Missing Photons that Count:Galaxy Evolution via Absorbing Gas

(and a little bit of fundamental physics to boot)

Chris Churchill(Penn State)

To Earth

CIVSiIVCIISiII

Lyem

Ly forest

Lyman limit

NVem

SiIVem

CIVem

Lyem

Ly SiII

quasar

Quasars: physics laboratories in the early universe

Ly

• Damped Lyman-Absorbers (DLAs): N(HI) > 2x1020 cm-2

• Lyman Limit Systems (LLSs): N(HI) > 2x1017 cm-2

• Lyman- Forest N(HI) < 6x1016 cm-2

Categories by Neutral Hydrogen

Compact Star forming objectsGalaxy centersMetal lines, low ionization dominate

Proto-galaxy structuresGalaxy outskirts (extended halos, disks)Metal lines, low, intermediate, and high ionization

Cosmic WebSheets and FilamentsMetal lines, weak to non-existent

“The Lyman Alpha Forest”

• Piercing the Cosmic Web• Tracing Structure Growth• Constraining Ionization Evolution

Ly forest

N(HI) < 1016 cm-2

Great Insights are gained from simulations of structure growth, but these simulations are starved for hard data to constrain the physics…

Note structure growth is rapid at for z>5 (a short cosmological time frame), and then evolution is slower, especially from z<1 (majority of time)…

(courtesy M. Haehnelt)

The Power of Simply Counting Lines

The redshift path density, dN/dz, places constraints on simulations of structure growth as a function of redshift…

(Dave’ etal 1999)

The Power of Simply Counting Lines

The redshift path density, dN/dz, places constraints on simulations of structure growth as a function of redshift…

(Dave’ etal 1999)

The Power of Simply Counting Lines

The redshift path density, dN/dz, places constraints on simulations of structure growth as a function of redshift…

(Dave’ etal 1999)

The Power of Simply Counting Lines

The redshift path density, dN/dz, places constraints on simulations of structure growth as a function of redshift…

(Dave’ etal 1999)

or

The Power of Simply Counting Lines

(Dave’ etal 1999)

(Weymann’ etal 1999)

“C IV Systems”

• Proto-galactic clumps• Tracing Pre-galactic Structure Growth• Constraining Kinematic/Dynamic Evolution

Metal Lines

N(HI) ~ 2 x 1017 cm-2

Efforts have been made to include ionization feedback, both in terms of spectral energy distributions, photon transport, and mechanical stirring of the gas…

QSO Absorption Lines: Anatonomy of a Simulation

(courtesy M. Steinmetz)

Technology and innovation is quickly outpacing observational data…

QSO Absorption Lines: Anatonomy of a Simulation

(courtesy M. Steinmetz)

Ly-

C IV

Velocity

The Power of Simply Counting Lines

Mg II shows no evolution (co-moving), but nothing in known above z=2.2

Lyman Limit systems (LLS) show no evolution, measured from continuum “break” at 916 A in the rest frame, N(HI)>1017.3 cm-2

C IV systems evolve rapidly! They increase with cosmic time until z=1.5 and then show no evolution

Structure, Ionization, or Chemical Evolution?

Evolution measures product of:• number• size• ionization fraction

Is this an increase in number, in ionization level, or in the chemical abundance of carbon?

We need low ionization data. Mg II.

Motivations and Astrophysical Context

Mg II arises in environments ranging over five decades of N(H I)

• Damped Lyman-Absorbers (DLAs): N(HI) > 2x1020 cm-2

• Lyman Limit Systems (LLSs): N(HI) > 2x1017 cm-2

• sub-LLSs: (low redshift forest!) N(HI) < 6x1016 cm-2

eg. Biosse’ etal (1998); Rao & Turnshek (2000); Churchill etal (2000b)

eg. Steidel & Sargent (1992); Churchill etal (2000a)

eg. Churchill & Le Brun (1998); Churchill etal (1999); Rigby etal (2001)

Mg II selection probes a wide range of astrophysical sites where star formation has enriched gas; these sites can be traced from redshift 0 to 5

Mg II -process ion – Type II SNe – enrichment from first stars (<1 Myr)

Fe II iron-group ion – Type Ia SNe – late stellar evolution (>few Gyr)

Present Day Coverage and Astrophysical Context

Simple Kinematic Models of Absorbing Gas from Galaxies

Absorption kinematics is symmetric about the galaxy’s systemic velocity

Absorption kinematics is offset in the direction of stellar rotation compared to the galaxy’s systemic velocity

Halo/infall + Rotating/disk produces both signatures in single profile

(Charlton & Churchill 1998)

Mg II 2796 Absorption Profiles from HIRES/Keck

Galaxy redshifts can be matched to the absorbers…

(Churchill 2001)

Mg II 2796 Absorption Profiles from HIRES/Keck

(Churchill & Vogt 2001)

Mg II 2796 Absorption Profiles from HIRES/Keck

Each Mg II system has several Fe II transitions and Mg I (neutral)

The clouds are modeled using Voigt profile decomposition…

Obtain number of clouds, temperatures, column densities, ionization conditions (from modeling)…

Build the Database and the Simulations will Follow

Ultimately, the simulations need to be driven by the data… as we have seen the great successes in this arena for the Lya forest to z=5, and are seeing the new successes for metal enriched diffuse objects to z=5….

