分类: 天文学 >> 天文学 提交时间: 2023-02-19
摘要: We present redshifts for 2753 low-redshift galaxies between $0.03 \lesssim z_{\rm spec}\lesssim0.5$ with 18 $\leq$ $r$ $\leq$ 22 obtained with Hectospec at the Multi-Mirror Telescope (MMT). The observations targeted the XMM-LSS, ELAIS-N1 and DEEP2-3 fields, each of which covers $\sim$ 1 deg$^2$. These fields are also part of the recently completed CFHT Large Area U-band Deep Survey (CLAUDS) and on-going Hyper Suprime-Cam deep fields surveys. The efficiency of our technique for selecting low-redshift galaxies is confirmed by the redshift distribution of our sources. In addition to redshifts, these high S/N spectra are used to measure ages, metallicities, and nuclear activity levels. In combination with the photometric catalogue in $u$, $g$, $r$, $i$, $z$, $y$ down to 27 AB mag, we are able to study the galaxy population down to stellar masses of $\sim$ 10$^8 M_\odot$ . This paper presents the observational strategy, the reduction procedure and properties of the galaxy sample.
分类: 天文学 >> 天文学 提交时间: 2023-02-19
摘要: The discovery and spectroscopic confirmation of Hyperion, a proto-supercluster at z~2.47, provides an unprecedented opportunity to study distant galaxies in the context of their large-scale environment. We carry out deep narrow-band imaging of a ~1*1 deg^2 region around Hyperion and select 157 Lya emitters (LAEs). The inferred LAE overdensity is delta_g~40 within an effective volume of 30*20*15 cMpc^3, consistent with the fact that Hyperion is composed of multiple protoclusters and will evolve into a super-cluster with a total mass of M_tot ~1.4*10^15 M_sun at z=0. The distribution of LAEs closely mirrors that of known spectroscopic members, tracing the protocluster cores and extended filamentary arms connected to them, suggesting that they trace the same large-scale structure. By cross-correlating the LAE positions with HI tomography data, we find weak evidence that LAEs may be less abundant in the highest HI regions, perhaps because Lya is suppressed in such regions. The Hyperion region hosts a large population of active galactic nuclei (AGN), ~12 times more abundant than that in the field. The prevalence of AGN in protocluster regions hints at the possibility that they may be triggered by physical processes that occur more frequently in dense environments, such as galaxy mergers. Our study demonstrates LAEs as reliable markers of the largest cosmic structures. When combined with ongoing and upcoming imaging and spectroscopic surveys, wide-field narrow-band imaging has the potential to advance our knowledge in the formation and evolution of cosmic structures and of their galaxy inhabitants.
分类: 天文学 >> 天文学 提交时间: 2023-02-19
摘要: Using the extended halo-based group finder developed by Yang et al. (2021), which is able to deal with galaxies via spectroscopic and photometric redshifts simultaneously, we construct galaxy group and candidate protocluster catalogs in a wide redshift range ($0 2.0$. By checking the galaxy number distributions within a $5-7\ h^{-1}\mathrm{Mpc}$ projected separation and a redshift difference $\Delta z \le 0.1$ around those richest groups at redshift $z>2$, we identified a list of 761, 343 and 43 protocluster candidates in the redshift bins $2\leq z<3$, $3\leq z<4$ and $z \geq 4$, respectively. In general, these catalogs of galaxy groups and protocluster candidates will provide useful environmental information in probing galaxy evolution along the cosmic time.