HOPCAT & Dark Galaxies

Dr. Marianne T. DoylePh.D. Project

University of Queensland

BAS Meeting March 2007

ContentAstronomy & I

The history of Dark Galaxies

HOPCAT & Isolated Dark

Galaxies

Results

Marianne Doyle Ph.D ProjectUniversity of

QueenslandAdvisor:Michael J. Drinkwater – UQAssoc. Advisors:Elaine Sadler – Uni SydneyJohn Ross - UQCollaborators David J. Rohde - UQKevin Pimbblet - UQMike Read – WFAU EdinburghHIPASS Team – ATNF Parkes &

Epping, Universities of : Melbourne, Cardiff, Western Sydney Macarthur, Wales, Swinburne, Technology Sydney, New Mexico, Manchester, Colorado, Sydney, LeicesterASTRON 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 PhD Thesis yesterday (hung over!)

Now a Doctor of Astrophysics

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Disney (1979)

http://www.hollywoodjesus.com/movie/disney/walt_mickey.jpg

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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 lensingGravity can bend lightGravity of massive foreground object lens the light of distant

objects

In this case the massive foreground object was invisible

Credit

J. Bahcall (IAS, Princeton),

M. Disney (Univ. Wales), NASA

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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 galaxyHIPASSJ0731-69 (Ryder et al. 2001)

Tidal encounter with a moderately massive companion or ram-pressure stripping

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The Antennae Galaxies with their tidal tails. Courtesy of the NASA Astronomy Picture of the day web site (http://antwrp.gsfc.nasa.gov/apod/ap971022.html)

UGC 10214

Credits: UQ Communications and & Arna Karic, Institute of Geophysics and Planetary Physics, Lawrence Livermore National Laboratory, Livermore, CA, 94550, U.S.A

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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

http://www.hero.ac.uk/uk/research/archives/2005/galactic_ghost.cfm

Or is this a Dark Galaxy?

CREDIT: Arecibo Observatory / Cardiff University / Isaac Newton Telescope / Westerbork Synthesis Radio Telescope.CREDIT: Arecibo Observatory / Cardiff University / Westerbork Synthesis Radio Telescope.

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So what are Dark Galaxies?Dark Galaxies:

Contain neutral hydrogen (fuel for star formation) Possibly contain dark matterHave no visible optical galaxy at the same positionNo stars have formedGravitationally bound

Dark Galaxies are not:Isolated HI clouds without structureVery faint LSB galaxiesTidal 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

http://www.cmis.csiro.au/features/NorthernSydney.htm

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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

HIPASS

position uncertainty

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Image Centred on HICAT positions

Original

HICAT parameters

6 optical galaxy choice

Visually matched by 3 people to minimise galaxy selection bias

Independent velocities

Image Analysisellipses

Yellow for correct match

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ResultsOptical 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, 34–44, 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

http://milkyway.phys.tku.edu.tw/einmann/icons/Narrabri.gif

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Inside the Eagle Nebulahttp://antwrp.gsfc.nasa.gov/apod/astropix