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Register a new userThe Properties of Radio and Mid-infrared Detected Galaxies and the Effect of Environment on the Co-evolution of AGN and Star Formation at $z sim 1$
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In this study we investigate 179 radio-IR galaxies drawn from a sample of spectroscopically-confirmed galaxies that are detected in radio and mid-infrared (MIR) in the redshift range of $0.55 leq z leq 1.30$ in the Observations of Redshift Evolution in Large Scale Environments (ORELSE) survey. We constrain the Active Galactic Nuclei (AGN) contribution in the total IR luminosity (f$_{text{AGN}}$), and estimate the AGN luminosity (L$_{text{AGN}}$) and the star formation rate (SFR) using the CIGALE Spectral Energy Distribution (SED) fitting routine. Based on the f$_{text{AGN}}$ and radio luminosity, radio-IR galaxies are split into: galaxies that host either high or low f$_{text{AGN}}$ AGN (high-/low-f$_{text{AGN}}$), and star forming galaxies with little to no AGN activity (SFGs). We study the colour, stellar mass, radio luminosity, L$_{text{AGN}}$ and SFR properties of the three radio-IR sub-samples, comparing to a spec-IR sample drawn from spectroscopically-confirmed galaxies that are also detected in MIR. No significant difference between radio luminosity of these sub-samples was found, which could be due to the combined contribution of radio emission from AGN and star formation. We find a positive relationship between L$_{text{AGN}}$and specific SFR (sSFR) for both AGN sub-samples, strongly suggesting a co-evolution scenario of AGN and SF in these galaxies. A toy model is designed to demonstrate this co-evolution scenario, where we find that, in almost all cases, a rapid quenching timescale is required, which we argue is a signature of AGN quenching. The environmental preference for intermediate/infall regions of clusters/groups remains across the co-evolution scenario, which suggests that galaxies might be in an orbital motion around the cluster/group during the scenario.
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Combining the catalogue of galaxy morphologies in the COSMOS field and the sample of H$alpha$ emitters at redshifts $z=0.4$ and $z=0.84$ of the HiZELS survey, we selected $sim$ 220 star-forming bulgeless systems (Sersic index $n leq 1.5$) at both epochs. We present their star formation properties and we investigate their contribution to the star formation rate function (SFRF) and global star formation rate density (SFRD) at $z < 1$. For comparison, we also analyse H$alpha$ emitters with more structurally evolved morphologies that we split into two classes according to their Sersic index $n$: intermediate ($ 1.5 < n leq 3 $) and bulge-dominated ($n > 3$). At both redshifts the SFRF is dominated by the contribution of bulgeless galaxies and we show that they account for more than 60% of the cosmic SFRD at $z < 1$. The decrease of the SFRD with redshift is common to the three morphological types but it is stronger for bulge-dominated systems. Star-forming bulgeless systems are mostly located in regions of low to intermediate galaxy densities ($Sigma sim 1 - 4$ Mpc$^{-2}$) typical of field-like and filament-like environments and their specific star formation rates (sSFRs) do not appear to vary strongly with local galaxy density. Only few bulgeless galaxies in our sample have high (sSFR $>$ 10$^{-9}$ yr$^{-1}$) and these are mainly low-mass systems. Above $M_* sim 10^{10}$ M$_{odot}$ bulgeless are evolving at a normal rate (10$^{-9}$ yr$^{-1} <$ sSFR $<$10$^{-10}$ yr$^{-1}$) and in the absence of an external trigger (i.e. mergers/strong interactions) they might not be able to develop a central classical bulge.
We study the star-forming (SF) population of galaxies within a sample of 209 IR-selected galaxy clusters at 0.3$,leq,z,leq,$1.1 in the ELAIS-N1 and XMM-LSS fields, exploiting the first HSC-SSP data release. The large area and depth of these data allows us to analyze the dependence of the SF fraction, $f_{SF}$, on stellar mass and environment separately. Using $R/R_{200}$ to trace environment, we observe a decrease in $f_{SF}$ from the field towards the cluster core, which strongly depends on stellar mass and redshift. The data show an accelerated growth of the quiescent population within the cluster environment: the $f_{SF}$ vs. stellar mass relation of the cluster core ($R/R_{200},leq,$0.4) is always below that of the field (4$,leq,R/R_{200},<,$6). Finally, we find that environmental and mass quenching efficiencies depend on galaxy stellar mass and distance to the center of the cluster, demonstrating that the two effects are not separable in the cluster environment. We suggest that the increase of the mass quenching efficiency in the cluster core may emerge from an initial population of galaxies formed ``in situ. The dependence of the environmental quenching efficiency on stellar mass favors models in which galaxies exhaust their reservoir of gas through star formation and outflows, after new gas supply is truncated when galaxies enter the cluster.
