30 research outputs found
Census of the Local Universe (CLU) Narrow-Band Survey I: Galaxy Catalogs from Preliminary Fields
We present the Census of the Local Universe (CLU) narrow-band survey to
search for emission-line (\ha) galaxies. CLU-\ha~has imaged 3 of
the sky (26,470~deg) with 4 narrow-band filters that probe a distance out
to 200~Mpc. We have obtained spectroscopic follow-up for galaxy candidates in
14 preliminary fields (101.6~deg) to characterize the limits and
completeness of the survey. In these preliminary fields, CLU can identify
emission lines down to an \ha~flux limit of
~ at 90\% completeness, and recovers 83\%
(67\%) of the \ha~flux from catalogued galaxies in our search volume at the
=2.5 (=5) color excess levels. The contamination from galaxies
with no emission lines is 61\% (12\%) for =2.5 (=5). Also, in
the regions of overlap between our preliminary fields and previous
emission-line surveys, we recover the majority of the galaxies found in
previous surveys and identify an additional 300 galaxies. In total, we
find 90 galaxies with no previous distance information, several of which are
interesting objects: 7 blue compact dwarfs, 1 green pea, and a Seyfert galaxy;
we also identified a known planetary nebula. These objects show that the
CLU-\ha~survey can be a discovery machine for objects in our own Galaxy and
extreme galaxies out to intermediate redshifts. However, the majority of the
CLU-\ha~galaxies identified in this work show properties consistent with normal
star-forming galaxies. CLU-\ha~galaxies with new redshifts will be added to
existing galaxy catalogs to focus the search for the electromagnetic
counterpart to gravitational wave events.Comment: 28 pages, 22 figures, 4 tables (Accepted to ApJ
Discovery of a Gas-Rich Companion to the Extremely Metal-Poor Galaxy DDO 68
We present HI spectral-line imaging of the extremely metal-poor galaxy DDO
68. This system has a nebular oxygen abundance of only 3% Z, making
it one of the most metal-deficient galaxies known in the local volume.
Surprisingly, DDO 68 is a relatively massive and luminous galaxy for its metal
content, making it a significant outlier in the mass-metallicity and
luminosity-metallicity relationships. The origin of such a low oxygen abundance
in DDO 68 presents a challenge for models of the chemical evolution of
galaxies. One possible solution to this problem is the infall of pristine
neutral gas, potentially initiated during a gravitational interaction. Using
archival HI spectral-line imaging obtained with the Karl G. Jansky Very Large
Array, we have discovered a previously unknown companion of DDO 68. This
low-mass (M 2.810 M), recently
star-forming (SFR 1.410 M yr,
SFR 710 M yr) companion has
the same systemic velocity as DDO 68 (V 506 km s; D
12.740.27 Mpc) and is located at a projected distance of 42 kpc. New HI
maps obtained with the 100m Robert C. Byrd Green Bank Telescope provide
evidence that DDO 68 and this companion are gravitationally interacting at the
present time. Low surface brightness HI gas forms a bridge between these
objects.Comment: Accepted for publication in the Astrophysical Journal Letter
Census of the Local Universe (CLU) Narrow-Band Survey I: Galaxy Catalogs from Preliminary Fields
We present the Census of the Local Universe (CLU) narrow-band survey to search for emission-line (Hα) galaxies. CLU-Hα has imaged ≈3π of the sky (26,470 deg^2) with 4 narrow-band filters that probe a distance out to 200 Mpc. We have obtained spectroscopic follow-up for galaxy candidates in 14 preliminary fields (101.6 deg^2) to characterize the limits and completeness of the survey. In these preliminary fields, CLU can identify emission lines down to an Hα flux limit of 10^(−14) erg s^(−1) cm^(−2) at 90\% completeness, and recovers 83% (67%) of the Hα flux from catalogued galaxies in our search volume at the Σ=2.5 (Σ=5) color excess levels. The contamination from galaxies with no emission lines is 61% (12%) for Σ=2.5 (Σ=5). Also, in the regions of overlap between our preliminary fields and previous emission-line surveys, we recover the majority of the galaxies found in previous surveys and identify an additional ≈300 galaxies. In total, we find 90 galaxies with no previous distance information, several of which are interesting objects: 7 blue compact dwarfs, 1 green pea, and a Seyfert galaxy; we also identified a known planetary nebula. These objects show that the CLU-Hα survey can be a discovery machine for objects in our own Galaxy and extreme galaxies out to intermediate redshifts. However, the majority of the CLU-Hα galaxies identified in this work show properties consistent with normal star-forming galaxies. CLU-Hα galaxies with new redshifts will be added to existing galaxy catalogs to focus the search for the electromagnetic counterpart to gravitational wave events
Constraining the Kilonova Rate with Zwicky Transient Facility Searches Independent of Gravitational Wave and Short Gamma-ray Burst Triggers
The first binary neutron star merger, GW170817, was accompanied by a
radioactivity-powered optical/infrared transient called a kilonova. To date, no
compelling kilonova has been found during optical surveys of the sky,
independent of gravitational-wave triggers. In this work, we searched the first
