70 research outputs found
Glycine receptor subunits -a2 and a3 participate in different inhibitory circuits that alter the receptive field organization of on- and off-center retinal ganglion cells.
In the retina, the receptive fields (RFs) of most neurons are comprised of an excitatory center and a suppressive surround. Retinal ganglion cell (RGC) RF center excitatory input arises from bipolar cell (BC) inputs, while their surround arises from lateral inhibitory inputs. Because of the availability of selective antagonists the role of GABAergic inputs has been well defined. In contrast, the role of individual glycine receptor (GlyR) subunit inhibition is less clear because the antagonist, strychnine, blocks all GlyR subunit combinations. To define individual retinal circuits that utilize specific glycinergic subunits, I examined maintained and visually-evoked responses of ON- and OFF-center GCs from mice lacking expression of the GlyRa2 (Glra2-/-) or GlyRa3 (Glra3-/-) subunits to those of C57Bl/6J (WT) RGCs using an in vivo extracellular approach. Previous observations have defined glycine and GABA inputs across BC classes and in a variety of amacrine and RGCs. Using this information and by comparing the responses of WT vs. Glra2-/- and Glra3-/- RGCs; I conclude that both subunits modulate local RF interactions. Within the On pathway, GlyRa2 and GlyRa3 inputs play similar roles. Their responses predict that they participate in serial inhibitory circuits that decrease a direct GABAergic inhibition that modulates maintained, but not peak firing rates. In contrast within the Off pathway, GlyRa2 and GlyRa3 inputs define two populations of RGCs. In one, GlyRa2 participates in a serial inhibitory circuit that modulates maintained firing, whereas in the other, GlyRa,3 mediates direct inhibition that controls the peak firing rate. Only GlyRa2 modulates lateral interactions to the RF surround where it mediates a direct inhibitory input to all OFF-center RGCs. My results suggest that GlyRa2 and GlyRa3 inputs define two populations of OFF-center RGCs. In addition, both subunits participate in retinal circuits that can be distinguished not only by the RGC RF center type, but also by the type of inhibitory circuit. These results are the first demonstration of subunit specific control of RGC visual responses and, are the first evidence of serial glycine to GABA as well as glycine to glycine circuits in the retina
Testing for redshift evolution of Type Ia supernovae using the strongly lensed PS1-10afx at
The light from distant supernovae (SNe) can be magnified through
gravitational lensing when a foreground galaxy is located along the line of
sight. This line-up allows for detailed studies of SNe at high redshift that
otherwise would not be possible. Spectroscopic observations of lensed
high-redshift Type Ia supernovae (SNe Ia) are of particular interest since they
can be used to test for evolution of their intrinsic properties. The use of SNe
Ia for probing the cosmic expansion history has proven to be an extremely
powerful method for measuring cosmological parameters. However, if systematic
redshift-dependent properties are found, their usefulness for future surveys
could be challenged. We investigate whether the spectroscopic properties of the
strongly lensed and very distant SN Ia PS1-10afx at deviates from the
well-studied populations of normal SNe Ia at nearby or intermediate distance.
