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Register a new userC IV absorbers tracing cool gas in dense galaxy group/cluster environments
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Aditya Manuwal
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We present analysis on three intervening H I-C IV absorption systems tracing gas within galaxy group/cluster environments, identified in the $HST$/COS far-UV spectra of the background quasars PG $1148+549$ ($z_{abs}=0.00346$), SBS~$1122+594$ ($z_{abs}=0.00402$) and RXJ~$1230.8+0115$ ($z_{abs}=0.00574$). The ionization models are consistent with the origin of metal lines and H I from a cool and diffuse photoionized gas phase with $T lesssim 4 times 10^{4}$ K and $n_{mathrm{H}} lesssim 5 times 10^{-4}$ cm$^{-3}$. The three absorbers have $89$, $51$ and $17$ galaxies detected within $1$ Mpc and $|Delta v| < 600$ km s$^{-1}$. The RXJ~$1230.8+0115$ sightline traces the outskirt regions of the Virgo cluster where the absorber is found to have super-solar metallicity. The detection of metal lines along with H I has enabled us to confirm the presence of cool, diffuse gas possibly enriched by outflows and tidal interactions in environments with significant galaxy density.
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We investigate the environmental dependence of the local gas-phase metallicity in a sample of star-forming galaxies from the MaNGA survey. Satellite galaxies with stellar masses in the range $9<log(M_{*}/M_{odot})<10$ are found to be $sim 0.05 , mathrm{dex}$ higher in metallicity than centrals of similar stellar mass. Within the low-mass satellite population, we find that the interstellar medium (ISM) metallicity depends most strongly on the stellar mass of the galaxy that is central to the halo, though there is no obvious difference in the metallicity gradients. At fixed total stellar mass, the satellites of high mass ($M_{*}>10^{10.5} , mathrm{M_{odot}}$) centrals are $sim 0.1 , mathrm{dex}$ more metal rich than satellites of low-mass ($M_{*} < 10^{10} , mathrm{M_{odot}}$) centrals, controlling for local stellar mass surface density and gas fraction. Fitting a gas-regulator model to the spaxel data, we are able to account for variations in the local gas fraction, stellar mass surface density and local escape velocity-dependent outflows. We find that the best explanation for the metallicity differences is the variation in the average metallicity of accreted gas between different environments that depends on the stellar mass of the dominant galaxies in each halo. This is interpreted as evidence for the exchange of enriched gas between galaxies in dense environments that is predicted by recent simulations.
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We compile a sample of spectroscopically- and photometrically-selected cluster galaxies from four high-redshift galaxy clusters ($1.59 < z < 1.71$) from the Spitzer Adaptation of the Red-Sequence Cluster Survey (SpARCS), and a comparison field sample selected from the UKIDSS Deep Survey. Using near-infrared imaging from the textit{Hubble Space Telescope} we classify potential mergers involving massive ($M_* geq 3times 10^{10}mathrm{M}_odot$) cluster members by eye, based on morphological properties such as tidal distortions, double nuclei, and projected near neighbors within 20 kpc. With a catalogue of 23 spectroscopic and 32 photometric massive cluster members across the four clusters and 65 spectroscopic and 26 photometric comparable field galaxies, we find that after taking into account contamination from interlopers, $11.0 ^{+7.0}_{-5.6}%$ of the cluster members are involved in potential mergers, compared to $24.7^{+5.3}_{-4.6}%$ of the field galaxies. We see no evidence of merger enhancement in the central cluster environment with respect to the field, suggesting that galaxy-galaxy merging is not a stronger source of galaxy evolution in cluster environments compared to the field at these redshifts.
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Whilst young massive clusters (YMCs; $M$ $gtrsim$ 10$^{4}$ M$_{odot}$, age $lesssim$ 100 Myr) have been identified in significant numbers, their progenitor gas clouds have eluded detection. Recently, four extreme molecular clouds residing within 200 pc of the Galactic centre have been identified as having the properties thought necessary to form YMCs. Here we utilise far-IR continuum data from the Herschel Infrared Galactic Plane Survey (HiGAL) and millimetre spectral line data from the Millimetre Astronomy Legacy Team 90 GHz Survey (MALT90) to determine their global physical and kinematic structure. We derive their masses, dust temperatures and radii and use virial analysis to conclude that they are all likely gravitationally bound -- confirming that they are likely YMC progenitors. We then compare the density profiles of these clouds to those of the gas and stellar components of the Sagittarius B2 Main and North proto-clusters and the stellar distribution of the Arches YMC. We find that even in these clouds -- the most massive and dense quiescent clouds in the Galaxy -- the gas is not compact enough to form an Arches-like ($M$ = 2x10$^{4}$ M$_{odot}$, R$_{eff}$ = 0.4 pc) stellar distribution. Further dynamical processes would be required to condense the resultant population, indicating that the mass becomes more centrally concentrated as the (proto)-cluster evolves. These results suggest that YMC formation may proceed hierarchically rather than through monolithic collapse.
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