We analyse a sample of 16 absorption systems intrinsic to long-duration gamma-ray burst (GRB) host galaxies at z ≳ 2 for which the metallicities are known. We compare the relation between the ...metallicity and cold gas velocity width for this sample to that of the QSO-DLAs (quasi-stellar object–damped Lyman α), and find complete agreement. We then compare the redshift evolution of the mass–metallicity relation of our sample to that of QSO-DLAs and find that also GRB hosts favour a late onset of this evolution, around a redshift of ≈2.6. We compute predicted stellar masses for the GRB host galaxies using the prescription determined from QSO-DLA samples and compare the measured stellar masses for the four hosts where stellar masses have been determined from spectral energy distribution (SED) fits. We find excellent agreement and conclude that, on basis of all available data and tests, long-duration GRB-DLA hosts and intervening QSO-DLAs are consistent with being drawn from the same underlying population. GRB host galaxies and QSO-DLAs are found to have different impact parameter distributions and we briefly discuss how this may affect statistical samples. The impact parameter distribution has two effects. First, any metallicity gradient will shift the measured metallicity away from the metallicity in the centre of the galaxy, and secondly, the path of the sightline through different parts of the potential well of the dark matter halo will cause different velocity fields to be sampled. We report evidence suggesting that this second effect may have been detected.
Context.
Classical Cepheids are primary distance indicators and a crucial stepping stone in determining the present-day value of the Hubble constant
H
0
to the precision and accuracy required to ...constrain apparent deviations from the ΛCDM Concordance Cosmological Model.
Aims.
We measured the iron and oxygen abundances of a statistically significant sample of 89 Cepheids in the Large Magellanic Cloud (LMC), one of the anchors of the local distance scale, quadrupling the prior sample and including 68 of the 70 Cepheids used to constrain
H
0
by the SH0ES program. The goal is to constrain the extent to which the luminosity of Cepheids is influenced by their chemical composition, which is an important contributor to the uncertainty on the determination of the Hubble constant itself and a critical factor in the internal consistency of the distance ladder.
Methods.
We derived stellar parameters and chemical abundances from a self-consistent spectroscopic analysis based on equivalent width of absorption lines.
Results.
The iron distribution of Cepheids in the LMC can be very accurately described by a single Gaussian with a mean Fe/H = −0.409 ± 0.003 dex and
σ
= 0.076 ± 0.003 dex. We estimate a systematic uncertainty on the absolute mean values of 0.1 dex. The width of the distribution is fully compatible with the measurement error and supports the low dispersion of 0.069 mag seen in the near-infrared
Hubble
Space Telescope LMC period–luminosity relation. The uniformity of the abundance has the important consequence that the LMC Cepheids alone cannot provide any meaningful constraint on the dependence of the Cepheid period–luminosity relation on chemical composition at any wavelength. This revises a prior claim based on a small sample of 22 LMC Cepheids that there was little dependence (or uncertainty) between composition and near-infrared luminosity, a conclusion which would produce an apparent conflict between anchors of the distance ladder with different mean abundance. The chemical homogeneity of the LMC Cepheid population makes it an ideal environment in which to calibrate the metallicity dependence between the more metal-poor Small Magellanic Cloud and metal-rich Milky Way and NGC 4258.
ESO’s two FOcal Reducer and low-dispersion Spectrographs (FORS) are the primary optical imaging instruments for the VLT. They are not direct-imaging instruments, as there are several optical elements ...in the light path. In particular, both instruments are attached to a field rotator. Obtaining truly photometric data with such instruments presents a significant challenge. In this article, we investigate in detail twilight flats taken with the FORS instruments. We find that a large fraction of the structure seen in these flat fields rotates with the field rotator. We discuss in detail the methods we use to determine the cause of this effect. The effect was tracked down to be caused by the Linear Atmospheric Dispersion Corrector (LADC). The results are thus of special interest for designers of instruments with LADCs and developers of calibration plans and pipelines for such instruments. The methods described here to find and correct it, however, are of interest also for other instruments using a field rotator. If not properly corrected, this structure in the flat field may degrade the photometric accuracy of imaging observations taken with the FORS instruments by adding a systematic error of up to 4% for broadband filters. We discuss several strategies to obtain photometric images in the presence of rotating flat-field pattern.
