585 research outputs found

    The missing metals problem. III How many metals are expelled from galaxies?

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    [Abridged] We revisit the metal budget at z~2. In the first two papers of this series, we already showed that ~30% (to <60% if extrapolating the LF) of the metals are observed in all z~2.5 galaxies detected in current surveys. Here, we extend our analysis to the metals outside galaxies, i.e. in intergalactic medium (IGM), using observational data and analytical calculations. Our results for the two are strikingly similar: (1) Observationally, we find that, besides the small (5%) contribution of DLAs, the forest and sub-DLAs contribute subtantially to make <30--45% of the metal budget, but neither of these appear to be sufficient to close the metal budget. The forest accounts for 15--30% depending on the UV background, and sub-DLAs for >2% to <17% depending on the ionization fraction. Together, the `missing metals' problem is substantially eased. (2) We perform analytical calculations based on the effective yield--mass relation. At z=2, we find that the method predicts that 2$--50% of the metals have been ejected from galaxies into the IGM, consistent with the observations. The metal ejection is predominantly by L<1/3L_B^*(z=2) galaxies, which are responsible for 90% the metal enrichment, while the 50 percentile is at L~1/10L^*_B(z=2). As a consequence, if indeed 50% of the metals have been ejected from galaxies, 3--5 bursts of star formation are required per galaxy prior to z=2. The ratio between the mass of metals outside galaxies to those in stars has changed from z=2 to z=0: it was 2:1 or 1:1 and is now 1:8 or 1:9. This evolution implies that a significant fraction of the IGM metals will cool and fall back into galaxies.Comment: 18pages, MNRAS, in press; small changes to match proofs; extended version with summary tabl

    H-alpha Imaging with HST+NICMOS of An Elusive Damped Ly-alpha Cloud at z=0.6

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    Despite previous intensive ground-based imaging and spectroscopic campaigns and wide-band HST imaging of the z=0.927 QSO 3C336 field, the galaxy that hosts the damped Ly-alpha system along this line-of-sight has eluded detection. We present a deep narrow-band H-alpha image of the field of this z=0.656 damped Ly-alpha absorber, obtained through the F108N filter of NICMOS 1 onboard the Hubble Space Telescope. The goal of this project was to detect any H-alpha emission 10 times closer than previous studies to unveil the damped absorber. We do not detect H-alpha emission between 0.05'' and 6'' (0.24 and 30 h−1h^{-1} kpc) from the QSO, with a 3-sigma flux limit of 3.70×10−17h−23.70 \times 10^{-17} h^{-2} erg/s/cm^2 for an unresolved source, corresponding to a star formation rate (SFR) of 0.3h−20.3 h^{-2} M_sun/yr. This leads to a 3-sigma upper limit of 0.15 M_sun/yr/kpc^2 on the SFR density, or a maximum SFR of 1.87 M_sun/yr assuming a disk of 4 kpc in diameter. This result adds to the number of low redshift damped Ly-alpha absorbers that are not associated with the central regions of Milky-Way-like disks. Damped Ly-alpha absorption can arise from high density concentrations in a variety of galactic environments including some that, despite their high local HI densities, are not conducive to widespread star formation.Comment: 18 pages, 3 figures. Replaced to match published version in ApJ, 550, 585 (Apr 1 2001

    The missing metals problem: I. How many metals are in submm galaxies?

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    We use a sample of submillimetre-selected galaxies (SMGs) with molecular gas and dynamical mass measurements from the literature to put constraints on the contribution of such galaxies to the total metal budget. Compared to Lyman break galaxies (LBGs), for example, SMGs are rarer (by a factor of 10 or more), but contain much more gas and are more metal rich. We estimate that SMGs brighter than 3 mJy contain only less than 9% of the metals when we combine the observed dynamical masses (few×1011\times 10^{11} \msun), number density (n≃10−4n\simeq 10^{-4} Mpc−3^{-3}), observed gas metallicity (1--2 x solar), and observed gas fractions (~40%) assuming a molecular to neutral hydrogen ratio of 1. Including SMGs fainter than 3 mJy, we estimate that SMGs contain at the most 15% of the metals, where our incompleteness correction is estimated from the dust mass function. Our results are strong upper limits given that high gas fractions and high overall metallicity are mutually exclusive. In summary, SMGs make a significant contribution to the metal budget (< 15%) but not sufficient to solve the `missing metals problem.' A consequence of our results is that SMGs can only add ≈3.5\approx 3.5% to ΩDLA\Omega_{\rm DLA}, and can not be the source of a significant population of dusty DLAs.Comment: 6 pages, 1 figure. Accepted for publication in MNRAS. Minor changes to match the published tex

    The missing metals problem: II. How many metals are in z ~ 2.2 galaxies?

