10522140
Evolution of the most massive galaxies to z ∼ 0.6 – II. The link between radio AGN activity and star formation
We analyze the optical spectra of massive (log M∗/M⊙ > 11.4) radio-loud galaxies at z � 0.2 and z � 0.6. Our samples are generated by crossmatching the SDSS DR7 and BOSS spectroscopic galaxy catalogues with the FIRST and NVSS radio continuum surveys. By comparing stellar population parameters of these radio-loud samples with radio-quiet control samples matched in stellar mass, velocity dispersion and redshift, we investigate how the presence of a radio-emitting jet relates to the recent star formation history of the host galaxy. We also investigate how the emissionline properties of the radio galaxies evolve with redshift by stacking their spectra. Our main results are the following. (1) Both at low and at high redshift, half as many radio-loud as radio-quiet galaxies have experienced significant star formation in the past Gyr. This difference in star formation history is independent of the luminosity of the radio AGN, except at radio luminosities greater than 10 25.5 W Hz −1 , where it disappears. (2) The Balmer absorption line properties of massive galaxies that have experienced recent star formation show that star formation occurred as a burst in many of these systems. (3) Both the radio and the emission-line luminosity of radio AGN evolve significantly with redshift. The average [O iii] rest equivalent width increases by 1 dex from z = 0.2 to z = 0.6, and emission line ratios change from LINER-like at low redshift to Seyfert-like at high redshift. However, radio galaxies with similar stellar population parameters, have similar emission-line properties both at high- and at low-redshift. These results suggest that massive galaxies experience cyclical episodes of gas accretion, star formation and black hole growth, followed by the production of a radio jet that shuts down further activity. The behaviour of galaxies with log M∗/M⊙ > 11.4 is the same at z = 0.6 as it is at z = 0.2, except that higher redshift galaxies experience more star formation and black hole growth and produce more luminous radio jets during each accretion cycle.
118466086
Autocorrelations of stellar light and mass at z∼ 0 and ∼1: from SDSS to DEEP2
We present measurements of projected autocorrelation functions wp(rp) for the stellar mass of galaxies and for their light in the U, B and V bands, using data from the third data release of the DEEP2 Galaxy Redshift Survey and the final data release of the Sloan Digital Sky Survey (SDSS). We investigate the clustering bias of stellar mass and light by comparing these to projected autocorrelations of dark matter estimated from the Millennium Simulations (MS) at z = 1 and 0.07, the median redshifts of our galaxy samples. All of the autocorrelation and bias functions show systematic trends with spatial scale and waveband which are impressively similar at the two redshifts. This shows that the well-established environmental dependence of stellar populations in the local Universe is already in place at z = 1. The recent MS-based galaxy formation simulation of Guo et al. (2011) reproduces the scale-dependent clustering of luminosity to an accuracy better than 30% in all bands and at both redshifts, but substantially overpredicts mass autocorrelations at separations below about 2 Mpc. Further comparison of the shapes of our stellar mass bias functions with those predicted by the model suggests that both the SDSS and DEEP2 data prefer a fluctuation amplitude of σ8 � 0.8 rather than the σ8 = 0.9 assumed by the MS.
118503079
Early Growth of Massive Black Holes in Quasars
Episodic activity of quasars is driving growth of supermassive black holes (SMBHs) via accretion of baryon gas. In this Letter, we develop a simple method to analyze the duty cycle of quasars up to the redshift -->z ~ 6 universe from luminosity functions (LFs). We find that the duty cycle below redshift -->z ~ 2 follows the cosmic history of star formation rate (SFR) density. Beyond -->z ~ 2, the evolutionary trends of the duty cycle are opposite to that of the cosmic SFR density history, implying the role of feedback from black hole activity. With the duty cycle, we get the net lifetime of quasars ( -->z ≤ 5) about ~109 yr. Based on the local SMBHs, the mean mass of SMBHs is obtained at any redshifts and their seeds are of -->105 M☉ at the reionization epoch ( -->zre) of the universe through the conservation of black hole number density in a comoving frame. We find that primordial black holes (~103 M☉) are able to grow up to the seeds via a moderate super-Eddington accretion of ~30 times the critical rate from -->z = 24 to -->zre. Highly super-Eddington accretion onto the primordial black holes is not necessary.
