Low Redshift Research Articles

Chemical diversity of gas in distant galaxies

The chemical composition of gas in galaxies can be measured in great detail using absorption spectroscopy. By studying gas in galaxies in this way, it is possible to investigate small and faint galaxies, which are the most numerous in the universe. In particular, the chemical distribution of gas in absorbing systems gives us insight into cycles of gas in and around galaxies. In this work we study chemical enrichment within 64 damped Lyman-α absorption systems (DLAs) for redshifts in the range 1.7 < z < 4.2. We use high-resolution spectra from VLT/UVES to infer dust depletion from relative abundances of several metals. Specifically, we performed a component-by-component analysis within DLAs, and characterised variations in their chemical enrichment. Unlike hydrogen, the metal columns can be characterised according to their individual components. We used them to derive the dust depletion, which is an indicator of chemical enrichment. Our main results are as follows. Firstly, we find that some DLAs are chemically diverse within themselves (with the measure of dust depletion [Zn/Fe]fit ranging up to 0.62 dex within a single system), suggesting that the absorbing gas within these galaxies is chemically diverse. Secondly, although we do not find a clear trend of decreasing dust depletion with redshift, we do see that the most chemically enriched systems are at lower redshifts. We also observe evidence for dust-poor components at all redshifts, which may be due to the accretion of pristine gas onto galaxies. By combining the chemical and kinematic properties of the individual gas components, we observe potential signatures of infalling gas with low depletion at velocities below ∼100 km s−1, and outflows with high depletion and velocities of ∼600 km s−1. Finally, we find over-abundances of α-elements (an enhancement of ∼0.3 dex) and under-abundances of Mn in several gas components, which is likely a signature of core-collapse supernovae nucleosythesis in the ISM. We observe these effects mostly at lower levels of chemical enrichment.

Constraining the Temperature-density Relation of the Inter-galactic Medium from Analytically Modeling Lyα Forest Absorbers

The absorption by neutral hydrogen in the intergalactic medium (IGM) produces the Lyα forest in the spectra of quasars. The Lyα forest absorbers have a broad distribution of neutral hydrogen column density N H I and Doppler b parameter. The narrowest Lyα absorption lines (of lowest b) with neutral hydrogen column density above ∼1013cm−2 are dominated by thermal broadening, which can be used to constrain the thermal state of the IGM. Here we constrain the temperature-density relation of the IGM at 1.6 < z < 3.6 by using N H I and b parameters measured from 24 high-resolution and high-signal-to-noise quasar spectra and by employing an analytic model to model the N H I-dependent low-b cutoff in the b distribution. In each N H I bin, the b cutoff is estimated using two methods, one non-parametric method from computing the cumulative b distribution and a parametric method from fitting the full b distribution. We find that the IGM temperature T 0 at the mean gas density shows a peak of ∼1.5 × 104 K at z ∼ 2.7–2.9. At redshift higher than this, the index γ approximately remains constant, and it starts to increase toward lower redshifts. The evolution in both parameters is in good agreement with constraints from completely different approaches, which signals that He ii reionization completes around z ∼ 3.

Searching for the warm-hot intergalactic medium usingXMM–Newtonhigh-resolution X-ray spectra

ABSTRACTThe problem of missing baryons in the local universe remains an open question. One proposed alternative is that at low redshifts missing baryons are in the form of the warm-hot intergalactic medium (WHIM). In order to test this idea, we present a detailed analysis of X-ray high-resolution spectra of six extragalactic sources, Mrk 421, 1ES 1028+511, 1ES 1553+113, H2356−309, PKS 0558−504, and PG 1116+215, obtained with the XMM–Newton Reflection Grating Spectrometer to search for signals of WHIM and/or circumgalactic medium X-ray-absorbing gas. We fit the X-ray absorption with the IONeq model, allowing us to take into account the presence of X-ray spectral features due to the multiphase component of the local interstellar medium (ISM). An additional IONeq component is included to model the WHIM absorption, instead of the traditional Gaussian absorption line modelling. We found no statistical improvement in the fits when including such component in any of the sources, concluding that we can safely reject a successful detection of WHIM absorbers towards these lines of sights. Our simulation shows that the presence of the multiphase ISM absorption features prevents the detection of low-redshift WHIM absorption features in the &amp;gt;17 Å spectral region for moderate exposures using high-resolution spectra.

