7,305 research outputs found
The WISE AGN Catalog
We present two large catalogs of AGN candidates identified across ~75% of the
sky from the Wide-field Infrared Survey Explorer's AllWISE Data Release. Both
catalogs, some of the largest such catalogs published to date, are selected
purely on the basis of mid-IR photometry in the WISE W1 and W2 bands. The
catalogs are designed to be appropriate for a broad range of scientific
investigations, with one catalog emphasizing reliability while the other
emphasizes completeness. Specifically, the R90 catalog consists of 4,543,530
AGN candidates with 90% reliability, while the C75 catalog consists of
20,907,127 AGN candidates with 75% completeness. We provide a detailed
discussion of potential artifacts, and excise portions of the sky close to the
Galactic Center, Galactic Plane, nearby galaxies, and other expected
contaminating sources. Our final catalogs cover 30,093 deg^2 of extragalactic
sky. These catalogs are expected to enable a broad range of science, and we
present a few simple illustrative cases. From the R90 sample we identify 45
highly variable AGN lacking radio counterparts in the FIRST survey, implying
they are unlikely to be blazars. One of these sources, WISEA
J142846.71+172353.1, is a mid-IR-identified changing-look quasar at z=0.104. We
characterize our catalogs by comparing them to large, wide-area AGN catalogs in
the literature, specifically UV-to-near-IR quasar selections from SDSS and
XDQSOz, mid-IR selection from Secrest et al. (2015) and X-ray selection from
ROSAT. From the latter work, we identify four ROSAT X-ray sources that each are
matched to three WISE-selected AGN in the R90 sample within 30". Palomar
spectroscopy reveals one of these systems, 2RXS J150158.6+691029, to consist of
a triplet of quasars at z=1.133 +/- 0.004, suggestive of a rich group or
forming galaxy cluster.(Abridged)Comment: Accepted for publication in the Astrophysical Journal Supplements.
Updated with comments from the referee. 20 pages, 15 figures, 8 tables. The
WISE AGN Catalogs can be made available upon request by writing to
[email protected]
The Porcupine Survey: A Distributed Survey and WISE Followup
Spitzer post-cryogen observations to perform a moderate depth survey distributed around the sky are proposed. Field centers are chosen to be WISE brown dwarf candidates, which will typically be 160 µJy at 4.7 µm and randomly distributed around the sky. The Spitzer observations will give much higher sensitivity, higher angular resolution, and a time baseline to measure both proper motions and possibly parallaxes. The distance and velocity data obtained on the WISE brown dwarf candidates will greatly improve our knowledge of the mass and age distribution of brown dwarfs. The outer parts of the Spitzer fields surrounding the WISE positions will provide a deep survey in many narrow fields of view distributed around the sky, and the volume of this survey will contain many more distant brown dwarfs, and many extragalactic objects
The Friendship Journey: Developing Global Understanding in the Middle Grades
The goals of developing a global perspective are consistent with the faith-based values of Catholicism. The primary goal is to prepare students academically, morally, and socially to participate in a globalized world that constantly faces new problems. A key component of this is the understanding that other people, who may appear on the surface to be very different from themselves, have differences which have value and similarities which unite us. The purpose of this article is to present one Catholic school’s attempts to prepare its students to meet the challenges of citizenry in an international community and to describe the impact of those efforts. The questions we explored are: (a) Does a student-focused, cultural exchange program enhance American students’ global perspectives? Does a student-focused, cultural exchange opportunity enrich students’ cultural understandings? Findings from this study revealed that students gained an appreciation for diverse cultures through social interaction. While the pre- and post-test survey data revealed some changes in students’ beliefs and attitudes, interviews and observations provided substantial evidence of students’ evolving awareness and respect for other cultures. The tangible connections formed produced young people who have a greater appreciation for our global community.
