976 research outputs found
Properties of the unusual galaxy PSC 09104+4109
The IRAS source PSC 09104+4109 is tentatively identified with a faint emission line galaxy having z = 0.442. Assuming this identification is correct, the total infrared luminosity of this galaxy is estimated to be 5 x 10 to the 12th power L sub 0, among the highest for galaxies detected by IRAS. This energy is concentrated at wavelengths less than 30 micrometers, and is approx. 50 times greater than the estimated optical luminosity. The serendipitous way in which this source was found in the PSC catalog suggests that many more similar objects may be found at the lowest levels of the IRAS survey
VLT/VIMOS Observations of an Occulting Galaxy Pair: Redshifts and Effective Extinction Curve
We present VLT/VIMOS IFU observations of an occulting galaxy pair previously
discovered in HST observations. The foreground galaxy is a low-inclination
spiral disk, which causes clear attenuation features seen against the bright
bulge and disk of the background galaxy. We find redshifts of and z=0.065 for the foreground and background galaxy respectively.
This relatively small difference does not rule out gravitational interaction
between the two galaxies. Emission line ratios point to a star-forming, not
AGN-dominated foreground galaxy.
We fit the Cardelli, Clayton & Mathis (CCM) extinction law to the spectra of
individual fibres to derive slope () and normalization (). The
normalization agrees with the HST attenuation map and the slope is lower than
the Milky Way relation (), which is likely linked to the spatial
sampling of the disk. We speculate that the values of point to either
coherent ISM structures in the disk larger than usual ( kpc) or higher
starting values of , indicative of recent processing of the dust.
The foreground galaxy is a low stellar mass spiral () with a high dust content (). The dust disk geometry visible in the HST image would explain the
observed SED properties of smaller galaxies: a lower mean dust temperature, a
high dust-to-stellar mass ratio but relatively little optical attenuation.
Ongoing efforts to find occulting pairs with a small foreground galaxies will
show how common this geometry is.Comment: 16 pages, 3 tables, 13 figures, accepted for publication in MNRA
The occulting galaxy pair UGC 3995 : dust properties from HST and CALIFA data.
UGC 3995 is an interacting and occulting galaxy pair. UGC 3995B is a foreground face-on spiral and UGC 3995A a bright background spiral with an AGN. We present analysis of the dust in the disc of UGC 3995B based on archival Hubble Space Telescope (HST) WFPC2 and PPAK IFU data from the CALIFA survey’s first data release. From the HST F606W image, we construct an extinction map by modeling the isophotes of the background galaxy UGC 3995A and the resulting transmission through UGC 3995B. This extinction map of UGC 3995B shows several distinct spiral extinction features. The radial distribution of AV values declines slowly with peaks corresponding to the spiral structures. The distribution of AV values in the HST extinction map peaks near AV = 0.3–0.4. Beyond this point, the distribution of AV values drops like an exponential: N(AV) = N0 × e(−AV/0.5). The 0.5 value is higher than typical for a spiral galaxy. The outer arms may be tidally distended; the extinction in the corresponding interarm regions is small to an unusually small radius. To analyze the PPAK IFU data, we take the ratio of a fibre spectrum in the overlap region and the corresponding background fiber spectrum to construct an extinction curve. We fit the Cardelli, Clayton and Mathis (CCM) curve to the extinction curve of each fiber element in the overlap region. A map of the extinction constructed from PPEX IFU data-cubes shows the same spiral structure of the HST extinction map but the some differences in the distribution of the normalization of the CCM fits (AV). The inferred extinction slopes (RV) maps do not display any structure and a range of values partly due to the sampling effects of the disc by fibers, sometimes due to bad fits, and possibly partly due to some reprocessing of dust grains in the interacting disc. We compare these findings to our other analysis of an occulting pair with HST and IFU data. In both cases the canonical RV = 3.1 is not recovered even though there is enough signal in the extinction curve. We attribute this to mixing opaque and more transparent sections of the disc in each resolution element (~3′′ or 0.9 kpc). To illustrate the difficulty of imposing a RV = 3.1 law over a section of a spiral disc, we average all spectra and show how a fully gray extinction curve is recovered
The Ultraviolet Attenuation Law in Backlit Spiral Galaxies
(Abridged) The effective extinction law (attenuation behavior) in galaxies in
the emitted ultraviolet is well known only for actively star-forming objects
and combines effects of the grain properties, fine structure in the dust
distribution, and relative distributions of stars and dust. We use GALEX, XMM
Optical Monitor, and HST data to explore the UV attenuation in the outer parts
of spiral disks which are backlit by other UV-bright galaxies, starting with
candidates provided by Galaxy Zoo participants. Our analysis incorporates
galaxy symmetry, using non-overlapping regions of each galaxy to derive error
estimates on the attenuation measurements. The entire sample has an attenuation
law close to the Calzetti et al. (1994) form; the UV slope for the overall
sample is substantially shallower than found by Wild et al. (2011), a
reasonable match to the more distant galaxies in our sample but not to the
weighted combination including NGC 2207. The nearby, bright spiral NGC 2207
alone gives accuracy almost equal to the rest of our sample, and its outer arms
have a very low level of foreground starlight. This "grey" law can be produced
from the distribution of dust alone, without a necessary contribution from
differential escape of stars from dense clouds. The extrapolation needed to
compare attenution between backlit galaxies at moderate redshifts, and local
systems from SDSS data, is mild enough to allow use of galaxy overlaps to trace
the cosmic history of dust. For NGC 2207, the covering factor of clouds with
small optical attenuation becomes a dominant factor farther into the
ultraviolet, which opens the possibility that widespread diffuse dust dominates
over dust in star-forming regions deep into the ultraviolet. Comparison with
published radiative-transfer models indicates that the role of dust clumping
dominates over differences in grain populations, at this spatial resolution.Comment: In press, Astronomical Journa
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