Fast rotating and low-turbulence discs atz ≃ 4.5: Dynamical evidence of their evolution into local early-type galaxies

Abstract

Massive starburst galaxies in the early Universe are estimated to have depletion times of ∼100 Myr and thus be able to convert their gas very quickly into stars, possibly leading to a rapid quenching of their star formation. For these reasons, they are considered progenitors of massive early-type galaxies (ETGs). In this paper, we study two high-z starbursts, AzTEC/C159 (z ≃ 4.57) and J1000+0234 (z ≃ 4.54), observed with ALMA in the [C II] 158-μm emission line. These observations reveal two massive and regularly rotating gaseous discs. A 3D modelling of these discs returns rotation velocities of about 500 km s−1 and gas velocity dispersions as low as ≈ 20 km s−1, leading to very high ratios between regular and random motion (V/σ ≳ 20), at least in AzTEC/C159. The mass decompositions of the rotation curves show that both galaxies are highly baryon-dominated with gas masses of ≈1011 M⊙, which, for J1000+0234, is significantly higher than previous estimates. We show that these high-z galaxies overlap with z = 0 massive ETGs in the ETG analogue of the stellar-mass Tully-Fisher relation once their gas is converted into stars. This provides dynamical evidence of the connection between massive high-z starbursts and ETGs, although the transformation mechanism from fast rotating to nearly pressure-supported systems remains unclear.

The ALPINE-ALMA [C ii] Survey: kinematic diversity and rotation in massive star-forming galaxies at z ~ 4.4–5.9

“…The majority of our sources have only 2−3 rings per model (Figure 2). This is much fewer than low-redshift studies (e.g., > 20 for de Blok et al 2008;Lang et al 2020), but is comparable to other > 4 studies (e.g., Jones et al 2017;Fraternali et al 2021). This low number of rings is a direct result of the relatively low spatial resolution of these observations (i.e., ∼ 1 ∼ 7 kpc), as this dictates the spatial scale that we may examine.…”

“…We choose to apply the 3-D tilted ring model fitting code 3D Barolo to the [CII] emission of the ALPINE sample. This code has already been well-tested on data cubes with relatively low resolution and sensitivity (Di Teodoro & Fraternali 2015) and has been successfully applied to high-redshift ( > 2) observations (e.g., Talia et al 2018;Fan et al 2019;Neeleman et al 2020;Fraternali et al 2021).…”

“…A vast sample of rotating galaxies has been well studied at < 4 (e.g., Epinat et al 2008;Förster Schreiber et al 2009;Gnerucci et al 2011), revealing dynamical masses and empirical scaling relations. While a number of clumpy or merging galaxies have been detected at > 4 (e.g., Carniani et al 2018;Pavesi et al 2018;Díaz-Santos et al 2018), and a handful of rotating starburst or quasar host galaxies at ∼ 4 − 6 have been well-modelled (e.g., Jones et al 2017;Pensabene et al 2020;Tadaki et al 2020;Fraternali et al 2021;Lelli et al 2021), only two unlensed rotating main sequence galaxies have been observed at ∼ 4 − 6: HZ9 (Capak et al 2015) and J0817 (Neeleman et al 2017(Neeleman et al , 2020 5 . In this section, we add six new ∼ 4 − 6 rotators from the ALPINE sample to this class: CG32, DC396844, DC494057, DC552206, DC881725, and VC.7875.…”

“…While a multitude of galaxies at < 3 have been well characterized kinematically, it is only recently, with the advent of the Atacama Large Millimeter/submillimeter Array (ALMA) and the Jansky Very Large Array (JVLA), that we are able to characterize the kinematics of high redshift ( > 4) galaxies, using rest-frame far-infrared (FIR) emission lines. This includes the clumpy nature of ∼ 5 − 7 galaxies observed with ALMA in [CII] emission (e.g., Carniani et al 2018), rotational model fitting of ∼ 4 − 6 galaxies (e.g., De Breuck et al 2014;Shao et al 2017;Jones et al 2017;Rizzo et al 2020;Fraternali et al 2021), and even evidence for ordered rotation of galaxies at > 6 (Smit et al 2018;Bakx et al 2020). However, the number of galaxies at > 4 that are kinematically characterizable (i.e., observed with great enough S/N and resolution) is still much less than at < 4.…”

Starbursts with suppressed velocity dispersion revealed in a forming cluster at z = 2.51

“…Recently, observations also found such phenomenon at z > 4 with the presence of massive (M * > 10 10 M ⊙ ) rotation-dominated SBs (faint red points in Fig. 3) [18][19][20][21] , but no information on their environment is yet available. The rotationally supported and dynamically cold disks of the two SBs imply low gas turbulent motions, lower than that in field SBs/MSs at the same redshift (Fig.…”