High Angular Resolution Radio Observations of (U-)LIRGs Antxon Alberdi (IAA, CSIC) (+ M.A. Pérez-Torres, C. Romero-Cañizales, R. Herrero-Illana + J. Conway + R Beswick + M Bondi + ST Garrington + TWB Muxlow …) RTS – “Resolving the Sky …” Manchester, 19 April 2012

10 10 – M sun SFR < 2 M sun yr -1 (e.g., the Milky Way) SFR ~ M sun yr -1 t ~ yr t ~ yr < galaxy lifetime starburst Starburst Galaxies  Typical SFRs are a few x Msun/yr  CCSN rates a few x (0.1-1) SNe/yr

ULIRGs LIRGs L IR > L sun (Caputi +07) z~2 (Caputi +07) L IR > L sun (Le Floc’h +05) z~1 (Le Floc’h +05) (U)LIRGs: scaled up starbursts (Magnelli et al., 2009) z - Significant fraction of the SF at high-z took place in (U-)LIRGs - Detection of SNe crucial for revising CCSN rates both locally and at high-z

Mrk 331 (D = 77 Mpc) NGC 1614 (D = 50 Mpc) Radio Observations of Starburst Galaxies  Compact (≤150 pc) high surface brightness (T b ≥ 10 3 K) central radio source  generated by a point-like source (AGN) and/or by the combined effect of SNe and RSNe  Low surface brightness circumnuclear halo  ongoing burst of star formation

Scientific cases Arp299 at 45 Mpc, L IR ~ 6.7 x L sun NGC 7469 at 70 Mpc, L IR ~ 5 x L sun IC883 at 100 Mpc, L IR ~ 4.7 x L sun IRAS at 252 Mpc, L IR ~ 1.4 x L sun

Early stage merger D ~ 45 Mpc  1 mas ~ 0.2 pc L IR ~ 6.7 x L sun ~ 40% in A  ~ 20% in B1  HST -WFPC2 814nm image (Neff et al., 2004) Arp299 1 IC694 NGC3690 ν CCSN ≈ 0.8 yr -1 ν CCSN ≈ 0.4yr -1

Stacking of the 6-epochs of (e)EVN images (April 2008 through Nov 2010) Bondi et al (A&A, 2012) - 26 sources detected - 8 new ones - Mixed population of CCSNe and SNRs - Evidence for at least 2 recent SNe - CCSN ~ 0.8 SN/yr - Taking into account the other 2 SNe that exploded in 2010 => uncomfortably large CCSN rate for Arp 299-A => Top heavy IMF!? rms = 18.5 microJy/b The Arp 299-A lab: Summary

The AGN-SB connection in Arp 299A Pérez-Torres+2010 (Letters to A&A) A1-A5 complex identified with the long-sought AGN (A1-core; A5-jet) Ratio of (5 GHz*L_5)/L_X => LLAGN A0 - A RSN just 2 pc away from a SMBH!! Is SB activity hindering BH accretion, and thus => LLAGN!? A

Arp 299: eMERLIN Image

- A highly luminous infrared, QSO-like, galaxy; - It interacted with IC 5283 more than 1.5 x 10 8 yrs ago; - There is evidence for a 10 7 M sun BH; - D ~ 70 Mpc  1 mas ~ 0.32 pc L IR ~ 5 x L sun 1.6 μm (Alonso-Herrero et al., 2004) NGC ν CCSN ≈ yr -1

SN 2000ft in NGC 7469 Colina et al. ApJ 553, L19 (2001); Alberdi et al. (2006); Pérez-Torres et al. (2009)  SN 2000ft is located in the circumnuclear ring (1 kpc), at a distance of 600 pc of the nucleus;  L SN2000ft = 1.1 x W/Hz, very luminous;  Fitting parameters are typical of type-II radio supernovae;  Mass loss rate ≤ ( ) x 10-5 M sun / yr, typical of a RSG-progenitor R1 R2 R3 SN2000ft

