Optical Variability of Infrared Power Law-Selected Galaxies & X-ray Sources in the GOODS-South Field

We investigate the use of optical variability to identify and study Active Galactic Nuclei (AGN) in the GOODS-South field. A sample of 22 mid-infrared power law sources and 102 X-ray sources with optical counterparts in the HST ACS images were selected. Each object is classified with a variability significance value related to the standard deviation of its magnitude in five epochs separated by 45-day intervals. The variability significance is compared to the optical, mid-IR, and X-ray properties of the sources. We find that 26% of all AGN candidates (either X-ray- or mid-IR-selected) are optical variables. The fraction of optical variables increases to 51% when considering sources with soft X-ray band ratios. For the mid-IR AGN candidates which have multiwavelength SEDs, we find optical variability for 64% of those classified with SEDs like Broad Line AGNs. While mostly unobscured AGN appear to have the most significant optical variability, some of the more obscured AGNs are also observed as variables. In particular, we find two mid-IR power law-selected AGN candidates without X-ray emission that display optical variability, confirming their AGN nature.Comment: 11 pages, 4 figures, 1 table, accepted for publication in Ap

Communication Challenges Associated With Voyageurs National Park: A Discourse Analysis

This dissertation analyzed interviews conducted with three key people who described their personal connections to Voyageurs National Park and the adjoining communities. These ethnographic details add insights expressed in the voices of community members who have demonstrated interest in and commitment to the park through their association with the staff and their interactions with the park ecosystems. These insights are valuable because the park mandate requires public involvement in management decisions as part of the public land stewardship but engaging public involvement proved to be complex. After the park was established a rift developed between local community members and those supporting Voyageurs National Park. Research conducted before this dissertation describes the history of political battles surrounding the creation of Voyageurs National Park, the need for wilderness to protect America\u27s national heritage, and the conflict between federal policies used to manage National Parks and Native American issues. This dissertation adds to the body of related research by contributing insights on discourse used to describe the shift away from traditional recreational and subsistence lifestyles in the communities near Voyageurs National Park and the move toward the sustainable, less environmentally invasive uses mandated by the park staff

Nonprofits and Volunteers in North Dakota Communities

This study looks at non-profit organizations in North Dakota to see how they attract and keep volunteers, how volunteer hours can be used to draw funding to nonprofits, and the increasingly important role non-profit groups play in local economies by creating jobs, services, and acting as a voice for those who might not be heard otherwise. Results show how universities can support local communities by developing research data nonprofit groups can use to solve practical problems, by acting as a bridge between student volunteers and appropriate organizations, and by creating a journal or online site communities can use to connect with each other and as a resource for information. This paper examines the following questions: which kinds of volunteer work do the people in North Dakota consider beneficial? What do residents consider to be the main benefits of volunteer work in U.S. society? What do they consider to be the main problems and challenges associated with volunteer work in U.S. society? The research used qualitative methods. The study made use of focus group data and panel discussions analysis published in academic journals.  The research concluded that the main issues confronting volunteer organizers are limited resources, and the need for information and knowledge about volunteer efforts in North Dakota. In these circumstances community engagement centers serve as vital sources of news and information. They can also serve as a prospective mobilizing platform for volunteer organizations

