The ALPINE–ALMA [C ii] Survey: Size of Individual Star-forming Galaxies at z = 4–6 and Their Extended Halo Structure

Abstract

We present the physical extent of [C II] 158 μm line-emitting gas from 46 star-forming galaxies at z=4-6 from the ALMA Large Program to INvestigate C II at Early Times (ALPINE). Using exponential profile fits, we measure the effective radius of the [C II] line ( [ ] r e, C II ) for individual galaxies and compare them with the rest-frame ultraviolet (UV) continuum (r e,UV ) from Hubble Space Telescope images. The effective radius [ ] r e, C II exceeds r e,UV by factors of ∼2-3, and the ratio of [ ] r r e, C e,UV II increases as a function of M star . We do not find strong evidence that the [C II] line, rest-frame UV, and far-infrared (FIR) continuum are always displaced over ;1 kpc scale from each other. We identify 30% of isolated ALPINE sources as having an extended [C II] component over 10 kpc scales detected at 4.1σ-10.9σ beyond the size of rest-frame UV and FIR continuum. One object has tentative rotating features up to ∼10 kpc, where the 3D model fit shows the rotating [C II]-gas disk spread over 4 times larger than the rest-frame UV-emitting region. Galaxies with the extended [C II] line structure have high star formation rate, high stellar mass (M star ), low Lyα equivalent width, and more blueshifted (redshifted) rest-frame UV metal absorption (Lyα line), as compared to galaxies without such extended [C II] structures. Although we cannot rule out the possibility that a selection bias toward luminous objects may be responsible for such trends, the star-formation-driven outflow also explains all these trends. Deeper observations are essential to test whether the extended [C II] line structures are ubiquitous to high-z star-forming galaxies.

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

“…While the spectral and moment zero residuals are low, the velocity dispersion peak is not coincident with the intensity peak, the major axis PVD is not symmetric across = 0 km s −1 , and the velocity field residuals are significant. As suggested by Fujimoto et al (2020), these discrepancies may be caused by interaction with an extended halo or an extended outflow. Despite these imperfections, we classify this as a rotator.…”

“…This has the benefit of excluding low-level noise within the mask, but the relatively high lower SNR threshold (SNR lower = 2.5) causes the 3D Barolo fits to miss diffuse, low-level emission, as seen in the nonzero residuals in the spectra and moment zero maps. Indeed, recent ALMA studies (e.g., Fujimoto et al 2019Fujimoto et al , 2020Ginolfi et al 2020a) have revealed extended [CII] emission around > 4 galaxies, implying the presence of an diffuse, enriched circumgalactic medium (CGM). Because this CGM emission is not captured with our signal isolation technique, the scope of the kinematic analysis in this paper is focused on the relatively compact interstellar medium (ISM) of the galaxy.…”

“…Finally, each of these tilted ring models includes a nonzero velocity dispersion for each ring, which is not accounted for in these dynamical masses. Interestingly, half of the ALPINE rotators also show significant [CII] halos (DC396844, DC881725, VC.7875; Fujimoto et al 2020). The coincidence of enriched (i.e., not pristine) halos and ordered rotation may be caused by a number of phenomena, including star formation-driven outflows, AGN activity (unlikely in the ALPINE sample, which was chosen to exclude type 1 AGN), and past merger activity.…”

The Atacama large aperture submillimeter telescope (AtLAST) concept

“…Although most models predict the CGM to be dominated by hot rarefied gas with T ≥ 10 5 K, in high redshift galaxies observed using deep and well sampled interferometric observations, the CGM was -quite surprisingly -found to include a significant fraction of molecular gas extending up to tens of kpcs. [16][17][18][19] The formation of such massive cold CGM reservoirs may be aided by massive molecular outflows 20,21 and/or galaxy interactions within a dense environment. 22 However, because of their low surface brightness and wide angular extent -molecular CGM components would escape observations conducted with current facilities.…”

ALMA Lensing Cluster Survey: Bright [C ii] 158 μm Lines from a Multiply Imaged Sub-L ⋆ Galaxy at z = 6.0719

“…Since heavy elements produced in stars are returned into the ISM, the metal gas properties traced by these fine-structure lines represent good probes of star formation history and related physical mechanisms (Maiolino & Mannucci 2019). In fact, recent ALMA spatial and kinematic [C II]-line studies have identified signatures of some key mechanisms, including disk rotations (e.g., Jones et al 2017;Smit et al 2018), galaxy mergers (e.g., Hashimoto et al 2019;Le Fèvre et al 2020), and outflows (e.g., Gallerani et al 2018;Spilker et al 2018;Fujimoto et al 2019Fujimoto et al , 2020bGinolfi et al 2020). In conjunction with other fine-structure lines of [O III] and [N II], recent ALMA observations also allow us to perform multiple line diagnostics to constrain the dominant ionization state of the ISM gas (e.g., Inoue et al 2016;Pavesi et al 2016;Laporte et al 2019;Novak et al 2019;Harikane et al 2020).…”