PoS(MeerKAT2016)024 http://pos.sissa.it/ ∗ [email protected] [email protected] [email protected] [email protected] [email protected] [email protected] [email protected] [email protected] [email protected] Copyright owned by the author(s) under the terms of the Creative Commons c Attribution-NonCommercial-NoDerivatives 4.0 International License (CC BY-NC-ND 4.0). Sugata Kaviraj Brooke Simmons University of California San Diego, CASSE-mail: 0424, 9500 Gilman Drive, La Jolla, CA 92093, USA Meg Urry Yale Center for Astronomy and Astrophysics andBox Department 208120, of New Haven, Physics, CT Yale University, 06520-8120,E-mail: P.O. USA Chris Lintott Oxford Astrophysics, Denys Wilkinson Building, Keble Road,E-mail: Oxford OX1 3RH, UK Karen Masters Institute of Cosmology Gravitation, University ofPortsmouth, Portsmouth, PO1 Dennis 3FX, Sciama UK Building, South East Physics Network (SEPNet) E-mail: Chandreyee Sengupta Korea Astronomy and Space Science Institute,305-348, 776, Korea Daedeokdae-ro, Yuseong-gu, Daejeon E-mail: Thomas Mauch SKA South Africa, The Park, ParkE-mail: Road, Pinelands, 7405, South Africa Kevin Schawinski Institute for Astronomy, ETH Zürich, Wolfgang-Pauli- StrasseE-mail: 27, 8093 Zürich, Switzerland. O. Ivy Wong International Centre for Radio Astronomy Research,35 The Stirling University Highway, of Crawley, Western WA Australia 6009, M468, Australia E-mail: G. I. G. Józsa SKA South Africa, The Park, ParkRhodes Road, University, Pinelands, RARG, 7405, RATT, South PO Africa BoxArgelander-Institut 94, für Grahamstown, Astronomie, 6140, Auf South dem Africa HügelE-mail: 71, D-53121 Bonn, Germany Blue Early Type Galaxies with the MeerKAT PoS(MeerKAT2016)024 to be removed farther and farther from the centre I [email protected] [email protected] Speaker. We discuss a potential MeerKATidentified campaign Blue to Early Type shed galaxies (BETGs), more aquenching light subset star of into formation the on the so-called time nature "green scales valley" of ofof population, less post-starburst the than galaxies. 0.25 optically Gyr Employing and a the WSRT likelyBETGs progenitor pilot have population survey radio of properties four that galaxies, fit to weby a have mechanical AGN shown removal activity, that of as star in forming particular material,of we potentially found the H galaxies with olderthe and optimal instrument older to age conduct of athis pointed the specific survey stellar transition of state, population. BETGs which to isplanned We become so sufficiently argue more sensitive rare conclusive that large-sky that about MeerKAT surveys, it is for will whichthe not order we be of expect 12 detected a objects. at total detection a number high of enough rate in ∗ MeerKAT Science: On the Pathway to25-27 the May, SKA, 2016, Stellenbosch, South Africa Peter Kamphuis National Centre for Radio Astrophysics, TIFR,E-mail: Ganeshkhind, Pune 411007, India Oxford Astrophysics, Denys Wilkinson Building, Keble Road,Centre for Oxford OX1 Astrophysics Research, 3RH, University UK ofAL10 Hertford- shire, 9AB, College UK Lane, Hatfield, Herts, E-mail: PoS(MeerKAT2016)024 25Gyr), . 0 G. I. G. Józsa < ] and passively 7 quench τ ] argue that on average ]. 10 9 ] were used to quantify a , 2 8 ]. The absence of a significant ], the first being characterised as 5 1 ] show that indeed while early type galaxies 10 1 ]. Most galaxies are either blue and star-forming galaxies 3 ]. In other words the colour bimodality does not perfectly reflect 10 2Gyr, while BETGs have a much shorter quenching time ( ]. Galaxies mostly reside within the “blue cloud” or are red passively-evolving ], making the green valley a specifically interesting region in the colour-magnitude 4 > 6 quench τ An even more detailed look making use of an optical identification of the galaxy type, re- Large sky surveys such as the Sloan Digital Sky Survey (SDSS) [ While the colour-magnitude diagram hence largely reveals two populations that can be distin- It is well known that galaxies can roughly be divided into two morphological categories, into ]. Actively forming stars or at least having had a