@article {2015A\&A...574A.114V, title = {{Subarcsecond international LOFAR radio images of the M82 nucleus at 118 MHz and 154 MHz}}, journal = {Astronomy and Astrophysics}, volume = {574}, year = {2015}, month = {feb}, pages = {A114}, abstract = {Context. The nuclear starburst in the nearby galaxy M82 provides an excellent laboratory for understanding the physics of star formation. This galaxy has been extensively observed in the past, revealing tens of radio-bright compact objects embedded in a diffuse free-free absorbing medium. Our understanding of the structure and physics of this medium in M82 can be greatly improved by high-resolution images at low frequencies where the effects of free-free absorption are most prominent.
Aims: The aims of this study are, firstly, to demonstrate imaging using international baselines of the Low Frequency Array (LOFAR), and secondly, to constrain low-frequency spectra of compact and diffuse emission in the central starburst region of M82 via high-resolution radio imaging at low frequencies.
Methods: The international LOFAR telescope was used to observe M82 at 110-126 MHz and 146-162 MHz. Images were obtained using standard techniques from very long baseline interferometry. images were obtained at each frequency range: one only using international baselines, and one only using the longest Dutch (remote) baselines.
Results: The 154 MHz image obtained using international baselines is a new imaging record in terms of combined image resolution (0.3{\textquoteright}{\textquoteright}) and sensitivity ({$\sigma$} = 0.15 mJy/beam) at low frequencies ({\l}t}327 MHz). We detected 16 objects at 154 MHz, six of these also at 118 MHz. Seven objects detected at 154 MHz have not been catalogued previously. For the nine objects previously detected, we obtained spectral indices and emission measures by fitting models to spectra (combining LOFAR with literature data). Four weaker but resolved features are also found: a linear (50 pc) filament and three other resolved objects, of which two show a clear shell structure. We do not detect any emission from either supernova 2008iz or from the radio transient source 43.78+59.3. The images obtained using remote baselines show diffuse emission, associated with the outflow in M82, with reduced brightness in the region of the edge-on star-forming disk.}, keywords = {galaxies: individual: M82, galaxies: star formation, galaxies: starburst, supernovae: individual: 2008iz, techniques: high angular resolution, techniques: interferometric}, doi = {10.1051/0004-6361/201425089}, url = {http://adsabs.harvard.edu/abs/2015A\%26A...574A.114V}, author = {Varenius, E. and Conway, J.~E. and Mart{\'\i}-Vidal, I. and Beswick, R. and Deller, A.~T. and Wucknitz, O. and Jackson, N. and Adebahr, B. and M. A. P{\'e}rez-Torres and Chy{\.z}y, K.~T. and Carozzi, T.~D. and Mold{\'o}n, J. and Aalto, S. and Beck, R. and Best, P. and Dettmar, R.-J. and van Driel, W. and Brunetti, G. and Br{\"u}ggen, M. and Haverkorn, M. and Heald, G. and Horellou, C. and Jarvis, M.~J. and Morabito, L.~K. and Miley, G.~K. and R{\"o}ttgering, H.~J.~A. and Toribio, M.~C. and White, G.~J.} } @article {2014ApJ...786..156H, title = {{A Multi-wavelength View of the Central Kiloparsec Region in the Luminous Infrared Galaxy NGC 1614}}, journal = {The Astrophysical Journal}, volume = {786}, year = {2014}, month = {may}, pages = {156}, abstract = {The Luminous Infrared Galaxy NGC 1614 hosts a prominent circumnuclear ring of star formation. However, the nature of the dominant emitting mechanism in its central \~{}100 pc is still under debate. We present sub-arcsecond angular resolution radio, mid-infrared, Pa{$\alpha$}, optical, and X-ray observations of NGC 1614, aimed at studying in detail both the circumnuclear ring and the nuclear region. The 8.4 GHz continuum emission traced by the Very Large Array and the Gemini/T-ReCS 8.7 {$μ$}m emission, as well as the Pa{$\alpha$} line emission, show remarkable morphological similarities within the star-forming ring, suggesting that the underlying emission mechanisms are tightly related. We used a Hubble Space Telescope/NICMOS Pa{$\alpha$} map of similar resolution to our radio maps to disentangle the thermal free-free and non-thermal synchrotron radio emission, from which we obtained the intrinsic synchrotron power law for each individual region within the central kiloparsec