The frequency and properties of young tidal dwarf galaxies in nearby gas-rich groups

We present high-resolution Giant Metrewave Radio Telescope (GMRT) HI observations and deep Canada-France-Hawaii Telescope (CFHT) optical imaging of two galaxy groups: NGC 4725/47 and NGC 3166/9. These data are part of a multi-wavelength unbiased survey of the gas-rich dwarf galaxy populations in three nearby interacting galaxy groups. The NGC 4725/47 group hosts two tidal knots and one dIrr. Both tidal knots are located within a prominent HI tidal tail, appear to have sufficient mass (M_gas~10^8 M_sol) to evolve into long-lived tidal dwarf galaxies (TDGs) and are fairly young in age. The NGC 3166/9 group contains a TDG candidate, AGC 208457, at least three dIrrs and four HI knots. Deep CFHT imaging confirms that the optical component of AGC 208457 is bluer -- with a 0.28 mag g-r colour -- and a few Gyr younger than its purported parent galaxies. Combining the results for these groups with those from the NGC 871/6/7 group reported earlier, we find that the HI properties, estimated stellar ages and baryonic content of the gas-rich dwarfs clearly distinguish tidal features from their classical counterparts. We optimistically identify four potentially long-lived tidal objects associated to three separate pairs of interacting galaxies, implying that TDGs are not readily produced during interaction events as suggested by some recent simulations. The tidal objects examined in this survey also appear to have a wider variety of properties than TDGs of similar mass formed in current simulations of interacting galaxies, which could be the result of pre- or post-formation environmental influences.Comment: 18 pages, 14 figures, accepted for publication in MNRA

Pre-existing dwarfs, tidal knots and a tidal dwarf galaxy: an unbiased H_I study of the gas-rich interacting galaxy group NGC 3166/9

We present Arecibo Legacy Fast ALFA (ALFALFA) and follow-up Giant Metrewave Radio Telescope (GMRT) H _I observations of the gas-rich interacting group NGC 3166/9. The sensitive ALFALFA data provide a complete census of H _I-bearing systems in the group while the high-resolution GMRT data elucidate their origin, enabling one of the first unbiased physical studies of gas-rich dwarf companions and the subsequent identification of second-generation, tidal dwarf galaxies in a nearby group. The ALFALFA maps reveal an extended H _I envelope around the NGC 3166/9 group core, which we mosaic at higher resolution using six GMRT pointings spanning ∼1 deg^2. A thorough search of the GMRT data cube reveals eight low-mass objects with gas masses ranging from 4 × 10^7 to 3 × 10^8 M_⊙ and total dynamical masses up to 1.4 × 10^9 M_⊙. A comparison of the H I fluxes measured from the GMRT data to those measured in the ALFALFA data suggests that a significant fraction (∼60 per cent) of the H _I is smoothly distributed on scales greater than 1 arcmin (∼7 kpc at the NGC 3166/9 distance). We compute stellar masses and star formation rates for the eight low-mass GMRT detections, using ancillary Sloan Digital Sky Survey (SDSS) and Galaxy Evolution Explorer (GALEX) data, and use these values to constrain their origin. Most of the detections are likely to be either pre-existing dwarf irregular galaxies or short-lived, tidally formed knots; however, one candidate, AGC 208457, is clearly associated with a tidal tail extending below NGC 3166, exhibits a dynamical to gas mass ratio close to unity and has a stellar content and star formation rate that are broadly consistent with both simulated as well as candidate tidal dwarf galaxies from the literature. Our observations therefore strongly suggest that AGC 208457 is a tidal dwarf galaxy

Current Meter Observations in the Old Bahama Channel

Current meter observations were made at 50, 250, and 435 m in 495 m of water at the center of the Old Bahama Channel between November 1990 and November 1991. The mean speed at those depths was 2.6, 50, and 26 cm s-1 toward the Straits of Florida. A maximum speed of 193 cm s-1 was found at the 250-m level. There was evidence of a speed maximum between 50 and 250 m. Large internal diurnal tidal currents were observed that produced high shears in the water column under some conditions. Transport calculated from the single mooring using simple assumptions varied from -2.4 to +6.6 Sv with a mean of +1.9 Sv toward the Straits of Florida. These values, while based on limited data, are very significant compared to the mean flow in the Straits of Florida. Thus flow through the Old Bahama Channel may be an important component of heat and salt transport in the straits

