Augmenting the power of time-delay cosmography in lens galaxy clusters by probing their member galaxies I. Type Ia supernovae

We present a simple and promising new method to measure the expansion rate and the geometry of the universe that combines observations related to the time delays between the multiple images of time-varying sources, strongly lensed by galaxy clusters, and Type Ia supernovae, exploding in galaxies belonging to the same lens clusters. By means of two different statistical techniques that adopt realistic errors on the relevant quantities, we quantify the accuracy of the inferred cosmological parameter values. We show that the estimate of the Hubble constant is robust and competitive, and depends only mildly on the chosen cosmological model. Remarkably, the two probes separately produce confidence regions on the cosmological parameter planes that are oriented in complementary ways, thus providing in combination valuable information on the values of the other cosmological parameters. We conclude by illustrating the immediate observational feasibility of the proposed joint method in a well-studied lens galaxy cluster, with a relatively small investment of telescope time for monitoring from a 2 to 3m class ground-based telescope.Comment: 6 pages, 2 figures, 1 table. Published in A&A Letter

Galaxy And Mass Assembly (GAMA): the Stellar Mass Budget by Galaxy Type

We report an expanded sample of visual morphological classifications from the Galaxy and Mass Assembly (GAMA) survey phase two, which now includes 7,556 objects (previously 3,727 in phase one). We define a local (z <0.06) sample and classify galaxies into E, S0-Sa, SB0-SBa, Sab-Scd, SBab-SBcd, Sd-Irr, and "little blue spheroid" types. Using these updated classifications, we derive stellar mass function fits to individual galaxy populations divided both by morphological class and more general spheroid- or disk-dominated categories with a lower mass limit of log(Mstar/Msun) = 8 (one dex below earlier morphological mass function determinations). We find that all individual morphological classes and the combined spheroid-/bulge-dominated classes are well described by single Schechter stellar mass function forms. We find that the total stellar mass densities for individual galaxy populations and for the entire galaxy population are bounded within our stellar mass limits and derive an estimated total stellar mass density of rho_star = 2.5 x 10^8 Msun Mpc^-3 h_0.7, which corresponds to an approximately 4% fraction of baryons found in stars. The mass contributions to this total stellar mass density by galaxies that are dominated by spheroidal components (E and S0-Sa classes) and by disk components (Sab-Scd and Sd-Irr classes) are approximately 70% and 30%, respectively

High star cluster formation efficiency in the strongly lensed Sunburst Lyman-continuum galaxy at z=2.37

We investigate the strongly lensed (\mu x10-100) Lyman continuum (LyC) galaxy, dubbed Sunburst, at z=2.37, taking advantage of a new accurate model of the lens. A characterization of the intrinsic (delensed) properties of the galaxy yields a size of ~3 sq.kpc, a luminosity Muv=-20.3,and a stellar mass M~10^9 Msun;16% of the ultraviolet light is located in a 3 Myr old gravitationally-bound young massive star cluster (YMC) with an effective radius of Re~8 pc and a dynamical mass of ~10^7 Msun (similar to the stellar mass), from which LyC radiation is detected (\lambda < 912A). The inferred outflowing gas velocity (>300 km/s) exceeds the escape velocity of the star cluster. The resulting escape fraction of the ionizing radiation emerging from the Sunburst galaxy is >6-12%, whilst it is >46-93% if inferred from the YMC. 12 additional likely star clusters with 3<Re<20 pc are identified in the galaxy from which we derive a cluster formation efficiency \Gamma>~30%, which is consistent with the high \Gamma derived in local galaxies experiencing extreme gas physical conditions. The presence of the YMC influences the morphology (nucleation), photometry (photometric jumps) and spectroscopic output (nebular emission) of the entire galaxy. The de-lensed LyC and UV (1600A) magnitudes of the YMC are ~30.6 and ~26.9, whilst the galaxy has m1600~24.8. A relatively large rest-frame equivalent width of EWrest(Hb+[OIII]4959-5007)~450A emerges from the galaxy with the YMC contributing to ~30%. If O-type stars are mainly forged in star clusters, then such engines were the key ionizing agents during reionization and the increasing occurrence of high EW lines (Hb+[OIII]) observed at z>6.5 might be an indirect signature of a high \Gamma at reionization.Future facilities (like VLT/MAVIS or ELT), will probe bound clusters on moderately magnified (\mu<5-10) galaxies across cosmic epochs up to reionization[ABRIDGED]Comment: 17 pages (12 main body), 10 Figures and 1 Table. Accepted for publication in Astronomy & Astrophysics. Figure 6 shows the stellar cluster formation efficiency of the Sunburst galaxy; Figure C.1 shows the MUSE narrow field mode image of the counter-ar

