scholarly journals Oxygen and zinc abundances in 417 Galactic bulge red giants

2018 ◽  
Vol 614 ◽  
pp. A149 ◽  
Author(s):  
C. R. da Silveira ◽  
B. Barbuy ◽  
A. C. S. Friaça ◽  
V. Hill ◽  
M. Zoccali ◽  
...  
Keyword(s):  
Chemical Evolution ◽  
High Redshift ◽  
Formation Rate ◽  
Red Giants ◽  
Galactic Bulge ◽  
Large Sample ◽  
Neutral Gas ◽  
Very Large Telescope ◽  
Red Giant ◽  
Damped Lyman Alpha Systems

Context. Oxygen and zinc in the Galactic bulge are key elements for the understanding of the bulge chemical evolution. Oxygen-to-iron abundance ratios provide a most robust indicator of the star formation rate and chemical evolution of the bulge. Zinc is enhanced in metal-poor stars, behaving as an α-element, and its production may require nucleosynthesis in hypernovae. Most of the neutral gas at high redshift is in damped Lyman-alpha systems (DLAs), where Zn is also observed to behave as an α-element. Aims. The aim of this work is the derivation of the α-element oxygen, together with nitrogen, and the iron-peak element zinc abundances in 417 bulge giants, from moderate resolution (R ~ 22 000) FLAMES-GIRAFFE spectra. For stars in common with a set of UVES spectra with higher resolution (R ~ 45 000), the data are intercompared. The results are compared with literature data and chemodynamical models. Methods. We studied the spectra obtained for a large sample of red giant stars, chosen to be one magnitude above the horizontal branch, using FLAMES-GIRAFFE on the Very Large Telescope. We computed the O abundances using the forbidden [OI] 6300.3 Å and Zn abundances using the Zn I 6362.34 Å lines. Stellar parameters for these stars were established in a previous work from our group. Results. We present oxygen abundances for 358 stars, nitrogen abundances for 403 stars and zinc abundances were derived for 333 stars. Having oxygen abundances for this large sample adds information in particular at the moderate metallicities of −1.6 < [Fe/H] < −0.8. Zn behaves as an α-element, very similarly to O, Si, and Ca. It shows the same trend as a function of metallicity as the α-elements, i.e., a turnover around [Fe/H] ~ − 0.6, and then decreasing with increasing metallicity. The results are compared with chemodynamical evolution models of O and Zn enrichment for a classical bulge. DLAs also show an enhanced zinc-to-iron ratio, suggesting they may be enriched by hypernovae.

scholarly journals Core rotation braking on the red giant branch for various mass ranges

2018 ◽  
Vol 616 ◽  
pp. A24 ◽  
Author(s):  
C Gehan ◽  
B. Mosser ◽  
E. Michel ◽  
R. Samadi ◽  
T. Kallinger
Keyword(s):  
Angular Momentum ◽  
Red Giants ◽  
Regular Pattern ◽  
Convective Envelope ◽  
Large Sample ◽  
The Mean ◽  
Mixed Modes ◽  
Red Giant ◽  
Core Rotation ◽  
Dipole Gravity

Context. Asteroseismology allows us to probe stellar interiors. In the case of red giant stars, conditions in the stellar interior are such as to allow for the existence of mixed modes, consisting in a coupling between gravity waves in the radiative interior and pressure waves in the convective envelope. Mixed modes can thus be used to probe the physical conditions in red giant cores. However, we still need to identify the physical mechanisms that transport angular momentum inside red giants, leading to the slow-down observed for red giant core rotation. Thus large-scale measurements of red giant core rotation are of prime importance to obtain tighter constraints on the efficiency of the internal angular momentum transport, and to study how this efficiency changes with stellar parameters. Aims. This work aims at identifying the components of the rotational multiplets for dipole mixed modes in a large number of red giant oscillation spectra observed by Kepler. Such identification provides us with a direct measurement of the red giant mean core rotation. Methods. We compute stretched spectra that mimic the regular pattern of pure dipole gravity modes. Mixed modes with the same azimuthal order are expected to be almost equally spaced in stretched period, with a spacing equal to the pure dipole gravity mode period spacing. The departure from this regular pattern allows us to disentangle the various rotational components and therefore to determine the mean core rotation rates of red giants. Results. We automatically identify the rotational multiplet components of 1183 stars on the red giant branch with a success rate of 69% with respect to our initial sample. As no information on the internal rotation can be deduced for stars seen pole-on, we obtain mean core rotation measurements for 875 red giant branch stars. This large sample includes stars with a mass as large as 2.5 M⊙, allowing us to test the dependence of the core slow-down rate on the stellar mass. Conclusions. Disentangling rotational splittings from mixed modes is now possible in an automated way for stars on the red giant branch, even for the most complicated cases, where the rotational splittings exceed half the mixed-mode spacing. This work on a large sample allows us to refine previous measurements of the evolution of the mean core rotation on the red giant branch. Rather than a slight slow-down, our results suggest rotation is constant along the red giant branch, with values independent of the mass.

