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Register a new userProperties of environment around AGN and luminous galaxy pairs through HSC wide survey
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We investigated the properties of AGN environments, particularly environments where the association of luminous galaxies (LGs) is found within 4~Mpc from AGNs with redshifts of 0.8 -- 1.1. For comparison, three additional AGN environments, (namely, AGNs of all types, type~1 AGNs with X-ray and/or radio detection, and type~2 AGNs) and an environment of blue $M_{*}$, characteristic luminosity of the Schechter function, galaxies were investigated. The cross-correlation function with the surrounding galaxies was measured and compared between the AGN and blue galaxy samples. We also compared the distributions of color, absolute magnitude, and stellar mass of the galaxies around such target objects. The properties of clusters detected using surrounding galaxies selected based on a photometric redshift were examined and compared for different samples. The target AGNs were drawn from the Million Quasars (MILLIQUAS) catalog, and the blue galaxies were drawn from six redshift survey catalogs (SDSS, WiggleZ, DEEP2, VVDS, VIPERS, and PRIMUS). The galaxies used as a measure of the environment around the targets are drawn from S18a internal data released by the Hyper Suprime-Cam Subaru Strategic Program (HSC-SSP). We found that, among the five AGN and blue galaxy samples considered, the environment of AGN-LG pairs is the most enriched with luminous galaxies. We also found an enhancement in the number of mass-selected clusters in the AGN-LG pair sample against those in the other samples. The results obtained in this study indicate that existence of multiple clusters is the major driver in the association of AGNs and LGs, rather than a single large-mass dark matter halo hosting the AGN.
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We have measured the clustering of galaxies around active galactic nuclei (AGN) for which single-epoch virial masses of the super-massive black hole (SMBH) are available to investigate the relation between the large scale environment of AGNs and the evolution of SMBHs. The AGN samples used in this work were derived from the Sloan Digital Sky Survey (SDSS) observations and the galaxy samples were from 240~deg$^{2}$ S15b data of the Hyper Suprime-Cam Subaru Strategic Program (HSC-SSP). The investigated redshift range is 0.6--3.0, and the masses of the SMBHs lie in the range $10^{7.5}$--$10^{10}$~M$_{odot}$. The absolute magnitude of the galaxy samples reaches to $M_{lambda 310}$ $sim$ $-$18 at rest frame wavelength 310~nm for the low-redshift end of the samples. More than 70% of the galaxies in the analysis are blue. We found a significant dependence of the cross-correlation length on redshift, which primarily reflects the brightness dependence of the galaxy clustering. At the lowest redshifts the cross-correlation length increases from 7~$h^{-1}$~Mpc around $M_{lambda 310}$$ = $$-19$~mag to $>$10~$h^{-1}$~Mpc beyond $M_{lambda 310}$$ = $$-20$~mag. No significant dependence of the cross-correlation length on BH mass was found for whole galaxy samples dominated by blue galaxies, while there was an indication of BH mass dependence in the cross-correlation with red galaxies. These results provides a picture of the environment of AGNs studied in this paper being enriched with blue starforming galaxies, and a fraction of the galaxies are being evolved to red galaxies along with the evolution of SMBHs in that system.
We study variability of active galactic nuclei (AGNs) by using the deep optical multiband photometry data obtained from the Hyper Suprime-Cam Subaru Strategic Program (HSC SSP) survey in the COSMOS field. The images analyzed here were taken with 8, 10, 13, and 15 epochs over three years in the $g$, $r$, $i$, and $z$ bands, respectively. We identified 491 robust variable AGN candidates, down to $i=25$ mag and with redshift up to $4.26$. Ninety percent of the variability-selected AGNs are individually identified with the X-ray sources detected in the Chandra COSMOS Legacy survey. We investigate their properties in variability by using structure function analysis and find that the structure function for low-luminosity AGNs ($L_{mathrm{bol}}lesssim10^{45}$ erg s$^{-1}$) shows a positive correlation with luminosity, which is the opposite trend for the luminous quasars. This trend is likely to be caused by larger contribution of the host galaxy light for lower-luminosity AGNs. Using the model templates of galaxy spectra, we evaluate the amount of host galaxy contribution to the structure function analysis and find that dominance of the young stellar population is needed to explain the observed luminosity dependence. This suggests that low-luminosity AGNs at $0.8lesssim zlesssim1.8$ are predominantly hosted in star-forming galaxies. The X-ray stacking analysis reveals the significant emission from the individually X-ray undetected AGNs in our variability-selected sample. The stacked samples show very large hardness ratios in their stacked X-ray spectrum, which suggests that these optically variable sources have large soft X-ray absorption by dust-free gas.