very recent period of active star fomation, they ], but becomes most evident in a scatter diagram showing the colour of galaxies vs. their abso- 8 3 veals that the transition regionis with larger mixed than naively morphological expected types [ in the colour-magnitude diagram evolving, as well as early[ type galaxies which are particularly blue, and star forming, the BETGs red late-type galaxies evolve passively, exhausting theirtime star of formation reservoir, with a quenching are thought to be potential progenitors of post-starburst E+A galaxies [ the morphological one and itmorphological types is separately. instructive Schawinski to et investigate al.with the a [ colour-magnitude blue diagrams colour of exist,ies, both on they the are contrary, rare, broadly populate andwith the that, populate green star the valley formation green and properties, exist valley withoutvalley. with only This any a suggests significant sparsely. that large evidence BETGs variety of Disk are in fast a galax- sively colour evolving suppression galaxies, evolving and, in while galaxies. red the disk green These galaxies are findingsusing slowly, are pas- UV- and supported optical by colours. the Onhigher analysis average, proportion late-type of of galaxies colour-colour exhibit very diagrams a youngstar light stars formation profile in is indicative comparison of shut down a to more anlate-type rapidly galaxies. intermediate in Making population, early-type use galaxies meaning of populating evolutionary that models, the Schawinski green et valley al. than [ in guished by their colour, no sharp divisionIt of contains the spiral two galaxies types which occurs are in the redder colour-magnitude than diagram. their average morphological type[ having an ellipsoid shape and being gas-poordisks and and forming in little general to no gas-rich stars, and the actively latter forming being stars. flattened strong colour bimodality of galaxies,with which the has morphological been bimodality roughly identified [ to be strongly correlated galaxy population in the intervening regiontwo (often populations infers referred that to the as transition the betweentively the "green quickly two [ valley") main between galaxy these populations mustdiagram. occur rela- indicating a mechanical removal of the starsame forming time material late-type from galaxies the become galaxies. redder Showing withformation that increasing in at mass, late-type the they galaxies propose is that mostly quenching due star to a gradual reduction of accretion, while for late-type galaxies that reside in the “redenhanced sequence” in when the replacing colour-magnitude diagram, absolute a magnitude tendency that by is stellar even mass [ or they are red and[ passively-evolving. This bimodalitylute is magnitude[ already evident in simple histograms elliptical or early-type galaxies and late-type or spiral galaxies [ Blue ETGs 1. Blue Early Type Galaxies PoS(MeerKAT2016)024 ]. 8 ]. 26 reservoir 05) PSGs gas in the I . I 0 G. I. G. Józsa < ]. z 10 ]. < 15 ] and are already too , 02 9 . ]. Therefore, we posit 14 , 24 , 13 25 Gyr) mode in early-type 9 , . 0 12 , < 11 ]. These blue ETGs are likely to be 25 quench observations also provide simultaneous τ I survey of four Northern BETGs using the I ]. These four pilot galaxies are selected to rep- 24 2 ]. ) is an excellent indicator of the potential for future 24 I gas morphology and kinematics because the H I 2 Gyr) mode in late-type galaxies (LTGs) [ ]. Our recent study of low redshift (0 9 > , 23 , quench 22 τ ]. Previous CO observations of blue ETGs show that the molecular gas , 8 21 , 05) blue ETGs are identified using SDSS and the Galaxy Zoo project [ . 20 0 , line and L-band continuum. The purpose of this project is to get better insight < I 19 z , < 18 , 02 . 