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The Evolution of Stars and Gas in Galaxies. PhD Thesis Proposal Philip Lah. Supervisor: Frank Briggs. Supervisory Panel: Erwin de Blok (RSAA) Jayaram Chengalur (National Centre for Radio Astrophysics, India) Matthew Colless (Anglo-Australian Observatory)

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the evolution of stars and gas in galaxies

The Evolution of Stars and Gas in Galaxies

PhD Thesis Proposal

Philip Lah

supervisor frank briggs

Supervisor: Frank Briggs

  • Supervisory Panel:
  • Erwin de Blok (RSAA)
  • Jayaram Chengalur (National Centre for Radio Astrophysics, India)
  • Matthew Colless (Anglo-Australian Observatory)
  • Roberto De Propris (University of Bristol, UK)
goal of phd
Goal of PhD
  • to relate the evolution in galaxies of their star formation rate, their stellar mass and their mass of neutral hydrogen gas (the fuel of star formation)
  • examine galaxy evolution over last 4 Gyr (going back third age of the universe)
  • study galaxies in a variety of different environments
  • UNIQUE PART study galaxy properties in same systems – optically selected galaxies
why do this
Why do this?

Should give a clearer picture of how, when and where stars and their host galaxies form.

Improves our understanding of our place in the universe, residing in our galaxy, the Milky Way, and orbiting our star, the Sun.

star formation rate

 Hα Spectroscopy

 Hα Narrow Band Imaging

 UV (with no dust correction)



Star Formation Rate
stellar mass density
Stellar Mass Density

Dickenson et al. 2003

neutral hydrogen gas mass1
Neutral Hydrogen Gas Mass



& Wolfe 2000

Rao & Turnshek 2003


HI 21cm

galaxy environment
Galaxy Environment
  • galaxy environment cluster, cluster outskirts and the field
  • density - morphology relation
  • density - star formation relation
  • density - neutral hydrogen relation
  • Cause of density relations?
previous highest redshift hi
Previous highest redshift HI

Westerbork Synthesis Radio Telescope (WSRT) Netherlands

Abell 2218 z = 0.18

integration time 36 days, Zwaan et al. 2001

Very Large Array (VLA)

Abell 2192 z = 0.1887

integration time ~80 hours, Veheijen et al. 2004

gmrt collecting area
GMRT Collecting Area

30 dishes of 45 m diameter

GMRT Collecting Area

 21 × ATCA

 15 × Parkes

 6.9 × WSRT

 3.6 × VLA

method of hi detection
Method of HI Detection
  • individual galaxies HI 21cm emission below radio observational detection limits
  • large sample of galaxies with known positions & precise redshifts (from optical observations)
  • coadd weak HI signals isolated in position & redshift (velocity) space
  • measure integrated HI signal – total HI mass of whole galaxy population – can calculate the average HI galaxy mass
galaxy cluster abell 370


Cluster Centre

Galaxy Cluster Abell 370

27’ × 27’


abell 370 data
Abell 370 Data
  • 42 literature redshifts for Abell 370 cluster members 33 are usable – large error in σz ≥ ± 300 kms-1(from Soucail et al. 1988 )
  • obtaining imaging data ESO 2.2m/WFI with VRI filters 34’ × 33’(queue scheduled by Sept) use to select sample for spectroscopic follow-up
  • using AF2/WYFFOS 4.2mWilliam Herschel Telescope, La Palma (sometime in Oct to Dec)  for redshifts and star formation rate from [OII]
radio data cube


HI Redshift



Radio Data Cube
mass hi
Mass HI

Assuming an optically thin neutral hydrogen cloud

MHI*= 6.2 ×109 M (Zwaan et al. 2003)

galaxy cluster cl0024 1654


Cluster Centre

Galaxy Cluster Cl0024+1654

21’ × 21’


cl0024 1654 data
Cl0024+1654 Data
  • HST imaging  2181 galaxies with morphologies of which 195 spectroscopically confirmed cluster members (Treu et al. 2003)
  • Hαnarrow band imaging with Subaru  star formation rates(Kodama et al. 2004)
  • 296 literature redshifts within HI frequency limits of the GMRT observation (Cszoke et al. 2001)
  • estimated HI Mass Upper Limit similar to Abell 370: ~1.7 × 109M
subaru field
Subaru Field


24’ × 30’


subaru field redshifts

GMRT HI Freq Range

Subaru Filter FWHM (120 Å)

Subaru Field Redshifts
subaru field redshifts1
Subaru Field Redshifts

number of target Hα emitting galaxies = 347

number of galaxies with quality ≥ 3 redshifts = 183

number of galaxies in GMRT HI freq range = 166

previous work
Previous Work

started PhD 1st March 2004

  • Mar to mid-July 1stThree Month Project - preliminary work on reducing Abell 370 GMRT data - creating data reduction pipeline
  • mid-July to Aug completed reduction of one sideband of the 7 days of data - prepared results for a GMRT telescope proposal for galaxy cluster Cl0024+1652
  • Sept to mid-Nov 2ndThree Month Project - 6dFGS working with Robert Proctor and Duncan Forbes (Swinburne University) and Matthew Colless (AAO)
previous work1
Previous Work
  • mid Nov to Dec Literature Review for Thesis Proposal
  • Jan 2005 traveled to India for GMRT observations galaxy cluster Cl0024+1652
  • beginning of March 5 nights 2dF AAT redshift observations of the Subaru Field
  • have been working on adapting and revising data reduction code for all GMRT data sets – developing partially automated flagging of data
future work
Future Work

rest 2005:

  • finish data reduction code
  • reduce Subaru data and publish results
  • reduce Cl0024+1652 data and publish results
  • Abell 370 spectroscopic observations  using AF2/WYFFOS 4.2mWilliam Herschel Telescope, La Palma (sometime in Oct to Dec) – for redshifts and star formation rate from [OII]
future work1
Future Work


  • beginning year finish reducing Abell 370 data and publish results
  • once published Subaru results may go back to GMRT TAC for another sample of field galaxies
  • other possibilities:

- obtain more redshifts for coadding particularly on the outskirts of the clusters

- stellar mass measurements using redshifts and additional near-infrared imaging

future work2
Future Work


  • first 6 months - finish write up thesis / finish off anything left over from previous years