scholarly journals Properties of five z ∼ 0.3–0.4 confirmed LyC leakers: VLT/XShooter observations

2020 ◽  
Vol 497 (4) ◽  
pp. 4293-4310 ◽  
Author(s):  
N G Guseva ◽  
Y I Izotov ◽  
D Schaerer ◽  
J M Vílchez ◽  
R Amorín ◽  
...  
Keyword(s):  
Production Efficiency ◽  
Neutral Hydrogen ◽  
Mean Value ◽  
Emission Lines ◽  
H Ii Regions ◽  
High Electron ◽  
Star Forming ◽  
Very Large Telescope ◽  
High Ionization ◽  
Hydrogen Column Density

ABSTRACT Using new Very Large Telescope (VLT)/XShooter spectral observations we analyse the physical properties of five z ∼ 0.3–0.4 confirmed Lyman continuum (LyC) leakers. Strong resonant Mg ii λλ2796, 2803 Å emission lines (I(λλ2796, 2803)/I(Hβ) ≃ 10–38 per cent) and non-resonant Fe ii* λλ2612, 2626 Å emission lines are observed in spectra of five and three galaxies, respectively. We find high electron densities Ne ∼ 400 cm−3, significantly higher than in typical low-z, but comparable to those measured in z ∼ 2–3 star-forming galaxies (SFGs). The galaxies have a mean value of log N/O = –1.16, close to the maximum values found for SFGs in the metallicity range of 12 + log O/H ≃ 7.7–8.1. All 11 low-z LyC emitting galaxies found by Izotov et al., including the ones considered in this study, are characterized by high equivalent width (EW) (Hβ) ∼ 200–400 Å, high ionization parameter (log(U) = –2.5 to –1.7), high average ionizing photon production efficiency ξ = 1025.54 Hz erg−1, and hard ionizing radiation. On the Baldwin–Phillips–Terlevich (BPT) diagram we find the same offset of our leakers from low-z main-sequence SFGs as that for local analogues of Lyman-break galaxies (LBGs) and extreme SFGs at z ∼ 2–3. We confirm the effectiveness of the He i emission lines diagnostics proposed by Izotov et al. in searching for LyC leaker candidates and find that their intensity ratios correspond to those in a median with low neutral hydrogen column density N(H i) = 1017–5 × 1017 cm−2 that permit leakage of LyC radiation, likely due to their density-bounded H ii regions.

scholarly journals Statistical Properties of Gamma-Ray Burst Host Galaxies

2012 ◽  
Vol 8 (S292) ◽  
pp. 190-190
Author(s):  
J. M. Chen ◽  
L. W. Jia ◽  
E. W. Liang
Keyword(s):  
Gamma Ray ◽  
Formation Rate ◽  
Neutral Hydrogen ◽  
Statistical Properties ◽  
Host Galaxy ◽  
Host Galaxies ◽  
Gamma Ray Burst ◽  
Star Forming ◽  
Hydrogen Column Density ◽  
Linear Fit

AbstractGRBs are the most luminous events in the Universe. They are detectable from local to high-z universe and may serve as probes for high-z galaxies (e.g., Savaglio et al. 2009; Kewley & Dopita 2002). We compile the observations for 61 GRB host galaxies from literature. Their redshifts range from 0.0085 to 6.295. We present the statistical properties of the GRB host galaxies, including the stellar mass (M*), star-forming rate (SFR), metallicity (Z), extinction (AV), and neutral hydrogen column density (NH). We explore possible correlations among the properties of gamma-ray burst host galaxies and their cosmic evolution with observations of 61 GRB host galaxies. Our results are shown in Figure 1. A clear Z-M* relation is found in our sample, which is Z ~ M0.4. The host galaxies of local GRBs with detection of accompanied supernovae also share the same relation with high-z GRB host galaxies. A trend that a more massive host galaxy tends to have a higher star-formation rate is found. The best linear fit gives a tentative relation, i.e, SFR ~ M0.75. No any correlation is found between AV and NH. A GRB host galaxy at a higher redshift also tends to have a higher SFR. Even in the same redshift, the SFR may vary over three orders of magnitude. The metallicity of the GRB host galaxies is statistically higher than that of the QSO DLAs. The full version of our results please refer to Chen et al. (2012).

