Abstract
By means of grid-based, 3D hydrodynamical simulations we study the formation of second-generation (SG) stars in a young globular cluster (GC) of mass 107 M⊙, the possible progenitor of an ...old GC with present mass ∼(1–5) × 106 M⊙. The cluster accretes external gas as its first generation (FG) asymptotic giant branch (AGB) stars release their ejecta and SG stars form. We consider two models characterized by different densities of the external gas. In both cases, we find that a very compact SG subsystem with central density $\gt 10^5~\mathrm{M}_{\odot }\, \mathrm{pc}^{-3}$ forms in the innermost regions of the cluster. The low-density model forms a population of extreme SG stars with high helium enhancement, followed by the formation of another SG group out of a mix of pristine gas and AGB ejecta and characterized by a modest helium enhancement. On the other hand, the high-density model forms in prevalence SG stars with modest helium enhancement. Our simulations illustrate the dynamical processes governing the formation of SG populations in GCs and shed light on the structural properties emerging at the end of this phase. The newly born SG groups have different concentrations, with more extreme SG stars more centrally concentrated than those with less extreme chemical abundances. The very high density of the SG subsystems implies that SG massive stars, if formed, might suffer frequent close encounters, collisions, and gas stripping, thus possibly contributing further gas to the SG formation.
Missing [C ii] emission from early galaxies Carniani, S; Ferrara, A; Maiolino, R ...
Monthly notices of the Royal Astronomical Society,
12/2020, Letnik:
499, Številka:
4
Journal Article
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ABSTRACT
ALMA observations have revealed that C ii 158 μm line emission in high-z galaxies is ≈2–3 × more extended than the UV continuum emission. Here we explore whether surface brightness dimming ...(SBD) of the C ii line is responsible for the reported C ii deficit, and the large $L_{\rm O\, \small {III}}/L_{\rm C\, \small {II}}$ luminosity ratio measured in early galaxies. We first analyse archival ALMA images of nine z > 6 galaxies observed in both C ii and O iii. After performing several uv-tapering experiments to optimize the identification of extended line emission, we detect C ii emission in the whole sample, with an extent systematically larger than the O iii emission. Next, we use interferometric simulations to study the effect of SBD on the line luminosity estimate. About 40 per cent of the extended C ii component might be missed at an angular resolution of 0.8 arcsec, implying that $L_{\rm C\, \small {II}}$ is underestimated by a factor ≈2 in data at low (<7) signal-to-noise ratio. By combining these results, we conclude that $L_{\rm C\, \small {II}}$ of z > 6 galaxies lies, on average, slightly below the local $L_{\rm C\, \small {II}}-\mathrm{ SFR}$ relation (Δz = 6–9 = −0.07 ± 0.3), but within the intrinsic dispersion of the relation. SBD correction also yields $L_{\rm O\, \small {III}}/L_{\rm C\, \small {II}}\lt 10$, i.e. more in line with current hydrodynamical simulations.
Abstract
The GLASS-JWST Early Release Science (hereafter GLASS-JWST-ERS) Program will obtain and make publicly available the deepest extragalactic data of the ERS campaign. It is primarily designed ...to address two key science questions, namely, “what sources ionized the universe and when?” and “how do baryons cycle through galaxies?”, while also enabling a broad variety of first look scientific investigations. In primary mode, it will obtain NIRISS and NIRSpec spectroscopy of galaxies lensed by the foreground Hubble Frontier Field cluster, Abell 2744. In parallel, it will use NIRCam to observe two fields that are offset from the cluster center, where lensing magnification is negligible, and which can thus be effectively considered blank fields. In order to prepare the community for access to this unprecedented data, we describe the scientific rationale, the survey design (including target selection and observational setups), and present pre-commissioning estimates of the expected sensitivity. In addition, we describe the planned public releases of high-level data products, for use by the wider astronomical community.
