DSA-2000

The Deep Synoptic Array 2000, or DSA-2000 is a large radio telescope currently under construction by the Owens Valley Radio Observatory, but located in Nevada USA. Its main goal is a sky survey, acting as a radio camera to produce an archive of images of the entire sky visible from that site. The completed array, scattered over an area of 19 x 15 km, will contain 2000 steerable 5 meter parabolic antennas that cover the 0.7 – 2 GHz frequency range. It is financed by Schmidt Sciences and expected to be operational in 2028.^[1][2] The DSA-110 was an earlier effort that demonstrated many of the needed technologies, but was not as general purpose and specialized in detecting and localizing fast radio bursts.^[3][4]

Technical advances

The DSA-2000 incorporates two main technical advances, both related to its architecture of a large number of small antennas. The first is that having a large number of randomly distributed antennas make it much easier to convert the radio signals into images. This strategy had never been practical before, however, since antennas sensitive enough for radio astronomy historically required cooling to very low temperatures, which made each antenna too expensive to build such a large array. So the second advance was a receiver, using modern semiconductor technology, that could achieve the needed sensitivity without cooling.

Easier imaging

Traditional radio telescope arrays have had a relatively small number of relatively large antennas (the VLA, for example, has 27 dishes of 25 meters diameter). This results in a hideous point spread function, which requires considerable post-processing to turn into useful images. In particular, additional non-linear constraints (such as positivity) must be assumed, both vastly complicating the aperture synthesis calculations and making them dependent on the particular assumptions used. In turn the need for complex processing requires huge data storage and transport requirements, as the raw data (or the visibilities, the correlations between pairs of antennas) need to be saved and delivered to the end user for later post-processing.

The DSA-2000, in comparison, will have near complete sampling of the uv-plane. This gives a native point spread function which is sufficiently good that much less complex algorithms can be used create images in real time, acting as a “radio camera”.

Ambient temperature receiver

Traditional radio telescope receivers have required cooling (often to cryogenic temperatures) to get low enough noise to be useful for astronomical observations. This typically resulted in a cost of at least $100,000 per receiver, making arrays with a large number of antennas impractical. However, recent developments in indium phosphide technology have resulted in transistors with a low enough noise figure at room temperature^[5] to remove the need for cooling.^[6] In addition, very low loss feeds and matching networks are required, since any losses in these components contribute directly to system noise in proportion to their physical temperature.

Uses and data products

Since the DSA-2000 digitizes the whole 0.7-2.0 GHz bandwidth, processing in software can simultaneously generate radio images at many different frequency resolutions for different purposes. These outputs of the radio camera are:

• 10 channels, intensity only, spanning the full bandwidth
• 605 channels (2.15 MHz resolution) with polarization data
• 2048 channels, intensity only, 1.05 kHz resolution, around the HI line of neutral hydrogen (1420 MHz). These images will allow the study of neutral hydrogen within our galaxy at a doppler resolution of 0.22 km/sec.
• 4096 channels, intensity only, 8 kHz resolution, again near the HI line. These images are for analysis of nearby galaxies (< 100 Mpc) with a doppler resolution of 1.8 km/sec.
• 5600 channels, 0.7-1.45 GHz, to be used for studying neutral hydrogen emission out to Z=1. Z=1 is the limit of this telescope, as beyond that redshift drops the neutral hydrogen frequency below the lower frequency limit of the telescope.

Although the main goal of DSA-2000 is a sky survey, it will pursue other projects as well. Operations other than radio imaging (such as pulsar timing and searches for transients) are possible as the signal processing is programmable since it is implemented in general purpose FPGAs and GPUs.

• 65% of the observing will be used for the sky survey. In a five-year initial survey, the DSA-2000 will image the entire sky (~31,000 deg²) viewable from the site 16 times over 5 years. These images will include both polarization and spectral information from 0.7 to 2 GHz. This survey is expected to increase the number of known radio sources by a factor of at least 100.
• 25% of time will be used to collect pulsar timing data, looking for nanoHertz gravitational waves in collaboration with the NANOGrav collaboration.
• 10% of the time will be used to conduct daily observations of select fields. These observations, in particular, will overlap with the deep fields of the Vera Rubin Observatory which will be doing optical observations at the same time, an example of multi-messenger astronomy.