ASKAP H i imaging of the galaxy group IC 1459

Abstract

We present H I imaging of the galaxy group IC 1459 carried out with six antennas of the Australian Square Kilometre Array Pathfinder equipped with phased-array feeds. We detect and resolve H I in 11 galaxies down to a column density of ∼10 20 cm −2 inside a ∼6 deg 2 field and with a resolution of ∼1 arcmin on the sky and ∼8 km s −1 in velocity. We present H I images, velocity fields and integrated spectra of all detections, and highlight the discovery of three H I clouds-two in the proximity of the galaxy IC 5270 and one close to NGC 7418. Each cloud has an H I mass of ∼10 9 M and accounts for ∼15 per cent of the H I associated with its host galaxy. Available images at ultraviolet, optical and infrared wavelengths do not reveal any clear stellar counterpart of any of the clouds, suggesting that they are not gas-rich dwarf neighbours of IC 5270 and NGC 7418. Using Parkes data, we find evidence of additional extended, low-column-density H I emission around IC 5270, indicating that the clouds are the tip of the iceberg of a larger system of gas surrounding this galaxy. This result adds to the body of evidence on the presence of intragroup gas within the IC 1459 group. Altogether, the H I found outside galaxies in this group amounts to several times 10 9 M , at least 10 per cent of the H I contained inside galaxies. This suggests a substantial flow of gas in and out of galaxies during the several billion years of the group's evolution.

H i debris in the IC 1459 galaxy group

“…The cloud properties, as measured from the presented ATCA H i data, are summarised in Table 4. These H i clouds are in addition to those discovered in ASKAP H i data of the IC 1459 galaxy group by Serra et al (2015) near the spiral galaxies IC 5270 and NGC 7418, both of which lie outside the area observed here. The lowest contour in Fig.…”

“…The detected H i debris near IC 1459 together with H i clouds near IC 5270 (∼2100 km s −1 ) and NGC 7418 (∼1450 km s −1 ), as identified by Serra et al (2015), make up a significant fraction of the groups' cold interstellar medium. The total amount of H i mass contained in clouds (7.2×10 8 M ) is almost 6 times the H i content of IC 5264 (1.2×10 8 M ).…”

“…4). High-resolution ASKAP H i maps of the galaxies, which are discussed below, are also shown by Serra et al (2015).…”

“…IC 1459 is an early-type galaxy located in the centre of a loose group at an approximate distance of 29 Mpc Tonry et al 2001); here we adopt this distance for the whole group (see also Serra et al 2015). The IC 1459 galaxy group contains ten bright galaxies, mostly of latetype morphology, (Brough et al 2006;Kilborn et al 2009), which form part of the larger-scale Grus cluster (Aaronson et al 1981;Huchra & Geller 1982).…”

“…This group was recently observed by Serra et al (2015) using the first six PAF-equipped antennas of the Australian Square Kilometre Array Pathfinder 1 (Hotan et al 2014, ASKAP). The wide-field ASKAP H i data, initially obtained with nine ∼1 deg PAF beams, resulted in the detection of 11 galaxies and three H i clouds, two in the proximity of the edge-on spiral galaxy IC 5270 and one close to the spiral galaxy NGC 7418 (Serra et al 2015). Here we explore the area around IC 1459 using single-beam Australia Telescope Compact Array (ATCA) archival H i data.…”