GSMT Science Use Case
Title: Detecting 2 < z < 6 Type IIn Supernovae: Probing Stellar and
Galactic Processes from the Peak of Star Formation to Reionization
Authors: Cooke, J., Barton, E. J., and Sullivan, M.
Abstract: Type IIn supernovae (SNe IIn) are the death throes and final detonations of the
most massive (>80 MSun) stars. The intrinsic luminosity and bright FUV continua of SNe
IIn have enabled photometric detections at z ~ 2 in existing deep optical surveys.
Moreover, the bright and long-lived bright spectroscopic features remain above the
thresholds of 8m-class telescopes for many years and provide a means for spectroscopic
confirmation and analysis. It is expected that planned deep wide-field optical surveys
will detect ~130 SNe IIn deg-2 (rest-frame) over 10 years to z ~ 6 and that the sensitivity
of a GSMT will facilitate spectroscopic detection and analysis of SN emission-line
properties to z ~ 6. We propose a two-phase deep spectroscopic program with the GMT
or TMT that utilizes high redshift SNe IIn and host galaxies to investigate stellar and
galactic processes from the epoch of peak universal star formation to reionization. First,
we will use GMACS or WFOS to obtain rest-frame FUV emission-line detections,
spectral properties, and inferred kinematics of a statistical (~150) sample of 2 < z < 6
SNe IIn and host galaxies. Second, we will use ISIS or MIFS to acquire NIR IFU
spectroscopic datacubes of a subset (~25-80) host galaxies to measure detailed rest-frame
optical morphology, spectral properties, and inferred kinematics. These data will trace
the density, evolution, and dynamics of SNe IIn events and their host galaxies over a
large redshift path that spans the era of galaxy formation. Furthermore, several lines of
evidence suggest that certain SNe IIn are pair-instability supernova (PISN) events; the
same process believed to be the fate of the first (pop III) stars in the universe. SNe IIn
are currently the only examples of this process, and as a result, provide our only
observational link toward understanding the mechanisms behind pop III stars.
Summary Table:
Telescope
Instrument
# Nights
Mode
GMT
GMACS
4
GMT
TMT
MIFS
WFOS
4
4
TMT
IRIS
4
queue
or
classic
queue
or
classic
 range(m)
0.35-1.0
/ AO Mode
FOV
1400
No
144'
0.9-2.5
0.34-1.0
4500
1500
Yes
No
3”
46'
0.8-2.5
4000
Yes
2”
Scientific Motivation:
SNe IIn are extremely bright events, MB = -19.0 +/-0.9, and comprise the brightest SNe
on record. In addition, SNe IIn are the brightest SN type in the rest-frame FUV. The
rest-frame FUV is redshifted to optical wavelengths for 2 < z < 6 events and enables
photometric detection of z > 2 SNe IIn in existing, and future, deep (mR ~ 27-28) multiepoch, wide-field optical surveys using 4-8m-class facilities. The ejecta of SNe IIn
interact with cold circumstellar material expelled during previous evolutionary episodes
and create extremely bright and long-lived emission lines. The strength and duration of
the emission lines permit spectroscopic detection of z < z < 6 using a 30m-class facility
for ~3-15 years after outburst. This is important in that follow-up spectroscopy of SNe
properties are not ToO observations. These data can be collected during a conventionally
scheduled observational program.
We present the case for a spectroscopic investigation of the rest-frame FUV and optical
properties of SNe IIn events and their host galaxies from 2 < z < 6 using a GSMT. This
work is complementary to local observations and will provide seamless coverage of SNe
IIn observations from z ~ 0 to reionization. Detections from our proposed program will
measure the SNe IIn density and rate, estimate the high redshift type II SN rate, and trace
the universal star formation rate from 2 < z < 6. Line measurements will enable
kinematic study of individual SNe and yield estimates of the SN contribution to outflows
and chemical enrichment to the ISM and IGM. Rest-frame optical IFU data combined
with rest-frame FUV data can potentially break the degeneracies between passive
evolution and dusty star formation histories of targeted host galaxies derived by stellar
synthesis modeling while pinpointing the sites of SNe IIn and subsequent investigations
will provide important information for studies of galaxy interactions and mergers.