ABSTRACT
We present a VLT/X-Shooter spectroscopy of the Lyman continuum (LyC) emitting galaxy Ion2 at z = 3.2121 and compare it to that of the recently discovered strongly lensed LyC emitter at ...z = 2.37, known as the Sunburst arc. Three main results emerge from the X-Shooter spectrum: (a) the Ly α has three distinct peaks with the central one at the systemic redshift, indicating a ionized tunnel through which both Ly α and LyC radiation escape; (b) the large O32 oxygen index (O iii λλ4959, 5007/O ii λλ3727, 3729) of $9.18_{-1.32}^{+1.82}$ is compatible to those measured in local (z ∼0.4) LyC leakers; (c) there are narrow nebular high-ionization metal lines with σv < 20 km s−1, which confirms the presence of young hot, massive stars. The He iiλ1640 appears broad, consistent with a young stellar component including Wolf–Rayet stars. Similarly, the Sunburst LyC emitter shows a triple-peaked Ly α profile and from VLT/MUSE spectroscopy the presence of spectral features arising from young hot and massive stars. The strong lensing magnification, (μ > 20), suggests that this exceptional object is a gravitationally bound star cluster observed at a cosmological distance, with a stellar mass M ≲ 107 M⊙ and an effective radius smaller than 20 pc. Intriguingly, sources like Sunburst but without lensing magnification might appear as Ion2-like galaxies, in which unresolved massive star clusters dominate the ultraviolet emission. This work supports the idea that dense young star clusters can contribute to the ionization of the IGM through holes created by stellar feedback.
Abstract
We report on five compact, extremely young (<10 Myr) and blue (βUV < −2.5, Fλ = λβ) objects observed with VLT/Multi Unit Spectroscopic Explorer at redshifts 3.1169 and 3.235, in addition to ...three objects at z = 6.145. These sources are strongly magnified (3–40 times) by the Hubble Frontier Field galaxy clusters MACS J0416 and AS1063. Their delensed half-light radii (Re) are between 16 and 140 pc, the stellar masses are ≃1–20 × 106 M⊙, the magnitudes are mUV = 28.8–31.4 (−17 < MUV < −15) and specific star formation rates can be as large as ∼800 Gyr−1. Remarkably, the inferred physical properties of two objects are similar to those expected in some globular cluster formation scenarios, representing the best candidate proto-GCs discovered so far. Rest-frame optical high-dispersion spectroscopy of one of them at z = 3.1169 yields a velocity dispersion σv ≃ 20 km s−1, implying a dynamical mass dominated by the stellar mass. Another object at z = 6.145, with delensed MUV ≃ −15.3 (mUV ≃ 31.4), shows a stellar mass and a star formation rate surface density consistent with the values expected from popular GC formation scenarios. An additional star-forming region at z = 6.145, with delensed mUV ≃ 32, a stellar mass of 0.5 × 106 M⊙ and a star formation rate of 0.06 M⊙ yr−1 is also identified. These objects currently represent the faintest spectroscopically confirmed star-forming systems at z > 3, elusive even in the deepest blank fields. We discuss how proto-GCs might contribute to the ionization budget of the Universe and augment Lyα visibility during reionization. This work underlines the crucial role of JWST in characterizing the rest-frame optical and near-infrared properties of such low-luminosity high-z objects.
We report the spectroscopic confirmation of 22 new multiply lensed sources behind the Hubble Frontier Field (HFF) galaxy cluster MACS J0416.1−2403 (MACS 0416), using archival data from the Multi Unit ...Spectroscopic Explorer (MUSE) on the VLT. Combining with previous spectroscopic measurements of 15 other multiply imaged sources, we have obtained a sample of 102 secure multiple images with measured redshifts, the largest to date in a single strong lensing system. The newly confirmed sources are largely low-luminosity Lyman-α emitters with redshift in the range 3.08−6.15 . With such a large number of secure constraints, and a significantly improved sample of galaxy members in the cluster core, we have improved our previous strong lensing model and obtained a robust determination of the projected total mass distribution of MACS 0416. We find evidence of three cored dark-matter halos, adding to the known complexity of this merging system. The total mass density profile, as well as the sub-halo population, are found to be in good agreement with previous works. We update and make public the redshift catalog of MACS 0416 from our previous spectroscopic campaign with the new MUSE redshifts. We also release lensing maps (convergence, shear, magnification) in the standard HFF format.