17 , 16 As laid out above, BETGs do not fit the canonical bimodal scheme of red ellipticals versus We are pursuing a radio campaign to characterise BETGS in the radio regime, in particular The neutral gas content (as traced by H Our recent stellar population study of early- and late-type galaxies find that there are two main Previous studies on this topic have been largely focussed on post-starburst galaxies (PSGs) , Starting our campaign, we completed a pilot H found that these galaxies typically have spheroidal early-type morphologies [ that the smoking gun for rapidpredecessor star population, formation namely, the quenching BETGs is [ more likely to be found in its proposed transition-type galaxies and are likelyredshift predecessors (0 of low redshiftThe PSGs. blue ETGs A account sample forrare of 5.7% in the 204 of Local low all Universe [ ETGs found within the same redshift range and are very resent 4 separate stagesthis spanning pilot the survey entire is range tonearest help of BETGs. prepare post-quenching for evolution. Subsequently, our we large The have observational recently purpose campaign conducted of to HI map observations the with H the GMRT and blue spirals. They are unlikely descendants of blue spirals [ reservoirs are being rapidly destroyed during the composite star formation and AGN phase [ focusing on the H in the physical mechanism(s) that cause(s)to the determine rapid whether shutdown BETGs of are star evenlead formation more in to complex galaxies than the and/or laid out sameinitiating above evolutionary star and formation stage, more in pathways like a may former e.g. passively evolving galaxy a [ (re-)accretion period of star forming material, 2. A radio campaign to characterise Blue Early Type Galaxies evolved to still exhibit the signatures for star formation quenching [ star formation as well as angalaxy excellent can tracer be of found past imprinted interactions. in Evidence its of H past interactions in a modes of quenching star formation in galaxies — a fast ( galaxies which are no longer formingstars stars [ but still have a dominant population of recently-formed Blue ETGs galaxies a more instantaneous, mechanical, gaspropose removal is explicitly required feedback to by explain active the galactic observations nuclei and as a potential quenching mechanism. galaxies (ETGs) and a slow ( typically extends to larger radii thanto the the stellar tidal component torques incurred within by a interactions. galaxy In and addition, is H more susceptible Westerbork Synthesis Radio Telescope (WSRT)[ observations of 1.4 GHz radio continuumgalaxy’s emission Active which Galactic is Nuclei an (AGN). excellent tracer of activity from the 2.1 A pilot survey with the WSRT PoS(MeerKAT2016)024 I , 1.51 quench 1 reser- τ − I ]. In the reservoir I 24 [ G. I. G. Józsa quench τ cloud, as well as the lack of a I ] —consistent with the idea that the 27 reservoir begins to exhibit increasingly I survey [ I 3 colour from blue to red as a tracer of time. The white scale bars for J1237, J1117, J0900 and J0836; respectively. It should be noted u 1 − − and radio continuum observations overlaid as white and green NUV content is comparable to other star-forming galaxies with simi- I and the green contours (logarithmic stretch) the radio continuum. The lowest I I and the highest contour is matched to the peak flux density of 0.87 mJy beam ]. The presence of these radio lobes suggest past AGN nuclear activity. σ SDSS composite images of the four blue early-type galaxies in our sample. The galaxies , 44.79 mJy beam 1 24 − gri colour. Of particular note is that every Atlas3D ETG exhibiting a disturbed r − reservoir [ colours and is observed to be undisturbed and in stable rotation. However, as I NUV r contours begin at 3 ] ] of nearby ETGs, we find that the Atlas3D ETGs span a large range of gas fractions , 0.86 mJy beam I 1 Top row: optical − 24 − 28 From the pilot survey, we find increasing projected spatial offsets between the main H The gas fractions of blue ETGs (Fig. 2) are generally lower compared to the ones of gas- NUV voir and the stellar component of the galaxies with advancing quenching age, neighbouring galaxy with which J0836 could have interacted; we hypothesise that the H process of quenching has already begunsurvey in [ these galaxies. Relative tofor the results a from given the Atlas3D Due to the alignment between the observed radio lobes and the H the VLA and have managed to increaseof our analysing sample these by two extra galaxies. 