Highredshift galaxies: Lymanbreak galaxies Rob Detmers

1
High-redshift galaxiesLyman-break galaxiesRob
Detmers Steven Rieder
2
(No Transcript)
3
The search for high-z galaxies

• Searches for primaeval galaxies in the late
  1970's and early 1980's.
• faint galaxy redshift surveys made possible by
  CCD cameras and higher resolution spectroscopy in
  the late 1980's and early 1990's.
• the launch of Hubble Space Telescope (HST) and
  its revelation of resolved galaxy images to
  significant redshifts.
• Breaktrough in 1995 due to new technique of color
  selection.
• the arrival of 8m telescopes bringing a new wave
  of faint Lyman-break galaxy spectroscopy at
  unprecedented redshifts.

4
Importance of high-z galaxy studies

• Constraining the history of galaxy evolution
• Formation of the Hubble Sequence.
• SFR in the early universe.

5
Lyman-Break Galaxies

• Starburst galaxies at high redshift ( 2.5ltzlt5 ).
• No AGN.
• Identified by the colors of their far UV SED
  around 912Å.

6
Important properties

• Starburst Star-Formation Rate.
• Chemical Abundances.
• Stellar Mass and Age.
• Morphology.
• Clustering.

7
LBG Starbursts

• A starburst galaxy is a galaxy with such a high
  star formation rate that it will turn all of its
  gas into stars in tb ltlt tHubble .
• LBG spectra similar to local starburst galaxies.
• Large velocity widths seen in spectra FWHM of
  400-700 km/s due to SN and stellar wind ejecta.
• Much more intense UV emission ? more massive (O
  and B) stars.

8
(No Transcript)
9
Star-Formation Rate

• Neglecting dust obscuration, the far UV
  luminosity is proportional to the SFR.
• Try to correct the UV data for the dust
  obscuration.
• But tight correlation between slope of UV
  continuum and dust obscuration!
• Compare the ratio of far-IR to the bolometric
  luminosity.
• SFR100-1000Msun/year.

10
The SFR vs redshift
11
Chemical Abundances

• Important for the evolutionary link to present
  galaxies.
• Problem lines are heavily saturated?cannot
  measure column density.
• One can only determine a lower boundary, which is
  about 1/10 solar metallicity.

12
Stellar Mass and Age

• UV spectrum only provides information on the
  young, massive stars.
• Use stellar population synthesis models to
  determine intrinsic parameters of the stellar
  population.
• Assume IMF, metallicity and extinction, adjust
  other parameters to the fit.
• Masses of about 1010 Msun are found.

13
Morphology

• HST can resolve individual starburst regions.
• Widely different morphologies, no visible Hubble
  types.
• Smaller, higher SFR and more compact than
  present-day starburst galaxies.
• But light is dominated by the starburst regions,
  which have different morphology from that of the
  underlying galaxies.

14
LBG Observations
15
Clustering

• Opened by the high efficiency of LBG technique.
• Samples, though adequate are still small?large
  fluctuations volume density in samples.
• Still it is apparent that LBGs have strong
  spatial clustering.
• Clustering has a large impact on SFR, tidal
  interactions between galaxies may trigger
  starbursts.

16
Conclusions

• No clear morphology?Hubble Sequence at a later
  epoch.
• LBGs have strong spatial clustering?testing
  ground for current theories on galaxy formation.
• SFR appears to increase with redshift.
• Important to continue the observations of the
  high redshift universe with higher resolution and
  larger samples.