of NGC 1614. The radio ring surrounds a relatively faint, steep-spectrum source at the very center of the galaxy, suggesting that the central source is not powered by an active galactic nucleus (AGN), but rather by a compact (r {\l}t}\~{} 90 pc) starburst (SB). Chandra X-ray data also show that the central kiloparsec region is dominated by SB activity, without requiring the existence of an AGN. We also used publicly available infrared data to model-fit the spectral energy distribution of both the SB ring and a putative AGN in NGC 1614. In summary, we conclude that there is no need to invoke an AGN to explain the observed bolometric properties of the galaxy.}, keywords = {galaxies: individual: NGC 1614, galaxies: nuclei, galaxies: starburst, infrared: galaxies, radio continuum: galaxies, supernovae: general}, doi = {10.1088/0004-637X/786/2/156}, url = {http://adsabs.harvard.edu/abs/2014ApJ...786..156H}, author = {R. Herrero-Illana and M. A. P{\'e}rez-Torres and Alonso-Herrero, A. and Alberdi, A. and Colina, L. and Efstathiou, A. and Hern{\'a}ndez-Garc{\'\i}a, L. and Miralles-Caballero, D. and V{\"a}is{\"a}nen, P. and Packham, C.~C. and Rajpaul, V. and Zijlstra, A.~A.} } @article {2014MNRAS.440.1052K, title = {{The nature of supernovae 2010O and 2010P in Arp 299 - I. Near-infrared and optical evolution}}, journal = {Monthly Notices of the Royal Astronomical Society}, volume = {440}, year = {2014}, month = {may}, pages = {1052-1066}, abstract = {We present near-infrared and optical photometry, plus optical spectroscopy of two stripped-envelope supernovae (SNe) 2010O and 2010P that exploded in two different components of an interacting luminous infrared galaxy Arp 299 within only a few days of one another. SN 2010O is found to be photometrically and spectroscopically similar to many normal Type Ib SNe and our multiwavelength observations of SN 2010P suggest it to be a Type IIb SN. No signs of clear hydrogen features or interaction with the circumstellar medium are evident in the optical spectrum of SN 2010P. We derive estimates for the host galaxy line-of-sight extinctions for both SNe, based on both light curve and spectroscopic comparison finding consistent results. These methods are also found to provide much more robust estimates of the SN host galaxy reddening than the commonly used empirical relations between extinction and equivalent width of Na I D absorption features. The SN observations also suggest that different extinction laws are present in different components of Arp 299. For completeness, we study high-resolution pre-explosion images of Arp 299 and find both SNe to be close to, but not coincident with, extended sources that are likely massive clusters. A very simple model applied to the bolometric light curve of SN 2010O implies a rough estimate for the explosion parameters of E$_{k}$ {\ap} 3 {\times} 10$^{51}$ erg, M$_{ej}$ {\ap} 2.9 M$_{\&sun;}$ and M$_{Ni}$ {\ap} 0.16 M$_{\&sun;}$.}, keywords = {galaxies: individual: Arp 299, galaxies: starburst, infrared: galaxies, supernovae: general, supernovae: individual: SN 2010O, supernovae: individual: SN 2010P}, doi = {10.1093/mnras/stt2289}, url = {http://adsabs.harvard.edu/abs/2014MNRAS.440.1052K}, author = {Kankare, E. and Mattila, S. and Ryder, S. and Fraser, M. and Pastorello, A. and Elias-Rosa, N. and Romero-Ca{\~n}izales, C. and Alberdi, A. and Hentunen, V.-P. and R. Herrero-Illana and Kotilainen, J. and M. A. P{\'e}rez-Torres and V{\"a}is{\"a}nen, P.} } @article {2014MNRAS.440.1067R, title = {{The nature of supernovae 2010O and 2010P in Arp 299 - II. Radio emission}}, journal = {Monthly Notices of the Royal Astronomical Society}, volume = {440}, year = {2014}, pages = {1067-1079}, abstract = {We report radio observations of two stripped-envelope supernovae (SNe), 2010O and 2010P, which exploded within a few days of each other in the luminous infrared galaxy Arp 299. Whilst SN 2010O remains undetected at radio frequencies, SN 2010P was detected (with an astrometric accuracy better than 1 milli arcsec in position) in its optically thin phase in epochs ranging from {\tilde}1 to {\tilde}3 yr after its explosion date, indicating a very slow radio evolution and a strong interaction of the SN ejecta with the circumstellar medium. Our late-time radio observations towards SN 2010P probe the dense circumstellar envelope of this SN, and imply dot$\{$M$\}$ [ $\{$M\_$\{${\sun}$\}$ yr\^{}$\{$-1$\}$$\}$] / v\_$\{$wind$\}$ [10 km s\^{}$\{$-1$\}$] =(3.0-5.1) {\times} 10$^{-5}$, with a 5 GHz peak luminosity of {\tilde}1.2 {\times} 10$^{27}$ erg s$^{- 1}$ Hz$^{- 1}$ on day {\tilde}464 after explosion. This is consistent with a Type IIb classification for SN 2010P, making it the most distant and most slowly evolving Type IIb radio SN detected to date.