We compare our analysis of the Baryon Acoustic Oscillations (BAO) feature in the correlation functions of SDSS BOSS DR12 LOWZ and CMASS galaxy samples with the findings of arXiv:1509.06371v2. Using ...subsets of the data we obtain an empirical estimate of the errors on the correlation functions which are in agreement with the simulated errors of arXiv:1509.06371v2. We find that the significance of BAO detection is the quantity most sensitive to the choice of the fitting range with the CMASS value decreasing from \(8.0\sigma\) to \(5.3\sigma\) as the fitting range is reduced. Although our measurements of \(D_V(z)\) are in agreement with those of arXiv:1509.06371v2, we note that their CMASS \(8.0\sigma\) (LOWZ \(4.0\sigma\)) detection significance reduces to \(4.7\sigma\) (\(2.8\sigma\)) in fits with their diagonal covariance terms only. We extend our BAO analysis to higher redshifts by fitting to the weighted mean of 2QDESp, SDSS DR5 UNIFORM, 2QZ and 2SLAQ quasar correlation functions, obtaining a \(7.6\%\) measurement compared to \(3.9\%\) achieved by eBOSS DR14. Unlike for the LRG surveys, the larger error on quasar correlation functions implies a smaller role for nuisance parameters (accounting for scale-dependent clustering) in providing a good fit to the fiducial \(\Lambda\)CDM model. Again using only the error bars of arXiv:1705.06373v2 and ignoring any off-diagonal covariance matrix terms, we find that the eBOSS peak significance reduces from 2.8 to \(1.4\sigma\). We conclude that for both LRGs and quasars, the reported BAO peak significances from the SDSS surveys depend sensitively on the accuracy of the covariance matrix at large separations.
We present a detailed investigation into the recent star formation histories of 5697 luminous red galaxies (LRGs) based on the Hδ (4101 Å), and O ii (3727 Å) lines and the D4000 index. LRGs are ...luminous (L > 3L*) galaxies which have been selected to have photometric properties consistent with an old, passively evolving stellar population. For this study, we utilize LRGs from the recently completed 2dF-SDSS LRG and QSO Survey (2SLAQ). Equivalent widths of the Hδ and O ii lines are measured and used to define three spectral types, those with only strong Hδ absorption (k+a), those with strong O ii in emission (em) and those with both (em+a). All other LRGs are considered to have passive star formation histories. The vast majority of LRGs are found to be passive (∼80 per cent); however, significant numbers of k+a (2.7 per cent), em+a (1.2 per cent) and em LRGs (8.6 per cent) are identified. An investigation into the redshift dependence of the fractions is also performed. A sample of SDSS MAIN galaxies with colours and luminosities consistent with the 2SLAQ LRGs is selected to provide a low-redshift comparison. While the em and em+a fractions are consistent with the low-redshift SDSS sample, the fraction of k+a LRGs is found to increase significantly with redshift. This result is interpreted as an indication of an increasing amount of recent star formation activity in LRGs with redshift. By considering the expected lifetime of the k+a phase, the number of LRGs which will undergo a k+a phase can be estimated. A crude comparison of this estimate with the predictions from semi-analytic models of galaxy formation shows that the predicted level of k+a and em+a activities is not sufficient to reconcile the predicted mass growth for massive early types in a hierarchical merging scenario.
Abstract
In this paper we investigate the properties of low X-ray-to-optical flux ratio sources detected in a wide-area (2.5 deg2) shallow f
X(0.5-8 keV) ≈ 10−14 erg s−1 cm−2XMM-Newton survey. We ...find a total of 26 sources (5 per cent of the total X-ray-selected population) with log f
X/f
opt < −0.9 to the above flux limit. Optical spectroscopy is available for 20 of these low X-ray-to-optical flux ratio objects. Most of them are found to be associated with Galactic stars (a total of eight) and broad-line active galactic nuclei (AGNs; a total of eight). We also find two sources with optical spectra showing absorption and/or narrow emission lines and X-ray/optical properties suggesting AGN activity. Another two sources are found to be associated with low-redshift galaxies with narrow emission-line optical spectra, X-ray luminosities L
X(0.5-8 keV) ≈ 1041 erg s−1 and log f
X/f
opt≈−2 suggesting 'normal' star-forming galaxies. Despite the small-number statistics the sky density of 'normal' X-ray-selected star-forming galaxies at the flux limit of the present sample is low, consistent with previous ROSAT High-Resolution Imager (HRI) deep surveys. Also, the number density estimated here is in good agreement with both the log N-log S of 'normal' galaxies in the Chandra Deep Field North (extrapolated to bright fluxes) and model predictions based on the X-ray luminosity function of local star-forming galaxies.
