449 research outputs found
The Comoving Infrared Luminosity Density: Domination of Cold Galaxies across 0<z<1
In this paper we examine the contribution of galaxies with different infrared
(IR) spectral energy distributions (SEDs) to the comoving infrared luminosity
density, a proxy for the comoving star formation rate (SFR) density. We
characterise galaxies as having either a cold or hot IR SED depending upon
whether the rest-frame wavelength of their peak IR energy output is above or
below 90um. Our work is based on a far-IR selected sample both in the local
Universe and at high redshift, the former consisting of IRAS 60um-selected
galaxies at z<0.07 and the latter of Spitzer 70um selected galaxies across
0.1<z<1. We find that the total IR luminosity densities for each
redshift/luminosity bin agree well with results derived from other deep
mid/far-IR surveys. At z<0.07 we observe the previously known results: that
moderate luminosity galaxies (L_IR<10^11 Lsun) dominate the total luminosity
density and that the fraction of cold galaxies decreases with increasing
luminosity, becoming negligible at the highest luminosities. Conversely, above
z=0.1 we find that luminous IR galaxies (L_IR>10^11 Lsun), the majority of
which are cold, dominate the IR luminosity density. We therefore infer that
cold galaxies dominate the IR luminosity density across the whole 0<z<1 range,
hence appear to be the main driver behind the increase in SFR density up to z~1
whereas local luminous galaxies are not, on the whole, representative of the
high redshift population.Comment: 5 pages, 3 figures, accepted for publication in MNRA
The link between SCUBA and Spitzer: cold galaxies at z lt 1
We show that the far-IR properties of distant Luminous and UltraLuminous InfraRed Galaxies (LIRGs and ULIRGs, respectively) are on average divergent from analogous sources in the local Universe. Our analysis is based on Spitzer Multiband Imaging Photometer (MIPS) and Infrared Array Camera (IRAC) data of LIR > 1010 L⊙, 70 μm selected objects in the 0.1 1 SubMillimetre Galaxies (SMGs) discovered in blank-field submillimetre surveys. The Herschel Space Observatory is well placed to fully characterize the nature of these objects, as its coverage extends over a major part of the far-IR/sub-mm SED for a wide redshift range
Characterizing the radio continuum emission from intense starburst galaxies
© 2016 The Authors Published by Oxford University Press on behalf of the Royal Astronomical Society.The intrinsic thermal (free-free) and non-thermal (synchrotron) emission components that comprise the radio continuum of galaxies represent unique, dust-free measures of star formation rates (SFR). Such high SFR galaxies will dominate the deepest current and future radio surveys. We disentangle the thermal and non-thermal emission components of the radio continuum of six ultraluminous infrared galaxies (LFIR > 1012.5 L?) at redshifts of 0.2 = z = 0.5 and 22 IR selected galaxies. Radio data over a wide frequency range (0.8 < ? <10 GHz) are fitted with a star-forming galaxy model comprising of thermal and non-thermal components. The luminosities of both radio continuum components are strongly correlated to the 60 µm luminosity across many orders of magnitude (consistent with the far-IR to radio correlation). We demonstrate that the spectral index of the radio continuum spectral energy distribution is a useful proxy for the thermal fraction. We also find that there is an increase in mean and scatter of the thermal fraction with FIR to radio luminosity ratio which could be influenced by different time-scales of the thermal and non-thermal emission mechanisms
The use and calibration of read-out streaks to increase the dynamic range of the Swift Ultraviolet/Optical Telescope
The dynamic range of photon counting micro-channel-plate (MCP) intensified
charged-coupled device (CCD) instruments such as the Swift Ultraviolet/Optical
Telescope (UVOT) and the XMM-Newton Optical Monitor (XMM-OM) is limited at the
bright end by coincidence loss, the superposition of multiple photons in the
individual frames recorded by the CCD. Photons which arrive during the brief
period in which the image frame is transferred for read out of the CCD are
displaced in the transfer direction in the recorded images. For sufficiently
bright sources, these displaced counts form read-out streaks. Using UVOT
observations of Tycho-2 stars, we investigate the use of these read-out streaks
to obtain photometry for sources which are too bright (and hence have too much
coincidence loss) for normal aperture photometry to be reliable. For
read-out-streak photometry, the bright-source limiting factor is coincidence
loss within the MCPs rather than the CCD. We find that photometric measurements
can be obtained for stars up to 2.4 magnitudes brighter than the usual
full-frame coincidence-loss limit by using the read-out streaks. The resulting
bright-limit Vega magnitudes in the UVOT passbands are UVW2=8.80, UVM2=8.27,
UVW1=8.86, u=9.76, b=10.53, v=9.31 and White=11.71; these limits are
independent of the windowing mode of the camera. We find that a photometric
precision of 0.1 mag can be achieved through read-out streak measurements. A
suitable method for the measurement of read-out streaks is described and all
necessary calibration factors are given.Comment: 11 pages, accepted for publication in MNRAS. Code available from the
calibration link at http://www.mssl.ucl.ac.uk/www_astro/uvo
The incidence of obscuration in active galactic nuclei
We study the incidence of nuclear obscuration on a complete sample of 1310
AGN selected on the basis of their rest-frame 2-10 keV X-ray flux from the
XMM-COSMOS survey, in the redshift range 0.3<z<3.5. We classify the AGN as
obscured or un-obscured on the basis of either the optical spectral properties
and the overall SED or the shape of the X-ray spectrum. The two classifications
agree in about 70% of the objects, and the remaining 30% can be further
subdivided into two distinct classes: at low luminosities X-ray un-obscured AGN
do not always show signs of broad lines or blue/UV continuum emission in their
optical spectra, most likely due to galaxy dilution effects; at high
luminosities broad line AGN may have absorbed X-ray spectra, which hints at an
increased incidence of small-scale (sub-parsec) dust-free obscuration. We
confirm that the fraction of obscured AGN is a decreasing function of the
intrinsic X-ray luminosity, while the incidence of absorption shows significant
evolution only for the most luminous AGN, which appear to be more commonly
obscured at higher redshift. We find no significant difference between the mean
stellar masses and star formation rates of obscured and un-obscured AGN hosts.
