We present the first scattered-light images of the debris disk around 49 Ceti, a ∼40 Myr A1 main-sequence star at 59 pc, famous for hosting two massive dust belts as well as large quantities of ...atomic and molecular gas. The outer disk is revealed in reprocessed archival Hubble Space Telescope NICMOS-F110W images, as well as new coronagraphic H-band images from the Very Large Telescope SPHERE instrument. The disk extends from 1 1 (65 au) to 4 6 (250 au) and is seen at an inclination of 73°, which refines previous measurements at lower angular resolution. We also report no companion detection larger than 3 MJup at projected separations beyond 20 au from the star (0 34). Comparison between the F110W and H-band images is consistent with a gray color of 49 Ceti's dust, indicating grains larger than 2 m. Our photometric measurements indicate a scattering efficiency/infrared excess ratio of 0.2-0.4, relatively low compared to other characterized debris disks. We find that 49 Ceti presents morphological and scattering properties very similar to the gas-rich HD 131835 system. From our constraint on the disk inclination we find that the atomic gas previously detected in absorption must extend to the inner disk, and that the latter must be depleted of CO gas. Building on previous studies, we propose a schematic view of the system describing the dust and gas structure around 49 Ceti and hypothetical scenarios for the gas nature and origin.
Aims.
We seek is to identify old and massive galaxies at 0.5 <
z
< 2.1 on the basis of the magnesium index Mg
UV
and then study their physical properties.
Methods.
We computed the Mg
UV
index based ...on the best spectral fitting template of ∼3700 galaxies using data from the VLT VIMOS Deep Survey (VVDS) and VIMOS Ultra Deep Survey (VUDS) galaxy redshift surveys. Based on galaxies with the largest signal to noise and the best fit spectra we selected 103 objects with the highest spectral Mg
UV
signature. We performed an independent fit of the photometric data of these galaxies and computed their stellar masses, star formation rates, extinction by dust and age, and we related these quantities to the Mg
UV
index.
Results.
We find that the Mg
UV
index is a suitable tracer of early-type galaxies at an advanced stage of evolution. Selecting galaxies with the highest Mg
UV
index allows us to choose the most massive, passive, and oldest galaxies at any epoch. The formation epoch
t
f
computed from the fitted age as a function of the total mass in stars supports the downsizing formation paradigm in which galaxies with the highest mass formed most of their stars at an earlier epoch.
Context. Strong nebular emission is ubiquitous in galaxies that contribute to cosmic reionization at redshift z ≳ 6. High-ionization UV metal lines, such as CIIIλ1908 Å, show high equivalent widths ...(EW) in these early galaxies, suggesting harder radiation fields at low metallicity than low-z galaxies of similar stellar mass. Understanding the physical properties driving the observed UV nebular line emission at high-z requires large and very deep spectroscopic surveys, which are now only accessible out to z ∼ 4. Aims. We study the mean properties of a large representative sample of 217 galaxies showing CIII emission at 2 < z < 4, selected from a parent sample of ∼750 main-sequence star-forming galaxies in the VANDELS survey. These CIII emitters have a broad range of UV luminosities, allowing for a detailed stacking analysis to characterize their stellar mass, star formation rate (SFR), and metallicity as a function of the UV emission line ratios, EWs, and the carbon-to-oxygen (C/O) abundance ratio. Methods. Stacking provides unprecedented high signal-to-noise (S/N) spectra for CIII emitters over more than three decades in luminosity, stellar mass, and SFR. This enables a full spectral fitting to derive stellar metallicities for each stack. Moreover, we use diagnostics based on photoionization models and UV line ratios to constrain the ionization sources of the galaxies and derive the C/O abundance. Results. Reliable CIII detections (S/N ≥ 3) represent ∼30% of the parent sample. However, stacked spectra of non-detections (S/N < 3) show weak (EW ≲ 2 Å) CIII emission, suggesting that this line is common in normal star-forming galaxies at z ∼ 3. On the other hand, extreme CIII emitters (EW(CIII) ≳ 8 Å) are exceedingly rare (∼3%) in VANDELS. The UV line ratios of the sample suggest no ionization source other than massive stars. Stacks with larger EW(CIII) show larger EW(Lyα) and lower metallicity, but not all CIII emitters are Lyα emitters. The stellar metallicities of CIII emitters are not significantly different from that of the parent sample, increasing from ∼10% to ∼40% solar for stellar masses log(M⋆/M⊙) ∼ 9−10.5. The stellar mass-metallicity relation of the CIII emitters is consistent with previous works, exhibiting a strong evolution from z = 0 to z ∼ 3. The C/O abundances of the sample range between 35%−150% solar, with a noticeable increase with FUV luminosity and a smooth decrease with the CIII EW. Here, we discuss the CIII emitters in the C/O–Fe/H and the C/O–O/H planes and we find that they follow stellar and nebular abundance trends consistent with those of Milky Way halo and thick-disk stars and local HII galaxies, respectively. A qualitative agreement is also found with chemical evolution models, which suggests that CIII emitters at z ∼ 3 are experiencing an active phase of chemical enrichment. Conclusions. Our results provide new insights into the nature of UV line emitters at z ∼ 2 − 4, paving the way for future studies at higher z using the James Webb Space Telescope.
