HOPCAT Dark Galaxies Dr Marianne T Doyle

HOPCAT & Dark Galaxies Dr. Marianne T. Doyle Ph. D. Project University of Queensland

Content ¶Astronomy & I ¶The history of Dark Galaxies ¶HOPCAT & Isolated Dark Galaxies ¶Results 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…. . . . BAS Meeting March 2007

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 Ph. D Thesis yesterday (hung over!) ¶ Now a Doctor of Astrophysics BAS Meeting March 2007

Disney (1979) http: //www. hollywoodjesus. com/movie/disney/walt_mickey. jpg BAS Meeting March 2007

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 BAS Meeting March 2007

Dark Galaxies? ¶ Term first used by astrophysicist investigating Quasars using gravitational lensing - (Mike Hawkins 1997) ¶ Quasars (QUASi-stell. AR objects) ¶Enormous energetic objects discovered in 1963 & lie near the edge of the observable universe ¶ Gravitational lensing Credit J. Bahcall (IAS, Princeton), M. Disney (Univ. Wales), NASA ¶Gravity can bend light ¶Gravity of massive foreground object lens the light of distant objects ¶ In this case the massive foreground object was invisible BAS Meeting March 2007

Is that a Dark Galaxy? ¶HIPASSJ 1712 -64 (Kilborn et al. 2000) ¶Extragalactic HI cloud with no Optical counterpart – high velocity cloud (HVC) ¶Dark galaxy DDO 154? (Kennicutt et al. 2001) ¶An average, low-mass, dwarf irregular galaxy ¶HIPASSJ 0731 -69 (Ryder et al. 2001) ¶Tidal encounter with a moderately massive companion or ram-pressure stripping BAS Meeting March 2007

Credits: UQ Communications and & Arna Karic, Institute of Geophysics and Planetary Physics, Lawrence Livermore National Laboratory, Livermore, CA, 94550, U. S. A The Antennae Galaxies with their tidal tails. Courtesy of the NASA Astronomy Picture of the day web site (http: //antwrp. gsfc. nasa. gov/apod/ap 971022. html) UGC 10214 BAS Meeting March 2007

Or is this a Dark Galaxy? ¶ VIRGOHI 21 in the Virgo cluster ¶ (Dr Robert Minchin, Mike Disney & Co 2005 – Cardiff University) http: //www. hero. ac. uk/uk/research/archives/2005/galactic_ghost. cfm / Cardiff University / Isaac Newton CREDIT: Arecibo Observatory Telescope / Westerbork Synthesis University / Westerbork Synthesis Radio Telescope. CREDIT: Arecibo Observatory / Cardiff Radio Telescope. ¶ Australian Group dispute this is a dark galaxy ¶ Tidal tail from NGC 4254 BAS Meeting March 2007

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 BAS Meeting March 2007

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 BAS Meeting March 2007

Parkes Survey & Catalogue ¶ HI Parkes All Sky Survey & catalogue http: //www. cmis. csiro. au/features/Northern. Sydney. htm HIPASS & HICAT ¶ Largest blind HI radio survey of the southern sky ¶ 4315 HI radio detected objects BAS Meeting March 2007

Optical Galaxy Match ¶ Objective: Find the optical galaxy for the HI radio sources ¶ Problem: Um…. . Which galaxy was the original HI detection? HIPASS position uncertainty ¶ Need an interactive program to visually match radio sources to their optical galaxy BAS Meeting March 2007

Visually matched by 3 people to minimise galaxy selection bias 6 optical galaxy choice Original HICAT parameters Image Analysis ellipses Yellow for correct match Image Centred on HICAT positions Independent velocities BAS Meeting March 2007

Results Optical counterparts for 84% of HICAT radio sources ¶ Optically Matched with velocity 58% 2512 26% 1106 11% 481 5% 216 ¶ Single Match (42% - 1798) ¶ Compact group member (16% - 714) ¶ Optically Matched with no velocity ¶ Single Match (20% - 848) ¶ Compact group member (6% - 258) ¶ No Guess ¶ Several galaxies no velocities ¶ Blank Field ¶ No visible galaxy BAS Meeting March 2007

HOPCAT- Isolated Dark Galaxies? ¶ 4315 HI radio detected objects ¶ Dust extinction cut 3692 objects ¶ Use only blank fields 13 objects BAS Meeting March 2007

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) BAS Meeting March 2007

HOPCAT - Isolated Dark Galaxies? No isolated dark galaxies are present within HOPCAT Doyle et al. (MNRAS 361, 34– 44, 2005) BAS Meeting March 2007

http: //milkyway. phys. tku. edu. tw/einmann/icons/Narrabri. gif 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 Ph. D 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 BAS Meeting March 2007

Inside the Eagle Nebula BAS Meeting March 2007 http: //antwrp. gsfc. nasa. gov/apod/astropix