The Galaxy Starburst/Main-sequence Bimodality over Five Decades in Stellar Mass at z ≈ 3–6.5

We study the relation between stellar mass (M*) and star formation rate (SFR) for star-forming galaxies over approximately five decades in stellar mass (5.5 <~ log10(M*/Msun) <~ 10.5) at z ~ 3-6.5. This unprecedented coverage has been possible thanks to the joint analysis of blank non-lensed fields (COSMOS/SMUVS) and cluster lensing fields (Hubble Frontier Fields) which allow us to reach very low stellar masses. Previous works have revealed the existence of a clear bimodality in the SFR-M* plane with a star-formation Main Sequence and a starburst cloud at z ~ 4-5. Here we show that this bimodality extends to all star-forming galaxies and is valid in the whole redshift range z ~ 3-6.5. We find that starbursts constitute at least 20% of all star-forming galaxies with M* >~ 10^9 Msun at these redshifts and reach a peak of 40% at z=4-5. More importantly, 60% to 90% of the total SFR budget at these redshifts is contained in starburst galaxies, indicating that the starburst mode of star-formation is dominant at high redshifts. Almost all the low stellar-mass starbursts with log10(M*/Msun) <~ 8.5 have ages comparable to the typical timescales of a starburst event, suggesting that these galaxies are being caught in the process of formation. Interestingly, galaxy formation models fail to predict the starburst/main-sequence bimodality and starbursts overall, suggesting that the starburst phenomenon may be driven by physical processes occurring at smaller scales than those probed by these models.Comment: 24 pages, including 15 figures (17 files in total) and 4 tables. The manuscript has been accepted for publication in the Ap

Exploring the low-mass regime of galaxy-scale strong lensing: Insights into the mass structure of cluster galaxies

We aim at a direct measurement of the compactness of three galaxy-scale lenses in massive clusters, testing the accuracy of the scaling laws that describe the members in strong lensing (SL) models of galaxy clusters. We selected the multiply imaged sources MACS J0416.1$-$2403 ID14 ($z=3.221$), MACS J0416.1$-$2403 ID16 ($z=2.095$), and MACS J1206.2$-$0847 ID14 ($z=3.753$). Eight images were observed for the first SL system, and six for the latter two. We focused on the main deflector of each galaxy-scale SL system (identified as members 8971, 8785, and 3910, respectively), and modelled its total mass distribution with a truncated isothermal sphere. We accounted for the lensing effects of the remaining cluster components, and included the uncertainty on the cluster-scale mass distribution through a bootstrapping procedure. We measured a truncation radius value of $6.1^{+2.3}_{-1.1} \, \mathrm{kpc}$, $4.0^{+0.6}_{-0.4} \, \mathrm{kpc}$, and $5.2^{+1.3}_{-1.1} \, \mathrm{kpc}$ for members 8971, 8785, and 3910, respectively. Alternative non-truncated models with a higher number of free parameters do not lead to an improved description of the SL system. We measured the stellar-to-total mass fraction within the effective radius $R_e$ for the three members, finding $0.51\pm0.21$, $1.0\pm0.4$, and $0.39\pm0.16$, respectively. We find that a parameterisation of the properties of cluster galaxies in SL models based on power-law scaling relations with respect to the total luminosity cannot accurately describe their compactness over their full total mass range. Our results agree with modelling of the cluster members based on the Fundamental Plane relation. Finally, we report good agreement between our values of the stellar-to-total mass fraction within $R_e$ and those of early-type galaxies from the SLACS Survey. Our work significantly extends the regime of the current samples of lens galaxies.Comment: Astronomy & Astrophysics, 679, A124 (2023), 15 pages, 12 figures, 8 table