Ettevõtte Atemix töötajate infosüsteemiga seotud vajaduste kaardistamine

Informatsiooni haldamiseks on asutustes kasutusele võetud erinevat laadi infosüsteemid. Infosüsteemide üldine eesmärk on töödelda andmeid infoks ning koondada ja esitada, seda kasutajatele efektiivsel kujul, mis tähendab seda, et infosüsteem on erinevate tööprotsesside juures toetavaks töövahendiks, lihtsustades kasutajate tööd. Lõputöös keskendusin ettevõtte infosüsteemile, mis on loodud toetama organisatsiooni põhivaldkondade tööd ja infovahetust. Eesmärgiks oli välja selgitada ettevõtte erinevate töörollide vajadused, seoses ettevõtte infosüsteemiga Erply. Organisatsioonis on kolm erinevat sihtrühmade gruppi: põhikasutajad, automaatikud ja projektijuht, kellest süsteemi igapäevaselt kasutavad ainult põhikasutajad. Soovitakse liikuda aga selles suunas, et pärast tööprotsesside kaardistust kasutaksid süsteemi kõik töögrupid, vastavalt oma töölõikudele ja vajadustele. Samuti uurisin, kuidas praegu ettevõtte infosüsteemi organisatsioonis kasutatakse ning kuidas seda edaspidi efektiivsemalt teha, arvestades kõikide sihtrühmade vajadusi. Uurimistöö valimis oli kokku kuus ettevõtte Atemix töötajat, kes kõik oma töölõikudes vajaksid Erply’s olevat infot. Andmete kogumiseks viisin läbi individuaalsed poolstandardiseeritud intervjuud iga töötajaga. Vestlused transkribeerisin ja kodeerisin vastavalt eelnevalt püstitatud uurimisküsimustele. Uuring on praktilise väärtusega ning sellest tulenevalt on tulemused põhiliselt suunatud uuritud ettevõtte juhtkonnale, tuues välja konkreetse ettevõtte vajadused seoses ettevõtte infosüsteemiga ning pakkudes lahendusi edasiseks süsteemi arendamiseks ja valimiseks. Tulemuste analüüsimisel selgus, et ettevõtte Atemix töötajad näevad kasutusel olevat ettevõtte infosüsteemi eesmärki erinevalt. See on tingitud sihtrühmade erinevatest infosüsteemi kasutamise kogemustest ning teadmatusest, milliseid võimalusi süsteem pakub. Sellest tulenevalt on kasutajate hoiak süsteemi osas kartlik. Ühiselt mõistetakse, et infosüsteem soodustab töö efektiivset tegemist, kuid samas väheste kogemuste tõttu kardetakse süsteemi kasutada. Olulist rolli mängib kasutajate koolitamine, mida seni pole tehtud ning kuna põhikasutajad ei tööta tegelikult igapäevaselt kõikide valdkondadega süsteemis, siis puudub inimene, kes oskaks ühiselt õpetada uutele kasutajatele kõiki infosüsteemi funktsioone. Kasutajate vajadused on seotud nii infoga kui ka erinevate funktsioonidega, mida süsteem võiks pakkuda. Praegu toimetavad igapäevaselt süsteemiga põhikasutajad ning kogu infovahetus käib läbi nende, mistõttu teised ettevõtte töötajad süsteemiga tööd ei tee ja nende vajadustega arvestamine on väike. Kõik töötajad peale põhikasutajate pelgavad süsteemi kasutada, kuna ei tea mida seal täpselt teha saab ja kuidas. Intervjuudest ja protsesside kaardistustest selgus, et mitmedki funktsionaalsused, mis muudaksid töö tegemise lihtsamaks, on puudu. Suure probleemina toodi välja erinevate programmide ühilduvuse teema ning toodete juurde lisatavate failide ja lisainfo funktsiooni puudumine. Praegu vajaks süsteem nii tehnilisi kui ka sisulisi muudatusi ning kindlasti on oluline töötajate ühtne koolitamine ja juhendmaterjalide loomine. Leitud tulemuste põhjal on ettevõttel kolm võimalust leitud vajaduste täitmiseks: võimaluse korral küsida praegu kasutusel oleva süsteemi täiendusi ja lisaarendust Erply klienditoest, leida arendaja, kes suudaks Erply’le programmeerida juurde soovitud lahendused või leida turult täiesti uus süsteem, mis vastab kasutajate välja toodud vajadustele. Kuna praegused protsessid ja vajadused on kaardistatud lähtudes praeguse süsteemi kogemustest, siis oleks ettevõttel kindlasti lihtsam proovida arendada praegu kasutusel olevat süsteemi.https://www.ester.ee/record=b5153935*es

A Multi-wavelength Survey of AGN in Massive Clusters: AGN Detection and Cluster AGN Fraction

We aim to study the effect of environment on the presence and fuelling of Active Galactic Nuclei (AGN) in massive galaxy clusters. We explore the use of different AGN detection techniques with the goal of selecting AGN across a broad range of luminosities, AGN/host galaxy flux ratios, and obscuration levels. From a sample of 12 galaxy clusters at redshifts 0.5 < z < 0.9, we identify AGN candidates using optical variability from multi-epoch HST imaging, X-ray point sources in Chandra images, and mid-IR SED power-law fits through the Spitzer IRAC channels. We find 178 optical variables, 74 X-ray point sources, and 64 IR power law sources, resulting in an average of ~25 AGN per cluster. We find no significant difference between the fraction of AGN among galaxies in clusters and the percentage of similarly-detected AGN in field galaxy studies (~2.5%). This result provides evidence that galaxies are still able to fuel accretion onto their supermassive black holes, even in dense environments. We also investigate correlations between the percentage of AGN and cluster physical properties such as mass, X-ray luminosity, size, morphology class and redshift. We find no significant correlations among cluster properties and the percentage of AGN detected.Comment: 68 pages, 22 figures, 15 table

Spectroscopic follow-up of variability-selected active galactic nuclei in the Chandra Deep Field South

