H2 emission from pre-PN and PN (in the UWISH2 survey) Tim Gledhill University of Hertfordshire Dirk Froebrich University of Kent + UWISH2 team H2 emission in pre-PNe Pre-PN phase: the central star is still cool. An ionization region has not yet developed. But H2 can be shock-excited in outflows. B0 These objects are nearly always bipolar, dusty and visible at optical and near-IR wavelengths in scattered light. H2 ro-vibrational lines (e.g. 1-0 S(1) and 2-1 S(1) in the K-band) show ratios characteristic of thermal excitation. Egg Nebula: Sahai et al. 1998 1-0 S(1) emission in red, scattered light in blue/green Pre-PN to PN transition phase: IRAS 18379-1707 At Teff ~ 20 000 K (B0), sufficient UV photons (λ ~ 100 nm) are emitted to photo-excite (and also dissociate) H2 - giving rise to a fluorescent ro-vibrational spectrum. Flux density x 10-14 W m-2 μm-1 A compact region of H+ (and He+) develops around the star. Initially this will be too small to resolve. 2.0 2.1 2.2 2.3 2.4 H2 line ratios are now more typical of fluorescence. Little evidence of scattered continuum from the nebula. NIFS (IFU) data Gledhill & Forde 2015 Pre-PN to PN transition phase: As the developing ionization front propagates into the envelope (already shaped during the pre-PN phase) the object becomes resolvable in Hα as an early PN. Both H2 and recombination lines are seen tracing molecular and ionized gas IRAS 22023+5249: a very young PN, Brγ emission in red, 1-0 S(1) in blue Gledhill & Forde 2015 Pre-PN to PN transition phase: As the PN develops, the ionized volume extends throughout the nebula H2 emission may disappear in the inner nebula (or maybe not if dust shielding is important) This object show evidence for an outer H2 shell IRAS 19306-0400: a very young PN, Brγ emission in red, He I in green Gledhill & Forde 2015 (pre)PN in UWISH2 UWISH2: Galactic plane survey in H2 1-0 S(1) line (Dirk’s talk on Monday) Expect sources to include: - pre-main sequence objects (especially outflows, jets) - supernova remnants - ISM structures, e.g. clouds, bubbles, filaments, heated by shocks or UV - Evolved objects such as pre-PNe and PNe A catalogue of pre-PN+PN candidates has been identified - H2 – K band difference images - auto-search for H2 emission above a given threshold - eyeball rejection of obvious contaminants - try to exclude artefacts! → 280 candidate objects so far (pre)PN in UWISH2 UWISH2 detections Pre/PN candidates symbol size proportional to radius of emission region known PN Galactic latitude GN J1941.3+2430 NGC 6537 G044.1+01.5 G017.6-01.1 SH 2-71 Galactic longitude Total of 280 sources with detected H2 emission 186 of these are new pre-PN/PN candidates PN in UWISH2 G062.7-00.7 SH 2-71 NGC 6537 PN in UWISH2 G062.7-00.7 G027.6-00.8 PN in UWISH2 G062.7-00.7 G027.7+00.7 G020.4+00.6 PN in UWISH2 G030.0+00.0 continuum 8continuum ─ 6 O(3) (pre)PN UWISH2 detections Objects with no Hα detection UWISH2_035.38919-1.17506 continuum UWISH2_032.28479-0.27816 UWISH2_035.76967-1.24531 8continuum ─ 6 O(3) UWISH2_031.63781+0.9959 Hα detected PNe within UWISH2 Hα detection + H2 detection 130 Hα detected PN candidates plotted from MASH I and MASH II, IPHAS (Sabin et al. 2014) plus some previously known Hα detection only Galactic latitude 65 objects detected in H2 (i.e. 50%) 8continuum ─ 6 O(3) continuum Galactic longitude 100 40 Total 50 45 14 17 32 0 T L 6 16 P 40 MASH PNe Sabin et al. PNe 20 20 20 10 0 0 0 T L P T L P Other PNe T L P Summary The pre-PN to PN transition is characterized by a developing ionized region within the molecular pre-PN: - molecular and atomic gas tracers are required to image this phase - dust scattered continuum is usually weak unless the object is highly bipolar As the PN switches on, the ionization front moves out through the pre-PN-sculpted structure - H2 may persist at large radius (pre-view of the PN structure) - may also exist within the ionized volume, especially if dusty We currently have 280 objects in the UWISH2 area that are pre-PN+PN candidates 186 of these are not known to be PNe - some may be pre-PN with no recombination emission (yet) - some may be optically obscured Pne - Some may be neither!