AntennaeBand7 for CASA 3.3

Draft casaguide for the Antennae at Band 7

Science Target Overview

Fig. 1. HST image of Antennae (Credit: NASA, ESA, and the Hubble Heritage Team STScI/AURA)-ESA/Hubble Collaboration. Acknowledgement: B. Whitmore ( Space Telescope Science Institute) and James Long (ESA/Hubble).

Fig. 2. Caltech millimeter array CO(1-0) integrated intensity map from Wilson et al. (2000) overlaid on the true-color HST image from Whitmore et al. (1999).

The Antennae galaxy is a colliding galaxy pair located at a distance of 22 Mpc in the southern sky, composed of NGC 4038 (north) and NGC 4039 (south) (Figure 1). NGC 4038 is located at RA 12h 01m 53.0s, Dec −18° 52′ 10″; and NGC 4039 at RA 12h 01m 53.6s, Dec −18° 53′ 11″. The two spiral galaxies started to interact only a few hundred million years ago, therefore, Antennae galaxies is one of the nearest and youngest examples of two galaxies merging. The yellow bright components to the south-east and north-west of the image center seem to correspond to the nuclei of the original galaxies and are composed mostly of old stars. Filaments of dust, which appears brown in the image, are also apparent, and there are abundant blue star-forming regions surrounded by HII regions (appearing in the image in pink). The properties of the bulk of the molecular gas of Antennae galaxies was studied by Wilson et al. (2000), who conducted CO(1-0) observations using OVRO with resolutions of 3.15 x 4"91 (see Figure 2). Molecular emission is seen toward the two nuclei. An overlap region between the two galaxies is seen to have prominent CO emission, and is concentrated in five supergiant molecular complexes (SGMC). There is also a partial ring of molecular gas to the west of NGC 4038, but this structure is not covered by our observations.

ALMA Data Overview

The ALMA CO(3-2) data presented here is similar to the Submillimeter Array data presented in Ueda et al. 2011 (submitted). ALMA Science verification data on Antennae galaxies in Band 7 were taken in ten different datasets over several nights in May and June 2011, in order to get good uv-coverage. The datasets are listed next, classified as observations for the northern -NGC4038- and southern components -NGC4039- of Antennae.

NGC 4038 (Northern mosaic)

• uid://A002/X1ff7b0/Xb
• uid://A002/X207fe4/X3a
• uid://A002/X207fe4/X3b9
• uid://A002/X2181fb/X49

NGC 4039 (Southern mosaic)

• uid://A002/X1ff7b0/X1c8
• uid://A002/X207fe4/X1f7
• uid://A002/X207fe4/X4d7
• uid://A002/X215db8/X1d5
• uid://A002/X215db8/X392
• uid://A002/X215db8/X18

These Band 7 observations utilized two basebands, which are associated with two different spectral windows: one in the Upper Sideband (USB) and one in the Lower Sideband (LSB). The first spectral window is centered on the CO(3-2) emission line in the galaxy Antenna. The additional spectral window in the USB is used to measure the continuum emission in the galaxy and may contain other emission lines as well. Each spectral window has a total bandwidth of 2 GHz divided over 3840 channels (FDM mode), for a channel width of 488.28 MHz, corresponding to 1634 km/s and 0.426 km/s respectively. For the antenna configuration that was used during these observations (similar to extended configuration in cycle 0), the angular resolution is expected to be about 1".

We acknowledge Junko Ueda for suggesting these observations of Antennae galaxies for ALMA Science Verification.

Obtaining the Data

To download the data, click on the region closest to your location:

North America Europe East Asia

Here you will find three gzipped tar files which, after unpacking, will create three directories:

• Antennae_Band7_UnCalibratedMSandTablesForReduction - Here we provide you with "starter" datasets, where we have taken the raw data in ALMA Science Data Model (ASDM) format and converted them to CASA Measurement Sets (MS). We did this using the importasdm task in CASA. Along with the raw data, we also provide some tables that you will need for the calibration which cannot currently be generated inside of CASA. (This functionality will be available in CASA for Early Science.)

• Antennae_Band7_CalibratedData - The fully-calibrated uvdata, ready for imaging and self-calibration

• Antennae_Band7_ReferenceImages - The final continuum and spectral line images

To see which files you will need, read on below. The downloads to your local computer will take some time, so you may wish to begin them now.

NOTE: CASA 3.2.1 or later is required to follow this guide. For more information on obtaining the latest version of CASA, see http://casa.nrao.edu.

Antennae Band 7 Data Reduction Tutorial

In this tutorial, or "casaguide", we will guide you step-by-step through the reduction of the ALMA science verification data on the Antennae galaxies and its subsequent imaging. This casaguide consists of two parts:

1) Antennae Band7 - Calibration

2) Antennae Band7 - Imaging

To complete the Calibration section of the tutorial, you will need the data in the first directory: Antennae_Band7_UnCalibratedMSandTablesForReduction. For those wishing to skip the calibration section and proceed to Imaging, we also provide the fully-calibrated data in the Antennae_Band7_CalibratedData directory. Finally, we provide the final continuum and spectral line images in the Antennae_Band7_ReferenceImages directory.

NOTE: These guides are dynamic and will evolve as our understanding of how best to reduce ALMA data improves. Check back for updates periodically.

For a similar tutorial on the reduction of ALMA Band 7 data on TW Hydra, and Band 3 on NGC 3256, see the casaguide TWHydraBand7 and NGC3256Band3.

How to use this casaguide

For both portions of the guide, we will provide you with the full CASA commands needed to carry out each step.

# In CASA
The commands you need to execute 
will be displayed in regions 
like this.

Simply copy and paste the commands in order into your CASA terminal. You may also type the commands in by hand if desired, but be mindful of typos. Note that you may need to hit Enter twice in order for the process to start running. Also note that copying and pasting multiple commands at a time may not work, so only copy and paste the contents of one region at a time.

To learn how to extract the CASA commands into an executable python script, click here.

Occasionally we will also show output to the CASA logger:

This output will be displayed 
in regions like this.

Other relevant information will be presented as follows:

This color shows you background information about the data or other types of reference material

For a brief introduction to the different ways CASA can be run, see the EVLA_Spectral_Line_Calibration_IRC+10216#How_to_Use_This_casaguide page. For further help getting started with CASA, see Getting_Started_in_CASA.

Daniel Espada 12:00 UT, 21 July 2011