Far-infrared properties of cluster galaxies

Far-infrared properties are derived for a sample of over 200 galaxies in seven clusters: A262, Cancer, A1367, A1656 (Coma), A2147, A2151 (Hercules), and Pegasus. The IR-selected sample consists almost entirely of IR normal galaxies, with Log of L(FIR) = 9.79 solar luminosities, Log of L(FIR)/L(B) = 0,79, and Log of S(100 microns)/S(60 microns) = 0.42. None of the sample galaxies has Log of L(FIR) greater than 11.0 solar luminosities, and only one has a FIR-to-blue luminosity ratio greater than 10. No significant differences are found in the FIR properties of HI-deficient and HI-normal cluster galaxies

The PDS vs. Markarian starburst galaxies: comparing strong and weak IRAS emitter at 12μ\mum and 25μ\mum in the nearby universe

(Abridged) The characteristics of the starburst galaxies from the Pico dos Dias survey (PDS) are compared with those of the nearby UV-bright Markarian starburst galaxies, having the same limit in redshift ($v_h < 7500$ km s$^{-1}$) and absolute $B$ magnitude ($M_B < -18$). An important difference is found: the Markarian galaxies are generally undetected at 12$\mu$m and 25$\mu$m in \textit{IRAS}. This is consistent with the UV excess shown by these galaxies and suggests that the youngest star forming regions dominating these galaxies are relatively free of dust. The FIR selection criteria for the PDS is shown to introduce a strong bias towards massive (luminous) and large size late-type spiral galaxies. This is contrary to the Markarian galaxies, which are found to be remarkably rich in smaller size early-type galaxies. These results suggest that only late-type spirals with a large and massive disk are strong emitter at 12$\mu$m and 25$\mu$m in \textit{IRAS} in the nearby universe.Comment: Accepted for publication in MNRA

van der Kruit to Spitzer: A New Look at the FIR-Radio Correlation

We present an initial look at the far infrared-radio correlation within the star-forming disks of four nearby, nearly face-on galaxies (NGC~2403, NGC~3031, NGC~5194, and NGC~6946). Using {\it Spitzer} MIPS imaging and WSRT radio continuum data, we are able to probe variations in the logarithmic 70~$\mu$m/22~cm ($q_{70}$) flux density ratios across each disk at sub-kpc scales. We find general trends of decreasing $q_{70}$ with declining surface brightness and with increasing radius. We also find that the dispersion in $q_{70}$ within galaxies is comparable to what is measured {\it globally} among galaxies at around 0.2 dex. We have also performed preliminary phenomenological modeling of cosmic ray electron (CR$e^{-}$) diffusion using an image-smearing technique, and find that smoothing the infrared maps improves their correlation with the radio maps. The best fit smoothing kernels for the two less active star-forming galaxies (NGC~2403 and NGC~3031) have much larger scale-lengths than that of the more active star-forming galaxies (NGC~5194 and NGC~6946). This difference may be due to the relative deficit of recent CR$e^{-}$ injection into the interstellar medium (ISM) for the galaxies having largely quiescent disks.Comment: 6 pages, 3 figures, To appear in the proceedings of the "Island Universes: Structure and Evolution of Disk Galaxies" conference held in Terschelling, Netherlands, July 2005, ed. R. de Jong (Springer: Dordrecht

Confirmation of SBS 1150+599A As An Extremely Metal-Poor Planetary Nebula

SBS 1150+599A is a blue stellar object at high galactic latitude discovered in the Second Byurakan Survey. New high-resolution images of SBS 1150+599A are presented, demonstrating that it is very likely to be an old planetary nebula in the galactic halo, as suggested by Tovmassian et al (2001). An H-alpha image taken with the WIYN 3.5-m telescope and its "tip/tilt" module reveals the diameter of the nebula to be 9.2", comparable to that estimated from spectra by Tovmassian et al. Lower limits to the central star temperature were derived using the Zanstra hydrogen and helium methods to determine that the star's effective temperature must be > 68,000K and that the nebula is optically thin. New spectra from the MMT and FLWO telescopes are presented, revealing the presence of strong [Ne V] lambda 3425, indicating that the central star temperature must be > 100,000K. With the revised diameter, new central star temperature, and an improved central star luminosity, we can constrain photoionization models for the nebula significantly better than before. Because the emission-line data set is sparse, the models are still not conclusive. Nevertheless, we confirm that this nebula is an extremely metal-poor planetary nebula, having a value for O/H that is less than 1/100 solar, and possibly as low as 1/500 solar.Comment: 19 pages, 6 figures. Accepted for publication in the Astronomical Journa

