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19 April 2024 |
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Morphology Dependence Of Stellar Age in Quenched Galaxies at Redshift ~ 1.2: Massive Compact Galaxies Are Older Than More Extended Ones | | Christina C. Williams
; Mauro Giavalisco
; Rachel Bezanson
; Nico Cappelluti
; Paolo Cassata
; Teng Liu
; Bomee Lee
; Elena Tundo
; Eros Vanzella
; | | Date: |
20 Jul 2016 | | Abstract: | We report the detection of morphology-dependent stellar age in massive
quenched galaxies at redshift z~1.2. The sense of the dependence is that
compact quenched galaxies are 0.5-2 Gyr older than normal-sized ones. The
evidence comes from three different age indicators, Dn4000, H$delta_{A}$, and
fits to spectral synthesis models, applied to the stacked optical spectra of
massive, quenched galaxies observed during the CANDELS project. All age
indicators consistently show that the dominant stellar populations of compact
passive galaxies are older than those of their normally-sized counterparts,
with the Dn4000 and model fitting in excellent quantitative agreement. We
detect weak [OII] emission in a fraction of passive galaxies, and the strength
of the line, when present, is similar between the two samples; however, compact
galaxies have a significantly lower frequency of [OII] emission than normal
ones. A fraction of both compact and normal galaxies are also individually
detected in the 4 Ms Chandra X-ray images, with luminosity in the range
10$^{40}$-10$^{41}$ erg/sec; while both [OII] emitters and non-emitters are
found to be X-ray sources among normal galaxies, no compact galaxy with [OII]
emission is an X-ray source, arguing against an AGN powering the line in
compact galaxies. We interpret the [OII] properties as further evidence that
compact galaxies are older and are further along into the process of quenching
star formation and suppressing gas accretion. Finally, we argue that the older
stellar age of the compact passive galaxies is further evidence of progenitor
bias: compact passive galaxies are older because they reflect the smaller sizes
of galaxies at their earlier quenching epoch, with stellar density most likely
having nothing directly to do with the cessation of their star formation. | | Source: | arXiv, 1607.6089 | | Services: | Forum | Review | PDF | Favorites | |
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