Priorities in gravitational waveforms for future space-borne detectors: vacuum accuracy or environment?

ABSTRACT In preparation for future space-borne gravitational-wave (GW) detectors, should the modelling effort focus on high-precision vacuum templates or on the astrophysical environment of the sources? We perform a systematic comparison of the phase contributions caused by (1) known environmental effects in both gaseous and stellar matter backgrounds, or (2) high-order post-Newtonian (PN) terms in the evolution of mHz GW sources during the inspiral stage of massive binaries. We use the accuracy of currently available analytical waveform models as a benchmark value, finding the following trends: the largest unmodelled phase contributions are likely environmental rather than PN for binaries lighter than ∼107/(1 + z)2 M⊙, where z is the redshift. Binaries heavier than ∼108/(1 + z) M⊙ do not require more accurate inspiral waveforms due to low signal-to-noise ratios (SNRs). For high-SNR sources, environmental phase contributions are relevant at low redshift, while high-order vacuum templates are required at z ≳ 4. Led by these findings, we argue that including environmental effects in waveform models should be prioritized in order to maximize the science yield of future mHz detectors.

Probing a polymerized black hole with the frequency shifts of photons

As is well-known, black hole plays an important role in probing the quantum effects of gravity in the strong-field regime. In this paper, we focus on a polymerized black hole and investigate the quantum effects on the redshift, blueshift and gravitational redshift of photons emitted by massive particles revolving around this black hole. With a general relativistic formalism, we obtain two elegant and concise expressions for the mass of the black hole and the quantum parameter in terms of few direct observables, and find that all the frequency shifts of photons decrease with the quantum parameter. By expanding the total frequency shift for large orbit of the emitter, low peculiar redshift, and small azimuthal angle, we find that the leading contributions to the frequency shift are originated from the kinematic shift and peculiar shift, and the quantum effects make a negligible contribution. In addition, we study the effects of the plasma on the redshift/blueshift for the first time, and conclude that the presence of plasma results in the decrease of the redshift/blueshift.

Probing the rapid formation of black holes and their Galaxy hosts in QSOs

ABSTRACTUsing the modelling code x-cigale, we reproduced the spectral energy distributions (SEDs) of 1359 SDSS quasi-stellar objects (QSOs) within the redshift range 0 &amp;lt; z &amp;lt; 4, for which we have NIR/MIR fluxes with the highest quality and spectral data characterizing their supermassive black hole (SMBHs). Consistent with a rapid formation of the host galaxies, the star formation histories (SFHs) have small e-folding, at most 750 Myr using an SFH function for spiral or 1000 Myr using one for elliptical. Above z ∼ 1.6, the two solutions are degenerate, the SEDs being dominated by the active galactic nucleus (AGN) continuum and high star formation rates (SFRs), typical of starburst galaxies, while at lower redshifts the starburst nature of the host, independent from its morphology, is better reproduced by a spiral SFH. In general, the SFR increases with the redshift, the mass of the bulge, the AGN luminosity, and Eddington ratio, suggesting there is no evidence of AGN quenching of star formation. Comparing the specific BH accretion rate (BHAR) with specific SFR, all the QSOs at any redshift trace a linear sequence below the Eddington luminosity, in parallel and above the one-to-one relation, implying that QSOs are in a special phase of evolution during which the growth in mass of their SMBH is more rapid than the growth in mass of their galaxy hosts. This particular phase is consistent with a scenario where the galaxy hosts of QSOs in the past grew in mass more rapidly than their SMBHs, suggesting that a high star formation efficiency during their formation was responsible in limiting their masses.

Searching for bounce signature in the early universe from current and future large-scale structure surveys

