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Register a new userStellar velocity dispersions and emission line properties of SDSS-III/BOSS galaxies
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D. Thomas
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We perform a spectroscopic analysis of 492,450 galaxy spectra from the first two years of observations of the Sloan Digital Sky Survey-III/Baryonic Oscillation Spectroscopic Survey (BOSS) collaboration. This data set has been released in the ninth SDSS data release, the first public data release of BOSS spectra. We show that the typical signal-to-noise ratio of BOSS spectra is sufficient to measure stellar velocity dispersion and emission line fluxes for individual objects. The typical velocity dispersion of a BOSS galaxy is 240 km/s, with an accuracy of better than 30 per cent for 93 per cent of BOSS galaxies. The distribution in velocity dispersion is redshift independent between redshifts 0.15 and 0.7, which reflects the survey design targeting massive galaxies with an approximately uniform mass distribution in this redshift interval. The majority of BOSS galaxies lack detectable emission lines. We analyse the emission line properties and present diagnostic diagrams using the emission lines [OII], Hbeta, [OIII], Halpha, and [NII] (detected in about 4 per cent of the galaxies). We show that the emission line properties are strongly redshift dependent and that there is a clear correlation between observed frame colours and emission line properties. Within in the low-z sample around 0.15<z<0.3, half of the emission-line galaxies have LINER-like emission line ratios, followed by Seyfert-AGN dominated spectra, and only a small fraction of a few per cent are purely star forming galaxies. AGN and LINER-like objects, instead, are less prevalent in the high-z sample around 0.4<z<0.7, where more than half of the emission line objects are star forming. This is a pure selection effect caused by the non-detection of weak Hbeta emission lines in the BOSS spectra. Finally, we show that star forming, AGN and emission line free galaxies are well separated in the g-r vs r-i target selection diagram.
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We calculate stellar masses for massive luminous galaxies at redshift 0.2-0.7 using the first two years of data from the Baryon Oscillation Spectroscopic Survey (BOSS). Stellar masses are obtained by fitting model spectral energy distributions to u,g,r,i,z magnitudes, and simulations with mock galaxies are used to understand how well the templates recover the stellar mass. Accurate BOSS spectroscopic redshifts are used to constrain the fits. We find that the distribution of stellar masses in BOSS is narrow (Delta log M~0.5 dex) and peaks at about logM ~ 11.3 (for a Kroupa initial stellar mass function), and that the mass sampling is uniform over the redshift range 0.2 to 0.6, in agreement with the intended BOSS target selection. The galaxy masses probed by BOSS extend over ~10^{12} M, providing unprecedented measurements of the high-mass end of the galaxy mass function. We find that the galaxy number density above ~ 2.5 10^{11} M agrees with previous determinations. We perform a comparison with semi-analytic galaxy formation models tailored to the BOSS target selection and volume, in order to contain incompleteness. The abundance of massive galaxies in the models compare fairly well with the BOSS data, but the models lack galaxies at the massive end. Moreover, no evolution with redshift is detected from ~0.6 to 0.4 in the data, whereas the abundance of massive galaxies in the models increases to redshift zero. Additionally, BOSS data display colour-magnitude (mass) relations similar to those found in the local Universe, where the most massive galaxies are the reddest. On the other hand, the model colours do not display a dependence on stellar mass, span a narrower range and are typically bluer than the observations. We argue that the lack of a colour-mass relation for massive galaxies in the models is mostly due to metallicity, which is too low in the models.
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General relativistic effects have long been predicted to subtly influence the observed large-scale structure of the universe. The current generation of galaxy redshift surveys have reached a size where detection of such effects is becoming feasible. In this paper, we report the first detection of the redshift asymmetry from the cross-correlation function of two galaxy populations which is consistent with relativistic effects. The dataset is taken from the Sloan Digital Sky Survey DR12 CMASS galaxy sample, and we detect the asymmetry at the $2.7sigma$ level by applying a shell-averaged estimator to the cross-correlation function. Our measurement dominates at scales around $10$ h$^{-1}$Mpc, larger than those over which the gravitational redshift profile has been recently measured in galaxy clusters, but smaller than scales for which linear perturbation theory is likely to be accurate. The detection significance varies by 0.5$sigma$ with the details of our measurement and tests for systematic effects. We have also devised two null tests to check for various survey systematics and show that both results are consistent with the null hypothesis. We measure the dipole moment of the cross-correlation function, and from this the asymmetry is also detected, at the $2.8 sigma$ level. The amplitude and scale-dependence of the clustering asymmetries are approximately consistent with the expectations of General Relativity and a biased galaxy population, within large uncertainties. We explore theoretical predictions using numerical simulations in a companion paper.
We present tables of velocity dispersions derived from CALIFA V1200 datacubes using Pipe3D. Four different dispersions are extracted from emission (ionized gas) or absorption (stellar) spectra, with two spatial apertures (5 and 30). Stellar and ionized gas dispersions are not interchangeable and we determine their distinguishing features. We also compare these dispersions with literature values and construct sample scaling relations to further assess their applicability. We consider revised velocity-based scaling relations using the virial velocity parameter S_K^2 = K V_rot^2 + sigma^2 constructed with each of our dispersions. Our search for the strongest linear correlation between S_K and i-band absolute magnitudes favors the common K ~ 0.5, though the range 0.3 - 0.8 is statistically acceptable. The reduction of scatter in our best stellar mass-virial velocity relations over that of a classic luminosity-velocity relation is minimal; this may however reflect the dominance of massive spirals in our sample.
We use near-infrared spectroscopic data from the inner few hundred parsecs of a sample of 47 active galaxies to investigate possible correlations between the stellar velocity dispersion (sigma_star), obtained from the fit of the K-band CO stellar absorption bands, and the gas velocity dispersion (sigma) obtained from the fit of the emission-line profiles of [SIII]0.953um, [Fe II]1.257um, [FeII]1.644um and H_2 2.122um. While no correlations with sigma_star were found for H_2 and [SIII], a good correlation was found for the two [Fe II] emission lines, expressed by the linear fit sigma_star = 95.4pm16.1 + (0.25pm0.08)sigma_[Fe II]. Excluding barred objects from the sample a better correlation is found between sigma_star and sigma_[FeII], with a correlation coefficient of R=0.80 and fitted by the following relation: sigma_star = 57.9pm23.5 + (0.42pm0.10)sigma_[FeII]. This correlation can be used to estimate $sigma_star$ in cases it cannot be directly measured and the [FeII] emission lines are present in the spectra, allowing to obtain the mass of the supermassive black hole (SMBH) from the M-sigma_star relation. The scatter from a one-to-one relationship between sigma_star and its value derived from sigma_[FeII] using the equation above for our sample is 0.07dex, which is smaller than that obtained in previous studies which use sigma_[OIII] in the optical as a proxy for sigma_star. The use of sigma_[Fe,II] in the near-IR instead of sigma_[OIII] in the optical is a valuable option for cases in which optical spectra are not available or are obscured, as is the case of many AGN.
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