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OH Megamaser Studies at Arecibo: Current Studies and Future Directions

OH Megamaser Studies at Arecibo: Current Studies and Future Directions

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OH Megamaser Studies at Arecibo: Current Studies and Future Directions

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  1. OH Megamaser Studies at Arecibo:Current Studies and Future Directions Jeremy Darling (Carnegie Observatories) Collaborators: Riccardo Giovanelli (Cornell) Ylva Pihlstroem (NRAO) James Cordes (Cornell) Karl Menten (MPIFR) Alison Peck (CfA) Years of Scientific Discovery at Arecibo November 2003

  2. I. OH Megamasers: Tracers of Major Mergers, Star Formation, and Massive Black HolesII. Variability in OHMs: Super-VLBI Resolution III. The FutureSane Directions Not Insane Directions

  3. I. What are OH Megamasers? • Luminous 18 cm masers produced in major galaxy mergers • Associated with starburst nuclei in merging galaxies ([U]LIRGs) • LOH = 101-104 L (106-109 “typical” OH masers) • Two lines: 1667 and 1665 MHz (9:5 in TDE) • Extremely rare: ~100 known

  4. Merging Galaxies: Feeding starbursts and black holes Barnes & Hernquist (1996)

  5. Merging Galaxies: Feeding starbursts and black holes Where does masing occur? Scales: arcsec  marcsec  μarcsec

  6. Arp 220: The First OH Megamaser • Discovered in 1982 at Arecibo by Baan, Wood, & Haschick • The first megamaser detected • (of any variety) • Two lines: 1667 and 1665 MHz (4.2:1) • Advanced merger with two masing starburst nuclei

  7. I. OH Megamasers: Tracers of Major Mergers, Star Formation, and Massive Black Holes • OH  FIR and favors dusty • environments • OHMs seem to indicate massive • black holes (small sample) • OHMs seem to favor a specific • stage of merging, star formation • Sampling a specific stage of • merging •  BH binary formation rate •  long-period GW background • There are many approaches to these • problems; no single method will be • a panacea.

  8. I. OH Megamasers: Tracers of Major Mergers, Star Formation, and Massive Black Holes • Must Know: • What are the hosts of OHMs? • How often are OHMs produced? • (function of LFIR, color, stage, etc) • Is LOH correlated with LFIR? • Are OHMs always associated with massive black holes? • What is the OHM lifetime? Major mergers ([U]LIRGs) ~ 1 in 3 in warm, IR excess ULIRGs LOH ~ LFIR1.2 ; OH luminosity fctn No (?) Underway: Magellan

  9. II. Variability in OH Megamasers: Super-VLBI Resolution A Case Study of Two OHMs: Both observed with VLBI, both variable IRAS 12032+1707 (z = 0.217) IRAS 02524+2046 (z = 0.182) “Martha” “Riccardo”

  10. Variability in OH Megamasers: “Bob” • Discovered at Arecibo!(unexpected) • 10-14% modulation, τ < 39d • 25-50% of masing is compact (< 2 pc)

  11. Imaging OH Megamasers: The Variability Approach Interstellar scintillation (ISS) provides a crude interferometer in the sky. VLBI: ISS: Both are limited to high Tb objects (Tb > 1010 K) • Interstellar scintillation (ISS) provides a crude interferometer in the sky. • Object moves through fringes • Earth rotation fills UV plane • Observer moves through fringes • Earth revolution fills UV plane • Both are limited to high Tb objects (Tb > 1010 K). • ISS depends on angular size (~ twinkling): μarcsec regime

  12. VLBA Map (Darling, Peck, & Menten) Beam ~ 30 pc

  13. Variability in OH Megamasers Multiple independent variable features with different timescales: Segregates sizescales May segregate positions  Offers sub- milliarcsecond resolution

  14. 02524+2046 • Observations: • Day-to-day (and intraday) variation • Multiple narrow variable components • 1665 MHz line varies, often (but not always) with 1667 • Components often (but not always) correspond to peaks

  15. 02524+2046 • Observations: • Day-to-day (and intraday) variation • Multiple narrow variable components • 1665 MHz line varies, often (but not always) with 1667 • Components often (but not always) correspond to peaks

  16. 02524+2046 • Observations: • Day-to-day (and intraday) variation • Multiple narrow variable components • 1665 MHz line varies, often (but not always) with 1667 • Components often (but not always) correspond to peaks

  17. 02524+2046 • Observations: • (continued) • “Flaring” events • Many components appear to shift by a few km/s over time • Variable features narrower than average features • > 30 components required to fit all epochs!

  18. 02524+2046 • Observations: • (continued) • “Flaring” events • Many components appear to shift by a few km/s over time • Variable features narrower than average features • > 30 components required to fit all epochs!

