Massive UV-Selected Galaxies at z~2

Dawn Erb (Caltech)

Chuck Steidel (Caltech), Alice Shapley (Berkeley), Max Pettini (IoA), Kurt Adelberger (OCIW),

Naveen Reddy (Caltech)

Overview• Masses, kinematics, metallicities and star-formation histories of

UV-selected galaxies at z~2, from optical and near-IR spectroscopy, optical through mid-IR imaging

• ~8% of total sample has M*>1011 M, K<20, J-K>2.3

• Why z~2?• Large fraction of today’s stars formed in this era• Bridge gap between z~1 and z~3• Much diagnostic info available, in rest-UV and optical

Optical Photometric Pre-Selection

• Green/yellow (LBGs): z=2.960.26

• Cyan (BX): z=2.260.32

• Magenta (BM): z=1.700.34

• Total surface density of BX+BM galaxies is ~9 arcmin-2 to R=25.5, ~25% of R-band surface density to R=25.5

Steidel et al 2004

Spectroscopic Sample

• Confirm redshifts in rest-frame UV

• BM, z=1.70: 170 galaxies

• BX, z=2.20: 780 galaxies

• LBG, z=2.96: 950 galaxies

• ~75 z~2 galaxies

with M*>1011 M

Steidel et al 2004

IR, Mid-IR Observations

• Deep J, K imaging with WIRC, Palomar 5-m, to Ks~22.5, J~23.8

• 4 fields, ~420 galaxies with zsp> 1.4

• Spitzer IRAC data in Q1700 field, 3.6, 4.5, 5.4, 8 m

• Use for modeling stellar populations, masses

IR, Mid-IR Observations

• Deep J, K imaging with WIRC, Palomar 5-m, to Ks~22.5, J~23.8

• 4 fields, ~420 galaxies with zsp> 1.4

• Spitzer IRAC data in Q1700 field, 3.6, 4.5, 5.4, 8 m

• Use for modeling stellar populations, masses

UV to mid-IR Model SEDs

K=20.1

K=20.6

• 72 galaxies detected in IRAC bands

• ~8% (6/72) have M*>1011 M

• 4/6 have J-K>2.3• Same 4/6 have

K<20 • 5/6 have ages of

2-3 Gyr• Best-fit implies

already massive at z~3

Stellar masses, with and without IRAC data

• Optical + IR + IRAC: log M* = 10.280.50; median 10.4

• Optical + IR only: log M* = 10.350.54; median 10.4

• Good news for ~300 galaxies without IRAC data

• Usually no evidence from IRAC points for underlying old populations

Steidel et al 2004, in prep

Stellar mass vs. restframe near-IR, optical luminosity

• At z~2, even mid-IR observations not direct tracers of stellar mass

• Inferred stellar mass can differ by factor of ~10 at a given 4.5 m luminosity, ~70 at K-band

Steidel et al 2004, in prep

Massive galaxies and R-K color

Circles=K<20

Near-IR Spectroscopy• H spectra of 101 z~2

galaxies with NIRSPEC, Keck II– Kinematics: line widths,

dynamical masses, some spatially resolved lines

– [NII]/H ratios metallicities

– H fluxes SFRs; compare UV, models

– Outflows: offsets between nebular, UV absorption and Ly redshifts

M*=41011 M

K=19.3, J-K=2.3 M*=5109 M

Stellar vs. Dynamical Masses

• 63 galaxies, z=2.280.14

• Dynamical masses from H line widths, stellar masses from UGRJK modeling

M*=71010 M

Mdyn=41010 M for r=0.2˝

Mdyn=11011 M for r=0.5˝

Erb et al 2004, in prep

Morphologies and Sizes

Erb et al 2004

Metallicities and Stellar Masses

• [NII]/H ratios for 30 galaxies in which [NII] detected

• Point from composite spectrum of 14 galaxies (more to come…)

• Mass-metallicity relation– Scatter expected when

galaxies still forming– Large uncertainties

• Galaxies with K~20 and M*~1011M have ~solar metallicities (Shapley et al 2004)

AGN

Erb et al 2004, in prep

Metallicity Evolution

• Galaxies with ~solar metallicity at z~2 will have super-solar metallicity at z=0

• Ellipticals and bulges

Blaizot et al2004; cosmologicalsimulations +semi-analyticrecipes

Galactic-scale winds

• Supernova-driven winds ubiquitous at z~2 and z~3

– Threshold > 0.1 M yr-

1 kpc-2 easily met• Velocities ~200-400 km s-1

with respect to nebular line redshifts

• Difference between Ly and interstellar absorption lines is ~500-1000 km s-1

• Winds enrich IGM, regulate star formation

Steidel et al 2004

z~2

z~3

Clustering• 26,000 galaxies• 21 fields• ~1500 spectroscopic redshifts• R=23.5-25.5• Correlation lengths

z=2.9 (LBG): r0=4.00.6 h-1 Mpc

z=2.2 (BX): r0=4.20.5 h-1 Mpc

z=1.7 (BM): r0=4.50.6 h-1 Mpc

• Implied halo masses ~1012 M

(from comparison with GIF-LCDM numerical simulation)

Adelberger et al 2004

Evolution of clustering to z~1 and z~0.2

• Follow evolution of halo clustering in simulation– Matches early-type

absorption line DEEP2 galaxies at z~1 (Coil et al. 2003)

– Matches SDSS ellipticals at z~0.2 (Budavari et al. 2003)

• Typical galaxy will evolve into elliptical by z=0

Adelberger et al 2004

Number density and clustering strength at z~0.2

Bright LBGs

Typical LBGs

Adelberger et al 2004 Galaxy populationsIn SDSS

Adelberger et al 2004, in prep

Clustering strength vs. K• Clustering vs. K mag

(1.8<z<2.6)

– Ks<20.5:

r0=103 h-1 Mpc

– Ks>20.5:

r0=40.4 h-1 Mpc

• Compare IR surveys• Caveat! Uncertainty

because field choices not random, chosen to have QSOs

Comparisons with z~3

• Average velocity dispersion, R-K color larger at z~2• Most massive z~2 galaxies have likely progenitors

among LBGs, and were already massive at z~3• More to come…

Erb et al 2004, in prep

Steidel et al2004

BzK colors of UV-selected galaxies

• Works very well for K<21, misses ~half with K>21

• Missed galaxies have M*=7109 M, mean age 100 Myr

• But UV selection misses reddest galaxies

• Joint UV+BzK promising

UV-selected star-forming galaxies at z~2: Summary

Typical z~2 K~20 z~2

Mhalo ~21012 M >1013 M

Mstar ~21010 M ~21011 M

SFR ~50 M yr-1 ~130 M yr-1

Age ~700 Myr ~2-3 Gyr

Metallicity ~0.6 solar ~solar

Space density ~6 x 10-3 h3 Mpc-3 ~5 x 10-4 h3 Mpc-3

r0 ~4 h-1 Mpc ~10 h-1 Mpc