426 research outputs found
First gravitational lensing mass estimate of a damped Lyman α galaxy at z = 2.2
No full textWe present the first lensing total mass estimate of a galaxy, at redshift 2.207, that acts as a gravitational deflector and damped Lyman α absorber on the background QSO SDSS J1135-0010, at redshift 2.888. The remarkably small projected distance, or impact parameter, between the lens and the source has been estimated to be 0.8 ± 0.1 kpc in a recent work. By exploiting the Sloan Digital Sky Survey data base, we establish a likely lensing magnification signal in the photometry of the QSO. This is determined to be 2.2 mag brighter (or eight times more luminous) than the median QSO at comparable redshifts. We describe the total mass distribution of the lens galaxy with a one-component singular isothermal sphere model and contrast the values of the observed and model-predicted magnification factors. For the former, we use conservatively the photometric data of the 95 per cent of the available distant QSO population. We estimate that the values of the lens effective velocity dispersion and two-dimensional total mass, projected within a cylinder with radius equal to the impact parameter, are included between 60 and 170 km s-1 and 2.1 × 109 and 1.8 × 1010 M⊙, respectively. We conclude by remarking that analyses of this kind are crucial to exploring the relation between the luminous and dark-matter components of galaxies in the high-redshift Universe
GRB Host Galaxies: An Unbiased Sample
No full textWe describe the current status and recent results from our Swift/VLT legacy survey, a VLT Large Programme aimed at characterizing the host galaxies of a homogeneously selected sub-sample of Swift GRBs. The immediate goals are to determine the host luminosity function, study the effects of reddening, determine the fraction of Lyα emitters in the hosts, and obtain redshifts for targets without a reported one. The main effort so far has been the definition of a very carefully selected sample, obeying strict and well-defined criteria: 68 targets in total. Among the preliminary results is a large optical detection rate, the lack of extremely red objects (only one possible case in the sample) and an update of the Swift GRB redshift distribution with ˜2.0
Fra fynbo til formand
No full textThis study stems from the problematization of the argument that media and thus journalists posses a great power due to their role as framers of news stories. The study therefore analyses the news framing of Annette Vilhelmsen, one of the two candidates in the party leader election campaign of the Danish party Socialistisk Folkeparti (SF). On a selection of 27 articles from seven different Danish newspapers the analysis examines if the framing of Annette Vilhelmsen is biased. The findings show that 19 of the articles were biased, of which 15 were positive towards Vilhelmsen and four were negative. Eight articles were neutral. The positive bias derives from both journalistic commentary and a biased set of wording as well as a one-sided selection of sources.This study stems from the problematization of the argument that media and thus journalists posses a great power due to their role as framers of news stories. The study therefore analyses the news framing of Annette Vilhelmsen, one of the two candidates in the party leader election campaign of the Danish party Socialistisk Folkeparti (SF). On a selection of 27 articles from seven different Danish newspapers the analysis examines if the framing of Annette Vilhelmsen is biased. The findings show that 19 of the articles were biased, of which 15 were positive towards Vilhelmsen and four were negative. Eight articles were neutral. The positive bias derives from both journalistic commentary and a biased set of wording as well as a one-sided selection of sources
Do Wolf-Rayet stars have similar locations in hosts as type Ib/c supernovae and long gamma-ray bursts?
No full textAims. We study the distribution of Wolf-Rayet (WR) stars and their subtypes with respect to their host galaxy light distribution. We thus want to investigate whether WR stars are potential progenitors of stripped-envelope core-collapse supernovae (SNe) and/or long-duration gamma-ray bursts (LGRBs).
Methods. We derived the relative surface brightness (fractional flux) at the locations of WR stars and compared with similar results for LGRBs and SNe.We examined two nearby galaxies,M 83 and NGC 1313, for which a comprehensive study of theWR population exists. These two galaxies contain a sufficiently large number ofWR stars and sample different metallicities. To enable the comparison,
the images of the galaxies were processed to make them appear as they would look at a higher redshift. The robustness of our results against several sources of uncertainty was investigated with the aid of Monte Carlo simulations.
Results. We find that the WC star distribution favours brighter pixels than the WN star population. WC stars are more likely drawn from the same distribution as SNe Ic than from other SN distributions, while WN stars show a higher degree of association with SNe Ib. It can also not be excluded that WR (especially WC) stars are related to LGRBs. Some differences between the two galaxies
do exist, especially in the subtype distributions, and may stem from differences in metallicity.
