Massive galaxies at z > 1.5

By Hans Buist

Supervisor Scott Trager

Date 22nd of june 2007

Outline

Introduction Measuring distant galaxies

Lyman break method (“drop outs”) Red galaxy method Submillimeter method

Results from surveys Discussing the results

Introduction

Introduction

How to measure distant galaxies?Spectroscopy gives distance

Slow and expensive

In the recent years, new methods have been developed:

Lyman break method (“drop outs”) Red galaxy method Submillimeter method

Lyman break method

Hydrogen gas in the galaxy causes a cut-off at 912 nm

Redshifting causes the cut-off to appear in optical wavelengths (z ~ 3)

The galaxy seems to disappear when using the right filters

True distance measured by spectroscopy

Lyman break method

Image from the Palomar Hale Telescope showing UV dropouts

Red galaxy method

Depends on the Ballmer break (400 nm) Found by using J-K>2.3

Corresponds to U-V>0

Adelberger et al., 2004

Submillimeter method

Local universe: Many galaxies emit in submm due to dust More starformation seems to cause more dust Much dust will cause the UV to be obscured

Submm galaxies would not be found using the Lyman break

Distant galaxies: Metal rich ISM thought to be present

Expected to find submm galaxies

M82, Subaru Telescope, Japan

Results

Results for Lyman break

Lyman Break Galaxies (LBGs)Comoving space density roughly half of

current high luminosity galaxiesSpectra similar to z~0 SF galaxies:

Flat continuum Weak or absent Ly-α emission Prominent high-ionization stellar lines Strong interstellar absorption lines

Results for Lyman break Lyman Break Galaxies (LBGs)

Star forming rate several 10’s of solar masses per year

Show spiral arm or irregular featuresMass around 1010 solar masses

Results for Red galaxy method

Distant Red Galaxies (DRGs)Quite different from LBGs:

Forster Schreiber et al, ApJ, in press (astro-ph/0408077)

Results for Red galaxy method

Distant Red Galaxies (DRGs)24 μm used as indicator for starformation

(SF): 45% is detected in 24 μm 45% is not detected in 24 μm but has other SF

spectral features 10% is not detected and has no other SF spectral

features

Results for Red galaxy method

DRG galaxies

High starformationgalaxies, obscured by

dust

Low starformationgalaxies

Old galaxies, nostarformation(quiescent DRGs)

Results for Red galaxy method

DRG Starburst galaxiesStarforming rate (SFR): 150 solar mass per year1011 solar masses

DRG quiescent galaxiesMore then 1 Gyr oldContribute at most 10% of the total mass at high z

Discussion of results / Conclusion

Madau et al., 1996

Discussion of results

From the LBGs:At around z ~ 1-2 a peak in starformation rateAt most 1/2 of the metals formed before z ~ 1

Discussion of results

From the LBGs:At around z ~ 1-2 a peak in starformation rateAt most 1/2 of the metals formed before z ~ 1~ 50% of the stars (=metals) are in spheroid

components (i.e. galaxy halo, ellipticals) These components formed quick (< 1Gyr) and a

long time ago

Discussion of results

It’s very likely that the LBGs are what later becomes the spheroid component of massive spiral galaxiesMasses seem to fitSFR is low enough to prevent the galaxy from

converting its gas completely into stars and becoming an E or S0

Timescales seem to be correct as well

Discussion of results

From the highly obscured DRGs:Much higher SFR and therefore run out of gas

quickly (less then a Gyr or so)Very likely to become the big E and S0

galaxies at z ~ 0Masses also are 1011 Msolar

Discussion of results

From the qDRGs:Are already early types and likely to remain

that way

From the moderate SFR DRGs:Probably end up as ellipticals and S0’s as

well. (Are they comparable to current-day spirals?)

Early type galaxies

SpiralsDRG

LBG

The end

Questions?