Abstract
Observations of star-forming galaxies in the distant Universe have confirmed the importance of massive stars in shaping galaxy emission and evolution. Distant stellar populations are ...unresolved, and the limited data available must be interpreted in the context of stellar population models. Understanding these populations, and their evolution with age and heavy element content is key to interpreting processes such as supernovae, cosmic reionization and the chemical enrichment of the Universe. With the upcoming launch of JWST and observations of galaxies within a billion years of the Big Bang, the uncertainties in modelling massive stars - particularly their interactions with binary companions - are becoming increasingly important to our interpretation of the high redshift Universe. In turn, observations of distant stellar populations provide ever stronger tests against which to gauge the success of, and flaws in, current massive star models. Here we briefly review the current status binary stellar population synthesis.
Identifying galaxy clustering at high redshift (i.e. z > 1) is essential to our understanding of the current cosmological model. However, at increasing redshift, clusters evolve considerably in star ...formation activity and so are less likely to be identified using the widely used red-sequence method. Here we assess the viability of instead identifying high-redshift clustering using actively star-forming galaxies (submillimetre galaxies, SMGs, associated with overdensities of BzKs/LBGs). We perform both a 2D and 3D clustering analysis to determine whether or not true (3D) clustering can be identified where only 2D data are available. As expected, we find that 2D clustering signals are weak at best and inferred results are method dependent. In our 3D analysis, we identify 12 SMGs associated with an overdensity of galaxies coincident both spatially and in redshift - just 8 per cent of SMGs with known redshifts in our sample. Where an SMG in our target fields lacks a known redshift, their sight line is no more likely to display clustering than blank sky fields; prior redshift information for the SMG is required to identify a true clustering signal. We find that the strength of clustering in the volume around typical SMGs, while identifiable, is not exceptional. However, we identify a small number of highly clustered regions, all associated with an SMG. The most notable of these, surrounding LESS J033336.8−274401, potentially contains an SMG, a quasi stellar object (QSO) and 36 star-forming galaxies (a >20σ overdensity) all at z ∼ 1.8. This region is highly likely to represent an actively star-forming cluster and illustrates the success of using star-forming galaxies to select sites of early clustering. Given the increasing number of deep fields with large volumes of spectroscopy, or high quality and reliable photometric redshifts, this opens a new avenue for cluster identification in the young Universe.
We describe the selection of a sample of photometrically defined Lyman break galaxies (LBGs) at z∼ 5 using the multiwavelength imaging data of the ESO (European Southern Observatory) Remote Galaxy ...Survey. The data are drawn from 10 widely separated fields covering a total sky area of 275 arcmin2. Starting with a simple colour (R−I > 1.3) and magnitude (I < 26.3) cut to isolate the Lyman break and then refining the sample by applying further optical and near-infrared photometric criteria we identify a sample of 253 LBG candidates. We carefully model the completeness of this sample and the factors that affect its reliability. There is considerable overlap between this sample and a spectroscopically confirmed sample drawn from the same survey and this allows us to determine the reliability of the optical photometric selection (∼60 per cent) and to show that the reliability can be significantly improved (to ∼80 per cent) by applying near-infrared waveband criteria to exclude very red contaminants. Even this high level of reliability may compromise some statistical studies of LBG properties. We show that over 30 per cent of the highest reliability candidates have multiple ultraviolet (UV) luminous components and/or disturbed morphology in Hubble Space Telescope imaging, though it is unclear whether this represents multiple interacting/merging sources or individual large sources with multiple UV bright regions. Using this sample we confirm that the normalization of the bright end of the z= 5 UV luminosity function (down to M*) is lower than the same at z= 4 by a factor of 3. Using a Schechter fit we determine M*UV=−20.9 ± 0.2. We discuss whether it is reasonable to expect the UV luminosity function to follow a Schechter function, given the UV emission is short lived and stochastic, and does not necessarily trace the underlying mass of the galaxy.
SN 2002cx-like Type Ia supernovae (also known as SNe Iax) represent one of the most numerous peculiar SN classes. They differ from normal SNe Ia by having fainter peak magnitudes, faster decline ...rates and lower photospheric velocities, displaying a wide diversity in these properties. We present both integral-field and long-slit visual-wavelength spectroscopy of the host galaxies and explosion sites of SNe Iax to provide constraints on their progenitor formation scenarios. The SN Iax explosion-site metallicity distribution is similar to that of core-collapse SNe and metal poor compared to either normal SNe Ia or SN 1991T-like events. Fainter members, speculated to form distinctly from brighter SN Iax, are found at a range of metallicities, extending to very metal poor environments. Although the SN Iax explosion-sites' ages and star formation rates are comparatively older and less intense than the distribution of star-forming regions across their host galaxies, we confirm the presence of young stellar populations (SPs) at explosion environments for most SNe Iax, expanded here to a larger sample. Ages of the young SPs (several x 10(7) to 10(8) yr) are consistent with predictions for young thermonuclear and electron-capture SN progenitors. The lack of extremely young SPs at the explosion sites disfavours very massive progenitors such as Wolf-Rayet explosions with significant fallback. We find weak ionized gas in the only SN Iax host without obvious signs of star formation. The source of the ionization remains ambiguous but appears unlikely to be mainly due to young, massive stars.
