ORCID Profile
0000-0002-7636-0534
Current Organisations
University of Oxford
,
European Space Research and Technology Centre
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Sensory Processes, Perception and Performance | Psychology | Behavioural Ecology |
Expanding Knowledge in the Biological Sciences | Expanding Knowledge in Psychology and Cognitive Sciences | Expanding Knowledge in Technology
Publisher: EDP Sciences
Date: 06-2022
DOI: 10.1051/0004-6361/202243348
Abstract: Aims. We investigate the ionizing properties of the pair of bright Ly α emitting galaxies BDF521 and BDF2195 at z = 7.012 in order to constrain their contribution to the formation of the Bremer Deep Field (BDF) ‘reionized bubble’ in which they have been shown to reside. Methods. We obtain constraints on four UV emission lines (the CIV λ 1548 doublet, HeII λ 1640, the OIII] λ 1660 doublet, and the CIII] λ 1909 doublet) from deep VLT X-shooter observations and compare them to those available for other high-redshift objects, and to models with mixed stellar and active galactic nucleus (AGN) emission. We use this spectroscopic information, together with the photometry available in the field, to constrain the physical properties of the two objects using the spectro-photometric fitting code BEAGLE. Results. We do not detect any significant emission at the expected position of the UV lines, with 3 σ upper limits of equivalent width (EW) ≲2–7 Å rest-frame. We find that the two objects have a lower CIII] emission than expected on the basis of the correlation between the Ly α and CIII] EWs. The EW limits on CIV and HeII emission exclude pure AGN templates at ∼2 − 3 σ significance, and only models with a ≲40% AGN contribution are compatible with the observations. The two objects are found to be relatively young (∼20–30 Myrs) and metal-poor (≲0.3 Z ⊙ ), with stellar masses of a few 10 9 M ⊙ . Their production rate of hydrogen ionizing photons per intrinsic UV luminosity is log( ξ ion * /Hz erg −1 ) = 25.02–25.26, consistent with values typically found in high-redshift galaxies, but more than twice lower than values measured in z 7 galaxies with strong CIII] and/or optical line emission (≃25.6–25.7). Conclusions. The two BDF emitters show no evidence of higher-than-average ionizing capabilities and are not capable of reionizing their surroundings by their own means, under realistic assumptions of the escape fraction of ionizing photons. Therefore, a dominant contribution to the formation of the reionized bubble must have been provided by fainter companion galaxies. The capabilities of the James Webb Space Telescope will be needed for spectroscopic confirmation of these objects.
Publisher: EDP Sciences
Date: 10-2202
Publisher: American Astronomical Society
Date: 02-2023
Abstract: The study of galaxy evolution hinges on our ability to interpret multiwavelength galaxy observations in terms of their physical properties. To do this, we rely on spectral energy distribution (SED) models, which allow us to infer physical parameters from spectrophotometric data. In recent years, thanks to wide and deep multiwave band galaxy surveys, the volume of high-quality data have significantly increased. Alongside the increased data, algorithms performing SED fitting have improved, including better modeling prescriptions, newer templates, and more extensive s ling in wavelength space. We present a comprehensive analysis of different SED-fitting codes including their methods and output with the aim of measuring the uncertainties caused by the modeling assumptions. We apply 14 of the most commonly used SED-fitting codes on s les from the CANDELS photometric catalogs at z ∼ 1 and z ∼ 3. We find agreement on the stellar mass, while we observe some discrepancies in the star formation rate (SFR) and dust-attenuation results. To explore the differences and biases among the codes, we explore the impact of the various modeling assumptions as they are set in the codes (e.g., star formation histories, nebular, dust and active galactic nucleus models) on the derived stellar masses, SFRs, and A V values. We then assess the difference among the codes on the SFR–stellar mass relation and we measure the contribution to the uncertainties by the modeling choices (i.e., the modeling uncertainties) in stellar mass (∼0.1 dex), SFR (∼0.3 dex), and dust attenuation (∼0.3 mag). Finally, we present some resources summarizing best practices in SED fitting.
Publisher: Springer Science and Business Media LLC
Date: 04-04-2023
Publisher: American Astronomical Society
Date: 20-09-2022
Abstract: The COS Legacy Archive Spectroscopic SurveY (CLASSY) is designed to provide the community with a spectral atlas of 45 nearby star-forming galaxies that were chosen to cover similar properties to those seen at high z ( z 6). The prime high-level science product of CLASSY is accurately coadded UV spectra, ranging from ∼1000 to 2000 Å, derived from a combination of archival and new data obtained with HST’s Cosmic Origins Spectrograph (COS). This paper details the multistage technical processes of creating this prime data product and the methodologies involved in extracting, reducing, aligning, and coadding far-ultraviolet and near-ultraviolet (NUV) spectra. We provide guidelines on how to successfully utilize COS observations of extended sources, despite COS being optimized for point sources, and best-practice recommendations for the coaddition of UV spectra in general. Moreover, we discuss the effects of our reduction and coaddition techniques in the scientific application of the CLASSY data. In particular, we find that accurately accounting for flux calibration offsets can affect the derived properties of the stellar populations, while customized extractions of NUV spectra for extended sources are essential for correctly diagnosing the metallicity of galaxies via C iii ] nebular emission. Despite changes in spectral resolution of up to ∼25% between in idual data sets (due to changes in the COS line-spread function), no adverse affects were observed on the difference in velocity width and outflow velocities of isolated absorption lines when measured in the final combined data products, owing in part to our signal-to-noise regime of S/N 20.
