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The Herschel Space Observatory and the Planck satellite are providing radical improvements to our knowledge of the spectral energy distributions of galaxies in the far-IR and submm. We here present the results of the first combination of Herschel and Planck fluxes of local galaxies from the Herschel Reference Sample (HRS) survey, covering galaxies at distances between 15 and 25 Mpc. This combination provides information on SEDs in eight bands from 60μm, using IRAS, to 1.4mm using Planck. We apply a similar fitting procedure to this data as applied to the Planck ERCSC-detected nearby galaxies and confirm the result that dust significantly colder than 20K is common in local galaxies. It is early days for this kind of study, but it is clear that the new generation of satellites are already adding considerably to our knowledge of the far-IR/submm properties of galaxies.
Even though attenuation by dust strongly attenuates and reddens the UV/optical spectral energy distributions of spiral galaxies, quantifying these effects is challenging, particularly when, as is most often the case, infrared measurements of the absorbed energy are not available. We have initiated a study to model the dependence on inclination of the attenuation of light from galaxies measured in the Galaxy and Mass Assembly (GAMA) survey. We present preliminary results using SDSS galaxies in the phase-I GAMA catalogue, comparing observed attenuation-inclination relations with the predictions of the radiation transfer model of Popescu et al. (2011) to derive a statistical measurement of the mean face-on B-band optical depth of disks τfB in a sample of spiral galaxies complete to the SDSS spectroscopic r-band limit of 17.8 mag.
UGC 12281 has been classified as having a pure disk and being a low surface brightness galaxy (LSBG), thus being an obvious member of the so-called superthin galaxies. At the same time it represents an extremely untypical type of LSBG due to its remarkable amount of current star formation and evidence for extraplanar ionized gas. This makes it become a perfect tool to investigate the triggering of star formation in LSB galaxies, located in an alleged isolated area. By means of deep photometry and long-slit spectroscopy we analyse the Hα halo and verify the existence of a potential dwarf companion which we found on processed SDSS images.
We stack FIRST survey cutout images of 811 K+A galaxies to derive a mean 1.4 GHz radio image of our sample from which we measure a mean K+A flux density of 56 μJy. We carry out Monte Carlo simulations by randomly selecting radio-quiet white dwarfs to create 10,000 stacks equivalent to our K+A stack. From the measured fluxes of these stacks, we establish a 5σ detection limit of 43 μJy for stacked images. For the average redshift of our sample, we find an mean star formation rate of ~1.7 M⊙ yr−1. We split the sample by age and find a mean radio flux of 60 μJy, which corresponds to a star formation rate of 1.6 M⊙ yr−1, for galaxies with starburst ages less than 250 Myr.
This review of future timing capabilities in X-ray astronomy includes missions in implementation (astro-h, gems, srg and astrosat), those under study (currently nicer, athena and loft), and new technologies that may be the seeds for future missions, such as lobster-eye optics. Those missions and technologies will offer exciting new capabilities that will take X-ray Astronomy into a new generation of achievements.
We investigate the correlation between the far-infrared (FIR) and radio continuum emission from NGC6946 on spatial scales between 0.9 and 17 kpc. We use the Herschel PACS (70, 100, 160μm) and SPIRE (250μm) data from the KINGFISH project. Separating the free-free and synchrotron components of the radio continuum emission, we find that FIR is better correlated with the free-free than the synchrotron emission. Compared to a similar study in M33 and M31, we find that the scale dependence of the synchrotron–FIR correlation in NGC6946 is more similar to M31 than M33. The scale dependence of the synchrotron–FIR correlation can be explained by the turbulent-to-ordered magnetic field ratio or, equivalently, the diffusion length of the cosmic ray electrons in these galaxies.
We investigate the three-dimensional structure of the nearby edge-on spiral galaxy NGC 891 using 3D Monte Carlo radiative transfer models, with realistic spiral structure and fractally clumped dust. Using the spiral and clumpiness parameters found from recently completed scattered light models we produce lower resolution SED models which reproduce the spatially-integrated UV-to-FIR SED of NGC 891. Our models contain a color gradient across the major axis of the galaxy - similar to what is seen in images of the NGC 891. With minor adjustment our SED models are able to match the SED of M51, a similar galaxy at a near face-on inclination.