ABSTRACT The bounce scenario has been an interesting research topic in cosmology, due to its ability to resolve both the singularity problem and the trans-Planckian issue, which are left from the standard inflationary theory. In previous works, we considered an inflationary cosmology with a preceding non-singular bounce and found that this model could suppress the primordial power spectrum at large scales and leave the signature on the angular power spectra of cosmic microwave background (CMB). In this work, we extend this analysis to the large-scale structure (LSS) measurements. Firstly, we consider the angular power spectrum of current LSS data sets, such as the 2MPZ, SDSS-DR12, and DES Y3 galaxy surveys at low redshifts and the NVSS radio survey at high redshifts, and do not obtain good constraint on the model parameters, due to the precision limitation at large scales. When we include the Planck CMB measurements, the constraints become a little bit better: the amplitude Ar = 0.8 ± 0.2 and the slope ${\rm log_{10}}(k_B)=-2.6^{+0.3}_{-1.0}$ at 68 per cent confidence level. In order to evaluate the constraining ability of future LSS surveys, we forecast the clustering measurements, such as the galaxy angular power spectrum and the galaxy lensing shear power spectrum, based on the China Space Station Telescope photometric survey. We find that the standard deviations of model parameters will be significantly shrunk, ΔAr = 0.1 and Δlog10(kB) = 0.1, due to the high precision measurements. Finally, we consider the bounce feature and the primordial non-Gaussianity from inflation theory simultaneously and find that in the bounce inflationary model the limit on fNL will be weaker than that obtained in the standard inflationary model, due to the strong degeneracy among parameters.

Offset between X-ray and optical centers in clusters of galaxies: Connecting eROSITA data with simulations

Context.The characterization of the dynamical state of galaxy clusters is key to studying their evolution, evaluating their selection, and using them as a cosmological probe. In this context, the offsets between different definitions of the center have been used to estimate the cluster disturbance.Aims.Our goal is to study the distribution of the offset between the X-ray and optical centers in clusters of galaxies. We study the offset for clusters detected by the extended ROentgen Survey with an Imaging Telescope Array (eROSITA) on board the Spectrum-Roentgen-Gamma (SRG) observatory. We aim to connect observations to predictions by hydrodynamical simulations andN-body models. We assess the astrophysical effects affecting the displacements.Methods.We measured the offset for clusters observed in the eROSITA Final Equatorial-Depth Survey (eFEDS) and the first eROSITA all-sky survey (eRASS1). We focus on a subsample of 87 massive eFEDS clusters at low redshift, withM500c&gt; 1×1014 M⊙and 0.15 &lt;z&lt; 0.4. We compared the displacements in such sample to those predicted by the TNG and the Magneticum simulations. We additionally link the observations to the offset parameterXoffmeasured for dark matter halos inN-body simulations, using the hydrodynamical simulations as a bridge.Results.We find that, on average, the eFEDS clusters show a smaller offset compared to eRASS1 because the latter contains a larger fraction of massive and disturbed structures. We measured an average offset of ΔX−O = 76.3−27.1+30.1kpc, when focusing on the subsample of 87 eFEDS clusters. This is in agreement with the predictions from TNG and Magneticum, and the distribution ofXofffrom dark matter only (DMO) simulations. However, the tails of the distributions are different. Using ΔX − Oto classify relaxed and disturbed clusters, we measured a relaxed fraction of 31% in the eFEDS subsample. Finally, we found a correlation between the offset measured on hydrodynamical simulations andXoffmeasured on their parent dark-matter-only run and we calibrated the relation between them.Conclusions.We conclude that there is good agreement between the offsets measured in eROSITA data and the predictions from simulations. Baryonic effects cause a decrement (increment) in the low (high) offset regime compared to theXoffdistribution from dark matter-only simulations. The offset–Xoffrelation provides an accurate prediction of the trueXoffdistribution in Magneticum and TNG. It allows for the offsets to be introduced in a cosmological context with a new method in order to marginalize over selection effects related to the cluster dynamical state.

The Kormendy relation of early-type galaxies as a function of wavelength in Abell S1063, MACS J0416.1-2403, and MACS J1149.5+2223