Résumé
Les objectifs consistant à développer une perspective mondiale s’accordent avec les valeurs religieuses du catholicisme. Le principal objectif est de préparer les élèves au niveau scolaire, moral et social à prendre part à une mondialisation qui rencontre constamment de nouveaux problèmes. Pour y parvenir, il est essentiel qu’ils comprennent que d’autres personnes qui ne leur ressemblent pas du tout en apparence, présentent des différences que nous apprécions et des ressemblances qui nous unissent. Cet article a pour objet de montrer comment une école catholique a essayé de préparer ses élèves à surmonter les problèmes rencontrés en tant que citoyen d’une communauté internationale et de décrire quel impact ces actions ont eu. Les questions étudiées sont les suivantes : (a) Un programme d’échanges culturels centré sur l’élève renforce-t-il les perspectives mondiales des élèves américains ? Leur compréhension des cultures se trouve-t-elle enrichie par la possibilité d’effectuer un échange culturel centré sur l’élève ? Les conclusions tirées de cette étude ont montré que les élèves ont appris à apprécier des cultures diverses par l’interaction sociale. Alors que les données de l’étude avant et après les tests ont révélé certaines modifications des croyances et attitudes des élèves, les entretiens et observations ont clairement prouvé une évolution de la sensibilisation des élèves et de leur respect vis-à-vis d’autres cultures. Les liens tangibles qui se sont tissés ont amené les jeunes à mieux apprécier notre communauté mondiale.
Resumen
Los objetivos para desarrollar una perspectiva global son consistentes con los valores basados en la fe del catolicismo. El principal objetivo es preparar a los estudiantes académica, moral y socialmente para participar en un mundo globalizado que se enfrenta constantemente a nuevos problemas. Un componente clave de esto es el entendimiento de que otra gente, que puede aparentar en la superficie ser de una manera muy distinta a ellos, tiene diferencias que resultan valiosas y a su vez similitudes que nos unen. El objetivo de este artículo es presentar la intención de una escuela católica de preparar a sus estudiantes para que logren los desafíos de la ciudadanía en una comunidad internacional y describir el impacto de estos esfuerzos. Las preguntas exploradas son: (a) ¿Puede un programa de intercambio cultural centrado en el alumno ampliar las perspectivas globales de los estudiantes estadounidenses? (b) ¿Puede una oportunidad de intercambio cultural centrado en el alumno enriquecer la comprensión cultural de los estudiantes? Los resultados de este estudio revelaron que los estudiantes ganaron apreciación por las diversas culturas a través de la interacción social. Aunque la información previa y posterior a las encuestas revelaron cambios en las creencias y actitudes de los estudiantes, las entrevistas y las observaciones ofrecieron pruebas sustanciales de evolución en la sensibilización y respeto de los estudiantes hacia otras culturas. Las conexiones tangibles que se formaron produjeron jóvenes con un mayor aprecio por nuestra comunidad global
Spectroscopic confirmation of a galaxy cluster associated with 7C1756+6520 at z=1.416
We present spectroscopic follow-up of an overdensity of galaxies
photometrically selected to be at 1.4<z<2.5 found in the vicinity of the radio
galaxy 7C1756+6520 at z=1.4156. Using the DEIMOS optical multi-object
spectrograph on the Keck 2 telescope, we observed a total of 129 BzK-selected
sources, comprising 82 blue, star-forming galaxy candidates (sBzK) and 47 red,
passively-evolving galaxy candidates (pBzK*), as well as 11 mid-infrared
selected AGN candidates. We obtain robust spectroscopic redshifts for 36 blue
galaxies, 7 red galaxies and 9 AGN candidates. Assuming all foreground
interlopers were identified, we find that only 16% (9%) of the sBzK (pBzK*)
galaxies are at z<1.4. Therefore, the BzK criteria are shown to be relatively
robust at identifying galaxies at moderate redshifts. Twenty-one galaxies,
including the radio galaxy, four additional AGN candidates and three red galaxy
candidates are found with 1.4156 +/- 0.025, forming a large scale structure at
the redshift of the radio galaxy. Of these, eight have projected offsets <2Mpc
relative to the radio galaxy position and have velocity offsets <1000km/s
relative to the radio galaxy redshift. This confirms that 7C1756+6520 is
associated with a high-redshift galaxy cluster. A second compact group of four
galaxies is found at z~1.437, forming a sub-group offset by Dv~3000km/s and
approximately 1.5' east of the radio galaxy.Comment: 9 pages, 6 figures, 2 tables, accepted for publication in A&A
Characterizing the Mid-IR Extragalactic Sky with WISE and SDSS
The Wide-field Infrared Survey Explorer (WISE) has completed its all-sky
survey at 3.4-22 micron. We merge the WISE data with optical SDSS data and
provide a phenomenological characterization of mid-IR, extragalactic sources.