2 galaxies. We are currently in the process rich star-forming galaxies from the ALFALFA H least-evolved case (J1237), the H lar increases, the gas-to-stellar fraction decreasesdisturbed and morphologies the and H kinematics. Inalso the observe case a of pair the ofdisplaced most 1.4 H evolved GHz pilot radio galaxy lobes (J0836), flanking we both sides of the galaxy and aligned with the could have been pushed outradio by lobes. a Figure previous 1 episode showscontours, of the respectively, H AGN on activity the associated optical SDSS with observations the of observed the four pilot galaxies. Figure 1: that the nuclear 1.4 GHz continuum point sources are not shown for J0900 and J1117 to avoid confusion with the H are arranged from left to right in terms of Blue ETGs mJy beam contours. [ represent 10 arcseconds. Bottom row: zoomed-outcontours optical images (asinh-stretch) with represent the WSRT the radio H observations overlaid.radio and The white H PoS(MeerKAT2016)024 G. I. G. Józsa ], argued to be 12 7 How are interactions and 6 J0836+30 5 J0900+46 reservoirs a result of previous mergers? I ] also has higher average gas fractions. The 4 H 29 J1117+51 J1237+39 NUV-r 3 4 ]. 29 2 1 Blue ETGs (this work) Blue & GV ETG (Wei et al 2010) ALFALFA-detected BETG (Huang et al 2012) al 2001) E+A galaxies (Zwaan et al. 2013, Buyle et al. 2006, Chang et et al 2013) Atlas3D ETGs (Serra et al 2012, Capellari et al 2013, Young Cluster Atlas3D ETGs with unsettled HI reside in pairs/groups/Virgo 0 2 1 0

-4 -1 -2 -3 outflows? Are the displaced log (gas fraction) (gas log I H gas reservoir is likely larger for galaxies with lower recent star formation, as I morphology reside in pairs or groups or the Virgo Cluster, and have higher gas I H I-to-stellar mass ratio as a function of galaxy colour. The solid line shows the average gas fractions found than those investigated by these previous studies. We find our gas fractions to be consistent withOur the pilot idea study that is our hence consistent pilot with sample the have hypothesis shorter that the fast star formation shutdown quench same is true for a sample of 14 blue-sequence E/S0s analysed by Wei et al. 2010 [ τ in blue ETGs isan due active to AGN the exhibiting bulk radio removalformation. jets of or neutral In outflows) gas particular, rather fromexpected if than that which the the the stars opposite H slow can path exhaustion form would of (possibly be gas by via true, star for our four galaxies, it would be Figure 2: from GASS survey of massive transition-type galaxies [ in a likely status of reaccretion. Thisthe sample morphology would likely of have the fallen out galaxieswith of is their our pilot gas indicative sample fraction. of as being also non-elliptical and/or interacting, consistent well as the absence ofwith little an ongoing intermediate or very stellar recent population starto formation (as (see be traced Fig. conclusive, which 2). by is Clearly, the the whybe sample blue we is answered continue light) not with our large in a campaign. enough galaxies more There statistically-representative areAGN sample related open of in questions galaxies. than these can blue only ETGsAGN feedback as result they in evolve into PSGsHow and many subsequently, BETGs passive may ETGs? be a Does result of gas capture instead of quenching? fractions than what wetransition-type find galaxies studied in by the our GASS survey pilot [ sample of isolated blue ETGs. Similarly, the massive Blue ETGs or unsettled H PoS(MeerKAT2016)024 G. I. G. Józsa ], with the in- 8 ) within a redshift range of surveys will yield serendip- 2 I we extrapolate this to 3 BETGs

