Serch for diffuse extended mid-ir emission in Luminous IR Glxies V. Chrmndris 1, E. Le Floc h 2, I.F. Mirel 2 1- Cornell University, Astronomy Deprtment, Ithc, NY, USA 2- Service d Astrophysique, CEA/Scly, Gif-sur-Yvette, Frnce The discovery y IRAS of luminous ( >10 11 L ) nd ultrluminous (L IR >1012 L ) IR glxies (LIRGs / ULIRGs) opened new window in extrglctic stronomy, since it reveled tht they re for those luminosities the dominnt popultion of extrglctic ojects in the locl Universe (z<0.3). It is now widely ccepted tht i) nerly ll ULIRGs re dvnced mergers hroring powerful nucler strursts nd/or enshrouded AGN, nd ii) the mid-ir is powerful trcer of the str formtion ctivity nd olometric luminosity of glxies. The poor sptil resolution of IRAS though, due to the lrge (~1rcmin) pixels used, mde it impossile to resolve the physicl extent of the region which produces the ulk of the mid-ir emission. Recently, ground sed 10 nd 18µm imging for numer of the nerest nd rightest ojects, hs reveled compct nucler emission from regions of just few rcsecs in dimeter, (i.e. Soifer et l. 2001)., even though the ground mesurements re hmpered in sensitivity y the low mid-ir tmospheric trnsmission. Using ISOCAM, the most sensitive mid-ir cmer to dte nd the good sptil resolution imges it provides, we serched for extended emission from smple of nery luminous IR glxies (Arp220, Arp299, NGC6240, VV114, IRAS14248-1447, IRAS19254-7245, IRAS23128-5919) for which the 5-16µm spectrl energy distriution ws ville. We find tht with the exception of VV114 more thn 90% of the integrted IRAS 12 micron flux origintes from their nucler regions (~5rcsec, <2kpc). This result suggests tht the 10-15µm properties of distnt unresolved ULIRGs would likely to lso e dominted not y their disks, ut y their nucler region insted.
Arp220 = 1.2x10 12 L, D=72Mpc (z=0.018), IRAS12=0.48Jy, f(12-18µm)~732mjy The prototypicl ULIRG. The two nuclei of the merger re seprted y 0.94 (~330pc) nd re unresolved y ISOCAM. No diffuse emission which cn not e ttriuted to the centrl point source hs een oserved down to our sensitivity limit (σ~0.02mjyrcsec -2 ). ) Imge of Arp220 oserved with ISOCAM t 6.75 µm (LW2 filter). The lowest contour is t 0.2mJy/pixel while the pek emission is 25mJy/pixel. ) The ISOCAM imge t 15µm (LW3 filter). The lowest contour is t 0.4mJy/pixel while the pek emission is 64mJy/pixel. The pixel size hs een convolved from 1.5rcsec to 3rcsec (~1kpc). In oth cses the two nuclei remin unresolved. The mid-ir SED of Arp220. Note the deep, nerly sturted, silicte sorption t 9.7µm. Tking into ccount the PAH emission fetures, the spectrum cn e fitted with wrm lckody of T~165K, extinct y Av~85mg ssuming screen model nd the extinction curve of Dudley & Wynn-Willims (1997). The red line indictes the IRAS12 flux nd ndwidth. For comprison we show n HST/NICMOS 2.2µm imge of Arp220 y Scoville et l. 2000 long with 7.9 nd 18µm imges tken with Keck (Soifer t l. 2001). We see tht the therml wrm dust emission is loclized to su-rcsec regions.
