PoS(AASKA14)109 http://pos.sissa.it/ 3 , 1 , and Richard Strom 1 ASTRON 3 ; , Ru-Rong Chen 2 , 1 JLRAT 2 [email protected] ; The missing baryons are usually thoughtmedium (WHIM). to From reside previous in studies, galaxy giant filaments radiogroups, as galaxies which are warm-hot normally usually intergalactic trace associated the withmake galaxy WHIM. a We census propose of observations giant with radioWHIM. the galaxies The powerful in radio SKA1 galaxies the to discovered southern will hemisphere, alsoWith which the be highly will investigated improved to probe sensitivity search and the for resolution ambient dying ofwill radio SKA1, be more sources. discovered than within 6,000 giant 250 radio hours. sources Copyright owned by the author(s) under the terms of the Creative Commons Attribution-NonCommercial-ShareAlike Licence. NAOC c

1 E-mail: Advancing Astrophysics with the Square KilometreJune Array, 8-13, 2014 Giardini Naxos, Sicily, Italy Bo Peng Giant radio galaxies as probes ofthe ambient era WHIM of in the SKA PoS(AASKA14)109 Bo Peng cold dark Λ 056 galaxy, the po- . 0 = z 461 galaxy (Minkowski 1960). Simulta- . 0 = z 0.7 Mpc, h = 0.71) are a quite unique category, 2 > (Miley 1968) before they could attain the dimensions found among the largest z K. Material in the WHIM is highly ionized and can only be observed at far-ultraviolet 7 CDM) cosmologies (e.g. Davé et al. (2010) ). However, because its density is relatively 10 Λ − 5 By 1950, several compact radio sources had been associated with distant galaxies (Bolton, Giant radio galaxies (GRGs) (linear size Much effort went into identifying (and measuring the redshifts of) radio sources from reliable Baryonic matter - protons, neutrons, and electrons - belongs to a class of massive elementary tential of radio sources for probingwhen the Universe 3C became 295 apparent. was This expectation shown was to confirmed be associated with a Stanley & Slee 1949; Ryle, Smithradio & source Elsmore Cygnus 1950), A and (Baade with & the Minkowski identification 1954; of Smith the 1951) very with strong a as they are the biggesttheir objects radio in lobes the are sky powered bynucleus. with beams large Radio of radio relativistic structures structures. particles of and(Lara It many magnetic is et known fields generally al. GRGs from believed an are 2001; that 2000; active asymmetric Machalski, Strom over Jamrozy et their al. & mega-parsec 2013) Zola extents (seemedium and Figure 2001; can 1). act Saripalli as As et tracers the ofa al. radio this good barely lobes 2005; opportunity detectable expand, material. Schoenmakers to they investigate The et interact the large with extent ambient al. of the gas. GRGs ambient provides 3. Radio galaxies and cosmology low, the detection remains a challenge (Davé et al. 2001; Dietrich et2. al. 2012; Werner Giant et radio al. 2008). galaxies (GRGs) matter ( catalogues, especially 3C. Higherbork resolution and radio the maps VLA) (made tied bytranslated down the into the One linear radio Mile dimensions. source Telescope,electrons structures. Inverse West- becomes The Compton increasingly angular scattering important size of atsources measured the greater at could radio redshift. high be emitting This high-energy radio effect galaxies could in the "snuff local out" Universe. radio neously, radio source structure was foundsizes ranging to from be parsecs double to lobed hundreds (Jennison of & kilo-parsecs. Das Gupta 1953), with particles which make up thetheory atoms and the of results all of materials WMAP, baryonic on matterthough contributes Earth it no remains and more not than in completely 5 the percent accountedin of stars. for. the the From cosmos, From current a the census Universe Big of (e.g.galaxies the Bang constitute observable Shull, less baryonic than Smith density 50 & percent ofdistant Danforth baryons quasars, (2012)), predicted the by all number the the of theory. baryons By stars,constant in analyzing even dust light cosmic going and from history back can gas to be within obtaining 10 counted. a billion Its complete years amount picture of has ago. galaxy remained formationthought Quantifying and to the evolution. reside missing The between baryons missing galaxies, baryons is as areof essential warm-hot generally 10 to intergalactic medium (WHIM) withor temperatures low-energy X-ray wavelengths. This diffuse plasma is a common prediction in the GRGs as probes of ambient WHIM 1. The WHIM PoS(AASKA14)109 Bo Peng 20 48 25 49 30 35 50 3 RIGHT ASCENSION (J2000) RIGHT ASCENSION (J2000) 40 51 45 09 52 16 50 NGC 6251 4C 73.08 45 40 35 30 25 20 15 10 05 00 16 14 12 10 08 22 20 18

82 50 73 24 DECLINATION (J2000) DECLINATION DECLINATION (J2000) DECLINATION WSRT map made at 92 cm wavelength of the radio galaxy NGC 6251. Like all of the GRGs, it WSRT map at 21 cm wavelength of the radio galaxy 4C 73.08. The brighter western lobe is more Figure 2: is srongly polarized at long wavelengths.and Note the how host unequal are. the distances between the ends of the two lobes Figure 1: compact than its eastern counterpart. A similar effect is seen in NGC 6251 (Figure.2). GRGs as probes of ambient WHIM PoS(AASKA14)109 . 2 − Bo Peng 1 rad m ∼ . In a more general 46 3 2 1 − 3 cm field surrounding the radio 5 . 3 − ◦ 4 − 29 47 cm 5 5 − 7 10 6 × 9 48 10 12 14 4 31 49 RIGHT ASCENSION (J2000) 17 19 20 21 07 50 25 G, the particle densities are of order 10 22 µ DA 240 45 40 35 05 00 50

55 55 56 10 DECLINATION (J2000) DECLINATION WSRT map made at 49 cm wavelength of the radio galaxy DA 240. Galaxies which are members As was clear from early WSRT observations of DA 240, 3C 236 and NGC 6251 (Figure 2), Several recent studies have explored the use of GRGs for probing the WHIM. In both the cases giant radio galaxies are strongly polarized atlow 608 ambient MHz (Willis, densities Strom were & Wilson at 1974).components. least The A qualitatively implied definitive consistent study with of the fivepolarization GRGs large carried at linear out wavelengths sizes by from of Mack et the 92many al. radio to places (1997) 2.8 mapped at their cm. the linear longest All wavelengths, of indicating the an sources internal were rotation found measure to of be polarized in of Subrahmanyan et al. (2008), andGRGs Safouris were et al. used (2009), to sensitive relate radio theirspectroscopic continuum morphology observations images to to of investigate the two galaxy ambient distribution within medium a on 2 the Mpc scale. They made Figure 3: of the DA 240 group have their positions indicated by symbols. 4. Tracing the WHIM with GRGs The implied densities within thefield lobes strengths depend of upon typically the 1 magneticconsideration field of strength. densities For associated equipartition withwhich GRGs, the Mack radio components et interact al. has (1998) a conclude density that of 1 the - IGM 4 with galaxy hosts. Both studies showedthe clear surrounding correspondence galaxy between distributions. the giant Such(Chen synchrotron a et lobes correspondence al. and was 2011b, also 2012a,b). foundgalaxy They (NGC in found 6251, a the NGC series existence 315 of and of 4C a papers 73.08) galaxy through group optical around spectroscopic each observations. giant However, radio GRGs as probes of ambient WHIM PoS(AASKA14)109 7 × − Bo Peng S). At L band, it will have ◦ ), which is expected to be low B 2 E is presumed (based on experience) ∼ (more than 80 percent of the whole . Adopting a number density of 10 ν ◦ ( 2 SNR B to avoid the confusion of the Milky Way, ◦ 5 . 