M 8 10 · . This column density limit is at least required 1 ] and argue that they are most likely the result of 5 − 8 ] and argue that a larger survey of this type is likely to 24 detection limit of 2 rms σ 5- I to determine its position and status as shown in our pilot survey. The I survey of Blue Early Type Galaxies as a potential small campaign with the I over a line width of 20kms 2 − atomscm 19 at the targeted column-density sensitivity). Only MeerKLASS (see contribution of M. Santos ApJ, 600, 681 We discuss an H As laid out above, MeerKAT with its predicted sensitivity is the most suitable instrument 00 10 ] find 204 BETGs within the survey area of SDSS (DR 6, ~9600 deg · [1] Hubble, E. P. 1926, ApJ, 64, 321 [2] York, D.G., et al. 2000, AJ, 120,[3] 1579 Strateva, I., et al. 2001, AJ, 122,[4] 1861 Baldry I. K., Glazebrook K., Brinkmann J., Ivezic Z., Lupton R. H., Nichol R. C., Szalay A. S., 2004, 8 shed more light into thevery nature good of example BETGs. for A a survey high-yield of special-purpose this survey. kind is not extremely expensive andReferences a a fast star formation quenchingobservations event, to potentially support AGN feedback. this hypothesis We use [ pilot WSRT in this conference) would provide a comparable sample. 3. Summary tegration time scaled up accordingly (8determine hours a per more target). complete Observations sample from of SkyMapper SouthernBETG help BETG. in us We expect to addition to to find several the hundredhence sample Southern intend reported to define by a Schawinski small survey etfor to al start which with 2009 the MeerKAT-32 to to total then select continue integration withgiven our time MeerKAT-64, the sub-sample. (without small local calibration) We density would of beitous BETGs, detections 70 none of hours. of a the sufficient We planned number emphasise[ blind of that, H BETGs at sufficient resolution.0.2-0.5. Schawinski et With al. an (2009) aspiredthat H can be detected inshallower the surveys MIGHTEE (APERTIF survey, shallow 8 and to WALLABY) 9 would(15 not in provide the the APERTIF medium-deep required survey, resolution while MeerKAT. We argue that MeerKAT is antransition optimal type telescope as to it conduct has aBETGs a galaxy as very survey defined sensitive of single-pixel by a receiver. Schawinski rare We et discuss al. the (2009) characteristics [ of to detect low-column density gas inrequired these to quenched resolve objects the at H the given resolution, which itself is to conduct our proposed survey.tially Our high aim impact. would betime Our a of intended comparably 2 sample small hours size campaign5 with is per a 35 pointing poten- BETGs with in the total full We array estimate to an be integration sufficient tointention detect would a be to column begin densityearlier) with from of observations a of sample of the Southern nearest BETGs BETGs as identified using by early Schawinski et MeerKAT-32 (or al. (2009) [ Blue ETGs 2.2 A MeerKAT campaign to observe Blue Early Type Galaxies PoS(MeerKAT2016)024 G. I. G. Józsa 6 T. 2006, MNRAS, 373, 469 ApJ, 769, 82 [5] Baldry, I. K., Balogh, M. L., Bower, R. G., Glazebrook, K., Nichol,[6] R. C.,Martin, Bamford, D.C., S. et P., al. Budavari, 2007, ApJS,[7] 173, 415 Masters, K. L., et al. 2010,[8] MNRAS, 405,Schawinski 783 K. et al., 2009, MNRAS,[9] 396, 818 Wong, O. I., et al. 2012, MNRAS, 420,1684 Blue ETGs [10] Schawinski, K., et al. 2014, MNRAS,[11] 440, 889 Kannappan, S. J., Guie, J. M.,[12] Baker, A.Wei, J. L. 2009, H., AJ, Kannappan, 138, S. 579 J.,[13] Vogel, S. N.,Wei, Baker, L. A. H., J. Vogel, S. 2010, N., ApJ, Kannappan, 708,[14] S. 841 J.,Moffett, Baker, A. A. J., J., Kannappan, Stark, S. D. J., V.,[15] Laine, Baker, A. S.Stark, J., 2010, D. Laine, ApJ, V., S. 725, Kannappan, 2012, L62 S. ApJ, J., 745, Wei, L. 34 H., Baker, A, J., Leroy,[16] A. K.,Dressler, Eckert, A., K. Gunn, D., J. Vogel, S. E. N. 1983,[17] 2013, ApJ, 270,Couch, 7 W. J., Sharples, R. M.[18] 1987, MNRAS, 229,Poggianti, 423 B.M., et al. 1999, ApJ,[19] 518, 576 Tran, K., et al. 2004, ApJ,[20] 609, 683 Goto, T. 2005, MNRAS, 357, 937 [21] Yan, R., et al. 2009, MNRAS,[22] 398, 735 Wild, V., et al. 2008, MNRAS, 395,[23] 144 Zwaan, M.A., et al. 2013, MNRAS,[24] 432, 492 Wong, O. I., et al. 2015,[25] MNRAS, 447, 3311 Tojeiro, R., et al. 2013, MNRAS,[26] 432, 359 Schawinski, K., et al. 2009, MNRAS,[27] 690, 1672 Huang, S., et al. 2012, ApJ,[28] 756, 113 Serra, P., et al. 2012, MNRAS,[29] 422, 1835 Catinella, B., et al. 2012, A&A, 544, A65