8,079 research outputs found
Mass-metallicity relation from z=5 to the present: Evidence for a transition in the mode of galaxy growth at z=2.6 due to the end of sustained primordial gas infall
We analyze the redshift evolution of the mass-metallicity relation in a
sample of 110 Damped Ly absorbers spanning the redshift range
and find that the zero-point of the correlation changes
significantly with redshift. The evolution is such that the zero-point is
constant at the early phases of galaxy growth (i.e. no evolution) but then
features a sharp break at with a rapid incline towards lower
redshifts such that damped absorbers of identical masses are more metal rich at
later times than earlier. The slope of this mass metallicity correlation
evolution is dex per unit redshift.
We compare this result to similar studies of the redshift evolution of
emission selected galaxy samples and find a remarkable agreement with the slope
of the evolution of galaxies of stellar mass log.
This allows us to form an observational tie between damped absorbers and
galaxies seen in emission.
We use results from simulations to infer the virial mass of the dark matter
halo of a typical DLA galaxy and find a ratio .
We compare our results to those of several other studies that have reported
strong transition-like events at redshifts around and argue that
all those observations can be understood as the consequence of a transition
from a situation where galaxies were fed more unprocessed infalling gas than
they could easily consume to one where they suddenly become infall starved and
turn to mainly processing, or re-processing, of previously acquired gas.Comment: 8 pages, 5 figures, accepted for publication in MNRA
External quality assessment of urinary methylmalonic acid quantification - results of a pilot study
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Population studies on Phytophthora infestans on potatoes and tomatoes in southern Germany
Fifty-seven isolates of Phytophthora infestans from blighted potato foliage were collected in 1995 in southern Germany and analysed for mating type and sensitivity to metalaxyl. Fifty-six of them were characterised as A1 and one as A2 mating types. Resistance to metalaxyl was observed frequently: 53 isolates were resistant, three were partially sensitive, and one was sensitive. In a subsequent field study in 1999, 84 isolates collected from blighted potato and tomato foliage were analysed for mating type. Seventy-two were characterised as A1 and twelve as A2 mating types. The response of 76 isolates to metalaxyl and to propamocarb was tested. The majority (42) of the 76 isolates was classified as resistant to metalaxyl; 31 were partially sensitive and only three isolates were sensitive. The results with propamocarb were less discrete; 10 isolates were classified as resistant and three were clearly sensitive. AFLP fingerprinting was used to examine the genetic structure of the southern German P. infestans population collected in 1999 and indicated that the tested population can be sub-divided into a tomato group, a potato group and a mixed group containing isolates collected from both crops. The presence of Ia and IIa mitochondrial DNA haplotypes indicates that the German P. infestans isolates belong to the new pathogen population that has also been reported in neighbouring regions of Europe. The present study indicates that at the beginning of the season only a few genotypes were present, and the population became genetically more variable at the end of the growing season
The Sightline to Q2343-BX415: Clues to Galaxy Formation in a Quasar Environment
(Abridged) We have discovered a strong DLA coincident in redshift with the
faint QSO Q2343-BX415 (R = 20.2, z_em = 2.57393). Follow-up observations at
intermediate spectral resolution reveal that the metal lines associated with
this 'proximate' DLA consist of two sets of absorption components. One set is
moving towards the quasar with velocities of ~ 150-600 km/s; this gas is highly
ionized and does not fully cover the continuum source, suggesting that it is
physically close to the active nucleus. The other, which accounts for most of
the neutral gas, is blueshifted relative to the QSO, with the strongest
component at ~ -160 km/s. We consider the possibility that the PDLA arises in
the outflowing interstellar medium of the host galaxy of Q2343-BX415, an
interpretation supported by strong C IV and N V absorption at nearby
velocities, and by the intense radiation field longward of the Lyman limit
implied by the high C II*/H I ratio. If Q2343-BX415 is the main source of these
UV photons, then the PDLA is located at either ~ 8 or ~ 37 kpc from the active
nucleus. Alternatively, the absorber may be a foreground star-forming galaxy
unrelated to the quasar and coincidentally at the same redshift, but our deep
imaging and follow-up spectroscopy of the field of Q2343-BX415 has not yet
produced a likely candidate. We measure the abundances of 14 elements in the
PDLA, finding an overall metallicity of ~ 1/5 solar and a normal pattern of
relative element abundances for this metallicity. Thus, in this PDLA there is
no evidence for the super-solar metallicities that have been claimed for some
proximate, high ionization, systems.Comment: Accepted for publication in the Astrophysical Journal. 27 pages, 8
tables, 21 postscript figure
Optical/near-infrared selection of red QSOs: Evidence for steep extinction curves towards galactic centers?
