WALLABY pre-pilot survey: Radio continuum properties of the Eridanus supergroup

Abstract

We present the highest resolution and sensitivity $\sim$ $1.4\,$ GHz continuum observations of the Eridanus supergroup obtained as a part of the Widefield Australian Square Kilometer Array Pathfinder (ASKAP) L-band Legacy All-sky Blind surveY (WALLABY) pre-pilot observations using the ASKAP. We detect 9461 sources at 1.37 GHz down to a flux density limit of $\sim$ $0.1$ mJy at $6.1''\times 7.9''$ resolution with a median root mean square of 0.05 mJy beam $^{-1}$ . We find that the flux scale is accurate to within 5 % (compared to NVSS at 1.4 GHz). We then determine the global properties of eight Eridanus supergroup members, which are detected in both radio continuum and neutral hydrogen (HI) emission, and find that the radio-derived star formation rates (SFRs) agree well with previous literature. Using our global and resolved radio continuum properties of the nearby Eridanus galaxies, we measure and extend the infrared-radio correlation (IRRC) to lower stellar masses and inferred SFRs than before. We find the resolved IRRC to be useful for: (1) discriminating between active galactic nuclei and star-forming galaxies; (2) identifying background radio sources; and (3) tracing the effects of group environment pre-processing in NGC 1385. We find evidence for tidal interactions and ram-pressure stripping in the HI, resolved spectral index and IRRC morphologies of NGC 1385. There appears to be a spatial coincidence (in projection) of double-lobed radio jets with the central HI hole of NGC 1367. The destruction of polycyclic aromatic hydrocarbons by merger-induced shocks may be driving the observed WISE W3 deficit observed in NGC 1359. Our results suggest that resolved radio continuum and IRRC studies are excellent tracers of the physical processes that drive galaxy evolution and will be possible on larger sample of sources with upcoming ASKAP radio continuum surveys.

H i, FRB, What’s Your z: The First FRB Host Galaxy Redshift from Radio Observations

“…yr −1 . We note that we are using a radio flux density measured between 1304 and 1420 MHz rather than at 1400 MHz as inMolnár et al (2021), butGrundy et al (2023) found that their unresolved 1.3675 GHz radio continuum fluxes were consistent with 1.4 GHz measurements within the scatter. The Wide-field Infrared Survey Explorer (WISE) colors of (W1 − W2) = 0.286 ± 0.075 and (W2 − W3) = 4.107 ± 0.092 suggest that the host of FRB 20230718A…”

“…An unresolved radio continuum source with a flux density of 0.97 mJy (from 1304 to 1420 MHz) is associated with the FRB and H I emission at ∼5σ significance. Assuming this radio continuum is entirely due to star formation, we use the method described in Grundy et al (2023;their Equations (9) and (10)), which applied the methodology of Molnár et al (2021) to galaxies detected in radio continuum at 1.3675 GHz to estimate the total global star formation rate (SFR). For the FRB host we find the SFR to be 1, for the two lower-resolution cubes.…”

The Rapid ASKAP Continuum Survey V: Cataloguing the sky at 1 367.5 MHz and the second data release of RACS-mid

“…We also perform a similar variable-separation cross-match to the WALLABY pre-pilot catalogue (Grundy et al 2023) using the primary RACS-mid catalogue. For this cross-match, we first extract a cut-out of the RACS-mid primary catalogue that covers the same image region of the WALLABY pre-pilot mosaic.…”

“…For direct comparisons of flux density measurements and astrometry we look to the NVSS (Condon et al 1998) at 1.4 GHz, FIRST (Becker et al 1995;White et al 1997;Helfand et al 2015), and the 42-deg 2 region of the WALLABY pre-pilot catalogue (Grundy et al 2023). FIRST is catalogued at both the same frequency as NVSS (for data prior to 2011) and at 1 335 MHz (for data from 2011).…”

“…While WALLABY is primarily a spectral line survey, the 10-h observations and subsequent imaging also result in deep 1 367.5-MHz continuum images. Currently prepilot observations of the Eridanus supergroup (For et al 2021) have been utilised to create an initial WALLABY continuum catalogue (hereinafter the WALLABY prepilot catalogue; Grundy et al 2023) containing 9 416 sources covering ∼42 deg 2 .…”