}, keywords = {galaxies: individual: Arp 299, galaxies: starburst, radio continuum: galaxies, supernovae: general, supernovae: individual: SN 2010O, supernovae: individual: SN 2010P}, doi = {10.1093/mnras/stu430}, url = {http://adsabs.harvard.edu/abs/2014MNRAS.440.1067R}, author = {Romero-Ca{\~n}izales, C. and R. Herrero-Illana and M. A. P{\'e}rez-Torres and Alberdi, A. and Kankare, E. and Bauer, F.~E. and Ryder, S.~D. and Mattila, S. and Conway, J.~E. and Beswick, R.~J. and Muxlow, T.~W.~B.} } @article {2012ApJ...756..111M, title = {{Core-collapse Supernovae Missed by Optical Surveys}}, journal = {The Astrophysical Journal}, volume = {756}, year = {2012}, month = {sep}, pages = {111}, abstract = {We estimate the fraction of core-collapse supernovae (CCSNe) that remain undetected by optical SN searches due to obscuration by large amounts of dust in their host galaxies. This effect is especially important in luminous and ultraluminous infrared galaxies, which are locally rare but dominate the star formation at redshifts of z \~{} 1-2. We perform a detailed investigation of the SN activity in the nearby luminous infrared galaxy Arp 299 and estimate that up to 83\% of the SNe in Arp 299 and in similar galaxies in the local universe are missed by observations at optical wavelengths. For rest-frame optical surveys we find the fraction of SNe missed due to high dust extinction to increase from the average local value of \~{}19\% to \~{}38\% at z \~{} 1.2 and then remain roughly constant up to z \~{} 2. It is therefore crucial to take into account the effects of obscuration by dust when determining SN rates at high redshift and when predicting the number of CCSNe detectable by future high-z surveys such as LSST, JWST, and Euclid. For a sample of nearby CCSNe (distances 6-15 Mpc) detected during the last 12 yr, we find a lower limit for the local CCSN rate of 1.5$^{+0.4}$ $_{- 0.3}$ {\times} 10$^{-4}$ yr$^{-1}$ Mpc$^{-3}$, consistent with that expected from the star formation rate. Even closer, at distances less than \~{}6 Mpc, we find a significant increase in the CCSN rate, indicating a local overdensity of star formation caused by a small number of galaxies that have each hosted multiple SNe.}, keywords = {galaxies: individual: Arp 299, galaxies: starburst, infrared: galaxies, supernovae: general, supernovae: individual: SN 2005at SN 2010P}, doi = {10.1088/0004-637X/756/2/111}, url = {http://adsabs.harvard.edu/abs/2012ApJ...756..111M}, author = {Mattila, S. and Dahlen, T. and Efstathiou, A. and Kankare, E. and Melinder, J. and Alonso-Herrero, A. and M. A. P{\'e}rez-Torres and Ryder, S. and V{\"a}is{\"a}nen, P. and {\"O}stlin, G.} } @article {2012ApJ...744L..19K, title = {{Discovery of Two Supernovae in the Nuclear Regions of the Luminous Infrared Galaxy IC 883}}, journal = {The Astrophysical Journal Letters}, volume = {744}, year = {2012}, pages = {L19}, abstract = {We report the discovery of two consecutive supernovae (SNe), 2010cu and 2011hi, located at 0farcs37 (180 pc) and 0farcs79 (380 pc) projected distance, respectively, from the center of the K-band nucleus of the luminous infrared galaxy (LIRG) IC 883. The SNe were discovered in an ongoing near-infrared K-band search for core-collapse SNe in such galaxies using the ALTAIR/NIRI adaptive optics system with laser guide star at the Gemini-North Telescope. These are thus the closest SNe yet discovered to an LIRG nucleus in optical or near-infrared wavelengths. The near-infrared light curves and colors of both SNe are consistent with core-collapse events. Both SNe seem to suffer from relatively low host galaxy extinction suggesting that regardless of their low projected galactocentric distances, they are not deeply buried in the nuclear regions of the host galaxy.