We conclude that the physical state of the medium responsible for obscuration
in AGN is complex, and mainly determined by the radiation environment (nuclear
luminosity) in a small region enclosed within the gravitational sphere of
influence of the central black hole, but is largely insensitive to the wider
scale galactic conditions.Comment: 18 pages, 17 figures, 2 tables. Accepted for publication by MNRA
Spontaneous traumatic macular hole closure in a 50-year-old woman: a case report
<p>Abstract</p> <p>Introduction</p> <p>Traumatic macular holes (TMH) are well-known complications of ocular contusion injury. Spontaneous closure occurs in approximately 50% of cases, but rarely after the age of thirty. We report a case of spontaneous closure of a full thickness macular hole due to a blunt trauma and we suggest possible mechanisms for this closure.</p> <p>Case presentation</p> <p>A 50-year-old Greek woman was referred with a history of reduced best-corrected visual acuity after blunt trauma to her right eye. Diagnosis was based on fundoscopic, optical coherence tomography as well as fluorescein angiography findings with follow-up visits at two days, 20 days and five months. Fundoscopy revealed a full-thickness TMH with a minor sub-retinal hemorrhage and posterior vitreous detachment. The presence of a coagulum in the TMH base was observed. Subsequently, TMH closure was observed.</p> <p>Conclusion</p> <p>The clot in the TMH base, potentially a hemorrhage by-product containing a significant quantity of platelets, may have simulated the clot observed after autologous serum use, thus facilitating a similar effect. This may have stimulated glial cell migration and proliferation, thus contributing to spontaneous hole closure.</p
The FMOS-COSMOS survey of star-forming galaxies at z ~ 1.6. I. H\alpha -based star formation rates and dust extinction
We present the first results from a near-IR spectroscopic survey of the
COSMOS field, using the Fiber Multi-Object Spectrograph on the Subaru
telescope, designed to characterize the star-forming galaxy population at
. The high-resolution mode is implemented to detect H in
emission between with erg cm s. Here, we specifically
focus on 271 sBzK-selected galaxies that yield a H detection thus
providing a redshift and emission line luminosity to establish the relation
between star formation rate and stellar mass. With further -band
spectroscopy for 89 of these, the level of dust extinction is assessed by
measuring the Balmer decrement using co-added spectra. We find that the
extinction () rises with stellar
mass and is elevated at high masses compared to low-redshift galaxies. Using
this subset of the spectroscopic sample, we further find that the differential
extinction between stellar and nebular emission
\hbox{} is 0.7--0.8, dissimilar to
that typically seen at low redshift. After correcting for extinction, we derive
an H-based main sequence with a slope () and normalization
similar to previous studies at these redshifts.Comment: 6 pages, 4 figures, and 1 table. Published in ApJ Letter
The Semantics of Movie Metadata: Enhancing User Profiling for Hybrid Recommendation
In movie/TV collaborative recommendation approaches, ratings users gave to already visited content are often used as the only input to build profiles. However, users might have rated equally the same movie but due to different reasons: either because of its genre, the crew or the director. In such cases, this rating is insufficient to represent in detail users’ preferences and it is wrong to conclude that they share similar tastes. The work presented in this paper tries to solve this ambiguity by exploiting hidden semantics in metadata elements. The influence of each of the standard description elements (actors, directors and genre) in representing user’s preferences is analyzed. Simulations were conducted using Movielens and Netflix datasets and different evaluation metrics were considered. The results demonstrate that the implemented approach yields significant advantages both in terms of improving performance, as well as in dealing with common limitations of standard collaborative algorithm.info:eu-repo/semantics/publishedVersio
The ultraviolet luminosity function of star-forming galaxies between redshifts of 0.6 and 1.2
We use ultraviolet imaging taken with the XMM-Newton Optical Monitor
telescope (XMM-OM), covering 280 square arcminutes in the UVW1 band (effective
wavelength 2910 Angstroms) to measure rest-frame ultraviolet (1500 Angstrom)
luminosity functions of galaxies with redshifts z between 0.6 and 1.2. The
XMM-OM data are supplemented by a large body of optical and infrared imaging to
provide photometric redshifts. The XMM-OM data have a significantly narrower
point-spread-function (resulting in less source confusion) and simpler
K-correction than the GALEX data previously employed in this redshift range.
Ultraviolet-bright active galactic nuclei are excluded to ensure that the
luminosity functions relate directly to the star-forming galaxy population.
Binned luminosity functions and parametric Schechter-function fits are derived
in two redshift intervals: 0.6<z<0.8 and 0.8<z<1.2. We find that the luminosity
function evolves such that the characteristic absolute magnitude M* is brighter
for 0.8<z<1.2 than for 0.6<z<0.8.Comment: 17 pages, 11 figures, accepted for publication in MNRA
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