ALBERT

Description: We use star, galaxy and quasar spectra taken by the Sloan Digital Sky Survey to map out the distribution of diffuse interstellar bands (DIBs) induced by the Milky Way. After carefully removing the intrinsic spectral energy distribution of each source, we show that by stacking thousands of spectra, it is possible to measure statistical flux fluctuations at the 10 –3 level, detect more than 20 DIBs and measure their strength as a function of position on the sky. We create a map of DIB absorption covering about 5000 deg 2 and measure correlations with various tracers of the interstellar medium: atomic and molecular hydrogen, dust and polycyclic aromatic hydrocarbons (PAHs). After recovering known correlations, we show that each DIB has a different dependence on atomic and molecular hydrogen: while they are all positively correlated with $N_{\rm {H\scriptscriptstyle I}}$ , they exhibit a range of behaviours with $N_{\rm {H_2}}$ showing positive, negative or no correlation. We show that a simple parametrization involving only $N_{\rm {H\scriptscriptstyle I}}$ and $N_{\rm {H_2}}$ applied to all the DIBs is sufficient to reproduce a large collection of observational results reported in the literature: it allows us to naturally describe the relations between DIB strength and dust reddening (including the so-called skin effect), the related scatter, DIB pair-wise correlations and families, the affinity for /-type environments and other correlations related to molecules. Our approach allows us to characterize DIB dependencies in a simple manner and provides us with a metric to characterize the similarity between different DIBs.

Description: We investigate the potential and accuracy of clustering-based redshift estimation using the method proposed by Ménard et al. This technique enables the inference of redshift distributions from measurements of the spatial clustering of arbitrary sources, using a set of reference objects for which redshifts are known. We apply it to a sample of spectroscopic galaxies from the Sloan Digital Sky Survey (SDSS) and show that, after carefully controlling the sampling efficiency over the sky, we can estimate redshift distributions with high accuracy. Probing the full colour space of the SDSS galaxies, we show that we can recover the corresponding mean redshifts with an accuracy ranging from z  = 0.001 to 0.01. We indicate that this mapping can be used to infer the redshift probability distribution of a single galaxy. We show how the lack of information on the galaxy bias limits the accuracy of the inference and show comparisons between clustering redshifts and photometric redshifts for this data set. This analysis demonstrates, using real data, that clustering-based redshift inference provides a powerful data-driven technique to explore the redshift distribution of arbitrary data sets, without any prior knowledge of the spectral energy distribution of the sources.

Description: Cross-correlating the Planck High Frequency Instrument maps against quasars from the Sloan Digital Sky Survey DR7, we estimate the intensity distribution of the cosmic infrared background (CIB) over the redshift range 0 〈  z  〈 5. We detect redshift-dependent spatial cross-correlations between the two data sets using the 857, 545, and 353 GHz channels and we obtain upper limits at 217 GHz consistent with expectations. At all frequencies with detectable signal we infer a redshift distribution peaking around z  ~ 1.2 and find the recovered spectrum to be consistent with emission arising from star-forming galaxies. By assuming simple modified blackbody and Kennicutt relations, we estimate dust and star formation rate density as a function of redshift, finding results consistent with earlier multiwavelength measurements over a large portion of cosmic history. However, we note that, lacking mid-infrared coverage, we are not able to make an accurate determination of the mean temperature for the dust responsible for the CIB. Our results demonstrate that clustering-based redshift inference is a valuable tool for measuring the entire evolution history of the cosmic star formation rate from a single and homogeneous data set.

Description: We map out calcium ii and sodium i absorption (Fraunhofer H, K & D lines) induced by both the interstellar medium and the circumgalactic medium of the Milky Way. Our measurements cover more than 9000 deg 2 and make use of about 300 000 extragalactic spectra from the Sloan Digital Sky Survey. We present absorption maps for these two species and then compare their distributions to those of neutral hydrogen and dust. We show that the abundance of Na i with respect to neutral hydrogen stays roughly constant in different environments, while that of Ca ii decreases with hydrogen column density. Studying how these tracers vary as a function of velocity, we show that, on average, the N Na i / N Ca ii ratio decreases at higher velocity with respect to the local standard of rest, similar to the local Routly–Spitzer effect but seen on Galactic scale. We show that it is likely caused by higher gas/dust density at lower velocity. Finally, we show that Galactic Ca ii and Na i absorption needs to be taken into account for precision photometry and, more importantly, for photometric redshift estimation with star-forming galaxies. Our maps of Ca ii and Na i absorption are publicly available.

Description: The Two-Micron All-Sky Survey (2MASS) has mapped out the low-redshift Universe down to K S  ~ 14 mag. As its near-infrared photometry primarily probes the featureless Rayleigh–Jeans tail of galaxy spectral energy distributions, colour-based redshift estimation is rather uninformative. Until now, redshift estimates for this data set have relied on optical follow-up suffering from selection biases. Here, we use the newly developed technique of clustering-based redshift estimation to infer the redshift distribution of the 2MASS sources regardless of their optical properties. We characterize redshift distributions of objects from the Extended Source Catalogue as a function of near-infrared colours and brightness and report some observed trends. We also apply the clustering redshift technique to dropout populations, sources with non-detections in one or more near-infrared bands, and present their redshift distributions. Combining all extended sources, we confirm with clustering redshifts that the distribution of this sample extends up to z  ~ 0.35. We perform a similar analysis with the Point Source Catalogue and show that it can be separated into stellar and extragalactic contributions with galaxies reaching z  ~ 0.7. We estimate that the Point Source Catalogue contains 1.6 million extragalactic objects: as many as in the Extended Source Catalogue but probing a cosmic volume 10 times larger.

