Abstract
ABSTRACT While the kinematics of galaxies up to z ∼ 3 have been characterized in detail, only a handful of galaxies at high redshift (z > 4) have been examined in such a way. The Atacama Large Millimeter/submillimeter Array (ALMA) Large Program to INvestigate [C ii] at Early times (ALPINE) survey observed a statistically significant sample of 118 star-forming main-sequence galaxies at z = 4.4–5.9 in [C ii]158 $\mu$m emission, increasing the number of such observations by nearly 10×. A preliminary qualitative classification of these sources revealed a diversity of kinematic types (i.e. rotators, mergers, and dispersion-dominated systems). In this work, we supplement the initial classification by applying quantitative analyses to the ALPINE data: a tilted ring model (TRM) fitting code (3Dbarolo), a morphological classification (Gini-M20), and a set of disc identification criteria. Of the 75 [C ii]-detected ALPINE galaxies, 29 are detected at sufficient significance and spatial resolution to allow for TRM fitting and the derivation of morphological and kinematic parameters. These 29 sources constitute a high-mass subset of the ALPINE sample ($M_*\gt 10^{9.5}\, \mathrm{M}_{\odot }$). We robustly classify 14 of these sources (six rotators, five mergers, and three dispersion-dominated systems); the remaining sources showing complex behaviour. By exploring the G-M20 of z > 4 rest-frame far-infrared and [C ii] data for the first time, we find that our 1 arcsec ∼ 6 kpc resolution data alone are insufficient to separate galaxy types. We compare the rotation curves and dynamical mass profiles of the six ALPINE rotators to the two previously detected z ∼ 4–6 unlensed main-sequence rotators, finding high rotational velocities (∼50–250 km s−1) and a diversity of rotation curve shapes.
Highlights
The past century has seen a massive broadening of scope in the study of galaxy kinematics
For the continuum maps of the 21 sources detected in [CII] and FIR emission, the majority of the galaxies lie at low G (i.e., ∼ 0.2−0.3), and there is no obvious separation between the kinematic classes
While the class 1-3 objects spread to higher G (i.e., ∼ 0.2 − 0.55), there again is no separation between the kinematic classes
Summary
The past century has seen a massive broadening of scope in the study of galaxy kinematics. Works focused on spectral line emission from single nearby galaxies (e.g., Pease 1918; Burbidge et al 1959), while current studies are able to probe the kinematics of many local objects (e.g., Garrido et al 2002; Conselice et al 2005; de Blok et al 2008; Shapiro et al 2008; Puech 2010; Gómez-López et al 2019; Korsaga et al 2019; den Brok et al 2020) or single objects in much greater detail (e.g., Carignan et al 2006; Cramer et al 2019; North et al 2019; Braine et al 2020) This detailed analysis has been extended to galaxies at intermediate redshift (i.e., z ∼ 1 − 3; tH ∼ 6 − 2 Gyr) with integral field spectroscopy, mostly in the restframe optical and near-infrared (e.g., Förster Schreiber et al 2006; Epinat et al 2012; Burkert et al 2016; Turner et al 2017; Harrison et al 2017; Molina et al 2017; Swinbank et al 2017; Wisnioski et al 2019; Loiacono et al 2019). This is quite similar to the rotation curves of local galaxies, which show nearly constant or only slightly declining velocities at large radii (e.g., de Blok et al 2008), indicating the additional gravitational force from an underlying dark matter halo (e.g., Rubin & Ford 1970)
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