A state-of-the-art strong-lensing model of MACS J0416.1-2403 with the largest sample of spectroscopic multiple images

The combination of multi-band imaging from the Hubble Space Telescope with Multi-Unit Spectroscopic Explorer integral field spectroscopy, obtained at the Very Large Telescope, has recently driven remarkable progress in strong-lensing (SL) modeling of galaxy clusters. From a few tens of multiple images with photometric redshifts per cluster, a new generation of high-precision SL models have recently been developed by exploiting in some cases over a hundred spectroscopically confirmed multiple images and cluster member galaxies. A further step forward is expected with James Webb Space Telescope observations of SL clusters (from hundreds of multiple images to possibly a thousand). In this context, we present a new state-of-the-art SL model of the galaxy cluster MACS J0416.1−2403, utilizing 237 spectroscopically confirmed multiple images, which is the largest sample of secure multiply-lensed sources utilized to date. In addition, this model incorporates stellar kinematics information of 64 cluster galaxies and the hot-gas mass distribution of the cluster, determined from Chandra X-ray observations. The observed positions of the many multiple images are reproduced with a remarkable average accuracy of 0.43″. To further assess the reliability of this lens model and to highlight the improvement over previously published models, we show the extended surface brightness reconstruction of several lensed galaxies through a newly developed forward modeling software. The comparison with other SL models of the same cluster demonstrates that this new model is better able to accurately reproduce the positions, shapes, and fluxes of the observed multiple images. In addition to a robust characterization of the total mass distribution of the cluster, our model can provide accurate and precise magnification maps that are key to studying the intrinsic physical properties of faint high-redshift lensed sources. The model is made publicly available through our newly developed Strong Lensing Online Tool (SLO

The Kormendy relation of early-type galaxies as a function of wavelength in Abell S1063, MACS J0416.1-2403, and MACS J1149.5+2223

Context. The wavelength dependence of the projection of the fundamental plane along the velocity dispersion axis, namely the Kormendy relation, is well characterised at low redshift but poorly studied at intermediate redshifts. The Kormendy relation provides information on the evolution of the population of early-type galaxies (ETGs). Therefore, by studying it, we may shed light on the assembly processes of these objects and their size evolution. As studies at different redshifts are generally conducted in different rest-frame wavebands, it is important to investigate whether the Kormendy relation is dependent on wavelength. Knowledge of such a dependence is fundamental to correctly interpreting the conclusions we might draw from these studies. Aims. We analyse the Kormendy relations of the three Hubble Frontier Fields clusters, Abell S1063 at z = 0.348, MACS J0416.1-2403 at z = 0.396, and MACS J1149.5+2223 at z = 0.542, as a function of wavelength. This is the first time the Kormendy relation of ETGs has been explored consistently over such a large range of wavelengths at intermediate redshifts. Methods. We exploit very deep Hubble Space Telescope photometry, ranging from the observed B-band to the H-band, and VLT/MUSE integral field spectroscopy. We improve the structural parameter estimation we performed in a previous work by means of a newly developed PYTHON package called MORPHOFIT. Results. With its use on cluster ETGs, we find that the Kormendy relation slopes increase smoothly with wavelength from the optical to the near-infrared (NIR) bands in all three clusters, with the intercepts becoming fainter at lower redshifts due to the passive ageing of the ETG stellar populations. The slope trend is consistent with previous findings at lower redshifts. Conclusions. The slope increase with wavelength implies that smaller ETGs are more centrally concentrated than larger ETGs in the NIR with respect to the optical regime. As different bands probe different stellar populations in galaxies, the slope increase also implies that smaller ETGs have stronger internal gradients with respect to larger ETGs

