ABSTRACT
We present forward modelling from the bpass code suite of the population of observed gravitational wave (GW) transients reported by the LIGO/VIRGO consortium (LVC) during their third ...observing run, O3(a+b). Specifically, we predict the expected chirp mass and mass ratio distributions for GW transients, taking account of detector sensitivity to determine how many events should have been detected by the current detector network in O3(a+b). We investigate how these predictions change by alternating between four different remnant mass estimation schemes and two supernovae (SNe) kick prescriptions. We find that none of the model populations resulting from these variations accurately match the whole O3(a+b) GW transient catalogue. However, agreement from some models to part of the catalogue suggests ways to achieve a more complete fit. These include reducing the number of low-mass black holes (BHs) close to the mass gap, while also increasing the number of higher mass BHs below the pair-instability SN limit. Finally, we find that the interaction between the value of the remnant mass from a stellar model and the choice of SN kick is complex and different kick prescriptions may be required depending on whether a neutron star or BH is formed.
Comparison with artificial galaxy models is essential for translating the incomplete and low signal-to-noise data we can obtain on astrophysical stellar populations to physical interpretations which ...describe their composition, physical properties, histories and internal conditions. In particular, this is true for distant galaxies, whose unresolved light embeds clues to their formations and evolutions, and their impacts on their wider environs. Stellar population synthesis models are now used as the foundation of analysis at all redshifts, but are not without their problems. Here we review the use of stellar population synthesis models, with a focus on applications in the distant Universe.
We present an analysis of the photometry and spectroscopy of the host galaxy of Swift-detected GRB 080517. From our optical spectroscopy, we identify a redshift of z = 0.089 plus or minus 0.003, ...based on strong emission lines, making this a rare example of a very local, low-luminosity, long gamma-ray burst. The galaxy is detected in the radio with a flux density of S(4.8 GHz) = 0.22 plus or minus 0.04 mJy -- one of relatively few known gamma-ray bursts hosts with a securely measured radio flux. Both optical emission lines and a strong detection at 22 mu m suggest that the host galaxy is forming stars rapidly, with an inferred star formation rate similar to 16 Msun/yr and a high dust obscuration (E(B - V) > 1, based on sightlines to the nebular emission regions). The presence of a companion galaxy within a projected distance of 25 kpc, and almost identical in redshift, suggests that star formation may have been triggered by galaxy-galaxy interaction. However, fitting of the remarkably flat spectral energy distribution from the ultraviolet through to the infrared suggests that an older, 500 Myr post-starburst stellar population is present along with the ongoing star formation. We conclude that the host galaxy of GRB 080517 is a valuable addition to the still very small sample of well-studied local gamma-ray burst hosts.
ABSTRACT
With the successful launch and commissioning of JWST we are now able to routinely spectroscopically probe the rest-frame optical emission of galaxies at z > 6 for the first time. Among the ...most useful spectral diagnostics used in the optical is the Balmer/4000 Å break; this is, in principle, a diagnostic of the mean ages of composite stellar populations. However, the Balmer break is also sensitive to the shape of the star formation history, the stellar (and gas) metallicity, the presence of nebular continuum emission, and dust attenuation. In this work, we explore the origin of the Balmer/4000 Å break using the synthesizer synthetic observations package. We then make predictions of the Balmer/4000 Å break using the First Light and Reionization Epoch Simulations at 5 < z < 10. We find that the average break strength weakly correlates with stellar mass and rest-frame far-ultraviolet luminosity, but that this is predominantly driven by dust attenuation. We also find that break strength provides a weak diagnostic of the age but performs better as a means to constrain star formation and stellar mass, alongside the ultraviolet and optical luminosity, respectively.
We study and compare different examples of stellar evolutionary synthesis input parameters used to produce photoionization model grids using the MAPPINGS V modeling code. The aim of this study is to ...(a) explore the systematic effects of various stellar evolutionary synthesis model parameters on the interpretation of emission lines in optical strong-line diagnostic diagrams, (b) characterize the combination of parameters able to reproduce the spread of local galaxies located in the star-forming region in the Sloan Digital Sky Survey, and (c) investigate the emission from extremely metal-poor galaxies using photoionization models. We explore and compare the stellar input ionizing spectrum (stellar population synthesis code Starburst99, SLUG, BPASS, stellar evolutionary tracks, stellar atmospheres, star formation history, sampling of the initial mass function), as well as parameters intrinsic to the H ii region (metallicity, ionization parameter, pressure, H ii region boundedness). We also perform a comparison of the photoionization codes MAPPINGS and CLOUDY. On the variations in the ionizing spectrum model parameters, we find that the differences in strong emission-line ratios between varying models for a given input model parameter are small, on average ∼0.1 dex. An average difference of ∼0.1 dex in emission-line ratio is also found between models produced with MAPPINGS and CLOUDY. Large differences between the emission-line ratios are found when comparing intrinsic H ii region parameters. We find that low-metallicity galaxies are better explained by a density-bounded H ii region and higher pressures better encompass the spread of galaxies at high redshift.
