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21141. VLT/X-shooter observations of PHL293B
ID:
ivo://CDS.VizieR/J/A+A/533/A25
Title:
VLT/X-shooter observations of PHL293B
Short Name:
J/A+A/533/A25
Date:
21 Oct 2021
Publisher:
CDS
Description:
We present VLT/X-shooter spectroscopic observations in the wavelength range {lambda}{lambda}3000-23000{AA} of the extremely metal-deficient blue compact dwarf (BCD) galaxy PHL 293B containing a luminous blue variable (LBV) star and compare them with previous data. This BCD is one of the two lowest-metallicity galaxies where LBV stars were detected, allowing us to study the LBV phenomenon in the extremely low metallicity regime. We determine abundances of nitrogen, oxygen, neon, sulfur, argon, and iron by analyzing the fluxes of narrow components of the emission lines using empirical methods and study the properties of the LBV from the fluxes and widths of broad emission lines.
21142. VLT/X-SHOOTER spectrum of COLA1
ID:
ivo://CDS.VizieR/J/A+A/619/A136
Title:
VLT/X-SHOOTER spectrum of COLA1
Short Name:
J/A+A/619/A136
Date:
21 Oct 2021
Publisher:
CDS
Description:
Distant luminous Lyman-{alpha} emitters (LAEs) are excellent targets for spectroscopic observations of galaxies in the epoch of reionisation (EoR). We present deep high-resolution (R=5000) VLT/X-shooter observations, along with an extensive collection of photometric data of COLA1, a proposed double peaked LAE at z=6.6. We rule out the possibility that COLA1's emission line is an [OII] doublet at z=1.475 on the basis of i) the asymmetric red line-profile and flux ratio of the peaks (blue/red=0.31+/-0.03) and ii) an unphysical [OII]/H{alpha} ratio ([OII]/H{alpha}>22). We show that COLA1's observed B-band flux is explained by a faint extended foreground LAE, for which we detect Ly{alpha} and [OIII] at z=2.142. We thus conclude that COLA1 is a real double-peaked LAE at z=6.593, the first discovered at z>6. COLA1 is UV luminous (M1500=-21.6+/-0.3), has a high equivalent width (EW0,Ly{alpha}=120_-40_^+50^{AA}) and very compact Ly{alpha} emission (r50,Ly{alpha}=0.33_-0.04_^+0.07^kpc). Relatively weak inferred H{beta}+[OIII] line-emission from Spitzer/IRAC indicates an extremely low metallicity of Z<1/20Z_{sun}_ or reduced strength of nebular lines due to high escape of ionising photons. The small Ly{alpha} peak separation of 220+/-20km/s implies a low HI column density and an ionising photon escape fraction of ~15-30%, providing the first direct evidence that such galaxies contribute actively to the reionisation of the Universe at z>6. Based on simple estimates, we find that COLA1 could have provided just enough photons to reionise its own ~0.3pMpc (2.3cMpc) bubble, allowing the blue Ly{alpha} line to be observed. However, we also discuss alternative scenarios explaining the detected double peaked nature of COLA1. Our results show that future high-resolution observations of statistical samples of double peaked LAEs at z>5 are a promising probe of the occurrence of ionised regions around galaxies in the EoR.
21143. Vmag/plx relation for Hyades stars
ID:
ivo://CDS.VizieR/J/other/NewA/8.645
Title:
Vmag/plx relation for Hyades stars
Short Name:
J/other/NewA/8.6
Date:
21 Oct 2021
Publisher:
CDS
Description:
In this paper, relation was established for Hyades stars between their apparent magnitudes and parallaxes. The precision criteria of this relation are very satisfactory. The importance of this relation was illustrated through its usages as: (1) A criterion for membership of the cluster, (2) a generating function for evaluating some parameters of the cluster.
21144. VMC Survey. VII. 30 Doradus reddening map
ID:
ivo://CDS.VizieR/J/A+A/554/A33
Title:
VMC Survey. VII. 30 Doradus reddening map
Short Name:
J/A+A/554/A33
Date:
21 Oct 2021
Publisher:
CDS
Description:
In this paper we present a detailed reddening map of the central 30 Doradus region of the Large Magellanic Cloud; for both community use and as a test of the methods used for future use on a wider area. The reddening, a measurement of dust extinction, acts as a tracer of the interstellar medium (ISM). Near-infrared (NIR) photometry of the red clump stars is used to measure reddening as their fixed luminosity and intermediate age make extinction the dominant cause of colour and magnitude variance. The star formation history derived previously from these data is used to produce an intrinsic colour to act as a zero point in converting colour to reddening values E(J-Ks) which are subsequently converted to visual extinction A_V_. Presented is a dust map for the 30 Doradus field in both A_V_ and E(J-Ks). This map samples a region of 1{deg}x1.5{deg}, containing ~1.5x10^5^ red clump stars which probe reddening up to A_V_~6mag. We compare our map with maps from the literature, including optical extinction maps and radio, mid- and far-infrared maps of atomic hydrogen and dust emission. Through estimation of column density we locate molecular clouds.