Context.
Strong nebular emission is ubiquitous in galaxies that contribute to cosmic reionization at redshift
z
≳ 6. High-ionization UV metal lines, such as CIII
λ
1908 Å, show high equivalent ...widths (EW) in these early galaxies, suggesting harder radiation fields at low metallicity than low-
z
galaxies of similar stellar mass. Understanding the physical properties driving the observed UV nebular line emission at high-
z
requires large and very deep spectroscopic surveys, which are now only accessible out to
z
∼ 4.
Aims.
We study the mean properties of a large representative sample of 217 galaxies showing CIII emission at 2 <
z
< 4, selected from a parent sample of ∼750 main-sequence star-forming galaxies in the VANDELS survey. These CIII emitters have a broad range of UV luminosities, allowing for a detailed stacking analysis to characterize their stellar mass, star formation rate (SFR), and metallicity as a function of the UV emission line ratios, EWs, and the carbon-to-oxygen (C/O) abundance ratio.
Methods.
Stacking provides unprecedented high signal-to-noise (S/N) spectra for CIII emitters over more than three decades in luminosity, stellar mass, and SFR. This enables a full spectral fitting to derive stellar metallicities for each stack. Moreover, we use diagnostics based on photoionization models and UV line ratios to constrain the ionization sources of the galaxies and derive the C/O abundance.
Results.
Reliable CIII detections (
S
/
N
≥ 3) represent ∼30% of the parent sample. However, stacked spectra of non-detections (
S
/
N
< 3) show weak (EW ≲ 2 Å) CIII emission, suggesting that this line is common in normal star-forming galaxies at
z
∼ 3. On the other hand, extreme CIII emitters (EW(CIII) ≳ 8 Å) are exceedingly rare (∼3%) in VANDELS. The UV line ratios of the sample suggest no ionization source other than massive stars. Stacks with larger EW(CIII) show larger EW(Ly
α
) and lower metallicity, but not all CIII emitters are Ly
α
emitters. The stellar metallicities of CIII emitters are not significantly different from that of the parent sample, increasing from ∼10% to ∼40% solar for stellar masses log(
M
⋆
/
M
⊙
) ∼ 9−10.5. The stellar mass-metallicity relation of the CIII emitters is consistent with previous works, exhibiting a strong evolution from
z
= 0 to
z
∼ 3. The C/O abundances of the sample range between 35%−150% solar, with a noticeable increase with FUV luminosity and a smooth decrease with the CIII EW. Here, we discuss the CIII emitters in the C/O–Fe/H and the C/O–O/H planes and we find that they follow stellar and nebular abundance trends consistent with those of Milky Way halo and thick-disk stars and local HII galaxies, respectively. A qualitative agreement is also found with chemical evolution models, which suggests that CIII emitters at
z
∼ 3 are experiencing an active phase of chemical enrichment.
Conclusions.
Our results provide new insights into the nature of UV line emitters at
z
∼ 2 − 4, paving the way for future studies at higher
z
using the
James Webb
Space Telescope.
