5' NGC 128 LGG 6 LGG 6 2' NGC 193 LGG 9 5' NGC 252 LGG 12 5' LGG 14 NGC 315 5' NGC 407 NGC 410 LGG 18 5' NGC 524 LGG 23 4' NGC 584 LGG 27 5' Cluster Background LGG 31 NGC 677 NGC 777 LGG 42 5' Group Background LGG 58 LGG 61 5' NGC 978 LGG 66 5' NGC 1066 NGC 1060 LGG 72 5' NGC 1106 LGG 78 5' NGC 1167 LGG 80 5' Cluster Background NGC 1395 LGG 97 5' NGC 1400 NGC 1407 LGG 100 5' NGC 1453 LGG 103 5' NGC 1550 LGG 113 4' NGC 1587 LGG117 NGC 2292 LGG 138 5' NGC 2563 LGG 158 2' NGC 2768 LGG 167 5' NGC 2914 NGC 2911 LGG 177 5' Cluster Background NGC 3078 LGG 185 5' NGC 3325 LGG 205 5' QSO Background NGC 3613 LGG 232 5' NGC 3665 LGG 236 5' NGC 3923 LGG 255 5' NGC 4008 LGG 262 5' NGC 4175 LGG 276 5' NGC 4261 LGG 278 4' ESO 507-25 LGG 310 5' NGC 4697 LGG 314 LGG 329 5' NGC 5044 LGG 338 NGC 5061 LGG 341 4' NGC 5084 LGG 345 5' Cluster Background NGC 5127 LGG 350 4' NGC 5153 LGG 351 5' NGC 5322 LGG 360 5' NGC 5350 NGC 5354 NGC 5353 LGG 363 5' NGC 5444 LGG 370 5' NGC 5490 LGG 376 5' NGC 5629 LGG 383 5' NGC 5846 LGG 393 5' NGC 5898 NGC 5903 LGG 398 5' NGC 5985 NGC 5982 LGG 402 5' 5' NGC 7252 LGG 457 5' NGC 7377 LGG 463 5' NGC 7626 NGC 7619 LGG 473 CLoGS: the complete local-volume groups sample E. O’Sullivan 1 , K. Kolokythas 2 , J.M. Vrtilek 1 , L. David 1 , G. Schellenberger 1 , M. Gitti 3 , S. Giacintucci 4 , A. Babul 5 , & S. Raychaudhury 6 1: Harvard-Smithsonian Center for Astrophysics, 2: North-West University, South Africa 3: Universitá di Bologna & INAF-Instituto di Radioastronomia, 4: Naval Research Laboratory, 5: University of Victoria, Canada, 6: IUCAA, India Galaxy groups in the local universe: results from a complete sample Background: Galaxy groups are arguably the most important environment for our understanding of galaxy evolution, AGN feedback, and the development of the hot intra-group and intra-cluster medium. Most previous studies of groups have either used optically-selected samples to examine galaxy populations, or X-ray selected samples (usually derived from the Rosat All-Sky Survey) to investigate gas properties. While these approaches have yielded important results, their selection methods mean they are subject to significant biases. Optically-selected samples often include false groups, since at low masses selection must be made using only a few galaxies. X-ray selection tends to produce samples dominated by cool-core systems with centrally-concentrated surface brightness, since these central peaks are most easily detected. Sample: We have created the Complete Local-Volume Groups Sample (CLoGS), an optically-selected statistically-complete sample of 53 groups in the nearby Universe (D<80 Mpc), with complete coverage in the X-ray (Chandra and XMM-Newton), multi-frequency radio (GMRT 235 and 610 MHz) and, for the dominant galaxies, CO (IRAM 30m and APEX). This combination of data allows us to examine the gas content of the groups, their dynamical state, and the role of AGN feedback in maintaining their thermal balance. We select our sample from the Lyon Galaxy Group catalogue (LGG, Garcia 1993, A&AS 100, 47), choosing groups which have: • ≥ 4 member galaxies (excluding pairs & triples which may lack a common halo) • ≥ 1 early-type member (as spiral-only groups tend to be hot gas poor) • Optical luminosity L B > 3x10 10 L ¤ for the brightest member • Declination > -30° (to ensure visibility from GMRT and VLA) We then expand and refine the galaxy membership using the LEDA galaxy catalogue, and exclude systems judged to be too rich (clusters) or too poor (too few galaxies to characterize the population). For more details of sample selection and X-ray properties, see O’Sullivan et al. (2017, MNRAS 472, 1482). CLoGS gallery: Each panel shows an adaptively smoothed 0.5-2 keV image of a CLoGS group, with an 2.5’x2.5’ optical (DSS or SDSS) image of the dominant early-type galaxy inset. For radio-detected systems, GMRT 610 or 235 MHz contours are