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    In the context of the ``missing metals problem'', the contributions of the UV-selected z=2.2 ``BX'' galaxies and z=2.5 ``distant red galaxies'' (DRGs) have not been discussed previously. Here we show that: (i) DRGs only make a marginal contribution to the metal budget (~ 5%); (ii) BX galaxies contribute as much as 18% to the metal budget; and (iii) the K-bright subsample (K<20K<20) of the BX sample (roughly equivalent to the `BzK' selected samples) contributes roughly half of this 18%, owing both to their larger stellar masses and higher metallicities, implying that the rare K-bright galaxies at z>2 are a major source of metals in the budget. We showed in the first paper of this series that submm galaxies (SMGs) brighter than 3 mJy contribute ~5% (<9% as an upper limit) to the metal budget. Adding the contribution of SMGs and damped Ly-alpha absorbers, to the contribution of UV selected galaxies, implies that at least 30% of the metals (in galaxies) have been accounted for at z=2. The cosmic metal density thus accounted for is ~ 1.3\times 10^6 \rhosun. This is a lower limit given that galaxies on the faint-end of the luminosity function are not included. An estimate of the distribution of metals in local galaxies as a function luminosity suggests that galaxies with luminosity less than L^{\star}$ contribute about half of the total mass of metals. If the metals in galaxies at z ~ 2 are similarly distributed then faint galaxies alone cannot solve the `missing metals problem.' Galaxy populations at z ~ 2 only account for about 50% of the total metals predicted.Comment: 4 pages, 1 figure, accepted for publication in MNRAS Letters; small changes to match the published tex

    Multiphase Plasma in Sub-Damped Lyman Alpha Systems: A Hidden Metal Reservoir

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    We present a VLT/UVES spectrum of a proximate sub-damped Lyman-alpha (sub-DLA) system at z=2.65618 toward the quasar Q0331-4505 (z_qso=2.6785+/-0.0030). Absorption lines of O I, Si II, Si III, Si IV, C II, C III, C IV, Fe II, Al II, and O VI are seen in the sub-DLA, which has a neutral hydrogen column density log N(H I)=19.82+/-0.05. The absorber is at a velocity of 1820+/-250 km/s from the quasar; however, its low metallicity [O/H]=-1.64+/-0.07, lack of partial coverage, lack of temporal variations between observations taken in 2003 and 2006, and non-detection of N V imply the absorber is not a genuine intrinsic system. By measuring the O VI column density and assuming equal metallicities in the neutral and ionized gas, we determine the column density of hot ionized hydrogen in this sub-DLA, and in two other sub-DLAs with O VI drawn from the literature. Coupling this with determinations of the typical amount of warm ionized hydrogen in sub-DLAs, we confirm that sub-DLAs are a more important metal reservoir than DLAs, in total comprising at least 6-22% of the metal budget at z~2.5.Comment: 5 pages, 3 color figures, accepted for publication in ApJ

    Measuring the halo mass of MgII absorbers from their cross-correlation with Luminous Red Galaxies

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    We study the cross-correlation between 716 MgII quasar absorption systems and about 100,000 Luminous Red Galaxies (LRGs) selected from the Sloan Digital Sky Survey Data Release 3 in the redshift range 0.4<z<0.8. The MgII systems were selected to have 2796 & 2803 rest-frame equivalent widths greater than 1.0 \AA and identifications confirmed by the FeII 2600 or MgI 2852 lines. Over co-moving scales 0.2--13/h Mpc, the MgII--LRG cross-correlation has an amplitude 0.69+/-0.09 times that of the LRG--LRG auto-correlation. Since LRGs have halo-masses of 10^{13} \msun, this strong cross-correlation implies that the absorber host-galaxies have halo-masses 1--2 times 10^{12} \msun.Comment: 3 pages, 2 figures, to appear in IAU 199 conf. proc.: "Probing Galaxies through Quasar Absorption Lines," eds. Williams, Shu, Menard; minor changes to match the edited versio

    The Keck+Magellan Survey for Lyman Limit Absorption I: The Frequency Distribution of Super Lyman Limit Systems

