very strong absorption, called Lyman a (Lya)

But not all atoms are neutral… they get ionized by high energy photons!

1x ionized Mg (MgII) acts like neutral Na (sodium like)

3x ionized C (CIV) acts like neutral Li (lithium like)

5x ionized O (OVI) acts like neutral Li (also lithium like)

These are special because of fine structure splitting that results in doublets

-> pairs of absorption line!

We do require a background light source with a continuous spectrum

Thank The Maker for the physics of giant black holes!

In the past, due to galaxy mergings, giant black holes formed and found plenty of “food” in the centers of train wrecks as they relaxed and settled down

QSO

We call them QSOs… short for quasi-stellar object… they beam with the power of 1,000,000,000,000,000,000 Suns blasting x-rays, UV, visible, and IR light in a smooth continuous spectrum

The line of sight to a QSO provides a core sample through the universe, recording the finger prints of every ion in every gas cloud it pierces!

Telling Cosmic Time: Cosmological Redshifting of Light

Not a Doppler effect; a stretching!

Photon wavelengths are “comoving” with space

(a) At some time in the past a photon is emitted (or absorbed) with wavelength l0

(b) At later time the universe has expanded and the photon has “stretched” in step with it

The present-day observed wavelength of a photon emitted (absorbed) in the past is

l = l0 (1+z)

z = redshift

Redshift is a measure of cosmic time

QSO

Very powerful for constraining cosmic structure growth and galaxy/IGM, chemical, and dynamical evolution.

The Business of QSO Absorption Lines: gaseous core samples of the universe

Hydrogen absorption is ubiquitous (IGM, filaments, galaxy ISM and halos)

Metal absorption tracks galactic structures (metal enriched by past stars!)

Their metal line doublets are easy to spot in spectra!

MgII 2786,2803 - low ionization; traces moderately dense gas with T~30,000 KCIV 1548,1550 - intermediate ionization; traces gas with T~30,000-100,000 KOVI 1031,1038 - high ionization; traces hot gas with 100,000<T<300,000 K

Schematic of QSO Absorption Lines: Intrinsic Emission Lines

l = l0 (1+z)

1215.7(1+3.000) = 4863

1549.8(1+3.000) = 6199

Schematic of QSO Absorption Lines: Cosmic Web HI (Lya) absorption lines

l = l0 (1+z)

1215.7(1+2.907) = 45711215.7(1+2.455) = 42031215.7(1+2.049) = 37121215.7(1+1.262) = 2750

Schematic of QSO Absorption Lines: Galaxy/Halo metal lines (MgII, CIV)

Keck Twins10-meter Mirrors

The dixie cup twins!

The Keck I in parked position before a night of observing.

The spectrograph “room” mounted on the west azimuth platform

Inside the dome…

The High Resolution Echelle Spectrograph (HIRES/Keck)

2-Dimensional Echelle Image

Dark features are absorption lines – atomic fingerprints

1-Dimensional Echelle Spectrum of a QSO at z=2.406

infrared -><- ultraviolet <- visible ->

Note that almost every feature is redshifted! Lya and CIV emission originate in the far UV!

The Level of Detail- is… just simply awesome!

Resolution = l/Dl = c/Dv = 45,000! Dv=6.5 km/s

The “velocity” interval sampled per pixel is 2 km/s!

A typical sample of the Lya forest lines at z=2

High Resolution yields numbers of clouds in a halo, and their line of sight velocities!

Observed spectra contain a mixture of both models

Blended Line Morphology;Asymmetric

Velocity

Resolved Line Morphology;

Symmetric Velocity

Simple model for interpreting complex absorption profiles

- Individual clouds provide projected velocity along line of sight (Doppler formula)

When studying absorption from galaxies, we prefer to view the absorption in the rest-frame velocity of the galaxy

neutral hydrogen

low ionization magnesium

mid ionization carbon

high ionization oxygen

Galaxy Halo A Galaxy Halo B

v = c (l-lz0)/lz0

lz0 = l0 (1+ zgal)

Converting to velocity in the galaxy rest frame

(Note the larger scale)

z=0.2981D=41.7

z=0.5915D=25.5

z=0.8514D=18.2

z=0.2981 z=0.5915

z=0.8514

Field by field, galaxy by galaxy, we build a consensus of the relationship between galaxies and their extended halos

QSO

The Q0002+051 Field

Our Sample: arranged by impact parameter

2796

2803

How do we try to make sense of these data?