Conclusions. Although a conclusive answer is not possible, the expectation thatWR stars are the progenitors of SNe Ib/c and LGRBs survives this test. The trend observed between the distributions of WN and WC stars, as compared to those of SNe Ib and Ic, is consistent with the theoretical picture that SNe Ic result from progenitors that have been stripped of a larger part of their envelope
The 4MOST–Gaia Purely Astrometric Quasar Survey (4G-PAQS)
No full textThe 4MOST–Gaia Purely Astrometric Quasar Survey (4G-PAQS) will carry out the first large-scale, colour-independent quasar survey selected solely on the basis of astrometry from Gaia. Our main objective is to quantify the selection effects of current colour-selected samples. These colour-selected samples bias our view of the neutral gas and its chemical enrichment because of dust obscuration and reddening of optical colours. Moreover, the broad absorption-line outflows observed in quasars are under-represented by optical colour selection. 4G-PAQS will provide the first sample to overcome these challenges and will constrain the physical and chemical properties of gas in galaxies and quasars at cosmic noon
No evidence for dust extinction in GRB 050904 at z ~ 6.3
No full textContext. Gamma-ray burst (GRB) afterglows are excellent and sensitive probes of gas and dust in star-forming galaxies at all epochs. It has been posited that dust in the early Universe must be different from dust at lower redshifts. To date two reports in the literature directly support this contention, one of which is based on the spectral shape of the afterglow spectrum of GRB050904 at z = 6.295.
Aims. Here we reinvestigate the afterglow of GRB050904 to understand cosmic dust at high redshift.We address the claimed evidence for unusual (supernova-origin) dust in its host galaxy by simultaneously examining the X-ray and optical/near-infrared spectrophotometric data of the afterglow.
Methods. We derived the intrinsic spectral energy distribution (SED) of the afterglow at three different epochs, 0.47, 1.25, and 3.4 days after the burst. We reduced again the Swift X-ray data, the 1.25 days FORS2 z-Gunn photometric data, the spectroscopic and z-band
photometric data at ∼3 days from the Subaru telescope, as well as the critical UKIRT Z-band photometry at 0.47 days, upon which the claim of dust detection largely relies.
Results. We find no evidence of dust extinction in the SED at any time.We computed flux densities at λrest = 1250Å directly from the observed counts at all epochs. In the earliest epoch, 0.47 days, where the claim of dust is strongest, the Z-band suppression is found to
be weaker (0.3 ± 0.2 mag) than previously reported and statistically insignificant (<1.5σ). Furthermore, we find that the photometry of this band is unstable and difficult to calibrate.
Conclusions. From the afterglow SED we demonstrate that there is no evidence of dust extinction in GRB 050904 – the SED at all times can be reproduced without dust, and at 1.25 days in particular, significant extinction can be excluded, with A(3000Å) < 0.27 mag at 95% confidence using the supernova-type extinction curve. We conclude that there is no evidence of any extinction in the afterglow
of GRB050904 and that the presence of supernova-origin dust in the host of GRB050904 must be viewed skeptically
The host of GRB 060206 : kinematics of a distant galaxy
No full textContext. GRB afterglow spectra are sensitive probes of interstellar matter along the line-of-sight in their host galaxies, as well as in intervening galaxies. The rapid fading of GRBs makes it very difficult to obtain spectra of sufficient resolution and S/N to allow for these kinds of studies.
Aims. We investigate the state and properties of the interstellar medium in the host of GRB060206 at z = 4.048 with a detailed study of groundstate and finestructure absorption lines in an early afterglow spectrum. This allows us to derive conclusions on the nature and origin of the absorbing structures and their connection to the host galaxy and/or the GRB.
Methods. We used early (starting 1.6 h after the burst) WHT/ISIS optical spectroscopy of the afterglow of the gamma-ray burst GRB060206 detecting a range of metal absorption lines and their finestructure transitions. Additional information is provided by the afterglow lightcurve. The resolution and wavelength range of the spectra and the bright afterglow have facilitated a detailed study and
fitting of the absorption line systems in order to derive column densities. We also used deep imaging to detect the host galaxy and probe the nature of an intervening system at z = 1.48 seen in absorption in the afterglow spectra.
Results. We detect four discrete velocity systems in the resonant metal absorption lines, best explained by shells within and/or around the host created by starburst winds. The finestructure lines have no less than three components with strengths decreasing from the redmost components. We therefore suggest that the finestructure lines are best explained as being produced by UV pumping from which follows that the redmost component is the one closest to the burst where Nv was detected as well. The host is detected in deep HST imaging with F814WAB = 27.48 ± 0.19 mag and a 3σ upper limit of H = 20.6 mag (Vega) is achieved. A candidate counterpart for the intervening absorption system is detected as well, which is quite exceptional for an absorber in the sightline towards a GRB
afterglow. The intervening system shows no temporal evolution as claimed by Hao et al. (2007, ApJ, 659, 99), which we prove from our WHT spectra taken before and Subaru spectra taken during those observations
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