The radio band is known to be rich in variable and transient sources, but exploration of it has only begun only in the last few years. Relevant time scales are as small as a fraction of a nanosecond (giant pulses from the Crab pulsar). Short transients (less than one second, say) have signal structure in the time-frequency plane at the very least because of interstellar plasma propagation effects (dispersion and scattering), and in some cases due to emission structure. Optimal detection requires handling a range of signal types in the time-frequency plane. Short bursts by necessity have very large effective radiation brightness temperatures associated with coherent emission processes. This paper surveys relevant source classes and summarizes propagation effects that must be considered to optimize detection in large-scale surveys. Scattering horizons for the interstellar and intergalactic media are defined, and the role of the radio band in panchromatic and multimessenger studies is discussed.
Early-type galaxies (ETGs) are thought to be devoid of dust and star-formation, having formed most of their stars at early epochs. We present the detection of the dustiest ETGs in a large area blind submillimetre survey with Herschel (H-ATLAS, Eales et al. 2010), where the lack of pre-selection in other bands makes it the first unbiased survey for cold dust in ETGs. We compare to a control sample of optically selected ETGs to investigate how the two populations are different. We also highlight the properties of an interesting population of passive spirals detected by Herschel.
Significant discrepancies have been found between the dust masses derived from various tracers (optical/near-IR, far-IR/sub-millimeter observations, and the variation of dust attenuation with viewing angle). Here we report the first detection of the extended far-UV (FUV) and near-UV (NUV) haloes perpendicular to the galactic plane of NGC 891, which can be interpreted as scattered stellar light from the galactic plane. An additional “geometrically thick” dust disk, which contains about the same mass as the standard thin dust disk, is needed to reproduce the vertically extended UV profiles
A workshop on Optical & Near Infrared Transients took place during the first afternoon of the Symposium. It ran for two sessions. The first was given over to talks about various current optical and near-infrared transient surveys, focussing on the Vista surveys, the Catalina Real-Time Transient Survey, Pan-STARRS, Gaia, TAOS and TAOS2. The second session was a panel-led discussion about coordinating multi-wavelength surveys and associated follow-ups.
The cooling rate of young neutron stars gives direct insight into their internal makeup. Using Chandra observations of the 330-year-old Cassiopeia A supernova remnant, we find that the temperature of the youngest-known neutron star in the Galaxy has declined by 4% over the last 10 years. The decline is explained naturally by superconductivity and superfluidity of the protons and neutrons in the stellar core. The protons became superconducting early in the life of the star and suppressed the early cooling rate; the neutron star thus remained hot before the (recent) onset of neutron superfluidity. Once the neutrons became superfluid, the Cooper pair-formation process produced a splash of neutrino emission which accelerated the cooling and resulted in the observed rapid temperature decline. This is the first time a young neutron star has been seen to cool in real time, and is the first direct evidence, from cooling observations, of superfluidity and superconductivity in the core of neutron stars.
The week's communications and deliberations concentrated on dQ/dt and how we could enhance our detection and interpretation of such occurrences, whether Q were a distance, an emission of energy, a velocity, a brightness, an orbital property or a spectroscopic feature. For us mortals, the derivative of Q is in respect of Time—yet rather little attention was paid during the week to Time itself. Maybe that was just as well. As was said by way of introducing the Astronomer Royal to give the public lecture, From Microseconds to Æons, Time is ever-present yet always elusive. It flies and yet it drags. We never seem to have enough of it, yet it can weigh heavily on our hands. It is free but it is priceless. You can't own it but you can spend it. Einstein said bluntly that the only reason for Time is so that everything doesn't happen at once.
The detection of fast (< 1 second) transient signals requires a challenging balance between the need to examine vast quantities of high time-resolution data and the impracticality of storing all the data for later analysis. This is the epitome of a “big data” issue—far more data will be produced by next generation-astronomy facilities than can be analyzed, distributed, or archived using traditional methods. JPL is developing technologies to deal with “big data” problems from initial data generation through real-time data triage algorithms to large-scale data archiving and mining. Although most current work is focused on the needs of large radio arrays, the technologies involved are widely applicable in other areas.
Because they are fast rotating objects, isolated neutron stars (INS) are obvious targets for high-time-resolution observations. With the number of optical/UV/IR INSs detections now at 24, timing observations become increasingly important in INS astrophysics.
