Massive Dead Galaxies at z~2 with HST Grism Spectroscopy I. Star Formation and Metallicity Enrichment Histories. (arXiv:1812.06980v1 [astro-ph.GA])
<a href="http://arxiv.org/find/astro-ph/1/au:+Morishita_T/0/1/0/all/0/1">T. Morishita</a>, <a href="http://arxiv.org/find/astro-ph/1/au:+Abramson_L/0/1/0/all/0/1">L. E. Abramson</a>, <a href="http://arxiv.org/find/astro-ph/1/au:+Treu_T/0/1/0/all/0/1">T. Treu</a>, <a href="http://arxiv.org/find/astro-ph/1/au:+Brammer_G/0/1/0/all/0/1">G. B. Brammer</a>, <a href="http://arxiv.org/find/astro-ph/1/au:+Jones_T/0/1/0/all/0/1">T. Jones</a>, <a href="http://arxiv.org/find/astro-ph/1/au:+Kelly_P/0/1/0/all/0/1">P. Kelly</a>, <a href="http://arxiv.org/find/astro-ph/1/au:+Stiavelli_M/0/1/0/all/0/1">M. Stiavelli</a>, <a href="http://arxiv.org/find/astro-ph/1/au:+Trenti_M/0/1/0/all/0/1">M. Trenti</a>, <a href="http://arxiv.org/find/astro-ph/1/au:+Vulcani_B/0/1/0/all/0/1">B. Vulcani</a>, <a href="http://arxiv.org/find/astro-ph/1/au:+Wang_X/0/1/0/all/0/1">X. Wang</a>

Observations have revealed log M*/Msun >11 galaxies that were already dead
when the universe was only ~2Gyr. Given the short time before these galaxies
were quenched, their past histories and quenching mechanism(s) are of
particular interests. In this paper, we study star formation and metallicity
enrichment histories of 24 massive galaxies at 1.650% of their
extant masses by ~1.5Gyr before the time of observed redshifts, with a trend
where more massive galaxies form earlier. Most of our galaxies already have
stellar metallicities compatible with, or even higher than, those of local
early-type galaxies, with a median value of log Z*/Zsun=0.25 and scatter of
~0.15dex. By using reconstructed star formation history, we reveal their rapid
metallicity enrichment history from z~5.5 to 2.2 at a rate of ~0.2dex/Gyr in
logZ*/Zsun. The inferred metallicities are on average ~0.25dex higher than
observed gas-phase metallicities of star forming galaxies at the time of
formation. This supports a view where quenched galaxies continue to form stars
at low-level until recently, rather than abrupt termination of star formation
activity.

Observations have revealed log M*/Msun >11 galaxies that were already dead
when the universe was only ~2Gyr. Given the short time before these galaxies
were quenched, their past histories and quenching mechanism(s) are of
particular interests. In this paper, we study star formation and metallicity
enrichment histories of 24 massive galaxies at 1.6<z<2.5. A deep slitless
spectroscopy + imaging data set collected from multiple HST surveys allows
robust determination of their SEDs. Our new SED modeling provides mass
accumulation/stellar metallicity enrichment histories of those galaxies over
the past ~3Gyr, with no functional assumptions on their star formation
histories. We find that most of our massive galaxies have formed >50% of their
extant masses by ~1.5Gyr before the time of observed redshifts, with a trend
where more massive galaxies form earlier. Most of our galaxies already have
stellar metallicities compatible with, or even higher than, those of local
early-type galaxies, with a median value of log Z*/Zsun=0.25 and scatter of
~0.15dex. By using reconstructed star formation history, we reveal their rapid
metallicity enrichment history from z~5.5 to 2.2 at a rate of ~0.2dex/Gyr in
logZ*/Zsun. The inferred metallicities are on average ~0.25dex higher than
observed gas-phase metallicities of star forming galaxies at the time of
formation. This supports a view where quenched galaxies continue to form stars
at low-level until recently, rather than abrupt termination of star formation
activity.

http://arxiv.org/icons/sfx.gif