Several New Active Galactic Nuclei Among X-ray Sources Detected by INTEGRAL and SWIFT Observatories

We present the results of the optical identifications of a set of X-ray sources from the all-sky surveys of INTEGRAL and SWIFT observatories. Optical data were obtained with Russian-Turkish 1.5-m Telescope (RTT150). Nine X-ray sources were identified as active galactic nuclei (AGNs). Two of them are hosted by nearby, nearly exactly edge-on, spiral galaxies MCG -01-05-047 and NGC 973. One source, IGR J16562-3301, is most probably BL Lac object (blazar). Other AGNs are observed as stellar-like nuclei of spiral galaxies, with broad emission lines in their spectra. For the majority of our hard X-ray selected AGNs, their hard X-ray luminosities are well-correlated with the luminosities in [OIII],5007 optical emission line. However, the luminosities of some AGNs deviate from this correlation. The fraction of these objects can be as high as 20%. In particular, the flux in [OIII] line turns to be lower in two nearby edge-on spiral galaxies, which can be explained by the extinction in their galactic disks.Comment: 9 pages, 3 figures, accepted for publication in Astronomy Letters, the original text in Russian can be found at http://hea.iki.rssi.ru/~rodion/poptid.pd

Radio spectral index images of the spiral galaxies NGC 0628, NGC 3627, and NGC 7331

In order to understand the cosmic ray propagation mechanism in galaxies, and its correlation with the sites of star formation, we compare the spatially resolved radio spectral index of three spiral galaxies with their IR distribution. We present new low-frequency radio continuum observations of the galaxies NGC 0628, NGC 3627, and NGC 7331, taken at 327 MHz with the Very Large Array. We complemented our data set with sensitive archival observations at 1.4 GHz and we studied the variations of the radio spectral index within the disks of these spiral galaxies. We also compared the spectral index distribution and the IR distribution, using 70 $\mu$m Spitzer observations. We found that in these galaxies the non-thermal spectral index is anticorrelated with the radio brightness. Bright regions, like the bar in NGC 3627 or the circumnuclear region in NGC 7331, are characterized by a flatter spectrum with respect to the underlying disk. Therefore, a systematic steepening of the spectral index with the increasing distance from the center of these galaxies is observed. Furthermore, by comparing the radio images with the 70 $\mu$m images of the Spitzer satellite we found that a similar anticorrelation exists between the radio spectral index and the infrared brightness, as expected on the basis of the local correlation between the radio continuum and the infrared emission. Our results support the idea that in regions of intense star formation the electron diffusion must be efficient. The observed anticorrelation between radio brightness and spectral index, may imply that the cosmic ray density and the magnetic field strength are significantly higher in these regions than in their surroundings.Comment: 12 pages, 11 figures, Accepted for pubblication in Astronomy & Astrophysics A high resolution version of the paper can be downloaded from: http://astro.uibk.ac.at/~rosita/paper/AA11870.pd

Cold dust in a selected sample of nearby galaxies. I. The interacting galaxy NGC4631

We have observed the continuum emission of the interacting galaxy NGC4631 at 0.87 and 1.23mm using the Heinrich-Hertz-Telescope on Mt. Graham and the IRAM 30-m telescope on Pico Veleta. We have obtained fully sampled maps which cover the optical emission out to a radius of about 7' at both wavelengths. For a detailed analysis, we carefully subtracted the line contributions and synchrotron and free-free emission from the data, which added up to 6% at 1.23mm and 10% at 0.87mm. We combined the flux densities with FIR data to obtain dust spectra and calculate dust temperatures, absorption cross sections, and masses. Assuming a ``standard'' dust model, which consists of two populations of big grains at moderate and warm temperatures, we obtained temperatures of 18K and 50K for the both components. However, such a model suffers from an excess of the radiation at 1.23mm, and the dust absorption cross section seems to be enhanced by a factor 3 compared to previous results and theoretical expectations. At large galactocentric radii, where the galaxy shows disturbances as a result of gravitational interaction, this effect seems to be even stronger. Some possibilities to resolve these problems are discussed. The data could be explained by a very cold dust component at a temperature of 4-6K, an increased abundance of very small grains, or a component of grains with unusual optical properties. We favour the latter possibility, since the first two lead to inconsistencies.Comment: 12 pages, 6 figures, accepted for publication in Astronomy & Astrophysics. Updated version with minor errors corrected (typos, LaTeX formatting, missing citation

