Star Formation & the Morphology-Density Relation in the Local Universe
Marianne T. DoylePh.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 – UQAssoc Supervisors:John Ross - UQElaine Sadler – Uni SydneyCollaborators David J. Rohde - UQMike Read – WFAU EdinburghBaerbel S Koribalski – ATNF, EppingHIPASS 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….......
Hickson Compact Group
HCG87
170,000 light year across
Galaxy cluster in Hercules
Abell 2151
650 million light year across
Morphology, Density & The Relationship Morphology?
Galaxy types: Irregular, Spiral and elliptical galaxies and everything in between.
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.
Spiral Galaxy
Elliptical Galaxy
Irregular galaxy
Centaurus A
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
Superimposed ellipses
Yellow for correct match
15 x 15 arcmin images to allow
for the 6 arcmin position errorCentred on
HICAT positions
Selection parametersOriginal
HICAT parameters
ADRIC Interactive Program written by David Rohde
Visually matching: M. Drinkwater, D. Rohde, D. Parmenter & Myself
Superimposed and listedPublished velocities
ResultsAnalysis of 4315 Radio Sources - 84% identified
Velocity Match 44% 1882 With published velocity
Good Guesses 20% 851 But no published velocity
Velocity Multi Match 14% 634 Compact group of galaxies with published velocity
Good Guess Multi Match 6% 256 Compact group of galaxies no velocity
No Guess 11% 476 Several galaxies no velocities
Blank Field 5% 216 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 non-
galactic plane blank fields
Sanity Check
Log HIPASS Peak Flux Vs Optical Apparent MagnitudeObjects matched by published velocities, educated guesses without
velocity and velocity matches where multiple galaxies match.
Radio flux from HIPASS radio sources and Apparent Magnitudes from Optical matches Totally independent
variables Correlation shown
(Faint to bright)
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
HI contours
Correct match:
HI contouring centred on
large galaxy
Possible galaxies
High Resolution Radio Observation
Large galaxy: NGC1532Small interacting galaxy:NGC1531
Continuing Path To The Answer
Optical matching process
CompletedHOPCAT
Use Infrared & Radio
Continumn to measure SFR
Determine local galaxy
density
Calculate SFE &
relate to galaxy
morphology
Determine which theory contributes toward the
Morphology-density relation
Luke Pegg – Continual support & wonderful hugsJacob Doyle – My wonderful teenage son
Thank youMichael Drinkwater – Supervisor extraordinaireDavid Rohde – Computer wizKevin Pimbblet – The answer giver
Lagoon Nebula100LY across
Contains many young stars
& hot gas