scholarly journals Interacting Binaries as Be Stars

1987 ◽  
Vol 92 ◽  
pp. 451-455
Author(s):  
Mirek J. Plavec
Keyword(s):  
Spectral Type ◽  
Binary Stars ◽  
Emission Lines ◽  
Close Binary ◽  
High Electron ◽  
Be Stars ◽  
Close Binary Stars ◽  
High Ionization ◽  
Mass Outflow ◽  
Balmer Lines

AbstractSemidetached close binary stars of the Algol type often have primary components of spectral type A0 or earlier and display emission at Hα (sometimes also at higher Balmer lines). They are therefore Be stars. Many binaries of this type are not eclipsing and must look like “ordinary” Be stars. We have discovered high-ionization emission lines of N V, C IV, Si IV, Fe III, etc. in the ultraviolet spectra of totally eclipsing Algols. They probably originate in circumstellar turbulent regions at fairly high electron temperatures, of the order of 100 000 K. They are not detectable in most non-eclipsing systems, but may be there and may play an important role in the dynamics of accretion and mass outflow from the systems.

scholarly journals Early Super Soft Source Spectra in RS Oph

2015 ◽  
Vol 2 (1) ◽  
pp. 222-225
Author(s):  
J.-U. Ness
Keyword(s):  
Neutral Hydrogen ◽  
Emission Lines ◽  
X Ray ◽  
Hydrogen Column Density ◽  
Recurrent Nova ◽  
Source Spectra ◽  
Short Time ◽  
First Time ◽  
Shell Ionization

Recent Swift X-ray monitoring campaigns of novae have revealed extreme levels of variability during the early super-softsource (SSS) phase. The first time this was observed was during the 2006 outburst of the recurrent nova RS Oph which was also extensively covered by grating observations with XMM-Newton and Chandra. I focus here on an XMM-Newton observation taken on day 26.1, just before Swift confirmed the start of the SSS phase, and a Chandra observation taken on day 39.7. The first observation probes the evolution of the shock emission produced by the collision of the nova ejecta with the stellar wind of the companion. The second observation contains bright SSS emission longwards of 15°A while at short wavelengths, the shock component can be seen to have hardly changed. On top of the SSS continuum, additional emission lines are clearly seen, and I show that they are much stronger than those seen on day 26.1, indicating line pumping caused by the SSS emission. The lightcurve on day 39.7 is highly variable on short time scales while the long-term Swift light curve was still variable. In 2007, we have shown that brightness variations are followed by hardness variations, lagging behind 1000 seconds. I show now that the hardness variations are owed to variations in the depth of the neutral hydrogen column density of order 25%, particularly affecting the oxygen K-shell ionization edge at 0.5 keV.

scholarly journals Blue Compact Galaxies and the Primordial 4Helium Abundance

2000 ◽  
Vol 198 ◽  
pp. 176-187 ◽  
Author(s):  
Trinh Xuan Thuan ◽  
Yuri I. Izotov
Keyword(s):  
Mean Value ◽  
Emission Lines ◽  
Electron Collision ◽  
H Ii Regions ◽  
Homogeneous Sample ◽  
Low Metallicity ◽  
Consistent Method ◽  
Compact Galaxies ◽  
The Universe ◽  
Linear Regressions

Blue compact galaxies (BCG) are ideal objects in which to derive the primordial 4He abundance because they are chemically young and have not had a significant stellar He contribution. We discuss a self-consistent method which makes use of all the brightest He I emission lines in the optical range and solves consistently for the electron density of the He II zone. We pay particular attention to electron collision and radiative transfer as well as underlying stellar absorption effects which may make the He I emission lines deviate from their recombination values. Using a large homogeneous sample of 45 low-metallicity H II regions in BCGs, and extrapolating the Y-O/H and Y-N/H linear regressions to O/H = N/H = 0, we obtain Yp = 0.2443±0.0015, in excellent agreement with the weighted mean value Yp = 0.2452±0.0015 obtained from the detailed analysis of the two most metal-deficient BCGs known, I Zw 18 and SBS 0335-052. The derived slope dY/dZ = 2.4±1.0 is in agreement with the value derived for the Milky Way and with simple chemical evolution models with homogeneous outflows. Adopting Yp = 0.2452±0.0015 leads to a baryon-to-photon ratio of (4.7+1.0-0.8) × 10−10 and to a baryon mass fraction in the Universe ωbh250 = 0-068+0.015-0.012, consistent with the value derived from the primordial D abundance of Burles &Tytler (1998).

scholarly journals An imaging spectroscopic survey of the planetary nebula NGC 7009 with MUSE