}, keywords = {galaxies: individual: IC 883, galaxies: starburst, infrared: galaxies, instrumentation: adaptive optics, supernovae: individual: SN 2010cu SN 2011hi}, doi = {10.1088/2041-8205/744/2/L19}, url = {http://adsabs.harvard.edu/abs/2012ApJ...744L..19K}, author = {Kankare, E. and Mattila, S. and Ryder, S. and V{\"a}is{\"a}nen, P. and Alberdi, A. and Alonso-Herrero, A. and Colina, L. and Efstathiou, A. and Kotilainen, J. and Melinder, J. and M. A. P{\'e}rez-Torres and Romero-Ca{\~n}izales, C. and Takalo, A.} } @article {2012A\&A...543A..72R, title = {{e-MERLIN and VLBI observations of the luminous infrared galaxy IC 883: a nuclear starburst and an AGN candidate revealed}}, journal = {Astronomy and Astrophysics}, volume = {543}, year = {2012}, month = {jul}, pages = {A72}, abstract = {Context. The high star formation rates of luminous infrared galaxies (LIRGs) make them ideal places for core-collapse supernova (CCSN) searches. Massive star formation can often be found in coexistence with an active galactic nucleus (AGN), contributing jointly to the energy source of LIRGs. At radio frequencies, where light is unaffected by dust extinction, it is possible to detect compact components within the innermost LIRG nuclear regions, such as SNe and SN remnants, as well as AGN buried deep in the LIRG nuclei.
Aims: Our study of the LIRG IC 883 aims at: (i) investigating the parsec-scale radio structure of the (circum-)nuclear regions of IC 883; (ii) detecting at radio frequencies the two recently reported circumnuclear SNe 2010cu and 2011hi, which were discovered by near-IR (NIR) adaptive optics observations of IC 883; and (iii) further investigating the nature of SN 2011hi at NIR wavelengths.
Methods: We used the electronic European very long baseline interferometry (VLBI) Network (e-EVN) at 5 GHz, and the electronic Multi-Element Remotely Linked Interferometer Network (e-MERLIN) at 6.9 GHz, to observe contemporaneously the LIRG IC 883 at high angular-resolution (from tens to hundreds of milliarcsec) and with high sensitivity ({\l}t}70 {$μ$}Jy), complemented by archival VLBI data at 5 GHz and 8.4 GHz. We also used the Gemini North telescope to obtain late-time JHK photometry for SN 2011hi.
Results: The circumnuclear regions traced by e-MERLIN at 6.9 GHz have an extension of \~{} 1 kpc, at a position angle of 130{\deg}, and show a striking double-sided structure, which very likely corresponds to a warped rotating ring, in agreement with previous studies. Our e-EVN observations at 5 GHz and complementary archival VLBI data at 5 GHz and 8.4 GHz, reveal various milliarcsec compact components in the nucleus of IC 883. A single compact source, an AGN candidate, dominates the emission at both nuclear and circumnuclear scales, as imaged with the e-EVN and e-MERLIN, respectively. The other milliarcsec components are strongly indicative of ongoing nuclear CCSN activity. Our e-EVN observations also provided upper limits to the radio luminosity of the two SNe in IC 883 recently discovered at NIR wavelengths. We refine the classification of SN 2011hi as a Type IIP SN according to our latest epoch of Gemini North observations acquired in 2012, in agreement with a low-luminosity radio SN nature. We estimate a CCSN rate lower limit of 1.1$_{-0.6}$$^{+1.3}$ yr$^{-1}$ for the entire galaxy, based on three nuclear radio SNe and the circumnuclear SNe 2010cu and 2011hi.}, keywords = {galaxies: individual: IC 883, galaxies: starburst, radiation mechanisms: non-thermal, radio lines: stars}, doi = {10.1051/0004-6361/201218816}, url = {http://adsabs.harvard.edu/abs/2012A\%26A...543A..72R}, author = {Romero-Ca{\~n}izales, C. and M. A. P{\'e}rez-Torres and Alberdi, A. and Argo, M.~K. and Beswick, R.~J. and Kankare, E. and Batejat, F. and Efstathiou, A. and Mattila, S. and Conway, J.~E. and Garrington, S.~T. and Muxlow, T.~W.~B. and Ryder, S.~D. and V{\"a}is{\"a}nen, P.} } @article {2012A\&A...540L...5H, title = {{Evidence of nuclear disks in starburst galaxies from their radial distribution of supernovae}}, journal = {Astronomy and Astrophysics}, volume = {540}, year = {2012}, pages = {L5}, abstract = {Galaxy-galaxy interactions are expected to be responsible for triggering massive star formation and possibly accretion onto a supermassive black hole, by providing large amounts of dense molecular gas down to the central kiloparsec region. Several scenarios to drive the gas further down to the central \~{}100 pc, have been proposed, including the formation of a nuclear disk around the black hole, where massive stars would produce supernovae. Here, we probe the radial distribution of supernovae and supernova remnants in the nuclear regions of the starburst galaxies M 82, Arp 299-A, and Arp 220, by using high-angular resolution ({\l}sim} 0.