Optical spectroscopy of young tidal objects around two interacting galaxy pairs

We present Gemini Multi-Object Spectrograph spectra of HI-rich tidal features located around the outskirts of two interacting galaxy pairs, NGC 3166/9 and NGC 4725/47. These follow-up observations are part of a multiwavelength campaign to study the properties and frequency of tidal dwarf galaxies (TDGs) in group environments. Based on the calculated gas-phase metallicity and redshift, in addition to the previously measured HI and stellar properties, we have confirmed the tidal origins of TDG candidate AGC 208457, which has emerged from the tidal debris of an interaction between the NGC 3166/9 galaxy pair. By comparing HI and optical recessional velocities, we have also confirmed a physical association of the gaseous knots and star clusters embedded in the metal-rich tidal tail of NGC 4747.Fil: Lee-Waddell, K.. CIRO Australia Telescope National Facility; AustraliaFil: Madrid, J. P.. CIRO Australia Telescope National Facility; AustraliaFil: Spekkens, K. Royal Military College of Canada; CanadáFil: Donzelli, Carlos Jose. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Córdoba. Instituto de Astronomía Teórica y Experimental. Universidad Nacional de Córdoba. Observatorio Astronómico de Córdoba. Instituto de Astronomía Teórica y Experimental; ArgentinaFil: Koribalski, B. S.. CIRO Australia Telescope National Facility; AustraliaFil: Serra, P.. Università Degli Studi Di Cagliari.; ItaliaFil: Cannon, J. Macalester College. Department of Physics and Astronomy; Estados Unido

WALLABY pre-pilot survey: ultra-diffuse galaxies in the Eridanus supergroup

We present a pilot study of the atomic neutral hydrogen gas (H I) content of ultra-diffuse galaxy (UDG) candidates. In this paper, we use the pre-pilot Eridanus field data from the Widefield ASKAP L-band Legacy All-sky Blind Survey to search for H I in UDG candidates found in the Systematically Measuring Ultra-diffuse Galaxies survey (SMUDGes). We narrow down to 78 SMUDGes UDG candidates within the maximum radial extents of the Eridanus subgroups for this study. Most SMUDGes UDGs candidates in this study have effective radii smaller than 1.5 kpc and thus fail to meet the defining size threshold. We only find one H I detection, which we classify as a low-surface-brightness dwarf. Six putative UDGs are H I-free. We show the overall distribution of SMUDGes UDG candidates on the size–luminosity relation and compare them with low-mass dwarfs on the atomic gas fraction versus stellar mass scaling relation. There is no correlation between gas-richness and colour indicating that colour is not the sole parameter determining their H I content. The evolutionary paths that drive galaxy morphological changes and UDG formation channels are likely the additional factors to affect the H I content of putative UDGs. The actual numbers of UDGs for the Eridanus and NGC 1332 subgroups are consistent with the predicted abundance of UDGs and the halo virial mass relation, except for the NGC 1407 subgroup, which has a smaller number of UDGs than the predicted number. Different group environments suggest that these putative UDGs are likely formed via the satellite accretion scenario

WALLABY Early Science – II. The NGC 7232 galaxy group

We report on neutral hydrogen (H I) observations of the NGC 7232 group with the Australian Square Kilometre Array Pathfinder (ASKAP). These observations were conducted as part of the Wide-field ASKAP L-Band Legacy All-sky Blind surveY (WALLABY) Early Science program with an array of 12 ASKAP antennas equipped with Phased Array Feeds, which were used to form 36 beams to map a field of view of 30 deg2. Analysing a subregion of the central beams, we detect 17 H I sources. Eleven of these detections are identified as galaxies and have stellar counterparts, of which five are newly resolved H I galaxy sources. The other six detections appear to be tidal debris in the form of H I clouds that are associated with the central triplet, NGC 7232/3, comprising the spiral galaxies NGC 7232, NGC 7232B, and NGC 7233. One of these H I clouds has a mass of MH I ∼ 3 × 108 M⊙ and could be the progenitor of a long-lived tidal dwarf galaxy. The remaining H I clouds are likely transient tidal knots that are possibly part of a diffuse tidal bridge between NGC 7232/3 and another group member, the lenticular galaxy IC 5181