LARGE-SCALE STRUCTURE AROUND A z = 2.1 CLUSTER Hung (洪肇伶), Chao-Ling; Casey, Caitlin M.; Chiang, Yi-Kuan ...
The Astrophysical journal,
08/2016, Letnik:
826, Številka:
2
Journal Article
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ABSTRACT The most prodigious starburst galaxies are absent in massive galaxy clusters today, but their connection with large-scale environments is less clear at . We present a search of large-scale ...structure around a galaxy cluster core at z = 2.095 using a set of spectroscopically confirmed galaxies. We find that both color-selected star-forming galaxies (SFGs) and dusty star-forming galaxies (DSFGs) show significant overdensities around the z = 2.095 cluster. A total of eight DSFGs (including three X-ray luminous active galactic nuclei, AGNs) and 34 SFGs are found within a 10′ radius (corresponds to ∼15 cMpc at ) from the cluster center and within a redshift range of , which leads to galaxy overdensities of and . The cluster core and the extended DSFG- and SFG-rich structures together demonstrate an active cluster formation phase, in which the cluster is accreting a significant amount of material from large-scale structure while the more mature core may begin to virialize. Our finding of this DSFG-rich structure, along with a number of other protoclusters with excess DSFGs and AGNs found to date, suggest that the overdensities of these rare sources indeed trace significant mass overdensities. However, it remains puzzling how these intense star formers are triggered concurrently. Although an increased probability of galaxy interactions and/or enhanced gas supply can trigger the excess of DSFGs, our stacking analysis based on 850 m images and morphological analysis based on rest-frame optical imaging do not show such enhancements of merger fraction and gas content in this structure.
ABSTRACT The recent advent of integral field spectrographs and millimeter interferometers has revealed the internal dynamics of many hundreds of star-forming galaxies. Spatially resolved kinematics ...have been used to determine the dynamical status of star-forming galaxies with ambiguous morphologies, and constrain the importance of galaxy interactions during the assembly of galaxies. However, measuring the importance of interactions or galaxy merger rates requires knowledge of the systematics in kinematic diagnostics and the visible time with merger indicators. We analyze the dynamics of star-forming gas in a set of binary merger hydrodynamic simulations with stellar mass ratios of 1:1 and 1:4. We find that the evolution of kinematic asymmetries traced by star-forming gas mirrors morphological asymmetries derived from mock optical images, in which both merger indicators show the largest deviation from isolated disks during strong interaction phases. Based on a series of simulations with various initial disk orientations, orbital parameters, gas fractions, and mass ratios, we find that the merger signatures are visible for ∼0.2-0.4 Gyr with kinematic merger indicators but can be approximately twice as long for equal-mass mergers of massive gas-rich disk galaxies designed to be analogs of z ∼ 2-3 submillimeter galaxies. Merger signatures are most apparent after the second passage and before the black holes coalescence, but in some cases they persist up to several hundred Myr after coalescence. About 20%-60% of the simulated galaxies are not identified as mergers during the strong interaction phase, implying that galaxies undergoing violent merging process do not necessarily exhibit highly asymmetric kinematics in their star-forming gas. The lack of identifiable merger signatures in this population can lead to an underestimation of merger abundances in star-forming galaxies, and including them in samples of star-forming disks may bias the measurements of disk properties such as intrinsic velocity dispersion.
ABSTRACT The classification of galaxy mergers and isolated disks is key for understanding the relative importance of galaxy interactions and secular evolution during the assembly of galaxies. Galaxy ...kinematics as traced by emission lines have been used to suggest the existence of a significant population of high-z star-forming galaxies consistent with isolated rotating disks. However, recent studies have cautioned that post-coalescence mergers may also display disk-like kinematics. To further investigate the robustness of merger/disk classifications based on kinematic properties, we carry out a systematic classification of 24 local (U)LIRGs spanning a range of morphologies: from isolated spiral galaxies, ongoing interacting systems, to fully merged remnants. We artificially redshift the Wide Field Spectrograph observations of these local (U)LIRGs to z = 1.5 to make a realistic comparison with observations at high-z, and also to ensure that all galaxies have the same spatial sampling of ∼900 pc. Using both kinemetry-based and visual classifications, we find that the reliability of kinematic classification shows a strong trend with the interaction stage of galaxies. Mergers with two nuclei and tidal tails have the most distinct kinematics compared to isolated disks, whereas a significant population of the interacting disks and merger remnants are indistinguishable from isolated disks. The high fraction of mergers displaying disk-like kinematics reflects the complexity of the dynamics during galaxy interactions. Additional merger indicators such as morphological properties traced by stars or molecular gas are required to further constrain the merger/disk classifications at high-z.
碩士
國立清華大學
天文研究所
98
We study the chemical and dynamical properties of a very low luminosity object - DCE065 using the Submillimeter Array and complementary single dish observations. The continuum and ...N2D+ emission show that DCE065’s parent core with a mass of 0.24 M⊙ is in flattened structure. A small velocity gradient along the major axis of the N2D+ disk is marginally detected, suggesting that the rotational energy alone is insufficient to support the parent core. The very young and cold chemical features are evidenced by the high N2D+/N2H+ abundance ratio of 0.1, non-detection of CO evaporation in the central region and a constant N2D+ abundance profile. These features suggest that DCE065 may not have experienced a strong accretion phase or it has already left the burst accretion phase for a long time. The 12CO emission shows a
large red shifted triangle feature in the PV diagrams which can be explained with an outward motion. Since the mass, momentum and energy of the expanding material are similar to those of the less energetic outflows in Perseus, the origin of the outward motion signature shown in the 12CO emission is probably due to outflow activities.
Because the parent core mass is very low, DCE065 may destined to form a brown dwarf if its current accretion rate is higher than 3 × 10−8 M⊙ yr−1. The young chemical features and possible outflow activities shown in DCE065 support the scenario that a brown dwarf forms from collapsing processes similar to typical low mass stars.
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