24 research outputs found
The Host Galaxies of Type Ia Supernovae Discovered by the Palomar Transient Factory
We present spectroscopic observations of the host galaxies of 82 low-redshift type Ia supernovae (SNe Ia) discovered by the Palomar Transient Factory (PTF). We determine star-formation rates, gas-phase stellar metallicities, and stellar masses and ages of these objects. As expected, strong correlations between the SN Ia light-curve width (stretch) and the host age mass metallicity are found: fainter, faster-declining events tend to be hosted by older massive metal-rich galaxies. There is some evidence that redder SNe Ia explode in higher metallicity galaxies, but we found no relation between the SN colour and host galaxy extinction based on the Balmer decrement, suggesting that the colour variation of these SNe does not primarily arise from this source. SNe Ia in higher-mass metallicity galaxies also appear brighter after stretch colour corrections than their counterparts in lower mass hosts, and the stronger correlation is with gas-phase metallicity suggesting this may be the more important variable. We also compared the host stellar mass distribution to that in galaxy targeted SN surveys and the high-redshift untargeted Supernova Legacy Survey (SNLS). SNLS has many more low mass galaxies, while the targeted searches have fewer. This can be explained by an evolution in the galaxy stellar mass function, coupled with a SN delay-time distribution proportional to t1. Finally, we found no significant difference in the mass--metallicity relation of our SN Ia hosts compared to field galaxies, suggesting any metallicity effect on the SN Ia rate is small
Galaxy Zoo Supernovae
This paper presents the first results from a new citizen science project:
Galaxy Zoo Supernovae. This proof of concept project uses members of the public
to identify supernova candidates from the latest generation of wide-field
imaging transient surveys. We describe the Galaxy Zoo Supernovae operations and
scoring model, and demonstrate the effectiveness of this novel method using
imaging data and transients from the Palomar Transient Factory (PTF). We
examine the results collected over the period April-July 2010, during which
nearly 14,000 supernova candidates from PTF were classified by more than 2,500
individuals within a few hours of data collection. We compare the transients
selected by the citizen scientists to those identified by experienced PTF
scanners, and find the agreement to be remarkable - Galaxy Zoo Supernovae
performs comparably to the PTF scanners, and identified as transients 93% of
the ~130 spectroscopically confirmed SNe that PTF located during the trial
period (with no false positive identifications). Further analysis shows that
only a small fraction of the lowest signal-to-noise SN detections (r > 19.5)
are given low scores: Galaxy Zoo Supernovae correctly identifies all SNe with >
8{\sigma} detections in the PTF imaging data. The Galaxy Zoo Supernovae project
has direct applicability to future transient searches such as the Large
Synoptic Survey Telescope, by both rapidly identifying candidate transient
events, and via the training and improvement of existing machine classifier
algorithms.Comment: 13 pages, 10 figures, accepted MNRA
The host galaxies of Type Ia supernovae discovered by the Palomar Transient Factory
We present spectroscopic observations of the host galaxies of 82 low-redshift Type Ia supernovae (SNe Ia) discovered by the Palomar Transient Factory. We determine star formation rates, gas-phase/stellar metallicities, and stellar masses and ages of these objects. As expected, strong correlations between the SN Ia light-curve width (stretch) and the host age/mass/metallicity are found: fainter, faster declining events tend to be hosted by older/massive/metal-rich galaxies. There is some evidence that redder SNe Ia explode in higher metallicity galaxies, but we found no relation between the SN colour and host galaxy extinction based on the Balmer decrement, suggesting that the colour variation of these SNe does not primarily arise from this source. SNe Ia in higher mass/metallicity galaxies also appear brighter after stretch/colour corrections than their counterparts in lower mass hosts, and the stronger correlation is with gas-phase metallicity suggesting this may be the more important variable. We also compared the host stellar mass distribution to that in galaxy-targeted SN surveys and the high-redshift untargeted Supernova Legacy Survey (SNLS). SNLS has many more low-mass galaxies, while the targeted searches have fewer. This can be explained by an evolution in the galaxy stellar mass function, coupled with an SN delay-time distribution proportional to t^−1. Finally, we found no significant difference in the mass–metallicity relation of our SN Ia hosts compared to field galaxies, suggesting any metallicity effect on the SN Ia rate is small
The Hubble Space Telescope Cluster Supernova Survey: V. Improving the Dark Energy Constraints Above z>1 and Building an Early-Type-Hosted Supernova Sample
We present ACS, NICMOS, and Keck AO-assisted photometry of 20 Type Ia
supernovae SNe Ia from the HST Cluster Supernova Survey. The SNe Ia were
discovered over the redshift interval 0.623 < z < 1.415. Fourteen of these SNe
Ia pass our strict selection cuts and are used in combination with the world's
sample of SNe Ia to derive the best current constraints on dark energy. Ten of
our new SNe Ia are beyond redshift , thereby nearly doubling the
statistical weight of HST-discovered SNe Ia beyond this redshift. Our detailed
analysis corrects for the recently identified correlation between SN Ia