21145. VMC survey. XIV. SFR in SMC
ID:
ivo://CDS.VizieR/J/MNRAS/449/639
Title:
VMC survey. XIV. SFR in SMC
Short Name:
J/MNRAS/449/639
Date:
21 Oct 2021
Publisher:
CDS
Description:
We analyse deep images from the VISTA survey of the Magellanic Clouds in the YJKs filters, covering 14deg^2^ (10 tiles), split into 120 subregions, and comprising the main body and Wing of the Small Magellanic Cloud (SMC). We apply a colour-magnitude diagram reconstruction method that returns their best-fitting star formation rate SFR(t), age-metallicity relation (AMR), distance and mean reddening, together with 68 percent confidence intervals. The distance data can be approximated by a plane tilted in the East-West direction with a mean inclination of 39{deg}, although deviations of up to +/-3kpc suggest a distorted and warped disc. After assigning to every observed star a probability of belonging to a given age-metallicity interval, we build high-resolution population maps. These dramatically reveal the flocculent nature of the young star-forming regions and the nearly smooth features traced by older stellar generations. They document the formation of the SMC Wing at ages <0.2Gyr and the peak of star formation in the SMC Bar at ~40Myr. We clearly detect periods of enhanced star formation at 1.5 and 5Gyr. The former is possibly related to a new feature found in the AMR, which suggests ingestion of metal-poor gas at ages slightly larger than 1Gyr. The latter constitutes a major period of stellar mass formation. We confirm that the SFR(t) was moderately low at even older ages.
21146. VMC survey XLIII. LMC star formation history
ID:
ivo://CDS.VizieR/J/MNRAS/508/245
Title:
VMC survey XLIII. LMC star formation history
Short Name:
J/MNRAS/508/245
Date:
21 Oct 2021 08:21:00
Publisher:
CDS
Description:
We derive the spatially resolved star formation history (SFH) for a 96deg^2^ area across the main body of the Large Magellanic Cloud (LMC), using the near- infrared photometry from the VISTA survey of the Magellanic Clouds (VMC). The data and analyses are characterized by a great degree of homogeneity and a low sensitivity to the interstellar extinction. 756 subregions of size 0.125deg^2^ - corresponding to projected sizes of about 296x322pc^2^ in the LMC - are analysed. The resulting SFH maps, with typical resolution of 0.2-0.3dex in logarithm of age, reveal main features in the LMC disc at different ages: the patchy star formation at recent ages, the concentration of star formation on three spiral arms and on the Bar up to ages of ~1.6Gyr, and the wider and smoother distribution of older populations. The period of most intense star formation occurred roughly between 4 and 0.5Gyr ago, at rates of ~0.3M_{sun}_/yr. We compare young and old star formation rates with the observed numbers of RR Lyrae and Cepheids. We also derive a mean extinction and mean distance for every subregion, and the plane that best describes the spatial distribution of the mean distances. Our results cover an area about 50 per cent larger than the classical SFH maps derived from optical data. Main differences with respect to those maps are lower star formation rates at young ages, and a main peak of star formation being identified at ages slightly younger than 1Gyr.
21147. VMC survey. XVI.
ID:
ivo://CDS.VizieR/J/MNRAS/454/839
Title:
VMC survey. XVI.
Short Name:
J/MNRAS/454/839
Date:
21 Oct 2021
Publisher:
CDS
Description:
We present results based on YJKs photometry of star clusters in the Large Magellanic Cloud (LMC), distributed throughout the central part of the galaxy's bar and the 30 Doradus region. We analysed the field-star-decontaminated colour-magnitude diagrams of 313 clusters to estimate their reddening values and ages. The clusters are affected by a mean reddening of E(B-V){in}[0.2, 0.3]mag, where the average internal LMC reddening amounts to ~0.1-0.2mag. The region covering 30 Doradus includes clusters with reddening values in excess of E(B-V)=0.4mag. Our cluster sample spans the age range 7.0<=log(t/yr)<9.0, represents an increase of 30 percent in terms of the number of clusters with robust age estimates and comprises a statistically complete sample in the LMC regions of interest here. The resulting cluster frequencies suggest that the outermost regions of the LMC bar first experienced enhanced cluster formation - log(t/yr){in}[8.5, 9.0] - before the activity proceeded, although in a patchy manner, to the innermost regions, for log(t/yr)<7.7. Cluster frequencies in the 30 Doradus region show that the area is dominated by very recent cluster formation. The derived star formation frequencies suggest that the cluster and field-star populations do not seem to have fully evolved as fully coupled systems during the last ~100Myr.
