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Register a new userA Cross-Correlation Analysis of Mg II Absorption Line Systems and Luminous Red Galaxies from the SDSS DR5
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We analyze the cross-correlation of 2,705 unambiguously intervening Mg II (2796,2803A) quasar absorption line systems with 1,495,604 luminous red galaxies (LRGs) from the Fifth Data Release of the Sloan Digital Sky Survey within the redshift range 0.36<=z<=0.8. We confirm with high precision a previously reported weak anti-correlation of equivalent width and dark matter halo mass, measuring the average masses to be log M_h(M_[solar]h^-1)=11.29 [+0.36,-0.62] and log M_h(M_[solar]h^-1)=12.70 [+0.53,-1.16] for systems with W[2796A]>=1.4A and 0.8A<=W[2796A]<1.4A, respectively. Additionally, we investigate the significance of a number of potential sources of bias inherent in absorber-LRG cross-correlation measurements, including absorber velocity distributions and the weak lensing of background quasars, which we determine is capable of producing a 20-30% bias in angular cross-correlation measurements on scales less than 2. We measure the Mg II - LRG cross-correlation for 719 absorption systems with v<60,000 km s^-1 in the quasar rest frame and find that these associated absorbers typically reside in dark matter haloes that are ~10-100 times more massive than those hosting unambiguously intervening Mg II absorbers. Furthermore, we find evidence for evolution of the redshift number density, dN/dz, with 2-sigma significance for the strongest (W>2.0A) absorbers in the DR5 sample. This width-dependent dN/dz evolution does not significantly affect the recovered equivalent width-halo mass anti-correlation and adds to existing evidence that the strongest Mg II absorption systems are correlated with an evolving population of field galaxies at z<0.8, while the non-evolving dN/dz of the weakest absorbers more closely resembles that of the LRG population.
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We present a generic and fully-automatic method aimed at detecting absorption lines in the spectra of astronomical objects. The algorithm estimates the source continuum flux using a dimensionality reduction technique, nonnegative matrix factorization, and then detects and identifies metal absorption lines. We apply it to a sample of ~100,000 quasar spectra from the Sloan Digital Sky Survey and compile a sample of ~40,000 Mg II & Fe II absorber systems, spanning the redshift range 0.4< z < 2.3. The corresponding catalog is publicly available. We study the statistical properties of these absorber systems and find that the rest equivalent width distribution of strong Mg II absorbers follows an exponential distribution at all redshifts, confirming previous studies. Combining our results with recent near-infrared observations of Mg II absorbers we introduce a new parametrization that fully describes the incidence rate of these systems up to z~5. We find the redshift evolution of strong Mg II absorbers to be remarkably similar to the cosmic star formation history over 0.4<z<5.5 (the entire redshift range covered by observations), suggesting a physical link between these two quantities.
We investigate the clustering properties of ~1550 broad-line active galactic nuclei (AGNs) at <z>=0.25 detected in the ROSAT All-Sky Survey (RASS) through their measured cross-correlation function with ~46,000 Luminous Red Galaxies (LRGs) in the Sloan Digital Sky Survey. By measuring the cross-correlation of our AGN sample with a larger tracer set of LRGs, we both minimize shot noise errors due to the relatively small AGN sample size and avoid systematic errors due to the spatially varying Galactic absorption that would affect direct measurements of the auto-correlation function (ACF) of the AGN sample. The measured ACF correlation length for the total RASS-AGN sample (<L_(0.1-2.4 keV)>=1.5 x 10^(44) erg/s) is r_0=4.3^{+0.4}_{-0.5} h^(-1) Mpc and the slope gamma=1.7^{+0.1}_{-0.1}. Splitting the sample into low and high L_X samples at L_(0.5-10 keV)=10^(44) erg/s, we detect an X-ray luminosity dependence of the clustering amplitude at the ~2.5 sigma level. The low L_X sample has r_0=3.3^{+0.6}_{-0.8} h^(-1) Mpc (gamma=1.7^{+0.4}_{-0.3}), which is similar to the correlation length of blue star-forming galaxies at low redshift. The high L_X sample has r_0=5.4^{+0.7}_{-1.0} h^(-1) Mpc (gamma=1.9^{+0.2}_{-0.2}), which is consistent with the clustering of red galaxies. From the observed clustering amplitude, we infer that the typical dark matter halo (DMH) mass harboring RASS-AGN with broad optical emission lines is log (M_DMH/(h^(-1) M_SUN)) =12.6^{+0.2}_{-0.3}, 11.8^{+0.6}_{-infty}, 13.1^{+0.2}_{-0.4} for the total, low L_X, and high L_X RASS-AGN samples, respectively.
