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$\alpha$ absorbers spanning the redshift range $z=0.11-5.06$ 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 $z=2.6\pm 0.2$ 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 $0.35 \pm 0.07$ 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$(M_{*}/M_\odot) \approx 8.5$. 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 $(M_{vir}/M_{*}) \approx 30$. We compare our results to those of several other studies that have reported strong transition-like events at redshifts around $z=2.5-2.6$ 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

This is an Open Access article distributed in accordance with the Creative Commons Attribution Non Commercial (CC BY-NC 3.0) license, which permits others to distribute, remix, adapt, build upon this work noncommercially, and license their derivative works on different terms, provided the original work is properly cited and the use is non-commercial. See: http:// creativecommons.org/licenses/by-nc/3.0

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-$\alpha$ 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