Are spiral galaxies optically thin or thick?

The opacity of spiral galaxies is examined by modelling the dust and stellar content of individual galaxies. The model is applied to five late-type spiral galaxies (NGC 4013, IC 2531, UGC 1082, NGC 5529 and NGC 5907). Having analyzed a total of seven galaxies thus far, the five galaxies mentioned above plus UGC 2048 and NGC 891 presented in (Xilouris et al. 1997, 1998), we are able to draw some general conclusions, the most significant of which are: 1) The face-on central optical depth is less than one in all optical bands indicating that typical spiral galaxies like the ones that we have modelled would be completely transparent if they were to be seen face-on. 2) The dust scaleheight is about half that of the stars, which means that the dust is more concentrated near the plane of the disk. 3) The dust scalelength is about 1.4 times larger than that of the stars and the dust is more radially extended than the stars. 4) The dust mass is found to be about an order of a magnitude more than previously measured using the IRAS fluxes, indicating the existence of a cold dust component. The gas-to-dust mass ratio calculated is close to the value derived for our Galaxy. 5) The derived extinction law matches quite well the Galactic extinction law, indicating a universal dust behaviour.Comment: 13 pages. Accepted for publication in A&

Search for AGN counterparts of unidentified Fermi-LAT sources with optical polarimetry: Demonstration of the technique

The third Fermi-LAT catalog (3FGL) presented the data of the first four years of observations from the Fermi Gamma-ray Space Telescope mission. There are 3034 sources, 1010 of which still remain unidentified. Identifying and classifying gamma-ray emitters is of high significance with regard to studying high-energy astrophysics. We demonstrate that optical polarimetry can be an advantageous and practical tool in the hunt for counterparts of the unidentified gamma-ray sources (UGSs). Using data from the RoboPol project, we validated that a significant fraction of active galactic nuclei (AGN) associated with 3FGL sources can be identified due to their high optical polarization exceeding that of the field stars. We performed an optical polarimetric survey within $3\sigma$ uncertainties of four unidentified 3FGL sources. We discovered a previously unknown extragalactic object within the positional uncertainty of 3FGL J0221.2+2518. We obtained its spectrum and measured a redshift of $z=0.0609\pm0.0004$. Using these measurements and archival data we demonstrate that this source is a candidate counterpart for 3FGL J0221.2+2518 and most probably is a composite object: a star-forming galaxy accompanied by AGN. We conclude that polarimetry can be a powerful asset in the search for AGN candidate counterparts for unidentified Fermi sources. Future extensive polarimetric surveys at high galactic latitudes (e.g., PASIPHAE) will allow the association of a significant fraction of currently unidentified gamma-ray sources.Comment: accepted to A&

RoboPol: Connection between optical polarization plane rotations and gamma-ray flares in blazars

We use results of our 3 year polarimetric monitoring program to investigate the previously suggested connection between rotations of the polarization plane in the optical emission of blazars and their gamma-ray flares in the GeV band. The homogeneous set of 40 rotation events in 24 sources detected by {\em RoboPol} is analysed together with the gamma-ray data provided by {\em Fermi}-LAT. We confirm that polarization plane rotations are indeed related to the closest gamma-ray flares in blazars and the time lags between these events are consistent with zero. Amplitudes of the rotations are anticorrelated with amplitudes of the gamma-ray flares. This is presumably caused by higher relativistic boosting (higher Doppler factors) in blazars that exhibit smaller amplitude polarization plane rotations. Moreover, the time scales of rotations and flares are marginally correlated.Comment: 12 pages, 16 figures, accepted to MNRA

RoboPol: the optical polarization of gamma-ray-loud and gamma-ray-quiet blazars

We present average R-band optopolarimetric data, as well as variability parameters, from the first and second RoboPol observing season. We investigate whether gamma-ray-loud and gamma-ray-quiet blazars exhibit systematic differences in their optical polarization properties. We find that gamma-ray-loud blazars have a systematically higher polarization fraction (0.092) than gamma-ray-quiet blazars (0.031), with the hypothesis of the two samples being drawn from the same distribution of polarization fractions being rejected at the 3σ level. We have not found any evidence that this discrepancy is related to differences in the redshift distribution, rest-frame R-band luminosity density, or the source classification. The median polarization fraction versus synchrotron-peak-frequency plot shows an envelope implying that high-synchrotron-peaked sources have a smaller range of median polarization fractions concentrated around lower values. Our gamma-ray-quiet sources show similar median polarization fractions although they are all low-synchrotron-peaked. We also find that the randomness of the polarization angle depends on the synchrotron peak frequency. For high-synchrotron-peaked sources, it tends to concentrate around preferred directions while for low-synchrotron-peaked sources, it is more variable and less likely to have a preferred direction. We propose a scenario which mediates efficient particle acceleration in shocks and increases the helical B-field component immediately downstream of the shock

