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Register a new userFluorescent C II* 1335A emission spectroscopically resolved in a galaxy at z = 5.754
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Sarah Elena Ivana Bosman
Publication date
2019
fields
Physics
and research's language is
English
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We report the discovery of the first spectroscopically resolved C II /C II* 1334, 1335A doublet in the Lyman-break galaxy J0215-0555 at z = 5.754. The separation of the resonant and fluorescent emission channels was possible thanks to the large redshift of the source and long integration time, as well as the small velocity width of the feature, 0.6 +- 0.2A. We model this emission and find that at least two components are required to reproduce the combination of morphologies of C II* emission, C II absorption and emission, and Lyman-alpha emission from the object. We suggest that the close alignment between the fluorescence and Lyman-alpha emission could indicate an ionisation escape channel within the object. While the faintness of such a C II /C II* doublet makes it prohibitively difficult to pursue for similar systems with current facilities, we suggest it can become a valuable porosity diagnostic in the era of JWST and the upcoming generations of ELTs.
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SPT0346-52 is one of the most most luminous and intensely star-forming galaxies in the universe, with L_FIR > 10^13 L_sol and Sigma_SFR ~ 4200 M_sol yr^-1 kpc^-2. In this paper, we present ~0.15 ALMA observations of the [CII]158micron emission line in this z=5.7 dusty star-forming galaxy. We use a pixellated lensing reconstruction code to spatially and kinematically resolve the source-plane [CII] and rest-frame 158 micron dust continuum structure at ~700 pc (~0.12) resolution. We discuss the [CII] deficit with a pixellated study of the L_[CII]/L_FIR ratio in the source plane. We find that individual pixels within the galaxy follow the same trend found using unresolved observations of other galaxies, indicating that the deficit arises on scales <700 pc. The lensing reconstruction reveals two spatially and kinematically separated components (~1 kpc and ~500 km s^-1 apart) connected by a bridge of gas. Both components are found to be globally unstable, with Toomre Q instability parameters << 1 everywhere. We argue that SPT0346-52 is undergoing a major merger, which is likely driving the intense and compact star formation.
We present the [CII]158$mu$m line luminosity functions (LFs) at $zsim4-6$ using the ALMA observations of 118 sources, which are selected to have UV luminosity $M_{1500A}<-20.2$ and optical spectroscopic redshifts in COSMOS and ECDF-S. Of the 118 targets, 75 have significant [CII] detections and 43 are upper limits. This is by far the largest sample of [CII] detections which allows us to set constraints to the volume density of [CII] emitters at $zsim4-6$. But because this is a UV-selected sample, we are missing [CII]-bright but UV-faint sources making our constraints strict lower limits. Our derived LFs are statistically consistent with the $zsim0$ [CII] LF at $10^{8.25} - 10^{9.75}L_odot$. We compare our results with the upper limits of the [CII] LF derived from serendipitous sources in the ALPINE maps (Loiacono et al. 2020). We also infer the [CII] LFs based on published far-IR and CO LFs at $zsim4-6$. Combining our robust lower limits with these additional estimates, we set further constraints to the true number density of [CII] emitters at $zsim 4 - 6$. These additional LF estimates are largely above our LF at $L_{[CII]}>10^9L_{odot}$, suggesting that UV-faint but [CII]-bright sources likely make a significant contributions to the [CII] emitter volume density. When we include all the LF estimates, we find that available model predictions underestimate the number densities of [CII] emitters at $zsim4-6$. Finally, we set a constraint on the molecular gas mass density at $zsim4-6$, with $rho_{mol} sim (2-7)times10^7M_odot$,Mpc$^{-3}$. This is broadly consistent with previous studies.
New high-resolution maps with the IRAM Interferometer of the redshifted [C II] 158 micron line and the 0.98mm dust continuum of HDF850.1 at z = 5.185 show the source to have a blueshifted northern component and a redshifted southern component, with a projected separation of 0.3 arcsec, or 2 kpc. We interpret these components as primordial galaxies that are merging to form a larger galaxy. We think it is the resulting merger-driven starburst that makes HDF850.1 an ultraluminous infrared galaxy, with an L(IR) of 1E13 Lsun. The observed line and continuum brightness temperatures and the constant line-to-continuum ratio across the source imply (1) high [C II] line optical depth, (2) a [C II] excitation temperature of the same order as the dust temperature, and (3) dust continuum emission that is nearly optically thick at 158 microns. These conclusions for HDF850.1 probably also apply to other high-redshift submillimeter galaxies and quasar hosts in which the [C II] 158 micron line has been detected, as indicated by their roughly constant [C II]-to-158 micron continuum ratios, in sharp contrast to the large dispersion in their [C II]-to-FIR luminosity ratios. In brightness temperature units, the [C II] line luminosity is about the same as the predicted CO(1-0) luminosity, implying that the [C II] line can also be used to estimate the molecular gas mass, with the same assumptions as for CO.
The scatter in the relationship between the strength of [CII] 158$mu$m emission and the star formation rate at high-redshift has been the source of much recent interest. Although the relationship is well-established locally, several intensely star-forming galaxies have been found whose [CII] 158$mu$m emission is either weak, absent or spatially offset from the young stars. Here we present new ALMA data for the two most distant, gravitationally-lensed and spectroscopically-confirmed galaxies, A2744_YD4 at $z=$8.38 and MACS1149_JD1 at $z=$9.11, both of which reveal intense [OIII] 88$mu$m emission. In both cases we provide stringent upper limits on the presence of [CII] 158$mu$m with respect to [OIII] 88$mu$m. We review possible explanations for this apparent redshift-dependent [CII] deficit in the context of our recent hydrodynamical simulations. Our results highlight the importance of using several emission line diagnostics with ALMA to investigate the nature of the interstellar medium in early galaxies.
Adami et al. (2010) have detected several cluster candidates at z>0.5 as part of a systematic search for clusters in the Canada France Hawaii Telescope Legacy Survey, based on photometric redshifts. We focus here on two of them, located in the D3 field: D3-6 and D3-43. We have obtained spectroscopy with Gemini/GMOS and measured redshifts for 23 and 14 galaxies in the two structures. These redshifts were combined with those available in the literature. A dynamical and a weak lensing analysis were also performed, together with the study of X-ray Chandra archive data. Cluster D3-6 is found to be a single structure of 8 spectroscopically confirmed members at an average redshift z=0.607, with a velocity dispersion of 423 km/s. It appears to be a relatively low mass cluster. D3-43-S3 has 46 spectroscopically confirmed members at an average redshift z=0.739. It can be decomposed into two main substructures, having a velocity dispersion of about 600 and 350 km/s. An explanation to the fact that D3-43-S3 is detected through weak lensing (only marginally, at the ~3sigma level) but not in X-rays could be that the two substructures are just beginning to merge more or less along the line of sight. We also show that D3-6 and D3-43-S3 have similar global galaxy luminosity functions, stellar mass functions, and star formation rate (SFR) distributions. The only differences are that D3-6 exhibits a lack of faint early type galaxies, a deficit of extremely high stellar mass galaxies compared to D3-43-S3, and an excess of very high SFR galaxies. This study shows the power of techniques based on photometric redshifts to detect low to moderately massive structures, even at z~0.75.
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