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Star Formation & the Morphology-Density
Relation in the Local Universe
Marianne T. Doyle
Ph.D. Project
Content
 The Morphology-density relation
 This Project’s Question: How does star
formation depend upon environment
and other factors?
 Proposed theories
 Progress
 The Radio Detected Galaxy Sample
 Optical Matches for Radio Detections
 High resolution Radio observations
 The continuing path to the answer
Supervisor:
Michael J. Drinkwater – UQ
Assoc Supervisors:
John Ross - UQ
Elaine Sadler – Uni Sydney
Collaborators
David J. Rohde - UQ
Mike Read – WFAU Edinburgh
Baerbel S Koribalski – ATNF, Epping
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….......
Morphology, Density & The Relationship
 Morphology?
 Galaxy types: Irregular, Spiral
and elliptical galaxies and
everything in between.
Spiral Galaxy
 Galaxy Density?
 Alone?
 Is the galaxy in a group?
 In a cluster?
 The Morphology-Density
Relation?
 The observation that there are
few spiral galaxies in areas of
high galaxy density.
Elliptical Galaxy
Galaxy cluster in Hercules
Abell
2151 Group
Hickson
Compact
650 millionHCG87
light year across
Centaurus A
170,000 light year across
Irregular galaxy
This Project
 The question: How does the conversion of
hydrogen to stars (star formation) depend upon
environment and other factors?
 Testing two theories:
 Either fewer “star forming galaxies” actually form in
regions of high galaxy density,
OR
 There are physical processes that directly suppresses
star formation.
This Project
 Use radio detected galaxy sample instead of optical sample
 Optical samples are biased towards star forming galaxies which is
what we are trying to measure.
 Measure the Star Formation Rate (SFR)
 The rate stars are forming in galaxies
 Calculated using luminosity of galaxy
 Determine the Star Formation Efficiency (SFE)
 A ratio of SFR and mass of neutral hydrogen (HI) in the galaxy
 Estimate the local galaxy density
The Radio Galaxy Sample
 Neutral hydrogen (HI) is:
 The fuel for star formation
 Has a rest wavelength of 21cm, detectable by radio
 HI Parkes Sky Survey (HIPASS) (Stavely-Smith et al 2001)
 HI blind radio survey of the southern sky
 HIPASS Catalogue (HICAT) (Meyer et al submitted)
 Very large survey containing 4315 HI radio sources
 Previous HI surveys have numbered in the hundreds (Braun et al 2003 & Lee et al
2003)
 Position error of ~ 6arcmins
 Accurate galaxy positions needed to measure luminosity to
estimate SFR
 Optically match all 4315 HI radio detections for accurate positions
Optical Counterparts
 Objective: Find the
optical counterparts 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 counterparts
HIPASS position error
 ADRIC Interactive Program written by David Rohde
 Visually matching: M. Drinkwater, D. Rohde, D. Parmenter & Myself
Selection parameters
Original
HICAT parameters
15 x 15 arcmin images to allow
for the 6 arcmin position error
Centred on
HICAT
positions
Superimposed
Superimposed
ellipses
and listed
Yellow for
Published
correct match
velocities
Results
Analysis of 4315 Radio Sources - 84% identified
Velocity Match
44%
1882
20%
851
14%
634
 With published velocity
 Good Guesses
 But no published velocity
 Velocity Multi Match
 Compact group of galaxies with published velocity
 Good Guess Multi Match
6%
256
11%
476
5%
216
 Compact group of galaxies no velocity
 No Guess
 Several galaxies no velocities
 Blank Field
 No visible galaxy
Optical Matching Conclusions
 ٠ Optical
Catalogue 1882
(44 %)
identified
 × “Confused”
Sources 2217
(51%)

High
resolution
radio
observations
needed
 + 216 (5%)
Blank Fields

19 nongalactic
plane blank
fields
Sanity Check
 Radio flux from HIPASS
radio sources and Apparent
Magnitudes from Optical
matches
 Totally independent
variables
 Correlation shown
(Faint to bright)
Log HIPASS Peak Flux Vs Optical Apparent Magnitude
Objects matched by published velocities, educated guesses without
velocity and velocity matches where multiple galaxies match.
Radio Telescope Resolution





Parkes Radio Telescope
HI rest λ 21cm detectable by radio
64 metre dish
15 arcmin beam
Large sky coverage





Australia Telescope Compact Array
HI rest λ 21cm detectable by radio
4.4 km baseline
2.5 arcmin beam
High resolution sky coverage
High Resolution Radio Observation
Correct
match:
Possible
HI
galaxies
contouring
centred on
large
galaxy
HI contours
Large galaxy: NGC1532
Small interacting galaxy:NGC1531
Continuing Path To The Answer
Optical
matching
process
Completed
HOPCAT
Use Infrared
& Radio
Continumn to
measure SFR
Calculate
SFE &
relate to
galaxy
morphology
Determine
local galaxy
density
Determine
which theory
contributes
toward the
Morphologydensity
relation
Thank you
Michael Drinkwater – Supervisor extraordinaire
David Rohde – Computer wiz
Kevin Pimbblet – The answer giver
Luke Pegg – Continual support & wonderful hugs
Jacob Doyle – My wonderful teenage son
Lagoon Nebula
100LY across
Contains
many young stars
& hot gas