Subscribe to the gold package and get unlimited access to Shamra Academy
Register a new userCarbon stars as standard candles: II. The median J magnitude as a distance indicator
133
0
0.0
(
0
)
Ask ChatGPT about the research
No Arabic abstract
We introduce a new distance determination method using carbon-rich asymptotic giant branch stars (CS) as standard candles and the Large and Small Magellanic Clouds (LMC and SMC) as the fundamental calibrators. We select the samples of CS from the ($(J-K_{s})_0$, $J_0$) colour-magnitude diagrams, as, in this combination of filters, CS are bright and easy to identify. We fit the CS $J$-band luminosity functions using a Lorentzian distribution modified to allow the distribution to be asymmetric. We use the parameters of the best-fit distribution to determine if the CS luminosity function of a given galaxy resembles that of the LMC or SMC. Based on this resemblance, we use either the LMC or SMC as the calibrator and estimate the distance to the given galaxy using the median $J$ magnitude ($overline{J}$) of the CS samples. We apply this new method to the two Local Group galaxies NGC 6822 and IC 1613. We find that NGC 6822 has an LMC-like CS luminosity function while IC 1613 is more SMC-like. Using the values for the median absolute $J$ magnitude for the LMC and SMC found in Paper I we find a distance modulus of $mu_{0}=23.54pm0.03$ (stat) for NGC 6822 and $mu_{0}=24.34pm0.05$ (stat) for IC 1613.
rate research
Read More
Despite vast improvements in the measurement of the cosmological parameters, the nature of dark energy and an accurate value of the Hubble constant (H$_0$) in the Hubble-Lema^itre law remain unknown. To break the current impasse, it is necessary to develop as many independent techniques as possible, such as the use of Type II supernovae (SNe II). The goal of this paper is to demonstrate the utility of SNe II for deriving accurate extragalactic distances, which will be an asset for the next generation of telescopes where more-distant SNe II will be discovered. More specifically, we present a sample from the Dark Energy Survey Supernova Program (DES-SN) consisting of 15 SNe II with photometric and spectroscopic information spanning a redshift range up to 0.35. Combining our DES SNe with publicly available samples, and using the standard candle method (SCM), we construct the largest available Hubble diagram with SNe II in the Hubble flow (70 SNe II) and find an observed dispersion of 0.27 mag. We demonstrate that adding a colour term to the SN II standardisation does not reduce the scatter in the Hubble diagram. Although SNe II are viable as distance indicators, this work points out important issues for improving their utility as independent extragalactic beacons: find new correlations, define a more standard subclass of SNe II, construct new SN II templates, and dedicate more observing time to high-redshift SNe II. Finally, for the first time, we perform simulations to estimate the redshift-dependent distance-modulus bias due to selection effects.
We present a new catalogue of ~2,400 optically selected quasars with spectroscopic redshifts and X-ray observations from either Chandra or XMM-Newton. The sample can be used to investigate the non-linear relation between the UV and X-ray luminosity of quasars, and to build a Hubble diagram up to redshift z~7.5. We selected sources that are neither reddened by dust in the optical/UV nor obscured by gas in the X-rays, and whose X-ray fluxes are free from flux-limit related biases. After checking for any possible systematics, we confirm, in agreement with our previous works, that (i) the X-ray to UV relation provides distance estimates matching those from supernovae up to z~1.5, and (ii) its slope shows no redshift evolution up to z~5. We provide a full description of the methodology for testing cosmological models, further supporting a trend whereby the Hubble diagram of quasars is well reproduced by the standard flat $Lambda$CDM model up to z~1.5-2, but strong deviations emerge at higher redshifts. Since we have minimized all non-negligible systematic effects, and proven the stability of the $L_{rm X}-L_{rm UV}$ relation at high redshifts, we conclude that an evolution of the expansion rate of the Universe should be considered as a possible explanation for the observed deviation, rather than some systematic (redshift-dependent) effect associated with high-redshift quasars.
Gamma-ray bursts (GRBs) are the most luminous explosions and can be detectable out to the edge of Universe. It has long been thought they can extend the Hubble diagram to very high redshifts. Several correlations between temporal or spectral properties and GRB luminosities have been proposed to make GRBs cosmological tools. However, those correlations cannot be properly standardized. In this paper, we select a long GRB sample with X-ray plateau phases produced by electromagnetic dipole emissions from central new-born magnetars. A tight correlation is found between the plateau luminosity and the end time of the plateau in X-ray afterglows out to the redshift $z=5.91$. We standardize these long GRBs X-ray light curves to a universal behavior by this correlation for the first time, with a luminosity dispersion of 0.5 dex. The derived distance-redshift relation of GRBs is in agreement with the standard $Lambda$CDM model both at low and high redshifts. The evidence of accelerating universe from this GRB sample is $3sigma$, which is the highest statistical significance from GRBs to date.
We revisit the observed correlation between Hbeta and FeII velocities for Type II-P supernovae (SNe~II-P) using 28 optical spectra of 13 SNe II-P and demonstrate that it is well modeled by a linear relation with a dispersion of about 300 km/s. Using this correlation, we reanalyze the publicly available sample of SNe II-P compiled by DAndrea et al. and find a Hubble diagram with an intrinsic scatter of 11% in distance, which is nearly as tight as that measured before their sample is added to the existing set. The larger scatter reported in their work is found to be systematic, and most of it can be alleviated by measuring Hbeta rather than FeII velocities, due to the low signal-to-noise ratios and early epochs at which many of the optical spectra were obtained. Their sample, while supporting the mounting evidence that SNe II-P are good cosmic rulers, is biased toward intrinsically brighter objects and is not a suitable set to improve upon SN II-P correlation parameters. This will await a dedicated survey.
We report the results of [OIII] lambda 5007 surveys for planetary nebulae (PNe) in NGC 2403, 3115, 3351, 3627, 4258, and 5866. Using on-band/off-band [OIII] and H-alpha images, we identify samples of PNe in these galaxies and derive distances using the planetary nebula luminosity function (PNLF). We then combine these measurements with previous data to compare the PNLF, Cepheid, and surface brightness fluctuation (SBF) distance scales. We use a sample of 13 galaxies to show that the absolute magnitude of the PNLF cutoff is fainter in small, low-metallicity systems, but the trend is well modelled theoretically. When this dependence is removed, the scatter between the Cepheid and PNLF distances becomes consistent with the internal errors of the methods and independent of any obvious galaxy parameter. We then use the data to recalibrate the zero point of the PNLF distance scale. We use a sample of 28 galaxies to show that the scatter between the PNLF and SBF distance measurements agrees with that predicted from the techniques internal errors, and that no systematic trend exists between the distance residuals and stellar population. However, we find the PNLF and SBF methods have a significant scale offset: Cepheid-calibrated PNLF distances are, on average, ~0.3 mag smaller than Cepheid-calibrated SBF distances. We discuss the possible causes of this offset, and suggest that internal extinction in the bulges of the SBF calibration galaxies is the principle cause of the discrepancy. If this is correct, the SBF-based Hubble Constant must be increased by ~7%. We use our distance to NGC 4258 to argue that the short distance scale to the LMC is correct, and that the global Hubble Constant inferred from the HST Key Project should be increased by 8 +/- 3% to H_0 = 78 +/- 7 km/s/Mpc. (abridged)
Log in to be able to interact and post comments
comments
Fetching comments
Sign in to be able to follow your search criteria