scholarly journals Mg II λ2797, λ2803 emission in a large sample of low-metallicity star-forming galaxies from SDSS DR14

2019 ◽  
Vol 624 ◽  
pp. A21 ◽  
Author(s):  
N. G. Guseva ◽  
Y. I. Izotov ◽  
K. J. Fricke ◽  
C. Henkel
Keyword(s):  
Noble Gas ◽  
Formation Rate ◽  
Sloan Digital Sky Survey ◽  
Large Sample ◽  
Star Forming ◽  
Magnesium Depletion ◽  
Sky Survey ◽  
Solar Metallicity ◽  
Low Metallicity ◽  
Damped Lyman Alpha Systems

A large sample of Mg II emitting star-forming galaxies with low metallicity [O/H] = log(O/H) – log(O/H)⊙ between –0.2 and –1.2 dex is constructed from Data Release 14 of the Sloan Digital Sky Survey. We selected 4189 galaxies with Mg II λ2797, λ2803 emission lines in the redshift range z ∼ 0.3–1.0 or 35% of the total Sloan Digital Sky Survey star-forming sample with redshift z ≥ 0.3. We study the dependence of the magnesium-to-oxygen and magnesium-to-neon abundance ratios on metallicity. Extrapolating this dependence to [Mg/Ne] = 0 and to solar metallicity we derive a magnesium depletion of [Mg/Ne] ≃ –0.4 (at solar metallicity). We prefer neon instead of oxygen to evaluate the magnesium depletion in the interstellar medium because neon is a noble gas and is not incorporated into dust, contrary to oxygen. Thus, we find that more massive and more metal abundant galaxies have higher magnesium depletion. The global parameters of our sample, such as the mass of the stellar population and star formation rate, are compared with previously obtained results from the literature. These results confirm that Mg II emission has a nebular origin. Our data for interstellar magnesium-to-oxygen abundance ratios relative to the solar value are in good agreement with similar measurements made for Galactic stars, for giant stars in the Milky Way satellite dwarf galaxies, and with low-metallicity damped Lyman-alpha systems.

scholarly journals Redshift evolution of the H2/H i mass ratio in galaxies

2021 ◽  
Vol 502 (1) ◽  
pp. L85-L89
Author(s):  
Laura Morselli ◽  
A Renzini ◽  
A Enia ◽  
G Rodighiero
Keyword(s):  
High Redshift ◽  
Strong Dependence ◽  
Formation Rate ◽  
Stellar Mass ◽  
Mass Ratio ◽  
Star Forming ◽  
Spatially Resolved ◽  
Internal Working ◽  
Neutral Gas ◽  
Grand Design

ABSTRACT In this paper, we present an attempt to estimate the redshift evolution of the molecular to neutral gas mass ratio within galaxies (at fixed stellar mass). For a sample of five nearby grand design spirals located on the main-sequence (MS) of star-forming galaxies, we exploit maps at 500 pc resolution of stellar mass and star formation rate (M⋆ and SFR). For the same cells, we also have estimates of the neutral (MH i) and molecular ($M_{\rm H_2}$) gas masses. To compute the redshift evolution, we exploit two relations: (i) one between the molecular-to-neutral mass ratio and the total gas mass (Mgas), whose scatter shows a strong dependence with the distance from the spatially resolved MS, and (ii) the one between $\log (M_{\rm {H_2}}/M_{\star })$ and log (MH i/M⋆). For both methods, we and that $M_{\rm H_2}$/MH i within the optical radius slightly decreases with redshift, contrary to common expectations of galaxies becoming progressively more dominated by molecular hydrogen at high redshifts. We discuss possible implications of this trend on our understanding of the internal working of high-redshift galaxies.

scholarly journals Physical Properties of Dlas: Metallicity and Neutral Hydrogen Column Density

2004 ◽  
Vol 217 ◽  
pp. 246-251
Author(s):  
J. L. Hou ◽  
C. G. Shu ◽  
W. P. Chen ◽  
R. X. Chang ◽  
C. Q. Fu
Keyword(s):  
Star Formation ◽  
Galaxy Formation ◽  
Column Density ◽  
High Redshift ◽  
Formation Rate ◽  
Neutral Hydrogen ◽  
Gas Content ◽  
Lyman Alpha ◽  
Formation Mode ◽  
Damped Lyman Alpha Systems