Description: We present a measurement of the correlation function between luminous red galaxies (LRGs) and cool gas traced by Mg ii 2796, 2803 absorption, on scales ranging from about 30 kpc to 20 Mpc. The measurement is based on cross-correlating the positions 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 LRGs to be about 10 13.5 M , in agreement with other methods. We also find the Mg ii gas-to-mass ratio around LRGs to be consistent with the cosmic mean 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 linewidth estimates, we show that the velocity dispersion of the gas clouds also shows the expected one- and two-halo behaviours. 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.

Description: We have obtained spectra of 163 quasars at z em  〉 4.4 with the Gemini Multi Object Spectrometers, the largest publicly available sample of high-quality, low-resolution spectra at these redshifts. From this data set, we generated stacked quasar spectra in three redshift intervals at z  ~ 5 to model the average rest-frame Lyman continuum flux and to assess the mean free path $\lambda _{\rm mfp}^{912}$ of the intergalactic medium to H  i -ionizing radiation. At mean redshifts z q = (4.56, 4.86, 5.16), we measure $\lambda _{\rm mfp}^{912}=\left(22.2 \pm 2.3, 15.1 \pm 1.8, 10.3 \pm 1.6\right)h_{70}^{-1}$ proper Mpc with uncertainties dominated by sample variance. Combining our results with measurements from lower redshifts, the data are well modelled by a power law $\lambda _{\rm mfp}^{912}=A\left[\left(1+z\right)/5\right]^\eta$ with $A=\left(37 \pm 2\right)h_{70}^{-1}$  Mpc and = –5.4 ± 0.4 at 2.3 〈  z  〈 5.5. This rapid evolution requires a physical mechanism – beyond cosmological expansion – which reduces the effective Lyman limit opacity. We speculate that the majority of H  i Lyman limit opacity manifests in gas outside galactic dark matter haloes, tracing large-scale structures (e.g. filaments) whose average density and neutral fraction decreases with cosmic time. Our measurements of the mean free path shortly after H  i reionization serve as a valuable boundary condition for numerical models thereof. Our measured $\lambda _{\rm mfp}^{912}\approx 10$  Mpc at z = 5.2 confirms that the intergalactic medium is highly ionized without evidence for a break that would indicate a recent end to H  i reionization.

Description: We characterize the luminosity functions of galaxies residing in z ~ 0 groups and clusters over the broadest ranges of luminosity and mass reachable by the Sloan Digital Sky Survey. Our measurements cover four orders of magnitude in luminosity, down to about M r = –12 mag or L = 10 7 L , and three orders of magnitude in halo mass, from 10 12 to 10 15 M . We find a characteristic scale, M r ~ –18 mag or L ~ 10 9 L , below which the slope of the luminosity function becomes systematically steeper. This trend is present for all halo masses and originates mostly from red satellites. This ubiquitous faint-end upturn suggests that it is formation, rather than halo-specific environmental effect, that plays a major role in regulating the stellar masses of faint satellites. We show that the satellite luminosity functions can be described in a simple manner by a double Schechter function with amplitudes scaling with halo mass over the entire range of observables. Combining these conditional luminosity functions with the dark matter halo mass function, we accurately recover the entire field luminosity function over 10 visual magnitudes and reveal that satellite galaxies dominate the field luminosity function at magnitudes fainter than –17. We find that the luminosity functions of blue and red satellite galaxies show distinct shapes and we present estimates of the stellar mass fraction as a function of halo mass and galaxy type. Finally, using a simple model, we demonstrate that the abundances and the faint-end slopes of blue and red satellite galaxies can be interpreted in terms of their formation history, with two distinct modes separated by some characteristic time.

Description: We apply clustering-based redshift inference to all extended sources from the Sloan Digital Sky Survey photometric catalogue, down to magnitude r  = 22. We map the relationships between colours and redshift, without assumption of the sources’ spectral energy distributions (SEDs). We identify and locate star-forming quiescent galaxies, and active galactic nuclei, as well as colour changes due to spectral features, such as the 4000 Å break, redshifting through specific filters. Our mapping is globally in good agreement with colour–redshift tracks computed with SED templates, but reveals informative differences, such as the need for a lower fraction of M-type stars in certain templates. We compare our clustering-redshift estimates to photometric redshifts and find these two independent estimators to be in good agreement at each limiting magnitude considered. Finally, we present the global clustering-redshift distribution of all Sloan extended sources, showing objects up to z  ~ 0.8. While the overall shape agrees with that inferred from photometric redshifts, the clustering-redshift technique results in a smoother distribution, with no indication of structure in redshift space suggested by the photometric-redshift estimates (likely artefacts imprinted by their spectroscopic training set). We also infer a higher fraction of high-redshift objects. The mapping between the four observed colours and redshift can be used to estimate the redshift probability distribution function of individual galaxies. This work is an initial step towards producing a general mapping between redshift and all available observables in the photometric space, including brightness, size, concentration, and ellipticity.

Description: 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.