12 5 > Jy/beam. Since the GRGs usually have intermediate | b µ | of radio synchrotron emission is proportional to the square ν W/Hz at 1.4 GHz, if the 26 2). Since the minimum elevation angle is about 15 degree (similar to and the ambient magnetic field . 1 E ∼ and 10 Pa, are lower than inferred from X-ray observations of dense filaments. This z 14 25 − 10 × (Saripalli et al. 2005), the SKA1_SUR is expected to detect about 12,000 GRGs in a total to 2.0 3 At the same time, the SKA1_MID will be equipped with 254 dishes in South Africa, including Furthermore, since the frequency A significant fraction of known giant radio galaxies were identified from the surveys of the − 15 − 64 dishes from MeerKAT. Compared withand 74 the times VLA, higher this survey speed. willAfter Moreover, provide the GRG 6.2 angular times candidates resolution will better have bea sensitivity been 6.4 deeper to obtained 200 investigation, times from especially better. theuse for SKA1_SUR, as low cosmological SKA1_MID surface probes. can brightnesswith be lobes, If SKA2_MID would used the which be SKA2_MID for is greatly could increased, importantinstrument and be for for this equipped discovering their will more with make of the PAFs, these SKA2_MID the faint, quite extended survey a radio speed powerful sources at higher redshift. sky). If the Galactic latitude is setMpc to be observing time of about 250 hourscapability), SKA1_SUR (formula will listed still in be the able Appendix).counterparts to detect obtained Even about from at 6,000 optical an GRGs, surveys, which earlysample such can phase be will as (50% identified then SDSS, with increase 2dF, by and more the than planned an LSST. order The of GRG magnitude. of the electrons’ energy the ASKAP), SKA1_SUR can observe the sky upthe to sky + coverage 48 will then be reduced to about 27,000 deg to be 150 (Machalski, Jamrozywill & be Zola 7825 2001; Schoenmakers Mpc et ( al. 2000), the luminosity distance and weak in the diffusefrom radio observations lobes using of the GRGs, SKA1 low detection frequency of array. new There radio may structures even be in discovery GRGs of is new ones likely power between 10 WSRT and VLA: WENSS, NVSS and FIRST.Western The Australia, SKA1_SUR including will 36 be dishes equipped of with ASKAP 96 (latitude dishes is in about 27 GRGs as probes of ambient WHIM in the case ofcoincide DA with a 240 galaxy (Chen group. etwhile The group the al. members isolated 2011a; evenly host reside Peng galaxy alongmuch lies et the higher in major al. than the axis the 2004), of middle observed the (Figurequite the values, lobes 3). low. relatively which A The symmetrical suggests similar expected that lobes conclusion X-raysample the was of luminosities matter obtained 12 are GRGs, by density they Malarechi within derived lobe et the energyarguments. al. densities lobes from (2013). The the is inferred radio In observations pressures the via in equipartition investigation10 the of lobes a of the giantdemonstrates radio the sources, potential which of using range GRGs fromand to 1.1 interact. study the WHIM gas within which their lobes evolve 5. Prospects with SKA1 a high survey speed figure ofbetter merit sensitivity (FoM) as of well about as 156 asurvey times 1.6 similar greater to to than 49 the the times NVSS, VLA, higher withL and angular integration 1.5 band, resolution times times the (Table of 1). noise 10 level If minutes should it and carries achieve a out 9.1 bandwidth a of 500 MHz at PoS(AASKA14)109 Bo Peng 6 GRGs, being able to compare them with low redshift sources z 265 124 1630 391 61 1000 0.25 0.25 0.49 18 14 27 1000 160 250 500 4 250 JVLA WSRT SKA1_MID SKA1_SUR