We created median spectra from nearby and intermediate-redshift
spectroscopically normal SNe Ia from the literature at -5 and +1 days from
light-curve maximum. We then compared these median spectra to those of
PS1-10afx. We do not find signs of spectral evolution in PS1-10afx. The
observed deviation between PS1-10afx and the median templates are within what
is found for SNe at low- and intermediate-redshift. There is a noticeable broad
feature centred at ~\AA{}, which is present only to a
lesser extent in individual low and intermediate redshift SN Ia spectra. From a
comparison with a recently developed explosion model, we find this feature to
be dominated by iron peak elements, in particular, singly ionized cobalt and
chromium.Comment: accepted for publication in section 4. Extragalactic astronomy of
Astronomy and Astrophysic
Probing gas and dust in the tidal tail of NGC 5221 with the type Ia supernova iPTF16abc
Context. Type Ia supernovae (SNe Ia) can be used to address numerous
questions in astrophysics and cosmology. Due to their well known spectral and
photometric properties, SNe Ia are well suited to study gas and dust along the
lines-of-sight to the explosions. For example, narrow Na I D and Ca II H&K
absorption lines can be studied easily, because of the well-defined spectral
continuum of SNe Ia around these features. Aims. We study the gas and dust
along the line-of-sight to iPTF16abc, which occurred in an unusual location, in
a tidal arm, 80 kpc from centre of the galaxy NGC 5221. Methods. Using a
time-series of high-resolution spectra, we examine narrow Na I D and Ca II H&K
absorption features for variations in time, which would be indicative for
circumstellar (CS) matter. Furthermore, we take advantage of the well known
photometric properties of SNe Ia to determine reddening due to dust along the
line-of-sight. Results. From the lack of variations in Na I D and Ca II H&K, we
determine that none of the detected absorption features originate from the CS
medium of iPTF16abc. While the Na I D and Ca II H&K absorption is found to be
optically thick, a negligible amount of reddening points to a small column of
interstellar dust. Conclusions. We find that the gas along the line-of-sight to
iPTF16abc is typical of what might be found in the interstellar medium (ISM)
within a galaxy. It suggests that we are observing gas that has been tidally
stripped during an interaction of NGC 5221 with one of its neighbouring
galaxies in the past years. In the future, the gas clouds could
become the locations of star formation. On a longer time scale, the clouds
might diffuse, enriching the circum-galactic medium (CGM) with metals. The gas
profile along the line-of-sight should be useful for future studies of the
dynamics of the galaxy group containing NGC 5221.Comment: 8 pages, 6 figure
The peculiar extinction law of SN2014J measured with The Hubble Space Telescope
The wavelength-dependence of the extinction of Type Ia SN2014J in the nearby
galaxy M82 has been measured using UV to near-IR photometry obtained with the
Hubble Space Telescope, the Nordic Optical Telescope, and the Mount Abu
Infrared Telescope. This is the first time that the reddening of a SN Ia is
characterized over the full wavelength range of - microns. A
total-to-selective extinction, , is ruled out with high
significance. The best fit at maximum using a Galactic type extinction law
yields . The observed reddening of SN2014J is also compatible
with a power-law extinction, as expected from multiple scattering of light, with
. After correction for differences in reddening, SN2014J appears
to be very similar to SN2011fe over the 14 broad-band filter light curves used
in our study.Comment: Accepted for publication in ApJ
Sifting for Sapphires: Systematic Selection of Tidal Disruption Events in iPTF
We present results from a systematic selection of tidal disruption events
(TDEs) in a wide-area (4800~deg), band, Intermediate Palomar
Transient Factory (iPTF) experiment. Our selection targets typical
optically-selected TDEs: bright (60\% flux increase) and blue transients
residing in the center of red galaxies. Using photometric selection criteria to
down-select from a total of 493 nuclear transients to a sample of 26 sources,
we then use follow-up UV imaging with the Neil Gehrels Swift Telescope,
ground-based optical spectroscopy, and light curve fitting to classify them as
14 Type Ia supernovae (SNe Ia), 9 highly variable active galactic nuclei
(AGNs), 2 confirmed TDEs, and 1 potential core-collapse supernova. We find it
possible to filter AGNs by employing a more stringent transient color cut ( 0.2 mag); further, UV imaging is the best discriminator for filtering
SNe, since SNe Ia can appear as blue, optically, as TDEs in their early phases.
