ORCID Profile
0000-0001-9697-7331
Current Organisation
University of Cambridge
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Publisher: American Astronomical Society
Date: 23-11-2015
Publisher: American Astronomical Society
Date: 18-08-2023
Abstract: We present an analysis of microlensing event OGLE-2019-BLG-0825. This event was identified as a planetary candidate by preliminary modeling. We find that significant residuals from the best-fit static binary-lens model exist and a xallarap effect can fit the residuals very well and significantly improves χ 2 values. On the other hand, by including the xallarap effect in our models, we find that binary-lens parameters such as mass ratio, q , and separation, s , cannot be constrained well. However, we also find that the parameters for the source system such as the orbital period and semimajor axis are consistent between all the models we analyzed. We therefore constrain the properties of the source system better than the properties of the lens system. The source system comprises a G-type main-sequence star orbited by a brown dwarf with a period of P ∼ 5 days. This analysis is the first to demonstrate that the xallarap effect does affect binary-lens parameters in planetary events. It would not be common for the presence or absence of the xallarap effect to affect lens parameters in events with long orbital periods of the source system or events with transits to caustics, but in other cases, such as this event, the xallarap effect can affect binary-lens parameters.
Publisher: American Astronomical Society
Date: 28-12-2017
Publisher: EDP Sciences
Date: 24-03-2023
DOI: 10.1051/0004-6361/202245542
Abstract: Context. The project called INvestigating Stellar Population In RElics ( INSPIRE ) is based on VLT/X-shooter data from the homonymous on-going ESO Large Program. It targets 52 ultra-compact massive galaxies at 0.1 z 0.5 with the goal of constraining their kinematics and stellar population properties in great detail and of analysing their relic nature. Aims. This is the second INSPIRE data release (DR2), comprising 21 new systems with observations completed before March 2022. For each system, we release four one-dimensional (1D) spectra to the ESO Science Archive, one spectrum for each arm of the X-Shooter spectrograph. They are at their original resolution. We also release a combined and smoothed spectrum with a full width at half maximum resolution of 2.51 Å. In this paper, we focus on the line-of-sight velocity distribution, measuring integrated stellar velocity dispersions from the spectra, and assessing their robustness and the associated uncertainties. Methods. For each of the 21 new systems, we systematically investigated the effect of the parameters and set-ups of the full spectral fitting on the stellar velocity dispersion ( σ ) measurements. In particular, we tested how σ changes when several parameters of the fit as well as the resolution and spectral coverage of the input spectra are varied. Results. We found that the effect that causes the largest systematic uncertainties on σ is the wavelength range used for the fit, especially for spectra with a lower signal-to-noise ratio ( S/N ≤ 30). When using blue wavelengths (UVB arm) one generally underestimates the velocity dispersion (by ~15 km s −1 ). The values obtained from the near-IR (NIR) arm present a larger scatter because the quality of the spectra is lower. We finally compared our results with those in literature, finding a very good agreement overall. Conclusions. Joining results obtained in DR1 with those presented here, INSPIRE contains 40 ultra-compact massive galaxies, corresponding to 75% of the whole survey. By plotting these systems in a stellar mass-velocity dispersion diagram, we identify at least four highly reliable relic candidates among the new systems. Their velocity dispersion is larger than that of normal-sized galaxies of similar stellar mass.
Publisher: EDP Sciences
Date: 02-2021
DOI: 10.1051/0004-6361/202038936
Abstract: Context. Massive elliptical galaxies are thought to form through a two-phase process. At early times ( z 2), an intense and fast starburst forms blue and disk-dominated galaxies. After quenching, the remaining structures become red, compact, and massive (i.e. red nuggets). Then, a time-extended second phase, which is dominated by mergers, causes structural evolution and size growth. Given the stochastic nature of mergers, a small fraction of red nuggets survive, without any interaction, massive and compact until today: these are relic galaxies. Since this fraction depends on the processes dominating the size growth, counting relics at low- z is a valuable way of disentangling between different galaxy evolution models. Aims. In this paper, we introduce the INvestigating Stellar Population In RElics ( INSPIRE ) Project, which aims to spectroscopically confirm and fully characterise a large number of relics at 0.1 z 0.5. We focus here on the first results based on a pilot study targeting three systems, representative of the whole s le. Methods. For these three candidates, we extracted 1D optical spectra over an aperture of r = 0.40″, which comprises ∼30% of the galaxies’ light, and we obtained the line-of-sight integrated stellar velocity and velocity dispersion. We also inferred the stellar [ α /Fe] abundance from line-index measurements and mass-weighted age and metallicity from full-spectral fitting with single stellar population models. Results. Two galaxies have large integrated stellar velocity dispersion values ( σ ⋆ ∼ 250 km s −1 ), confirming their massive nature. They are populated by stars with super-solar metallicity and [ α /Fe]. Both objects have formed ≥80% of their stellar mass within a short (∼0.5−1.0 Gyr) initial star formation episode occurred only ∼1 Gyr after the Big Bang. The third galaxy has a more extended star formation history and a lower velocity dispersion. Thus we confirm two out of three candidates as relics. Conclusions. This paper is the first step towards assembling the final INSPIRE catalogue that will set stringent lower limits on the number density of relics at z 0.5, thus constituting a benchmark for cosmological simulations, and their predictions on number densities, sizes, masses, and dynamical characteristics of these objects.