Furthermore, the data will provide a working laboratory for PISN study and lend crucial
information regarding pop III processes, effects, and observational signatures. Finally,
pre-GSMT deep multi-epoch wide-field surveys will detect a very large number of SNe
IIn. For example, projects such as the LSST will detect ~500,000 2 < z < 6 SNe IIn in
observations over 10 years. With such large datasets, it is likely that a subset of SNe IIn
may be calibrated as a standard candle. Because of their bright FUV luminosity and the
fact that they do not suffer from a delay time (~1-2 Gyr) as do SNe Ia, SNe IIn may
provide a deep cosmological probe and a critical independent check on current SNe Ia
results.
Approach:
Because the emission lines of 2 < z < 6 SNe IIn remain bright for ~3-15 yr after outburst,
we can acquire data from SNe of various ages to increase the SN density and to explore
property evolution. We will compile a database of SNe IIn targets from existing surveys
and those that will exist by the time a GSMT is online, such as the CFHTLS Deep
survey, HST archival surveys, LSST, Pan-STARRS, and MEDIC (described below).
Deep (mR ~ 28) optical surveys are expected to yield a 2 < z < 6 SNe IIn density of ~0.3
(0.18) SNe IIn arcmin-2 optimized (random) over 10 years. We will select our targets
from these surveys with density, age, and cosmic variance in consideration.
Phase I: We will use deep multi-object spectroscopy (MOS) with GMACS or WFOS to
obtain SN and host galaxy rest-frame FUV data. Galaxies at z > 2 exhibit many strong
FUV transitions that are identifiable with low to moderate signal-to-noise (S/N) ratio (~5
or greater). These data will provide redshift confirmations, host galaxy global property
information, and SN Ly-alpha detection. Observations show that the Ly-alpha emission
of SNe IIn is typically blueshifted by ~1000-4000 km sec-1 and easily separated from host
galaxy Ly-alpha features. Figure 1 shows a simulated 1800s WFOS spectrum of a z = 2.5
galaxy and SN IIn. The SN Ly-alpha equivalent width (EW) and centroid will supply
energy and kinematic information. In certain cases, depending on SN age and redshift,
the data will place upper limits on these values. The 2 < z < 6 SNe IIn density from deep
preparatory surveys corresponds to ~45 (30) SNe per GMACS pointing or ~15 (10) SNe
per WFOS pointing. This density is reduced by a factor of ~5 for existing shallower
surveys that only sample the bright-end tail of the SNe IIn distribution.
Figure 1: Simulated spectra of z = 2.5 SNe IIn and their host galaxies. The galaxy spectra are modified
from the survey of Cooke et al. 2005 and were taken with the LRIS instrument on the Keck 10-m telescope.
Galaxies spectra at high redshift are comprised of approximately an equal number displaying Ly-alpha in
emission (Left) and absorption (Right). The SNe are based on the rest-frame low redshift FUV data of
Fransson et al. 2002, 2005. The SN Ly-alpha emission in this simulation are blueshifted by 1500 km sec -1.
Phase II: We will obtain NIR IFU spectra and datacubes of a subset of the statistical
sample for rest-frame optical velocity structure and property analysis. Star-forming host
galaxies monitored for SNe IIn at 2 < z < 6 have typical apparent magnitudes of mR ~ 2327. Minimum S/N ratios of ~10 are sufficient to obtain the necessary emission-line flux
of star-forming regions to map the velocity structure of the host galaxy, detect the MgII
or H-alpha SN emission, and pinpoint the SN in the collapsed datacubes. This can be
achieved with ~3-10 hr integrations with MIFS or ~1-4 hr integrations with ISIS.
Limiting Factors and the Current State of the Art:
Current facilities do not have the spectral sensitivity to detect the Ly-alpha emission of z
> 3 SNe IIn. Figure 2 illustrates the expected sensitivity of a GSMT versus existing 8mclass facilities. In addition, 8m-class telescopes cannot obtain sufficient S/N ratios using
NIR IFU instruments to study the rest-frame optical properties of typical z > 3 host
galaxies (mR ~ 25-27). Nonetheless, current facilities are now being used to confirm the
redshifts of 1.9 < z < 3.3 SNe IIn, detect Ly-alpha emission, and refine this process.
