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Register a new userA Systematic Search for Galaxy Proto-Cluster Cores at $zsim 2$
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A proto-cluster core is the most massive dark matter halo (DMH) in a given proto-cluster. To reveal the galaxy formation in core regions, we search for proto-cluster cores at $zsim 2$ in $sim 1.5, mathrm{deg}^{2}$ of the COSMOS field. Using pairs of massive galaxies ($log(M_{*}/M_{odot})geq11$) as tracers of cores, we find 75 candidate cores, among which 54% are estimated to be real. A clustering analysis finds that these cores have an average DMH mass of $2.6_{-0.8}^{+0.9}times 10^{13}, M_{odot}$, or $4.0_{-1.5}^{+1.8}, times 10^{13} M_{odot}$ after contamination correction. The extended Press-Schechter model shows that their descendant mass at $z=0$ is consistent with Fornax-like or Virgo-like clusters. Moreover, using the IllustrisTNG simulation, we confirm that pairs of massive galaxies are good tracers of DMHs massive enough to be regarded as proto-cluster cores. We then derive the stellar mass function (SMF) and the quiescent fraction for member galaxies of the 75 candidate cores. We find that the core galaxies have a more top-heavy SMF than field galaxies at the same redshift, showing an excess at $log(M_{*}/M_{odot})gtrsim 10.5$. The quiescent fraction, $0.17_{-0.04}^{+0.04}$ in the mass range $9.0leq log(M_{*}/M_{odot})leq 11.0$, is about three times higher than that of field counterparts, giving an environmental quenching efficiency of $0.13_{-0.04}^{+0.04}$. These results suggest that stellar mass assembly and quenching are accelerated as early as at $zsim 2$ in proto-cluster cores.
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Many processes within galaxy clusters, such as those believed to govern the onset of thermally unstable cooling and AGN feedback, are dependent upon local dynamical timescales. However, accurately mapping the mass distribution within individual clusters is challenging, particularly towards cluster centres where the total mass budget has substantial radially-dependent contributions from the stellar, gas, and dark matter components. In this paper we use a small sample of galaxy clusters with deep Chandra observations and good ancillary tracers of their gravitating mass at both large and small radii to develop a method for determining mass profiles that span a wide radial range and extend down into the central galaxy. We also consider potential observational pitfalls in understanding cooling in hot cluster atmospheres, and find tentative evidence for a relationship between the radial extent of cooling X-ray gas and nebular H-alpha emission in cool core clusters. Amongst this small sample we find no support for the existence of a central entropy floor, with the entropy profiles following a power-law profile down to our resolution limit.
Clouds of high infrared extinction are promising sites of massive star/cluster formation. A large number of cloud cores discovered in recent years allows investigation of possible evolutionary sequence among cores in early phases. We have conducted a survey of deuterium fractionation toward 15 dense cores in various evolutionary stages, from high-mass starless cores to ultracompact Hii regions, in the massive star-forming clouds of high extinction, G34.43+0.24, IRAS 18151-1208, and IRAS 18223-1243, with the Submillimeter Telescope (SMT). Spectra of N2H+ (3 - 2), N2D+ (3 - 2), and C18O (2 - 1) were observed to derive the deuterium fractionation of N2H+, Dfrac equiv N(N2D+)/N(N2H+), as well as the CO depletion factor for every selected core. Our results show a decreasing trend in Dfrac with both gas temperature and linewidth. Since colder and quiescent gas is likely to be associated with less evolved cores, larger Dfrac appears to correlate with early phases of core evolution. Such decreasing trend resembles the behavior of Dfrac in the low-mass protostellar cores and is consistent with several earlier studies in high-mass protostellar cores. We also find a moderate increasing trend of Dfrac with the CO depletion factor, suggesting that sublimation of ice mantles alters the competition in the chemical reactions and reduces Dfrac. Our findings suggest a general chemical behavior of deuterated species in both low- and high-mass proto-stellar candidates at early stages. In addition, upper limits to the ionization degree are estimated to be within 2 times 10^-7 and 5 times 10^-6. The four quiescent cores have marginal field-neutral coupling and perhaps favor turbulent cooling flows.
We present the spectroscopic confirmation of a $z=2.45$ proto-cluster. Its member galaxies lie within a radius of 1.4Mpc (physical) on the sky and within $Delta v pm 700$km/s along the line of sight. We estimate an overdensity of 10, suggesting that the structure has made the turn-around but is not assembled yet. Comparison to the Millennium simulation suggests that analogous structures evolve into $10^{14}-10^{15}$M$_{odot}$/h type dark matter haloes by $z=0$ qualifying the notion of proto-cluster. The search for the complete census of mock progenitor galaxies at $zsim2.5$ of these massive $z=0$ mock clusters reveals that they are widely spread over areas with a diameter of 3-20Mpc. This suggests that the optical selection of such proto-clusters can result in a rich diversity regarding their $z=0$ descendants. We also searched for signs of environmental differentiation in this proto-cluster. Whilst we see a weak trend for more massive and more quiescent galaxies in the proto-cluster, this is not statistically significant.
We present results from two high-resolution hydrodynamical simulations of proto-cluster regions at z~2.1. The simulations have been compared to observational results for the socalled Spiderweb galaxy system, the core of a putative proto-cluster region at z = 2.16, found around a radio galaxy. The simulated regions have been chosen so as to form a poor cluster with M200~10^14 h-1 Msun (C1) and a rich cluster with M200~2x10^15 h-1 Msun (C2) at z = 0. The simulated proto-clusters show evidence of ongoing assembly of a dominating central galaxy. The stellar mass of the brightest cluster galaxy (BCG) of the C2 system is in excess with respect to observational estimates for the Spiderweb galaxy, with a total star formation rate which is also larger than indicated by observations. We find that the projected velocities of galaxies in the C2 cluster are consistent with observations, while those measured for the poorer cluster C1 are too low compared to the observed velocities. We argue that the Spiderweb complex resemble the high-redshift progenitor of a rich galaxy cluster. Our results indicate that the included supernovae feedback is not enough to suppress star formation in these systems, supporting the need of introducing AGN feedback. According to our simulations, a diffuse atmosphere of hot gas in hydrostatic equilibrium should already be present at this redshift, and enriched at a level comparable to that of nearby galaxy clusters. The presence of this gas should be detectable with future deep X-ray observations.
The origin of dust in galaxy halos or in the circum-galactic medium (CGM) is still a mystery. We investigate if the radiation pressure in high-redshift ($zsim 10$) galaxies can efficiently transport dust to halos. To clarify the first dust enrichment of galaxy halos in the early Universe, we solve the motion of a dust grain considering radiation pressure, gas drag, and gravity in the vertical direction of the galactic disc. Radiation pressure is estimated in a consistent manner with the stellar spectra and dust extinction. As a consequence, we find that dust grains with radii $asim 0.1~mu$m successfully escape from the galactic disc if the ongoing star formation episode converts more than 15 per cent of the baryon content into stars and lasts $gtrsim 30$ Myr, while larger and smaller grains are trapped in the disc because of gravity and gas drag, respectively. We also show that grain charge significantly enhances gas drag at a few--10 scale heights of the galactic disc, where the grain velocities are suppressed to $sim 1$ km s$^{-1}$. There is an optimum dust-to-gas ratio ($sim 10^{-3}$) in the galactic disc and an optimum virial mass $sim 10^{10}$--$10^{11}$ M$_{odot}$ for the transport of $asim 0.1~mu$m grains to the halo. We conclude that early dust enrichment of galaxy halos at $zgtrsim 10$ is important for the origin of dust in the CGM.
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