GALAXY GROUPS, CLUSTERS AND LARGE SCALE STRUCTURE: OPEN QUESTIONS AND OPPORTUNITIES. Melanie Johnston-Holli/

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1 GALAXY GROUPS, CLUSTERS AND LARGE SCALE STRUCTURE: OPEN QUESTIONS AND OPPORTUNITIES Melanie Johnston-Holli/

2 OUTLINE Clusters and open queshons OpportuniHes: Era of the Survey Examples: QuesHons we need mulh-wavelength data to answer Challenges: What are we missing? Conclusion A3888: Radio halo from Shakouri et al (2016)

3 CLUSTER ECO-SYSTEM Filament Star forming galaxies Cluster Head-tail Galaxy EllipHcal galaxies Original cartoon from NASA/JPL-Caltech: modified by MJH

4 CLUSTER ECO-SYSTEM Filament Star forming galaxies Halo Cluster Head-tail Galaxy EllipHcal galaxies Relics Original cartoon from NASA/JPL-Caltech: modified by MJH

5 QUESTIONS Understanding the role of environment on the formahon and evoluhon of galaxies How do cluster mergers affect star formahon and AGN? How do AGN and SF galaxies relate to environment over Hme? Similarly how then do galaxies influence their environment? AGN Feedback in clusters? Seed electrons for cluster halos and relics? Jet-induced star formahon?

6 Star formahon studies Relic & Halo studies RADIO CONTINUUM CLUSTER SCIENCE (PART 1) MulHvariate analysis on cluster merger state & environmental condihons versus SF rate in the local (z< 0.1) universe ie do mergers induce star-formahon? At what point in the merger history does this occur? How does the richness of the environment affect the results? The first stahshcally significant study of the radio Butcher-Oemler effect in clusters out to z = 0.3 ie how does the radio-detected SF rate in clusters evolve with redshih? A first detailed inveshgahon of the star-forming history of cluster filaments. Blind detechon of radio halos in greater numbers allowing unbiased tests on their generahon and presumed correlahon with X-ray luminosity and constraints on the turbulence and magnehc fields in clusters to be determined. Blind detechon of accrehon shocks and radio relics in greater numbers allowing unambiguous signposts of merging to be detected, the first relic luminosity funchon to be calculated.

7 RADIO CONTINUUM CLUSTER SCIENCE (PART 2) AGN studies The first inveshgahon of a large sample of bent double radio galaxies in terms of environmental condihons and potenhally the use of such probes to detect new galaxy clusters out to z = 1. CalculaHon of a new cluster Radio Luminosity FuncHon for both early and late-type galaxies. An examinahon of Low luminosity radio galaxies and AGN feedback. How are AGN related to relics and halos in clusters?

8 OPPORTUNITIES: MULTI-WAVELENGTH SURVEY ERA The next decade will see a vast increase in astronomical surveys, parhcularly in the Southern Hemisphere. This mulh-wavelength data will provide unparalleled samples of galaxies across different environments and epochs. PotenHally allowing for the first Hme detailed stahshcal studies of queshons of how environment shapes galaxy formahon and evoluhon. Including understanding the evoluhon of gas content and the influence of magnehc fields

9 NEW & FORTHCOMING SURVEYS Radio ConHnuum: GLEAM, LOTSS, WODAN, EMU, MIGHTEE etc Radio PolarizaHon: POSSUM etc X-ray: erosita etc OpHcal Photometry: SDSS, PanSTARRS, SkyMapper etc.. OpHcal Spectroscopic: Taipan Galaxy Survey etc Spectroscopic Surveys: I. Baldry

10 NEW & FORTHCOMING SURVEYS

11 NEW & FORTHCOMING SURVEYS Radio ConHnuum Surveys: Norris et al GLEAM source: Callingham et al. 2017

12 EXAMPLE: LARGE SCALE STRUCTURE IN THE CDF-S 0.11 < z 0.< 175 Dehghan & Johnston-Holli/ (2014)

13 RADIO GALAXIES AND ENVIRONMENT - AN EXAMPLE We characterized the environment in the CDFS using the ~5000 spectroscopic redshihs available in the literature finding 62 overdense regions in the 0.3 square degree field. This included 13 massive galaxy clusters and 6 groups. (Dehghan & Johnston- Holli/ 2014) These detechons have since been verified independently (Finoguenov et al. 2015) We then looked at the correlahon between density of environment and radio emission based off the radio source populahon catalogue of Bonzini et al (2013) of 883 radio sources down to 6 ujy at 1.4 GHz. We limited this sample to 196 so as to be in the range z > 0.8

14 RADIO SOURCES IN THE CDFS Bonzini et al. split the radio sources in the CDFS into three categories based on their FIR-radio raho and presence or otherwise of hard X-ray emission: Radio Loud AGN Radio Quiet AGN Star forming Galaxies