Context. The wavelength dependence of the projection of the fundamental plane along the velocity dispersion axis, namely the Kormendy relation, is well characterised at low redshift but poorly studied at intermediate redshifts. The Kormendy relation provides information on the evolution of the population of early-type galaxies (ETGs). Therefore, by studying it, we may shed light on the assembly processes of these objects and their size evolution. As studies at different redshifts are generally conducted in different rest-frame wavebands, it is important to investigate whether the Kormendy relation is dependent on wavelength. Knowledge of such a dependence is fundamental to correctly interpreting the conclusions we might draw from these studies. Aims. We analyse the Kormendy relations of the three Hubble Frontier Fields clusters, Abell S1063 at z = 0.348, MACS J0416.1-2403 at z = 0.396, and MACS J1149.5+2223 at z = 0.542, as a function of wavelength. This is the first time the Kormendy relation of ETGs has been explored consistently over such a large range of wavelengths at intermediate redshifts. Methods. We exploit very deep Hubble Space Telescope photometry, ranging from the observed B-band to the H-band, and VLT/MUSE integral field spectroscopy. We improve the structural parameter estimation we performed in a previous work by means of a newly developed PYTHON package called MORPHOFIT. Results. With its use on cluster ETGs, we find that the Kormendy relation slopes increase smoothly with wavelength from the optical to the near-infrared (NIR) bands in all three clusters, with the intercepts becoming fainter at lower redshifts due to the passive ageing of the ETG stellar populations. The slope trend is consistent with previous findings at lower redshifts. Conclusions. The slope increase with wavelength implies that smaller ETGs are more centrally concentrated than larger ETGs in the NIR with respect to the optical regime. As different bands probe different stellar populations in galaxies, the slope increase also implies that smaller ETGs have stronger internal gradients with respect to larger ETGs.

Spatially Resolved Stellar Populations of 0.3 < z < 6.0 Galaxies in WHL 0137–08 and MACS 0647+70 Clusters as Revealed by JWST: How Do Galaxies Grow and Quench over Cosmic Time?

We study the spatially resolved stellar populations of 444 galaxies at 0.3 < z < 6.0 in two clusters (WHL 0137–08 and MACS 0647+70) and a blank field, combining imaging data from the Hubble Space Telescope and JWST to perform spatially resolved spectral energy distribution (SED) modeling using piXedfit. The high spatial resolution of the imaging data combined with magnification from gravitational lensing in the cluster fields allows us to resolve a large fraction of our galaxies (109) to subkiloparsec scales. At redshifts around cosmic noon and higher (2.5 ≲ z ≲ 6.0), we find mass-doubling times to be independent of radius, inferred from flat specific star formation rate (sSFR) radial profiles and similarities between the half-mass and half-SFR radii. At lower redshifts (1.5 ≲ z ≲ 2.5), a significant fraction of our star-forming galaxies shows evidence for nuclear starbursts, inferred from a centrally elevated sSFR and a much smaller half-SFR radius compared to the half-mass radius. At later epochs, we find more galaxies suppress star formation in their centers but are still actively forming stars in the disk. Overall, these trends point toward a picture of inside-out galaxy growth consistent with theoretical models and simulations. We also observe a tight relationship between the central mass surface density and global stellar mass with ∼0.38 dex scatter. Our analysis demonstrates the potential of spatially resolved SED analysis with JWST data. Future analysis with larger samples will be able to further explore the assembly of galaxy mass and the growth of their structures.

The Missing Link between Black Holes in High-mass X-Ray Binaries and Gravitational-wave Sources: Observational Selection Effects

There are few observed high-mass X-ray binaries (HMXBs) that harbor massive black holes (BHs), and none are likely to result in a binary black hole (BBH) that merges within a Hubble time; however, we know that massive merging BBHs exist from gravitational-wave (GW) observations. We investigate the role that X-ray and GW observational selection effects play in determining the properties of their respective detected binary populations. We find that, as a result of selection effects, detectable HMXBs and detectable BBHs form at different redshifts and metallicities, with detectable HMXBs forming at much lower redshifts and higher metallicities than detectable BBHs. We also find disparities in the mass distributions of these populations, with detectable merging BBH progenitors pulling to higher component masses relative to the full detectable HMXB population. Fewer than 3% of detectable HMXBs host BHs >35M ⊙ in our simulated populations. Furthermore, we find the probability that a detectable HMXB will merge as a BBH system within a Hubble time is ≃0.6%. Thus, it is unsurprising that no currently observed HMXB is predicted to form a merging BBH with high probability.

O iii] 5007 Å Emission Line Width as a Surrogate for σ ∗ in Type 1 AGNs?