We present results of a Gemini adaptive optics (AO) imaging program to investigate the host galaxies of typical QSOs at z approx 2. Our aim is to study the host galaxies of typical Limage QSOs at the ...epoch of peak QSO and star formation activity. The large database of faint QSOs provided by the Two-Degree Field QSO Redshift Survey allows us to select a sample of QSOs at z = 1.75-2.5 that have nearby (<12arc sec separation) bright stars suitable for use as AO guide stars. We have observed a sample of nine QSOs. The images of these sources have AO-corrected FWHM of between 0.11arc sec and 0.25arc sec. We use multiple observations of point-spread function (PSF) calibration star pairs to quantify any uncertainty in the PSF. We then factored these uncertainties into our modeling of the QSO plus host galaxy. In only one case did we convincingly detect a host (2QZ J133311.4+001949, at z = 1.93). This host galaxy has K = 18.5 plus or minus 0.2 mag with a half-light radius R sub(e) = 0.55arc sec plus or minus 0.1arc sec equivalent to approx3Limage, assuming a simple passively evolving model. From detailed simulations of our host galaxy modeling process, we find that for four of our targets we should be sensitive to host galaxies that are equivalent to approx2Limage (passively evolved). Our nondetections therefore place tight constraints on the properties of Limage QSO host galaxies, which can be no brighter (after allowing for passive evolution) than the host galaxies of Limage active galactic nuclei at low redshift, although the QSOs themselves are a factor of approx50 brighter. This implies that either the fueling efficiency is much greater at high redshift or that more massive black holes are active at high redshift.
Using published Hubble Space Telescope (HST) Cepheid data from 25 galaxies, we have found a correlation between the dispersion in the Cepheid period–luminosity (P–L) relation and host galaxy ...metallicity, which is significant at the ≈3σ level in the V band. In the I band the correlation is less significant, although the tighter intrinsic dispersion of the P–L relation in I may make it harder to detect such a correlation in the HST sample. One possibility is that low metallicity galaxies have smaller metallicity gradients than high metallicity galaxies; if the Cepheid P–L relation has a significant dependence on metallicity then this might explain the higher P–L dispersion in the higher metallicity galaxies. A second possibility is that the increased P–L dispersion is driven by metallicity dispersion but now due to a relation between metallicity and Cepheid colour rather than luminosity. A third possibility is that the increased P–L dispersion is caused by an increase in the width of the instability strip with metallicity. Whatever the explanation, the high observed dispersions in the HST Cepheid P–L relations have the important consequence that the bias due to incompleteness in the P–L relation at faint magnitudes is more significant than previously thought. Using a maximum likelihood technique which takes into account the effect on the P–L relations of truncation by consistently defined magnitude completeness limits, we rederive the Cepheid distances to the 25 galaxies. In the case of the galaxies with the highest P–L dispersion at the largest distances, we find that the published distance modulus underestimates the true distance modulus by up to ≈0.5 mag. When both metallicity and magnitude incompleteness corrections are made, a scale error in the published Cepheid distances is seen in the sense that the published distance moduli are increasingly underestimated at larger distances. This results in the average distance modulus to the four galaxies in the Virgo cluster core increasing from (m−M)0= 31.2 ± 0.19 to (m−M)0= 31.4 ± 0.19 if the γVI=−0.24 mag dex−1 metallicity correction of Kennicutt et al. is assumed. For the 18 HST galaxies with good Tully–Fisher (TF) distances and (m−M)0 > 29.5 the Cepheid–TF distance modulus average residual increases from 0.44 ± 0.09 to 0.63 ± 0.1 mag with γVI=−0.24. This indicates a significant scale error in TF distances, which reduces the previous Pierce & Tully TF estimate of H0= 85 ± 10 km s−1 Mpc−1 to H0= 63 ± 7 km s−1 Mpc−1, assuming γVI=−0.24 and a still uncertain Virgo infall model. Finally, for the eight HST galaxies with Type Ia supernovae (SNIa), the metallicity and incompleteness corrected Cepheid distances marginally suggest there may be a metallicity dependence of SNIa peak luminosity in the sense that metal-poor hosts have lower luminosity SNIa. Thus, SNIa Hubble diagram estimates of both H0 and q0 may therefore also require significant corrections for metallicity, once the exact sizes of the Cepheid metallicity corrections become better established.
PDF