2018 ◽  
Vol 620 ◽  
pp. A169 ◽  
Author(s):  
J. R. Walsh ◽  
A. Monreal-Ibero ◽  
M. J. Barlow ◽  
T. Ueta ◽  
R. Wesson ◽  
...  
Keyword(s):  
Line Emission ◽  
Emission Lines ◽  
Ionized Gas ◽  
Physical Conditions ◽  
Very Large Telescope ◽  
High Ionization ◽  
Integral Field Spectrograph ◽  
First Time ◽  
Considerable Detail ◽  
Standard Techniques

Aims. The spatial structure of the emission lines and continuum over the 50″ extent of the nearby, O-rich, PN NGC 7009 (Saturn Nebula) have been observed with the MUSE integral field spectrograph on the ESO Very Large Telescope. This study concentrates on maps of line emission and their interpretation in terms of physical conditions. Methods. MUSE Science Verification data, in <0.6″ seeing, have been reduced and analysed as maps of emission lines and continuum over the wavelength range 4750–9350 Å. The dust extinction, the electron densities and temperatures of various phases of the ionized gas, abundances of species from low to high ionization and some total abundances are determined using standard techniques. Results. Emission line maps over the bright shells are presented, from neutral to the highest ionization available (He II and [Mn V]). For collisionally excited lines (CELs), maps of electron temperature (Te from [N II] and [S III]) and density (Ne from [S II] and [Cl III]) are available and for optical recombination lines (ORLs) temperature (from the Paschen jump and ratio of He I lines) and density (from high Paschen lines). These estimates are compared: for the first time, maps of the differences in CEL and ORL Te’s have been derived, and correspondingly a map of t2 between a CEL and ORL temperature, showing considerable detail. Total abundances of only He and O were formed, the latter using three ionization correction factors. However, the map of He/H is not flat, departing by ~2% from a constant value, with remnants corresponding to ionization structures. An integrated spectrum over an area of 2340 arcsec2 was also formed and compared to 1D photoionization models. Conclusions. The spatial variation of a range of nebular parameters illustrates the complexity of the ionized media in NGC 7009. These MUSE data are very rich with detections of hundreds of lines over areas of hundreds of arcsec2 and follow-on studies are outlined.

scholarly journals Structure and expansion law of H ii regions in structured molecular clouds

2019 ◽  
Vol 487 (2) ◽  
pp. 2200-2214 ◽  
Author(s):  
Manuel Zamora-Avilés ◽  
Enrique Vázquez-Semadeni ◽  
Ricardo F González ◽  
José Franco ◽  
Steven N Shore ◽  
...  
Keyword(s):  
Molecular Clouds ◽  
Massive Star ◽  
Mean Value ◽  
Neutral Medium ◽  
H Ii Regions ◽  
Star Forming ◽  
Star Forming Regions ◽  
H Ii Region ◽  
Analytical Result ◽  
Magnetohydrodynamic Simulations

Abstract We present radiation-magnetohydrodynamic simulations aimed at studying evolutionary properties of H ii regions in turbulent, magnetized, and collapsing molecular clouds formed by converging flows in the warm neutral medium. We focus on the structure, dynamics, and expansion laws of these regions. Once a massive star forms in our highly structured clouds, its ionizing radiation eventually stops the accretion (through filaments) towards the massive star-forming regions. The new overpressured H ii regions push away the dense gas, thus disrupting the more massive collapse centres. Also, because of the complex density structure in the cloud, the H ii regions expand in a hybrid manner: they virtually do not expand towards the densest regions (cores), while they expand according to the classical analytical result towards the rest of the cloud, and in an accelerated way, as a blister region, towards the diffuse medium. Thus, the ionized regions grow anisotropically, and the ionizing stars generally appear off-centre of the regions. Finally, we find that the hypotheses assumed in standard H ii-region expansion models (fully embedded region, blister-type, or expansion in a density gradient) apply simultaneously in different parts of our simulated H ii regions, producing a net expansion law (R∝ tα, with α in the range of 0.93–1.47 and a mean value of 1.2 ± 0.17) that differs from any of those of the standard models.

scholarly journals Physical conditions in two high-redshift H2-bearing GRB-DLAs, 120815A and 121024A