NGC 7469 Pérez-Torres et al. 2009, MNRAS 399, 1641; Alberdi et al. 2012

Structure Variability of the nucleus of NGC 7469 at λ 6cm Alberdi et al. 2012

Radio spectrum of the nucleus of NGC 7469 Alberdi et al Spectral index map

The nuclear region of NGC 7469 A BCD  C1: AGN (L = 3×10 38 erg/s)  flux density/structural variability;  C2: rather compact + flux density variability +  -variable;  C3: very compact (θ 5×106 K) + quite steady in flux + (  ~0.5)  Long-lasting SNR candidate?  C4: flux density variability; compact source within extended flux (  ~1). C4C3C2C1

IC883 Romero-Cañizales et al., 2012, (A&A, submitted) Advanced stage merger (starburst-AGN composite) D ~ 100 Mpc  1 mas ~ 0.5 pc L IR ~ 4.7 x L sun  ν CCSN ≈ 2.4 yr -1 Two new SNe discovered: SN 2010cu (Ryder et al., 2010) & SN 2011hi (Kankaré et al. 2011) ν CCSN ≈ yr-1 HST -NICMOS 1.6 μm image (Haan et al., 2011)

IC 883: e-MERLIN + e-EVN observations ~ 1 kpc structure at 144 o, showing components of a warped rotating ring Romero-Cañizales et al., 2012, (A&A, submitted)

IC 883: e-MERLIN + e-EVN observations

IC 883: Results AGN & SB together AGN A1 (e-EVN) and A (e-MERLIN)  AGN A2, A3, A4 … non-thermal compact components in a 100 x 100 pc region  CCSNe candidates

The EVN ULIRG sample: IRAS Advanced stage merger (starburst-AGN composite) D ~ 252 Mpc  1 mas ~ 1.2 pc L IR ~ 1.4 x L sun Farrah et al., 2003 Farrah et al., 2003 : AGN contributes with 35% to L IR  ν SN ≈ 2.4 yr -1 HST -NICMOS 1.6 μm image (Haan et al., 2011) Romero-Cañizales et al., 2012 (MNRAS)

IRAS : 6/18cm EVN observations x 38 mas, 46 o L-band area (200pc) > C-band area (100pc)  e - lifetime L-band area (200pc) > C-band area (100pc)  e - lifetime Evidence for a nuclear starburst/AGN Evidence for a nuclear starburst/AGN 60 pc Romero-Cañizales et al., 2012 (MNRAS)

IRAS : Results longer lifetime of e - emitting at lower frequencies (L-band vs. C-band emission occupies a larger extension) different populations of radio emitters different populations of radio emitters (peak component at L- and C-bands do not coincide) Ongoing nuclear activity, e.g., SNe and AGN Ongoing nuclear activity, e.g., SNe and AGN (Peak variable in position and intensity through time  source variability within the nuclear region and/or appearance of new sources) Romero-Cañizales et al., 2012 (MNRAS)

IRAS : IRAS : Spectral index (pixel-to-pixel) Ongoing nuclear activity - SNe and AGN Ongoing nuclear activity - SNe and AGN ( α evolution) Presence of old radio emitters at the edges of the nuclear region - SNRs Presence of old radio emitters at the edges of the nuclear region - SNRs ( α distribution ) Magnetic Field in the nuclear region (~175 μG)  typical of advanced mergers Magnetic Field in the nuclear region (~175 μG)  typical of advanced mergers

Summary Radio observations of (U)LIRGs at the highest resolution and sensitivity are extremely useful to: (i) discern SB from AGN driven activity in the innermost regions; (ii) determine their CCSN rate; and (iii) test the IMF of the massive stars. VLBI radio searches on large samples needed to get meaningful statistical results (=> LIRGI: It will allow to establish a phenomenological sequence and timescale for the evolution of a nuclear starburst for a statistically significant sample of (U)LIRGs in the local universe ).

Thanks to … JIVE-Staff for all the support along these years EVN, for the improving quality of the data (eEVN, network session experiments …) We are the USERS, another “essential” ingredient for these facilities (we have benefitted from research funding from the European Community FP7 and FP6)

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