The Mysterious Connection between Superluminous Supernovae and Gamma-Ray Bursts STScI Tue, May 24, 2016 11:05 AM Janice Lee: How to be a Good Host (galaxy) should have low metallicity low mass high specific star-formation rates will be topic of next several talks this will be a speculative talk five phenomena assoc with dwarf starburst galaxies which may favor formation of high-mass stars 1. SLSNe and GRB preferentially found in them 2. starbursting dwarf galaxies have higher filling factors of high-mass star formation 3. they are metal-poor outliers of stellar-mass/metallicity relationship 4. UV spectroscopic obs show very high-mass stars in starbursting dwarfs 5. hydrogen-ionizing photons leaking out of galaxies finally being detected in dwarf starbursting galaxies, at long last higher filling factor of high-mass SF (star-formation) is nature of SF dependent on environment, on small scales? need samples of physical measurements 400 galaxies, 80% dwarfs ground-based, GALEX UV, Spitzer IR -- see IRSA GALEX imaging, resolution of 20-260 pc FUV connected closely to star formation lum funcs fit by power laws then correlate fits with large-scale properties of galaxies find higher gas densities and SF efficiencies result in higher filling factor of SF can we get better spatial resolution -- pc scale? pick subsample, use HST to zoom in HST LEGUS sample 154 orbits, 50 star-forming galaxies, 3 < dist < 12 Mpc cover range of galaxy parameters WFC3 resolution to 1-4 pc can identify stars down to 7 solar masses based on 12 LEGUS galaxies look at SF regions larger than a given physical size find power laws, steeper in starburst galaxies larger fraction of GPE in gas clouds again, in low-mass galaxies, higher filling factors galaxy stellar-mass-to-metallicity relation in general, high stellar masses -> high metallicities is there a second parameter to explain some of the residual scatter? could star-formation rate be that second parameter yes, weak correlation decrease specific SFR -> lower metallicities weak correlation, but grows stronger for low-mass galaxies masses like 10^(9.5) solar could there be two modes of SFR dependence? greater impact of inflows and outflows on dwarf galaxies metal-poor outliers tend to have morphological evidence for interaction UV spectra show evidence of high-mass in starbursting dwarf galaxies NGC 5253 dist = 3.15 Mpc Z=0.35 solar looks like giant HII region spectra similar to that of R136 in LMC stellar masses 70-180 solar strong high-ionizations lines: N VI, He II the He II line is particular important much of it can be produced in just a few very massive stars Finally we are seeing evidence for hydrogen-ionizing photons wavelengths < 912 Angstroms see Izotov et al. 2016 a, b, Hernandez et al. 2016 eight examples of galaxies with this feature use HST COS escape fractions of 8 percent or so these galaxies tend to be metal-poor dwarf starbursting galaxies 11:27 AM Q: at high z, escape fraction is very low, 1 percent or so not sure how to combine low and high redshift A: yes Q: the LMC isn't a starbursting galaxy, is it? A: true, but 30 Doradus is a star-bursting-like region closest thing to a starburst galaxy in the local group Q: but on galaxy-side scale ... A: yes, this could be a local phenomenon Q: why more massive stars and H II regions in dwarfs -- could be chaotic nature of dwarf galaxies, leads to cloud collisions A: yes, big galaxies are more organized A: also interaction can be important; LMC is interacting with MW Q: NGC 5253 has had 2 SNe in past 120 years if stats mean anything, some of you may see a third Q: to see very massive stars, you need a very massive cluster and it must be only very young < 5 Myr Q: about Lyman-alpha photons which escape A: most dwarf starbursting galaxies have VERY low escape fraction today I mentioned the few which we can detect, is exciting things aren't isotropic 11:33 AM Emily Levesque: Host Environments and Progenitor evolution of GRBs how to connect host properties to the GRB itself core-collapse events are probes of star-forming galaxies progenitors are young, massive stars probes of star formation history in nearby galaxies can use GRBs can explore star-forming galaxies out to z=8,9 but let's go the other way: use galaxies as probes of core-collapse events ex: host of GRB 980425 sometimes can see pre-explosion progenitor location of progen reveals clues in environment normal CC SNe lots of types of evidence Long GRBs and SLSNe fewer types of evidence one of which is host galaxies let's focus now on host galaxies - which can be seen at great distances common terms: "kinda metal-poor" "dinky" "weird little galaxies" "REALLY star forming" "kinda metal poor" long GRB hosts have lower metallicity than general star-forming galaxies no obvious cutoff in metallicity ex: GRB 020819 host was studied in detail can see region of the GRB was the region metal-poor compared to rest of host? NOPE! so some Long GRBs can be produced in metal-rich environments What is the effect of metallicity on stars? What does it do? simple, single-star progenitor massive star, rapidly rotating core wind's mass-loss rate depends on metallicity high metallicity -> high mass-loss rate star slows down slow-rotating core, so no GRB ? so expect GRB in low-metallicity stars at low metallicity weaker mass-loss rate minimum Teff of LBV is cooler far fewer WR stars, stars at high-mass end turn into Red SGs much less surface nitrogen enrichment from overshooting Hayashi limit is slightly warmer so metallicty affects pre-death star properties Look at nearby metal-poor galaxies in local group, can get to 5%, 10% solar ratio of RSGs to WR stars goes up at low metallicity ratio of WC to WN stars goes DOWN at low