overlaid. http://www.sr.bham.ac.uk/~ejos/CLoGS.html CO survey O’Sullivan et al. (2015, 2018) A&A 573, A111 and A&A 618, A126 All 53 group-dominant early-type galaxies have been observed in CO(2-1) and/or CO(1-0) using the IRAM 30m or APEX telescopes. We detect CO in 21 galaxies (~40%), with masses 1-610 x10 7 M ¤ . This detection rate is roughly double that of the general early-type population. Comparing radio luminosity to molecular gas mass (see Figure above), we find that while some of our galaxies have properties consistent with star formation (the grey band), a large fraction are AGN dominated. However, the presence of CO is not clearly linked to radio power, or to the presence of hot gas. This suggests that while group-dominant galaxies can build up a CO reservoir through cooling from the hot halo (as in galaxy clusters), many acquire it through gas-rich mergers. Radio properties Kolokythas et al. (2018, 2019) MNRAS, 481, 1550 and MNRAS, 489, 2488 Our GMRT 235 and 610 MHz observations (~4hrs/target, rms ~0.1mJy/bm @610 MHz, ~0.6mJy/bm @ 235 MHz) are well suited to identifying AGN over a wide range of scales and ages. For the group-dominant ellipticals we find: • 46/53 (87%) are detected in our GMRT data (or the NVSS or FIRST surveys) • 13 host jet sources (implying a duty cycle ~1/3) • 28 host point-like sources • 5 host diffuse sources (e.g., LGGs 31, 117, 185, 310). The origin of emission in these sources is unclear (star formation? disrupted jets? radio phoenices?) 11 of the 13 galaxies with jet sources reside in systems with group-scale X-ray halos and cool cores. The plot above shows cavity enthalpy vs. cooling time (P cav vs L cool ) for 5 of our richest groups. Three fall on the relation, with cooling and heating in balance, but two (LGGs 9 and 278) have P cav =50xL cool , suggesting that these AGN may be dramatically over-heating their groups. X-ray properties Group detection fraction: Of our 53 systems, • 26 (~50%) have a full group-scale X-ray halo (>65 kpc extent, L X >10 41 erg/s) • 16 (~30%) have a galaxy-scale halo (L X =10 40 -10 41 erg/s) • the remainder have only point-source emission in the dominant galaxy. Of the group-scale halos, ~1/3 are dynamically active, showing signs of ongoing mergers or sloshing (indicating a recent minor merger or tidal encounter). Roughly 65% have cool cores, a higher fraction than in clusters (~50%). Unlike clusters, many of the merging groups retain their cool cores. The temperature range of our systems is ~0.4-1.5 keV, equivalent to masses of ~0.5-5 x10 13 M ¤ . New groups One goal of our sample was to search for new groups, previously undetected in the X-ray. Of our 26 systems with a full-scale intra-group medium (IGM), 12 were identified as X-ray bright groups for the first time, of which 8 were undetected in the Rosat All-Sky Survey (RASS). Examples include: LGG 402 / NGC 5982 (bottom row) a faint (L X =3x10 41 erg/s), cool (0.59 keV) group which lacks a cool core; LGG 72 / NGC 1060 (above left) a train-wreck merger with a 100 kpc arc of stripped gas linking the two cores; and LGG 398 / NGC 5903 (bottom row) in which a combination of galaxy interactions and a powerful AGN outburst seem to have disrupted the group core (see O’Sullivan et al. 2018 MNRAS, 473, 5248 for more details). In each case, the lack of a relaxed cool core with a strong surface brightness peak probably explains the RASS non-detection. Future plans We are currently working on several aspects of the sample, including: • MUSE observations of 17 dominant galaxies, providing information on stellar populations and cooling from the hot gas halo. • Collecting interferometric observations of our CO-detected systems (via NOEMA and ALMA/ACA) to map the gas and understand its origin. • Detailed studies of particularly interesting individual systems, e.g., the asymmetric radio source in LGG 113 / NGC 1550. • Expanding the sample to include southern and spiral-dominated groups.