We present a measurement of the correlation function between luminous red galaxies and cool gas traced by Mg II lambda lambda 2796, 2803 absorption, on scales ranging from about 30 kpc to 20 Mpc. The measurement is based on cross-correlating the posi
tions of about one million red galaxies at z~0.5 and the flux decrements induced in the spectra of about 10^5 background quasars from the Sloan Digital Sky Survey. We find that: (i) This galaxy-gas correlation reveals a change of slope on scales of about 1 Mpc, consistent with the expected transition from a dark matter halo dominated environment to a regime where clustering is dominated by halo-halo correlations. Assuming that, on average, the distribution of Mg II gas follows that of dark matter up to a gas-to-mass ratio, we find the standard halo model to provide an accurate description of the gas distribution over three orders of magnitude in scale. Within this framework we estimate the average host halo mass of luminous red galaxies to be about 10^{13.5} M_solar, in agreement with other methods. We also find the Mg II gas-to-mass ratio around LRGs to be consistent with the cosmic value estimated on Mpc scales. Combining our galaxy-gas correlation and the galaxy-mass correlation function from galaxy-galaxy lensing analyses we can directly measure the Mg II gas-to-mass ratio as a function of scale and reach the same conclusion. (ii) From line-width estimates, we show that the velocity dispersion of the gas clouds also shows the expected 1- and 2-halo behaviors. On large scales the gas distribution follows the Hubble flow, whereas on small scales we observe the velocity dispersion of the Mg II gas clouds to be lower than that of collisionless dark matter particles within their host halo. This is in line with the fact that cool clouds are subject to the pressure of the virialized hot gas.
We present a measurement of the mean density profile of Ca II gas around galaxies out to ~ 200 kpc, traced by Fraunhofers H & K absorption lines. The measurement is based on cross-correlating the positions of about one million foreground galaxies at
z ~ 0.1 and the flux decrements induced in the spectra of about 10^5 background quasars from the Sloan Digital Sky Survey. This technique allows us to trace the total amount of Ca II absorption induced by the circumgalactic medium, including absorbers too weak to be detected in individual spectra. We can statistically measure Ca II rest equivalent widths down to several mA, corresponding to column densities of about 5x10^10 cm^{-2}. We find that the Ca II column density distribution follows N ~ rp^{-1.4} and the mean Ca II mass in the halo within 200 kpc is ~ 5x10^3 Msolar, averaged over the foreground galaxy sample with median mass ~ 10^10.3 Msolar. This is about an order-of-magnitude larger than the Ca II mass in the interstellar medium of the Milky Way, suggesting more than 90% of Ca II in the Universe is in the circum- and inter-galactic environments. Our measurements indicate that the amount of Ca II in halos is larger for galaxies with higher stellar mass and higher star formation rate. For edge-on galaxies we find Ca II to be more concentrated along the minor axis, i.e. in the polar direction. This suggests that bipolar outflows induced by star formation must have played a significant role in producing Ca II in galaxy halos.
Determining accurate redshift distributions for very large samples of objects has become increasingly important in cosmology. We investigate the impact of extending cross-correlation based redshift distribution recovery methods to include small scale
clustering information. The major concern in such work is the ability to disentangle the amplitude of the underlying redshift distribution from the influence of evolving galaxy bias. Using multiple simulations covering a variety of galaxy bias evolution scenarios, we demonstrate reliable redshift recoveries using linear clustering assumptions well into the non-linear regime for redshift distributions of narrow redshift width. Including information from intermediate physical scales balances the increased information available from clustering and the residual bias incurred from relaxing of linear constraints. We discuss how breaking a broad sample into tomographic bins can improve estimates of the redshift distribution, and present a simple bias removal technique using clustering information from the spectroscopic sample alone.
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.
In order to investigate the origin of the excess of strong MgII systems towards GRB afterglows as compared to QSO sightlines, we have measured the incidence of MgII absorbers towards a third class of objects: the Blazars. This class includes the BL L
ac object population for which a tentative excess of MgII systems had already been reported. We observed with FORS1 at the ESO-VLT 42 Blazars with an emission redshift 0.8<z_em<1.9, to which we added the three high z northern objects belonging to the 1Jy BL Lac sample. We detect 32 MgII absorbers in the redshift range 0.35-1.45, leading to an excess in the incidence of MgII absorbers compared to that measured towards QSOs by a factor ~2, detected at 3 sigma. The amplitude of the effect is similar to that found along GRB sightlines. Our analysis provides a new piece of evidence that the observed incidence of MgII absorbers might depend on the type of background source. In front of Blazars, the excess is apparent for both strong (w_ r(2796) > 1.0 A) and weaker (0.3 < w_r(2796) < 1.0 A) MgII systems. The dependence on velocity separation with respect to the background Blazars indicates, at the ~1.5 sigma level, a potential excess for beta = v/c ~0.1. We show that biases involving dust extinction or gravitational amplification are not likely to notably affect the incidence of MgII systems towards Blazars. Finally we discuss the physical conditions required for these absorbers to be gas entrained by the powerful Blazar jets. More realistic numerical modelling of jet-ambient gas interaction is required to reach any firm conclusions as well as repeat observations at high spectral resolution of strong MgII absorbers towards Blazars in both high and low states.
We study the kinematically narrow, low-ionization line emission from a bright, starburst galaxy at z = 0.69 using slit spectroscopy obtained with Keck/LRIS. The spectrum reveals strong absorption in MgII and FeII resonance transitions with Doppler sh
ifts of -200 to -300 km/s, indicating a cool gas outflow. Emission in MgII near and redward of systemic velocity, in concert with the observed absorption, yields a P Cygni-like line profile similar to those observed in the Ly alpha transition in Lyman Break Galaxies. Further, the MgII emission is spatially resolved, and extends significantly beyond the emission from stars and HII regions within the galaxy. Assuming the emission has a simple, symmetric surface brightness profile, we find that the gas extends to distances > ~7 kpc. We also detect several narrow FeII* fine-structure lines in emission near the systemic velocity, arising from energy levels which are radiatively excited directly from the ground state. We suggest that the MgII and FeII* emission is generated by photon scattering in the observed outflow, and emphasize that this emission is a generic prediction of outflows. These observations provide the first direct constraints on the minimum spatial extent and morphology of the wind from a distant galaxy. Estimates of these parameters are crucial for understanding the impact of outflows in driving galaxy evolution.
Using a sample of almost 7000 strong MgII absorbers with 0.4 < z < 2.2 detected in the SDSS DR4 dataset, we investigate the gravitational lensing and dust extinction effects they induce on background quasars. After carefully quantifying several selec
tion biases, we isolate the reddening effects as a function of redshift and absorber rest equivalent width, W_0. We find the amount of dust to increase with cosmic time as (1+z)^(-1.1 +/- 0.4), following the evolution of cosmic star density or integrated star formation rate. We measure the reddening effects over a factor 30 in E(B-V) and we find the dust column density to be proportional to W_0^(1.9 +/- 0.2), which provides an important scaling for theoretical modeling of metal absorbers. We also measure the dust-to-metals ratio and find it similar to that of the Milky Way. In contrast to previous studies, we do not detect any gravitational magnification by MgII systems. We measure the upper limit mu<1.10 and discuss the origin of the discrepancy. Finally, we estimate the fraction of absorbers missed due to extinction effects and show that it rises from 1 to 50% in the range 1<W_0<6 Angstrom. We parametrize this effect and provide a correction for recovering the intrinsic distribution of absorber rest equivalent widths.
