分类： 天文学 >> 天文学 提交时间： 2023-02-19
Qiong Li
Ran Wang
Helmut Dannerbauer
Zheng Cai
Bjorn Emonts
Jason Xavier Prochaska
Fabrizio Arrigoni Battaia
Roberto Neri
Chengpeng Zhang
Xiaohui Fan
Shuowen Jin
Ilsang Yoon
Shane Bechtel
摘要： The MAMMOTH-1 nebula at $z=2.317$ is an enormous Ly$\alpha$ nebula (ELAN) extending to a $\sim$440 kpc scale at the center of the extreme galaxy overdensity BOSS 1441. In this paper, we present observations of the $\rm CO(3-2)$ and 250 GHz dust-continuum emission from the MAMMOTH-1 using the IRAM NOrthern Extended Millimeter Array. Our observations show that $\rm CO(3-2)$ emission in this ELAN has not extended widespread emission into the circum- and inter-galactic media. We also find a remarkable concentration of six massive galaxies in $\rm CO(3-2)$ emission in the central $\sim$100 kpc region of the ELAN. Their velocity dispersions suggest a total halo mass of $M_{200c} \sim 10^{13.1} M_{\odot}$, marking a possible protocluster core associated with the ELAN. The peak position of the $\rm CO(3-2)$ line emission from the obscured AGN is consistent with the location of the intensity peak of MAMMOTH-1 in the rest-frame UV band. Its luminosity line ratio between the $\rm CO(3-2)$ and $\rm CO(1-0)$ $r_{3,1}$ is 0.61$\pm$0.17. The other five galaxies have $\rm CO(3-2)$ luminosities in the range of (2.1-7.1)$\times 10^9$ K $\rm km\,s^{-1}$ pc$^2$, with the star-formation rates derived from the 250GHz continuum of ($<$36)-224 $M_{\odot}$yr$^{-1}$. Follow-up spectroscopic observations will further confirm more member galaxies and improve the accuracy of the halo mass estimation.
分类： 天文学 >> 天文学 提交时间： 2023-02-19
Yuheng Zhang
Xian Zhong Zheng
Dong Dong Shi
Yu Gao
Helmut Dannerbauer
Fang Xia An
Xinwen Shu
Zhen-Kai Gao
Wei-Hao Wang
Xin Wang
Zheng Cai
Xiaohui Fan
Min Fang
Zhizheng Pan
Wenhao Liu
Qinghua Tan
Jianbo Qin
Jian Ren
Man Qiao
Run Wen
摘要： Submillimetre galaxies represent a rapid growth phase of both star formation and massive galaxies. Mapping SMGs in galaxy protoclusters provides key insights into where and how these extreme starbursts take place in connections with the assembly of the large-scale structure in the early Universe. We search for SMGs at 850$\,\mu m$ using JCMT/SCUBA-2 in two massive protoclusters at $z=2.24$, BOSS1244 and BOSS1542, and detect 43 and 54 sources with $S_{850}>4\,$mJy at the $4\sigma$ level within an effective area of 264$\,$arcmin$^2$, respectively. We construct the intrinsic number counts and find that the abundance of SMGs is $2.0\pm0.3$ and $2.1\pm0.2$ times that of the general fields, confirming that BOSS1244 and BOSS1542 contain a higher fraction of dusty galaxies with strongly enhanced star formation. The volume densities of the SMGs are estimated to be $\sim15-$30 times the average, significantly higher than the overdensity factor ($\sim 6$) traced by H$\alpha$ emission-line galaxies (HAEs). More importantly, we discover a prominent offset between the spatial distributions of the two populations in these two protoclusters -- SMGs are mostly located around the high-density regions of HAEs, and few are seen inside these regions. This finding may have revealed for the first time the occurrence of violent star formation enhancement in the outskirts of the HAE density peaks, likely driven by the boosting of gas supplies and/or starburst triggering events. Meanwhile, the lack of SMGs inside the most overdense regions at $z\sim2$ implies a transition to the environment disfavouring extreme starbursts.
分类： 天文学 >> 天文学 提交时间： 2023-02-19
Marta Frias Castillo
Jacqueline Hodge
Matus Rybak
Paul van der Werf
Ian Smail
Jack Birkin
Chian-Chou Chen
Scott Chapman
Ryley Hill
Claudia del P. Lagos
Cheng-Lin Liao
Elisabete da Cunha
Gabriela Calistro Rivera
Jianhang Chen
Eric Jimenez Andrade
Eric Murphy
Douglas Scott
Mark Swinbank
Fabian Walter
Rob Ivison
摘要： We present initial results of an ongoing survey with the Karl G. Jansky Very Large Array targeting the CO($J$ = 1-0) transition in a sample of 30 submillimeter-selected, dusty star-forming galaxies at $z =$ 2-5 with existing mid--$J$ CO detections from ALMA and NOEMA, of which 17 have been fully observed. We detect CO(1-0) emission in 11 targets, along with three tentative ($\sim$1.5-2$\sigma$) detections; three galaxies are undetected. Our results yield total molecular gas masses of 6-23$\times$10$^{10}$ ($\alpha_\mathrm{CO}$/1) M$_\odot$, with gas mass fractions, $f_\mathrm{gas}$=$M_\mathrm{mol}$/($M_*$+$M_\mathrm{mol}$), of 0.1-0.8 and a median depletion time of (140$\pm$70) Myr. We find median CO excitation ratios of $r_{31}$ = 0.75$\pm$0.39 and $r_{41}$ = 0.63$\pm$0.44, with a significant scatter. We find no significant correlation between the excitation ratio and a number of key parameters such as redshift, CO(1-0) line width or $\Sigma_\mathrm{SFR}$. We only find a tentative positive correlation between $r_{41}$ and the star-forming efficiency, but we are limited by our small sample size. Finally, we compare our results to predictions from the SHARK semi-analytical model, finding a good agreement between the molecular gas masses, depletion times and gas fractions of our sources and their SHARK counterparts. Our results highlight the heterogeneous nature of the most massive star-forming galaxies at high-redshift, and the importance of CO(1--0) observations to robustly constrain their total molecular gas content and ISM properties.
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