Road Map Cycle 2

What is ALMA?

ALMA is an interferometer of 50 x 12 m antennas (the 12-m Array), 12 x 7 m antennas (the 7-m Array) and 4 x 12 m Total Power antennas (the TP Array) located at an altitude of 5000 m in northern Chile. It operates in the submillimeter/mm range, from 3.6 mm to 420 µm (84 - 720 GHz).

ALMA is operated by the Joint ALMA Observatory in Chile. The interface between the ALMA observatory and the astronomical community is provided by the three ALMA Regional Centers (ARCs).

An overview of the ALMA observatory, instrument and science goals can be found here.

The ALMA Proposer's Guide

An introductory ALMA Primer for those new to ALMA & interferometry.

The Observing Tool is used to prepare your proposal.

Technical aspects of ALMA operations: the Technical Handbook.

The ALMA Science Portal is the entry to the ALMA web.

The overview guides to the ARCs.

ALMA Science Capability

ALMA excels at observing the cool Universe, including dust at temperatures from a few degrees about absolute zero to ~200 deg K, and an extraordinary wealth of molecular and atomic lines, some probing regions of even higher temperatures.

The primary science drivers for ALMA are our cosmic origins: the formation and evolution of galaxies, stars and planets as well as the origin of the elements, complex molecules and of the organic building blocks of life itself.

ALMA can observe environments from Solar System interplanetary dust to CO and [CII] lines in quasar hosts at z>6.

ALMA can achieve angular resolutions as small as 0.08" in Cycle 2, and spectral resolution as high as 0.02 km/s.

Some examples:

– ALMA can detect continuum emission from typical submillimeter galaxies (SMGs) at z~2–3 at 870 µm in under a minute on source.

– In Cycle 2, ALMA will be able to image a large part of a galaxy in the Virgo Cluster (d~15 Mpc) with an angular resolution (50 pc) and sensitivity to see individual Orion-like clouds in CO in less than an hour on source.

ALMA's capabilities are growing with time. The current ALMA capabilities and limitations can be found in the Proposer's Guide.

The ALMA Cycle 2 Capabilities.

The ALMA Primer gives some introductory ideas to ALMA science opportunities.

Examples of ALMA science themes and highlights can be found here.

Some of ALMA's science capabilities are illustrated here.

Developing a Research Program with ALMA

Before investing a lot of time in preparation of a proposal you can get a sense of whether the Cycle 2 ALMA capabilities are appropriate for your goals.

In brief: for Cycle 2 observations will be available in Bands 3, 4, 6, 7, 8, and 9. The maximum baselines will be about 1.5 km in the 4 lower frequency bands and 1.0 km for Bands 8 & 9. Polarization is a new capability offered in Cycle 2, for on-axis observations only and with a limited set of modes.

Key elements you should consider before developing a proposal:

What rms sensitivity is required to achieve your science?

What angular and spectral resolution do you need?

What are the size scales of the sources of interest to you?

Depending on the configuration ALMA may resolve (or filter) out the larger angular scales of emission in extended sources

What is the total area you wish to map? Will you need a mosaic to achieve your goals?

Do you need to observe the polarization structure of your source?

What elevation will your sources have at the ALMA site?

An overview of all of these parameters is provided in the ALMA Primer, Chap 4.

A detailed explanation of each of these parameters is given in Chapters 5 & 7 of the ALMA Technical Handbook.

The size scales of interest in your source will govern your observational setup. A useful short (4 minute) video on this topic is available here.

Your experiment will depend on the assumed water vapour column density, which is frequency and elevation-dependent. See, for example, Figure 6 in the ALMA Primer.

The ALMA Sensitivity Calculator (ASC) will help you with this step.

In radio astronomy, source fluxes are generally expressed in terms of flux density using Jansky (Jy) units, or brightness temperature, T_b, in Kelvin.

Line fluxes are generally expressed in terms of velocity-integrated flux, S, in units of Jy km/s, or in intensity, I, in units of K km/s

Chapter 9 of the ALMA Technical Handbook explains the operation of the ASC.

You may need to decide whether to setup your experiment in terms of T_b or flux density.

