545 research outputs found
IR-TF Relation In The Zone Of Avoidance With 2MASS
Using the Tully-Fisher relation, one can map the peculiar velocity field and
estimate the mass in regions such as the Great Attractor. 2MASS is surveying
the full sky in J, H and K bands and has the great advantage that it allows us
to detect galaxies more uniformly to lower Galactic latitude than optical
surveys. This study shows the feasibility of using 2MASS and the TF relation to
probe large scale structure. We found that (i) we can use axis ratio up
to 0.5; (ii) intrinsic extinction is present (up to 0.5mag at J, 0.1 mag at K);
(iii) the zero-point of the TF relation is independent of the 2MASS magnitude
measurement and is consistent with the HST Key-Project value; (iv) the 2MASS
K-band 20th mag/arcsec isophotal aperture magnitude produces the best TF
relation; and (v) there is no type dependence of the residualsComment: 8 pages, Latex using newpasp.sty. Matches version to appear in
Mapping the Hidden Universe: The Universe Behind the Milky Way - The Universe
in HI, ASP Conference Series 2000, eds R.C.Kraan-Korteweg, P.A. Henning and
H. Andernach (matched to published version; abstract bug in v2 fixed
The missing metals problem. III How many metals are expelled from galaxies?
[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
The missing metals problem: I. How many metals are in submm galaxies?
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 \msun), number density ( Mpc), 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 % to , 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?
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 ()
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
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
Elephants can determine ethnicity, gender, and age from acoustic cues in human voices
Animals can accrue direct fitness benefits by accurately classifying predatory threat according to the species of predator and the magnitude of risk associated with an encounter. Human predators present a particularly interesting cognitive challenge, as it is typically the case that different human subgroups pose radically different levels of danger to animals living around them. Although a number of prey species have proved able to discriminate between certain human categories on the basis of visual and olfactory cues, vocalizations potentially provide a much richer source of information. We now use controlled playback experiments to investigate whether family groups of free-ranging African elephants (Loxodonta africana) in Amboseli National Park, Kenya can use acoustic characteristics of speech to make functionally relevant distinctions between human subcategories differing not only in ethnicity but also in sex and age. Our results demonstrate that elephants can reliably discriminate between two different ethnic groups that differ in the level of threat they represent, significantly increasing their probability of defensive bunching and investigative smelling following playbacks of Maasai voices. Moreover, these responses were specific to the sex and age of Maasai presented, with the voices of Maasai women and boys, subcategories that would generally pose little threat, significantly less likely to produce these behavioral responses. Considering the long history and often pervasive predatory threat associated with humans across the globe, it is likely that abilities to precisely identify dangerous subcategories of humans on the basis of subtle voice characteristics could have been selected for in other cognitively advanced animal species
The Keck+Magellan Survey for Lyman Limit Absorption I: The Frequency Distribution of Super Lyman Limit Systems
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
SINFONI Integral Field Spectroscopy of z~2 UV-selected Galaxies: Rotation Curves and Dynamical Evolution
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
Post-transcriptional gene silencing triggered by sense transgenes involves uncapped antisense RNA and differs from silencing intentionally triggered by antisense transgenes
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
The History of Cosmological Star Formation: Three Independent Approaches and a Critical Test Using the Extragalactic Background Light
Taking three independent approaches, we investigate the simultaneous
constraints set on the cosmic star formation history from various observations,
including stellar mass density and extragalactic background light (EBL). We
compare results based on: 1) direct observations of past light-cone, 2) a model
using local fossil evidence constrained by SDSS observations at z~0 (the
`Fossil' model), and 3) theoretical ab initio models from three calculations of
cosmic star formation history: (a) new (1024)^3 Total Variation Diminishing
(TVD) cosmological hydrodynamic simulation, (b) analytic expression of
Hernquist & Springel based on cosmological Smoothed Particle Hydrodynamics
(SPH) simulations, and (c) semi-analytic model of Cole et al. We find good
agreement among the three independent approaches up to the order of
observational errors, except that all the models predict bolometric EBL of
I_tot ~= 37-52 nW m^-2 sr^-1, which is at the lower edge of the the
observational estimate by Hauser & Dwek. We emphasize that the Fossil model
that consists of two components -- spheroids and disks --, when normalized to
the local observations, provides a surprisingly simple but accurate description
of the cosmic star formation history and other observable quantities. Our
analysis suggests that the consensus global parameters at z=0 are: Omega_* =
0.0023+-0.0004, I_EBL = 43+-7 nW m^-2 sr^-1 rho_SFR=(1.06+-0.22)e-2 Msun yr^-1
Mpc^-3, j_bol = (3.1+-0.2)e8 Lsun Mpc^-3.Comment: 40 page, 10 figures. ApJ in press. Matched to the accepted versio
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