We present a study of the relation between the [O iii] 5007 Å emission line width (σ [OIII]) and stellar velocity dispersion (σ *), utilizing a sample of 740 type 1 active galactic nuclei (AGNs) with high-quality spectra at redshift z < 1.0. We find the broad correlation between the core component of the [O iii] emission line width () and σ * with a scatter of 0.11 dex for the low redshift (z < 0.1) sample; for redshift (0.3 < z < 1.0) AGNs, the scatter is larger, being 0.16 dex. We also find that the Eddington ratio (L bol/L Edd) may play an important role in the discrepancies between and σ *. As the L bol/L Edd increases, tends to be larger than σ *. By classifying our local sample with different minor-to-major axis ratios, we find that σ * is larger than for those edge-on spiral galaxies. In addition, we also find that the effects of outflow strength properties such as maximum outflow velocity () and the broader component of the [O iii] emission line width and line shift (σ [OIII,out] and V [OIII,out]) may play a major role in the discrepancies between and σ *. The discrepancies between and σ * are larger when , V [OIII,out], and σ [OIII,out] increase. Our results show that the outflow strengths may have significant effects on the differences between narrow-line region gas and stellar kinematics in AGNs. We suggest that caution should be taken when using as a surrogate for σ *. In addition, the substitute of for σ * could be used only for low luminosity AGNs.

VST-GAME: Galaxy assembly as a function of mass and environment with VST

Context. Observational studies have widely demonstrated that galaxy physical properties are strongly affected by the surrounding environment. On one side, gas inflows provide galaxies with new fuel for star formation. On the other side, the high temperatures and densities of the medium are expected to induce quenching in the star formation. Observations of large structures, in particular filaments at the cluster outskirts (r &gt; 2r200), are currently limited to the low redshift Universe. Deep and wide photometric data, better if combined with spectroscopic redshifts, are required to explore several scenarios on galaxy evolution at intermediate redshift. Aims. We present a multi-band dataset for the cluster MACS J0416.1-2403 (z = 0.397), observed in the context of the Galaxy Assembly as a function of Mass and Environment with the VLT Survey Telescope (VST-GAME) survey. The project is aimed at gathering deep (r &lt; 24.4) and wide (approx. 20x20 Mpc2) observations at optical (u, ɡ, r, i, VST) wavelengths for six massive galaxy clusters at 0.2 &lt; z &lt; 0.6, complemented with near-infrared data (Y, J, Ks, VISTA, ESO public survey GCAV). The aim is to investigate galaxy evolution in a wide range of stellar masses and environmental conditions. This work describes the photometric analysis of the cluster and the definition of a density field, which will be a key ingredient for further studies on galaxy properties in the cluster outskirts. Methods. We extracted sources paying particular attention to recovering the faintest ones and simultaneously flagging point sources and sources with photometry affected by artifacts in the images. We combined all the extractions in a multiband catalog that is used to derive photometric redshifts through spectral energy distribution (SED) fitting. We then defined cluster memberships up to 5r200 from the cluster core and measure the density field, comparing galaxy properties in different environments. Results. We find that the ɡ – r colors show bimodal behaviors in all the environments, but the peak of the distribution of red galaxies shifts toward redder colors with increasing density, and the fraction of galaxies in the blue cloud increases with decreasing density. We also found three overdense regions in the cluster outskirts at r ~ 5r200. Galaxies in these structures have mean densities and luminosities similar to those of the cluster core. The color of galaxies suggests the presence of evolved galaxy populations, an insight into preprocessing phenomena over these substructures. We release the multiband catalog, down to the completeness limit of r &lt; 24.4 mag.

The Size-Dependent Photonic Characteristics of Colloidal-Quantum-Dot-Enhanced Micro-LEDs

Colloidal CdSe/ZnS quantum dots (QD) enhanced micro-LEDs with sizes varying from 10 to 100 μm were fabricated and measured. The direct photolithography of quantum-dot-contained photoresists can place this color conversion layer on the top of an InGaN-based micro-LED and have a high throughput and semiconductor-grade precision. Both the uncoated and coated devices were characterized, and we determined that much higher brightness of a QD-enhanced micro-LED under the same current level was observed when compared to its AlGaInP counterpart. The color stability across the device sizes and injection currents were also examined. QD LEDs show low redshift of emission wavelength, which was recorded within 1 nm in some devices, with increasing current density from 1 to 300 A/cm2. On the other hand, the light conversion efficiency (LCE) of QD-enhanced micro-LEDs was detected to decrease under the high current density or when the device is small. The angular intensities of QD-enhanced micro-LEDs were measured and compared with blue devices. With the help of the black matrix and omnidirectional light emission of colloidal QD, we observed that the angular intensities of the red and blue colors are close to Lambertian distribution, which can lead to a low color shift in all angles. From our study, the QD-enhanced micro-LEDs can effectively increase the brightness, the color stability, and the angular color match, and thus play a promising role in future micro-display technology.

