Estimating galaxy HI mass from optical properties

Transcription

1 Estimating galaxy HI mass from optical properties The Wallaby HI catalogue prediction Virginia Kilborn Swinburne University

2 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

3 Galaxies come in all shapes and sizes (and colours) which of these parameters can we use to predict HI content?

4 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

5 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.

6 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

7 HI mass vs d 25 (opt) for HIPASS

8 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? Over 110,000 galaxies with redshifts

9 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

10 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?

11 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?

12 Global HI deficiency map The WALLABY predicted HI catalogue can be used to make a global HI deficiency map of the Southern sky 1985 Def(HI) = M HI (pred) M HI (obs)) This provides an indication of the effect of environment on the HI content of galaxies Composite HI def map for clusters

13 Effect of environment on HI content of galaxies Southern sky global HI deficiency from HIPASS

14 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?

15 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

16 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!)