The Arecibo Ultra-Deep Survey Xi, Hongwei; Staveley-Smith, Lister; For, Bi-Qing ...
Monthly notices of the Royal Astronomical Society,
03/2021, Letnik:
501, Številka:
3
Journal Article
Recenzirano
Odprti dostop
ABSTRACT
The Arecibo Ultra-Deep Survey (AUDS) is a blind H i survey aimed at detecting galaxies beyond the local Universe in the 21-cm emission line of neutral hydrogen (H i). The Arecibo L-band Feed ...Array (ALFA) was used to image an area of 1.35 deg2 to a redshift depth of 0.16, using a total on-source integration time of over 700 h. The long integration time and small observation area makes it one of the most sensitive H i surveys, with a noise level of ∼75 μJy per 21.4 kHz (equivalent to 4.5 km s−1 at redshift z = 0). We detect 247 galaxies in the survey, more than doubling the number already detected in AUDS60. The mass range of detected galaxies is $\log (M_{\rm H\,{\small I}}~h_{70}^{-2}\, {\rm M}_\odot ) = 6.32\!-\!10.76$. A modified maximum likelihood method is employed to construct an H i mass function (HIMF). The best fitting Schechter parameters are low-mass slope α = −1.37 ± 0.05, characteristic mass $\log (M^*~h_{70}^{-2}\, {\rm M}_\odot ) = 10.15 \pm 0.09$, and density $\Phi _* = (2.41 \pm 0.57) \times 10^{-3} h_{70}^3$ Mpc−3 dex−1. The sample was divided into low- and high-redshift bins to investigate the evolution of the HIMF. No change in low-mass slope α was measured, but an increased characteristic mass M*, was noted in the higher redshift sample. Using Sloan Digital Sky Survey data to define relative galaxy number density, the dependence of the HIMF with environment was also investigated in the two AUDS regions. We find no significant variation in α or M*. In the surveyed region, we measured a cosmic H i density $\Omega _{\rm H\,{\small I}} = (3.55 \pm 0.30) \times 10^{-4}\, h_{70}^{-1}$. There appears to be no evolutionary trend in $\Omega _{\rm H\,{\small I}}$ above 2σ significance between redshifts of 0 and 0.16.
ABSTRACT
We investigate how damped Lyman α absorbers (DLAs) at $z$ ∼ 2 − 3, detected in large optical spectroscopic surveys of quasars, trace the population of star-forming galaxies. Building on ...previous results, we construct a model based on observed and physically motivated scaling relations in order to reproduce the bivariate distributions of metallicity, Z, and H i column density, $N_{\rm H\, \rm{\small {I}}}$. Furthermore, the observed impact parameters for galaxies associated to DLAs are in agreement with the model predictions. The model strongly favours a metallicity gradient, which scales with the luminosity of the host galaxy, with a value of γ* = −0.019 ± 0.008 dex kpc−1 for L* galaxies that gets steeper for fainter galaxies. We find that DLAs trace galaxies over a wide range of galaxy luminosities, however, the bulk of the DLA cross-section arises in galaxies with L ∼ 0.1 L* at $z$ ∼ 2.5 consistent with numerical simulations.
We investigate how damped Lyman-α absorbers (DLAs) at z ∼ 2 − 3, detected in large optical spectroscopic surveys of quasars, trace the population of star-forming galaxies. Building on previous ...results, we construct a model based on observed and physically motivated scaling relations in order to reproduce the bivariate distributions of metallicity, Z, and H column density , N H. Furthermore, the observed impact parameters for galaxies associated to DLAs are in agreement with the model predictions. The model strongly favours a metallicity gradient, which scales with the luminosity of the host galaxy, with a value of γ * = −0.019 ± 0.008 dex kpc −1 for L * galaxies that gets steeper for fainter galaxies. We find that DLAs trace galaxies over a wide range of galaxy luminosities, however, the bulk of the DLA cross-section arises in galaxies with L ∼ 0.1 L * at z ∼ 2.5 consistent with numerical simulations.
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