Zusammenfassung
The first quenched galaxies (z>2) are both the most massive, and most
compact, suggesting a physical connection between high stellar density and
efficient, rapid cessation of star-formation. We present rest-frame UV spectra
of Lyman-break galaxies (LBGs) at z~3 selected to be candidate progenitors of
the quenched galaxies at z~2, compared to other LBGs of similar mass and
star-formation rate (non-candidates). We find that candidate progenitors have
faster outflow velocities and higher equivalent widths of interstellar
absorption lines, implying larger velocity spread among absorbing clouds.
Candidates deviate from the relationship between equivalent widths of
Lyman-alpha and interstellar absorption lines in that their Lyman-alpha
emission remains strong despite high interstellar absorption, possibly
indicating that the neutral HI fraction is patchy, such that Lyman-alpha
photons can escape. We detect stronger CIV P-Cygni features (emission and
absorption) and HeII emission in candidates, indicative of larger populations
of metal-rich Wolf-Rayet stars compared to non-candidates. The faster outflows,
broader spread of gas velocity, and Lyman-alpha properties of candidates are
consistent with their ISM being subject to more energetic feedback than
non-candidates. Together with their larger metallicity (implying more evolved
star-formation activity) this leads us to propose, if speculatively, that they
are likely to quench sooner than non-candidates, supporting the validity of
selection criteria used to identify them as progenitors of z~2 passive
galaxies. We propose that massive, compact galaxies undergo more rapid growth
of their stellar mass content, perhaps because the gas accretion mechanisms are
different, and quench sooner than normally-sized LBGs at these (early) epochs.
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