STRONG C⁺EMISSION IN GALAXIES ATz∼ 1-2: EVIDENCE FOR COLD FLOW ACCRETION POWERED STAR FORMATION IN THE EARLY UNIVERSE

Abstract

We have recently detected the [CII] 157.7 µm line in eight star forming galaxies at redshifts 1 to 2 using the redshift(z) Early Universe Spectrometer (ZEUS). Our sample targets star formation dominant sources detected in PAH emission. This represents a significant addition to [CII] observations during the epoch of peak star formation. We have augmented this survey with observations of the [OI] 63 µm line and far infrared photometry from the PACS and SPIRE Herschel instruments as well as Spitzer IRS spectra from the literature showing PAH features. Our sources exhibit above average gas heating efficiency, many with both [OI]/FIR and [CII]/FIR ∼1% or more. The relatively strong [CII] emissionis consistent with our sources being dominated by star formation powered PDRs, extending to kpc scales. We suggest that the star formation mode in these systems follows a Schmidt-Kennicutt law similar to local systems, but at a much higher rate due to molecular gas surface densities 10 to 100 times that of local star forming systems. The source of the high molecular gas surface densities may be the infall of neutral gas from the cosmic web. In addition to the high [CII]/FIR values, we also find high [CII]/PAH ratios and, in at least one source, a cool dust temperature. This source, SWIRE 4-5, bears a resemblance in these diagnostics to shocked regions of Stephan's Quintet, suggesting that another mode of [CII] excitation in addition to normal photoelectric heating may be contributing to the observed [CII] line.

ALMA Reveals Strong Emission in a Galaxy Embedded in a Giant Lyα Blob at z = 3.1

“…The result implies different conditions responsible for [C II] emission between ALMA3 and the majority of previously known IR-luminous galaxies. It has also been reported that some z∼1-2 ULIRGs show L [C II] /L IR ratios comparable to ALMA3, although they have slightly higher L IR than ALMA3 (Brisbin et al 2015). One possible explanation for elevated [C II]-IR ratios is that the galaxies host widely spread star formation, and the UV radiation field is therefore diluted, which make the [C II] line a more efficient coolant (see, e.g., Brisbin et al 2015;Cicone et al 2015 and references therein).…”

“…It has also been reported that some z∼1-2 ULIRGs show L [C II] /L IR ratios comparable to ALMA3, although they have slightly higher L IR than ALMA3 (Brisbin et al 2015). One possible explanation for elevated [C II]-IR ratios is that the galaxies host widely spread star formation, and the UV radiation field is therefore diluted, which make the [C II] line a more efficient coolant (see, e.g., Brisbin et al 2015;Cicone et al 2015 and references therein). The size of the dust continuum core in ALMA3 is 4.1 kpc, which is larger than a typical continuum size of bright SMGs at similar redshifts (2.4 kpc; Simpson et al 2015; see also Ikarashi et al 2015;Umehata et al 2016).…”

“…This supports that a relatively extended star-forming region in ALMA3 contributes the high [C II]/IR ratio for ALMA3. Gas accretion from the cosmic web is expected to accumulate a large amount of molecular gas necessary to fuel such widespread star formation (Brisbin et al 2015).…”

The nature of the [C ii] emission in dusty star-forming galaxies from the SPT survey

“…The number of [CII] detections has been steadily increasing since then, thanks to facilities such as the Caltech Submillimeter Observatory (CSO), the Submillimeter Array, the IRAM 1 Plateau de Bure Interferometer, the Atacama Pathfinder EXperiment (APEX), the Herschel Space Observatory, the Combined Array for Research in Millimeter-wave Astronomy, and the Atacama Large Millimeter/submillimeter Array (ALMA). At 1 < z < 2, 21 [CII] detections were made using the redshift (z) and Early Universe Spectrometer (ZEUS) on CSO Stacey et al 2010;Brisbin et al 2015), while Herchel detected three [CII] lines at 1.5 < z < 3 (Ivison et al 2010; Valtchanov et al…”

“…Maiolino et al 2005;Stacey et al 2010;Wang et al 2013), while others have been selected as starburst galaxies (e.g. Ivison et al 2010;Hailey-Dunsheath et al 2010;Stacey et al 2010;Cox et al 2011;Swinbank et al 2012;Walter et al 2012;Riechers et al 2013;Brisbin et al 2015). This leads to a heterogeneous sample of high-z [CII] detections, containing a mixture of AGN and starburst-dominated systems.…”