Lyman-break galaxies (LBGs) represent one of the kinds of star-forming galaxies that are found in the high-redshift universe. The detection of LBGs in the far-infrared (FIR) domain can provide very important clues on their dust attenuation and total star-formation rate (SFR), allowing a more detailed study than has been performed so far. In this work we explore the FIR emission of a sample of 16 LBGs at z ∼ 3 in the GOODS-North and GOODS-South fields that are individually detected in PACS-100 μm or PACS-160 μm. These detections demonstrate the possibility of measuring the dust emission of LBGs at high redshift. We find that PACS-detected LBGs at z ∼ 3 are highly obscured galaxies which belong to the ultra-luminous or hyper-luminous IR galaxy class. Their total SFR cannot be recovered with the dust attenuation factors obtained from their UV continuum slope or their SED-derived dust attenuation employing Bruzual & Charlot (2003) templates. Both methods underestimate the results for most of the galaxies. Comparing with a sample of PACS-detected LBGs at z ∼ 1, we find evidence that the FIR emission of LBGs might have changed with redshift, in the sense that the dustiest LBGs found at z ∼ 3 have more prominent FIR emission, are dustier for a given UV slope, and have higher SFR for a given stellar mass than the dustiest LBGs found at z ∼ 1.
A high-resolution spectroscopic survey of post-outburst novae reveals short-lived heavy element absorption systems in a majority of novae near maximum light, having expansion velocities of 400Y1000 km s À1 and velocity dispersions between 35 and 350 km s À1 . A majority of systems are accelerated outward, and they all progressively weaken and disappear over timescales of weeks. A few of the systems having narrow, deeper absorption reveal a rich spectrum of singly ionized Sc, Ti, V, Cr, Fe, Sr, Y, Zr, and Ba lines. Analysis of the richest such system, in LMC 2005, shows the excitation temperature to be 10 4 K and elements lighter than Fe to have abundance enhancements over solar values by up to an order of magnitude. The gas causing the absorption systems must be circumbinary and its origin is most likely mass ejection from the secondary star. The absorbing gas exists before the outburst and may represent episodic mass transfer events from the secondary star that initiate the nova outburst(s). If SNe Ia originate in single degenerate binaries, such absorption systems could be detectable before maximum light.
Context. The connection between active galactic nuclei (AGN) and their host galaxies has been widely studied and found to be of great importance for providing answers to some fundamental questions related to AGN fuelling mechanisms, and both their formation and evolution. Aims. Using X-ray data and one of the deepest broad-band optical data sets available, we study how morphology and colours are related to X-ray properties for sources at redshifts z ≤ 2.0, using a sample of 262 AGN in the Subaru/XMM-Newton Deep Survey (SXDS). Methods. We performed our morphological classification using the galSVM code, which is a new method that is particularly suited to dealing with high-redshift sources. Colour-magnitude diagrams were studied in relationship to redshift, morphology, X-ray obscuration, and X-ray-to-optical flux ratio. We analysed the different regions in the colour-magnitude diagrams, and searched for correlations with the observed properties of AGN populations using models of their formation and evolution. Results. We confirm that a robust and reliable morphological classification of a general galaxy population at high redshift should be based on a multi-parametric approach. At least 50% of X-ray detected AGN at z ≤ 2.0 analysed in this work reside in spheroidal and bulge-dominated galaxies, while at least 18% have disk-dominated hosts. This suggests that different mechanisms may be responsible for triggering the nuclear activity. When analysing populations of X-ray detected AGN in both colour-magnitude and colour-stellar mass diagrams, the highest number of sources is found to reside in the green valley at redshifts ≈0.5-1.5. However, a larger number of low-luminosity AGN have been detected than in previous works owing to the substantial depth of the SXDS optical data. Whether AGN are hosted by early-or late-type galaxies, no clear relationship has been found with the optical colours (independently of redshift), as is typical of normal galaxies. Both early-and late-type AGN cover similar ranges of X-ray obscuration, for both unobscured and obscured sources. Conclusions. Our findings appear to confirm some previous suggestions that X-ray selected AGN residing in the green valley represent a transitional population, quenching star formation by means of different AGN feedback mechanisms and evolving to red-sequence galaxies. They might be hosted by similar sources (the majority of sources being late-type elliptical and lenticular galaxies, and early-type spirals) with similar stellar populations, which are triggered mainly by major and/or minor mergers, and in some cases by means of secular mechanism, as shown in previous numerical simulations. In the aforementioned transition we observe different phases of AGN activity, with some AGN being in the "QSO-mode" detected as compact, blue, and unobscured in X-rays, and with others passing through different phases before and after the "QSO-mode", being obscured and unobscured in X-rays, respectively.
Aims. We aim to derive the physical properties of the recurrent nova T Pyx and the structure of the ejecta during the early stages of expansion of the 2011 outburst. Methods. The nova was observed with high resolution spectroscopy (R ≈ 65 000), from one day after discovery of the outburst and until the last visibility of the star at the end of May 2011. The interstellar absorption lines of Na I, Ca II, CH, CH + , and archival H I 21 cm emission line observations were used to determine a kinematical distance. Interstellar diffuse absorption features have been used to determine the extinction independent of previous assumptions. Sample Fe-peak line profiles show the optical depth and radial velocity evolution of the discrete components. Results. We propose a distance to T Pyx ≥ 4.5 kpc, with a strict lower limit of 3.5 kpc (the previously accepted distance). We derive an extinction, E(B − V) ≈ 0.5 ± 0.1, that is higher than previous estimates. The first observation, Apr. 15, displayed He I, He II, C III, and N III emission lines and a maximum velocity derived from the P Cyg profiles of the Balmer and He I lines of ≈2500 km s −1 that is characteristic of the fireball stage. These ions were undetectable in the second spectrum, Apr. 23, and we use the recombination time to estimate the mass of the ejecta, 10 −5 f M for a filling factor f . Numerous absorption-line systems were detected in the Balmer, Fe-peak, Ca II, and Na I lines, mirrored in broader emission-line components, that showed an "accelerated" displacement in velocity. We also show that the time sequence of these absorptions, which are common to all lines and arise only in the ejecta, can be described by a recombination front moving outward in the expanding gas without either a stellar wind or circumstellar collisions. By the end of May, the ejecta were showing signs of turning optically thin in the ultraviolet.
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