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Highredshift galaxies: Lymanbreak galaxies Rob Detmers

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The search for high-z galaxies. Searches for primaeval galaxies in the late 1970's and early 1980's. ... LBG spectra similar to local starburst galaxies. ... – PowerPoint PPT presentation

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Title: Highredshift galaxies: Lymanbreak galaxies Rob Detmers


1
High-redshift galaxiesLyman-break galaxiesRob
Detmers Steven Rieder
2
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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
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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.
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