119299152
Spectral Classification and Redshift Measurement for the SDSS-III Baryon Oscillation Spectroscopic Survey
We describe the automated spectral classification, redshift determination, and parameter measurement pipeline in use for the Baryon Oscillation Spectroscopic Survey (BOSS) of the Sloan Digital Sky Survey III (SDSS-III) as of the survey's ninth data release (DR9), encompassing 831,000 moderate-resolution optical spectra. We give a review of the algorithms employed, and describe the changes to the pipeline that have been implemented for BOSS relative to previous SDSS-I/II versions, including new sets of stellar, galaxy, and quasar redshift templates. For the color-selected "CMASS" sample of massive galaxies at redshift 0.4 ≲ z ≲ 0.8 targeted by BOSS for the purposes of large-scale cosmological measurements, the pipeline achieves an automated classification success rate of 98.7% and confirms 95.4% of unique CMASS targets as galaxies (with the balance being mostly M stars). Based on visual inspections of a subset of BOSS galaxies, we find that approximately 0.2% of confidently reported CMASS sample classifications and redshifts are incorrect, and about 0.4% of all CMASS spectra are objects unclassified by the current algorithm which are potentially recoverable. The BOSS pipeline confirms that ~51.5% of the quasar targets have quasar spectra, with the balance mainly consisting of stars and low signal-to-noise spectra. Statistical (as opposed to systematic) redshift errors propagated from photon noise are typically a few tens of km s–1 for both galaxies and quasars, with a significant tail to a few hundreds of km s–1 for quasars. We test the accuracy of these statistical redshift error estimates using repeat observations, finding them underestimated by a factor of 1.19-1.34 for galaxies and by a factor of two for quasars. We assess the impact of sky-subtraction quality, signal-to-noise ratio, and other factors on galaxy redshift success. Finally, we document known issues with the BOSS DR9 spectroscopic data set and describe directions of ongoing development.
118555570
The Metallicity Gradient of the Thick Disk Based on Red Horizontal-branch Stars from SDSS DR8
Based on SDSS DR8, we have selected a sample of 1728 red horizontal-branch (RHB) stars with |Z| < 3 kpc by using a color-metallicity relation and stellar parameters. The sample stars clearly trace a typical thick disk population with peaks at |Z| = 1.26 kpc and [Fe/H] = –0.54. The vertical metallicity gradient of the thick disk is estimated in two ways. One is a fit to the Gaussian peaks of the metallicity histograms of the thick disk by subtracting minor contributions from the thin disk and the inner halo based on the Besancon Galaxy Model. The resulting gradient is –0.12 ± 0.01 dex kpc–1 for 0.5 < |Z| < 3 kpc. The other method is to linearly fit the data based on stars with 1 < |Z| < 3 kpc being the main component of the thick disk. Five subgroups are then selected in different directions in the X-|Z| plane to investigate the difference in the vertical metallicity gradient between the Galactocenter and anti-Galactocenter directions. We found that a vertical gradient of –0.22 ± 0.07 dex kpc–1 is detected for five directions except for one involving the pollution of stars from the bulge. The results indicate that the vertical gradient is dominant, but a radial gradient has a minor contribution for the thick disk population represented by RHB stars with 1 < |Z| < 3 kpc. The present work strongly suggests the existence of a metallicity gradient in the thick disk, which is thought to be negligible in most previous works in the literature.
119228842
A New AF gravitational instanton
Abstract It has long been conjectured that the Euclidean Schwarzschild and Euclidean Kerr instantons are the only non-trivial asymptotically flat (AF) gravitational instantons. In this Letter, we show that this conjecture is false by explicitly constructing a new two-parameter AF gravitational instanton with a U ( 1 ) × U ( 1 ) isometry group, using the inverse-scattering method. It has Euler number χ = 3 and Hirzebruch signature τ = 1 , and its global topology is C P 2 with a circle S 1 removed appropriately. Various other properties of this gravitational instanton are also discussed.