21148. VMC survey. XXIX. Star formation in the SMC
ID:
ivo://CDS.VizieR/J/ApJ/858/31
Title:
VMC survey. XXIX. Star formation in the SMC
Short Name:
J/ApJ/858/31
Date:
21 Oct 2021
Publisher:
CDS
Description:
In this paper we report a clustering analysis of upper main-sequence stars in the Small Magellanic Cloud, using data from the VMC survey (the VISTA near-infrared YJKs survey of the Magellanic system). Young stellar structures are identified as surface overdensities on a range of significance levels. They are found to be organized in a hierarchical pattern, such that larger structures at lower significance levels contain smaller ones at higher significance levels. They have very irregular morphologies, with a perimeter-area dimension of 1.44+/-0.02 for their projected boundaries. They have a power-law mass-size relation, power-law size/mass distributions, and a log-normal surface density distribution. We derive a projected fractal dimension of 1.48+/-0.03 from the mass-size relation, or of 1.4+/-0.1 from the size distribution, reflecting significant lumpiness of the young stellar structures. These properties are remarkably similar to those of a turbulent interstellar medium, supporting a scenario of hierarchical star formation regulated by supersonic turbulence.
21149. VMC survey. XXVI. SMC RR Lyrae stars
ID:
ivo://CDS.VizieR/J/MNRAS/473/3131
Title:
VMC survey. XXVI. SMC RR Lyrae stars
Short Name:
J/MNRAS/473/3131
Date:
21 Oct 2021
Publisher:
CDS
Description:
We present results from the analysis of 2997 fundamental mode RR Lyrae variables located in the Small Magellanic Cloud (SMC). For these objects, near-infrared time series photometry from the VISTA survey of the Magellanic Clouds system (VMC) and visual light curves from the OGLE IV (Optical Gravitational Lensing Experiment IV) survey are available. In this study, the multi-epoch Ks-band VMC photometry was used for the first time to derive intensity-averaged magnitudes of the SMC RR Lyrae stars. We determined individual distances to the RR Lyrae stars from the near-infrared period-absolute magnitude-metallicity (PM_Ks_Z) relation, which has some advantages in comparison with the visual absolute magnitude-metallicity (M_V_-[Fe/H]) relation, such as a smaller dependence of the luminosity on interstellar extinction, evolutionary effects and metallicity. The distances we have obtained were used to study the three-dimensional structure of the SMC. The distribution of the SMC RR Lyrae stars is found to be ellipsoidal. The actual line-of-sight depth of the SMC is in the range 1-10kpc, with an average depth of 4.3+/-1.0kpc. We found that RR Lyrae stars in the eastern part of the SMC are affected by interactions of the Magellanic Clouds. However, we do not see a clear bimodality observed for red clump stars, in the distribution of RR Lyrae stars.
21150. VMC Survey. XXXVII. MC AGB stars
ID:
ivo://CDS.VizieR/J/A+A/636/A48
Title:
VMC Survey. XXXVII. MC AGB stars
Short Name:
J/A+A/636/A48
Date:
21 Oct 2021
Publisher:
CDS
Description:
Variability is a key property of stars on the asymptotic giant branch (AGB). Selection criteria are derived based on colour-colour and colour-magnitude diagrams from the combination of VISTA Magellanic Cloud (VMC) survey, Spitzer IRAC, and AllWISE data. After eliminating LPVs with known periods shorter than 450 days, a sample of 1299 candidate obscured AGB stars is selected. K-band LCs are constructed combining the epoch photometry available in the VMC survey with literature data, analysed for variability and fitted with a single period sine curve to derive mean magnitudes, amplitudes and periods. A subset of 254 stars are either new variables, or known variables where the period we find is better determined than the literature value, or longer than 1000 days. The spectral energy distributions (SEDs) of these stars are fitted to a large number of templates. For this purpose the SEDs and Spitzer IRS spectra of some non-AGB stars (Be stars, Hii regions and young stellar objects [YSOs]) are also fitted to have templates of the most likely contaminants in the sample. A sample of 217 likely LPVs is found. Thirty-four stars have periods longer than 1000 days although some of them have alternative shorter periods.