The SAMI survey: evidence for dynamical coupling of ionized gas and young stellar populations

ABSTRACT We explore local and global dynamical differences between the kinematics of ionized gas and stars in a sample of galaxies from Data Release 3 of the SAMI Galaxy Survey. We find better agreement between local (i.e. comparing on a spaxel-to-spaxel basis) velocities and dispersion of gas and stars in younger systems as with previous work on the asymmetric drift in galaxies, suggesting that the dynamics of stars and ionized gas are initially coupled. The intrinsic scatter around the velocity and dispersion relations increases with increasing stellar age and mass, suggesting that subsequent mechanisms, such as internal processes, divergent star formation, and assembly histories, also play a role in setting and altering the dynamics of galaxies. The global (flux-weighted) dynamical support of older galaxies is hotter than in younger systems. We find that the ionized gas in galaxies is almost always dynamically colder than the stars with a steeper velocity gradient. In absolute terms, the local difference in velocity dispersion is more pronounced than the local difference in velocity, possibly reflecting inherent differences in the impact of turbulence, inflow and/or feedback on gas compared to stars. We suggest how these findings may be taken into account when comparing high and low redshift galaxy samples to infer dynamical evolution.

Position-dependent correlation function of weak-lensing convergence

We provide a systematic study of the position-dependent correlation function in weak-lensing convergence maps and its relation to the squeezed limit of the three-point correlation function (3PCF) using state-of-the-art numerical simulations. We relate the position-dependent correlation function to its harmonic counterpart, i.e., the position-dependent power spectrum or equivalently the integrated bispectrum (IB). We use a recently proposed improved fitting function, BiHalofit, for the bispectrum to compute the theoretical predictions as a function of source redshifts. In addition to low redshift results (${z}_{s}=1.0--2.0$) we also provide results for maps inferred from lensing of the cosmic microwave background (CMB), i.e., ${z}_{s}=1100$. We include a Euclid-type realistic survey mask and noise. In agreement with the recent studies on the position-dependent power spectrum, we find that the results from simulations are consistent with the theoretical expectations when appropriate corrections are included. Performing a rough estimate, we find that the signal-to-noise (S/N) for the detection of position-dependent correlation function from Euclid-type mask with ${f}_{\mathrm{sky}}=0.35$, can range between 6--12 depending on the value of the intrinsic ellipticity distribution parameter ${\ensuremath{\sigma}}_{\ensuremath{\epsilon}}=0.3--1.0$. For reconstructed $\ensuremath{\kappa}$ maps using an ideal CMB survey the $\mathrm{S}/\mathrm{N}\ensuremath{\approx}1.8$. We also found that a 10% deviation in ${\ensuremath{\sigma}}_{8}$ can be detected using IB for the optimistic case of ${\ensuremath{\sigma}}_{\ensuremath{\epsilon}}=0.3$ with a $\mathrm{S}/\mathrm{N}\ensuremath{\approx}5$. The S/N for such detection in case of ${\mathrm{\ensuremath{\Omega}}}_{M}$ is lower.

A Better Reconciliation of Hubble Tension in the Dark Energy Scalar Field

Hubble tension between the local measurement and global observation has been a key problem in cosmology. In this paper, we consider the quintessence scalar field, phantom field and quintom field as the dark energy to reconcile this problem. Different from most previous work, we start from the dimensionless equation of state (w) of dark energy, not a parameterization of potential. The combined analysis shows that observational data sets favor Hubble constant , which can reconcile Hubble tension within 1.20σ. We also perform a Bayes factor analysis using the MCEvidence code, and confirm that the phantom scalar field is still the most effective. To investigate the reason of Hubble tension, we analyze the density parameter. The comparison shows that the scalar fields provide a slightly larger Ω b h 2 and smaller Ω c h 2 than the standard ΛCDM model. We finally analyze a possible reason of Hubble tension from the kinematic acceleration . We find an interesting physical phenomenon. The acceleration in these scalar fields are similar as the ΛCDM model at about redshift z > 0.5. However, they increase and deviate from each other at low redshift, especially in the near future. Only the in phantom scalar field will decrease in the future.

