-
Daniel Stern,
Roberto J. Assef,
Dominic J. Benford,
Andrew Blain,
Roc Cutri,
Arjun Dey,
Peter Eisenhardt,
Roger L. Griffith,
T. H. Jarrett,
Sean Lake,
Frank Masci,
Sara Petty,
S. A. Stanford,
Chao-Wei Tsai,
E. L. Wright,
Lin Yan,
Fiona Harrison, Kristin Madsen
The Astrophysical Journal 07/2012; 753:30. · 6.02 Impact Factor
-
Daniel Stern,
Roberto J. Assef,
Dominic J. Benford,
Andrew Blain,
Roc Cutri,
Arjun Dey,
Peter Eisenhardt,
Roger L. Griffith,
T. H. Jarrett,
Sean Lake,
Frank Masci,
Sara Petty,
S. A. Stanford,
Chao-Wei Tsai,
E. L. Wright,
Lin Yan,
Fiona Harrison, Kristin Madsen
[show abstract]
[hide abstract]
ABSTRACT: The Wide-field Infrared Survey Explorer (WISE) is an extremely capable and
efficient black hole finder. We present a simple mid-infrared color criterion,
W1-W2 \geq 0.8 (i.e., [3.4]-[4.6] \geq 0.8, Vega), which identifies 61.9 \pm
5.4 AGN candidates per deg2 to a depth of W2 = 15.0. This implies a much larger
census of luminous AGN than found by typical wide-area surveys, attributable to
the fact that mid-infrared selection identifies both unobscured (type 1) and
obscured (type 2) AGN. Optical and soft X-ray surveys alone are highly biased
towards only unobscured AGN, while this simple WISE selection likely identifies
even heavily obscured, Compton-thick AGN. Using deep, public data in the COSMOS
field, we explore the properties of WISE-selected AGN candidates. At the
mid-infrared depth considered, 160 uJy at 4.6 microns, this simple criterion
identifies 78% of Spitzer mid-infrared AGN candidates according to the criteria
of Stern et al. (2005) and the reliability is 95%. We explore the demographics,
multiwavelength properties and redshift distribution of WISE-selected AGN
candidates in the COSMOS field.
05/2012;
-
R. Scott Barrows,
Daniel Stern, Kristin Madsen,
Fiona Harrison,
Roberto J. Assef,
Julia M. Comerford,
Michael C. Cushing,
Christopher D. Fassnacht,
Anthony H. Gonzalez,
Roger Griffith,
Ryan Hickox,
J. Davy Kirkpatrick,
and David J. Lagattuta
[show abstract]
[hide abstract]
ABSTRACT: The X-ray source CXOXBJ142607.6+353351 (CXOJ1426+35), which was identified in a 172 ks Chandra image in the Boötes field, shows double-peaked rest-frame optical/UV emission lines, separated by 069 (5.5 kpc) in the spatial dimension and by 690 km s–1 in the velocity dimension. The high excitation lines and emission line ratios indicate both systems are ionized by an active galactic nucleus (AGN) continuum, and the double-peaked profile resembles that of candidate dual AGNs. At a redshift of z = 1.175, this source is the highest redshift candidate dual AGN yet identified. However, many sources have similar emission line profiles for which other interpretations are favored. We have analyzed the substantial archival data available in this field as well as acquired near-infrared (NIR) adaptive optics (AO) imaging and NIR slit spectroscopy. The X-ray spectrum is hard, implying a column density of several 1023 cm–2. Though heavily obscured, the source is also one of the brightest in the field, with an absorption-corrected 2-10 keV luminosity of ~1045 erg s–1. Outflows driven by an accretion disk may produce the double-peaked lines if the central engine accretes near the Eddington limit. However, we may be seeing the narrow line regions of two AGNs following a galactic merger. While the AO image reveals only a single source, a second AGN would easily be obscured by the significant extinction inferred from the X-ray data. Understanding the physical processes producing the complex emission line profiles seen in CXOJ1426+35 and related sources is important for interpreting the growing population of dual AGN candidates.
