ALMA finds dew drops in the dusty spider’s web

Abstract

We present 0 . 5 resolution ALMA detections of the observed 246 GHz continuum, [CI] 3 P 2 → 3 P 1 fine structure line ([CI]2-1), CO(7-6), and H 2 O lines in the z = 2.161 radio galaxy MRC1138-262, the so-called Spiderweb galaxy. We detect strong [CI]2-1 emission both at the position of the radio core, and in a second component ∼4 kpc away from it. The 1100 km s −1 broad [CI]2-1 line in this latter component, combined with its H 2 mass of 1.6 × 10 10 M , implies that this emission must come from a compact region <60 pc, possibly containing a second active galactic nucleus (AGN). The combined H 2 mass derived for both objects, using the [CI]2-1 emission, is 3.3 × 10 10 M . The total CO(7-6)/[CI]2-1 line flux ratio of 0.2 suggests a low excitation molecular gas reservoir and/or enhanced atomic carbon in cosmic ray dominated regions. We detect spatially-resolved H 2 O 2 11 −2 02 emission -for the first time in a high-z unlensed galaxy -near the outer radio lobe to the east, and near the bend of the radio jet to the west of the radio galaxy. No underlying 246 GHz continuum emission is seen at either position. We suggest that the H 2 O emission is excited in the cooling region behind slow (10-40 km s −1 ) shocks in dense molecular gas (10 3−5 cm −3 ). The extended water emission is likely evidence of the radio jet's impact on cooling and forming molecules in the post-shocked gas in the halo and inter-cluster gas, similar to what is seen in low-z clusters and other high-z radio galaxies. These observations imply that the passage of the radio jet in the interstellar and inter-cluster medium not only heats gas to high temperatures, as is commonly assumed or found in simulations, but also induces cooling and dissipation, which can lead to substantial amounts of cold dense molecular gas. The formation of molecules and strong dissipation in the halo gas of MRC1138-262 may explain both the extended diffuse molecular gas and the young stars observed around MRC1138-262.

Giant galaxy growing from recycled gas: ALMA maps the circumgalactic molecular medium of the Spiderweb in [C i]

“…2). At the highest velocities, the [C i] 3 P 1 -3 P 0 peaks ∼7 kpc SE of the core of the radio galaxy, at a location where previous high-resolution ALMA data found a concentration of [C i] 3 P 2 -3 P 1 (Gullberg et al 2016). The CO(4-3) and [C i] show similar morphologies.…”

“…MRC 1138-262 also has a high L [CI] /L CO ∼0.67, exceeding that of most submm galaxies (SMGs), quasi-stellar objects (QSOs), and lensed galaxies (Walter et al 2011;Alaghband-Zadeh et al 2013;Bothwell et al 2017). We compare our [C i] 3 P 1 -3 P 0 detection with [C i] 3 P 2 -3 P 1 data from Gullberg et al (2016), which we tapered and smoothed to the same spatial resolution ( Fig. 1).…”

“…Some of the CO(1-0) spectra are scaled up by a factor indicated at the bottom-right, to better visualize them. For MRC 1138-262 we also show the [C i] 3 P 2 -3 P 1 line (light blue), derived by tapering and smoothing the ALMA data fromGullberg et al (2016) to the resolution of our [C i] 3 P 1 -3 P 0 data. Galaxy #2 is Hα emitter HAE 229, for whichDannerbauer et al (2017) detected CO(1-0) across a large disk.…”

Quenching by gas compression and consumption

“…To convert the neutral carbon mass to global molecular hydrogen mass M H 2 , we adopt an [C i]-to-H 2 abundance, X [C i] = 3 × 10 −5 following the value derived for M82 (Weiß et al 2003) and adopted in subsequent studies Wagg et al 2006;Gullberg et al 2016b). The conversion to molecular mass includes the mass in Helium by a correction factor of 1.36 (e.g., Solomon & Vanden Bout 2005).…”

Molecular gas on large circumgalactic scales at z = 3.47

“…However, observational evidence for cold accretion in this system is still unclear or marginal. Indeed, observations of molecular gas of this system have either been at very low angular resolution (9.5 × 5.3 arcsec = 80 × 45 kpc; Emonts et al 2013), preventing the association of the molecular emission with intracluster molecular gas or with the blending of CO emission from the various merging galaxies optically identified within the beam of the radio observation, or have resulted in the detection of a few individual clumps associated with either AGN nuclei or clumps excited by the radio jets produced by the central radio galaxy (Gullberg et al 2016). Our detection is likely resulting from a combination of several factors, specifically: 1) sensitivity enabled by ALMA; 2) instrument configuration (enabling the detection of diffuse/extended emission on large scales); 3) properly selected target at the proper cosmic epoch (a massive galaxy at the centre of a protocluster, at redshift z=3.47, when accretion from cosmic streams is expected to be particularly prominent and not yet significantly disrupted by halo-induced shocks); 4) observation of a high enough transition, CO J=4-3, which does not suffer from the reduced contrast against the Cosmic Microwave Background (CMB) (warmer by a factor of 1 + z), which may prevent the detection of very extended emission in lower CO transitions observations (Zhang et al 2016).…”