The Bulk Flow Motion and the Hubble-Lemaître Law in the Local Universe with the ALFALFA Survey

The knowledge of the main features of the bulk flow in the Local Universe is important for a better determination of the relative motions there, an information that would contribute to a precise calculation of the Hubble-Lemaître law at very low redshifts. We study how to obtain the Hubble-Lemaître law in two sky regions using the catalogue of HI sources of the ALFALFA survey, with data $$cz_{\odot } < 6000$$ km/s. Our methodology aims to compute $$H_0$$ in two regions — located in opposite galactic hemispheres — mapped by the ALFALFA survey, and look for dependence with distance, direction, and also test for reference frame changes. We calculate the Hubble constant, in the Cosmic Microwave Background reference frame, in opposite galactic hemispheres: $$H_0^N = 70.87 \pm 2.38$$ and $$H_0^S = 66.07 \pm 3.02$$ , which allows us to measure the bulk flow velocity $$V_{\mathrm {BF}} = 401.06 \pm 150.55$$ km/s at the effective distance $$31.3 \pm 6.26$$ Mpc, a novel result found analyzing the ALFALFA data at low redshift. We confirm the influence of the bulk flow on the structures of the Local Universe which manifests through a dipolar behavior of the Hubble constant in opposite hemispheres.

Spectroscopy of CASSOWARY gravitationally lensed galaxies in SDSS: characterization of an extremely bright reionization-era analogue at z = 1.42

ABSTRACT We present new observations of 16 bright (r = 19–21) gravitationally lensed galaxies at z ≃ 1–3 selected from the CASSOWARY survey. Included in our sample is the z = 1.42 galaxy CSWA-141, one of the brightest known reionization-era analogues at high redshift (g = 20.5), with a large specific star formation rate (31.2 Gyr−1) and an [O iii]+H β equivalent width (EW[O iii] + H β = 730 Å) that is nearly identical to the average value expected at z ≃ 7–8. In this paper, we investigate the rest-frame UV nebular line emission in our sample with the goal of understanding the factors that regulate strong C iii] emission. Although most of the sources in our sample show weak UV line emission, we find elevated C iii] in the spectrum of CSWA-141 (EWC iii] = 4.6 ± 1.9 Å) together with detections of other prominent emission lines (O iii], Si iii], Fe ii⋆, Mg ii). We compare the rest-optical line properties of high-redshift galaxies with strong and weak C iii] emission, and find that systems with the strongest UV line emission tend to have young stellar populations and nebular gas that is moderately metal-poor and highly ionized, consistent with trends seen at low and high redshift. The brightness of CSWA-141 enables detailed investigation of the extreme emission line galaxies which become common at z &amp;gt; 6. We find that gas traced by the C iii] doublet likely probes higher densities than that traced by [O ii] and [S ii]. Characterization of the spectrally resolved Mg ii emission line and several low-ionization absorption lines suggests neutral gas around the young stars is likely optically thin, potentially facilitating the escape of ionizing radiation.

EAGLE-like simulation models do not solve the entropy core problem in groups and clusters of galaxies

ABSTRACTRecent high-resolution cosmological hydrodynamic simulations run with a variety of codes systematically predict large amounts of entropy in the intra-cluster medium at low redshift, leading to flat entropy profiles and a suppressed cool-core population. This prediction is at odds with X-ray observations of groups and clusters. We use a new implementation of the EAGLE galaxy formation model to investigate the sensitivity of the central entropy and the shape of the profiles to changes in the sub-grid model applied to a suite of zoom-in cosmological simulations of a group of mass M500 = 8.8 × 1012 M⊙ and a cluster of mass 2.9 × 1014 M⊙. Using our reference model, calibrated to match the stellar mass function of field galaxies, we confirm that our simulated groups and clusters contain hot gas with too high entropy in their cores. Additional simulations run without artificial conduction, metal cooling or active galactic nuclei (AGN) feedback produce lower entropy levels but still fail to reproduce observed profiles. Conversely, the two objects run without supernova feedback show a significant entropy increase which can be attributed to excessive cooling and star formation. Varying the AGN heating temperature does not greatly affect the profile shape, but only the overall normalization. Finally, we compared runs with four AGN heating schemes and obtained similar profiles, with the exception of bipolar AGN heating, which produces a higher and more uniform entropy distribution. Our study leaves open the question of whether the entropy core problem in simulations, and particularly the lack of power-law cool-core profiles, arise from incorrect physical assumptions, missing physical processes, or insufficient numerical resolution.