Search for AGN counterparts of unidentified Fermi-LAT sources with optical polarimetry Demonstration of the technique

Context. The third Fermi-LAT catalog (3FGL) presented the data of the first four years of observations from the Fermi Gamma-ray Space Telescope mission. There are 3034 sources, 1010 of which still remain unidentified. Identifying and classifying gamma-ray emitters is of high significance with regard to studying high-energy astrophysics.Aims. We demonstrate that optical polarimetry can be an advantageous and practical tool in the hunt for counterparts of the unidentified gamma-ray sources (UGSs).Methods. Using data from the RoboPol project, we validated that a significant fraction of active galactic nuclei (AGN) associated with 3FGL sources can be identified due to their high optical polarization exceeding that of the field stars. We performed an optical polarimetric survey within 3 sigma uncertainties of four unidentified 3FGL sources.Results. We discovered a previously unknown extragalactic object within the positional uncertainty of 3FGL J0221.2 + 2518. We obtained its spectrum and measured a redshift of z = 0.0609 +/- 0.0004. Using these measurements and archival data we demonstrate that this source is a candidate counterpart for 3FGL J0221.2 + 2518 and most probably is a composite object: a star-forming galaxy accompanied by AGN.Conclusions. We conclude that polarimetry can be a powerful asset in the search for AGN candidate counterparts for unidentified Fermi sources. Future extensive polarimetric surveys at high Galactic latitudes (e.g., PASIPHAE) will allow the association of a significant fraction of currently unidentified gamma-ray sources

Search for AGN counterparts of unidentified Fermi-LAT sources with optical polarimetry: Demonstration of the technique

Context. The third Fermi-LAT catalog (3FGL) presented the data of the first four years of observations from the Fermi Gamma-ray Space Telescope mission. There are 3034 sources, 1010 of which still remain unidentified. Identifying and classifying γ-ray emitters is of high significance with regard to studying high-energy astrophysics. Aims. We demonstrate that optical polarimetry can be an advantageous and practical tool in the hunt for counterparts of the unidentified γ-ray sources (UGSs). Methods. Using data from the RoboPol project, we validated that a significant fraction of active galactic nuclei (AGN) associated with 3FGL sources can be identified due to their high optical polarization exceeding that of the field stars. We performed an optical polarimetric survey within 3σ uncertainties of four unidentified 3FGL sources. Results. We discovered a previously unknown extragalactic object within the positional uncertainty of 3FGL J0221.2+2518. We obtained its spectrum and measured a redshift of z = 0.0609 ± 0.0004. Using these measurements and archival data we demonstrate that this source is a candidate counterpart for 3FGL J0221.2+2518 and most probably is a composite object: a star-forming galaxy accompanied by AGN. Conclusions. We conclude that polarimetry can be a powerful asset in the search for AGN candidate counterparts for unidentified Fermi sources. Future extensive polarimetric surveys at high Galactic latitudes (e.g., PASIPHAE) will allow the association of a significant fraction of currently unidentified γ-ray sources

Motivation and job satisfaction among medical and nursing staff in a Cyprus public general hospital

<p>Abstract</p> <p>Background</p> <p>The objective of this study was to investigate how medical and nursing staff of the Nicosia General Hospital is affected by specific motivation factors, and the association between <it>job satisfaction </it>and <it>motivation</it>. Furthermore, to determine the motivational drive of socio-demographic and job related factors in terms of improving work performance.</p> <p>Methods</p> <p>A previously developed and validated instrument addressing four work-related motivators (<it>job attributes, remuneration, co-workers and achievements</it>) was used. Two categories of health care professionals, medical doctors and dentists (N = 67) and nurses (N = 219) participated and motivation and job satisfaction was compared across socio-demographic and occupational variables.</p> <p>Results</p> <p>The survey revealed that <it>achievements </it>was ranked first among the four main motivators, followed by <it>remuneration</it>, <it>co-workers </it>and <it>job attributes</it>. The factor <it>remuneration </it>revealed statistically significant differences according to gender, and hospital sector, with female doctors and nurses and accident and emergency (A+E) outpatient doctors reporting greater mean scores (p < 0.005). The medical staff showed statistically significantly lower job satisfaction compared to the nursing staff. Surgical sector nurses and those >55 years of age reported higher job satisfaction when compared to the other groups.</p> <p>Conclusions</p> <p>The results are in agreement with the literature which focuses attention to management approaches employing both monetary and non-monetary incentives to motivate health care professionals. Health care professionals tend to be motivated more by intrinsic factors, implying that this should be a target for effective employee motivation. Strategies based on the survey's results to enhance employee motivation are suggested.</p