Highredshift galaxies: Lymanbreak galaxies Rob Detmers - PowerPoint PPT Presentation
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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
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High-redshift galaxiesLyman-break galaxiesRob
Detmers Steven Rieder
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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.
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Importance of high-z galaxy studies
- Constraining the history of galaxy evolution
- Formation of the Hubble Sequence.
- SFR in the early universe.
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Lyman-Break Galaxies
- Starburst galaxies at high redshift ( 2.5ltzlt5 ).
- No AGN.
- Identified by the colors of their far UV SED
around 912Å.
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Important properties
- Starburst Star-Formation Rate.
- Chemical Abundances.
- Stellar Mass and Age.
- Morphology.
- Clustering.
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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.
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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.
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The SFR vs redshift
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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.
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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.
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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.
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LBG Observations
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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.
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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.
