Disturbed Cold Gas at High Redshift
We have studied the first complete sample of 66 absorbers at 1.5 < z < 3.0 , selected based on the presence of neutral carbon (CI) absorption lines in SDSS spectra. These were re-observed using the ESO-VLT X-Shooter/UVES spectrograph. The CI systems are characterized by being rich in metals and dust (Zou+18). Molecular gas (such as CO and H2) has been identified in these systems (Noterdaeme+18). Interestingly, these systems exhibit disturbed kinematics structure, suggesting that they may be significantly influenced by feedback from star formation. Detections of NaI and CaII in the CI systmes, which may be associated with stellar activities, are presented in Zou+18.
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Cool CGM Traces Star-forming Galaxies and Galaxy Overdensity
The Mg II doublet is known to trace cool gas (T~10^4 K) in both the inflows and outflows of galaxies.
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We selected 114 quasars from the COSMOS field, which were observed during the DESI commissioning stage. From these, we detected 51 MgII and 49 CIV absorbers at 1.5 < z < 3.1. In combination with the COSMOS2020 catalog, we identified potential counterparts for the absorbing gas. Our findings indicate that the covering fraction of MgII has evolved significantly in main-sequence (MS) star-forming galaxies. This suggests a co-evolution between cool gas and MS galaxies at 1.5 < z < 2.5 .
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At 2 < z < 6, we selected 32 strong Mg II systems (Wr > 0.8 Å) from a total of 50 quasars with z > 5.7 from the Gemini-NIR sample (Shen+12). The comoving line density (dN/dX) of these strong Mg II systems diminishes with increasing redshift for z > 3. Notably, these systems exhibit much broader velocity widths than DLA-tracing Mg II systems at comparable redshifts. This characteristic suggests that these systems might be influenced by star formation activities or might be located within interacting galaxy groups.
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Further details on the CGM-galaxy connection for z > 6, utilizing VLT+JWST data, will be presented in Zou+23b.
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Possible First Star Signature from Pristine Gas and Primeval Galaxies
The pristine gas and primeval galaxies offers insights into the formation of the first generation stars by comparing their observed metal abundance. We have detected a Lyman limit system with a notably high carbon enhancement relative to iron ([C/Fe] ~ +2.2 at [Fe/H] ~ -1.6). This is reminiscent of a distinctive sub-class of the first generation of stars, known as the carbon-enhanced metal-poor (CEMP) stars. More interestingly, the strong C I absorption is associated with a neutral hydrogen column density of log N(H I) (/cm^2) = 18 — a value too small to shield the gas from any external UV flux. We also see such carbon and oxygen enhancement in the absorbing systems at the end of reionization epoch (z = 6.0-6.5). If the metals are from the nearby galaxies detected by JWST, the galaxies favor a top-heavy IMF and possibly, the PopIII IMF.
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Galaxy Cluster L-T relation
We present a study using Chandra observations of 23 galaxy groups and low-mass galaxies within the redshift range 0.03 < z <0.15. Our sample represents a statistically complete, flux-limited subset from the 400 deg2 cluster survey. In this research, I examined the scaling relation between X-ray luminosity (L) and temperature (T), taking the selection biases into consideration. The L-T relation slope aligns with the values typically observed for samples of more massive clusters, may suggest the feedback processes.
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