Formulae for deriving expected line fluxes can be found in Solomon & Vanden Bout, 2005, Annual Review of Astronomy and Astrophysics (ARAA), 43, 677, section 2.

Spectral lines and their frequencies can be researched using the spectral line database Splatalogue, which is also available from within the OT.

An overview of Splatalogue is available here.

If you would like to learn more about the wealth of molecular lines that have been observed to date (interstellar sugar anyone?) check out this link.

Since interferometric observations must be Fourier transformed before an image can be made, it is sometime not intuitive to visualize what your images will look like.

Simulation tools you can use to directly simulate your images include the CASA simulator tool "simalma", and ALMA images can also be simulated with the ALMA Observation Support Tool (OST).

The CASA simulator allows the most detailed experimentation with observing setups.

The web-based ALMA OST (Observer's Simulation Tool) makes simple simulated images.

These example simulations may be sufficient for your purposes without  having to perform your own simulations.

The ALMA 12-m Array can be configured into several sizes, from 150 m in the most compact configuration up to 16 km in the most extended configuration when fully constructed. These numbers refer to the longest distance (or baseline) between any two antennas in the array.

The length of the longest baselines governs the smallest angular resolution you will get in your image.

The length of the shortest baselines governs the Maximum Recoverable Scale (MRS) that the 12m Array will detect. The Largest Angular Structure (LAS) of interest in your source must be smaller than the MRS of the 12-m Array configuration in order for your image to contain all the emission of interest.

It is very important not to confuse LAS with target size. The 12m Array will not be sensitive to emission larger than the MRS: it will spatially filter out that emission, leaving holes (sometimes called bowls) on scales larger than the MRS. This is true even if you make a mosaic that covers a larger target size than the MRS.

In the Observing Tool, do not select "Point Source" in the Control and Performance panel unless you don't care which configuration is used for your observations.

If you expect there may be slightly extended emission select "Extended Source" and choose a small MRS, but larger than your LAS.

LAS and MRS are explained and illustrated in the ALMA Primer, and a useful short video.

The ALMA Technical Handbook Chapter 7 provides full descriptions of interferometric imaging.

The 7-m Array and the Total Power Array together make up the Atacama Compact Array (ACA), also know as the Morita Array. Depending on range of angular scales important for your science, you may need the complete ACA, or just the 7-m Array. The OT will recommend whether the ACA is needed, based on the requested resolution and anticipated angular size (Largest Angular Structure – LAS) of your target.

Note that any proposal decisions against the OT recommendation need to be clearly justified in the technical justification.

The conditions describing the need for ACA are described in the ALMA Primer and the ALMA Technical Handbook, Chapter 7.

Details of how the ACA time will be allocated are provided in the Proposer's Guide, Section 5.2.

Proposal Preparation (Phase 1)

Investigators must use the software package, the ALMA Observing Tool (OT), to prepare and submit their proposals.

To prepare and submit an ALMA proposal, the Principal Investigator and all co-Investigators must be registered ALMA users. The registration tab can be found at the top banner of this page.

ALMA proposals are grouped into one of the following categories::

Cosmology and the High Redshift Universe

Circumstellar disks, exoplanets and the solar system.

Galaxies and Galactic Nuclei

Stellar Evolution and the Sun

ISM, star formation and astrochemistry

Proposal preparation involves development of the Scientific Justification, optimizing the observational parameters in the OT, and providing a Technical Justification within the OT

Proposals are subject to peer review for scientific value, and to expert assessment for technical feasibility.

The OT Phase 1 Quickstart Guide will give you a high level overview to using the OT.

OT Video tutorials: a General Overview, and 10 Easy Steps to Creating a Proposal.

The OT User Manual will give you a more in-depth guide to the OT, including installation instructions in Chapter 2, and OT basic concepts in Chapter 3.

The ALMA Technical Handbook gives complete explanations of how ALMA operates.

The ALMA proposal review process is described in the Proposer's Guide, Section 7.

The Scientific Justification is a free format document which is uploaded as a pdf into the OT. It is recommended you use the provided Proposal Template to ensure you include all required aspects of your proposal

The guidelines for writing your Scientific Justification are given in the Proposer's Guide, Section 6.3.