LOFAR SKA1_LOW 1.76E4 3.84E3 1.3E6 2.75E6 5.21E4 2.7E7 1.4 - 44 16 0.22 0.9 5 11 2 − K 4 m K 2 2 / 2 m deg Summary of system sensitivity, survey speed and angular resolution of SKA1, VLA, WSRT at L sys T / Recently, Luo & Sadler (2010) modelled the evolution of FRI and II radio sources, finding With the highly improved system sensitivity, survey speed and angular resolution of SKA1, At low redshifts, SKA1 with its excellent sensitivity and angular resolution will be able to Our goal with SKA1 is to carry out a large-scale survey to search for giant radio galaxies. The sys FoV deg Resolution arcsec Bandwidth MHz A Survey Speed FoM that the latter evolve withincreases decreasing with monochromatic radio age. power, while Thefades the final away, power stage of the for the lobes former bothdecline, receiving sees their little rapidly radio or declining spectra no emission willradio energy as spectrum steepen, from and the so no the radio a jets source host dyingwell-suited or to nucleus radio nuclear the component. galaxy or SKA1 should capability jets. Finding at have candidates low lobes for As frequencies. this with the GRG a lobes phase steep there will be should be more than140 at one present order (a of small magnitude2009)). fraction With of increase their which ability in to have trace the redshifts the numberand ambient greater IGM, physical than of more state GRGs 0.5 GRGs will of (Komverg help from & the illuminate about theAnd Pashchenko WHIM distribution with and identify more whether details it on can high- explain the missing baryon problem. investigate GRG groups in(2011a); unprecedented Peng et detail. al. (2004); In andlarge fraction 4C several of 73.08, groups the Chen companion et (like galaxies al.us are DA (2012b); to weak explore 240, Strom radio the et sources. Chen weak al. The radio (2013)) et SKA1group emissions we sensitivity galaxies of al. will find companion appear enable that galaxies to a further. be Innumber spiral addition, of galaxies. a detections. number 21 of cm One the HI canthe observations use group of the kinematics. them HI are data likely to to estimate turn the up amount a of mass present, and6. study Conclusions survey should be unbiased anda complete specified down sky to area. a The well-defined GRGs brightness found or will flux be density, used over to trace out the WHIM, while we also hope band, and LOFAR at low frequency (extracted from Dewdney et al. (2013)). (like the discovery of GRG UGCequipped 09555 with with 250,000 LOFAR). The antennas lowtimes in frequency quicker array Western survey of Australia, speed SKA1 compared with will with 16 LOFAR. be times higher sensitivity and 520 will help to clarify howtheir giant radio radio galaxies structures, evolve, and andmorphology, especially etc., whether how with there their cosmic epoch. environments are affect significant differences in group size, composition, Table 1: GRGs as probes of ambient WHIM PoS(AASKA14)109 Bo Peng GRGs will be z 7 giant radio galaxies to investigate how radio galaxies evolve? z Among the questions we hope to answer, we note the following: Can one use the GRGs to This work was partially supported by the Chinese Ministry of Science and Technology un- Baseline Design", Document number SKA-TEL-SKO-DD-001 Revision 1 Dietrich, J., Werner, N., Clowe, D., Finoguenov,Jennison, A., R. Kitching, & T. Das et Gupta, al., M., 2012,Komberg, 1953, B. Nat, Nat, & 487, 172, Pashchenko, 202 996 I., 2009,Lara, ARep, L., 52, Cotton, 1086 W., Feretti, L.,Luo, Giovannini, Q. G., & Marcaide, Sadler, J. E. et M., al.,Mack, 2010, 2001, K., ApJ, A&A, Klein, 713, 370, U., 398 409 O’ Dea,Mack, C. K., P., Klein, & U., Willis, A. O’ G. Dea,McCarthy, 1997, P., P., Willis, van A&A, G., Breugel, 