High-redshift galaxies and low-mass stars Wilkins, Stephen M; Stanway, Elizabeth R; Bremer, Malcolm N
Monthly Notices of the Royal Astronomical Society,
03/2014, Letnik:
439, Številka:
1
Journal Article
Recenzirano
Odprti dostop
The sensitivity available to near-infrared surveys has recently allowed us to probe the galaxy population at z 7 and beyond. The existing Hubble Wide Field Camera 3 (WFC3) and Visible and Infrared ...Survey Telescope for Astronomy (VISTA) Infrared Camera (VIRCam) instruments allow deep surveys to be undertaken well beyond 1 μm - a capability that will be further extended with the launch and commissioning of the James Webb Space Telescope (JWST). As new regions of parameter space in both colour and depth are probed, new challenges for distant galaxy surveys are identified. In this paper, we present an analysis of the colours of L- and T-dwarf stars in widely used photometric systems. We also consider the implications of the newly identified Y-dwarf population - stars that are still cooler and less massive than T-dwarfs for both the photometric selection and spectroscopic follow-up of faint and distant galaxies. We highlight the dangers of working in the low-signal-to-noise regime, and the potential contamination of existing and future samples. We find that Hubble/WFC3 and VISTA/VIRCam Y-drop selections targeting galaxies at z ∼ 7.5 are vulnerable to contamination from T- and Y-class stars. Future observations using JWST, targeting the z ∼ 7 galaxy population, are also likely to prove difficult without deep medium-band observations. We demonstrate that single emission line detections in typical low-signal-to-noise spectroscopic observations may also be suspect, due to the unusual spectral characteristics of the cool dwarf star population.
We present a search for galaxies at 7.6 < z < 9.8 using the latest Hubble Space Telescope/Wide Field Camera 3 (WFC3) near-infrared data, based on the Lyman-break technique. We search for galaxies ...which have large (Y−J) colours (the 'Y-drops') on account of the Lyman α forest absorption, and with (J−H) colours inconsistent with being low-redshift contaminants. We identify 24 candidates at redshift z≈ 8-9 (15 are robust and a further nine more marginal but consistent with being high redshift) over an area of ≈50 arcmin2. Previous searches for Y-drops with WFC3 have focused only on the Hubble Ultra Deep Field, and our larger survey (involving two other nearby deep fields and a wider area survey) has trebled the number of robust Y-drop candidates. For the first time, we have sufficient z≈ 8-9 galaxies to fit both φ* and M* of the UV Schechter luminosity function. There is evidence for evolution in this luminosity function from z= 6-7 to z= 8-9, in the sense that there are fewer UV-bright galaxies at z≈ 8-9, consistent with an evolution mainly in M*. The candidate z≈ 8-9 galaxies we detect have insufficient ionizing flux to reionize the Universe, and it is probable that galaxies below our detection limit provide a significant UV contribution. The faint-end slope, α, is not well constrained. However, adopting a similar faint-end slope to that determined at z= 3-6 (α=−1.7) and a Salpeter initial mass function (IMF), then the ionizing photon budget still falls short if f
esc < 0.5, even integrating down to M
UV=−8. A steeper faint-end slope or a low-metallicity population (or a top-heavy IMF) might still provide sufficient photons for star-forming galaxies to reionize the Universe, but confirmation of this might have to await the James Webb Space Telescope.
Star-forming galaxies at high redshift show ubiquitously high-ionization parameters, as measured by the ratio of optical emission lines. We demonstrate that local (z < 0.2) sources selected as Lyman ...break analogues also manifest high line ratios with a typical O iii/H
$\beta =3.36^{+0.14}_{-0.04}$
– comparable to all but the highest ratios seen in star-forming galaxies at z ∼ 2–4. We argue that the stellar population synthesis code bpass can explain the high-ionization parameters required through the ageing of rapidly formed star populations, without invoking any AGN contribution. Binary stellar evolution pathways prolong the age interval over which a starburst is likely to show elevated line ratios, relative to those predicted by single stellar evolution codes. As a result, model galaxies at near-solar metallicities and with ages of up to ∼100 Myr after a starburst typically have a line ratio O iii/Hβ ∼ 3, consistent with those seen in Lyman break galaxies and local sources with similar star formation densities. This emphasises the importance of including binary evolution pathways when simulating the nebular line emission of young or bursty stellar populations.
The recent Hubble Space Telescope near-infrared imaging with the Wide-Field Camera #3 (WFC 3) of the Great Observatories Origins Deep Survey South (GOODS-S) field in the Cosmic Assembly Near-infrared ...Deep Extragalactic Legacy Survey (CANDELS) programme covering nearly 100 arcmin2, along with already existing Advanced Camera for Surveys optical data, makes possible the search for bright galaxy candidates at redshift z 7-9 using the Lyman break technique. We present the first analysis of z
′-drop z 7 candidate galaxies in this area, finding 19 objects. We also analyse Y-drops at z 8, trebling the number of bright (H
AB < 27 mag) Y-drops from our previous work, and compare our results with those of other groups based on the same data. The bright high-redshift galaxy candidates we find serve to better constrain the bright end of the luminosity function at those redshift, and may also be more amenable to spectroscopic confirmation than the fainter ones presented in various previous work on the smaller fields (the Hubble Ultra Deep Field and the WFC 3 Early Release Science observations). We also look at the agreement with previous luminosity functions derived from WFC 3 drop-out counts, finding a generally good agreement, except for the luminosity function of Yan et al. at z 8, which is strongly ruled out.
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