Extremely Large Telescope

Abstract:

Coma is frequently used as the archetype z ∼ 0 galaxy cluster to compare higher redshift work against. It is not clear, however, how representative the Coma cluster is for galaxy clusters of its mass or X-ray luminosity, and significantly, recent works have suggested that the galaxy population of Coma may be in some ways anomalous. In this work, we present a comparison of Coma to an X-ray-selected control sample of clusters. We show that although Coma is typical against the control sample in terms of its internal kinematics (sub-structure and velocity dispersion profile), it has a significantly high (∼3σ) X-ray temperature set against clusters of comparable mass. By de-redshifting our control sample cluster galaxies star formation rates using a fit to the galaxy main-sequence evolution at z < 0.1, we determine that the typical star formation rate of Coma galaxies as a function of mass is higher than for galaxies in our control sample at a confidence level of >99 per cent. One way to alleviate this discrepancy and bring Coma in line with the control sample would be to have the distance to Coma to be slightly lower, perhaps through a non-negligible peculiar velocity with respect to the Hubble expansion, but we do not regard this as likely given precision measurements using a variety of approaches. Therefore, in summary, we urge caution in using Coma as a z ∼ 0 baseline cluster in galaxy evolution studies. © 2014 The Authors Published by Oxford University Press on behalf of the Royal Astronomical Society.

Abstract:

We report on the Herschel/PACS observations of OH in Mrk 231, with detections in nine doublets observed within the PACS range, and present radiative-transfer models for the outflowing OH. Clear signatures of outflowing gas are found in up to six OH doublets with different excitation requirements. At least two outflowing components are identified, one with OH radiatively excited, and the other with low excitation, presumably spatially extended and roughly spherical. Particularly prominent, the blue wing of the absorption detected in the in-ladder 2Π3/2J= 9/2 - 7/2 OH doublet at 65 μm, with Elower = 290 K, indicates that the excited outflowing gas is generated in a compact and warm (circum)nuclear region. Because the excited, outflowing OH gas in Mrk 231 is associated with the warm, far-infrared continuum source, it is most likely more compact (diameter of ~200-300 pc) than that probed by CO and HCN. Nevertheless, its mass-outflow rate per unit of solid angle as inferred from OH is similar to that previously derived from CO, ≥ 70 × (2.5 × 10-6/XOH) M yr-1 sr-1, where XOH is the OH abundance relative to H nuclei. In spherical symmetry, this would correspond to ≥850 × (2.5 × 10-6/XOH) M yr-1, though significant collimation is inferred from the line profiles. The momentum flux of the excited component attains ~15 LAGN/c, with an OH column density of (1.5-3) × 1017 cm-2 and a mechanical luminosity of ~1011L. In addition, the detection of very excited, radiatively pumped OH peaking at central velocities indicates the presence of a nuclear reservoir of gas rich in OH, plausibly the 130 pc scale circumnuclear torus previously detected in OH megamaser emission, that may be feeding the outflow. An exceptional 18OH enhancement, with OH/18OH ≤ 30 at both central and blueshifted velocities, is most likely the result of interstellar-medium processing by recent starburst and supernova activity within the circumnuclear torus or thick disk. © ESO, 2013.

Abstract:

We present a stellar mass-metallicity relation at z ~ 1.4 with an unprecedentedly large sample of ~340 star-forming galaxies obtained with FibreMulti-Object Spectrograph (FMOS) on the Subaru Telescope. We observed K-band selected galaxies at 1.2 ≤ zph ≤ 1.6 in the Subaru XMM-Newton Deep Survey/Ultra Deep Survey fields with M*> 109.5M⊙, and expected F(Hα) > 5 × 10-17 erg s-1 cm-2. Among the observed ~1200 targets, 343 objects show significant Ha emission lines. The gas-phase metallicity is obtained from [N II] λ6584/Hα line ratio, after excluding possible active galactic nuclei. Due to the faintness of the [N II] λ6584 lines, we apply the stacking analysis and derive the mass-metallicity relation at z ~ 1.4. Our results are compared to past results at different redshifts in the literature. The mass-metallicity relation at z ~ 1.4 is located between those at z ~ 0.8 and z ~ 2.2; it is found that the metallicity increases with decreasing redshift from z ~ 3 to z ~ 0 at fixed stellar mass. Thanks to the large size of the sample, we can study the dependence of the mass-metallicity relation on various galaxy physical properties. The average metallicity from the stacked spectra is close to the local Fundamental Metallicity Relation (FMR) in the higher metallicity part but >0.1 dex higher in metallicity than the FMR in the lower metallicity part.We find that galaxies with larger E(B -V), B -R and R -H colours tend to show higher metallicity by ~0.05 dex at fixed stellar mass. We also find relatively clearer size dependence that objects with smaller half-light radius tend to show higher metallicity by ~0.1 dex at fixed stellar mass, especially in the low-mass part. © 2013 The Authors Published by Oxford University Press on behalf of the Royal Astronomical Society.