Aims. We seek is to identify old and massive galaxies at 0.5 < z < 2.1 on the basis of the magnesium index MgUV and then study their physical properties.Methods. We computed the MgUV index based on ...the best spectral fitting template of ∼3700 galaxies using data from the VLT VIMOS Deep Survey (VVDS) and VIMOS Ultra Deep Survey (VUDS) galaxy redshift surveys. Based on galaxies with the largest signal to noise and the best fit spectra we selected 103 objects with the highest spectral MgUV signature. We performed an independent fit of the photometric data of these galaxies and computed their stellar masses, star formation rates, extinction by dust and age, and we related these quantities to the MgUV index.Results. We find that the MgUV index is a suitable tracer of early-type galaxies at an advanced stage of evolution. Selecting galaxies with the highest MgUV index allows us to choose the most massive, passive, and oldest galaxies at any epoch. The formation epoch tf computed from the fitted age as a function of the total mass in stars supports the downsizing formation paradigm in which galaxies with the highest mass formed most of their stars at an earlier epoch.Key words: galaxies: formation / galaxies: high-redshift / techniques: photometric / techniques: spectroscopic⋆ Based on data obtained with the European Southern Observatory Very Large Telescope, Paranal, Chile, under Large Programmes 070.A-9007 and 177.A-0837. Based on observations obtained with MegaPrime/MegaCam, a joint project of CFHT and CEA/DAPNIA, at the Canada-France-Hawaii Telescope (CFHT) which is operated by the National Research Council (NRC) of Canada, the Institut National des Sciences de l’Univers of the Centre National de la Recherche Scientifique (CNRS) of France, and the University of Hawaii. This work is based in part on data products produced at TERAPIX and the Canadian Astronomy Data Centre as part of the CFHT Legacy Survey, a collaborative project of NRC and CNRS.
Aims.The first star forming galaxies in the early universe should be copious Lyα emitters and may play a significant role in ionizing the intergalactic medium (IGM). It has been proposed that the ...luminosity function of Lyα emitting galaxies beyond z ~ 6 may be used to constrain the neutral fraction of the IGM during this epoch. In this work we report on a search for Lyα emitters at redshift 8.8. Methods.We performed a narrow band imaging programme using ISAAC at the ESO VLT. Seven fields, covering a total area of 31 sq. arcmin and for which optical and broad band infra-red images have been obtained in the GOODS survey, were imaged to a limiting flux (respectively luminosity) of ~1.3 $\times$ 10-17 erg s-1 cm-2 (respectively ~1.3 $\times$ 1043 erg s-1) in a narrow band filter centered in a region of low OH sky emission at 1.19 μm. Candidate Lyα emitters are objects that are detected in the ISAAC NB images and undetected in the visible broad band images. Results.No $z=8.8$ Lyα emitting galaxies were detected to a limit approaching recent estimates of the luminosity function at $z\sim 6$. Our results do suggest, however, that detections or substantial constraints could be achieved by this method in the near future with larger field instruments planned for various telescopes.
Aims. The first star forming galaxies in the early universe should be copious Ly\alpha emitters and may play a significant role in ionizing the intergalactic medium (IGM). It has been proposed that ...the luminosity function of Ly\alpha emitting galaxies beyond z similar to 6 may be used to constrain the neutral fraction of the IGM during this epoch. In this work we report on a search for Ly\alpha emitters at redshift 8.8. Methods. We performed a narrow band imaging programme using ISAAC at the ESO VLT. Seven fields, covering a total area of 31 sq. arcmin and for which optical and broad band infra-red images have been obtained in the GOODS survey, were imaged to a limiting flux (respectively luminosity) of similar to 1.3 \times 10 super(-17) erg s super(- 1) cm super(-2) (respectively similar to 1.3 \times 10 super(43) erg s super(-1)) in a narrow band filter centered in a region of low OH sky emission at 1.19 \mum. Candidate Ly\alpha emitters are objects that are detected in the ISAAC NB images and undetected in the visible broad band images. Results. No z =8.8 Ly\alpha emitting galaxies were detected to a limit approaching recent estimates of the luminosity function at z\sim 6. Our results do suggest, however, that detections or substantial constraints could be achieved by this method in the near future with larger field instruments planned for various telescopes.