15 PRELIMINARY RESULTS: STAR FORMING GALAXIES The environment (surface) density was calculated and corrected for Malmquist bias in two ways: i) by assuming a Schechter Luminosity FuncHon with values aher Rizzo et al (2004) and ii) by using the detected galaxy clusters as standard candles. Preliminary results for SF galaxies are consistent with GAMA (Wijesinghe et al. 2012) in bin 1. Field Cluster cores

16 TAILED RADIO GALAXIES: SIGNPOSTS TO HIGH DENSITY ENVIRONMENTS Tailed radio galaxies (WATs, NATs) have been shown to mark the most dense regions in galaxy clusters in the local (z <0.07) Universe (Mao et al. 2009) and trace over-densihes out to redshihs of 2 (Dehghan et al & 2014). Thus, tailed radio galaxies discovered in ASKAP & SKA surveys will be valuable early indicators for sites of mass concentrahon which can then be compared with other indicators such as clustering of radio point sources, or ophcal/ X-ray data.

17 RADIO GALAXY POPULATION STUDIES How does environment affect the radio galaxy populahon in clusters & filaments? Do mergers induce star-formahon? At what point in the merger history does this occur? How does the richness of the environment affect the results? How does the radio-detected SF rate in clusters evolve with redshih?

18 SENSITIVITY ISSUES NOW Cluster source counts to date mainly probing AGN; due to lack of sensihvity SF AGN SF AGN Source counts for parts of Shapley concentration (Venturi et al ) overlaid with line representing background counts (Prandoni et al. 2001).

19 EMU GIVES LEAP FORWARD IN SENSITIVITY SHOWS FAINT RADIO SPECIES SensiHvity increase to 10 µjy with improved uvcoverage means we can probe the radio source populahon across clusters and superclusters over the whole sky. Probe both the AGN & SF populahon in clusters Sadler et al. 2001

20 MERGER SUPPRESSION OF AGN, TIDAL STARFORMATION INCREASE? Current literature suggests that there is a strong environmental dependence in low z (> 0.1) clusters as to the radio emissions seen with a crihcal difference in AGN & SF populahons. Late stage mergers are increasingly associated with suppression of AGN (Venturi et al. 2000, Johnston-Holli/ et al. 2008) while at the same Hme we see increased blue, low-powered radio galaxies (Miller et al , Johnston-Holli/ et al. 2008) which are likely to be Hdally induced SF galaxies. Miller, Johnston-Holli/ et al. in prep

21 MERGER EFFECTS ON RADIO GALAXY POPULATIONS Cluster Source counts Early type RLF Merger stage A3556 consistent consistent early A3558 consistent suppressed late A3528 consistent consistent early A3571 consistent suppressed late A3558 outskirts consistent but weak excess suppressed late A2125 excess low-power Late; merging along axis of lowpower excess A2255 excess low-power late A2111 excess low-power? A3158 excess low-power suppressed merging along axis of low power excess

22 LACK OF STANDARDS Now Some improvement eg Yan et al. (2016), but not for the whole cluster populahon Now

23 AGN, RELICS AND HALOS It s long been known that relics and halos in clusters need a seed populahon of electrons to be reaccelerated. DaHng back 20 years AGN have been the suggested source. Strong evidence of this has only recently been found (Shimwell et al. 2015, van Weeren et al. 2017) van Weeren et al. 2017

24 LOW FREQUENCY SURVEYS THE KEY Surveys at LOW Frequencies Show Evidence for more AGN in clusters at an earlier epoch StarHng to find lots of dead RGs in clusters seemingly associated with BCGs Gives the seed electrons we need for halos and relics, but also points to evoluhon of RG populahon Red 200 MHz MWA, Blue XMM 200 MHz MWA (red), 408 MHz (Blue), 843 MHz (green), 2.8 GHz (purple) Zheng et al. in prep

25 OTHER DATA/ INFORMATION HI surveys will probe gas movement in galaxies in clusters OpHcal imaging of Jellyfish galaxies Polarimetry will constrain magnehc fields SimulaHons of cluster mergers, AGN feedback etc. Jellyfish galaxies Serra et al. ASKAP HI images

26 STATISTICAL DATA EXTRACTION How do we extract informahon from all of these surveys? Do we have the algorithms and the human resource to do this work at scale? How do we connect survey teams? Astronomers are good at this but I think we could be be/er

27 PUTTING ALL THIS TOGETHER Need teams of people working on ophcal/ir/hi/ ConHnuum/PolarisaHon/simulaHon/ICT in the same place to really leverage this science. Not only is this the decade of the rise of the survey, it needs to be the era of the trans-disciplinary team. Effort needs to be put into not just looking at how we can run these surveys but how we connect them.

28 CONCLUSION Different types of radio emission appear to trace different condihons and dynamical states within galaxy clusters. We are constrained by current sensihvity and missing large samples to test the full range of correlahons in the cluster ecology. MulHwavelength data, will do this. PolarisaHon Surveys ConHnuum Surveys HI Surveys ExciHng Science! SimulaHons Also X-ray OpHcal Surveys