97 research outputs found
Selection of high-z supernovae candidates
Deep, ground based, optical wide-field supernova searches are capable of
detecting a large number of supernovae over a broad redshift range up to z~1.5.
While it is practically unfeasible to obtain spectroscopic redshifts of all the
supernova candidates right after the discovery, we show that the magnitudes and
colors of the host galaxies, as well as the supernovae, can be used to select
high-z supernova candidates, for subsequent spectroscopic and photometric
follow-up.
Using Monte-Carlo simulations we construct criteria for selecting galaxies in
well-defined redshift bands. For example, with a selection criteria using B-R
and R-I colors we are able to pick out potential host galaxies for which z>0.85
with 80% confidence level and with a selection efficiency of 64-86%. The method
was successfully tested using real observations from the HDF.
Similarly, we show that that the magnitude and colors of the supernova
discovery data can be used to constrain the redshift. With a set of cuts based
on V-R and R-I in a search to m_I~25, supernovae at z~1 can be selected in a
redshift interval sigma_z <0.15.Comment: 33 pages, 13 figures, accepted for publication in PASP (March 2002
issue
Steadily Increasing Star Formation Rates in Galaxies Observed at 3 <~ z <~ 5 in the CANDELS/GOODS-S Field
We investigate the star formation histories (SFHs) of high redshift (3 <~ z
<~ 5) star-forming galaxies selected based on their rest-frame ultraviolet (UV)
colors in the CANDELS/GOODS-S field. By comparing the results from the
spectral-energy-distribution-fitting analysis with two different assumptions
about the SFHs --- i.e., exponentially declining SFHs as well as increasing
ones, we conclude that the SFHs of high-redshift star-forming galaxies increase
with time rather than exponentially decline. We also examine the correlations
between the star formation rates (SFRs) and the stellar masses. When the
galaxies are fit with rising SFRs, we find that the trend seen in the data
qualitatively matches the expectations from a semi-analytic model of galaxy
formation. The mean specific SFR is shown to increase with redshift, also in
agreement with the theoretical prediction. From the derived tight correlation
between stellar masses and SFRs, we derive the mean SFH of star-forming
galaxies in the redshift range of 3 <~ z <~ 5, which shows a steep power-law
(with power alpha = 5.85) increase with time. We also investigate the formation
timescales and the mean stellar population ages of these star-forming galaxies.
Our analysis reveals that UV-selected star-forming galaxies have a broad range
of the formation redshift. The derived stellar masses and the stellar
population ages show positive correlation in a sense that more massive galaxies
are on average older, but with significant scatter. This large scatter implies
that the galaxies' mass is not the only factor which affects the growth or star
formation of high-redshift galaxies.Comment: 31 pages, 8 figures, 2 table
SuperNova Acceleration Probe (SNAP): Investigating Photometric Redshift Optimization
The aim of this paper is to investigate ways to optimize the accuracy of
photometric redshifts for a SNAP like mission. We focus on how the accuracy of
the photometric redshifts depends on the magnitude limit and signal-to-noise
ratio, wave-length coverage, number of filters and their shapes and observed
galaxy type. We use simulated galaxy catalogs constructed to reproduce observed
galaxy luminosity functions from GOODS, and derive photometric redshifts using
a template fitting method. By using a catalog that resembles real data, we can
estimate the expected number density of galaxies for which photometric
redshifts can be derived. We find that the accuracy of photometric redshifts is
strongly dependent on the signal-to-noise (S/N) (i.e., S/N>10 is needed for
accurate photometric redshifts). The accuracy of the photometric redshifts is
also dependent on galaxy type, with smaller scatter for earlier type galaxies.
Comparing results using different filter sets, we find that including the
U-band is important for decreasing the fraction of outliers, i.e.,
``catastrophic failures''. Using broad overlapping filters with resolution
~4gives better photometric redshifts compared to narrower filters (resolution
>~5) with the same integration time. We find that filters with square response
curves result in a slightly higher scatter, mainly due to a higher fraction of
outliers at faint magnitudes. We also compare a 9-filter set to a 17-filter
set, where we assume that the available exposure time per filter in the latter
set is half that of the first set. We find that the 9-filter set gives more
accurate redshifts for a larger number of objects and reaches higher redshift,
while the 17-filter set is gives better results at bright magnitudes.Comment: 30 pages, 10 figures. Submitted to A
The Dwarf Starburst Host Galaxy of a Type Ia SN at z = 1.55 from CANDELS
We present VLT/X-shooter observations of a high redshift, type Ia supernova
host galaxy, discovered with HST/WFC3 as part of the CANDELS Supernova project.
The galaxy exhibits strong emission lines of Ly{\alpha}, [O II], H{\beta}, [O
III], and H{\alpha} at z = 1.54992(+0.00008-0.00004). From the emission-line
fluxes and SED fitting of broad-band photometry we rule out AGN activity and
characterize the host galaxy as a young, low mass, metal poor, starburst galaxy
with low intrinsic extinction and high Ly{\alpha} escape fraction. The host
galaxy stands out in terms of the star formation, stellar mass, and metallicity
compared to its lower redshift counterparts, mainly because of its high
specific star-formation rate. If valid for a larger sample of high-redshift SN
Ia host galaxies, such changes in the host galaxy properties with redshift are
of interest because of the potential impact on the use of SN Ia as standard
candles in cosmology.Comment: 25 pages, 8 figures. Accepted for publication in Ap
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