{\textquoteright}{\textquoteright}1) radio observations published in the literature (for M 82 and Arp 220), or obtained by ourselves from the European VLBI Network (Arp 299-A). Our main goal was to characterize the nuclear starbursts in those galaxies and thus test scenarios that propose that nuclear disks of sizes \~{}100 pc form in the central regions of starburst galaxies. We obtained the radial distribution of supernovae (SNe) in the nuclear starbursts of M 82, Arp 299-A, and Arp 220, and derived scale-length values for the putative nuclear disks powering the bursts in those central regions. The scale lengths for the (exponential) disks range from \~{}20-30 pc for Arp 299-A and Arp 220, up to \~{}140 pc for M 82. The radial distribution of SNe for the nuclear disks in Arp 299-A and Arp 220 is also consistent with a power-law surface density profile of exponent {$\gamma$} = 1, as expected from detailed hydrodynamical simulations of nuclear disks. Our results support scenarios where a nuclear disk of size \~{}100 pc is formed in (U)LIRGs, and sustained by gas pressure, in which case the accretion onto the black hole could be lowered by supernova feedback. Appendices are available in electronic form at http://www.aanda.org}, keywords = {galaxies: individual: Arp 299-A, galaxies: luminosity function, galaxies: starburst, mass function, radiation mechanisms: non-thermal, radio continuum: stars, supernovae: general}, doi = {10.1051/0004-6361/201118545}, url = {http://adsabs.harvard.edu/abs/2012A\%26A...540L...5H}, author = {R. Herrero-Illana and M. A. P{\'e}rez-Torres and Alberdi, A.} } @article {2012MNRAS.422..510R, title = {{EVN observations of the farthest and brightest ULIRGs in the local Universe: the case of IRAS 23365+3604}}, journal = {Monthly Notices of the Royal Astronomical Society}, volume = {422}, year = {2012}, month = {may}, pages = {510-520}, abstract = {We present high-resolution, high-sensitivity radio images of the ultra-luminous infrared galaxy (ULIRG) IRAS 23365+3604. We performed contemporaneous observations at 1.7 and 5.0 GHz, in three epochs separated by 1 year from each other, with the European Very Long Baseline Interferometry (VLBI) Network (EVN). We also present complementary Multi-Element Radio Linked Interferometry Network (MERLIN) at 1.6 and 5.0 GHz, and archival Very Large Array data, taken at 1.4 and 4.9 GHz. We find that the emission at {\tilde}5.0 GHz remains quite compact as seen at different resolutions, whereas at {\tilde}1.7 GHz, high-resolution imaging reveals some extended structure. The nuclear region has an approximate linear size of 200 pc and shows the presence of two main emission components: (i) one with a composite spectrum due to ongoing non-thermal activity (probably due to recently exploded supernovae and the presence of an active galactic nucleus), and (ii) the other with a steep spectrum, likely dominated by an old population of radio emitters, such as supernova remnants. Radiative losses are important, so re-acceleration or replenishment of new electrons is necessary. We estimate a magnetic field strength of {\tilde} 18 {$μ$}G at galactic and {\tilde} 175 {$μ$}G at nuclear scales, which are typical for galaxies in advanced mergers.}, keywords = {galaxies: individual: IRAS 23365+3604, galaxies: starburst, radio continuum: general}, doi = {10.1111/j.1365-2966.2012.20627.x}, url = {http://adsabs.harvard.edu/abs/2012MNRAS.422..510R}, author = {Romero-Ca{\~n}izales, C. and M. A. P{\'e}rez-Torres and Alberdi, A.} } @article {2012A\&A...539A.134B, title = {{The nuclear starburst in Arp 299-A: from the 5.0 GHz VLBI radio light-curves to its core-collapse supernova rate}}, journal = {Astronomy and Astrophysics}, volume = {539}, year = {2012}, pages = {A134}, abstract = {Context. The nuclear region of the luminous infrared galaxy (LIRG) Arp 299-A hosts a recent ( {\sime} 10 Myr) intense burst of massive star formation that is expected to lead to numerous core-collapse supernovae (CCSNe). Previous VLBI observations, carried out with the European VLBI Network (EVN) at 5.0 GHz and with the VLBA at 2.3 and 8.4 GHz, resulted in the detection of many compact, bright, non-thermal sources in a region {\l}sim} 150 pc in size.