We investigate some basic properties of Damped Lyman alpha systems based on the Semi-Analytical model of disk galaxy formation theory. We derive the DLA metallicity, column density, number density, gas content and cosmic star formation rate by assuming that disks form at the center of dark halos, and the modelled DLAs are selected by Monte Carlo simulation according to the distributions of halo properties. We find that DLA hosts are dominated by small galaxies and biased to extended galaxies. In terms of model results, DLAs could naturally arise in a ACDM universe from radiatively cooled gas in dark matter halos. However, model predicts a reverse correlation between metallicity and the column density when compared with observations, regardless of the proposed observational bias. We argue that this could be resulted from the model limitations, or the inadequacy of Schmidt-type star formation mode at high redshift, or/and the diversities of DLA populations.

scholarly journals Constraints on the [C ii] luminosity of a proto-globular cluster at z ∼ 6 obtained with ALMA

2020 ◽  
Vol 500 (3) ◽  
pp. 3083-3094
Author(s):  
Francesco Calura ◽  
Eros Vanzella ◽  
Stefano Carniani ◽  
Roberto Gilli ◽  
Piero Rosati ◽  
...  
Keyword(s):  
Globular Cluster ◽  
High Redshift ◽  
Formation Rate ◽  
Galaxy Cluster ◽  
Careful Analysis ◽  
Data Set ◽  
Limit Values ◽  
Stellar Feedback ◽  
Neutral Gas ◽  
The Galaxy

ABSTRACT We report on ALMA observations of D1, a system at z ∼ 6.15 with stellar mass $M_{*} \sim 10^7 \, \mathrm{M}_{\odot }$ containing globular cluster (GC) precursors, strongly magnified by the galaxy cluster MACS J0416.1-2403. Since the discovery of GC progenitors at high redshift, ours is the first attempt to probe directly the physical properties of their neutral gas through infrared observations. A careful analysis of our data set, performed with a suitable procedure designed to identify faint narrow lines and which can test various possible values for the unknown linewidth value, allowed us to identify a 4σ tentative detection of [C ii] emission with intrinsic luminosity $L_{\rm [C\, \rm {\small II}]}=(2.9 \pm 1.4)~10^6 \, {\it L}_{\odot }$, one of the lowest values ever detected at high redshift. This study offers a first insight on previously uncharted regions of the $L_{\rm [C\, \rm {\small II}]}{-}{\rm SFR}$ relation. Despite large uncertainties affecting our measure of the star formation rate, if taken at face value our estimate lies more than ∼1 dex below the values observed in local and high redshift systems. Our weak detection indicates a deficiency of [C ii] emission, possibly ascribed to various explanations, such as a low-density gas and/or a strong radiation field caused by intense stellar feedback, and a low metal content. From the non-detection in the continuum, we derive constraints on the dust mass, with 3σ upper limit values as low as ∼ a few 104 M⊙, consistent with the values measured in local metal-poor galaxies.

scholarly journals See Change: VLT spectroscopy of a sample of high-redshift Type Ia supernova host galaxies

2020 ◽  
Vol 495 (4) ◽  
pp. 3859-3880 ◽  
Author(s):  
S C Williams ◽  
I M Hook ◽  
B Hayden ◽  
J Nordin ◽  
G Aldering ◽  
...  
Keyword(s):  
Hubble Space Telescope ◽  
High Redshift ◽  
Formation Rate ◽  
Stellar Mass ◽  
Light Curves ◽  
Host Galaxy ◽  
Host Galaxies ◽  
Very Large Telescope ◽  
Type Ia ◽  
Ia Supernovae

ABSTRACT The Supernova Cosmology Project has conducted the ‘See Change’ programme, aimed at discovering and observing high-redshift (1.13 ≤ z ≤ 1.75) Type Ia supernovae (SNe Ia). We used multifilter Hubble Space Telescope (HST) observations of massive galaxy clusters with sufficient cadence to make the observed SN Ia light curves suitable for a cosmological probe of dark energy at z &gt; 0.5. This See Change sample of SNe Ia with multi-colour light curves will be the largest to date at these redshifts. As part of the See Change programme, we obtained ground-based spectroscopy of each discovered transient and/or its host galaxy. Here, we present Very Large Telescope (VLT) spectra of See Change transient host galaxies, deriving their redshifts, and host parameters such as stellar mass and star formation rate. Of the 39 See Change transients/hosts that were observed with the VLT, we successfully determined the redshift for 26, including 15 SNe Ia at z &gt; 0.97. We show that even in passive environments, it is possible to recover secure redshifts for the majority of SN hosts out to z = 1.5. We find that with typical exposure times of 3−4 h on an 8-m-class telescope we can recover ∼75 per cent of SN Ia redshifts in the range of 0.97 &lt; z &lt; 1.5. Furthermore, we show that the combination of HST photometry and VLT spectroscopy is able to provide estimates of host galaxy stellar mass that are sufficiently accurate for use in a mass-step correction in the cosmological analysis.

