EVOLUTION OF GALAXIES AND THEIR ENVIRONMENTS AT z = 0.1-3 IN COSMOS

Abstract

Large-scale structures (LSS) out to z < 3.0 are measured in the Cosmic Evolution Survey (COSMOS) using extremely accurate photometric redshifts (photoz). The Ks-band selected sample (from Ultra-Vista) is comprised of 155,954 galaxies. Two techniques -adaptive smoothing and Voronoi tessellation -are used to estimate the environmental densities within 127 redshift slices. Approximately 250 statistically significant overdense structures are identified out to z = 3.0 with shapes varying from elongated filamentary structures to more circularly symmetric concentrations. We also compare the densities derived for COSMOS with those based on semi-analytic predictions for a ΛCDM simulation and find excellent overall agreement between the mean densities as a function of redshift and the range of densities. The galaxy properties (stellar mass, spectral energy distributions (SEDs) and star formation rates (SFRs)) are strongly correlated with environmental density and redshift, particularly at z < 1.0−1.2. Classifying the spectral type of each galaxy using the rest-frame b-i color (from the photoz SED fitting), we find a strong correlation of early type galaxies (E-Sa) with high density environments, while the degree of environmental segregation varies systematically with redshift out to z ∼ 1.3. In the highest density regions, 80% of the galaxies are early types at z=0.2 compared to only 20% at z = 1.5. The SFRs and the star formation timescales exhibit clear environmental correlations. At z > 0.8, the star formation rate density (SFRD) is uniformly distributed over all environmental density percentiles, while at lower redshifts the dominant contribution is shifted to galaxies in lower density environments.

SPECTROSCOPIC STUDY OF STAR-FORMING GALAXIES IN FILAMENTS AND THE FIELD ATz∼ 0.5: EVIDENCE FOR ENVIRONMENTAL DEPENDENCE OF ELECTRON DENSITY

“…An LSS with a thread-like morphology is evidently seen in the lower left side of Figure 1(a), with a significance of σ∼8-18. 6 The same structure can also be seen in the density maps produced by Scoville et al (2013) at z∼0.53.…”

“…Although they are expected to occupy 10% of the volume of the cosmic web, simulations have shown that galaxy filaments contain most of the mass in the universe (∼40%;Aragón-Calvo et al 2010) and host a significant fraction of baryons in the form of a warm-hot intergalactic medium gas in the temperature range 10 5 -10 7 K (Cen & Ostriker 1999Davé et al 2001Davé et al , 2010Klar & Mücket 2012). Filaments are seen in the optical wavelengths as the large-scale thread-like concentration of galaxies (e.g., Pimbblet et al 2004;Scoville et al 2007aScoville et al , 2013Kovač et al 2010;Guzzo & The Vipers Team 2013;Alpaslan et al 2014;Darvish et al 2014Darvish et al , 2015Tempel et al 2014), in X-ray as a warm-hot gas in emission and absorption (e.g., Scharf et al 2000;Zappacosta et al 2002Zappacosta et al , 2010Finoguenov et al 2003;Kaastra et al 2003;Nicastro et al 2005aNicastro et al , 2005bNicastro et al , 2010Werner et al 2008;Danforth et al 2010), in the infrared as possible sites of enhanced star-formation activity, linking clusters (e.g., Koyama et al 2008;Biviano et al 2011;Coppin et al 2012;Pintos-Castro et al 2013), and in the weak-lensing studies as a bridging distribution of dark matter, connecting galaxy clusters (e.g., Dietrich et al 2012;Jauzac et al 2012;Higuchi et al 2015).…”

Passive galaxies as tracers of cluster environments atz~ 2

“…The photo-z distribution is very compact, consistent with a single structure. An overdensity at a consistent position and redshift is also visible in Scoville et al (2013) density maps. We also note the proximity (a few to 14 Mpc) of confirmed/candidate structures at similar redshift (Diener et al 2014;Castignani et al 2014;Chiang et al 2014;Yuan et al 2014).…”

“…In comparison with most other (proto-)cluster search techniques at these redshifts, e.g. the "IRAC selection" (e.g., Papovich et al 2010;Stanford et al 2012), targeted searches around radio galaxies (e.g., Venemans et al 2007;Chiaberge et al 2010;Wylezalek et al 2013), 3D mapping (with spectroscopic or photometric redshifts, e.g., Diener et al 2013;Scoville et al 2013;Chiang et al 2014;Mei et al 2014), or overdensities of optically red galaxies (e.g., Andreon et al 2009;Spitler et al 2012), the approach discussed in this work is likely, by definition, to favor the most evolved environments, thus allowing a better probe of the diversity of cluster progenitors at a crucial time for the formation of both clusters and their massive galaxies.…”

The GALEX Ultraviolet Virgo Cluster Survey (GUViCS)

“…For each galaxy, we first define the Voronoi cells as the polygonal cells centred on the galaxy and enclosing all the surrounding empty space closest to that point. This method has proven to be very efficient in determining galaxy densities in different environments (Platen et al 2011;Scoville et al 2013;Cybulski et al 2014) and in finding bound structures like galaxy groups (Marinoni et al 2002;Gerke et al 2005;Cucciati et al 2010). The local density around the galaxy is then simply given by the inverse of the area of the Voronoi cell.…”