We investigate the effect of environment on the presence and fuelling of Active Galactic Nuclei (AGN) by identifying galaxies hosting AGN in massive galaxy clusters and the fields around them. We have identified AGN candidates via optical variability (178), X-ray emission (74), and mid-IR SEDs (64) in multi- wavelength surveys covering regions centered on 12 galaxy clusters at redshifts 0.5 < z < 0.9. In this paper, we present the radial distribution of AGN in clusters to examine how local environment affects the presence of an AGN and its host galaxy. While distributions vary from cluster to cluster, we find that the radial distribution of AGN generally differs from that of normal galaxies. AGN host galaxies also show a different colour distribution than normal galaxies, with many AGN hosts displaying galaxy colours in the green valley between the red sequence and blue star-forming normal galaxies. This result is similar to those found in field galaxy studies. The colour distribution of AGN hosts is more pronounced in disturbed clusters where minor mergers, galaxy harassment, and interactions with cluster substructure may continue to prompt star-formation in the hosts. However, we find no relationship between host galaxy colour and cluster radius among AGN hosts. This may indicate that processes related to the accreting supermassive black hole have a greater impact on the star-forming properties of the host galaxy than the intracluster medium and/or local galaxy environment.
The next generation Very Large Array (ngVLA) will have unprecedented sensitivities and mapping speeds at $1-8$ GHz. We discuss how the active galactic nuclei (AGN) community can benefit from a wide-area, medium depth ngVLA survey. We propose a 10 deg$^2$ survey in the Stripe 82 field using the 8 GHz band with an rms depth of $1,mu$Jy beam$^{-1}$. We will detect $sim$130,000 galaxies, including radio-quiet AGN out to $zsim7$. We can measure the luminosity and space density evolution of radio-quiet and radio-loud AGN. We can also measure AGN evolution through clustering of both populations using cross-correlation functions. A wide area ngVLA survey will benefit from existing multiwavelength AGN populations, particularly in the Stripe 82 field, as well as new information from next-generation optical and infrared survey instruments such as LSST and WFIRST.
We present the first results from our survey of intervening and proximate Lyman limit systems (LLSs) at $z$$sim$2.0-2.5 using the Wide Field Camera 3 on-board the Hubble Space Telescope. The quasars in our sample are projected pairs with proper transverse separations $R_perp$$leq$150 kpc and line of sight velocity separations $lesssim$11,000 km/s. We construct a stacked ultraviolet (rest-frame wavelengths 700-2000AA) spectrum of pairs corrected for the intervening Lyman forest and Lyman continuum absorption. The observed spectral composite presents a moderate flux excess for the most prominent broad emission lines, a $sim$30% decrease in flux at $lambda$=800-900AA compared to a stack of brighter quasars not in pairs at similar redshifts, and lower values of the mean free path of the HI ionizing radiation for pairs ($lambda_{rm mfp}^{912}=140.7pm20.2~h_{70}^{-1}$Mpc) compared to single quasars ($lambda_{rm mfp}^{912}=213.8pm28~h_{70}^{-1}$Mpc) at the average redshift $zsimeq2.44$. From the modelling of LLS absorption in these pairs, we find a higher ($sim$20%) incidence of proximate LLSs with $log N_{rm HI}geq17.2$ at $delta v$$<$5,000 km/s compared to single quasars ($sim$6%). These two rates are different at the 5$sigma$ level. Moreover, we find that optically-thick absorbers are equally shared between foreground and background quasars. Based on these pieces of evidence, we conclude that there is a moderate excess of gas absorbing Lyman continuum photons in our closely-projected quasar pairs compared to single quasars. We argue that this gas arises mostly within large-scale structures or partially neutral regions inside the dark matter haloes where these close pairs reside.
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