Publisher: American Astronomical Society
Date: 11-2019
Publisher: American Astronomical Society
Date: 07-05-2020
Publisher: American Astronomical Society
Date: 11-2018
Publisher: American Astronomical Society
Date: 02-03-2016
Publisher: EDP Sciences
Date: 07-2021
DOI: 10.1051/0004-6361/202039921
Abstract: Context. In this paper, we present ultra-deep images of the compact group of galaxies HCG 86 as part of the VEGAS survey. Aims. Our main goals are to estimate the amount of intra-group light (IGL) as well as to study the light and colour distributions in order to address the main formation process of the IGL component in groups of galaxies. Methods. We derived the azimuthally averaged surface brightness profiles in the g , r , and i bands with g − r and r − i average colours and colour profiles for all group members. By fitting the light distribution, we extrapolated the contribution of the stellar halos plus the diffuse light from the brightest component of each galaxy. The results are compared with theoretical predictions. Results. The long integration time and wide area covered make our data reach deeper than previous literature studies of the IGL in compact groups of galaxies and allow us to produce an extended (∼160 kpc) map of the IGL, down to a surface brightness level of ∼30 mag arcsec −2 in the g band. The IGL in HCG 86 is mainly in diffuse form and has average colours of g − r ∼ 0.8 mag and r − i ∼ 0.4 mag. The fraction of IGL in HCG 86 is ∼16% of the total luminosity of the group, and this is consistent with estimates available for other compact groups and loose groups of galaxies of similar virial masses. A weak trend is present between the amount of IGL and the early-type to late-type galaxy ratio. A lack of a clear correlation is found between the amount of diffuse light and the cluster or group virial mass. Conclusions. By comparing the IGL fraction and colours with those predicted by simulations, the amount of IGL in HCG 86 would be the result of the disruption of satellites at an epoch of z ∼ 0.4. At this redshift, the observed colours are consistent with the scenario where the main contribution to the mass of the IGL comes from the intermediate-to-massive galaxies (10 10 ≤ M * ≤ 10 11 M ⊙ ).
Publisher: American Astronomical Society
Date: 22-03-2016
Publisher: Springer Science and Business Media LLC
Date: 06-2017
DOI: 10.1038/NATURE22392
Abstract: The amount of ultraviolet irradiation and ablation experienced by a planet depends strongly on the temperature of its host star. Of the thousands of extrasolar planets now known, only six have been found that transit hot, A-type stars (with temperatures of 7,300-10,000 kelvin), and no planets are known to transit the even hotter B-type stars. For ex le, WASP-33 is an A-type star with a temperature of about 7,430 kelvin, which hosts the hottest known transiting planet, WASP-33b (ref. 1) the planet is itself as hot as a red dwarf star of type M (ref. 2). WASP-33b displays a large heat differential between its dayside and nightside, and is highly inflated-traits that have been linked to high insolation. However, even at the temperature of its dayside, its atmosphere probably resembles the molecule-dominated atmospheres of other planets and, given the level of ultraviolet irradiation it experiences, its atmosphere is unlikely to be substantially ablated over the lifetime of its star. Here we report observations of the bright star HD 195689 (also known as KELT-9), which reveal a close-in (orbital period of about 1.48 days) transiting giant planet, KELT-9b. At approximately 10,170 kelvin, the host star is at the iding line between stars of type A and B, and we measure the dayside temperature of KELT-9b to be about 4,600 kelvin. This is as hot as stars of stellar type K4 (ref. 5). The molecules in K stars are entirely dissociated, and so the primary sources of opacity in the dayside atmosphere of KELT-9b are probably atomic metals. Furthermore, KELT-9b receives 700 times more extreme-ultraviolet radiation (that is, with wavelengths shorter than 91.2 nanometres) than WASP-33b, leading to a predicted range of mass-loss rates that could leave the planet largely stripped of its envelope during the main-sequence lifetime of the host star.
Publisher: American Astronomical Society
Date: 27-03-2017
Publisher: American Astronomical Society
Date: 28-06-2016
Publisher: American Astronomical Society
Date: 16-10-2015
Publisher: Oxford University Press (OUP)
Date: 21-02-2023
Abstract: In the last decade, growing evidence has emerged supporting a non-universal stellar initial mass function (IMF) in massive galaxies, with a larger number of dwarf stars with respect to the Milky Way (bottom-heavy IMF). However, a consensus about the mechanisms that cause IMF variations is yet to be reached. Recently, it has been suggested that stars formed early-on in cosmic time, via a star formation burst, could be characterized by a bottom-heavy IMF. A promising way to confirm this is to use relics, ultra-compact massive galaxies, almost entirely composed by these ‘pristine’ stars. The INvestigating Stellar Population In RElics (INSPIRE) Project aims at assembling a large s le of confirmed relics, that can serve as laboratory to investigate on the conditions of star formation in the first 1–3 Gyr of the Universe. In this third INSPIRE paper, we build a high signal-to-noise spectrum from five relics, and one from five galaxies with similar sizes, masses, and kinematical properties, but characterized by a more extended star formation history (non-relics). Our detailed stellar population analysis suggests a systematically bottom-heavier IMF slope for relics than for non-relics, adding new observational evidence for the non-universality of the IMF at various redshifts and further supporting the above proposed physical scenario.
