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 range(m) / AO Mode FOVGMT

GMT

GMACS

MIFS

4

4

queue or

classic

0.35-1.0

0.9-2.5

1400

4500

No

Yes

144'

3”TMT

TMT

WFOS

IRIS

4

4

queue or

classic

0.34-1.0

0.8-2.5

1500

4000

No

Yes

46'

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) multi-epoch, 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 ~ 23-27. 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 8m-class 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 30-m 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 multi-object 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 ~1800-30000s 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 WFOSThe 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 MIFSThe 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. Rest-frame 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.

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