A Radio-to-mm Census of Star-forming Galaxies in Protocluster 4C23.56 at Z=2.5: Gas Mass and Its Fraction Revealed with ALMA

作者：Lee Minju M; Tanaka Ichi; Kawabe Ryohei; Kohno Kotaro; Kodama Tadayuki; Kajisawa Masaru; Yun Min S; Nakanishi Kouichiro; Iono Daisuke; Tamura Yoichi; Hatsukade Bunyo; Umehata Hideki; Saito Toshiki; Izumi Takuma; Aretxaga Itziar; Tadaki Ken ichi; Zeballos Milagros; Ikarashi Soh; Wilson Grant W; Hughes David H; Ivison R J

来源：Astrophysical Journal, 2017, 842(1): 55.

DOI：10.3847/1538-4357/aa74c2

• galaxies: clusters: general
• galaxies: evolution
• galaxies: high-redshift
• galaxies: ISM
• large-scale structure of universe
• submillimeter: galaxies

We investigate gas contents of star-forming galaxies associated with protocluster 4C23.56 at z = 2.49. by using the redshifted CO (3-2) and 1.1mm dust continuum with the Atacama Large Millimeter/submillimeter Array. The observations unveil seven CO detections out of 22 targeted Ha emitters (HAEs). and four out of 19 in 1.1 mm dust continuum. They have high stellar mass (M-star > 4 x 10(10) M-circle dot) and exhibit a. specific star-formation rate typical of main-sequence star-forming. galaxies at z similar to 2.5. Different gas-mass estimators from CO. (3-2) and 1.1mm yield consistent values for simultaneous detections. The gas mass (M-gas) and gas fraction (f(gas)) are comparable to those of field galaxies, with M-gas = [0.3, 1.8] x 10(11) x (alpha(CO)/(4.36 x A(Z))) M-circle dot, where alpha(CO) is the CO-to-H-2 conversion factor and A(Z) is the additional correction factor for the metallicity dependence of alpha(CO), and < f(gas)> = 0.53 +/- 0.07 from CO (3-2). Our measurements place a constraint on the cosmic gas density of high-z protoclusters, indicating that. the protocluster is characterized by a gas density higher than that of the general fields by an order of magnitude. We found rho(H-2) similar to 5 x 10(9) M-circle dot Mpc(-3) with the CO(3-2) detections. The five ALMA CO detections occur in the region of. highest galaxy surface density,. where the density positively correlates with global star-forming efficiency (SFE) and stellar mass. Such correlations possibly indicate a critical role of the. environment on early galaxy evolution at high-z protoclusters, though future observations are necessary for confirmation.

• 出版日期2017-6-10
• 单位中国科学院国家天文台