The Galaxy Evolution Science Case for a Large Ground-based Telescope

Betsy Gillespie

December 4, 2002

Grateful acknowledgements to: Arjun Dey’s “Galaxy Formation and Evolution” The team for the Canadian XLT science case

In particular: Bev Oke Bob Abraham

Ray Carlberg Jean-Pierre Veran Laurent Jolissaint

Galaxy Evolution

• What are the assembly histories of galaxies?Where and when did the first stars form?Where and when did the first galaxies form?How did they come to be the way they are today?

• We must: – Test hierarchical CDM, origin of the luminosity

function, the morphology-density relation, the Hubble sequence, the Milky Way– Relate distant galaxies to local fossil evidence

The Requirements for Progress

• The star formation and chemical enrichment histories of galaxies as a function of time: – Star formation histories (rest-frame optical at least); want both for a Sloan-

sized sample and as a function of position in the galaxy– Chemical enrichment (rest-frame UV and optical); want as a function of

position in the galaxy

• Identifying the intrinsic properties, ultimately the masses, of galaxies at high redshift–Mass measures from internal dynamics–Mass measures from strong lensing

The Requirements for Progress

• Measuring morphologies and the merger rate as a function of time (to constrain hierarchical models) to z=6:

– Evolution of different morphological types; identification of most strongly evolving populations at different redshifts

– Pair counts at higher redshift (coupled with an understanding of pair selection effects and a theoretical understanding of merger timescales)

• Detecting the first objects in the universe

Wide-field case: large samples for redshift/abundance surveys

• Need large samples to break into sub-types (500,000 galaxies MINIMUM, nearly size of SDSS)

• Want many categories:–Mass–Luminosity–Redshift–Environment–Metallicity–Morphological type

(Lilly et al. 1995)

Sensitivity is vital for a survey down the luminosity function

• Arrows show S/N=3 limits for 10,000 seconds in 0.3-arcsec seeing

• 500,000 galaxies in <100 clear nights requires at least 1700 galaxies per exposure

• >=16-meter requires deeper imaging than HDF to feed a large survey (JWST!)

PHOTOMETRIC REDSHIFT

RAB

Major advantages with some correction over the wide field (in the optical)

• Arrows show S/N=3 limits for 10,000 seconds in 0.5-arcsec seeing

PHOTOMETRIC REDSHIFT

RAB

If seeing degrades to 0.5arcsec, sensitivity worse by 0.5 magnitudes for unresolvedsources

Requires 2.4 x longer exposures

Near-IR case: for chemical abundances, star formation

histories

Lines in the optical and near-infrared

[OII] to z = 6

H to z = 3

JH

K

L/M

optical

weak absorption

•Few strong lines in opticalbetween redshifts of about 1 to 3•NEED near-IR

Plot from Oke & Barton (2000)

The importance of the NIR: sensitivity as a function z in Hand [OII]

• At z < 1.5, [OII] in optical and Hin NIR are comparable even with no dust; no metallicity effects in using Hstar formation rate

• Beyond z=1.5, both lines perform well in NIR; for z=2-3, H is best

Sensitivity to unresolved emission lines, R=3000, T=10,000 sec

30m [OII]

30m H

NGST HNGST [OII]

Globular cluster forming in 1 dynamicaltimescale

Internal kinematics: absorption lines

(from NOAO GSMT Book)

Most distant galaxiesfall below the contiuumsurface brightness limit

Emission lines: “Typical galaxies” at z=1.5

z=0 z=1.58m

z=1.530m

z=1.520m

20-hour exposure 8-meter telescopes only detect the center!

Assumed psf for these simulations

Image-quality studies at HIA:

• Chris Morbey -- telescope

• Laurent Jolissaint and Jean-Pierre Veran --- added atmosphere and AO

K-band PSF

Bulk property like Strehl ratio likelyimportant, but detailed features ofpsf not important…

Major issue for image quality: how lumpy is star formation?

Diameter(pc)

redshift

30-meter telescope diffraction limits

Typical ground-based Resolution for local galaxies

Star clusters in Antennaehave <Re> = 4 pc(Whitmore et al. 1999)

Higher redshifts: z > 3

• Galaxy morphologies “more challenging” to recognize

• Large disks may not be in place, but relative velocities of lumps will provide information about dynamical state and/or total mass

(z=3 galaxy from Hubble Deep Field;HST psf ~ 0.1” ~ 770 pc)

Distant Galaxy Morphology: details help enable merger rate measurement

z=0.8

z=0.8

z=0.6

z=0.6

CFHT2-hour exp.

20-meter2-hour exp.

(“seeing” 2xDiffraction limit)

Simulationby Bob Abraham

Detecting the first objects in the universe

• At z=6-10, Ly is at 0.85 < < 1.4 m: regime where a 30-meter is much more sensitive than JWST

• JWST NIRcam proposal science case: parameters of first objects, with Charlot & Fall (1993) Ly analysis, gives Ly fluxes up to

~10-18.4 erg s-1 cm2 at z=10

Sensitivity to unresolved emissionlines, R=3000, t=10,000 seconds

Progress with 8-10 meter telescopes

• Large redshift surveys to z=3-4 (not too far down LF and most not in NIR)

–Most diagnostics will be rest-frame UV (exception is VIRMOS)

–Will measure unobscured SFR as a function of redshift

• Kinematics of bright or strongly star-forming galaxies to perhaps z=1.5 (plus occasional shear of Lyman break galaxy)

Complementarity to JWST, ALMA

• Spectroscopic follow-up to JWST imaging surveys

• Locally, the huge bursts of star formation are dust-enshrounded (e.g., ultraluminous infrared galaxies)

– argues for complementary imaging and spectroscopy at longer wavelengths

Summary of Requirements• Sensitivity.

– For spectroscopic surveys of huge samples– For internal dynamics with no systematic problems– To detect the “first” objects in the universe

• Near-IR capabilities.– For accurate chemical abundances directly comparable to what we know at low

redshift– For H star formation rates to z=3– For [OII](3727) star formation rates beyond z=5.

• Wide field.– Large survey (~106 galaxies) of luminosity function as a function of galaxy type

• Good image quality. – For better sensitivity– If star formation in the universe is lumpy on small scales– For high-redshift morphologies: the diffraction limit of a 30-meter telescope is

nearly 5 times better than a 6.5-meter JWST

Major unresolved issues and required work• What will the image quality be? Over what field and fraction of

the sky? Is some wide-field correction feasible?

• What is the expected distribution of emission-line (and UV) flux from high-redshift galaxies? Is it lumpy? Is it likely to remain resolved or unresolved? (Both spatially and in velocity width?)

– If this question cannot be answered, what is the best strategy to adopt?

• Kinematic simulations “from scratch” for adjustable parameters.

• Worth pursing issue of comparison with NGST at 2.5 to 4 microns.

REFERENCE

SLIDES

Scalings: Magnitude Limits

Scalings: Exposure Times

Not just a matter of patience! Many studies require large samples of objects.

Lookback Time

Lambda cosmology:

~9 Gyr to z=1.5

(only 4 Gyr from

z=1.5 to z=6)

z

Time

H0=70 km/s/Mpc0=0.3=0.7

“Average” Galaxies at Intermediate Redshift: z=1

z=0 z=18m

z=130m

z=120m

10-hour exposure

“Average” Galaxies at Intermediate Redshift: z=1.5

z=0 z=1.58m

z=1.530m

z=1.520m

10-hour exposure

Longer Exposures

z=0 z=1.58m

z=1.530m

z=1.520m

20-hour exposure

still onlysee the center!