We present the results of a MgII absorption-line survey using QSO spectra from the SDSS EDR. Over 1,300 doublets with rest equivalent widths greater than 0.3AA and redshifts $0.366 le z le 2.269$ were identified and measured. We find that the $lambda2796$ rest equivalent width ($W_0^{lambda2796}$) distribution is described very well by an exponential function $partial N/partial W_0^{lambda2796} = frac{N^*}{W^*} e^{-frac{W_0}{W^*}}$, with $N^*=1.187pm0.052$ and $W^*=0.702pm0.017$AA. Previously reported power law fits drastically over-predict the number of strong lines. Extrapolating our exponential fit under-predicts the number of $W_0 le 0.3$AA systems, indicating a transition in $dN/dW_0$ near $W_0 simeq 0.3$AA. A combination of two exponentials reproduces the observed distribution well, suggesting that MgII absorbers are the superposition of at least two physically distinct populations of absorbing clouds. We also derive a new redshift parameterization for the number density of $W_0^{lambda2796} ge 0.3$AA lines: $N^*=1.001pm0.132(1+z)^{0.226pm0.170}$ and $W^*=0.443pm0.032(1+z)^{0.634pm 0.097}$AA. We find that the distribution steepens with decreasing redshift, with $W^*$ decreasing from $0.80pm0.04$AA at $z=1.6$ to $0.59pm0.02$AA at $z=0.7$. The incidence of moderately strong MgII $lambda2796$ lines does not show evidence for evolution with redshift. However, lines stronger than $approx 2$AA show a decrease relative to the no-evolution prediction with decreasing redshift for $z lesssim 1$. The evolution is stronger for increasingly stronger lines. Since $W_0$ in saturated absorption lines is an indicator of the velocity spread of the absorbing clouds, we interpret this as an evolution in the kinematic properties of galaxies from moderate to low z.
We analyse the large-scale angular correlation function (ACF) of the CMASS luminous galaxies (LGs), a photometric-redshift catalogue based on the Data Release 8 (DR8) of the Sloan Digital Sky Survey-III. This catalogue contains over $600 , , 000$ LGs in the range $0.45 leq z leq 0.65$, which was split into four redshift shells of constant width. First, we estimate the constraints on the redshift-space distortion (RSD) parameters $bsigma_8$ and $fsigma_8$, where $b$ is the galaxy bias, $f$ the growth rate and $sigma_8$ is the normalization of the perturbations, finding that they vary appreciably among different redshift shells, in agreement with previous results using DR7 data. When assuming constant RSD parameters over the survey redshift range, we obtain $fsigma_8 = 0.69 pm 0.21$, which agrees at the $1.5sigma$ level with Baryon Oscillation Spectroscopic Survey DR9 spectroscopic results. Next, we performed two cosmological analyses, where relevant parameters not fitted were kept fixed at their fiducial values. In the first analysis, we extracted the baryon acoustic oscillation peak position for the four redshift shells, and combined with the sound horizon scale from 7-year textit{Wilkinson Microwave Anisotropy Probe} $(WMAP7)$ to produce the constraints $Omega_{m}=0.249 pm 0.031$ and $w=-0.885 pm 0.145$. In the second analysis, we used the ACF full shape information to constrain cosmology using real data for the first time, finding $Omega_{m} = 0.280 pm 0.022$ and $f_b = Omega_b/Omega_m = 0.211 pm 0.026$. These results are in good agreement with $WMAP7$ findings, showing that the ACF can be efficiently applied to constrain cosmology in future photometric galaxy surveys.
We apply a new model for the spherically averaged correlation function at large pair separations to the measurement of the clustering of luminous red galaxies (LRGs) made from the SDSS by Cabre and Gaztanaga(2009). Our model takes into account the form of the BAO peak and the large scale shape of the correlation function. We perform a Monte Carlo Markov chain analysis for different combinations of datasets and for different parameter sets. When used in combination with a compilation of the latest CMB measurements, the LRG clustering and the latest supernovae results give constraints on cosmological parameters which are comparable and in remarkably good agreement, resolving the tension reported in some studies. The best fitting model in the context of a flat, Lambda-CDM cosmology is specified by Omega_m=0.261+-0.013, Omega_b=0.044+-0.001, n_s=0.96+-0.01, H_0=71.6+-1.2 km/s/Mpc and sigma_8=0.80+-0.02. If we allow the time-independent dark energy equation of state parameter to vary, we find results consistent with a cosmological constant at the 5% level using all data sets: w_DE=-0.97+-0.05. The large scale structure measurements by themselves can constrain the dark energy equation of state parameter to w_DE=-1.05+-0.15, independently of CMB or supernovae data. We do not find convincing evidence for an evolving equation of state. We provide a set of extended distance priors that contain the most relevant information from the CMB power spectrum and the shape of the LRG correlation function which can be used to constrain dark energy models and spatial curvature. Our model should provide an accurate description of the clustering even in much larger, forthcoming surveys, such as those planned with NASAs JDEM or ESAs Euclid mission.
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