An X-ray survey of the 2Jy sample. II: X-ray emission from extended structures [GA]

http://arxiv.org/abs/1705.09578


The 2Jy sample is a survey of radio galaxies with flux densities above 2 Jy at 2.7 GHz. As part of our ongoing work on the southern subset of 2Jy sources, in paper I of this series we analysed the X-ray cores of the complete 2Jy sample with redshifts 0.05<z<0.7. For this work we focus on the X-ray emission associated with the extended structures (jets, lobes, and environments) of the complete subset of 2Jy sources with 0.05<z<0.2, that we have observed with Chandra. We find that hotspots and jet knots are ubiquitous in FRII sources, which also inhabit systematically poorer environments than the FRI sources in our sample. Spectral fits of the hotspots with good X-ray statistics invariably show properties consistent with synchrotron emission, and we show that inverse-Compton mechanisms under-predict the X-ray emission we observe by 1-2 orders of magnitude. Inverse-Compton emission is detected from many of the lobes in our sample, and we find that the lobes of the FRII sources show magnetic fields lower by up to an order of magnitude than expected from equipartition extrapolations. This is consistent with previous results, which show that most FRII sources have electron energy densities higher than minimum energy requirements.

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B. Mingo, M. Hardcastle, J. Ineson, et. al.
Mon, 29 May 17
-75/35

Comments: 18 pages, 3 tables, 29 figures, accepted for publication in Monthly Notices of the Royal Astronomical Society (MNRAS)

The structural evolution of galaxies with both thin and thick discs [GA]

http://arxiv.org/abs/1705.09240


We perform controlled N-body simulations of disc galaxies growing within live dark matter (DM) haloes to present-day galaxies that contain both thin and thick discs. We consider two types of models: a) thick disc initial conditions to which stars on near-circular orbits are continuously added over ~10 Gyr and b) models in which the birth velocity dispersion of stars decreases continuously over the same timescale. We show that both schemes produce double-exponential vertical profiles similar to that of the Milky Way (MW). We indicate how the spatial age structure of galaxies can be used to discriminate between scenarios. We show that the presence of a thick disc significantly alters and delays bar formation and thus makes possible models with a realistic bar and a high baryon-to-DM mass ratio in the central regions, as required by microlensing constraints. We examine how the radial mass distribution in stars and DM is affected by disc growth and non-axisymmetries. We discuss how bar buckling shapes the vertical age distribution of thin and thick disc stars in the bar region. The extent to which the combination of observationally motivated inside-out growth histories and cosmologically motivated dark halo properties leads to the spontaneous formation of non-axisymmetries which steer the models towards present-day MW-like galaxies is noteworthy.

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M. Aumer and J. Binney
Fri, 26 May 17
-43/63

Comments: Accepted for publication in MNRAS, 22 pages, 13 figures, 2 tables

Quasar Lenses and Galactic Streams: Outlier Selection and GAIA Multiplet Detection [GA]

http://arxiv.org/abs/1705.08900


I describe two novel techniques originally devised to select strongly lensed quasar candidates in wide-field surveys. The first relies on outlier selection in optical and mid-infrared magnitude space; the second combines mid-infrared colour selection with GAIA spatial resolution, to identify multiplets of objects with quasar-like colours. Both methods have already been applied successfully to the SDSS, ATLAS and DES footprints: besides recovering known lenses from previous searches, they have led to new discoveries, including quadruply lensed quasars, which are rare within the rare-object class of quasar lenses. As a serendipitous by-product, at least four candidate Galactic streams in the South have been identified among foreground contaminants. There is considerable scope for tailoring the WISE-GAIA multiplet search to stellar-like objects, instead of quasar-like, and to automatically detect Galactic streams.

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A. Agnello
Fri, 26 May 17
-39/63

Comments: MNRAS subm. 21/04, revised version after referee report. 10 pages, 5 figures

Experimental evidence for Glycolaldehyde and Ethylene Glycol formation by surface hydrogenation of CO molecules under dense molecular cloud conditions [GA]

http://arxiv.org/abs/1705.09235


This study focuses on the formation of two molecules of astrobiological importance – glycolaldehyde (HC(O)CH2OH) and ethylene glycol (H2C(OH)CH2OH) – by surface hydrogenation of CO molecules. Our experiments aim at simulating the CO freeze-out stage in interstellar dark cloud regions, well before thermal and energetic processing become dominant. It is shown that along with the formation of H2CO and CH3OH – two well established products of CO hydrogenation – also molecules with more than one carbon atom form. The key step in this process is believed to be the recombination of two HCO radicals followed by the formation of a C-C bond. The experimentally established reaction pathways are implemented into a continuous-time random-walk Monte Carlo model, previously used to model the formation of CH3OH on astrochemical time-scales, to study their impact on the solid-state abundances in dense interstellar clouds of glycolaldehyde and ethylene glycol.