Radio Active Galactic Nuclei (RAGNs) are mainly found in dense structures (i.e., clusters/groups) at redshifts of z$<$2 and are commonly used to detect protoclusters at higher redshift. Here, we attempt to study the host and environmental properties of two relatively faint ($mathrm L_mathrm{1.4GHz} sim10^{25}$ W Hz$^{-1}$) RAGNs in a known protocluster at z=3.3 in the PCl J0227-0421 field, detected using the latest radio observation obtained as part of the Observations of Redshift Evolution in Large-Scale Environments (ORELSE) Survey. Using new spectroscopic observations obtained from Keck/MOSFIRE as part of the Charting Cluster Construction with the VIMOS Ultra-Deep Survey (VUDS) and ORELSE (C3VO) survey and previous spectroscopic data obtained as part of the VIMOS-VLT Deep Survey (VVDS) and VUDS, we revise the three-dimensional overdensity field around this protocluster. The protocluster is embedded in a large scale overdensity protostructure. This protostructure has an estimated total mass of $sim$2.6$times10^{15} M_odot$ and contains several overdensity peaks. Both RAGNs are hosted by very bright and massive galaxies, while their hosts show extreme differences color, indicating that they have different ages and are in different evolutionary stages. Furthermore, we find that they are not in the most locally dense parts of the protostructure, but are fairly close to the centers of their parent overdensity peaks. We propose a scenario where merging might already have happened in both cases, which lowered the local density of their surrounding area and boosted their stellar mass. This work is the first time that two RAGNs at low luminosity have been found and studied within a high redshift protostructure.
Using the Herschel Space Observatory we have observed a representative sample of 87 powerful 3CR sources at redshift z < 1. The far-infrared (FIR, 70-500 micron) photometry is combined with mid-infrared (MIR) photometry from the Wide-Field Infrared Survey Explorer (WISE) and catalogued data to analyse the complete spectral energy distributions (SEDs) of each object from optical to radio wavelength. To disentangle the contributions of different components, the SEDs are fitted with a set of templates to derive the luminosities of host galaxy starlight, dust torus emission powered by active galactic nuclei (AGN) and cool dust heated by stars. The level of emission from relativistic jets is also estimated, in order to isolate the thermal host galaxy contribution. The new data are in line with the orientation-based unification of high-excitation radio-loud AGN, in that the dust torus becomes optically thin longwards of 30 micron. The low excitation radio galaxies and the MIR weak sources represent MIR- and FIR-faint AGN population different from the high-excitation MIR-bright objects; it remains an open question whether they are at a later evolutionary state or an intrinsically different population. The derived luminosities for host starlight and dust heated by star formation are converted to stellar masses and star formation rates (SFR). The host-normalized SFR of the bulk of the 3CR sources is low when compared to other galaxy populations at the same epoch. Estimates of the dust mass yield a 1--100 times lower dust/stellar mass ratio than for the Milky Way, indicating that these 3CR hosts have very low levels of interstellar matter explaining the low level of star formation. Less than 10% of the 3CR sources show levels of star formation above those of the main sequence of star forming galaxies.
We investigate the dependance of galaxy sizes and star-formation rates (SFRs) on environment using a mass-limited sample of quiescent and star-forming galaxies with M>10^9.5 at z=0.92 selected from the NMBS survey. Using the GEEC2 spectroscopic cluster catalog and the accurate photometric redshifts from NMBS, we select quiescent and star-forming cluster (sigma=490 km/s) galaxies within two virial radius, Rvir, intervals of 0.5<Rvir<2 and Rvir<0.5. Galaxies residing outside of 2 Rvir of both the cluster centres and additional candidate over-densities are defined as our field sample. Galaxy structural parameters are measured from the COSMOS legacy HST/ACS F814W image. The sizes and Sersic indices of quiescent field and cluster galaxies have the same distribution regardless of Rvir. However, cluster star-forming galaxies within 0.5 Rvir have lower mass-normalised average sizes, by 16${pm}7%$, and a higher fraction of Sersic indices with n>1, than field star-forming galaxies. The average SFRs of star-forming cluster galaxies show a trend of decreasing SFR with clustocentric radius. The mass-normalised average SFR of cluster star-forming galaxies is a factor of 2-2.5 (7-9 sigma) lower than that of star-forming galaxies in the field. While we find no significant dependence on environment for quiescent galaxies, the properties of star-forming galaxies are affected, which could be the result of environment acting on their gas content.
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