23 months of the Zwicky Transient Facility (ZTF) data stream for candidate
kilonovae in the form of rapidly evolving transients. We combined ZTF alert
queries with forced point-spread-function photometry and nightly flux stacking
to increase our sensitivity to faint and fast transients. Automatic queries
yielded candidates, 24 of which passed quality checks and strict
selection criteria based on a grid of kilonova models tailored for both binary
neutron star and neutron star-black hole mergers. None of the candidates in our
sample was deemed a possible kilonova after thorough vetting, catalog
cross-matching, and study of their color evolution. The sources that passed our
selection criteria are dominated by Galactic cataclysmic variables. In
addition, we identified two fast transients at high Galactic latitude, one of
which is the confirmed afterglow of long-duration GRB190106A, and the other is
a possible cosmological afterglow. Using a survey simulation code, we
constrained the kilonova rate for a range of models including top-hat and
linearly decaying light curves and synthetic light curves obtained with
radiative transfer simulations. For prototypical GW170817-like kilonovae, we
constrain the rate to be Gpc yr at 95% confidence
level by requiring at least 2 high-significance detections. By assuming a
population of kilonovae with the same geometry and composition of GW170817
observed under a uniform viewing angle distribution, we obtained a constraint
on the rate of Gpc yr.Comment: Submitted for publication in Ap
Constraining the Kilonova Rate with Zwicky Transient Facility Searches Independent of Gravitational Wave and Short Gamma-Ray Burst Triggers
The first binary neutron star merger, GW170817, was accompanied by a radioactivity-powered optical/infrared transient called a kilonova. To date, no compelling kilonova has been found in all-sky optical surveys, independently of short gamma-ray burst and gravitational-wave triggers. In this work, we searched the first 23 months of the Zwicky Transient Facility (ZTF) data stream for candidate kilonovae in the form of rapidly evolving transients. We combined ZTF alert queries with forced point-spread-function photometry and nightly flux stacking to increase our sensitivity to faint and fast transients. Automatic queries yielded >11,200 candidates, 24 of which passed quality checks and selection criteria based on a grid of kilonova models tailored for both binary neutron star and neutron star–black hole mergers. None of the candidates in our sample was deemed a possible kilonova after thorough vetting. The sources that passed our selection criteria are dominated by Galactic cataclysmic variables. We identified two fast transients at high Galactic latitude, one of which is the confirmed afterglow of long-duration GRB 190106A, the other is a possible cosmological afterglow. Using a survey simulation code, we constrained the kilonova rate for a range of models including top-hat, linearly decaying light curves, and synthetic light curves obtained with radiative transfer simulations. For prototypical GW170817-like kilonovae, we constrain the rate to be R < 1775 Gpc⁻³ yr⁻¹ (95% confidence). By assuming a population of kilonovae with the same geometry and composition of GW170817 observed under a uniform viewing angle distribution, we obtained a constraint on the rate of R < 4029 Gpc⁻³ yr⁻¹
Constraining the Kilonova Rate with Zwicky Transient Facility Searches Independent of Gravitational Wave and Short Gamma-Ray Burst Triggers
The first binary neutron star merger, GW170817, was accompanied by a radioactivity-powered optical/infrared transient called a kilonova. To date, no compelling kilonova has been found in all-sky optical surveys, independently of short gamma-ray burst and gravitational-wave triggers. In this work, we searched the first 23 months of the Zwicky Transient Facility (ZTF) data stream for candidate kilonovae in the form of rapidly evolving transients. We combined ZTF alert queries with forced point-spread-function photometry and nightly flux stacking to increase our sensitivity to faint and fast transients. Automatic queries yielded >11,200 candidates, 24 of which passed quality checks and selection criteria based on a grid of kilonova models tailored for both binary neutron star and neutron star-black hole mergers. None of the candidates in our sample was deemed a possible kilonova after thorough vetting. The sources that passed our selection criteria are dominated by Galactic cataclysmic variables. We identified two fast transients at high Galactic latitude, one of which is the confirmed afterglow of long-duration GRB 190106A, the other is a possible cosmological afterglow. Using a survey simulation code, we constrained the kilonova rate for a range of models including top-hat, linearly decaying light curves, and synthetic light curves obtained with radiative transfer simulations. For prototypical GW170817-like kilonovae, we constrain the rate to be Gpc-3 yr-1 (95% confidence). By assuming a population of kilonovae with the same geometry and composition of GW170817 observed under a uniform viewing angle distribution, we obtained a constraint on the rate of R < 4029 Gpc-3 yr-1. © 2020. The American Astronomical Society