scholarly journals Neutral Gas and Metals From z = 4 to z = 0.5

2006 ◽  
Vol 2 (S235) ◽  
pp. 273-274
Author(s):  
Céline Péroux
Keyword(s):  
Star Formation ◽  
Gas Phase ◽  
High Redshift ◽  
Formation Rate ◽  
High Redshift Galaxies ◽  
Complementary Method ◽  
Neutral Gas ◽  
History Of ◽  
The Universe ◽  
Selection Of

AbstractA complementary method to the emission selection of high-redshift galaxies consists in the observation of absorbers along the line of sight toward a background quasar. This selection technique has a constant sensitivity at all redshifts up to z = 6 (i.e. no redshift desert) and allow to select all types of galaxies regardless of their luminosity or star formation rate. The highest column density absorbers, the Damped Lyman-α (DLAs) systems, in particular, can be used to determine the cosmic evolution of HI gas in the Universe, ΩHI, and the global metallicity in the gas phase. Since stars are known to form from HI gas, ΩHI provides an indirect tracer of the history of star formation. Recent results from several parallel VLT programmes aiming at determining the cosmological evolution of the metallicity in the neutral gas phase are presented.

scholarly journals Probing the Interstellar Medium and Stellar Environments of Long-Duration GRBs

2007 ◽  
Vol 3 (S250) ◽  
pp. 457-462
Author(s):  
Miroslava Dessauges-Zavadsky ◽  
Jason X. Prochaska ◽  
Hsiao-Wen Chen
Keyword(s):  
Interstellar Medium ◽  
Gamma Ray ◽  
High Redshift ◽  
Local Environment ◽  
Host Galaxy ◽  
Time Variability ◽  
Neutral Gas ◽  
Derived Properties ◽  
H Ii Region ◽  
Damped Lyman Alpha Systems

AbstractWe review the properties of the gas surrounding high-redshift gamma-ray bursts (GRBs) assessed through the analysis of damped Lyman-alpha systems (DLAs) identified in their afterglow spectra. These GRB-DLAs are characterized by large H I column densities with a median of N(H I) = 1021.7 cm−2, no molecular gas signatures, metallicities ranging from 1/100 to nearly solar with a median exceeding 1/10 solar, and no anomalous abundance patterns. The detection of the atomic Mg lines and the time-variability of the fine-structure lines demonstrates that the majority of the neutral gas along the GRB sightlines is located between 50 pc and a few kpc from the GRB. This implies that this gas is presumably associated with the ambient interstellar medium of the host galaxy and that the derived properties from low-ionization lines do not directly constrain the local environment of the GRB progenitor. The highly ionized gas, traced by N V lines, which could result from a pre-existing H II region produced by the GRB progenitor and neighboring OB stars, appears on the other hand to be very local to the GRB at about 10 pc, yielding a snapshot of the medium's physical conditions at this radius.

scholarly journals Neutral gas and the escape of ionizing radiation: Lessons from the low-redshift Green Peas

2019 ◽  
Vol 15 (S352) ◽  
pp. 304-308
Author(s):  
Anne Jaskot ◽  
Jed McKinney ◽  
Tara Dowd ◽  
Sally Oey ◽  
Min Yun ◽  
...  
Keyword(s):  
High Redshift ◽  
Formation Rate ◽  
Uv Spectra ◽  
Gas Content ◽  
Stellar Feedback ◽  
Neutral Gas ◽  
High Ionization ◽  
Green Pea ◽  
Open Question ◽  
Green Peas

AbstractHow galaxies reionized the universe remains an open question, but we can gain insights from the low-redshift Green Pea galaxies, one of the only known populations of Lyman continuum (LyC) emitters. Using VLA H i 21 cm observations and HST UV spectra of Green Peas, we investigate how neutral gas content and geometry influence LyC and Lyα escape. Our results suggest that LyC Emitters may have high ratios of star formation rate to H i mass. Low gas covering fractions are common among the population, but not all sightlines are optically thin. Based on the observed relationship between high ionization parameters, low metallicities, and narrow Lyα profiles, we propose that weak stellar feedback at low metallicities results in a gas geometry of dense clumps within a low-density medium, which facilitates Lyα and LyC escape. We address the implications of these results for identifying LyC emitters at high redshift with JWST and ALMA.

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