PowerPoint Presentation - Arecibo Observatory by linzhengnd

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									OH Megamaser Studies at Arecibo:
   Current Studies and Future
           Directions
                 Jeremy Darling
                 (Carnegie Observatories)

                                     Collaborators:
                                     Riccardo Giovanelli (Cornell)
   Years of Scientific               Ylva Pihlstroem (NRAO)
                                     James Cordes (Cornell)
 Discovery at Arecibo                Karl Menten (MPIFR)
    November 2003                    Alison Peck (CfA)
I. OH Megamasers:
    Tracers of Major Mergers, Star
    Formation, and Massive Black Holes

II. Variability in OHMs:
    Super-VLBI Resolution

III. The Future
    Sane Directions
    Not Insane Directions
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
     Merging Galaxies:
Feeding starbursts and black holes
                                Barnes &
                                Hernquist
                                 (1996)
     Merging Galaxies:
Feeding starbursts and black holes




         Where does masing occur?
    Scales: arcsec  marcsec  μarcsec
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
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.
I. OH Megamasers:
Tracers of Major Mergers, Star
Formation, and Massive Black Holes
  Must Know:
  • What are the hosts of OHMs?
      Major mergers ([U]LIRGs)
  • How often are OHMs produced?
    (function of LFIR, color, stage, etc)
     ~ 1 in 3 in warm, IR excess ULIRGs
  • Is LOH correlated with LFIR?
      LOH ~ LFIR1.2 ; OH luminosity fctn
  • Are OHMs always associated with
  massive black holes?
      No (?)
  • What is the OHM lifetime?
      Underway: Magellan
II. Variability in OH Megamasers:
            Super-VLBI Resolution
A Case Study of Two OHMs:
     Both observed with VLBI, both variable
      IRAS 02524+2046                 IRAS 12032+1707
         (z = 0.182)                     (z = 0.217)
         “Martha”                       “Riccardo”
 Variability in OH Megamasers:




                                     “Bob”

Discovered at Arecibo!        (unexpected)
     • 10-14% modulation, τ < 39d
     • 25-50% of masing is compact (< 2 pc)
         Imaging OH Megamasers:
               The Variability Approach
Interstellar scintillation (ISS) provides a crude
interferometer in the sky.

VLBI:     • Object moves through fringes
          • Earth rotation fills UV plane

ISS:      • Observer moves through fringes
          • Earth revolution fills UV plane

Both are limited to high Tb objects (Tb > 1010 K)
                                               K).

ISS depends on angular size (~ twinkling): μarcsec regime
VLBA Map
(Darling, Peck, & Menten)




                            Beam ~ 30 pc
      Variability in OH Megamasers
Multiple independent variable features with different timescales:

 Segregates
  sizescales

 May segregate
  positions

 Offers sub-
  milliarcsecond
  resolution
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
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
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
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!
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!
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?
      Is Interstellar Scintillation the
          Correct Interpretation?

Scintillation timescales can show dramatic annual variation
  Strong annual
     variation


  Little annual
     variation




Plot and predictions
courtesty of B. Coles &
B. Rickett.
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
12032+1707
VLBA
Observations:
• Some extended OH
emission (~120 pc)       120 parsec

• Velocity gradient in
OH4 (5 km/s/pc)                       Pihlström, Baan,
                                      Klöckner & Darling
                                                   (2004)

• Arecibo HI
absorption matches
extended OH

• Blueshifted OH is
compact (< 25 pc)…
12032+1707
Arecibo                                           Assuming ISS
Observations:                                     Variable features:
                                                     < 1.2 parsec
• Broad emission is
                                                  Quiescent features:
quiescent                                            > 4 parsec

• Narrow blueshifted
peaks are variable       Pihlström, Baan,
                         Klöckner & Darling      III Zw 35 Model
                                      (2004)

• No narrow line
acceleration (as
expected for IIIZw35
geometry)              120 parsec              Pihlström et al. 2001
      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
        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)
  OH Megamasers: Future Directions
   Cosmology & Galaxy                       Understanding OH
       Evolution                              Megamasers

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




                            OH and HI, CO:
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
 OH and the Fine Structure Constant
Microwave OH lines have a   6 cm OH:
 unique dependence on α:


 18 cm OH not required!

CH has analogous structure
                            5 cm OH:
                  6 cm
     5 cm


    18 cm
     Future Directions: Extragalactic
                        Molecular Studies
 Detection and Physics of
                                           Cosmology & Reionization
 Extragalactic Molecules

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

								
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