UV-continuum β slopes of individual z ∼2-6 clumps and their evolution

We study the ultraviolet (UV) continuum βslope of a sample of 166 clumps, individual star-forming regions observed in high- redshift galaxies. They are hosted by 67 galaxies with redshift between 2 and 6.2, strongly lensed by the Hubble Frontier Fields cluster of galaxies MACS J0416.1 −2403. The βslope is sensitive to a variety of physical properties, such as the metallicity, the age of the stellar population, the dust attenuation throughout the galaxy, the stellar initial mass function (IMF), and the star formation history (SFH). The aim of this study is to compare the β-values of individual clumps with those measured on the entire galaxy, to investigate possible physical differences between these regions and their hosts. We found a median value of β∼−2.4, lower than that of integrated galaxies. This result confirms that clumps are sites of intense star formation, populated by young, massive stars, whose spectrum strongly emits in the UV. This is also consistent with the assumption that the dust extinction at the location of the clumps is lower than the av erage e xtinction of the galaxy, or that clumps have a different IMF or SFH. We made use of the correlations, disco v ered for high-redshift galaxies, of the β-value with those of redshift and UV magnitude, M UV, finding that clumps follow the same relations, extended to much fainter magnitudes ( M UV &lt; −13). We also find evidence of eight clumps with extremely blue ( β ≲−2.7) slopes, which could be the signpost of low-metallicity stars and constrain the emissivity of ionizing photons at high redshift

On the lack of correlation between [O III ]/[O II ] and Lyman continuum escape fraction

We present the first results of our pilot study of eight photometrically selected Lyman-continuum (LyC) emitting galaxy candidates from the COSMOS field and focus on their optical emission line ratios. Observations were performed in the H and K bands using the Multi-Object Spectrometer for Infra-Red Exploration (MOSFIRE) instrument at the Keck Observatory, targeting the [O ii], H β, and [Oiii] emission lines. We find that photometrically selected LyC emitting galaxy candidates have high ionization parameters, based on their high [O iii]/[O ii] ratios (O32), with an average ratio for our sample of 2.5 ± 0.2. Preliminary results of our companion Low-Resolution Imaging Spectrometer (LRIS) observations, targeting LyC and Ly α, show that those galaxies with the largest O32 are typically found to also be Ly α emitters. High O32 galaxies are also found to have tentative non-zero LyC escape fractions (f esc (LyC)) based on u band photometric detections. These results are consistent with samples of highly ionized galaxies, including confirmed LyC emitting galaxies from the literature. We also perform a detailed comparison between the observed emission line ratios and simulated line ratios from density bounded H ii regions modelled using the photoionization code MAPPINGS V. Estimates of f esc (LyC) for our sample fall in the range from 0.0 to 0.23 and suggest possible tension with published correlations between O32 and f esc (LyC), adding weight to dichotomy of arguments in the literature. We highlight the possible effects of clumpy geometry and mergers that may account for such tension.Fil: Bassett, R.. Swinburne University of Technology; Australia. Australian Research Council. Centre of Excellence for All Sky Astrophysics in 3 Dimensions; AustraliaFil: Ryan-Weber, E.V.. Swinburne University of Technology; Australia. Australian Research Council. Centre of Excellence for All Sky Astrophysics in 3 Dimensions; AustraliaFil: Cooke, J.. Swinburne University of Technology; AustraliaFil: Diaz, Carlos Gonzalo. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - San Juan. Instituto de Ciencias Astronómicas, de la Tierra y del Espacio. Universidad Nacional de San Juan. Instituto de Ciencias Astronómicas, de la Tierra y del Espacio; Argentina. Gemini Observatory; ChileFil: Nanayakkara, T.. Leiden University; Países BajosFil: Yuan, T. T.. Swinburne University of Technology; Australia. Australian Research Council. Centre of Excellence for All Sky Astrophysics in 3 Dimensions; AustraliaFil: Spitler, L.R.. Australian Astronomical Observatories; Australia. Macquarie University; Australia. Macquarie University; AustraliaFil: Mestric, U.. Swinburne University of Technology; Australia. Australian Research Council. Centre of Excellence for All Sky Astrophysics in 3 Dimensions; AustraliaFil: Garel, T.. Centre de Recherche Astrophysique de Lyon; FranciaFil: Sawicki, Silvana Mabel. Saint Mary's University; CanadáFil: Gwyn, S.. National Research Council Canada; CanadáFil: Golob, A.. Saint Mary's University; Canad