Aims. Lyα emitters (LAEs) can be detected out to very high redshifts during the epoch of reionization. The evolution of the LAE luminosity function with redshift is a direct probe of the Lyα ...transmission of the intergalactic medium (IGM), and therefore of the IGM neutral-hydrogen fraction. Measuring the Lyα luminosity function (LF) of Lyα emitters at redshift z = 7.7 therefore allows us to constrain the ionizing state of the Universe at this redshift. Methods. We observed three 7'.5 × 7'.5 fields with the HAWK-I instrument at the VLT with a narrow band filter centred at 1.06 μm and targeting Lyα emitters at redshift z ~ 7.7. The fields were chosen for the availability of multiwavelength data. One field is a galaxy cluster, the Bullet Cluster, which allowed us to use gravitational amplification to probe luminosities that are fainter than in the field. The two other fields are subareas of the GOODS Chandra Deep Field South and CFHTLS-D4 deep field. We selected z = 7.7 LAE candidates from a variety of colour criteria, in particular from the absence of detection in the optical bands. Results. We do not find any LAE candidates at z = 7.7 in ~2.4 × 104 Mpc3 down to a narrow band AB magnitude of ~26, which allows us to infer robust constraints on the Lyα LAE luminosity function at this redshift. Conclusions. The predicted mean number of objects at z = 6.5, derived from somewhat different luminosity functions of Hu et al. (2010, ApJ, 725, 394), Ouchi et al. (2010, ApJ, 723, 869), and Kashikawa et al. (2011, ApJ, 734, 119) are 2.5, 13.7, and 11.6, respectively. Depending on which of these luminosity functions we refer to, we exclude a scenario with no evolution from z = 6.5 to z = 7.7 at 85% confidence without requiring a strong change in the IGM Lyα transmission, or at 99% confidence with a significant quenching of the IGM Lyα transmission, possibly from a strong increase in the high neutral-hydrogen fraction between these two redshifts.
Aims. Uncovering the ingredients and the architecture of planetary systems is a very active field of research that has fuelled many new theories on giant planet formation, migration, composition, and ...interaction with the circumstellar environment. We aim at discovering and studying new such systems, to further expand our knowledge of how low-mass companions form and evolve. Methods. We obtained high-contrast H-band images of the circumstellar environment of the F5V star HD206893, known to host a debris disc never detected in scattered light. These observations are part of the SPHERE High Angular Resolution Debris Disc Survey (SHARDDS) using the InfraRed Dual-band Imager and Spectrograph (IRDIS) installed on VLT/SPHERE. Results. We report the detection of a source with a contrast of 3.6 x 10 super(-5) in the H-band, orbiting at a projected separation of 270 milliarcsec or 10au, corresponding to a mass in the range 24 to 73 M sub(Jup) for an age of the system in the range 0.2 to 2 Gyr. The detection was confirmed ten months later with VLT/NaCo, ruling out a background object with no proper motion. A faint extended emission compatible with the disc scattered light signal is also observed. Conclusions. The detection of a low-mass companion inside a massive debris disc makes this system an analog of other young planetary systems such as beta Pictoris, HR8799 or HD95086 and requires now further characterisation of both components to understand their interactions.
VANDELS is an ESO Public Spectroscopic Survey designed to build a sample of high-signal-to-noise ratio, medium-resolution spectra of galaxies at redshifts between 1 and 6.5. Here we present the final ...Public Data Release of the VANDELS Survey, comprising 2087 redshift measurements. We provide a detailed description of sample selection, observations, and data reduction procedures. The final catalogue reaches a target selection completeness of 40% at iAB = 25. The high signal-to-noise ratio of the spectra (above 7 in 80% of the spectra) and the dispersion of 2.5 Å allowed us to measure redshifts with high precision, the redshift measurement success rate reaching almost 100%. Together with the redshift catalogue and the reduced spectra, we also provide optical mid-infrared photometry and physical parameters derived through fitting the spectral energy distribution. The observed galaxy sample comprises both passive and star forming galaxies covering a stellar mass range of 8.3 < Log(M*/M⊙) < 11.7.
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