Galaxy Formation: What are we missing?

C. Steidel (Caltech)

Quenching: How to Move from the Blue Cloud Through the Green Valley and to the Red Sequence in 9 Easy Steps

in the Face of Downsizing

Some Questions:

• How efficient is galaxy formation as a function of time, environment, mass?

• Do we understand gas cooling and star formation on galaxy scales?

• Feedback in general: is it needed, is it observed, how does it modify the process?

– What process ends major star formation in galaxies?

• AGN: when do they happen, how do they influence the life of a (massive) galaxy?

• Where or how do “massive galaxies’’ fit in with other galaxies?

– What did they look like when they were forming most of their stars?

Using optical (rest-UV) and near-IR (rest optical) to quantify physical properties of z~2-3 galaxies

Optical spectra: •IMF

• stellar photospheric abundances

•ISM metallicity •ISM kinematics

Near-IR spectra:•Kinematics/dynamical masses•Ionized gas metallicity•SFR estimate•(cold) gas mass estimates•precise redshifts!

Bolometric Luminosity vs. Stellar Mass

Reddy et al 2006; see also Papovich et al 2006

Note that only ~20% of “red” z~2

galaxies are consistent with

being passive. The rest are dusty

LIRG-ULIRGs.

•Typical mean velocities are ~200-400 km/s with respect to nebular line (systemic)

redshifts

•Typical line widths are ~650 km/sec (barely resolved in

typical spectra)

• Difference between Ly alpha emission peak and

interstellar absorption centroid is ~650 km/s at both

z~3 and z~2; full velocity fields of +/- 500-1000 km/sec

•Close to unity covering fraction is common

•Lines of all accessible ionization stages seen (e.g.,

OI to OVI)

Galactic Scale Outflows are Ubiquitous @ high redshift

Ly emission relative to H

emission

<vISM> relative to H emission

CS et al 2006

Blue: Mbar<5x1010 M

Red: Mbar>5x1010 M

(Mbar=M*+Mgas)

Vmax ~800 km s-1

Sample of ~100 galaxies with accurate (H) systemic redshifts, good UV

spectra

CS et al 2006

OSIRIS+LGSAO: Spatially Resolved Emission Line Mapsof z~2-3 Galaxies

Collapsed H line flux maps for galaxies at z ~ 2 which show no coherent velocity shear and

~ 80-100 km/s.

Collapsed [O III] line flux map for a galaxy at z ~ 3 which shows velocity shear of ~ 150

km/s over 4 kpc. Shear was previously undetected with long-slit spectrographs.

0.05” Resolution

Law et al 2006

vabs~1000 km s-1

Stellar Mass/Metallicity Relation at z~2.2

Erb et al 2006

No Lum-Metallicity Relation

Based on H-alpha (K-band) Spectroscopy of ~90 z~2-2.6 galaxies

Mass Comparisons, z~2 star forming galaxies(masses on physical scales of r~5 kpc)

Erb et al 2006b

Dynamical vs. M* Dynamical vs. (Mgas+M*)

Gas Fraction vs. Stellar Mass, z~2-2.5 star forming galaxies (H sample, rest-UV selected)

Erb et al 2006b

Gas fraction inferred from H surface

brightness, inverting Kennicutt/Schmidt Law

“Specific Star Formation Rate” vs. Stellar Mass @z~2S

FR

/M*

Reddy et al 2006

Blue/Blue/yellowyellow dots: rest-UV

selected

Red boxes: DRGs

triangles: triangles: BzKBzK

Simple Chemical Evolution Models, z~2 Galaxies

(Cold) Gas Fraction ()

Met

alli

city

Erb et al 2006a

Curves:Curves:

Black: Closed box (no outflow)Black: Closed box (no outflow)

Blue: outflow=1xSFRBlue: outflow=1xSFR

Green: outflow=2xSFRGreen: outflow=2xSFR

Red : outflow=4xSFRRed : outflow=4xSFR

Yield of Salpeter IMF

What Does All of this Mean?• Almost looks like galaxies receive their full gas supply at the beginning of an extended

starburst episode, which is then “processed”, much of which (~80%?) leaves the galaxy and ~20% of which becomes stars. – a typical galaxy in SF samples is 50% cold gas and 50% stars in the central few kpc

@z=2-3 (accounts for ~30% of total baryons given halo masses of ~1012 M). – low stellar mass objects in current samples are not low mass objects, they are just

almost entirely gas and very young. • Range of properties among star forming galaxies is dictated by where we catch them in

working their way through their gas supply• Because high stellar mass galaxies have low gas fractions, both the ISM metallicity and

the opacity increase very rapidly, hence they are extremely dusty just prior to running out of gas.– clear evidence for increasing prominence (or duty cycle) of AGN in high stellar

mass, low gas fraction objects (~25% compared to ~3-4% in lower stellar mass objects)

– most of the gas is already gone by the time this occurs (though SFR can still be fairly high).