Luminous AGNs are usually selected by their non-stellar colours or their X-ray emission. Colour selection cannot be used to select low-luminosity AGNs, since their emission is dominated by the host galaxy. Objects with low X-ray to optical ratio escape even the deepest X-ray surveys performed so far. In a previous study we presented a sample of candidates selected through optical variability in the Chandra Deep Field South, where repeated optical observations were performed for the STRESS supernova survey. We obtained new optical spectroscopy for a sample of variability selected candidates with the ESO NTT telescope. We analysed the new spectra, together with those existing in the literature and studied the distribution of the objects in U-B and B-V colours, optical and X-ray luminosity, and variability amplitude. A large fraction (17/27) of the observed candidates are broad-line luminous AGNs, confirming the efficiency of variability in detecting quasars. We detect: i) extended objects which would have escaped the colour selection and ii) objects of very low X-ray to optical ratio. Several objects resulted to be narrow-emission line galaxies where variability indicates nuclear activity, while no emission lines were detected in others. Some of these galaxies have variability and X-ray to optical ratio close to active galactic nuclei, while others have much lower variability and X-ray to optical ratio. This result can be explained by the dilution of the nuclear light due to the host galaxy. Our results demonstrate the effectiveness of supernova search programmes to detect large samples of low-luminosity AGNs. A sizable fraction of the AGN in our variability sample had escaped X-ray detection (5/47) and/or colour selection (9/48). Spectroscopic follow-up to fainter flux limits is strongly encouraged.Comment: 14 pages, 11 figures, to appear in A&

Optical Spectroscopy of Active Galactic Nuclei in SA57

The cosmological evolution of X-ray-selected and optically selected Active Galactic Nuclei (AGNs) show different behaviours interpreted in terms of two different populations. The difference is evident mainly for low luminosity AGNs (LLAGNs), many of which are lost by optical photometric surveys. We are conducting a spectroscopical study of a composite sample of AGN candidates selected in SA57 following different searching techniques, to identify low luminosity AGNs and break down the sample into different classes of objects. AGN candidates were obtained through optical variability and/or X-ray emission. Of special interest are the extended variable objects, which are expected to be galaxies hosting LLAGNs. Among the 26 classified objects a fair number (9) show typical AGN spectra. 10 objects show Narrow Emission Line Galaxy spectra, and in most of them (8/10) optical variability suggests the presence of LLAGNs.Comment: 7 pages, 8 figures, to appear in A&

Variability and Multiwavelength Detected AGN in the GOODS Fields

We identify 85 variable galaxies in the GOODS North and South fields using 5 epochs of HST ACS V-band (F606W) images spanning 6 months. The variables are identified through significant flux changes in the galaxy's nucleus and represent ~2% of the survey galaxies. With the aim of studying the active galaxy population in the GOODS fields, we compare the variability-selected sample with X-ray and mid-IR AGN candidates. Forty-nine percent of the variables are associated with X-ray sources identified in the 2Ms Chandra surveys. Twenty-four percent of X-ray sources likely to be AGN are optical variables and this percentage increases with decreasing hardness ratio of the X-ray emission. Stacking of the non-X-ray detected variables reveals marginally significant soft X-ray emission. Forty-eight percent of mid-IR power-law sources are optical variables, all but one of which are also X-ray detected. Thus, about half of the optical variables are associated with either X-ray or mid-IR power-law emission. The slope of the power-law fit through the Spitzer IRAC bands indicates that two-thirds of the variables have BLAGN-like SEDs. Among those galaxies spectroscopically identified as AGN, we observe variability in 74% of broad-line AGNs and 15% of NLAGNs. The variables are found in galaxies extending to z~3.6. We compare the variable galaxy colors and magnitudes to the X-ray and mid-IR sample and find that the non-X-ray detected variable hosts extend to bluer colors and fainter intrinsic magnitudes. The variable AGN candidates have Eddington ratios similar to those of X-ray selected AGN.Comment: 36 pages, 12 figures, ApJ accepte

Variability-selected active galactic nuclei from supernova search in the Chandra deep field south

Variability is a property shared by virtually all active galactic nuclei (AGNs), and was adopted as a criterion for their selection using data from multi epoch surveys. Low Luminosity AGNs (LLAGNs) are contaminated by the light of their host galaxies, and cannot therefore be detected by the usual colour techniques. For this reason, their evolution in cosmic time is poorly known. Consistency with the evolution derived from X-ray detected samples has not been clearly established so far, also because the low luminosity population consists of a mixture of different object types. LLAGNs can be detected by the nuclear optical variability of extended objects. Several variability surveys have been, or are being, conducted for the detection of supernovae (SNe). We propose to re-analyse these SNe data using a variability criterion optimised for AGN detection, to select a new AGN sample and study its properties. We analysed images acquired with the wide field imager at the 2.2 m ESO/MPI telescope, in the framework of the STRESS supernova survey. We selected the AXAF field centred on the Chandra Deep Field South where, besides the deep X-ray survey, various optical data exist, originating in the EIS and COMBO-17 photometric surveys and the spectroscopic database of GOODS. We obtained a catalogue of 132 variable AGN candidates. Several of the candidates are X-ray sources. We compare our results with an HST variability study of X-ray and IR detected AGNs, finding consistent results. The relatively high fraction of confirmed AGNs in our sample (60%) allowed us to extract a list of reliable AGN candidates for spectroscopic follow-up observations.Comment: language revised, table reformatted. To Appear on A&