We will begin to see the successes of galaxy evolution in more detail, including structure evolution, kinematics, metallicity, and ionization. The data are lacking.Wholesale inventory of Mg II absorbers is the best approach.

(courtesy M. Haehnelt)

Q0827+243 Q1038+064 Q1148+387

(Steidel etal 2002)

Kinematics: Stellar, Mg II 2796, and C IV 1548, 1551

Mg II traces stellar kinematics yet is difficult to explain as extended disk rotation (at 72 kpc impact parameter!). C IV traces Mg II kinematics but has strongest component at galaxy’s systemic velocity, as highlighted in 1551.

What physical entity is giving rise to this C IV component?

(Churchill 2003; Churchill etal, in prep)

Population of Weak Systems: Where do they arise?

1. Their equivalent width distribution follows a power law down to 0.02 A

2. Arise in optically thin H I (Ly clouds)

25%-100% of all Lya clouds with column densities 1015.5<N(HI)<1016.5 cm-2

3. Constrained to not have supersolar metallicity, almost all have z>0.1 solar

4. Many are iron rich, suggesting later stages of star formation

5. 90% cannot be associated with galaxies (within 70 kpc)

(Churchill etal 1999; Rigby etal 2002)

Equivalent Width Distribution

Differential Number Density Distribution

Redshift Path Density

Using HIRES/Keck, we discovered that the EW distribution followed a power law, with no observable cut off down to W=0.02 A. - these are high metallicity “forest” clouds.

5 papers over 10 years predicted that none of these “weak” systems existed! They outnumber galaxies by 1:106.

As the lower EW cutoff of the sample, Wmin, is increased, the number of systems per unit redshift decreases…

(As Wmin increases, the mean redshift increases – ) differential redshift evolution

Comoving redshift path density is consistent with no structure/ionization evolution for Wmin=0.02 A (red) and Wmin=0.3 A (blue).

dN/dz ~ n(1+z) .

Evolution of Strongest Systems

As Wmin increased – evolution is stronger

dN/dz = N0(1+z)

What is the nature of the evolution???

Is it related to high velocity clouds, presence of supperbubbles, or superwinds???

REDSHIFT

Scenario of kinematic evolution of gas…

Present Day Coverage and Astrophysical Context

The epochs of greatest evolution are un-probed…

(Based upon Pei etal 1999)

(stars)

(gas)

(baryons)(gas flow)

(IGM metals)

No coverage for Mg II for z>2.2No high resolution coverage for Mg II for z>1.4

Mg II provides metalicity for high-z forest in lower ionization gas- heretofore un-probed

Constraints on Global Galaxy Evolution Models

(Pei etal 1999)

Some Future Plans

• High Resolution optical spectra of QSOs to get Mg II kinematics to cover 1.4<z<2.2• High Resolution HST ultraviolet spectra of higher ionization gas

• Low Resolution infrared spectra of QSOs to get Mg II statistics for 2.2<z<4.0 • Moderated Resolution HST ultraviolet spectra of higher ionization gas

• High Resolution infrared spectra of QSOs to get Mg II kinematics for 2.2<z<4.0

• Leading international collaboration: Keck, Subaru, VLT, HET, BLT• Student opportunities include observing, echelle data reduction, data analysis• --- VP decomposition, statistics, distribution function (DF) evolution

• Collaborating with N. Kobayashi: Subaru, VLT • Student opportunities include observing, UV and IR data reduction, data analysis• --- visibility function, sample completeness, statistics, DF evolution

• This is 5-10 years future:VLT, BLT

“And now… for something completely different.”

Evidence For Cosmological Evolution of the Fine Structure Constant?

= (z-0)/0

= e2/hc

Relativistic shift of the central line in the multiplet

Procedure1. Compare heavy (Z~30) and light (Z<10) atoms, OR

2. Compare s p and d p transitions in heavy atoms.

Shifts can be of opposite sign.

Illustrative formula:

1qEE2

0

z0zz

Ez=0 is the laboratory frequency. 2nd term is non-zero only if has changed. q is derived from relativistic many-body calculations.

)S.L(KQq K is the spin-orbit splitting parameter.

Numerical examples:

Z=26 (s p) FeII 2383A: = 38458.987(2) + 1449x

Z=12 (s p) MgII 2796A: = 35669.298(2) + 120x

Z=24 (d p) CrII 2066A: = 48398.666(2) - 1267xwhere x = z02 - 1 MgII “anchor”

/ = -5×10-5High-z Low-z

Uncorrected: Quoted Results