•Use dense sampling of galaxies, AGN to try to directly detect signatures of feedback (both radiative and hydrodynamical)

true IGM “tomography” is possible now.

Galaxy/AGN/IGM Interface @High Redshift

z

QuickTime™ and aTIFF (Uncompressed) decompressorare needed to see this picture.

QSO

BackgroundBackground

ForegroundForeground

Densely Sampling the Universe @z~1.8-3.2

Galaxy/CIV Cross-Correlation: 542 CIV systems, 1044 Galaxies

•Above N(CIV)~1013, galaxy/absorber cross-correlation is equal to or exceeds the galaxy auto-correlation function

•Suggests causal connection of the strongest systems with the observed galaxies.

•In any case, metals (as traced by CIV) are where the observed galaxies are.

Adelberger et al 2005

QSO sightline, 85 kpc awayGalaxy BX210:

v~660 km/sec

vmax~ -600 km/sec

2 sightlines separated by 0.45 kpc @76 kpc distance from z=2.356 galaxy

(separate gravitationally lensed images of the QSO)

Z=2.109Z=2.012

•Separation: 43 kpc (proper)

•MD80: M*=5x109 Msun

•BX513: M*=1011 Msun

•High ions >> low ions, at same velocity in MD80 spectrum and in

BX513 spectrum

~20 hours, Keck/LRIS-B

Where are the QSOs/AGN relative to the galaxies @z~2-3?

Adelberger & CS 2005a,b

Where are the QSOs/AGN relative to the galaxies?

Adelberger & CS 2005 galaxy-galaxy correlation length

z~2-3 galaxies

Inferences about Black Hole Masses and Host Halos at z~2-3

Adelberger & Steidel 2005b

Environments of Very Bright QSOs (m~16-17) @z2.5-2.8

In 12 fields of ultraluminous QSOs, only 1

bright QSO is in a substantial over-

density: HS1549+19

@z=2.84

~7’x5’, ~140 ~7’x5’, ~140 objects objects

z~1.8-3.2z~1.8-3.2

Two m~24 QSOs @ same redshift as HS1549 (2.845)

AGN and Star-forming galaxies at z~2-3.5:

• Bright and faint (optical) AGN, over ~ 10 mags of dynamic range, inhabit essentially the same dark matter halos and the same environments as the blue star-forming galaxies in the spectroscopic sample– r0~5h-1 Mpc at z~2-3, independent of AGN (UV) luminosity– Significantly weaker clustering than red galaxies at similar

redshifts (cf. Quadri et al 2006- see also his poster)• Faint AGN have much longer duty cycle (they are “on” for a much

larger fraction of the time) than bright ones• Apparently, quasars cluster like ~ L* star forming galaxies (galaxies

with the largest gas supplies) at all redshifts– e.g., Coil et al 2006 z~1: r0~3.7h-1 Mpc

HS1700+64 z=2.300 Proto-cluster

186 spec. 1.7<z<3.2

8 AGN

Data Include:

•Optical and near-IR spectroscopy (Keck)

•Deep J,K imaging (Palomar)

•Deep H (2.17m) (Palomar, 25 hours)

•Ly imaging (in progress)

•HST/ACS

•Chandra (coming soon)

•Spitzer/IRAC, extremely deep MIPS

Inferred Properties vs. Environment

Spike: <Age>=1450 Myr

Field: <Age>=700 Myr <M*>spike/<M*>field=1.8

CS et al 2005

HS1700+64 z=2.300 Proto-cluster “Map”

Black: spec. confirmed z=2.30 (rest-UV selected)

Blue: H n.b. candidate z=2.30

Red: all DRGs K<21.0

Green: LyGreen: Ly n.b. n.b. candidatecandidate

“(Some) Ways Forward”

• Establish the details of the spatial relationship between galaxies and AGN/QSOs at the redshifts where big galaxies are emerging. – Lots of spectroscopy is required, both optical and near-IR

• Understand “feedback” processes: beyond “hand waving”– Would like in situ, not just circumstantial, evidence – Probably involves observing gas, not stars

• Do we really understand the implications of “down-sizing”?– Are we missing something important in our understanding of how gas

cooling/SF works at high redshifts?