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    We present the results of a survey for super Lyman limit systems (SLLS; defined to be absorbers with 19.0 <= log(NHI) <= 20.3 cm^-2) from a large sample of high resolution spectra acquired using the Keck and Magellan telescopes. Specifically, we present 47 new SLLS from 113 QSO sightlines. We focus on the neutral hydrogen frequency distribution f(N,X) of the SLLS and its moments, and compare these results with the Lyman-alpha forest and the damped Lyman alpha systems (DLA; absorbers with log(NHI) >= 20.3 cm^-2). We find that that f(N,X) of the SLLS can be reasonably described with a power-law of index alpha = -1.43^{+0.15}_{-0.16} or alpha = -1.19^{+0.20}_{-0.21} depending on whether we set the lower N(HI) bound for the analysis at 10^{19.0} cm^-2 or 10^{19.3}$ cm^-2, respectively. The results indicate a flattening in the slope of f(N,X) between the SLLS and DLA. We find little evidence for redshift evolution in the shape of f(N,X) for the SLLS over the redshift range of the sample 1.68 < z < 4.47 and only tentative evidence for evolution in the zeroth moment of f(N,X), the line density l_lls(X). We introduce the observable distribution function O(N,X) and its moment, which elucidates comparisons of HI absorbers from the Lyman-alpha through to the DLA. We find that a simple three parameter function can fit O(N,X) over the range 17.0 <= log(NHI) <=22.0. We use these results to predict that f(N,X) must show two additional inflections below the SLLS regime to match the observed f(N,X) distribution of the Lyman-alpha forest. Finally, we demonstrate that SLLS contribute a minor fraction (~15%) of the universe's hydrogen atoms and, therefore, an even small fraction of the mass in predominantly neutral gas.Comment: 15 pages, 10 figures, accepted to the Astrophysical Journal. Revision includes updated reference

    Post-transcriptional gene silencing triggered by sense transgenes involves uncapped antisense RNA and differs from silencing intentionally triggered by antisense transgenes

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    Although post-transcriptional gene silencing (PTGS) has been studied for more than a decade, there is still a gap in our understanding of how de novo silencing is initiated against genetic elements that are not supposed to produce double-stranded (ds)RNA. Given the pervasive transcription occurring throughout eukaryote genomes, we tested the hypothesis that unintended transcription could produce antisense (as)RNA molecules that participate to the initiation of PTGS triggered by sense transgenes (S-PTGS). Our results reveal a higher level of asRNA in Arabidopsis thaliana lines that spontaneously trigger S-PTGS than in lines that do not. However, PTGS triggered by antisense transgenes (AS-PTGS) differs from S-PTGS. In particular, a hypomorphic ago1 mutation that suppresses S-PTGS prevents the degradation of asRNA but not sense RNA during AS-PTGS, suggesting a different treatment of coding and non-coding RNA by AGO1, likely because of AGO1 association to polysomes. Moreover, the intended asRNA produced during AS-PTGS is capped whereas the asRNA produced during S-PTGS derives from 3' maturation of a read-through transcript and is uncapped. Thus, we propose that uncapped asRNA corresponds to the aberrant RNA molecule that is converted to dsRNA by RNA-DEPENDENT RNA POLYMERASE 6 in siRNA-bodies to initiate S-PTGS, whereas capped asRNA must anneal with sense RNA to produce dsRNA that initiate AS-PTGS

    SINFONI Integral Field Spectroscopy of z~2 UV-selected Galaxies: Rotation Curves and Dynamical Evolution

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    We present 0.5" resolution near-IR integral field spectroscopy of the Ha line emission of 14 z~2 UV-selected BM/BX galaxies obtained with SINFONI at ESO/VLT. The mean Ha half-light radius r_1/2 is about 4kpc and line emission is detected over > ~20kpc in several sources. In 9 sources, we detect spatially-resolved velocity gradients, from 40 to 410 km/s over ~10kpc. The observed kinematics of the larger systems are consistent with orbital motions. Four galaxies are well described by rotating disks with clumpy morphologies and we extract rotation curves out to radii > ~10kpc. One or two galaxies exhibit signatures more consistent with mergers. Analyzing all 14 galaxies in the framework of rotating disks, we infer mean inclination- and beam-corrected maximum circular velocities v_c of 180+-90 km/s and dynamical masses of (0.5-25)x10^10 Msun within r_1/2. On average, the dynamical masses are consistent with photometric stellar masses assuming a Chabrier/Kroupa IMF but too small for a 0.1-100 Msun Salpeter IMF. The specific angular momenta of our BM/BX galaxies are similar to those of local late-type galaxies. The specific angular momenta of their baryons are comparable to those of their dark matter halos. Extrapolating from the average v_c at 10kpc, the virial mass of the typical halo of a galaxy in our sample is 10^(11.7+-0.5) Msun. Kinematic modeling of the 3 best cases implies a ratio of v_c to local velocity dispersion of order 2-4 and accordingly a large geometric thickness. We argue that this suggests a mass accretion (alternatively, gas exhaustion) timescale of ~500Myr. We also argue that if our BM/BX galaxies were initially gas rich, their clumpy disks will subsequently lose their angular momentum and form compact bulges on a timescale of ~1 Gyr. [ABRIDGED]Comment: Accepted for publication in the Astrophysical Journal. 17 pages, 5 color figure
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