estimating galaxy hi mass from optical properties

Estimating galaxy HI mass from optical properties

The Wallaby HI catalogue prediction…

WALLABY Science Meeting, Dec 2010

Virginia Kilborn Swinburne University

Aims of project

•  To investigate the relationship between optical galaxy parameters and HI mass

•  To calculate the expected HI mass of a large a Southern Sky optical redshift survey (e.g. 6dF)

•  Apply the WALLABY observing parameters to this sample create an “expected” WALLABY catalogue

•  Use this for science such as investigating the effect of environment


Galaxies come in all shapes and sizes (and colours)…


… which of these parameters can we use to predict HI content?

Determining HI mass of galaxies: Morphology and optical extent

•  The HI mass of a late-type galaxy correlates quite well with its morphology, and optical extent (e.g. Haynes & Giovanelli 1984; Kilborn, Koribalski et al 2005)

•  Need to be careful when using such relationships – ie which radius to use? Corrections for dust extinction, inclination, etc.


Haynes & Giovanelli 1984

Determining HI mass of galaxies: Morphology and optical magnitudes


HI mass correlates less well with morphology and B-band colour …but sometimes it makes more sense to use optical colours rather than diameters – e.g. in compact groups (Verdes-Montenegro et al.

HIPASS HI mass relations •  My summer student Andrew Butler (Swinburne) is

working on this project in Nov/Dec 2010

•  First task – using HOPCAT, and the HI mass relations in HIPASS, check the relationships from the BGC

•  Then – find a suitable optical catalogue to apply these relationships


HI mass vs d25(opt) for HIPASS


•  Over 110,000 galaxies with redshifts


Over 110,000 galaxies with redshifts in the 6dFGS catalogue – can we harness this optical information to make a prediction on what we will detect with WALLABY?

6dFGS data products

•  6dFGS comes with an array of measurements on the catalogued galaxies: – B and R-mag, 2MASS mags (j,h,k), total

radius (from 2MASS), redshift –  Ideally, we want to use only a combination of

the above parameters to estimate the HI masses of the galaxies in the catalogue

– We can test how well we are predicting the HI masses using existing data such as HIPASS


Constructing the HI catalogue

•  Once we have the predicted HI masses for the galaxies, we can apply the WALLABY observing parameters, and predict which galaxies we will detect with WALLABY.

•  What will we miss ? –  Obviously, anything not in the optical catalogue to begin

with, including: •  Low surface brightness galaxies •  Extra-galactic HI (clouds, streams, dark galaxies?) •  Galaxies in areas of high optical extinction (e.g. in the Galactic

plane) •  WALLABY is a synthesis array – we may not detect all the

emission in the resolved nearby galaxies –  We can learn from the HIPASS example – how many

galaxies do we expect to miss?


Other predictions •  How many (and which) galaxies will be resolved in

WALLABY? – Use a optical diameter/HI diameter relationship to

predict which galaxies will be resolved(?) •  This helps with planning for the survey

•  Find out difficulties in the optical data early-on •  Allow for early science – we will already have an idea

of what to expect in each WALLABY cube –  But, the WALLABY cubes won’t be the same as the

predicted catalogue… what can this tell us?


Global HI deficiency map

The WALLABY predicted HI catalogue can be used to make a global HI deficiency map of the Southern sky

Def(HI) = MHI(pred) – MHI(obs))

This provides an indication of the effect of environment on the HI content of galaxies


1985

Composite HI def map for clusters

Effect of environment on HI content of galaxies


Southern sky global HI deficiency from HIPASS

Preparation for WALLABY: SkyMapper

•  Ideally, the methods employed to 6dF catalogue will be applied to Skymapper data…

–  What will the data products be for the southern sky survey?

–  For e.g. will we obtain redshifts for the galaxies?


Challenges for the future

•  Homogeneous data set •  Morphological classification (needed?) •  Colour corrections for extinction, inclination

etc. •  Diameter measurements ? •  Redshifts/distances

•  However – the relationships can be refined as more data is added…


Northern WALLABY advertisement: WNSHS

•  Northern sky HI survey using Apertif on WSRT

•  EOI submitted, PI Josza, other co-I’s Kilborn, Koribalksi, Staveley-Smith, Oosterloo, Serra

•  Full proposal submission April/May next year, working groups are being formed now.

•  New team members are welcome to join (and help with the proposal!)

www.astron.nl/~jozsa/wnshs


estimating galaxy hi mass from optical properties

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