HOPCAT

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HOPCAT Dark Galaxies

• Dr. Marianne T. Doyle
• Ph.D. Project
• University of Queensland

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Content
Marianne Doyle Ph.D Project University of
Queensland Advisor Michael J. Drinkwater
UQ Assoc. Advisors Elaine Sadler Uni
Sydney John Ross - UQ Collaborators David J.
Rohde - UQ Kevin Pimbblet - UQ Mike Read WFAU
Edinburgh HIPASS Team ATNF Parkes Epping,
Universities of Melbourne, Cardiff, Western
Sydney Macarthur, Wales, Swinburne, Technology
Sydney, New Mexico, Manchester, Colorado, Sydney,
Leicester ASTRON The Netherlands, AAO
Sydney, WIYN Tucson etc.......

• Astronomy I
• The history of Dark Galaxies
• HOPCAT Isolated Dark Galaxies
• Results

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Astronomy I

• Always wanted to be an astronomy
• Single parent broke my leg in 1994
  Wonderful kite!
• High school 1995/6 - Complete senior subjects
• Undergraduates degree 1997 to 2001
• First Class Honours 2002
• July - Submitted my PhD Thesis yesterday (hung
  over!)
• Now a Doctor of Astrophysics

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Disney (1979)
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Mike Disney - Nature (1979 )

• Strong indirect evidence already exists that our
  knowledge of galaxies is heavily biased by the
  sky background
• Hitchhikers Guide to the galaxy Cricket..
• No good reason for believing that low surface
  brightness (LSB) objects, and parts of objects,
  do not exist
• Extreme case of LSB galaxies are dark galaxies

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Dark Galaxies?

• Term first used by astrophysicist investigating
  Quasars using gravitational lensing - (Mike
  Hawkins 1997)
• Quasars (QUASi-stellAR objects)
• Enormous energetic objects discovered in 1963
  lie near the edge of the observable universe
• Gravitational lensing
• Gravity can bend light
• Gravity of massive foreground object lens the
  light of distant objects
• In this case the massive foreground object was
  invisible

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Is that a Dark Galaxy?

• HIPASSJ1712-64 (Kilborn et al. 2000)
• Extragalactic HI cloud with no Optical
  counterpart high velocity cloud (HVC)
• Dark galaxy DDO154? (Kennicutt et al. 2001)
• An average, low-mass, dwarf irregular galaxy
• HIPASSJ0731-69 (Ryder et al. 2001)
• Tidal encounter with a moderately massive
  companion or ram-pressure stripping

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Or is this a Dark Galaxy?

• VIRGOHI21 in the Virgo cluster
• (Dr Robert Minchin, Mike Disney Co 2005
  Cardiff University)
• Australian
• Group dispute
• this is a
• dark galaxy
• Tidal tail from
• NGC4254

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So what are Dark Galaxies?

• Dark Galaxies
• Contain neutral hydrogen (fuel for star
  formation)
• Possibly contain dark matter
• Have no visible optical galaxy at the same
  position
• No stars have formed
• Gravitationally bound
• Dark Galaxies are not
• Isolated HI clouds without structure
• Very faint LSB galaxies
• Tidal outflows from galaxies

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Lets go looking for Isolated Dark Galaxies

• How do we look? (since they are dark)
• Neutral Hydrogen (HI) detections
• Match the HI detections with optical galaxies
• Investigate those with NO optical galaxies

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Parkes Survey Catalogue

• HI Parkes All Sky Survey catalogue
• HIPASS
• HICAT
• Largest blind
• HI radio survey
• of the
• southern sky
• 4315 HI radio
• detected objects

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Optical Galaxy Match

• Objective Find the optical galaxy for the HI
  radio sources
• Problem Um.. Which galaxy was the original HI
  detection?
• Need an interactive program to visually match
  radio sources to their optical galaxy

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Visually matched by 3 people to minimise galaxy
selection bias
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Results

• Optical counterparts for 84 of HICAT radio
  sources
• Optically Matched with velocity 58 2512
• Single Match (42 - 1798)
• Compact group member (16 - 714)
• Optically Matched with no velocity 26 1106
• Single Match (20 - 848)
• Compact group member (6 - 258)
• No Guess 11 481
• Several galaxies no velocities
• Blank Field 5 216
• No visible galaxy

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HOPCAT- Isolated Dark Galaxies?

• 4315 HI radio detected objects
• Dust extinction cut
• 3692 objects
• Use only blank fields
• 13 objects

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HOPCAT - Isolated Dark Galaxies?

• Take out over crowded fields
• 2 objects
• 2 remaining objects?
• 1 - very faint previously observed optical galaxy
  in the Centaurus group Banks et al (1999)
• 1- non-detection - Narrow-band follow-up
  observations at Parkes (Thank you Dr. Ivy Wong)

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HOPCAT - Isolated Dark Galaxies?

• No
• isolated dark galaxies
• are present within
• HOPCAT
• Doyle et al. (MNRAS 361, 3444, 2005)

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Future?

• No fame - Not finding any isolated dark galaxies
  is not as exciting as finding one (sigh!!!!)
• Hopefully get to wear a floppy cap (i.e. be
  awarded a PhD and become Dr. Doyle. I did
  graduate and I even bought the floopy cap!
• Reduce data from observing runs at the Australia
  Telescope Compact Array and write another paper
• Postdoctoral position somewhere - 2008 onwards

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