Aims: We aim to establish the nature of all non-thermal compact components in Arp 299-A, as well as to estimate its core-collapse supernova rate. While the majority of the compact components are expected to be young radio supernovae (RSNe) and supernova remnants (SNRs), a definitive classification is still lacking. Yet, this is very relevant for eventually establishing the CCSN rate, as well as the star formation rate, for this galaxy.
Methods: We used multi-epoch EVN observations taken at 5.0 GHz to image the compact radio sources in the nuclear region of Arp 299-A with milliarcsecond resolution. We also used one single-epoch 5.0 GHz Multi-Element Radio Linked Interferometer Network (MERLIN) observation to image the extended emission in which these compact radio sources are embedded.
Results: We present the first 5.0 GHz radio light-curve (spanning \~{}2.5 yr) of all compact components in the nuclear starburst of Arp 299-A. Twenty-six compact sources are detected, eight of which are new objects. The properties of all detected objects are consistent with them being a mixed population of CCSNe and SNRs. We find clear evidence for at least two new CCSNe, implying a lower limit to the CCSN rate of {$ν$}$_{SN}$ {\gsim} 0.80 SN/yr, indicating that the bulk of the current star formation in Arp 299-A is taking place in the innermost \~{}150 pc.A few more objects show variability consistent with them being recently exploded SNe, but only future observations will clarify this point. Our MERLIN observations trace a region of diffuse extended emission that is cospatial to the region where all compact sources are found. From this diffuse non-thermal radio emission traced by MERLIN we obtain an independent estimate for the CCSN rate, which is in the range {$ν$}$_{SN}$ = 0.40-0.65 SN/yr, in agreement with previous estimates and our direct estimate of the CCSN rate from the compact radio emission.
Conclusions: Our \~{}2.5 yr monitoring of Arp 299-A has allowed us to obtain for the first time a direct estimate of the CCSN rate of {$ν$}$_{SN}$ {\gsim} 0.80 SN/yr for the innermost \~{}150 pc of Arp 299-A.}, keywords = {galaxies: individual: Arp 299, galaxies: luminosity function, galaxies: starburst, mass function, radiation mechanisms: non-thermal, radio continuum: stars, supernovae: general}, doi = {10.1051/0004-6361/201118446}, url = {http://adsabs.harvard.edu/abs/2012A\%26A...539A.134B}, author = {Bondi, M. and M. A. P{\'e}rez-Torres and R. Herrero-Illana and Alberdi, A.} } @article {2011MNRAS.415.2688R, title = {{The core-collapse supernova rate in Arp 299 revisited}}, journal = {Monthly Notices of the Royal Astronomical Society}, volume = {415}, year = {2011}, pages = {2688-2698}, abstract = {We present a study of the core-collapse supernova (CCSN) rate in nuclei A and B1, of the luminous infrared galaxy (LIRG) Arp 299, based on {\tilde}11 yr of Very Large Array (VLA) monitoring of their radio emission at 8.4 GHz. Significant variations in the nuclear radio flux density can be used to identify the CCSN activity in the absence of high-resolution very long baseline interferometry (VLBI) observations. In the case of the B1-nucleus, the small variations in its measured diffuse (synchrotron plus free-free) radio emission are below the fluxes expected from radio supernovae (RSNe), thus making it well-suited to detect RSNe through flux density variability. In fact, we find strong evidence for at least three RSNe this way, which results in a lower limit for the CCSN rate ({$ν$}$_{SN}$) of {\gt}0.28$^{+0.27}$$_{-0.15}$ yr$^{-1}$. This value agrees within the uncertainties with the infrared (IR) luminosity based SN rate estimate, and with previously reported radio estimates. In the A-nucleus, we did not detect any significant