Proposal preparation consists of setting up one or more Science Goals (SG) using the Observing tool (OT). The Science Goal contains the complete observational setups: spatial coordinates and imaging characteristics, frequency band, spectral windows and spectral resolutions, sensitivity requirements and integration time for one or more science targets.

ALMA will later use the Science Goals to build one or more Scheduling Blocks (SBs), which provide the controlling inputs for the telescope control, which is the reason the Science Goals must have strict limitations.

Scheduling Blocks and Science Goals are described in OT Quickstart Guide and the OT User Manual

A more detailed explanation of the way that ALMA observations are set up can be found in the Technical Handbook, Chapter 8.

The detailed guidance and limitations for ALMA proposals are in the Proposer's Guide

The Observation mode for each science goal depends on the expected structure and distribution of your targets.

A number of unresolved, but widely separated targets (but within ~10 deg) are best observed with Individual Pointings.

Targets which are larger than 1/3 of the Field of View (FOV) of the 12-m Array will require a Nyquist sampled Rectangular Mosaic to obtain uniform sensitivity across the field due to the sensitivity roll off towards the edges of the primary beam.

Targets which contain size scales which are larger than the Maximum Recoverable Scale (MRS) of the most compact configuration of the 12-m Array will also require ACA observations; either the 7-m Array alone, or the entire ACA

ALMA operations will automatically select the array configuration that will deliver your required resolution - thus you will not choose the configuration; instead you specify the angular resolution you need, and the Largest Angular Structure (LAS) expected for your targets.

If you have targets spread further afield than ~10 degrees, use additional Science Goals to include them

Refer to this OT video and OT User Manual sect. 5.3.2 to explain field setup.

LAS, MRS and spatial filtering are explained and illustrated in the ALMA Primer, and also in a short video.

Scheduling Block design and calibration requirements are described in the ALMA Technical Handbook Chapters 8 & 10.

The ALMA Technical Handbook Chapters 6 & 7 provide full descriptions of interferometric observing and imaging.

Three doppler corrections types can be selected, depending on the source velocity. Two approximations to the true relativistic velocity are generally used: radio velocities for Galactic targets and optical velocities for extragalactic observations.

Radio velocities become inaccurate at large redshifts. A summary of velocity systems and frames is available here.

The OT can set up standard baseband and spectral window (spw) frequencies for continuum observations, avoiding parts of the spectrum with high atmospheric opacity.

Spectral lines and their frequencies can be selected from Splatalogue, which is available standalone, and also from within the OT, for plotting on your graphical spectral setup display

Mixed mode spectral observations, using different spectral resolutions in each spectral window are possible in Cycle 2

Spectral scans are available in Cycle 2, benefitting redshift or chemical surveys, for example.

Details of spectral window and baseband set up are given in the ALMA Technical Handbook, Chapter 5.

See also Section 5.3.3 of the OT User Manual for more spectral-setup information

The OT video has step-by-step assistance with spectral setups.

If you cannot fit all of the lines you want to observe for every source in your Science Goal, consider splitting them into two or more SGs.

Integration times are calculated for the first line in a nominated spectral window. Ensure your estimated integration time is appropriate for other target spectral windows that might have a higher opacity

Each Science Goal requires an accompanying Technical Justification. This allows the Technical Assessors to confirm the technical feasibility of your experiment.

The Technical Justification is a form within the OT where you must justify the observational setup, as well as non-standard requests.

Any item that requires written justification will be highlighted for you when you 'validate' the proposal in the OT. This arrangement is different to that of Cycles 0 and 1, where the justification was included in the proposal document.

The Technical Justification (see Sect 6.3 in the Proposer's Guide) simply determines if your ALMA proposal is capable of meeting the stated science goals, in terms of e.g. resolution, uv coverage and frequency access. More information is available in the ALMA Primer.

What if I need assistance from an Expert?

You can ask questions via the ALMA Helpdesk, which also has a public KnowledgeBase containing many articles that address common questions.

You can attend a Workshop, Webinar or Community Day Event if your local ARC hosts one or more of these learning opportunities. You can also plan a visit to your local ARC or ARC node for assistance.

The KnowledgeBase is accessible without registration.

For Helpdesk questions, register here.

The ARC Guides and ARC web sites will help you with visit and training event planning