55754943
A doubly rotating black ring with dipole charge
A bstractWe present a dipole-charged generalisation of the Pomeransky-Sen’kov black ring in five-dimensional Kaluza-Klein theory. It rotates in two independent directions, although one of the rotations has been tuned to achieve balance, so that the space-time does not contain any conical singularities. This solution was constructed using the inverse-scattering method in six-dimensional vacuum gravity. We then study various physical properties of this solution, with particular emphasis on the new features that the dipole charge introduces.
15339664
Lithium abundances for 185 main-sequence stars - Galactic evolution and stellar depletion of lithium
We present a survey of lithium abundances in 185 main-sequence field stars with $5600 \la T_{\rm eff} \la 6600$ K and $-1.4 \la {\rm [Fe/H]} \la +0.2$ based on new measurements of the equivalent width of the $\lambda 6708$ Lii line in high-resolution spectra of 130 stars and a reanalysis of data for 55 stars from Lambert et al. ([CITE]). The survey takes advantage of improved photometric and spectroscopic determinations of effective temperature and metallicity as well as mass and age derived from Hipparcos absolute magnitudes, offering an opportunity to investigate the behaviour of Li as a function of these parameters. An interesting result from this study is the presence of a large gap in the $\log \varepsilon ({\rm Li}) - T_{\rm eff}$ plane, which distinguishes "Li-dip"stars like those first identified in the Hyades cluster by Boesgaard & Tripicco ([CITE]) from other stars with a much higher Li abundance. The Li-dip stars concentrate on a certain mass, which decreases with metallicity from about 1.4 $M_{\odot}$ at solar metallicity to 1.1 $M_{\odot}$ at ${\rm [Fe/H]} \simeq -1.0$. Excluding the Li-dip stars and a small group of lower mass stars with $T_{\rm eff} < 5900$ K and $\log \varepsilon ({\rm Li}) < 1.5$, the remaining stars, when divided into four metallicity groups, may show a correlation between Li abundance and stellar mass. The dispersion around the $\log \varepsilon ({\rm Li})$-mass relation is about 0.2 dex below ${\rm [Fe/H]} \simeq -0.4$ and 0.3 dex above this metallicity, which cannot be explained by observational errors or differences in metallicity. Furthermore, there is no correlation between the residuals of the $\log \varepsilon ({\rm Li})$-mass relations and stellar age, which ranges from 1.5 Gyr to about 15 Gyr. This suggests that Li depletion occurs early in stellar life and that parameters other than stellar mass and metallicity affect the degree of depletion, e.g. initial rotation velocity and/or the rate of angular momentum loss. It cannot be excluded, however, that a cosmic scatter of the Li abundance in the Galaxy at a given metallicity contributes to the dispersion in Li abundance. These problems make it difficult to determine the Galactic evolution of Li from the data, but a comparison of the upper envelope of the distribution of stars in the $\log \varepsilon ({\rm Li}) - {\rm [Fe/H]}$ plane with recent Galactic evolutionary models by Romano et al. ([CITE]) suggests that novae are a major source for the Li production in the Galactic disk; their occurrence seems to be the explanation for the steep increase of Li abundance at ${\rm [Fe/H]} \simeq -0.4$.
119214150
Metallicity calibration for solar type stars based on red spectra
Based on a high resolution and high signal-to-noise ratio (S/N) spectral analysis of 90 solar-type stars, we have established several new metallicity calibrations in the Teff range [5600, 6500] K based on red spectra with the wavelength range of 560–880 nm. The new metallicity calibrations are applied to determine the metallicity of solar analogs selected from Sloan Digital Sky Survey (SDSS) spectra. There is a good consistent result with the adopted value presented in SDSS-DR7 and a small scatter of 0.26 dex for stars with S/N > 50 being obtained. This study provides a new reliable way to derive the metallicity for solar-like stars with low resolution spectra. In particular, our calibrations are useful for finding metal-rich stars, which are missing in the SEGUE Stellar Parameter Pipeline.