Extending this work to early epochs of galaxy formation requires the sensitivity of a 30m facility. Such observations will enable solid host galaxy redshift confirmations and
emission-line detections to z ~ 6 and provide important detailed SN emission-line and
host galaxy information at lower redshift.
Figure 2: SNe IIn emission-line flux evolution. Plotted are long-term H-alpha emission-line flux
measurements (red curves) for 10 SNe IIn compiled from the literature. Values are shown for SNe IIn
redshifted to z = 2,6 (left) and z = 6.0 (right). The ~4 hr exposure sensitivity thresholds of 8m-class and
projected sensitivity of 30m-class facilities are indicated. Ly-alpha emission line evolution is estimated to
be between the H-alpha values and the dotted blue curves based on low redshift FUV data.
Technical Details:
Detections of SNe IIn Ly-alpha emission require a spectroscopic sensitivity of 10-18-10-19
erg cm-2 s-1. As illustrated in Figure 2, 30m-class facilities have the sensitivity to detect
the emission from SNe IIn to z ~ 6. Moreover, the duration of the emission-line flux in
the observed-frame allows detections accumulated over ~10 years to be observed with a
single GSMT multi-object spectroscopic exposure. This is also true for SN emission-line
detection and analysis in GMST NIR IFU data. With that in mind, we describe the two
phases of our proposal.
Phase I: Observations using GMACS or WFOS to acquire deep rest-frame FUV multiobject spectroscopy. Expected integrations to obtain S/N ratio > 5 for 2 < z < 6 SNe IIn
Ly-alpha detections with GMACS or WFOS range from ~1800-22000s. Each GSMT
pointing will contain SNe IIn with various redshifts and ages. Each particular pointing
will be assessed to optimize exposure time. We expect that the multi-object masks will
acquire deep spectra of a total of ~150 SNe IIn at 2 < z < 6 in ~40 hr (4 nights). The
targets will be selected from wide-field surveys that typically image square-degree fields.
The specific pointings of GMACS and WFOS will be tailored to maximize the number of
targets. To address cosmic variance, we foresee ~4 GMACS and ~10 WFOS pointings.
Observations are amenable to either queue or classical observing. The long-lived nature
(~3-15 yr detectability) of SNe IIn emission lines does not require ToO observations,
therefore this program can be scheduled and performed in a conventional manner.
Phase II: Adaptive optics assisted, NIR IFU rest-frame optical observations of SNe and
their host galaxies. We will place the multiple (~10) IFUs of MIFS on a subset of the SN
host galaxies from the above sample that fall in the MIFS FOV or point ISIS at select
individual targets. Typical apparent magnitudes of 2 < z < 6 SN host galaxies are mR ~
23-27. We will target hosts brighter than mR ~ 26.5 and will therefore require ~180030000s per pointing (depending on instrument and host magnitude) to achieve the S/N
ratio necessary for the goals of this program. Typical exposure times are expected to be
~6000s for ISIS and 18000s for each of the ~10 MIFS IFUs. We therefore expect to
obtain IFU data of ~80 MIFS or ~25 ISIS 2 < z < 6 SNe hosts in ~40 hr (4 night)
program.
Preparatory, Supporting, and Follow-up Observations:
Deep multi-epoch, wide-field optical imaging surveys are needed prior to spectroscopic
observations with a 30-m facility. Existing and planned deep wide-field surveys (i.e.,
CFHTLS, LSST, and Pan-STARRS) will be very useful but will provide a low SNe IIn
density and less efficient WFOS or GMACS observations. In addition, the expected
depth (mR ~ 27) of the yearly stacked images from these surveys are only sensitive to the
extreme bright-end tail of the SNe IIn mag distribution for z > 3 events.
To remedy this, we intend to propose a Multi-Epoch Deep Imaging Campaign (MEDIC)
to acquire very deep (mR ~ 28) wide-field ugriz broadband images. This will provide the
deepest wide-field multi-epoch multi-color imaging survey to date and will therefore
result in a large number of additional science applications. For the purposes here, the
deep images will be used to color-select and monitor 2 < z < 6 galaxies for SNe IIn
events as outlined in Cooke (2008) and will be sensitive to SNe IIn detections to z ~ 6.