Abstract
We present 1.2 mm MAMBO-2 observations of a field which is overdense in Lyman break galaxies (LBGs) at z ∼ 5. The field includes seven spectroscopically confirmed LBGs contained within a ...narrow (z = 4.95 ± 0.08) redshift range and an eighth at z = 5.2. We do not detect any individual source to a limit of 1.6 mJy/beam (2 × rms). When stacking the flux from the positions of all eight galaxies, we obtain a limit to the average 1.2 mm flux of these sources of 0.6 mJy/beam. This limit is consistent with far-infrared (FIR) imaging in other fields which are overdense in ultraviolet-bright galaxies at z ∼ 5. Independently and combined, these limits constrain the FIR luminosity (8-1000 μm) to a typical z ∼ 5 LBG of L
FIR ≲ 3 × 1011 L⊙, implying a dust mass of M
dust ≲ 108 M⊙ (both assuming a grey body at 30 K). This L
FIR limit is an order of magnitude fainter than the L
FIR of lower redshift submillimetre sources (z ∼ 1-3). We see no emission from any other sources within the field at the above-mentioned level. While this is not unexpected, given millimetre source counts, the clustered LBGs trace significant overdense large-scale structure in the field at z = 4.95. The lack of any such detection in either this or the previous work implies that massive, obscured star-forming galaxies may not always trace the same structures as overdensities of LBGs, at least on the length scale probed here. We briefly discuss the implications of these results for future observations with ALMA.
We report the discovery of a luminous z = 5.78 star-forming galaxy in the Chandra Deep Field South. This galaxy was selected as an ‘i-drop’ from the GOODS public survey imaging with the Hubble Space ...Telescope/Advanced Camera for Surveys (object 3 in the work of Stanway, Bunker & McMahon 2003). The large colour of (i′−z′)AB = 1.6 indicated a spectral break consistent with the Lyman α forest absorption shortward of Lyman α at z≈ 6. The galaxy is very compact (marginally resolved with ACS with a half-light radius of 0.08 arcsec, so rhl < 0.5 h−170 kpc). We have obtained a deep (5.5 h) spectrum of this z′AB = 24.7 galaxy with the DEIMOS optical spectrograph on the Keck Telescope, and here we report the discovery of a single emission line centred on 8245 Å detected at 20σ with a flux of ƒ≈ 2 × 10−17 erg cm−2 s−1. The line is clearly resolved with detectable structure at our resolution of better than 55 km s−1, and the only plausible interpretation consistent with the ACS photometry is that we are seeing Lyman α emission from a z = 5.78 galaxy. This is the highest redshift galaxy to be discovered and studied using HST data. The velocity width (ΔvFWHM = 260 km s−1) and rest-frame equivalent width (WLyαrest = 20 Å) indicate that this line is most probably powered by star formation, as an AGN would typically have larger values. The starburst interpretation is supported by our non-detection of the high-ionization N vλ1240- Å emission line, and the absence of this source from the deep Chandra X-ray images. The star formation rate inferred from the rest-frame UV continuum is 34 h−270 M⊙ yr−1 (ΩM = 0.3, ΩΛ = 0.7). This is the most luminous starburst known at z > 5. Our spectroscopic redshift for this object confirms the validity of the i′-drop technique of Stanway et al. to select star-forming galaxies atz≈ 6.
