Next Generation Very Large Array Model Repository

Introduction

This repository holds a set of standard models that have been used for science verification and array configuration testing for the Next Generation Very Large Array (ngVLA). The models are in FITS format. The surface brightness scales are in Jy/pixel -- appropriate as input to the CASA simulator to obtain visibility units in Jy. A detailed guide to ngVLA simulations in CASA can be found in:

https://casaguides.nrao.edu/index.php/Simulating_ngVLA_Data-CASA5.4.1

Following are a few notes on usage of these models, short summaries of the models, and links to references that have more detail in each case.

(i) The ngVLA configurations can be found in:

https://ngvla.nrao.edu/page/tools

Alternatively, these configuration files are included as part of CASA distributions 5.5 and greater. They can also be added to older versions of CASA by running the following command inside CASA to update CASA's data repository:

# In CASA
!update-data

The configuration files are stored inside CASA in a folder along with configuration files for other observatories. Since the path to this folder may depend on your operating system and CASA version, a convenient way to find the path to the configuration files is to run the following command inside CASA:

# In CASA
configdir = casa.values()[0]['data']+'/alma/simmos/'

(ii) Models vary significantly in source size and pixel scale. Make sure to use the appropriate configuration for the imaging test of interest.

(iii) The models are noiseless. Noise should be added to the visibilities as specified in the CASA guide.

If you need assistance in using these models, or if you would like advice on generating your own model, please consult the CASA guide, or contact the CASA help desk.

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Models in the Repository

1. CO velocity cube models for high redshift galaxies

A model to test imaging of CO emission using the PLAINS array.

Models for the velocity field of CO emission from a typical spiral galaxy, placed at various redshifts. The intrinsic model is based on the velocity field of the CO 1-0 emission from M51 presented in Helfer et al. (2003, ApJS, 145, 259), scaled in line luminosity, velocity width, and galaxy size to match the galaxy types given below.

M51.Z0.5.FITS: CO 1-0 at z = 0.5, Mgas = 0.8e10 (alpha/3.4) Mo

M51.Z2.FITS: CO 2-1 at z = 2.0, Mgas = 2.0e10 Mo

M51.Z4.2.FITS: CO 2-1 at z = 2.0, Mgas = 6.9e10 Mo

Reference: Imaging Molecular Gas at High Redshift, Carilli & Shao 2018, in ASP Vol 517: Science with the ngVLA, p. 535

http://aspbooks.org/a/volumes/article_details/?paper_id=38715

2. Imaging of CO Emission

SPIDERWEB.FITS: A model to test imaging of CO emission using the PLAINS array.

Velocity integrated CO 1-0 emission of an extreme starburst galaxy with very extended CO emission at z = 2.2. The model is based on a high resolution cosmological simulation of an extreme starburst (Narayanan D., et al., 2015, Nature, 525, 496), scaled in size and luminosity to match the CO emission seen in the Spiderweb radio galaxy at z = 2.1, with a molecular gas mass of 2e11 (alpha/3.4) M_o (Emonts B. et al., 2016, Science, 354, 1128)

Reference: The Molecular High-z Universe on Large Scales: Low-Surface-Brightness CO and the Strength of the ngVLA Core 2018, Emonts et al. in ASP Vol 517: Science with the ngVLA, p. 587

http://aspbooks.org/a/volumes/article_details/?paper_id=38748

3. Stellar Photospheres

A set of models of stellar radio photospheres used to test imaging of the FULL array.

The 38 GHz models of the red supergiant, Betelgeuse, is based on parameters derived from high resolution imaging with the VLA (Lim et al. 1998, Nature, 392, 575; O?Gorman et al. 2017, A & A, 602, L10). The models for the hot main sequence stars at 85 GHz, Sirius and Theta Leonis, are based on optical properities in the Hipparcos catalog (Perryman et al. 1997, A & A, 323, L49). For Betelgeuse and Sirius, both a uniform disk model, and a model with 10% surface brightness structures, on different scales ('spots'), is available.

BETEL38-UNIFORM.FITS: alpha Orionis (Betelgeuse), M1 Ia star at 222 pc at 38 GHz, uniform disk

BETEL-SPOTS38.FITS: alpha Orionis (Betelgeuse), M1 Ia star at 222 pc at 38 GHz, uniform disk

SIRIUS85.FITS: alpha Canis Majoris (Sirius), A0 star at 2.6 pc, 85 GHz, uniform disk

SIRIUS85-SPOTS.FITS: Same, but with +/- 10% brightness fluctuations.

THETLEO.FITS: Theta Leonis, A2 V star at 51 pc, 85 GHz

Reference: Imaging Stellar Radio Photospheres with the Next Generation Very Large Array, Carilli et al. in ASP Vol 517: Science with the ngVLA, p. 369

http://aspbooks.org/a/volumes/article_details/?paper_id=38696

4. High Fidelity Imaging

CYGXMOD2.FITS: A model developed to test high fidelity imaging for the MAIN array.

The model is based on the best 8 GHz VLA image, scaled to a smaller size, and clipped and blanked to remove off-source noise. The core was also removed and replaced with point source.

Reference: High Dynamic Range Imaging, Carilli 2019, ngVLA Memo 64

http://library.nrao.edu/public/memos/ngvla/NGVLA_64.pdf

5. Deep Field Imaging

EGSPS8.4.FITS: A model to test deep field imaging using the MAIN array.

The model is comprised of 6000 point sources over a 6arcmin field, derived using S-cubed radio sky simulator (Wilman et al. 2008 , MNRAS, 388, 1335), in a power law distribution, ranging from 100 nJy to 4 mJy (note: the brightest source was increased from 1 mJy to 4 mJy for more stringent dynamic range tests for ngVLA reference configuration tests).

Reference: Deep Fields at 8 GHz, Carilli et al. 2018, ngVLA memo 35

http://library.nrao.edu/public/memos/ngvla/NGVLA_35.pdf

6. Deep Imaging of Free-Free Emission

NGC5713.FFB.JY.PIX.FITS: A model to explore deep imaging of Free-Free emission from nearby galaxies using the CORE array.

The 30 GHz free-free model was derive from the H-alpha image of the star forming galaxy, NGC 5713, at a distance of 27 Mpc, with a native resolution of 2".

Reference: Project Overview, Carilli et al. 2015, ngVLA memo 5

http://library.nrao.edu/public/memos/ngvla/NGVLA_05.pdf

7. Proto-planetary Disks pp_model_3mm.fits:A model to explore imaging of planetary systems. The model is at 3 mm and the disk is at +24 Declination. Reference: Ricci, L., Isella, A., Liu, S., & Li, H. 2018, in Astronomical Society of the Pacific Conference Series, Vol. 517, Science with a Next Generation Very Large Array, ed. E. Murphy, 147.