Radio Observations of AGN in Low Surface Brightness Galaxies

We present preliminary results of a study of the low frequency radio continuum emission from the nuclei of Giant Low Surface Brightness (LSB) galaxies. We have mapped the emission and searched for extended features such as radio lobes/jets associated with AGN activity. LSB galaxies are poor in star formation and generally less evolved compared to nearby bright spirals. This paper presents low frequency observations of 3 galaxies; PGC 045080 at 1.4 GHz, 610 MHz, 325MHz, UGC 1922 at 610 MHz and UGC 6614 at 610 MHz. The observations were done with the GMRT. Radio cores as well as extended structures were detected and mapped in all three galaxies; the extended emission may be assocated with jets/lobes associated with AGN activity. Our results indicate that although these galaxies are optically dim, their nuclei can host AGN that are bright in the radio domain.Comment: To appear in proceedings IAU Symp 244, 'Dark Galaxies and Lost Baryons', June 2007, 2 pages including 1 figur

A parameterisation of the soot aging for global climate models

International audienceThe representation of soot in global climate models is desirable since it contributes to both the direct and indirect climate effect. While freshly emitted soot is initially hydrophobic and externally mixed, it can be transferred into an internal mixture by coagulation, condensation or photochemical processes. These aging processes affect the hygroscopic qualities and hence the growth behaviour, the optical properties and eventually the lifetime of the soot particles. However, due to computational limits the aging of soot in global climate models is often only parameterised by an estimated turnover rate resulting in a lifetime of soot of several days. Based on the results of our simulations with a comprehensive mesoscale model, we derive the timescale on which diesel soot is transferred from an external to internal mixture, and propose a parameterisation for the use in global climate models. This parameterisation is applicable to continental conditions in industrialised areas as can be found in Central Europe and North America. For daytime conditions, away from the sources, condensation is dominant and the aging process occurs very fast with a timescale of ?=2 h. During night time condensation is not effective. Then coagulation is the most important aging process and our parameterisation leads to a timescale between 10 h and 40 h

Soot aging time scales in polluted regions during day and night

The aging of soot is one of the key uncertainties in the estimation of both the direct and indirect climate effect. While freshly emitted soot is initially hydrophobic and externally mixed, it can be transferred into an internal mixture by coagulation, condensation or photochemical processes. These aging processes affect the hygroscopic qualities and hence the growth behaviour, the optical properties and eventually the lifetime of the soot particles. However, due to computational limits the aging of soot in global climate models is often only parameterised by an estimated turnover rate resulting in a lifetime of soot of several days. Hence, the aging process of soot is one of the key uncertainties governing the burden and effect of black carbon. In this study, we discuss the time scale on which diesel soot is transferred from an external to an internal mixture based on the results of our simulations with a comprehensive mesoscale model. For daytime conditions during summer condensation of sulphuric acid is dominant and the aging process occurs on a time scale of τ =8h close to the sources and τ =2h above the source region. During winter comparable time scales are found but ammonium nitrate becomes more important. During night time condensation is not effective. Then coagulation is the most important aging process and our results show time scales between 10h and 40h

Radio Observations of the AGN and Gas in Low Surface Brightness Galaxies

LSB galaxies have low metallicities, diffuse stellar disks, and massive HI disks. We have detected molecular gas in two giant LSB galaxies, UGC 6614 and F568-6. A millimeter continuum source has been detected in UGC 6614 as well. At centimeter wavelengths we have detected and mapped the continuum emission from the giant LSB galaxy 1300+0144. The emission is extended about the nucleus and is most likely originating from the AGN in the galaxy. The HI gas distribution and velocity field in 1300+0144 was also mapped. The HI disk extends well beyond the optical disk and appears lopsided in the intensity maps.Comment: one page; submitted to proceedings of IAU Symposium 235: Galaxy Evolution across the Hubble Tim

The AGN and Gas Disk in the Low Surface Brightness Galaxy PGC045080

We present radio observations and optical spectroscopy of the giant low surface brightness (LSB) galaxy PGC 045080 (or 1300+0144). PGC 045080 is a moderately distant galaxy having a highly inclined optical disk and massive HI gas content. Radio continuum observations of the galaxy were carried out at 320 MHz, 610 MHz and 1.4 GHz. Continuum emission was detected and mapped in the galaxy. The emission appears extended over the inner disk at all three frequencies. At 1.4 GHz and 610 MHz it appears to have two distinct lobes. We also did optical spectroscopy of the galaxy nucleus; the spectrum did not show any strong emission lines associated with AGN activity but the presence of a weak AGN cannot be ruled out. Furthermore, comparison of the H$\alpha$ flux and radio continuum at 1.4 GHz suggests that a significant fraction of the emission is non-thermal in nature. Hence we conclude that a weak or hidden AGN may be present in PGC 045080. The extended radio emission represents lobes/jets from the AGN. These observations show that although LSB galaxies are metal poor and have very little star formation, their centers can host significant AGN activity. We also mapped the HI gas disk and velocity field in PGC 045080. The HI disk extends well beyond the optical disk and appears warped. In the HI intensity maps, the disk appears distinctly lopsided. The velocity field is disturbed on the lopsided side of the disk but is fairly uniform in the other half. We derived the HI rotation curve for the galaxy from the velocity field. The rotation curve has a flat rotation speed of ~ 190 km/s.Comment: Paper contains 14 figures and 4 tables. Figures 8, 10 (color) and 13 supplied separately. Accepted for publication in MNRA