WISE is most sensitive at 3.4micron(W1) and least at 22micron(W4). The W1 band
probes massive early-type galaxies out to z\gtrsim1. This is more distant than
SDSS identified early-type galaxies, consistent with the fact that 28% of
3.4micron sources have faint or no r-band counterparts (r>22.2). In contrast,
92-95% of 12 and 22micron sources have SDSS optical counterparts with r<22.2.
WISE 3.4micron detects 89.8% of the entire SDSS QSO catalog at SNR(W1)>7, but
only 18.9% at 22micron with SNR(W4)>5. We show that WISE colors alone are
effective in isolating stars (or local early-type galaxies), star-forming
galaxies and strong AGN/QSOs at z<3. We highlight three major applications of
WISE colors: (1) Selection of strong AGN/QSOs at z0.8 and
W2<15.2 criteria, producing a census of this population. The surface density of
these strong AGN/QSO candidates is 67.5+-0.14/deg^2. (2) Selection of
dust-obscured, type-2 AGN/QSO candidates. We show that WISE W1-W2>0.8, W2<15.2
combined with r-W2>6 (Vega) colors can be used to identify type-2 AGN
candidates. The fraction of these type-2 AGN candidates is 1/3rd of all WISE
color-selected AGNs. (3) Selection of ULIRGs at z\sim2 with extremely red
colors, r-W4>14 or well-detected 22micron sources lacking detections in the 3.4
and 4.6micron bands. The surface density of z~2 r-W4>14 ULIRGs is
0.9+-0.07/deg^2 at SNR(W4)>5 (flux(W4)>=2.5mJy), which is consistent with that
inferred from smaller area Spitzer surveys. Optical spectroscopy of a small
number of these high-redshift ULIRGs confirms our selection, and reveals a
possible trend that optically fainter or r-W4 redder candidates are at higher
redshifts.Comment: 41 pages, 20 figures, Accepted for publication by the Astronomical
Journa
The Cluster and Field Galaxy AGN Fraction at z = 1 to 1.5: Evidence for a Reversal of the Local Anticorrelation Between Environment and AGN Fraction
The fraction of cluster galaxies that host luminous AGN is an important probe
of AGN fueling processes, the cold ISM at the centers of galaxies, and how
tightly black holes and galaxies co-evolve. We present a new measurement of the
AGN fraction in a sample of 13 clusters of galaxies (M >= 10^{14} Msun) at
1<z<1.5 selected from the Spitzer/IRAC Shallow Cluster Survey, as well as the
field fraction in the immediate vicinity of these clusters, and combine these
data with measurements from the literature to quantify the relative evolution
of cluster and field AGN from the present to z~3. We estimate that the cluster
AGN fraction at 1<z<1.5 is f_A = 3.0^{+2.4}_{-1.4}% for AGN with a rest-frame,
hard X-ray luminosity greater than L_{X,H} >= 10^{44} erg/s. This fraction is
measured relative to all cluster galaxies more luminous than M*_{3.6}(z)+1,
where M*_{3.6}(z) is the absolute magnitude of the break in the galaxy
luminosity function at the cluster redshift in the IRAC 3.6um bandpass. The
cluster AGN fraction is 30 times greater than the 3sigma upper limit on the
value for AGN of similar luminosity at z~0.25, as well as more than an order of
magnitude greater than the AGN fraction at z~0.75. AGN with L_{X,H} >= 10^{43}
erg/s exhibit similarly pronounced evolution with redshift. In contrast with
the local universe, where the luminous AGN fraction is higher in the field than
in clusters, the X-ray and MIR-selected AGN fractions in the field and clusters
are consistent at 1<z<1.5. This is evidence that the cluster AGN population has
evolved more rapidly than the field population from z~1.5 to the present. This
environment-dependent AGN evolution mimics the more rapid evolution of
star-forming galaxies in clusters relative to the field.Comment: ApJ Accepted. 16 pages, 8 figures in emulateapj forma
Galaxy Cluster Correlation Function to z ~ 1.5 in the IRAC Shallow Cluster Survey
We present the galaxy cluster autocorrelation function of 277 galaxy cluster
candidates with 0.25 \le z \le 1.5 in a 7 deg^2 area of the IRAC Shallow
Cluster Survey. We find strong clustering throughout our galaxy cluster sample,