123, & W. 423 & Saripalli, Kapahi, L.Machalski, V., 1998, 1991, J., A&A, ApJ, Jamrozy, 329, M., 371, 431 Zola, 478 S., 2001, A&A, 371, 445 detect the WHIM? And ifsurrounding so, companions can to we trace the pinpoint distribution the andenough physical missing state high- baryons? of the Can WHIM? one Finally, are use there GRGs and their Acknowledgements der the State Key2012CB821800, Development the Projects Program of International for Cooperation and Basic Exchange,40641, NSFC, the Research, Grant No. key Grant 112611- research program Nos.EW-T01, of and the the 2013CB837900 Chinese Open and Project Academy Program ofto of Sciences thank the the (CAS), Key Chinese Grant Laboratory Academy No. of ofthis Radio Sciences KJZD- research Astronomy. for was RGS the done. award wishes of a visiting professorship, when most of References Baade, W. & Minkowski, R., 1954,Bolton, ApJ, J., 119, Stanley, 215 G., & Slee,Burns, O., J., 1949, 1998, Nature, Sci, 164, 280, 101 400 Chen, R., Peng, B., Strom, R.,Chen, Wei, R., J., Peng, & B., Zhao, Strom, Y., 2011a, R.,Chen, A&A, & R., 529, Wei, Peng, J., A5 B., 2011b, Strom, MNRAS, R., 412,Chen, & 2433 R., Wei, Peng, J., B., 2012a, Strom, MNRAS, R., 420,de & 2715 Zotti, Wei, G., J., Massardi, 2012b, M., MNRAS, Negrello, 422,Davé, M., 3004 R., & Cen, Wall, R., J., Ostriker, 2010, J., A&ARv,Davé, Bryan, 18, R., G., 1 Oppenheimer, Hernquist, B., L. 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The high- PoS(AASKA14)109 (A.6) (A.7) (A.4) (A.5) (A.1) (A.2) (A.3) Bo Peng ) b ( sin ∆ × l ∆ σ 3 co − obs z D ν co τ × ) L S L V B + π D sys sky 2 1 4 × S A Dec √ 8 SNR ( ρ 3 1 = r = = = sin = co = ∆ σ N D L obs co W/Hz at 1.4 GHz × D S V 26 RA 10 ∆ − = ¨ ottgering, H. & van der Laan, H. 2001, A&A, 374, 861 25 ) sky 3 A , 10 − ν L : (Mpc ν ) 7 3 − 150 10 > ) = 2 ρ SNR : (www.icosmos.co.uk) z Noise level with two polarizations: (Jy/beam) Flux density observed with telescope: (Jy) Sigma to noise: Redshift Luminosity at frequency of Luminosity distance: (Mpc) Number of giant radio galaxies: Comoving volume: (Mpc Number density: Sky coverage: (deg Comoving distance: (Mpc) A&AS, 146, 293 432, 200 Appendix A. Formula used to estimate the number of GRGs for SKA_SUR Schoenmakers, A., de Bruyn, A., R Shull, J., Smith, B. & Danforth,Smith, C., F., 2012, 1951, ApJ, Nat, 759, 168, 23 555 Strom, R., Chen, R., Yang, J.,Subrahmanyan, & R., Peng, Saripalli, B., L., 2013, Safouris, MNRAS, V., 430, &Werner, N., 2090 Hunstead, Finoguenov, R., A., 2008, Kaastra, ApJ,677, J., 63 Simionescu,Willis, A., A.G., Dietrich, Strom, J. R.G. et & al., Wilson, A.S., 2008, 1974, A&A, Nat, 482, 250, L29 625 Miley, G., 1968, Nat, 218, 933 Minkowski, R., 1960, ApJ, 132, 908 Peng, B., Strom, R., Wei, J.,Ryle, & M., Zhao, Smith, Y., 2004, F., & A&A, Elsmore, 415,Safouris, B., 487 V., 1950, Subrahmanyan, MNRAS, R., 110, Bicknell, 508 G., &Saripalli, Saripalli, L., L., Hunstead, 2009, R., MNRAS,393, Subrahmanyan, R., 2 Schoenmakers, & A., Boyce, Mack, E., K.-H, 2005, de AJ, Bruyn, A., 130,896 Rottgering, H., Klein, U., & van der Laan, H., 2000, GRGs as probes of ambient WHIM Malarecki, J., Staveley-Smith, L., Saripalli, L., Subrahmanyan, R., Jones, D. et al., 2013, MNRAS, PoS(AASKA14)109 (B.1) (A.8) Bo Peng 500 MHz = B 10 minutes with NVSS observing model; = τ ; bandwidth: 1 sys − T eff K b sky A 2 k A 2 FoV 9 τ = = ); integrated time: 391 m t 2 sys = S eff sys A T 18 (deg J/K = 23 − 10 FoV × 38 . 1 = b 10 minutes with NVSS observing model k = τ (equation A.3) sky A Integrated time: For SKA1_SUR, sensitivity specification: System equivalent flux density: Boltzman constant: For SKA1_SUR, field of view: B. Estimate of the total observing time GRGs as probes of ambient WHIM sky coverage: