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Massive galaxies at z > 1.5 By Hans Buist Supervisor Scott Trager Date 22nd of june 2007
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?