  19. 02524+2046 • Observations: • (continued) • Unprecedented matching between 1665 and 1667 MHz lines in average and variable fits, including flaring lines • Variation envelope shows proportional 1667:1665 modulation of ~20% (~30% expected for point source) • Size scales < 1 parsec (0.3 milliarcsec) • What is line separation in sky?

  20. Is Interstellar Scintillation the Correct Interpretation? Scintillation timescales can show dramatic annual variation

  21. Strong annual variation Little annual variation Plot and predictions courtesty of B. Coles & B. Rickett.

  22. Characterizing Variability • 10% modulation • 4.5 day timescale • Assuming ISS • Variable features: • < 1.2 parsec • Quiescent features: • > 4 parsec III Zw 35 Model Pihlström et al. 2001

  23. 12032+1707 • VLBA Observations: • Some extended OH emission (~120 pc) • Velocity gradient in OH4 (5 km/s/pc) • Arecibo HI absorption matches extended OH • Blueshifted OH is compact (< 25 pc)… 120 parsec Pihlström, Baan, Klöckner & Darling (2004)

  24. 120 parsec Pihlström, Baan, Klöckner & Darling (2004) III Zw 35 Model Pihlström et al. 2001 12032+1707 • Arecibo Observations: • Broad emission is quiescent • Narrow blueshifted peaks are variable • No narrow line acceleration (as expected for IIIZw35 geometry) Assuming ISS Variable features: < 1.2 parsec Quiescent features: > 4 parsec

  25. Variability Studies: Byproducts • Exceptional S/N average spectra • Deep searches for 18 cm satellite lines • Deep searches for isotopes (18OH) • Very low τ HI absorption (see IRAS 12032+1707 aka “Riccardo”) • Variability studies can identify/constrain OH line accelerations. • (NGC 4258 H2O Disk: a = 9.3 km s-1 yr-1; Herrnstein et al. 1999) OHMs: a < 2-3 km s-1 yr-1

  26. Variability Studies: Summary • Variability studies can segregate size scales and on-sky projections of OH megamaser components with super-VLBI resolution (sub-parsec at z = 0.2). • Roughly half of luminous OMHs at z > 0.1 are variable/compact. • We have identified compact 1665 MHz emission coincident with compact 1667 MHz lines. • Observed phenomena are consistent with strong refractive ISS • (and detailed tests are possible) • ISS predictions are consistent with VLBI observations • Long-term monitoring can identify small accelerations (eg - disks)

  27. OH Megamasers: Future Directions Cosmology & Galaxy Evolution Understanding OH Megamasers • High Frequencies • 5 & 6 cm OH lines: gas physics • Related molecular species • VLBI Studies with Arecibo • Larger sample, higher redshifts • OHMs and massive black holes • Variability Studies • Maser sizes, geometries • Line accelerations • Local Starbursts • Understanding OH “kilomasers” • OH and proto globular clusters • Tracing dust-obscured SF • High Redshift Surveys • The evolution of merging • Dust-obscured star formation • Massive black holes • Massive black hole pairs and GWs • Fine Structure Constant Evolution • OH can constrain a(z) without comparison to other species • Independent test (1 part in 106-7) • Geometric Distances? • OH in disks?

  28. OH and the Fine Structure Constant OH alone: Microwave OH lines have a unique dependence on α: OH and HI, CO:

  29. Aside: OH and the Fine Structure Constant OH and HI: • Unoptimized OH and HI spectra provide high precision measurements from a single object • Shortage of OH systems at high z… • Multiple independent measurements required

  30. OH and the Fine Structure Constant Microwave OH lines have a unique dependence on α: 6 cm OH: 18 cm OH not required! CH has analogous structure 5 cm OH: 6 cm 5 cm 18 cm

  31. Future Directions: Extragalactic Molecular Studies Detection and Physics of Extragalactic Molecules Cosmology & Reionization • Fine Structure Constant Evolution • OH can constrain a(z) without comparison to other species • Independent test (1 part in 106-7) • 18 cm OH not necessary • Other molecules, transitions: the more, the merrier (good control on systematics) • Epoch of Reionization • 4+ groups searching for radio loud quasars at z > 6 • Arecibo is in a unique position to observe HI, molecular absorption • High Redshift Absorption Surveys • Evolution of the molecular ISM • OH, CH3OH, CH, H2CO, etc • 1-10 GHz: Arecibo can be a giant in molecular surveys and studies • Arecibo is an efficient molecular absorption machine to any z! • Extragal. Molecular ISM Physics • Multiple transitions • Multiple species • VLBI now possible