MEDIC will utilize existing wide-field cameras on 8-m facilities to provide the necessary
depth, temporal coverage, and multi-year density for efficient and effective 30-m SNe IIn
observations. MEDIC using the MMT (ugriz), MMT (u-band) and Subaru SuprimeCam
(griz), or LBT (ugriz) will require a total of ~260.000s, ~160,000s, and ~120,000 per
year, respectively. As a result, the project will require 2-4 nights per semester (depending
on facility), ideally structured as half-night observations where applicable, for 5-10 years.
The ~10 separate epochs per year will be used to select high-quality SNe IIn candidates
and will greatly improve selection efficiency.
Based on the calculations of Cooke (2008), MEDIC will detect ~55 SNe IIn deg-1 yr-1
(observed-frame) to z ~ 6 and provide the efficient SN density discussed above. This
data will be combined with data from the CFHTLS, Pan-STARRS, and LSST to form the
best and most interesting list of targets possible. Follow-up spectroscopic observations
can include re-observing confirmed z > 2 SNe IIn targets to quantify emission-line
evolutionary effects and improve the S/N ratio of the data.
Anticipated Results:
Phase I: GMACS or WFOS
The proposed program using the GMT and/or TMT will provide ~150 2 < z < 6 SNe IIn
redshift confirmations. The primary goal of these data will be to measure the properties,
effects, and evolution of SNe IIn events at high redshift. The data will consist of deep
rest-frame FUV spectra and will permit study of global host galaxy properties and
dynamics and SN emission-line properties, such as line strength, asymmetry, and
blueshift. The sensitivity of a GSMT will enable detailed investigations of the lower
redshift (1.7 < z ~ 3) host and SNe confirmations to be carefully extrapolated to the
higher redshift (3 < z < 6) sample.
From the data, we expect to: (1) measure the SNe IIn density and rate, (2) trace the high-z
type II SN rate and universal star formation rate, (3) measure the energies and kinematics
of the ejecta and circumstellar material, (4) analyze the rest-frame FUV features of the
host galaxies including the Ly-alpha and several low- and high-ionization transitions, (5)
estimate the SN contribution to galaxy outflows and star formation, (6) quantify the
ISM/IGM enrichment from massive stars, (7) study the general rest-frame FUV
properties of SNe IIn after the era of HST, (8) probe the 2 < z < 6 IMF and search for
evolution, (9) observe the fundamental properties of PISN and pop III stars, and (10)
potentially define and utilize a homogeneous SNe IIn subset for cosmology.
Phase II: ISIS or MIFS
The proposed program will obtain spectra and 3-D datacubes for ~50 SNe IIn host
galaxies, culled from the above larger sample, with the main goal of defining the optical
properties of high redshift SNe IIn and their host galaxies. We expect to map the velocity
structure of host galaxies and pinpoint the SNe IIn to study the sites of massive star
production and recent or triggered star formation.
We envision using the IFU data to: (1) investigate the rest-frame optical properties and
morphologies of high redshift SNe IIn host galaxies, (2) interpret rest-frame FUV
features from the analysis of the stacked IFU data, (3) study preferred SNe IIn
environments and evolution, (3) quantify host-SNe IIn morphological and kinematic
dependencies, (4) test high redshift interaction and merger indicators and help quantify
triggered star formation effects, (5) resolve history degeneracies in stellar synthesis
modeling, (6) study diffuse and nucleated flux and emission-line abundances and
kinematics to constrain SN feedback behavior.
Requirements and Goals Beyond the GMT and TMT Baseline Instrument Designs:
Are there capabilities needed for this science that are not in the TMT and GMT
telescope, AO system and baseline instrument configurations?
Phase II of our program would be greatly enhanced with the realization of MIFS or an
equivalent instrument on the TMT. Such a design is extremely challenging, but would
provide very efficient galaxy data acquisition. We could, in principle, achieve a large
fraction of the proposed science using only a sensitive MIFS-type instrument with not
much more then the estimated time outlined in Phase II above.