We present the results of a search for red QSOs using a selection based on
optical imaging from SDSS and near-infrared imaging from UKIDSS. For a sample
of 58 candidates 46 (79%) are confirmed to be QSOs. The QSOs are predominantly
dust-reddened except a handul at redshifts z>3.5. The dust is most likely
located in the QSO host galaxies. 4 (7%) of the candidates turned out to be
late-type stars, and another 4 (7%) are compact galaxies. The remaining 4
objects we could not identify. In terms of their optical spectra the QSOs are
similar to the QSOs selected in the FIRST-2MASS red Quasar survey except they
are on average fainter, more distant and only two are detected in the FIRST
survey. We estimate the amount of extinction using the SDSS QSO template
reddened by SMC-like dust. It is possible to get a good match to the observed
(restframe ultraviolet) spectra, but for nearly all the reddened QSOs it is not
possible to match the near-IR photometry from UKIDSS. The likely reasons are
that the SDSS QSO template is too red at optical wavelengths due to
contaminating host galaxy light and that the assumed SMC extinction curve is
too shallow. Our survey has demonstrated that selection of QSOs based on
near-IR photometry is an efficent way to select QSOs, including reddened QSOs,
with only small contamination from late-type stars and compact galaxies. This
will be useful with ongoing and future wide-field near-IR surveys such as the
VISTA and EUCLID surveys. [Abridged]Comment: 74 pages, 6 figures. Accepted for for publication in ApJ
Stellar Populations of Luminous Evolved Galaxies at z~1.5
Observational evidence has been mounting over the past decade that at least
some luminous (~2 L*) galaxies have formed nearly all of their stars within a
short period of time only 1-2x10^9 years after the Big Bang. These are examples
of the first major episodes of star formation in the Universe and provide
insights into the formation of the earliest massive galaxies. We have examined
in detail the stellar populations of six z~1.5 galaxies that appear to be
passively evolving, using both ground and space-based photometry covering
rest-frame UV to visible wavelengths. In addition, we have obtained
medium-resolution spectroscopy for five of the six galaxies, covering the
rest-frame UV portion of the spectrum. Spectral synthesis modeling for four of
these galaxies favors a single burst of star formation more than 1 Gyr before
the observed epoch. The other two exhibit slightly younger ages with a higher
dust content and evidence for a small contribution from either recent star
formation or active nuclei. The implied formation redshifts for the oldest of
these sources are consistent with previous studies of passive galaxies at high
redshift, and improved stellar modeling has shown these results to be quite
robust. It now seems clear that any valid galaxy formation scenario must be
able to account for these massive (2x10^11 M_sun) galaxies at very early times
in the Universe.Comment: 10 pages, 3 figures (2 in color), accepted for publication in Ap
Using Gravitational Lensing to study HI clouds at high redshift
We investigate the possibility of detecting HI emission from gravitationally
lensed HI clouds (akin to damped Lyman- clouds) at high redshift by
carrying out deep radio observations in the fields of known cluster lenses.
Such observations will be possible with present radio telescopes only if the
lens substantially magnifies the flux of the HI emission. While at present this
holds the only possibility of detecting the HI emission from such clouds, it
has the disadvantage of being restricted to clouds that lie very close to the
caustics of the lens. We find that observations at a detection threshold of 50
micro Jy at 320 MHz (possible with the GMRT) have a greater than 20%
probability of detecting an HI cloud in the field of a cluster, provided the
clouds have HI masses in the range 5 X 10^8 M_{\odot} < M_{HI} < 2.5 X 10^{10}
M_{\odot}. The probability of detecting a cloud increases if they have larger
HI masses, except in the cases where the number of HI clouds in the cluster
field becomes very small. The probability of a detection at 610 MHz and 233 MHz
is comparable to that at 320 MHz, though a definitive statement is difficult
owing to uncertainties in the HI content at the redshifts corresponding to
these frequencies. Observations at a detection threshold of 2 micro Jy
(possible in the future with the SKA) are expected to detect a few HI clouds in
the field of every cluster provided the clouds have HI masses in the range 2 X
10^7 M_{\odot} < M_{HI} < 10^9 M_{\odot}. Even if such observations do not
result in the detection of HI clouds, they will be able to put useful