2020 ◽  
Vol 493 (4) ◽  
pp. 5153-5161
Author(s):  
Gargi Shaw ◽  
G J Ferland
Keyword(s):  
Gamma Ray ◽  
Numerical Study ◽  
Spectral Synthesis ◽  
High Redshift ◽  
Large Fraction ◽  
Neutral Hydrogen ◽  
Star Forming ◽  
Physical Conditions ◽  
Hydrogen Column Density ◽  
Cloud Thickness

ABSTRACT The gamma-ray burst (GRB) afterglows provide a unique opportunity to study the interstellar medium (ISM) of star-forming galaxies at high-redshift. The GRB-DLAs (damped Lyman-α absorbers) contain a large neutral hydrogen column density, N(H i), and are observed against the GRB afterglow. A large fraction of GRB-DLAs show presence of molecular hydrogen (H2) which is an indicator of star-formation. Hence it is important to study those GRB-DLAs which have H2 lines to decipher and understand their physical conditions. The GRB-DLAs 121024A and 120815A, situated at redshift 2.30 and 2.36, respectively, are two such important H2-bearing GRB-DLAs. Besides H2, these two GRB-DLAs also show many metal lines. In this work we have carried out a detail numerical study on the H2 lines, as well as on those metal lines, in GRB-DLAs 121024A and 120815A self-consistently. We use the spectral synthesis code cloudy for this study. This modelling helps us to determine the underlying physical conditions which give rise to such lines and hence to understand these two GRB-DLAs in much more detail than any other previous investigation. We find that the hydrogen densities for these two H2-bearing DLAs are ≥60 cm−3. Moreover our study infers that the linear sizes are ≤17.7 pc for these two GRB-DLAs, and the mean gas temperatures averaged over the cloud thickness, are ≤140 K. Overall, we find that these two H2-bearing GRB-DLAs are denser, cooler, and smaller compared to those without H2.

scholarly journals The ALPINE-ALMA [CII] survey

2020 ◽  
Vol 643 ◽  
pp. A6 ◽  
Author(s):  
P. Cassata ◽  
L. Morselli ◽  
A. Faisst ◽  
M. Ginolfi ◽  
M. Béthermin ◽  
...  
Keyword(s):  
Early Universe ◽  
High Redshift ◽  
Neutral Hydrogen ◽  
Far Infrared ◽  
Line Of Sight ◽  
Star Forming ◽  
Very Large Telescope ◽  
Large Program ◽  
Systemic Velocity ◽  
Combining Data

Context. The Lyman-α line in the ultraviolet (UV) and the [CII] line in the far-infrared (FIR) are widely used tools to identify galaxies in the early Universe and to obtain insights into interstellar medium (ISM) properties in high-redshift galaxies. By combining data obtained with ALMA in band 7 at ∼320 GHz as part of the ALMA Large Program to INvestigate [CII] at Early Times (ALPINE) with spectroscopic data from DEIMOS at the Keck Observatory, VIMOS and FORS2 at the Very Large Telescope, we assembled a unique sample of 53 main-sequence star-forming galaxies at 4.4 <  z <  6 in which we detect both the Lyman-α line in the UV and the [CII] line in the FIR. Aims. The goal of this paper is to constrain the properties of the Lyα emission in these galaxies in relation to other properties of the ISM. Methods. We used [CII], observed with ALMA, as a tracer of the systemic velocity of the galaxies, and we exploited the available optical spectroscopy to obtain the Lyα-[CII] and ISM-[CII] velocity offsets. Results. We find that 90% of the selected objects have Lyα-[CII] velocity offsets in the range 0 <  ΔvLyα − [CII] <  400 km s−1, in line with the few measurements available so far in the early Universe, and significantly smaller than those observed at lower redshifts. At the same time, we observe ISM-[CII] offsets in the range −500 <  ΔvISM−[CII] <  0 km s−1, in line with values at all redshifts, which we interpret as evidence for outflows in these galaxies. We find significant anticorrelations between ΔvLyα−[CII] and the Lyα rest-frame equivalent width EW0(Lyα) (or equivalently, the Lyα escape fraction fesc(Lyα)): galaxies that show smaller ΔvLyα−[CII] have larger EW0(Lyα) and fesc(Lyα). Conclusions. We interpret these results in the framework of available models for the radiative transfer of Lyα photons. According to the models, the escape of Lyα photons would be favored in galaxies with high outflow velocities, producing large EW0(Lyα) and small ΔvLyα-[CII], in agreement with our observations. The uniform shell model would also predict that the Lyα escape in galaxies with slow outflows (0 <  vout <  300 km s−1) is mainly determined by the neutral hydrogen column density (NHI) along the line of sight, while the alternative model by Steidel et al. (2010, ApJ, 717, 289) would more highly favor a combination of NHI at the systemic velocity and covering fraction as driver of the Lyα escape. We suggest that the increase in Lyα escape that is observed in the literature between z ∼ 2 and z ∼ 6 is not due to a higher incidence of fast outflows at high redshift, but rather to a decrease in average NHI along the line of sight, or alternatively, a decrease in HI covering fraction.

