PHIBSS: MOLECULAR GAS CONTENT AND SCALING RELATIONS INz∼ 1-3 MASSIVE, MAIN-SEQUENCE STAR-FORMING GALAXIES

Abstract

We present PHIBSS, the IRAM Plateau de Bure high-z blue sequence CO 3-2 survey of the molecular gas properties in normal star forming galaxies (SFGs) near the cosmic star formation peak. PHIBSS provides 52 CO detections in two redshift slices at z~1.2 and 2.2, with log(M * (M  )) ≥10.4 and log(SFR(M  /yr)) ≥ 1.5.Including a correction for the incomplete coverage of the M * -SFR plane, we infer average gas fractions of ~0.33 at z~1.2 and ~0.47 at z~2.2. Gas fractions drop with stellar mass, in agreement with cosmological simulations including strong star formation feedback. Most of the z~1-3 SFGs are rotationally supported turbulent disks. The sizes of CO and UV/optical emission are comparable. The molecular gasstar formation relation for the z=1-3 SFGs is near-linear, with a ~0.7 Gyrs gas depletion timescale; changes in depletion time are only a secondary effect. Since this timescale is much less than the Hubble time in all SFGs between z~0 and 2, fresh gas must be supplied with a fairly high duty cycle over several billion years. At given z and M * , gas fractions correlate strongly with the specific star formation rate. The variation of specific star formation rate between z~0 and 3 is mainly controlled by the fraction of baryonic mass that resides in cold gas.

Dusty star-forming galaxies at high redshift

“…Measurements of high-z star forming galaxies (ranging from relatively quiescent BzK galaxies, forming at ∼ 10 − 100 M yr −1 , to dusty starbursts), suggest gas fractions ranging from f gas ∼ 0.2 − 0.8 (e.g. Daddi et al, 2010a;Tacconi et al, 2010;Geach et al, 2011;Magdis et al, 2012b;Combes et al, 2013;Tacconi et al, 2013). This is to be compared to local galaxies, which show typical gas fractions f gas < 10% (e.g.…”

Redshift evolution of stellar mass versus gas fraction relation in 0 <z< 2 regime: observational constraint for galaxy formation models

“…CO data were retrieved from nine studies Daddi et al 2010;Geach et al 2011;Saintonge et al 2011a;Bauermeister et al 2013;Tacconi et al 2013;Boselli et al 2014;Bothwell et al 2014;Morokuma-Matsui et al 2015) to cover a wide range of redshifts and stellar masses. We adopted the Galactic conversion factor of αCO = 4.35 M⊙(K km s −1 pc 2 ) −1 (including the contribution of helium; Bolatto et al 2013) for all the sample galaxies 2 considered in this study to estimate the molecular gas mass as where L ′ CO represents the luminosity of the 12 CO(J = 1−0) line in units of K km s −1 pc 2 .…”

“…We adopted the Galactic conversion factor of αCO = 4.35 M⊙(K km s −1 pc 2 ) −1 (including the contribution of helium; Bolatto et al 2013) for all the sample galaxies 2 considered in this study to estimate the molecular gas mass as where L ′ CO represents the luminosity of the 12 CO(J = 1−0) line in units of K km s −1 pc 2 . The CO data of Leroy et al (2008), Bothwell et al (2014), Tacconi et al (2013), and Daddi et al (2010) are not based on 12 CO(J = 1 − 0) observations but based on 12 CO(J = 3 − 2) or 12 CO(J = 2 − 1). The conversions to 12 CO(J = 1 − 0) intensity assumed in these studies are described in the following lists.…”

“…• Tacconi et al (2013): Tacconi et al conducted the largest CO survey of z ∼ 1 − 2 galaxies with stellar mass of (0.6 − 17) × 10 10 M⊙ and SFR of 26 − 480 M⊙ yr −1 with the IRAM PdBI and detected CO emissions from 52 galaxies (IRAM Plateau de Bure HIgh-z Blue Sequence Survey, PHIBSS). The stellar mass was estimated from SED fitting.…”

“…Although most HI emission studies 1 in high redshift have been limited to the z ≈ 0.1 − 0.2 regime due to instrumental frequency coverage and sensitivity (Catinella et al 2008;Freudling et al 2011;Fernández et al 2013;Rhee et al 2013), emissions from CO have been detected farther out to z ∼ 6; these emissions have been used to measure the H2 mass in the high-z universe (Carilli & Walter 2013, and references therein). Recent CO surveys of both local and high-z galaxies have revealed molecular gas fractions as a function of stellar mass (Saintonge et al 2011a;Tacconi et al 2013). In addition to these direct measurements of cold gas, newer advances in the observational studies of cold-gas components are also expected from other indirect methods based on the starformation-rate-molecular-gas relation (e.g.…”