High star cluster formation efficiency in the strongly lensed Sunburst Lyman-continuum galaxy at z=2.37

We investigate the strongly lensed (mu similar or equal to x10-100) Lyman continuum (LyC) galaxy, dubbed Sunburst, at z = 2.37, taking advantage of a new accurate model of the lens. A characterization of the intrinsic (delensed) properties of the system yields a size of similar or equal to 3 sq. kpc, a luminosity of M-UV = -20.3, and a stellar mass of M similar or equal to 10(9) M-circle dot; 16% of the ultraviolet light is located in a 3 Myr old gravitationally bound young massive star cluster (YMC), with an effective radius of similar to 8 pc (corresponding to 1 milliarcsec without lensing) and a dynamical mass of -107 M. (similar to the stellar mass) - from which LyC radiation is detected (lambda 330 Gyr(-1), consistent with the values observed in local young massive star clusters. The inferred outflowing gas velocity (>300 km s(-1)) exceeds the escape velocity of the cluster. The resulting relative escape fraction of the ionizing radiation emerging from the entire galaxy is higher than 6-12%, whilst it is greater than or similar to 46-93% if inferred from the YMC multiple line of sights. At least 12 additional unresolved star-forming knots with radii spanning the interval 3-20 pc (the majority of them likely gravitationally bound star clusters) are identified in the galaxy. A significant fraction (40-60%) of the ultraviolet light of the entire galaxy is located in such bound star clusters. In adopting a formation timescale of the star clusters of 20 Myr, a cluster formation efficiency Gamma greater than or similar to 30%. The star formation rate surface density of the Sunburst galaxy (Log(10)(Sigma(SFR)) = 0.5(-0.2)(+0.3)) is consistent with the high inferred Gamma, as observed in . local galaxies experiencing extreme gas physical conditions. Overall, the presence of a bursty event (i.e., the 3 Myr old YMC with large sSFR) significantly influences the morphology (nucleation), photometry (photometric jumps), and spectroscopic output (nebular emission) of the entire galaxy. Without lensing magnification, the YMC would be associated to an unresolved 0.5 kpc-size starforming clump. The delensed LyC and UV magnitude m(1600) (at 1600 angstrom) of the YMC are similar or equal to 30.6 and similar or equal to 26.9, whilst the entire galaxy has M1600 similar or equal to 24.8. The Sunburst galaxy shows a relatively large rest-frame equivalent width of EWrest (H beta [O III]lambda lambda 4959, 5007) similar or equal to 450 angstrom, with the YMC contributing to similar to 30% (having a local EWrest 1100 angstrom) and similar to 1% of the total stellar mass. If O-type (ionizing) stars are mainly forged in star clusters, then such engines were the key ionizing agents during reionization and the increasing occurrence of high equivalent width lines (H beta + [O III]) observed at z > 6.5 might be an indirect signature of a high frequency of forming massive star clusters (or high Gamma) at reionization. Future facilities, which will perform at few tens milliarcsec resolution (e.g., VLT/MAVIS or ELT), will probe bound clusters on moderately magnified (mu < 5-10) galaxies across cosmic epochs up to reionization