Evidence for Non-smooth Quenching in Massive Galaxies at z ∼ 1

Abstract

We investigate a large sample of massive galaxies at z ∼ 1 with combined HST broad-band and grism observations to constrain the star-formation histories of these systems as they transition from a star-forming state to quiescence. Among our sample of massive (M * > 10 10 M ) galaxies at 0.7 < z < 1.2, dust-corrected Hα and UV star-formation indicators agree with a small dispersion (∼ 0.2 dex) for galaxies on the main sequence, but diverge and exhibit substantial scatter (∼ 0.7 dex) once they drop significantly below the star-forming main sequence. Significant Hα emission is present in galaxies with low dust-corrected UV SFR values as well as galaxies classified as quiescent using the UV J diagram. We compare the observed Hα flux distribution to the expected distribution assuming bursty or smooth star-formation histories, and find that massive galaxies at z ∼ 1 are most consistent with a quick, bursty quenching process. This suggests that mechanisms such as feedback, stochastic gas flows, and minor mergers continue to induce low-level bursty star formation in massive galaxies at moderate redshift, even as they quench.

Clues on the history of early-type galaxies from SDSS spectra and GALEX photometry

“…Works by the SAURON collaboration have found that ETGs can be divided in fast and slow rotators (Emsellem et al 2007) according to the prominence of their rotational component, a classification that has been linked to different formation processes (Cappellari et al 2011;Penoyre et al 2017;Smethurst et al 2018). A recent paper by Carleton et al (2020) shows a discrepancy between UV and H α star-formation rates in massive galaxies at z ∼ 1, indicative of low-level bursty star-formation. A series of papers from the SPIDER project also shed light on the diversity of the population of ETGs and the environmental processes involved in their formation (e.g La Barbera et al 2010Barbera et al , 2014.…”

H$α$-based Star Formation Rates in and around z $\sim$ 0.5 EDisCS clusters

“…The mass-metallicity relation is derived from Zahid et al (2014), which is then transformed into an H𝛼/[NII] ratio (Kewley & Ellison 2008), resulting in a flux reduction of ∼ 33% for our sample. Carleton et al (2020) required a ∼ 25% correction for z ∼ 1 galaxies, while 3D-HST (Wuyts et al 2011) found ∼ 20%. There is a secondary dependence of the metallicity on the SFR at a fixed stellar mass known as the Fundamental Metallicity Relation (FMR; Mannucci et al 2010).…”

“…GRIZLI outputs a line flux, but there are several intrinsic properties that need to be accounted for while calculating a SFR. Following the prescription in Carleton et al (2020), a series of corrections are applied to achieve a correct H𝛼-based SFR. The resolution of the grism is not fine enough to distinguish between the H𝛼 and [NII] line doublet emission, indicating that measured line fluxes include the contribution of [NII] and therefore need to be reduced to account for the additional flux.…”

“…The resolution of the grism is not fine enough to distinguish between the H𝛼 and [NII] line doublet emission, indicating that measured line fluxes include the contribution of [NII] and therefore need to be reduced to account for the additional flux. Strom et al (2017) find that the [NII] contribution is uniform across SFR per given stellar mass, so Carleton et al (2020) calculates this reduction through a mass-dependent metallicity relation. The mass-metallicity relation is derived from Zahid et al (2014), which is then transformed into an H𝛼/[NII] ratio (Kewley & Ellison 2008), resulting in a flux reduction of ∼ 33% for our sample.…”

H α-based star formation rates in and around z ∼ 0.5 EDisCS clusters

“…The GRIZLI -extracted redshifts with a spectroscopic (top right) or photometric (bottom right) prior are shown in comparison to their blind redshift. luminosity (Carleton et al 2020 ), where the factor of two comes from the 1:1 ratio of [N II ]/H α lines (Belfiore et al 2016 ) and the 1.37 × 10 29 factor comes from the expected contribution of ionization by the post-AGB stars. When compared to the H α line luminosity ( ∼10 40 -10 42 ), the post-AGB emission is negligible.…”