luminosity and host galaxy mass and corrects the NICMOS zeropoint at the count
rates appropriate for very distant SNe Ia. Adding these supernovae improves the
best combined constraint on the dark energy density \rho_{DE}(z) at redshifts
1.0 < z < 1.6 by 18% (including systematic errors). For a LambdaCDM universe,
we find \Omega_\Lambda = 0.724 +0.015/-0.016 (68% CL including systematic
errors). For a flat wCDM model, we measure a constant dark energy
equation-of-state parameter w = -0.985 +0.071/-0.077 (68% CL). Curvature is
constrained to ~0.7% in the owCDM model and to ~2% in a model in which dark
energy is allowed to vary with parameters w_0 and w_a. Tightening further the
constraints on the time evolution of dark energy will require several
improvements, including high-quality multi-passband photometry of a sample of
several dozen z>1 SNe Ia. We describe how such a sample could be efficiently
obtained by targeting cluster fields with WFC3 on HST.Comment: 27 pages, 11 figures. Submitted to ApJ. This first posting includes
updates in response to comments from the referee. See
http://www.supernova.lbl.gov for other papers in the series pertaining to the
HST Cluster SN Survey. The updated supernova Union2.1 compilation of 580 SNe
is available at http://supernova.lbl.gov/Unio
Nebular spectra of 111 Type Ia supernovae disfavour single-degenerate progenitors
We place statistical constraints on Type Ia supernova (SN Ia) progenitors using 227 nebular-phase spectra of 111 SNe Ia. We find no evidence of stripped companion emission in any of the nebular-phase spectra. Upper limits are placed on the amount of mass that could go undetected in each spectrum using recent hydrodynamic simulations. With these null detections, we place an observational 3 sigma upper limit on the fraction of SNe Ia that are produced through the classical H-rich non-degenerate companion scenario of < 5.5 per cent. Additionally, we set a tentative 3 sigma upper limit otan He star progenitor scenarios of < 6.4 per cent, although further theoretical modelling is required. These limits refer to our most representative sample including normal, 91bg-like, 91T-like, and 'super-Chandrasekhar' SNe Ia but excluding SNe Iax and SNe Ia-CSM. As part of our analysis, we also derive a Nebular Phase Phillips Relation, which approximates the brightness of an SN Ia from 150 to 500 d after maximum using the peak magnitude and decline rate parameter Delta m(15)(B)
The Hubble Space Telescope Cluster Supernova Survey: V. Improving the Dark Energy Constraints Above z\u3e1 and Building an Early-Type-Hosted Supernova Sample
We present Advanced Camera for Surveys, NICMOS, and Keck adaptive-optics-assisted photometry of 20 Type Ia supernovae (SNe Ia) from the Hubble Space Telescope (HST) Cluster Supernova Survey. The SNe Ia were discovered over the redshift interval 0.623 \u3c z \u3c 1.415. of these sne ia, 14 pass our strict selection cuts and are used in combination with the world\u27s sample of sne ia to derive the best current constraints on dark energy. of our new sne ia, 10 are beyond redshift z = 1, thereby nearly doubling the statistical weight of hst-discovered sne ia beyond this redshift. our detailed analysis corrects for the recently identified correlation between sn ia luminosity and host galaxy mass and corrects the nicmos zero point at the count rates appropriate for very distant sne ia. adding these sne improves the best combined constraint on dark-energy density, {rho}{sub de}(z), at redshifts 1.0 \u3c z \u3c 1.6 by 18% (including systematic errors). for a flat {lambda}cdm universe, we find {omega}{sub {lambda}} = 0.729 {+-} 0.014 (68% confidence level (cl) including systematic errors). for a flat wcdm model, we measure a constant dark-energy equation-of-state parameter w = -1.013{sup +0.068}{sub -0.073} (68% cl). curvature is constrained to {approx}0.7% in the owcdm model and to {approx}2% in a model in which dark energy is allowed to vary with parameters w{sub 0} and w{sub a} . further tightening the constraints on the time evolution of dark energy will require several improvements, including high-quality multi-passband photometry of a sample of several dozen z \u3e 1 SNe Ia. We describe how such a sample could be efficiently obtained by targeting cluster fields with WFC3 on board HST. The updated supernova Union2.1 compilation of 580 SNe is available at http://supernova.lbl.gov/Union
PTF10ops - a subluminous, normal-width lightcurve Type Ia supernova in the middle of nowhere
PTF10ops is a Type Ia supernova (SN Ia), whose lightcurve and spectral
properties place it outside the current SN Ia subtype classifications. Its
spectra display the characteristic lines of subluminous SNe Ia, but it has a
normal-width lightcurve with a long rise-time, typical of normal luminosity SNe
Ia. The early-time optical spectra of PTF10ops were modelled using a spectral
fitting code and found to have all the lines typically seen in subluminous SNe
Ia, without the need to invoke more uncommon elements. The host galaxy
environment of PTF10ops is also unusual with no galaxy detected at the position
of the SN down to an absolute limiting magnitude of r \geq -12.0 mag, but a
very massive galaxy is present at a separation of ~148 kpc and at the same
redshift as suggested by the SN spectral features. The progenitor of PTF10ops
is most likely a very old star, possibly in a low metallicity environment,
which affects its explosion mechanism and observational characteristics.
PTF10ops does not easily fit into any of the current models of either
subluminous or normal SN Ia progenitor channels.Comment: 12 pages, 9 figures. Accepted for publication in MNRA