The Astrophysical Journal 12/2011; 744(1):7. · 6.02 Impact Factor
-
[show abstract]
[hide abstract]
ABSTRACT: Merger-remnant galaxies with kpc-scale separation dual active galactic nuclei
(AGNs) should be widespread as a consequence of galaxy mergers and triggered
gas accretion onto supermassive black holes, yet very few dual AGNs have been
observed. Galaxies with double-peaked narrow AGN emission lines in the Sloan
Digital Sky Survey are plausible dual AGN candidates, but their double-peaked
profiles could also be the result of gas kinematics or AGN-driven outflows and
jets on small or large scales. To help distinguish between these scenarios, we
have obtained spatial profiles of the AGN emission via follow-up long-slit
spectroscopy of 81 double-peaked narrow-line AGNs in SDSS at 0.03 < z < 0.36
using Lick, Palomar, and MMT Observatories. We find that all 81 systems exhibit
double AGN emission components with ~kpc projected spatial separations on the
sky, which suggests that they are produced by kpc-scale dual AGNs or kpc-scale
outflows, jets, or rotating gaseous disks. In addition, we find that the
subsample (58%) of the objects with spatially compact emission components may
be preferentially produced by dual AGNs, while the subsample (42%) with
spatially extended emission components may be preferentially produced by AGN
outflows. We also find that for 32% of the sample the two AGN emission
components are preferentially aligned with the host galaxy major axis, as
expected for dual AGNs orbiting in the host galaxy potential. Our results both
narrow the list of possible physical mechanisms producing the double AGN
components, and suggest several observational criteria for selecting the most
promising dual AGN candidates from the full sample of double-peaked narrow-line
AGNs. Using these criteria, we determine the 17 most compelling dual AGN
candidates in our sample.
11/2011;
-
R. Scott Barrows,
Daniel Stern, Kristin Madsen,
Fiona Harrison,
Roberto J. Assef,
Julia M. Comerford,
Michael C. Cushing,
Christopher D. Fassnacht,
Anthony Gonzalez,
Roger Griffith,
Ryan Hickox,
J. Davy Kirkpatrick,
David J. Lagattuta
[show abstract]
[hide abstract]
ABSTRACT: The X-ray source CXOXBJ142607.6+353351 (CXOJ1426+35), which was identified in
a 172 ks Chandra image in the Bootes field, shows double-peaked rest-frame
optical/UV emission lines, separated by 0.69" (5.5 kpc) in the spatial
dimension and by 690 km s^-1 in the velocity dimension. The high excitation
lines and emission line ratios indicate both systems are ionized by an AGN
continuum, and the double-peaked profile resembles that of candidate dual AGN.
At a redshift of z=1.175, this source is the highest redshift candidate dual
AGN yet identified. However, many sources have similar emission line profiles
for which other interpretations are favored. We have analyzed the substantial
archival data available in this field, as well as acquired near-infrared (NIR)
adaptive optics (AO) imaging and NIR slit spectroscopy. The X-ray spectrum is
hard, implying a column density of several 10^23 cm^-2. Though heavily
obscured, the source is also one of the brightest in the field, with an
absorption-corrected 2-10 keV luminosity of ~10^45 erg s^-1. Outflows driven by
an accretion disk may produce the double-peaked lines if the central engine
accretes near the Eddington limit. However, we may be seeing the narrow line
regions of two AGN following a galactic merger. While the AO image reveals only
a single source, a second AGN would easily be obscured by the significant
extinction inferred from the X-ray data. Understanding the physical processes
producing the complex emission line profiles seen in CXOJ1426+35 and related
sources is important for interpreting the growing population of dual AGN
candidates.
09/2011;
-
Roger L. Griffith,
Chao-Wei Tsai,
Daniel Stern,
Andrew Blain,
Peter R. M. Eisenhardt,
Fiona Harrison,
Thomas H. Jarrett, Kristin Madsen,
Spencer A. Stanford,
Edward L. Wright,
Jingwen Wu,
Yanling Wu,
and Lin Yan
[show abstract]
[hide abstract]
ABSTRACT: We report two new low-metallicity blue compact dwarf galaxies (BCDs), WISEP J080103.93+264053.9 (hereafter W0801+26) and WISEP J170233.53+180306.4 (hereafter W1702+18), discovered using the Wide-field Infrared Survey Explorer (WISE). We identified these two BCDs from their extremely red colors at mid-infrared wavelengths and obtained follow-up optical spectroscopy using the Low Resolution Imaging Spectrometer on Keck I. The mid-infrared properties of these two sources are similar to the well-studied, extremely low metallicity galaxy SBS 0335-052E. We determine metallicities of 12 + log (O/H) = 7.75 and 7.63 for W0801+26 and W1702+18, respectively, placing them among a very small group of very metal deficient galaxies (Z ≤ 1/10 Z ☉). Their >300 Å Hβ equivalent widths, similar to SBS 0335-052E, imply the existence of young (<5 Myr) star-forming regions. We measure star formation rates of 2.6 and 10.9 M ☉ yr–1 for W0801+26 and W1702+18, respectively. These BCDs, showing recent star formation activity in extremely low metallicity environments, provide new laboratories for studying star formation in extreme conditions and are low-redshift analogs of the first generation of galaxies to form in the universe. Using the all-sky WISE survey, we discuss a new method to identify similar star-forming, low-metallicity BCDs.
The Astrophysical Journal Letters 06/2011; 736(1):L22. · 5.53 Impact Factor