Publisher: American Astronomical Society
Date: 2021
Abstract: We present an analysis of the optical properties of three Ultra Luminous X-ray (ULX) sources identified in NGC 925. We use Integral field unit data from the George Mitchel spectrograph in the context of the Metal-THINGS survey. The optical properties for ULX-1 and ULX-3 are presented, while the spaxel associated with ULX-2 had a low S/N, which prevented its analysis. We also report the kinematics and dimensions of the optical nebula associated with each ULX using ancillary data from the PUMA Fabry–Perot spectrograph. A BPT analysis demonstrates that most spaxels in NGC 925 are dominated by star-forming regions, including those associated with ULX-1 and ULX-3. Using the resolved gas-phase metallicities, a negative metallicity gradient is found, consistent with previous results for spiral galaxies, while the ionization parameter tends to increase radially throughout the galaxy. Interestingly, ULX-1 shows a very low gas metallicity for its galactocentric distance, identified by two independent methods, while exhibiting a typical ionization. We find that such low gas metallicity is best explained in the context of the high-mass X-ray binary population, where the low-metallicity environment favors active Roche lobe overflows that can drive much higher accretion rates. An alternative scenario invoking accretion of a low-mass galaxy is not supported by the data in this region. Finally, ULX-3 shows both a high metallicity and ionization parameter, which is consistent with the progenitor being a highly accreting neutron star within an evolved stellar population region.
Publisher: Springer Science and Business Media LLC
Date: 19-07-2023
Publisher: American Astronomical Society
Date: 27-10-2023
Publisher: Springer Science and Business Media LLC
Date: 04-04-2023
Publisher: American Astronomical Society
Date: 20-11-2018
Publisher: American Astronomical Society
Date: 27-07-2022
Abstract: Far-ultraviolet (FUV ∼1200–2000 Å) spectra are fundamental to our understanding of star-forming galaxies, providing a unique window on massive stellar populations, chemical evolution, feedback processes, and reionization. The launch of the James Webb Space Telescope will soon usher in a new era, pushing the UV spectroscopic frontier to higher redshifts than ever before however, its success hinges on a comprehensive understanding of the massive star populations and gas conditions that power the observed UV spectral features. This requires a level of detail that is only possible with a combination of le wavelength coverage, signal-to-noise, spectral-resolution, and s le ersity that has not yet been achieved by any FUV spectral database. We present the Cosmic Origins Spectrograph Legacy Spectroscopic Survey (CLASSY) treasury and its first high-level science product, the CLASSY atlas. CLASSY builds on the Hubble Space Telescope (HST) archive to construct the first high-quality (S/N 1500 Å ≳ 5/resel), high-resolution ( R ∼ 15,000) FUV spectral database of 45 nearby (0.002 z 0.182) star-forming galaxies. The CLASSY atlas, available to the public via the CLASSY website, is the result of optimally extracting and coadding 170 archival+new spectra from 312 orbits of HST observations. The CLASSY s le covers a broad range of properties including stellar mass (6.2 log M ⋆ ( M ⊙ ) 10.1), star formation rate (−2.0 log SFR ( M ⊙ yr −1 ) +1.6), direct gas-phase metallicity (7.0 12+log(O/H) 8.8), ionization (0.5 O 32 38.0), reddening (0.02 E ( B − V ) 0.67), and nebular density (10 n e (cm −3 ) 1120). CLASSY is biased to UV-bright star-forming galaxies, resulting in a s le that is consistent with the z ∼ 0 mass–metallicity relationship, but is offset to higher star formation rates by roughly 2 dex, similar to z ≳ 2 galaxies. This unique set of properties makes the CLASSY atlas the benchmark training set for star-forming galaxies across cosmic time.
Publisher: EDP Sciences
Date: 09-2023
Publisher: American Astronomical Society
Date: 25-07-2023
Abstract: Recent JWST/NIRCam imaging taken for the ultra-deep UNCOVER program reveals a very red dropout object at z phot ≃ 7.6, triply imaged by the galaxy cluster A2744 ( z d = 0.308). All three images are very compact, i.e., unresolved, with a delensed size upper limit of r e ≲ 35 pc. The images have apparent magnitudes of m F444W ∼ 25−26 AB, and the magnification-corrected absolute UV magnitude of the source is M UV,1450 = −16.81 ± 0.09. From the sum of observed fluxes and from a spectral energy distribution (SED) analysis, we obtain estimates of the bolometric luminosities of the source of L bol ≳ 10 43 erg s −1 and L bol ∼ 10 44 –10 46 erg s −1 , respectively. Based on its compact, point-like appearance, its position in color–color space, and the SED analysis, we tentatively conclude that this object is a UV-faint dust-obscured quasar-like object, i.e., an active galactic nucleus at high redshift. We also discuss other alternative origins for the object’s emission features, including a massive star cluster, Population III, supermassive, or dark stars, or a direct-collapse black hole. Although populations of red galaxies at similar photometric redshifts have been detected with JWST, this object is unique in that its high-redshift nature is corroborated geometrically by lensing, that it is unresolved despite being magnified—and thus intrinsically even more compact—and that it occupies notably distinct regions in both size–luminosity and color–color space. Planned UNCOVER JWST/NIRSpec observations, scheduled in Cycle 1, will enable a more detailed analysis of this object.
Location: United Kingdom of Great Britain and Northern Ireland
Start Date: 2014
End Date: 12-2017
Amount: $360,000.00
Funder: Australian Research Council
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