NGC6240 = 0.6x10 12 L, D=97Mpc (z=0.025), IRAS12=0.56Jy, f(12-18µm)~785mjy A nerly ultrluminous merger of two counter-rotting gs rich glxies. The two nuclei re seprted y 1.6rcsec(~0.8kpc). The southern glxy is righter, more dusty thn the norther one (see Scoville et l. 2000) nd it displys LINER spectrum. Strong emission from wrm H 2 gs hs een oserved in the ner-ir (vn der Werf 1993). We oserved no diffuse emission. Furthermore the AGN does not contriute significntly in the mid-ir to e identified vi our low spectrl resolution mid-ir dignostic (see Lurent et l. 2000) or vi the high-ioniztion lines (see Genzel et l. 1998, ApJ, 498, 579) The mid-ir SED of NGC6240. Tking into ccount the PAH emission fetures the spectrum cn e fitted with wrm lckody of T~150K, extinct y Av~30mg ssuming screen model nd the extinction curve of Dudley & Wynn-Willims (1997). The red line indictes the IRAS12 flux nd ndwidth. Note the strong H 2 lines (this is the only system in our smple displying them s prominently) which re due to wrm shocked moleculr gs s the two progenitor counter-rotting disks interct in the regions etween the nuclei. ) Imge of NGC6240 oserved with ISOCAM t 6.75µm (LW2 filter). The lowest contour is t 0.2mJy/pixel while the pek emission is 18mJy/pixel. ) The ISOCAM imge t 15µm (LW3 filter). The lowest contour is t 0.4mJy/pixel while the pek emission is 32mJy/pixel. The pixel size is 1.5rcsec (~750pc). We cn mrginlly oserve n extension long the north/south direction of the two nuclei. For comprison we present the HST/NICMOS 2.2µm imge of NGC6240 y Scoville et l. 2000
Arp299 (IC694/NGC3690) = 0.52x10 12 L, D=41Mpc (z=0.01) A system with two glxies (IC694, NGC3690) violently intercting. Its morphology chnges drmticlly etween the opticl nd mid-ir where the enshrouded nucler source in IC694 domintes the emission of the system. Even though some diffuse emission is detected in the vrious str forming regions of the tidl deris nd disks it does not contriute sustntilly to the IRAS12 wrm dust emission nd it only ccounts for less thn 30% of the olometric luminosity of Arp299. The ltter ws quntified vi KAO imging of the 37µm emission, which unlike the 15µm flux directly trces the IR luminosity. We present s ckground the HST/NICMOS J-nd imge of Arp299 otined y Alonso-Herrero (2000) overlid with contours of ) the 7µm emission, ) the 15µm emission, nd c) the 38µm emission. Note how IC694 domintes s we move to longer wvelengths. For more detils see Chrmndris et l., ApJ, 2002, 571, 282. IC694 => ~40% L ol NGC3690 => ~20% L ol Region C => ~10% L ol ) A 12.5µm imge of Arp299 tken with Keck (Soifer t l. 2001) which displys the compct mid-ir morphology. ) Curves of growth (x-xis rdius in kpc / y-xis normlized to IRAS12 flux) indicting tht most mid-ir emission is compct (solid line 12.5µm, dshed line 2µm (from Soifer t l. 2001) The SED of the vrious components of Arp299. IC694 (shown in red) even though inconspicuous in the opticl is responsile for the ulk of the olometric luminosity (Chrmndris et l. 2002).
IRAS 19254-7245 (The Superntenne) = 1.03x10 12 L, D=250Mpc (z=0.06), IRAS12=0.22Jy, f(12-18µm)~290mjy Well known system of two gs rich intercting glxies the nuclei of which re seprted y 10kpc, displying long tidl tils extending to 350kpc. The northern glxy is strurst of LINER while southern glxy hs een clssified s Seyfert 2. The presence of the Seyfert is visile in our spectrum s we cn detect the elevted emission of hot dust originting from the AGN torus t the of the 5-6µm region. We find tht more thn 95% of the mid-ir flux (12-18µm) origintes from the unresolved nucler region of the southern glxy. The 12-18µm luminosity of the system is ~4% of the totl emitted in the IR (8-1000µm). For more info see Chrmndris et l. 2002 (stro-ph/0206150). ) Imge of IRAS19254-7245 oserved with ISOCAM t 6.75µm (LW2 filter). The contours re 5, 10, 20, 40, 80, 160 nd 320σ (σ=0.027 mjy /pixel). ) Imge of IRAS 19254-7245 oserved with ISOCAM t 15µm (LW3 filter). The contours re 5, 10, 20, 40, 80, 160 nd 320σ (σ=0.041 mjy /pixel) Note tht the PSF hs cler symmetry in the southwest direction of the Airy ring. The two verticl rs correspond to 10kpc. The integrted mid-ir SED of the glxy summing ll flux ove 5σ. The 5-11µm spectrum of Rigopoulou et l. (1999) is included. K-nd imge of the glxy from Duc et l. 1997. The r is 5kpc is size. The mid-ir SED of the two glxy components. The red line indictes the IRAS12 flux nd ndwidth. Note tht the southern glxy emits more thn 95% the mid-ir flux of the system.