variability and found a SN detection threshold luminosity of {\ap}3.1 {\times} 10$^{28}$ erg s$^{-1}$ Hz$^{-1}$, allowing only the detection of the most luminous RSNe known. Our method is basically blind to normal CCSN explosions occurring within the A-nucleus, which result in too small variations in the nuclear flux density, remaining diluted by the strong diffuse emission of the nucleus itself. Additionally, we have attempted to find near-IR (NIR) counterparts for the earlier reported RSNe in the Arp 299 nucleus A, by comparing NIR adaptive optics images from the Gemini-N Telescope with contemporaneous observations from the European VLBI Network (EVN). However, we were not able to detect NIR counterparts for the reported radio SNe within the innermost regions of nucleus A. While our NIR observations were sensitive to typical CCSNe at {\tilde}300 mas (or 70 pc projected distance) from the centre of the nucleus A, suffering from extinction up to A$_{V}${\tilde} 15 mag, they were not sensitive to such highly obscured SNe within the innermost nuclear regions where most of the EVN sources were detected.}, keywords = {galaxies: individual: NGC 3690:IC 694, galaxies: starburst, supernovae: general}, doi = {10.1111/j.1365-2966.2011.18886.x}, url = {http://adsabs.harvard.edu/abs/2011MNRAS.415.2688R}, author = {Romero-Ca{\~n}izales, C. and Mattila, S. and Alberdi, A. and M. A. P{\'e}rez-Torres and Kankare, E. and Ryder, S.~D.} } @article {2010A\&A...519L...5P, title = {{Serendipitous discovery of the long-sought active galactic nucleus in Arp 299-A}}, journal = {Astronomy and Astrophysics}, volume = {519}, year = {2010}, month = {sep}, pages = {L5}, abstract = {Context. The dusty nuclear regions of luminous infra-red galaxies (LIRGs) are heated by either an intense burst of massive star formation, an active galactic nucleus (AGN), or a combination of both. Disentangling the contribution of each of those putative dust-heating agents is a challenging task, and direct imaging of the innermost few pc can only be accomplished at radio wavelengths, using very high-angular resolution observations.
Aims: We observed the nucleus A of the interacting starburst galaxy Arp 299, using very long baseline interferometry (VLBI) radio observations at 1.7 and 5.0 GHz. Our aim was to characterize the compact sources in the innermost few pc region of Arp 299-A, as well as to detect recently exploded core-collapse supernovae.
Methods: We used the European VLBI Network (EVN) to image the 1.7 and 5.0 GHz compact radio emission of the parsec-scale structure in the nucleus of Arp 299-A with milliarcsecond resolution.
Results: Our EVN observations show that one of the compact VLBI sources, A1, previously detected at 5.0 GHz, has a flat spectrum between 1.7 and 5.0 GHz and is the brightest source at both frequencies. Our 1.7 GHz EVN image shows also diffuse, low-surface brightness emission extending westwards from A1 and displays a prominent core-jet structure.
Conclusions: The morphology, radio luminosity, spectral index and ratio of radio-to-X-ray emission of the A1-A5 region is consistent with a low-luminosity AGN (LLAGN), and rules out the possibility that it is a chain of young radio supernovae (RSNe) and supernova remnants (SNRs). We therefore conclude that A1-A5 is the long-sought AGN in Arp 299-A. This finding may suggest that both starburst and AGN are frequently associated phenomena in mergers.}, keywords = {galaxies: individual: Arp 299, galaxies: starburst, Galaxy: nucleus, radiation mechanisms: non-thermal, radio continuum: stars}, doi = {10.1051/0004-6361/201015462}, url = {http://adsabs.harvard.edu/abs/2010A\%26A...519L...5P}, author = {M. A. P{\'e}rez-Torres and Alberdi, A. and Romero-Ca{\~n}izales, C. and Bondi, M.} }