R Coronæ Borealis was found to be variable in the year 1783, and was one of the first variable stars to be so identified. Its class, the R Coronæ Borealis (RCB) stars, are rare hydrogen-deficient carbon-rich supergiants. RCB stars undergo massive declines of up to 8 mag due to the formation of carbon dust at irregular intervals. The mechanism of dust formation around RCB stars is not well understood, but the dust is thought to form in or near the atmosphere of the star. Their rarity may stem from the fact that they are in an extremely rapid phase of the evolution, or are in an evolutionary phase that most stars do not undergo. Several evolutionary models have been suggested to account for the RCB stars, including a merger of two white dwarfs (WDs) or a final helium-shell flash (FF) in a PN central star. The large overabundance of 18O found in most of the RCB stars favours the WD merger model, while the presence of Li in the atmospheres of five RCB stars favours the FF one. In particular, the measured isotopic abundances imply that many, if not most, RCB stars are produced by WD mergers, which may be the low-mass counterparts of the more massive mergers thought to produce type Ia supernovæ. Understanding these enigmatic stars depends to a large extent on continuous monitoring to catch their irregular but rapid variations caused by dust formation, their variations due to stellar pulsations, and long-term changes that may occur over centuries. I will use observations of R Coronæ Borealis obtained over 200 years to demonstrate what kinds of monitoring are necessary for these and similar classes of variables.
The Herschel Space Observatory is revolutionizing our view of dust in galaxies with high sensitivity observations in the far infrared(FIR)/submillimeter (submm) regime from 70 to 500 μm. Herschel is confirming the submm excess that has been noted previously in low metallicity dwarfs. We present here the Dwarf Galaxies Survey sample through a Herschel colour-colour diagram. We will then focus on two galaxies, Haro11 and NGC4449 presenting different interesting behaviours in the FIR as revealed by Herschel.
We investigate the possibility of using Luminous Red Galaxies (LRGs) as “Cosmic chronometers” to measure the expansion rate of the universe to 3% over a redshift range 0.1 < z < 1.0. In this method, H(z) is directly measured by using the ages of passively evolving galaxies to determine dz/dt. We first present results from our study of LRGs in simulations Crawford et al. where we explore the impact of extended star formation histories on the measurements of the Hubble parameter. We then extract a carefully selected sample of LRGs taken from Sloan Digital Sky Survey (SDSS) Data Released Seven (DR7), stack spectra in redshift bins to increase the signal-to-noise, and use the Lick index modelling presented in Thomas et al. to age-date the sample. We discuss the implications for expansion rate measurements and outline a proposal to observe LRGs with the Southern African Large Telescope (SALT).
Extracting star formation histories from spectra is a process plagued by numerous degeneracies among the parameters that contribute to the definition of the underlying stellar populations. Traditional approaches to overcome such degeneracies involve carefully defined line strength or spectral fitting procedures. However, all these methods rely on comparisons with population synthesis models. This paper illustrates alternative approaches based on the statistical properties of the information that can be extracted from uniformly selected samples of observed spectra, without any prior reference to modelling. Such methods are more useful with large datasets, such as surveys, where the information from thousands of spectra can be exploited to classify galaxies. An illustrative example is presented on the classification of early-type galaxies with optical spectra from the Sloan Digital Sky Survey.
One of the principal motivations of wide-field and synoptic surveys is the search for, and study of, transients. By transients I mean those sources that arise from the background, are detectable for some time, and then fade away to oblivion. Transients in distant galaxies need to be sufficiently bright as to be detectable, and in almost all cases those transients are catastrophic events, marking the deaths of stars. Exemplars include supernovæ and gamma-ray bursts. In our own Galaxy, the transients are strongly variable stars, and in almost all cases are at best cataclysmic rather than catastrophic. Exemplars include flares from M dwarfs, novæ of all sorts (dwarf novæ, recurrent novæ, classical novæ, X-ray novæ) and instabilities in the surface layers of stars such as S Dor or η Carina. In the nearby Universe (say out to the Virgo cluster) we have sufficient sensitivity to see novæ. In 1 I review the history of transients (which is intimately related to the advent of wide-field telescopic imaging). In 2 I summarize wide-field imaging projects, and I then review the motivations that led to the design of the Palomar Transient Factory (PTF). Next comes a summary of the astronomical returns from PTF (3), and that is followed by lessons that I have learnt from PTF (4). I conclude that, during this decade, the study of optical transients will continue to flourish (and may even accelerate as surveys at other wavelengths—notably radio, UV and X-ray—come on-line). Furthermore, it is highly likely that there will be a proliferation of highly-specialized searches for transients. Those searches may well remain active even in the era of LSST (5). I end the article by discussing the importance of follow-up telescopes for transient object studies—a topical issue, given the Portfolio Review that is being undertaken in the US.