IRAS 23128-5919 = 0.92x10 12 L, D=180Mpc (z=0.04), IRAS12=0.24Jy, f(12-18µm)~316mjy Intercting system with two glxies seprted y 4kpc nd displying two tidl tils stretching 40kpc in opposite directions. The northern glxy is strurst, while the southern shows evidence of Seyfert/LINER ctivity. We find tht 75% of the mid-ir flux (12-18µm) origintes from the unresolved nucler region of the southern component. The 12-18µm luminosity of the system is ~3% of the totl emitted in the IR (8-1000µm). For more info see Chrmndris et l. 2002 (stro-ph/0206150). 10kpc 10kpc ) Imge of IRAS 23128-5919 oserved with ISOCAM t 6.75µm (LW2 filter). The contours re 5, 10, 20, 40 nd 80σ (σ=0.055 mjy /pixel). ) Imge of IRAS23128-5919 oserved with ISOCAM t 15µm (LW3 filter). The contours re 5, 8, 10, 20, 40 nd 80σ (σ=0.093 mjy/pixel). The two glxies re unresolved nd ll mid-ir emission origintes from their nucler region. No emission is seen from the disk or tils. The integrted mid-ir SED of the glxy summing ll flux ove 5σ. Note tht we cn ccount for the whole IRAS12 flux indicted in red. K-nd imge of the glxy from Duc et l. 1997. The r is 5kpc is size. The mid-ir SED of the two glxy components. The red line indictes the IRAS12 flux nd ndwidth. Note tht the southern glxy domintes the mid-ir emission of the system.
IRAS 14348-1447 = 1.85x10 12 L, D=335Mpc (z=0.08), IRAS12 <0.14Jy, f(12-18µm)~97mjy This intercting system is the most distnt in the BGS.Its two glxies re seprted y 6kpc with til extending to more thn 10kpc to the north. It is one of the most H 2 rich ULIRGs contining ~6x10 10 M of moleculr gs. The nucleus of the southern glxy is Seyfert 1.5 while the northern one is Seyfert 2. We estimte tht ~75% of the mid-ir flux origintes from the unresolved nucleus of the southern glxy. Due to limited mid-ir color informtion we re unle to comment on the evidence of AGN ctivity. The 12-18µm luminosity of the system is ~2% of the totl emitted in the IR (8-1000µm). For more info see Chrmndris et l. 2002 (stro-ph/0206150). ) Imge of IRAS14348-1447 oserved with ISOCAM t 6.75µm (LW2 filter). The contours re 5, 10, 20, 40 nd 80σ (σ=0.048 mjy/pixel). ) Imge of IRAS14348-1447 oserved with ISOCAM t 15µm (LW3 filter). The contours re 5, 10, 20 nd 30 σ (σ=0.073 mjy/pixel). The integrted mid-ir SED of the glxy summing ll flux ove 5σ. The horizontl lines indicte our ISOCAM rod nd mesurements while the 5-11µm spectrum is the ISO/PHOT-S dt of Rigopoulou et l. 1999. Note tht we cn ccount for the whole IRAS12 flux indicted in red. R-nd imge of the glxy from Duc et l. 1997. The northern til extending to more thtn 10kpc is visile. The verticl r corresponds to 10kpc.