However, when UV-optical color is unavailable, higher precision astrometry can
also effectively reduce SNe contamination in the optical. Our most stringent
optical photometric selection criteria yields a 4.5:1 contamination rate,
allowing for a manageable number of TDE candidates for complete spectroscopic
follow-up and real-time classification in the ZTF era. We measure a TDE per
galaxy rate of 1.7 10 gal yr (90\%
CL in Poisson statistics). This does not account for TDEs outside our selection
criteria, thus may not reflect the total TDE population, which is yet to be
fully mapped.Comment: 24 pages, 21 figures. Accepted for publication in the Astrophysical
Journal Supplement Serie
iPTF16geu: A multiply imaged, gravitationally lensed type Ia supernova
We report the discovery of a multiply-imaged gravitationally lensed Type Ia
supernova, iPTF16geu (SN 2016geu), at redshift . This phenomenon could
be identified because the light from the stellar explosion was magnified more
than fifty times by the curvature of space around matter in an intervening
galaxy. We used high spatial resolution observations to resolve four images of
the lensed supernova, approximately 0.3" from the center of the foreground
galaxy. The observations probe a physical scale of 1 kiloparsec, smaller
than what is typical in other studies of extragalactic gravitational lensing.
The large magnification and symmetric image configuration implies close
alignment between the line-of-sight to the supernova and the lens. The relative
magnifications of the four images provide evidence for sub-structures in the
lensing galaxy.Comment: Matches published versio
Near-IR Type Ia SN distances: host galaxy extinction and mass-step corrections revisited
We present optical and near-infrared (NIR, YJH-band) observations of 42 Type Ia supernovae (SNe Ia) discovered by the untargeted intermediate Palomar Transient Factory (iPTF) survey. This new data-set covers a broad range of redshifts and host galaxy stellar masses, compared to previous SN Ia efforts in the NIR. We construct a sample, using also literature data at optical and NIR wavelengths, to examine claimed correlations between the host stellar masses and the Hubble diagram residuals. The SN magnitudes are corrected for host galaxy extinction using either a global total-to-selective extinction ratio, R_V = 2.0 for all SNe, or a best-fit RV for each SN individually. Unlike previous studies which were based on a narrower range in host stellar mass, we do not find evidence for a "mass-step", between the color- and stretch-corrected peak J and H magnitudes for galaxies below and above log(M_∗/M_⊙) = 10. However, the mass-step remains significant (3σ) at optical wavelengths (g,r,i) when using a global R_V, but vanishes when each SN is corrected using their individual best-fit R_V. Our study confirms the benefits of the NIR SN Ia distance estimates, as these are largely exempted from the empirical corrections dominating the systematic uncertainties in the optical
A hot and fast ultra-stripped supernova that likely formed a compact neutron star binary.
Compact neutron star binary systems are produced from binary massive stars through stellar evolution involving up to two supernova explosions. The final stages in the formation of these systems have not been directly observed. We report the discovery of iPTF 14gqr (SN 2014ft), a type Ic supernova with a fast-evolving light curve indicating an extremely low ejecta mass (≈0.2 solar masses) and low kinetic energy (≈2 × 1050 ergs). Early photometry and spectroscopy reveal evidence of shock cooling of an extended helium-rich envelope, likely ejected in an intense pre-explosion mass-loss episode of the progenitor. Taken together, we interpret iPTF 14gqr as evidence for ultra-stripped supernovae that form neutron stars in compact binary systems
Multiwavelength observations of the extraordinary accretion event AT2021lwx
We present observations from X-ray to mid-infrared wavelengths of the most
energetic non-quasar transient ever observed, AT2021lwx. Our data show a single
optical brightening by a factor to a luminosity of erg
s, and a total radiated energy of erg, both greater
than any known optical transient. The decline is smooth and exponential and the
ultra-violet - optical spectral energy distribution resembles a black body with
temperature K. Tentative X-ray detections indicate a secondary
mode of emission, while a delayed mid-infrared flare points to the presence of
dust surrounding the transient. The spectra are similar to recently discovered
optical flares in known active galactic nuclei but lack some characteristic
features. The lack of emission for the previous seven years is inconsistent
with the short-term, stochastic variability observed in quasars, while the
extreme luminosity and long timescale of the transient disfavour the disruption
of a single solar-mass star. The luminosity could be generated by the
disruption of a much more massive star, but the likelihood of such an event
occurring is small. A plausible scenario is the accretion of a giant molecular
cloud by a dormant black hole of solar masses. AT2021lwx thus
represents an extreme extension of the known scenarios of black hole accretion.Comment: 11 pages, 5 figures, Accepted for publication in MNRA
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