A dense, solar metallicity ISM in the z = 4.2 dusty star-forming galaxy SPT 0418−47

Abstract

We present a study of six far-infrared fine structure lines in the z=4.225 lensed dusty star-forming galaxy SPT 0418-47 to probe the physical conditions of its inter stellar medium (ISM). In particular, we report Atacama Pathfinder EXperiment (APEX) detections of the [OI] 145µm and [OIII] 88µm lines and Atacama Compact Array (ACA) detections of the [NII] 122 and 205µm lines. The [OI] 145µm / [CII] 158µm line ratio is ∼5× higher compared to the average of local galaxies. We interpret this as evidence that the ISM is dominated by photo-dissociation regions with high gas densities. The line ratios, and in particular those of [OIII] 88µm and [NII] 122µm imply that the ISM in SPT 0418-47 is already chemically enriched close to solar metallicity. While the strong gravitational amplification was required to detect these lines with APEX, larger samples can be observed with the Atacama Large Millimeter/submillimeter Array (ALMA), and should allow observers to determine if the dense, solar metallicity ISM is common among these highly star-forming galaxies.

A dynamically cold disk galaxy in the early Universe

“…Here we report the presence of a dynamically cold, but highly star-forming, rotating disk in a galaxy at redshift 6 z = 4.2, when the Universe was just 1.4 billion years old. Galaxy SPT-S J041839-4751.9 is strongly gravitationally lensed by a foreground galaxy at z = 0.263, and it is a typical dusty starburst, with global star-forming 7 and dust properties 8 that are in agreement with current numerical simulations 9 and observations 10 . Interferometric imaging at a spatial resolution of about 60 parsecs reveals a ratio of rotational to random motions of 9.7 ± 0.4, which is at least four times larger than that expected from any galaxy evolution model at this epoch [1][2][3][4][5] but similar to the ratios of spiral galaxies in the local Universe 11 .…”

In pursuit of giants

“…Our assumption is additionally motivated by recent spectroscopy studies of DSFGs in the HUDF field, for which metallicities consistent with solar are inferred at 1 < z < 3 (Boogaard et al 2019, see also Nagao et al 2012;Kriek et al 2016;De Breuck et al 2019) 2 . We adopt the flexible star-formation historiy (SFH), which is composed of a delayed component with an additional burst.…”

Big Three Dragons: A [N II] 122 $μ$m Constraint and New Dust-continuum Detection of A $z = 7.15$ Bright Lyman Break Galaxy with ALMA

“…Observations of [N II] lines are limited at high-redshift, but the number of detections has been increasing. [NII] 122 µm lines are detected in quasars at z = 7.54 (Novak et al 2019) and at z = 6.003 (Li et al 2020), a dusty star-forming galaxy (DSFG) at z = 4.22 (De Breuck et al 2019), and a submillimeter galaxy (SMG) and quasar system at z = 4.69 (Lee et al 2019), whereas Harikane et al (2020) reported three LBGs at z ∼ 6 that are not detected in [N II] 122 µm lines despite detecting them in [C II] and [O III] lines. In another excitation state, [N II] 205 µm lines are detected in galaxies at z = 5-6 (Pavesi et al 2016), SMGs at 3 < z < 6 (Cunningham et al 2020), and z > 4 objects, including quasars and DSFGs (e.g., Decarli et al 2014;De Breuck et al 2019;Novak et al 2019;Cheng et al 2020).…”