Turbulent Gas in Lensed Planck-selected Starbursts at z ∼ 1–3.5

Abstract

Abstract Dusty star-forming galaxies at high redshift (1 &lt; z &lt; 3) represent the most intense star-forming regions in the universe. Key aspects to these processes are the gas heating and cooling mechanisms, and although it is well known that these galaxies are gas-rich, little is known about the gas excitation conditions. Only a few detailed radiative transfer studies have been carried out owing to a lack of multiple line detections per galaxy. Here we examine these processes in a sample of 24 strongly lensed star-forming galaxies identified by the Planck satellite (LPs) at z ∼ 1.1–3.5. We analyze 162 CO rotational transitions (ranging from J up = 1 to 12) and 37 atomic carbon fine-structure lines ([C i ]) in order to characterize the physical conditions of the gas in the sample of LPs. We simultaneously fit the CO and [C i ] lines and the dust continuum emission, using two different non-LTE, radiative transfer models. The first model represents a two-component gas density, while the second assumes a turbulence-driven lognormal gas density distribution. These LPs are among the most gas-rich, IR-luminous galaxies ever observed ( μ L <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" overflow="scroll"> <mml:msub> <mml:mrow> <mml:mi>L</mml:mi> </mml:mrow> <mml:mrow> <mml:mi>IR</mml:mi> <mml:mo stretchy="false">(</mml:mo> <mml:mn>8</mml:mn> <mml:mo>−</mml:mo> <mml:mn>1000</mml:mn> <mml:mspace width="0.25em"/> <mml:mi>μ</mml:mi> <mml:mi mathvariant="normal">m</mml:mi> <mml:mo stretchy="false">)</mml:mo> </mml:mrow> </mml:msub> <mml:mo>∼</mml:mo> <mml:msup> <mml:mrow> <mml:mn>10</mml:mn> </mml:mrow> <mml:mrow> <mml:mn>13</mml:mn> <mml:mo>−</mml:mo> <mml:mn>14.6</mml:mn> </mml:mrow> </mml:msup> </mml:math> L ⊙ ; <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" overflow="scroll"> <mml:mo stretchy="false">〈</mml:mo> </mml:math> μ L M ISM <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" overflow="scroll"> <mml:mo stretchy="false">〉</mml:mo> </mml:math> = (2.7 ± 1.2) × 10 12 M ⊙ , with μ L ∼ 10–30 the average lens magnification factor). Our results suggest that the turbulent interstellar medium present in the LPs can be well characterized by a high turbulent velocity dispersion ( <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" overflow="scroll"> <mml:mo stretchy="false">〈</mml:mo> </mml:math> Δ V turb <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" overflow="scroll"> <mml:mo stretchy="false">〉</mml:mo> </mml:math> ∼ 100 km s −1 ) and ratios of gas kinetic temperature to dust temperature <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" overflow="scroll"> <mml:mo stretchy="false">〈</mml:mo> </mml:math> T kin / T d <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" overflow="scroll"> <mml:mo stretchy="false">〉</mml:mo> </mml:math> ∼ 2.5, sustained on scales larger than a few kiloparsecs. We speculate that the average surface density of the molecular gas mass and IR luminosity, <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" overflow="scroll"> <mml:msub> <mml:mrow> <mml:mi mathvariant="normal">Σ</mml:mi> </mml:mrow> <mml:mrow> <mml:msub> <mml:mrow> <mml:mi>M</mml:mi> </mml:mrow> <mml:mrow> <mml:mi>ISM</mml:mi> </mml:mrow> </mml:msub> </mml:mrow> </mml:msub> </mml:math> ∼ 10 3–4 M ⊙ pc −2 and <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" overflow="scroll"> <mml:msub> <mml:mrow> <mml:mi mathvariant="normal">Σ</mml:mi> </mml:mrow> <mml:mrow> <mml:msub> <mml:mrow> <mml:mi>L</mml:mi> </mml:mrow> <mml:mrow> <mml:mi>IR</mml:mi> </mml:mrow> </mml:msub> </mml:mrow> </mml:msub> </mml:math> ∼ 10 11–12 L ⊙ kpc −2 , arise from both stellar mechanical feedback and a steady momentum injection from the accretion of intergalactic gas.