The Dark Energy Survey : more than dark energy – an overview

This overview paper describes the legacy prospect and discovery potential of the Dark Energy Survey (DES) beyond cosmological studies, illustrating it with examples from the DES early data. DES is using a wide-field camera (DECam) on the 4 m Blanco Telescope in Chile to image 5000 sq deg of the sky in five filters (grizY). By its completion, the survey is expected to have generated a catalogue of 300 million galaxies with photometric redshifts and 100 million stars. In addition, a time-domain survey search over 27 sq deg is expected to yield a sample of thousands of Type Ia supernovae and other transients. The main goals of DES are to characterize dark energy and dark matter, and to test alternative models of gravity; these goals will be pursued by studying large-scale structure, cluster counts, weak gravitational lensing and Type Ia supernovae. However, DES also provides a rich data set which allows us to study many other aspects of astrophysics. In this paper, we focus on additional science with DES, emphasizing areas where the survey makes a difference with respect to other current surveys. The paper illustrates, using early data (from ‘Science Verification’, and from the first, second and third seasons of observations), what DES can tell us about the Solar system, the Milky Way, galaxy evolution, quasars and other topics. In addition, we show that if the cosmological model is assumed to be +cold dark matter, then important astrophysics can be deduced from the primary DES probes. Highlights from DES early data include the discovery of 34 trans-Neptunian objects, 17 dwarf satellites of the Milky Way, one published z > 6 quasar (and more confirmed) and two published superluminous supernovae (and more confirmed)

Bright Lyman-alpha emitters in MUSE/COSMOS field

VizieR online Data Catalogue associated with article published in journal Astronomy &amp; Astrophysics with title 'Bright Lyman-alpha emitters among Spitzer SMUVS galaxies in the MUSE/COSMOS field.' (bibcode: 2020A&amp;A...633A.159R

Identification of low luminosity high redshift galaxies using galaxy clusters as cosmic telescopes

Current models of structure formation suggest that the first galaxies formed at z >10 when the universe was < 500 Myr old. The detection and characterization of galaxies at these early epochs is therefore critical to estimate the star formation rate density and their contribution to the reionization. The CLASH project (Cluster Lensing And Supernova survey with Hubble) combines an HST Treasury program to obtain panchromatic (ACS + WFC3) imaging of 25 carefully selected massive clusters, with other multi-wavelength observations, including a large spectroscopic campaign with VLT/VIMOS. Gravitational lensing, which is particularly powerful in several CLASH clusters, boost the efficiency of finding low-luminosity (i.e. L < L*) galaxies, which are thought to play a critical role in reionizing the Universe beyond z ∼ 10. In this letter, we will give some highlights of the construction of a sample of ∼ 200 magnified lensed galaxies at 2 < z < 7, collected as part of the CLASH-VLT project, whose spectro-photometric data can be used to characterize the physical properties of the low-luminosity galaxy population at high-z

VLT/MUSE Observations of SDSS J1029+2623:Toward a High-precision Strong Lensing Model

We present a strong lensing analysis of the galaxy cluster SDSS J1029+2623 at $z=0.588$, one of the few currently known lens clusters with multiple images of a background ($z=2.1992$) quasar with a measured time delay. We use archival Hubble Space Telescope multi-band imaging and new Multi Unit Spectroscopic Explorer follow-up spectroscopy to build an accurate lens mass model, a crucial step towards future cosmological applications. The spectroscopic data enable the secure identification of 57 cluster members and of two nearby perturbers along the line-of-sight. We estimate the inner kinematics of a sub-set of 20 cluster galaxies to calibrate the scaling relations parametrizing the sub-halo mass component. We also reliably determine the redshift of 4 multiply imaged sources, provide a tentative measurement for one system, and report the discovery of a new four-image system. The final catalog comprises 26 multiple images from 7 background sources, spanning a wide redshift range, from 1.02 to 5.06. We present two parametric lens models, with slightly different cluster mass parametrizations. The observed positions of the multiple images are accurately reproduced within approximately $0''.2$, the three image positions of the quasar within only $\sim0''.1$. We estimate a cluster projected total mass of $M(<300~ {\rm kpc}) \sim 2.1 \times 10^{14}~ M_{\odot}$, with a statistical uncertainty of a few percent. Both models, that include a small galaxy close to one of the quasar images, predict magnitude differences and time delays between the quasar images that are consistent with the observations.Comment: 24 pages, 10 figures, 6 Tables. Submitted to ApJ. The full MUSE spectroscopic catalog of SDSS J1029+2623 presented here is made publicly available at https://www.fe.infn.it/astro/lensin