Publisher: EDP Sciences
Date: 07-2022
DOI: 10.1051/0004-6361/202243290
Abstract: This work is based on high-quality integral-field spectroscopic data obtained with the Multi Unit Spectroscopic Explorer (MUSE) on the Very Large Telescope (VLT). The 21 brightest ( m B ≤ 15 mag) early-type galaxies (ETGs) inside the virial radius of the Fornax cluster are observed out to distances of ∼2−3 R e . Deep imaging from the VLT Survey Telescope (VST) is also available for the s le ETGs. We investigated the variation of the galaxy structural properties as a function of the total stellar mass and cluster environment. Moreover, we correlated the size scales of the luminous components derived from a multi-component decomposition of the VST surface-brightness radial profiles of the s le ETGs with the MUSE radial profiles of stellar kinematic and population properties. The results are compared with both theoretical predictions and previous observational studies and used to address the assembly history of the massive ETGs of the Fornax cluster. We find that galaxies in the core and north-south clump of the cluster, which have the highest accreted mass fraction, show milder metallicity gradients in their outskirts than the galaxies infalling into the cluster. We also find a segregation in both age and metallicity between the galaxies belonging to the core and north-south clump and the infalling galaxies. The new findings fit well within the general framework for the assembly history of the Fornax cluster.
Publisher: Oxford University Press (OUP)
Date: 29-01-2019
DOI: 10.1093/MNRAS/STZ306
Publisher: American Astronomical Society
Date: 23-05-2016
Publisher: American Astronomical Society
Date: 26-10-2016
Publisher: EDP Sciences
Date: 08-2022
DOI: 10.1051/0004-6361/202142894
Abstract: Aims. We present a study of the intra-cluster population of low-mass X-ray binaries (LMXB) residing in globular clusters (GC) in the central 1 deg 2 of the Fornax galaxy cluster. Differently from previous studies, which were restricted to the innermost regions of in idual galaxies, this work is aimed at comparing the properties of the intra-cluster population of GC-LMXBs with those of the host galaxy. Methods. The data used in this work are a combination of the VLT Survey Telescope (VST) and Chandra observations. We performed a cross-match between the optical and the X-ray catalogue in order to identify the LMXBs residing in GCs. We ided the GC-LMXBs into host-galaxy and intra-cluster objects based on their distance from the nearest galaxy in terms of effective radius ( R eff ). We found 82 intra-cluster GC-LMXBs and 86 objects that are hosted in galaxies. As the formation of LMXBs also depends on the host GC colour, we performed a Gaussian mixture model to ide the population into red and blue GCs. Results. As has been found for the innermost regions of galaxies, LMXBs tend to form in red and bright GCs in intra-cluster space as well. We find, however, that the likelihood of a red GC to host an LMXB decreases with galactocentric distance, but it remains approximately constant for the blue GC population. Investigating the X-ray properties of the LMXBs residing in GCs, we find a difference in the X-ray luminosity function between the intra-cluster and host-galaxy s le: both follow a power-law down to ∼8.5 × 10 37 erg s −1 , which is consistent with field LMXBs for the intra-cluster s le, while the latter agree with previous estimates for LMXBs in GCs. We observe a deficiency of bright LMXBs in blue intra-cluster GCs, however. This might indicate a lack of black hole binaries in metal-poor systems. We further investigated the spectral properties of the GC-LMXBs through their hardness-ratio. We detect a tentative difference in the hardness ratio of two populations, where the intra-cluster GC-LMXBs appear to have harder spectra than the host-galaxy objects. We find the same trend when we compare red and blue GC-LMXBs: the spectra of the blue s le are harder spectra than those of the red s le. This result could suggest a relation between the spectral properties of LMXBs and the host GC colour and therefore its metallicity. We discuss the possibilities of spatial biases due to uncertainties in the X-ray spectral response correction and due to contamination by background active galactic nuclei.
Publisher: American Astronomical Society
Date: 07-11-2016
Publisher: American Astronomical Society
Date: 29-08-2016
Publisher: American Astronomical Society
Date: 03-12-2020
Publisher: Oxford University Press (OUP)
Date: 20-09-2018
Publisher: American Astronomical Society
Date: 02-2018
Publisher: Oxford University Press (OUP)
Date: 09-12-2016
Publisher: IOP Publishing
Date: 25-10-2016
Location: United Kingdom of Great Britain and Northern Ireland
Location: Italy
No related grants have been discovered for Giuseppe D'Ago.