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G. Fedoseev, H. Cuppen, S. Ioppolo, et. al.
Fri, 26 May 17
-38/63

Comments: N/A

Low Temperature Surface Formation of NH3 and HNCO: hydrogenation of nitrogen atoms in CO-rich interstellar ice analogues [GA]

http://arxiv.org/abs/1705.09184


Solid state astrochemical reaction pathways have the potential to link the formation of small nitrogen-bearing species, like NH3 and HNCO, and prebiotic molecules, specifically amino acids. To date, the chemical origin of such small nitrogen containing species is still not well understood, despite the fact that ammonia is an abundant constituent of interstellar ices toward young stellar objects and quiescent molecular clouds. This is mainly because of the lack of dedicated laboratory studies. The aim of the present work is to experimentally investigate the formation routes of NH3 and HNCO through non-energetic surface reactions in interstellar ice analogues under fully controlled laboratory conditions and at astrochemically relevant temperatures. This study focuses on the formation of NH3 and HNCO in CO-rich (non-polar) interstellar ices that simulate the CO freeze-out stage in dark interstellar cloud regions, well before thermal and energetic processing start to become relevant. We demonstrate and discuss the surface formation of solid HNCO through the interaction of CO molecules with NH radicals – one of the intermediates in the formation of solid NH3 upon sequential hydrogenation of N atoms. The importance of HNCO for astrobiology is discussed.

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G. Fedoseev, S. Ioppolo, D. Zhao, et. al.
Fri, 26 May 17
-34/63

Comments: N/A

Can Dust Injected by SNe Explain the NIR-MIR Excess in Young Massive Stellar Clusters? [GA]

http://arxiv.org/abs/1705.08899


We present a physically-motivated model involving the different processes affecting supernova dust grains as they are incorporated into the thermalized medium within young massive star clusters. The model is used to explain the near- to mid-infrared (NIR-MIR) excess found in such clusters and usually modeled as a blackbody with temperature $\sim (400-1000)$ K. In our approach, dust grains are efficiently produced in the clumpy ejecta of core-collapse supernovae, fragmented into small pieces ($\lesssim 0.05$ $\mu$m) as they are incorporated into the hot and dense ISM, heated via frequent collisions with electrons and the absorption of energetic photons. Grains with small sizes can more easily acquire the high temperatures ($\sim 1000$ K) required to produce a NIR-MIR excess with respect to the emission of foreground PAHs and starlight. However, the extreme conditions inside young massive clusters make difficult for these small grains to have a persistent manifestation at NIR-MIR wavelengths as they are destroyed by efficient thermal sputtering. Nevertheless, the chances for a persistent manifestation are increased by taking into account that small grains become increasingly transparent to their impinging ions as their size decreases. For an individual SN event, we find that the NIR-MIR excess last longer if the time required to incorporate all the grains into the thermalized medium is also longer, and in some cases, comparable to the characteristic interval between supernova explosions. Our models, can successfully explain the near-infrared excesses found in the star clusters observed in M33 (Rela\~no et al. 2016) assuming a low heating efficiency and mass-loading. In this scenario, the presence of the NIR-MIR excess is an indication of efficient dust production in SNe and its subsequent destruction

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S. Martinez-Gonzalez, R. Wunsch and J. Palous
Fri, 26 May 17
-31/63

Comments: 13 pages, 8 figures, Accepted for publication in The Astrophysical Journal

Deuterium enrichment of ammonia produced by surface N+H/D addition reactions at low temperature [GA]

http://arxiv.org/abs/1705.09209


The surface formation of NH3 and its deuterated isotopologues – NH2D, NHD2, and ND3 – is investigated at low temperatures through the simultaneous addition of hydrogen and deuterium atoms to nitrogen atoms in CO-rich interstellar ice analogues. The formation of all four ammonia isotopologues is only observed up to 15 K, and drops below the detection limit for higher temperatures. Differences between hydrogenation and deuteration yields result in a clear deviation from a statistical distribution in favour of deuterium enriched species. The data analysis suggests that this is due to a higher sticking probability of D atoms to the cold surface, a property that may generally apply to molecules that are formed in low temperature surface reactions. The results found here are used to interpret ammonia deuterium fractionation as observed in pre-protostellar cores.

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G. Fedoseev, S. Ioppolo and H. Linnartz
Fri, 26 May 17
-30/63

Comments: N/A