We investigate the strongly lensed (
μ
≃ ×10 − 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 ≃3 sq. kpc, a luminosity of
M
UV
= −20.3, and a stellar mass of
M
≃ 10
9
M
⊙
; 16% of the ultraviolet light is located in a 3 Myr old gravitationally bound young massive star cluster (YMC), with an effective radius of ∼8 pc (corresponding to 1 milliarcsec without lensing) and a dynamical mass of ∼10
7
M
⊙
(similar to the stellar mass) – from which LyC radiation is detected (
λ
< 912 Å). The star formation rate and stellar mass surface densities for the YMC are Log
10
(Σ
SFR
M
⊙
yr
−1
kpc
−2
) ≃ 3.7 and Log
10
(Σ
M
M
⊙
pc
−2
) ≃ 4.1, with sSFR > 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 ≳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 Γ ≳ 30%. The star formation rate surface density of the Sunburst galaxy (Log
10
(Σ
SFR
) = 0.5
−0.2
+0.3
) is consistent with the high inferred Γ, 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 star-forming clump. The delensed LyC and UV magnitude
m
1600
(at 1600 Å) of the YMC are ≃30.6 and ≃26.9, whilst the entire galaxy has
m
1600
≃ 24.8. The Sunburst galaxy shows a relatively large rest-frame equivalent width of EW
rest
(H
β
+ O
III
λλ
4959, 5007) ≃ 450 Å, with the YMC contributing to ∼30% (having a local EW
rest
≃ 1100 Å) and ∼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
β
+ O
III
) observed at
z
> 6.5 might be an indirect signature of a high frequency of forming massive star clusters (or high Γ) 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 (
μ
< 5 − 10) galaxies across cosmic epochs up to reionization.
We present the results of CANDELSz7, a European Southern Observatory (ESO) Large Program aimed at spectroscopically confirming a homogeneous sample of z ≃ 6 and z ≃ 7 star forming galaxies. The ...candidates were selected in the GOODS-South, UDS, and COSMOS fields using the official CANDELS catalogs based on H160-band detections. Standard color criteria, which were tailored depending on the ancillary multi-wavelength data available for each field, were applied to select more than 160 candidate galaxies at z ≃ 6 and z ≃ 7. Deep, medium-resolution FORS2 spectroscopic observations were then conducted with integration times ranging from 12 to 20 h to reach a Lyα flux limit of approximately 1 − 3 × 10−18 erg s−1 cm−2 at 3σ. We could determine a spectroscopic redshift for about 40% of the galaxies, mainly through the detection of a single emission line that we interpret as Lyα emission, or for some of the brightest objects (H160 ≤ 25.5) from the presence of faint continuum and a sharp drop that we interpret as a Lyα break. In this paper we present the redshifts and main properties of 65 newly confirmed high-redshift galaxies. Adding previous proprietary and archival data we assemble a sample of ≃260 galaxies that we use to explore the evolution of the Lyα fraction in Lyman break galaxies and the change in the shape of the emission line between z ∼ 6 and z ∼ 7. We also discuss the accuracy of the CANDELS photometric redshifts in this redshift range.
We carried out a detailed strong lensing analysis of a sub-sample of eight galaxy clusters of the Cluster Lensing And Supernova survey with Hubble (CLASH) in the redshift range of zcluster = 0.23 − ...0.59 using extensive spectroscopic information, primarily from the Multi Unit Spectroscopic Explorer (MUSE) archival data and complemented with CLASH-VLT redshift measurements. The observed positions of the multiple images of strongly lensed background sources were used to constrain parametric models describing the cluster total mass distributions. Different models were tested in each cluster depending on the complexity of its mass distribution and on the number of detected multiple images. Four clusters show more than five spectroscopically confirmed multiple image families. In this sample, we did not make use of families that are only photometrically identified in order to reduce model degeneracies between the values of the total mass of a cluster source redshifts, in addition to systematics due to the potential misidentifications of multiple images. For the remaining four clusters, we used additional families without any spectroscopic confirmation to increase the number of strong lensing constraints up to the number of free parameters in our parametric models. We present spectroscopic confirmation of 27 multiply lensed sources, with no previous spectroscopic measurements, spanning over the redshift range of zsrc = 0.7 − 6.1. Moreover, we confirm an average of 48 galaxy members in the core of each cluster thanks to the high efficiency and large field of view of MUSE. We used this information to derive precise strong lensing models, projected total mass distributions, and magnification maps. We show that, despite having different properties (i.e. number of mass components, total mass, redshift, etc.), the projected total mass and mass density profiles of all clusters have very similar shapes when rescaled by independent measurements of M200c and R200c. Specifically, we measured the mean value of the projected total mass of our cluster sample within 10 (20)% of R200c to be 0.13 (0.32) of M200c, with a remarkably small scatter of 5 (6)%. Furthermore, the large number of high-z sources and the precise magnification maps derived in this work for four clusters add up to the sample of high-quality gravitational telescopes to be used to study the faint and distant Universe.
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