A VLA Search for Radio Signals from M31 and M33

Abstract

Observing nearby galaxies would facilitate the search for artificial radio signals by sampling many billions of stars simultaneously, but few efforts have been made to exploit this opportunity. An added attraction is that the Milky Way is the second-largest member of the Local Group, so our galaxy might be a probable target for hypothetical broadcasters in nearby galaxies. We present the first relatively high spectral resolution (<1 kHz) 21-cm band search for intelligent radio signals of complete galaxies in the Local Group with the Jansky VLA, observing the galaxies M31 (Andromeda) and M33 (Triangulum)-the first and third largest members of the group respectively-sampling more stars than any prior search of this kind. We used 122 Hz channels over a 1 MHz spectral window in the target galaxy velocity frame of reference, and 15 Hz channels over a 125 kHz window in our local standard of rest. No narrowband signals were detected above a signal-tonoise ratio of 7, suggesting the absence of continuous narrowband flux greater than approximately 0.24 Jy and 1.33 Jy in the respective spectral windows illuminating our part of the Milky Way during our observations in December 2014 and January 2015. This is also the first study in which the upgraded VLA has been used for SETI.

The Breakthrough Listen Search for Intelligent Life: 1.1–1.9 GHz Observations of 692 Nearby Stars

“…L AO is the EIRP of the Arecibo Planetary Radar at 10 13 W. To visualize the previously compared surveys vis-a-vis the CWTFM, in Figure 7, we plot each survey's EIRP versus n -( ) N stars rel 1 , we call the later the Transmitter Rate. As shown in Figure 7, this work provides the most stringent limit on low power radio transmitters around nearby stars, while the work from Gray & Mooley (2017) does the same for the high power transmitters associated with nearby galaxies. This suggests that by using these two results together we can put a joint constraint on a luminosity function of artificial transmitters.…”

“…These future surveys will provide increasingly strong statistical constraints on the space density of technologically advanced civilizations in the Milky Way, if not resulting in a detection of advanced extraterrestrial life. Observations of hundreds of galaxies could potentially provide estimates for the occurrence rate of the most Gray & Mooley (2017) by using Equation (12). The points labeled "All," show the total for a given project, this value is calculated by the sum of Transmitter Rates and taking the largest EIRP.…”

“…We assume an isotropic transmitter with = G 1 ant , and thus = P tx EIRP. Fitting between this work and Gray & Mooley (2017) results in a » 0.74 (indicated in Figure 7), showing the transmitter occurrence space ruled out by this constraint. As a point of comparison, a fit to the EIRP of the strongest terrestrial radars shows a roughly power-law distribution with a » 0.5 (Shostak 2000, and references there in).…”

“…The potential spectral similarity between anthropogenic radio-frequency interference (RFI) and extraterrestrial technological transmissions brings additional complications. The sheer immensity of the parameter space that must be explored is a potential explanation to the absence of radio detections of extraterrestrial intelligence, despite numerous previous efforts (Verschuur 1973;Tarter et al 1980;Bowyer et al 1983Bowyer et al , 1995Horowitz et al 1986;Steffes & Deboer 1994;Mauersberger et al 1996;Backus 1998;Werthimer et al 2000;Korpela et al 2011;Siemion et al 2013;Harp et al 2016;Gray & Mooley 2017).…”

A Search for Technosignatures from 14 Planetary Systems in the Kepler Field with the Green Bank Telescope at 1.15–1.73 GHz

“…In these units, we find DFM;2×10 6 . Referring to the values provided in Enriquez et al (2017), our search is about 150 times larger than that of Horowitz & Sagan (1993) and 10 times larger than that of Gray & Mooley (2017). It amounts to about 2% and 12% of the recent large surveys by Enriquez et al (2017) and Harp et al (2016), respectively.…”