VV114 (Arp236) = 0.4x10 12 L, D=80Mpc (z=0.02), IRAS12=0.64Jy VV114E VV114W Intercting system with two glxies seprted y 6kpc. Even though VV114W domintes the opticl, ner- nd mid-ir emission, it is VV114E (which is resolved in two components) tht is ~4x more mid-ir luminous. Bsed on our dignostic (Lurent et l. 2000, A&A, 359, 887) VV114E ppers to hror n emedded AGN which cn e responsile for ~40% of mid-ir flux. VV114E NE ) A 15µm imge of VV114 with n overly of the integrted PAH emission. ) An HST/NICMOS J-nd imge of VV114 (Scoville et l. 2000) with n overly of the 15µm contours. The contour levels re 0.45, 0.65, 0.90, 1.35, 2.10, 4.45 nd 8.45 mjy/rcsec 2. Note how even though the pek of the mid-ir emission origintes from VV114E, diffuse emission is seen from the whole overlp region of the system (Le Floc h et l. 2002 A&A, stro-ph/0205401) VV114W AGN VV114E SW VV114E ) A 12.5µm imge of VV114E tken with Keck (Soifer t l. 2001), resolving the NE nd SW components. ) Curves of growth (x-xis rdius in kpc / y-xis flux normlized to IRAS12) reveling the presence of extended mid-ir emission (solid line) following the ner-ir light profile (Soifer et l.2001). ) The mid-ir SED of the two nuclei of the two intercting components, with VV114W normlized to the 14µm flux of VV114E. Note the hot continuum excess t 5µm indictive of n AGN t VV114E. ) The integrted spectrum of VV114 seprted in vrious regions. The red line indictes the IRAS12 flux nd ndwidth. Contrry to the other glxies presented here, we oserve the extended mid-ir emission of the syttem is more thn 1/3 of the totl.
Conclusions / Perspectives Using deep ISOCAM mid-ir imging we serched for the presence of extended emission in the 8-16µm rnge in numer of nery luminous nd ultrluminous infrred glxies which were detected y IRAS t 12µm. Our gol ws to exmine whether cses of extended extrnucler ctivity which cn ccount for considerle frction of the mid-ir therml emission similr to those oserved y ISO in intercting systems such s NGC4038/39 (Mirel et l. 1998) or Stephn s Quintet (Xu et l. 1999) re lso present in LIRGs or ULIRGs. All systems exmined re rther close-y nd consist of two well defined glxies which re either currently violently intercting, or re mergers contining doule nuclei. For most glxies high resolution ner-ir dt were ville. Ground sed mid-ir imging for the rightest glxies (Arp220, Arp299, VV114) only identified emission compct regions ssocited with the nuclei of the glxies. Our results indicte tht: Despite re superior sensitivity nd improved sptil resolution (~4 t 15µm) of ISOCAM compred to IRAS no significnt extended emission ws oserved nd we cn ccount for nerly ll of the IRAS12 flux from res confined in the nuclei of the glxies. This would suggest tht the excess of therml emission t 15µm which is oserved in distnt unresolved IR luminous glxies does not originte from n ensemle of discrete sources in their intercting memers ut more likely is due to the enshrouded energy source of their nuclei. VV114 is the only exception to the ovementioned result (Le Floc h et l. 2002). This could e due to the fct the VV114 ( LIRG) is in the process of ecoming ULIRG. The strong rdition from the AGN nd circumnucler strursts of its estern component cn het the gs/dust which ws stripped during n erlier phse of the interction out to distnces of ~3kpc. Since ll glxies presented here re trgets of the SIRTF GTO progrms, nd severl of them hve reveled numerous young str clusters, it would e interesting to tke dvntge of the ~100x increse of sensitivity provided y SIRTF to re-exmine this issue t the 3-8µm region y trcing the PAH emission from wek extr-nucler enshrouded str forming regions. For more informtion see our recent work t: Chrmndris, Stcey, & Gull, 2002, ApJ, 571, 282 Le Floc h, Chrmndris, Lurent, et l. 2002, A&A, in press (lso t stro-ph/0205401) Chrmndris, Lurent, Le Floc h, et l. 2002, A&A, in press (lso t srto-ph/0206150)