scholarly journals The effect of stellar multiplicity on protoplanetary discs: a near-infrared survey of the Lupus star-forming region

2020 ◽  
Vol 501 (2) ◽  
pp. 2305-2315
Author(s):  
Alice Zurlo ◽  
Lucas A Cieza ◽  
Megan Ansdell ◽  
Valentin Christiaens ◽  
Sebastián Pérez ◽  
...  
Keyword(s):  
Adaptive Optics ◽  
Molecular Cloud ◽  
Near Infrared ◽  
Main Sequence Stars ◽  
Multiple Systems ◽  
Star Forming ◽  
Very Large Telescope ◽  
Pms Stars ◽  
First Time ◽  
Infrared Survey

ABSTRACT We present results from a near-infrared (NIR) adaptive optics (AO) survey of pre-main-sequence stars in the Lupus molecular cloud with NACO at the Very Large Telescope (VLT) to identify (sub)stellar companions down to ∼20-au separation and investigate the effects of multiplicity on circumstellar disc properties. We observe for the first time in the NIR with AO a total of 47 targets and complement our observations with archival data for another 58 objects previously observed with the same instrument. All 105 targets have millimetre Atacama Large Millimetre/sub-millimetre Array (ALMA) data available, which provide constraints on disc masses and sizes. We identify a total of 13 multiple systems, including 11 doubles and 2 triples. In agreement with previous studies, we find that the most massive (Mdust &gt; 50 M⊕) and largest (Rdust &gt; 70 au) discs are only seen around stars lacking visual companions (with separations of 20–4800 au) and that primaries tend to host more massive discs than secondaries. However, as recently shown in a very similar study of &gt;200 PMS stars in the Ophiuchus molecular cloud, the distributions of disc masses and sizes are similar for single and multiple systems for Mdust &lt; 50 M⊕ and radii Rdust &lt; 70 au. Such discs correspond to ∼80–90 per cent of the sample. This result can be seen in the combined sample of Lupus and Ophiuchus objects, which now includes more than 300 targets with ALMA imaging and NIR AO data, and implies that stellar companions with separations &gt;20 au mostly affect discs in the upper 10${{\ \rm per\ cent}}$ of the disc mass and size distributions.

scholarly journals A synergy of the velocity gradients technique and the probability density functions for identifying gravitational collapse in self-absorbing media

2021 ◽  
Vol 502 (2) ◽  
pp. 1768-1784
Author(s):  
Yue Hu ◽  
A Lazarian
Keyword(s):  
Magnetic Fields ◽  
Probability Density ◽  
Column Density ◽  
Mass Density ◽  
Probability Density Functions ◽  
Emission Lines ◽  
Density Functions ◽  
Star Forming ◽  
Velocity Gradients ◽  
Self Gravity

ABSTRACT The velocity gradients technique (VGT) and the probability density functions (PDFs) of mass density are tools to study turbulence, magnetic fields, and self-gravity in molecular clouds. However, self-absorption can significantly make the observed intensity different from the column density structures. In this work, we study the effects of self-absorption on the VGT and the intensity PDFs utilizing three synthetic emission lines of CO isotopologues 12CO (1–0), 13CO (1–0), and C18O (1–0). We confirm that the performance of VGT is insensitive to the radiative transfer effect. We numerically show the possibility of constructing 3D magnetic fields tomography through VGT. We find that the intensity PDFs change their shape from the pure lognormal to a distribution that exhibits a power-law tail depending on the optical depth for supersonic turbulence. We conclude the change of CO isotopologues’ intensity PDFs can be independent of self-gravity, which makes the intensity PDFs less reliable in identifying gravitational collapsing regions. We compute the intensity PDFs for a star-forming region NGC 1333 and find the change of intensity PDFs in observation agrees with our numerical results. The synergy of VGT and the column density PDFs confirms that the self-gravitating gas occupies a large volume in NGC 1333.

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