Describe the need for specific observing conditions or operations mode(s) (needed image
quality; atmospheric transmission; need for ‘interrupt-driven’ observations)
The goals of our proposed program can be achieved with either queue or classical
observing. We would require dark, good-seeing nights to capitalize on the dark sky and
sensitivity of a GSMT for Phase I. A classical or interactive queue, in which the observer
would be made aware of the likelihood of the observations over a defined window of
time, would suit the observations best. For example, because of the range of SNe IIn
line-strengths for given optical properties, actual exposure times would need adjustment
once sufficient SN Ly-alpha emission-line S/N ratio is reached to maximize observing
time. Similarly, either mode is efficient for our Phase II observations. The example
given is also relevant for MgII or H-alpha SN emission for the NIR observations.
Describe the potential of the resulting database for ‘mining’ in service of carrying out
complementary scientific programs; planning future programs
The deep z > 2 galaxy rest-frame FUV and optical spectra from this proposal will have
multiple uses in the community including intervening absorption system study. Restframe optical IFU velocity structure analysis of high-redshift galaxies has multiple
applications as well, including testing galaxy formation scenarios. Future 30-m
observations of a selection of the targets from this program would increase the S/N ratio
of the data and would enable SN emission-line evolution measurements.
Describe the potential role of other ground- and space- based facilities in carrying out
the proposed investigation
The role of 4-8m-class facilities is described above. In addition, deep IR imaging and
spectral observations using JWST would greatly enhance the results. Spectroscopy of
rest-frame MgII and H-alpha emission line properties not observed by ISIS or MIFS data
would refine SN evolution and provide valuable kinematic and abundance information.
Deep rest-frame high-resolution photometry would complement GSMT stacked
datacubes and provide accurate SED measurements and morphological information.
Observations of neutral atomic transitions using facilities such as ALMA will provide an
independent means and a long lever-arm to accurately measure host star formation rates.
Summary:
The sensitivity of a GSMT will enable spectroscopic confirmations and emission-line
measurements of 2 < z < 6 SNe IIn and provide a detailed investigation of their host
galaxies. Combined with current and future studies using existing facilities, the proposed
GSMT observations will enable seamless research on the stellar processes of massive
stars and their contribution to galactic formation and evolution from z ~ 0 to reionization.
In addition, the data will provide valuable insight into areas such as high redshift
ISM/IGM enrichment, high redshift supernova rates and kinematics, pop III stars, and
cosmology.
We propose a two-phase program to study a statistical (~150) sample of high redshift
SNe IIn that requires ~40 hr (4 night) GMACS or WFOS and ~40 hr (4 night) ISIS/MIFS
observations. Phase I of the program will utilize GMACS or WFOS data to probe the
rest-frame FUV of 2 < z < 6 events with the main objectives of confirming SNe
photometric detections obtained in deep wide-field surveys using 8m-class facilities,
quantifying the FUV properties of host galaxies from their ISM atomic transitions and
kinematics, and measuring the SN energies, kinematics, and implied contribution to
galactic-scale outflows and chemical enrichment via SN Ly-alpha emission-line behavior.
Phase II of the program will use adaptive-optics assisted NIR IFU spectra and collapsed
datacubes of ISIS or MIFS to investigate the rest-frame optical properties of the host
galaxies and SN emission-lines with the main goals of quantifying high-redshift SNe IIn
environments, interpreting the rest-frame FUV features from the GMOS or WFOS data,
quantifying host-SNe IIn morphological and kinematic dependencies, and testing high
redshift interaction and merger indicators. If recent lines of evidence that certain SNe IIn
are PISN, this work will provide crucial observations to formulate an accurate picture of
pop II star processes and potential observables. Finally, if a subset of SNe IIn, selected
from the enormous number (~400,000) of expected z > 2 SNe IIn detections from
planned future surveys such as LSST and Pan-STARRS, are calibrated as standard
candles, they would provide an important check on the current type Ia cosmological
results and have the potential to probe the universe to z ~ 6.
References
Cooke, J. 2008, ApJ, 677, 137
Cooke, J., et al. 2005, ApJ, 621, 596
Fransson, C. et al. 2002, ApJ, 572, 350
Fransson, C. et al. 2005, ApJ, 622, 991