We measure the ages, stellar masses, and star formation histories of z∼ 6 galaxies, observed within 1 Gyr of the big bang. We use imaging from the Hubble Space Telescope (HST) and the Spitzer Space ...Telescope from the public ‘Great Observatories Origins Deep Survey’ (GOODS), coupled with ground-based near-infrared imaging, to measure their spectral energy distributions (SEDs) from 0.8–5 μm, spanning the rest-frame ultraviolet (UV) and optical. From our sample of ≈50 ‘i′-drop’ Lyman-break star-forming galaxies in GOODS-South with z′AB < 27, we focus on ≈30 with reliable photometric or spectroscopic redshifts. Half of these are confused with foreground sources at Spitzer resolution, but from the 16 with clean photometry we find that a surprisingly large fraction (40 per cent) have evidence for substantial Balmer/4000-Å spectral breaks. This indicates the presence of old underlying stellar populations that dominate the stellar masses. For these objects, we find ages of ∼200–700 Myr, implying formation redshifts of 7 ≤zf≤ 18, and large stellar masses in the range ∼1–3 × 1010 M⊙. Analysis of seven i′-drops that are undetected at 3.6 μm indicates that these are younger, considerably less massive systems. We calculate that emission line contamination should not severely affect our photometry or derived results. Using SED fits out to 8 μm, we find little evidence for substantial intrinsic dust reddening in our sources. We use our individual galaxy results to obtain an estimate of the global stellar mass density at z∼ 6. Correcting for incompleteness in our sample, we find the z∼ 6 comoving stellar mass density to be 2.5 × 106 M⊙ Mpc−3. This is a lower limit, as post-starburst and dust-obscured objects, and also galaxies below our selection thresholds, are not accounted for. From our results, we are able to explore the star formation histories of our selected galaxies, and we suggest that the past global star formation rate may have been much higher than that observed at the z∼ 6 epoch. The associated UV flux we infer at z > 7 could have played a major role in reionizing the Universe.
We analyse near-infrared Hubble Space Telescope (HST)/Near-Infrared Camera and Multi-Object Spectrometer F110W (J) and F160W (H) band photometry of a sample of 27 i′-drop candidate z≃ 6 galaxies in ...the central region of the HST/Advanced Camera for Surveys Ultra Deep Field. The infrared colours of the 20 objects not affected by near neighbours are consistent with a high-redshift interpretation. This suggests that the low-redshift contamination of this i′-drop sample is smaller than that observed at brighter magnitudes, where values of 10–40 per cent have been reported. The J–H colours are consistent with a slope flat in fν(fλ∝λ−2), as would be expected for an unreddened starburst. However, there is evidence for a marginally bluer spectral slope (fλ∝λ−2.2), which is perhaps indicative of an extremely young starburst (∼10 Myr old) or a top heavy initial mass function and little dust. The low levels of contamination, median photometric redshift of z∼ 6.0 and blue spectral slope, inferred using the near-infrared data, support the validity of the assumptions in our earlier work in estimating the star formation rates, and that the majority of the i-drop candidates galaxies lie at z∼ 6.
The past few decades have seen substantial improvements in cancer survival, but concerns exist about long-term cardiovascular disease risk in survivors. Evidence is scarce on the risks of specific ...cardiovascular diseases in survivors of a wide range of cancers to inform prevention and management. In this study, we used large-scale electronic health records data from multiple linked UK databases to address these evidence gaps.
For this population-based cohort study, we used linked primary care, hospital, and cancer registry data from the UK Clinical Practice Research Datalink to identify cohorts of survivors of the 20 most common cancers who were 18 years or older and alive 12 months after diagnosis and controls without history of cancer, matched for age, sex, and general practice. We compared risks for a range of cardiovascular disease outcomes using crude and adjusted Cox models. We fitted interactions to investigate effect modification, and flexible parametric survival models to estimate absolute excess risks over time.
Between Jan 1, 1990, and Dec 31, 2015, 126 120 individuals with a diagnosis of a cancer of interest still being followed up at least 1 year later were identified and matched to 630 144 controls. After exclusions, 108 215 cancer survivors and 523 541 controls were included in the main analyses. Venous thromboembolism risk was elevated in survivors of 18 of 20 site-specific cancers compared with that of controls; adjusted hazard ratios (HRs) ranged from 1·72 (95% CI 1·57–1·89) in patients after prostate cancer to 9·72 (5·50–17·18) after pancreatic cancer. HRs decreased over time, but remained elevated more than 5 years after diagnosis. We observed increased risks of heart failure or cardiomyopathy in patients after ten of 20 cancers, including haematological (adjusted HR 1·94, 1·66–2·25, with non-Hodgkin lymphoma; 1·77, 1·50–2·09, with leukaemia; and 3·29, 2·59–4·18, with multiple myeloma), oesophageal (1·96, 1·46–2·64), lung (1·82, 1·52–2·17) kidney (1·73, 1·38–2·17) and ovarian (1·59, 1·19–2·12). Elevated risks of arrhythmia, pericarditis, coronary artery disease, stroke, and valvular heart disease were also observed for multiple cancers, including haematological malignancies. HRs for heart failure or cardiomyopathy and venous thromboembolism were greater in patients without previous cardiovascular disease and in younger patients. However, absolute excess risks were generally greater with increasing age. Increased risks of these outcomes seemed most pronounced in patients who had received chemotherapy.
Survivors of most site-specific cancers had increased medium-term to long-term risk for one or more cardiovascular diseases compared with that for the general population, with substantial variations between cancer sites.
Wellcome Trust and Royal Society.
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