Observationally: compare relative kinematics

Does the gas co-rotate with the disk?It should if it is coupled to the galaxy angular momentum

We line a slit along the galaxy and take its spectrum too… we use emission lines and the Doppler effect to measure the galaxy rotation

Usually the gas cannot be fully coupled to the galaxy (blue curves give predictions)

Observationally: compare relative kinematics

Sometimes higher ionization gas kinematics different than low ionization kinematics!

Note CIV is moving away from us compared to the galaxy, while MgII is moving toward us

But we do not know where the gas is located spatially compared to the galaxy… so

USE SIMULATIONS….

z = 2.3

z = 1.3

z = 0.2

stars density cm-3 temp K Z solar

1000 kpc

Temperature Evolution from z=3 to z=1

z=3

By z=1 (~7 billion yrs ago), the gas is spread over 600 radius kpc (volume of Local Group!) and has cooled in substructures of T=1000 K , others (the majority) of T= 10,000, and warm to hot substructures of 100,000 K; note the filaments have been disrupted; also appearing (white, near galaxy) is shock heated (T=10 million K) X-ray gas

z=1

At z=3 (~11 billion yrs ago), hot T=100,000 K gas expanding outward over 200 kpc radius while filaments from the cosmic web/IGM are infalling with T=10,000 (not yet heated)

Material is outflowing due to star forming activity (supernova winds)

Metal Enrichment Evolution from z=3 to z=1

z=3

By z=1 (~7 billion yrs ago), the vast majority of the halo gas is 1/10th solar over a volume of the local group

- By present day (z=0), however, much of this enriched material falls back in toward the galaxy, leaving much patchier halos

z=1

At z=3 (~11 billion yrs ago), metals are differentiated somewhat uniformly; - blue halo is entrained IGM metal poor gas - yellow is ~1/100th solar- red is ~1/10th solar- white is nearly solar

-Upper infalling filament enriched in situ by dwarf galaxies

Cosmic Structure Evolution in 10 Mpc Box Track metals, account for ionization balance, and present regions where CII, CIV and OVI are dominant ionization stages of C and O

credit: Ben Oppenhiemer

Examining CII and CIV Absorption Evolution in a Single Halo

Place line of sight (LOS) through simulation, compute absorption spectrum at each time step and animate…

-30 kpc

+30 kpc

60 kpc

LOS

vel (

km/s

) at x

LOS position x, kpc

CII

CIV

Inte

nsity

at v

el (k

m/s

)

credit: Matias Steinmetzr

A Example Detailed Study…

view from the sky side view in plane of

Example showing 2 “QSOs” lines of sight (LOS) through a z=0.8 simulated galaxy

These two LOS pass through fairly low density structures of a well evolved galaxy

How we get spatial and kinematic information

Putting it altogether…

Summary/Conclusions

1. QSO absorption lines provide a powerful method for probing the role of gas in galaxy evolution. The sensitivity remains constant with redshift and an otherwise invisible component of the universe is revealed in all its physical detail.

2. The method itself is limited; only line of sight velocity information can be directly observed; we need simulations to interpret observations and obtain 3D spatial, temporal, and contextual/cosmic environmental information.

3. Cosmological simulations need QSO absorption line observations to test that they in fact correctly model both large and small scale gas hydrodynamics in the cosmological setting; these simulations include the physics of star formation, supernovae winds, and stellar feedback- all brand new physics being explored only now.

4. We find that the extended gaseous “halos” discovered via QSO absorption line studies are complex entities coupled to both the small parsec scale physics within galaxies and the large scale physics of galaxy formation in the cosmic web setting.

5. There is much work to do; we give the simulations a “B-” at this time… (I could give another hour lecture on the shortcomings based upon statistical and quantitative tests); over the next years this line of research holds great promise for developing a new era marked by a comprehensive understanding of how galaxies form and evolve.

Thank you Rose City Astronomers!