as expected for these massive structures. Specifically, at = 0.5 we find a
correlation length of r_0 = 17.40^{+3.98}_{-3.10} h^-1 Mpc, in excellent
agreement with the Las Campanas Distant Cluster Survey, the only other
non-local measurement. At higher redshift, = 1, we find that strong
clustering persists, with a correlation length of r_0=19.14^{+5.65}_{-4.56}
h^-1 Mpc. A comparison with high resolution cosmological simulations indicates
these are clusters with halo masses of \sim 10^{14} Msun, a result supported by
estimates of dynamical mass for a subset of the sample. In a stable clustering
picture, these clusters will evolve into massive (10^{15} Msun) clusters by the
present day.Comment: 4 pages, 4 figures, 1 table. ApJ Letters, in pres
A z=5.34 Galaxy Pair in the Hubble Deep Field
We present spectrograms of the faint V-drop (V(606) = 28.1, I(814) = 25.6)
galaxy pair HDF3-951.1 and HDF3-951.2 obtained at the Keck II Telescope.
Fernandez-Soto, Lanzetta, & Yahil (1998) derive a photometric redshift of z(ph)
= 5.28 (+0.34,-0.41; 2 sigma) for these galaxies; our integrated spectrograms
show a large and abrupt discontinuity near 7710 (+- 5) Angstroms. This break is
almost certainly due to the Lyman alpha forest as its amplitude (1 - fnu(short)
/ fnu(long) > 0.87; 95% confidence limit) exceeds any discontinuities observed
in stellar or galaxian rest-frame optical spectra. The resulting
absorption-break redshift is z=5.34 (+- 0.01). Optical/near-IR photometry from
the HDF yields an exceptionally red (V(606)-I(814)) color, consistent with this
large break. A more accurate measure of the continuum depression blueward of
Lyman alpha utilizing the imaging photometry yields D(A) = 0.88.
The system as a whole is slightly brighter than L*(1500) relative to the z~3
Lyman break population and the total star formation rate inferred from the UV
continuum is ~22 h(50)^-2 M(sun) yr^-1 (q(0) = 0.5) assuming the absence of
dust extinction. The two individual galaxies are quite small (size scales < 1
h(50)^-1 kpc). Thus these galaxies superficially resemble the Pascarelle etal
(1996) ``building blocks''; if they comprise a gravitationally bound system,
the pair will likely merge in a time scale ~100 Myr.Comment: 18 pages, 4 figures; accepted to A
Heavy X-ray obscuration in the most-luminous galaxies discovered by WISE
Hot Dust-Obscured Galaxies (Hot DOGs) are hyperluminous
() infrared galaxies with
extremely high (up to hundreds of K) dust temperatures. The sources powering
both their extremely high luminosities and dust temperatures are thought to be
deeply buried and rapidly accreting supermassive black holes (SMBHs). Hot DOGs
could therefore represent a key evolutionary phase in which the SMBH growth
peaks. X-ray observations can be used to study their obscuration levels and
luminosities. In this work, we present the X-ray properties of the 20
most-luminous () known Hot DOGs at
. Five of them are covered by long-exposure ( ks) Chandra and
XMM-Newton observations, with three being X-ray detected, and we study their
individual properties. One of these sources (W01160505) is a Compton-thick
candidate, with column density
derived from X-ray spectral fitting. The remaining 15 Hot DOGs have been
targeted by a Chandra snapshot (3.1 ks) survey. None of these 15 is
individually detected; therefore we applied a stacking analysis to investigate
their average emission. From hardness-ratio analysis, we constrained the
average obscuring column density and intrinsic luminosity to be
log and
, which are consistent with
results for individually detected sources. We also investigated the
and relations, finding hints that Hot
DOGs are typically X-ray weaker than expected, although larger samples of
luminous obscured QSOs are needed to derive solid conclusions.Comment: MNRAS, accepted 2017 November 29 . Received 2017 November 29 ; in
original form 2017 October 11. 15 pages, 6 figure
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