metallicity few carbon-rich WR stars, which would create Type Ib/c SNe but -- most long-duration GRBs occur in low-metallicity environments this is not what we'd expect -- contradiction Are there other metallicity effects? look for correlations between metallicity and properties of long GRBs nope, didn't find any could metallicity affect LGRB/SN subtypes? no obvious connection what about SLSN host galaxies? they do appear at low-metallicity region of metallicity/mass diagram So, are there complicating factors in real stellar evolution? is the simple model insufficient? ignores binary evolution binarity changes end-of-life location in HR diagram rotation also can make a big difference differential rotation is important rotation-driven mixing impacts evolution strongly WR population increases with rotation diff rotation leads to polarish winds, smaller loss of ang mom w/ wind von Zeipel theorem says Teff is higher at poles also yields larger terminal velocity of wind at poles complicated: can lead to winds being stronger at poles OR at equator can depend on temperatures at poles, equator and this effect depends on metallicity strongly what's next? look at stellar populations in long-GRB hosts currently most work based on photometry, more spectroscopy would be good continue to use local analogs to GRB hosts the giant telescopes in near future _will_ be able to study more galaxies -- out to 40 Mpc maybe can reach some real GRB hosts 11:55 AM Q: "metallicity" is not the same for all elements -- stars care about Fe in particular; there is a rare class of O stars with strong stellar winds and rapid rotation; they may be binaries or mergers some GRBs do occur in high-ish metallicity galaxies A: yes, we often measure "metallicity" using just a few elements but I'm not sure I agree that Fe is the most important element Q: WR stars prob not so closely related to LGRBs (?) Q: mass-metallicity plot requires cautions in use, please be careful A: yes, I agree Q: WR stars in LMC are unlike WR stars in MW not just the numbers that matter Q: only a tiny fraction of stars produces GRBs or SNe, so they can be very unusual evolutionary paths 12:00 PM John Graham: Explaining the relative and absolute LGRB rate with metallicity A Tale of two numbers: 30 and 40 Look at host metallicity-mass relationship Type II and Ic-BL Sne track star formation but LGRBs occur in very low metallicity galaxies prefer log[O/H] < 8.3 in another way, LGRBs occur about 30 times more frequently in low-metallicity regions A Drake Equation for LGRBs R(LGRB) = R(SF) x f(CC/SF) x f(Ibc/CC) x f(Ic-BL/Ic) x [Z- + (Z+/R_RF)] x f(eff) x f(beam) fill in the numbers and we have reasonable values for rate of LGRB so, how do the many factors vary with redshift? R(SF) and the Z- and Z+ terms considers a number of simple models for metallicity evolution with redshift applies the models to estimate evolution of SFR with redshift use redshift range 1 < z < 4 use these model fits to apply to the Drake Equation and try to figure out the values of unknown terms result: 4000 +- 2000 low metallicty Type Ic-BL SNe for every aligned LGRB then correct for beaming 40 +- 20 low metallicity Type Ic-BL SNe for every LGRB 12:11 PM Q: SDSS results have issues: fibers, weak lines A: GRB hosts are small, so metallicity gradient not a big problem Q: must do better job of computing metallicity on large scales completeness issues A: can do some things better, but there will always be problems yes, you point remains Q: what is fraction of CC SNe which are Ic or Ic-BL, in your calcs? A: I'd have to do those calculations, don't have numbers at hand Q: our knowledge of SN rates for different types have range of precisions Q: the factor of 30 depends on the metallicity to which you are comparing solar, or MW, or higher-than-8.3 could there be 2 mechanisms to form GRBs, for high-metallicity and low-metallicity regions? A: yes, perhaps. location of GRBs in their hosts doesn't show trend to low-metallicity regions Q: I'd like to see more accounting for uncertainties A: it's often hard to show these uncertainties in graphs 12:19 PM Chris Curtin: 3 Seasons of High-z SLSNe from SUDSS and DES Disclaimers 30 SLSN with good obs high-z SLSNe are seen in rest-frame FUV u-SUDSS is a boutique survey I will not mention GRBs Surveys and techniques based on SUDSS, DES, u-SUDSS uses z-band photometry based on DEC-Cam of Dark Energy Survey expect to find about 100 SLSNe with our survey example of SUDSS field in i-band goes to i < 26.2 mag LBG selection and monitoring star-forming galaxies have flat SED look for break in brightness in one filter break shows location of Lyman-alpha can estimate redshift from photometry alone "dropout" technique SN 1000+0216 host at z=3.9 and mag = 26.5 -- faint! addition of u-band data fills in gaps to higher redshifts candidates examine images by season (co-added per season) use image subtraction to isolate the transient signal once having identified the candidates go back and make light curves based on individual images one candidate may show evidence for a double peak spectroscopic followup have applied for followup on Keck, applied for Magellan and Gemini but we will observe in rest-frame UV, a region about we know little take-home points candidates are being found need FUV spectra of nearby examples for comparison this technique needs long baseline, regular cadence 12:34 PM Q: were 2 of your candidates inside the nucleus of host? A: we're working on it, they are close Q: are you also looking for objects without detected host galaxies? A: not at the moment Q: others have identified candidates as maybe SN IIn, not SLSNe A: we expect to find some IIn, we think we can tell the difference 12:36 PM break for lunch