Spectroscopic and photometric studies of low-metallicity star-forming dwarf galaxies. I. SBS 1129+576

Spectroscopy and V,I CCD photometry of the dwarf irregular galaxy SBS 1129+576 are presented for the first time. The CCD images reveal a chain of compact H II regions within the elongated low-surface-brightness (LSB) component of the galaxy. Star formation takes place mainly in two high-surface-brightness H II regions. The mean (V-I) colour of the LSB component in the surface brightness interval between 23 and 26 mag/sq.arcsec is relatively blue ~0.56+/-0.03 mag, as compared to the (V-I)~0.9-1.0 for the majority of known dwarf irregular and blue compact dwarf (BCD) galaxies. Spectroscopy shows that the galaxy is among the most metal-deficient galaxies with an oxygen abundance 12+log(O/H)= 7.36+/-0.10 in the brightest H II region and 7.48+/-0.12 in the second brightest H II region, or 1/36 and 1/28 of the solar value, respectively. Hbeta and Halpha emission lines and Hdelta and Hgamma absorption lines are detected in a large part of the LSB component. We use two extinction-insensitive methods based on the equivalent widths of (1) emission and (2) absorption Balmer lines to put constraints on the age of the stellar populations in the galaxy. In addition, we use two extinction-dependent methods based on (3) the spectral energy distribution (SED) and (4) the (V-I) colour. The observed properties of the LSB component can be reproduced by a stellar population forming continuously since 10 Gyr ago, provided that the star formation rate has increased during the last 100 Myr by a factor of 6 to 50 and no extinction is present. However, the observational properties of the LSB component can be reproduced equally well by continuous star formation which started not earlier than 100 Myr ago and stopped at 5 Myr, if some extinction is assumed.(Abridged)Comment: 17 pages, 12 figures, Accepted for publication in A&

UV and FIR selected samples of galaxies in the local Universe. Dust extinction and star formation rates

We have built two samples of galaxies selected at 0.2micron (hereafter UV) and 60micron (hereafter FIR) covering a sky area of 35.36 deg^2. The UV selected sample contains 25 galaxies brighter than AB_0.2=17mag. All of them, but one elliptical, are detected at 60micron with a flux density larger or equal to 0.2Jy. The UV counts are significantly lower than the euclidean extrapolation towards brighter fluxes of previous determinations. The FIR selected sample contains 42 galaxies brighter than f_60=0.6Jy. Excepting four galaxies, all of them have a UV counterpart at the limiting magnitude AB_0.2=20.3mag. The mean extinction derived from the analysis of the FIR to UV flux ratio is ~1mag for the UV selected sample and ~2mag for the FIR selected one. For each sample we compare several indicators of the recent star formation rate (SFR) based on the FIR and/or the UV emissions and we find linear relationships with slopes close to unity, meaning that no trend with the SFR exists when converting between each other. Various absolute calibrations for both samples are discussed in this paper. A positive correlation between extinction and SFR is found when both samples are considered together although with a considerable scatter. A similar result is obtained when using the SFR normalized to the optical surface of the galaxies.Comment: 34 pages, 17 figures. Accepted for publication in A&

SBS 1150+599A: an extremely oxygen-poor planetary nebula in the Galactic halo?

We report results of a spectrophotometric study of SBS 1150+599A and discuss the nature of this object based upon our data. Our study shows that SBS 1150+599A is most probably a planetary nebula located in the Galactic halo and not a cataclysmic variable as originally proposed by the authors of the Second Byurakan Survey from low resolution spectroscopy. We have further elaborated on the properties of SBS 1150+599A (now becoming PN G135.9+55.9) with tools used for planetary nebula analysis. Our photoionization models show that, in order to match the observational constraints, the oxygen abundance in the nebula is probably extremely low, around 1/500 solar, which is one order of magnitude lower than the most oxygen-poor planetary nebulae known so far. This finding has strong implications on our understanding of the formation of planetary nebulae and of the evolution of the Galactic halo.Comment: 13 pages, 5 figures, accepted for publication in Astronomy and Astrophysic