constraints on the HI content of the clouds.Comment: 21 pages, 7 figures, minor changes in figures, accepted for
publication in Ap
A controlled study of the effect of domiciliary tuberculosis chemotherapy programme in a rural community in South India
To study thc ellicttq of a domiciliary drug-therapy programme in the control of tuberculosis in a rural community, an investigation was set lip in 1958 under the auspices of the Indian Council of Medlenl I{C!IClln:h ill 12 towns with populations ranging from 6000 to 25000, all within 160 km of Madanapallc (Andhra Pradt'Sh). The prevalences of bacillary and radioloj.(ic~ll cases of pulmonary tuberculosis in adults (llgcd 15 )T or more) were estimated in .. ch town by carrying out a hase-Iine random sample survey iu 1959; also, the prevalences of tuberculous infcl'tion in all schoolchildrt,n aged 5 to 9yr wen' estimated. These thn.'t' in.dices of prevalence were used to rank the 12 towns and tben ndomlyallocate them into two l'omparable groups of 6 towns each, designated as 'Ireatment' and '~:ontmJ' tOWIlS. In treatment tOWIIS, intensi"e case finding ,,-as undertaken hy means of 2 X-ray surveys (suney I during 1960-61 and survey II during 1962-64) l'ovcring alllldults, sputum examinations by microSl'op' Hnd culture when indicated, and eriodic follow lip of all 'suspect' cases with X-ray and SPlltuDl examinations. All bacillary cases were offered domiciliary treatment for onc ~'ear with isoniazid and PAS in the J treatment IOWll~ (selected at random) a.nd with isoniazid alone in the other 3 town.·,. Of 148 2easc~ eligible for trcat-at ment in tJlC 6 treatment towns, 15 per l'en.t refused treatment nd 29 per cent discontin.ued chemotherapy prematurely. In lhe rontrol towns, 0.0 spcdal faeililies for di~gn()sis 01'
calment ,vere introduced, and patients w~'re left to the routine treatment facilities aV:lilahk' locally. A tuberculosis prcntlcm:e survey (~ul'l'ey Ill) t'O\'cri~ all adults was 1.1lrried out iD 9.1112 towns during 1965-68, am! lhi:; ~:l." followed hy a random tuberculin sample survey during 1966-69.
The overall results of treatment at the end of one year ,,'eJ'e.' (i) among cases initially positive hy micro~opy, 10 per' nt died, 33 per locnt rcmllincd sputum-positive IUld 51 per cent became sputum-negative in INH-PAS towns, the mrl'lsponding percentages fur INH lowns being 15, 48 and 37 per cent respectivel~'; (ii): moug cases initially positive by culture ()nJy, 6 per ent died, 26 J1er cent remained sputum-posithc and 68 per cent became sputum negative in lNH-PAS towns, tbe correspondi percentages for tile INH town~ being 1, 38 an. 55 IJer cent respectively.
All the bacillary cases (treated or untrcatt'lf) were followed up and their status at the end of 5 yr was 40.4 per cent dead, 18.2 per cent sputum-positive and 41.4 pCT cent sputum-ne'~ative. Spntum status at one year had considerable prognostic value. Of 532 sputum-negative ea .. at one year, 18 per l'ent were dead, 16 per CCDt sputuDl-posithe and 66 per cent sputum-ncgath'e 5 yr aftenvards, where'd!! the corresponding percentagt'S for (JIC 319 sputum-positive cases at one year were 56, 20 llnd 24 respectively.
There was an intennl of about 2l ~'r between sunc)' [ and survey [[ and ahout 4 yr between survey [J and survey 111 in the 6 treatmellt towns. The prevalence of badllary cases in these sUr\'eys was age-standardised, cousidering separately l'UseS found hy microscopy and cases found by culture only. The lJlean prevalence of cases (Wsitive hy microscopy in the 6 treatment towns was 6.81 per thousand in survey I and it decre~sed significanUy (P < 0,01) to 5.01 in survey nand 4.83 in survey Ill. Change of culture technique during the course of the investi~ation complicated the interpretation of prcva· lenl'C:l of culture-positive cases.
BetwCCR the 1959 base-line survey and tbe resurvey in 1965·68, the prevalence ()f smear-positive tuberculosis decreas~d from 5.92 per thousand adults to 4.78 in the 6 treatment towns, and similarly from 5.72 to 4.21 in the 6 control towns. The prcvalenl-e of 'culture only-positive' cases was 3.85 and 2.44 per thousand adults in the treatment and control towns respectively at the base-line survey and (with the more sesnsitive culture technique) 4.92 and 4.82 per thousand adults at the resurvey in 1965·68. Lastly, tho tuberculin survey in 1966·69 did not I" .,'ell! any' significant differences between the tr t· ment and the control towns.
The inability ofthe domiciliary treatment programme to make an impact on the prevalefl:lc of tuberculosis in the rural community around Madanapalle is a finding that has cOllsidera lie siJ,(nilicance in the context of the tubercUlosis control programme in fndia; the rl'asons for the failure aud its implications are discussed
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