570 research outputs found
A multiwavelength exploration of the [C II]/IR ratio in H-ATLAS/GAMA galaxies out to z = 0.2
We explore the behaviour of [C ii] λ157.74 μm forbidden fine-structure line observed in a sample of 28 galaxies selected from ∼ 50 deg^2 of the Herschel-Astrophysical Terahertz Large Area Survey survey. The sample is restricted to galaxies with flux densities higher than S160 μm > 150 mJy and optical spectra from the Galaxy and Mass Assembly survey at 0.02 2.5 × 10^(−3) with respect to those showing lower ratios. In particular, those with high ratios tend to have: (1) L_(IR) <10^(11) L_⊙; (2) cold dust temperatures, T_d < 30 K; (3) disc-like morphologies in r-band images; (4) a Wide-field Infrared Survey Explorer colour 0.5 ≲ S_(12 μm)/S_(22 μm) ≲ 1.0; (5) low surface brightness Σ_(IR) ≈ 10^(8–9) L_⊙ kpc^(−2), (6) and specific star formation rates of sSFR ≈0.05–3 Gyr^(−1). We suggest that the strength of the far-UV radiation fields (〈G_O〉) is main parameter responsible for controlling the [C _(ii)]/IR ratio. It is possible that relatively high 〈G_O〉 creates a positively charged dust grain distribution, impeding an efficient photoelectric extraction of electrons from these grains to then collisionally excite carbon atoms. Within the brighter IR population, 11 < log(L_(IR)/L_⊙) < 12, the low [C_( ii)]/IR ratio is unlikely to be modified by [C _(ii)] self-absorption or controlled by the presence of a moderately luminous AGN (identified via the BPT diagram)
A new perspective on the submillimetre galaxy MM 18423+5938 at redshift 3.9296 from radio continuum imaging
The bright submillimetre (sub-mm) galaxy MM 18423+5938 at redshift 3.9296 has
been predicted from mid-infrared and millimetre photometry to have an
exceptionally large total infrared (IR) luminosity. We present new radio
imaging at 1.4 GHz with the Westerbork Synthesis Radio Telescope that is used
to determine a radio-derived total IR luminosity for MM 18423+5938 via the well
established radio-far-infrared correlation. The flux density is found to be
S_1.4 GHz = 217 +/- 37 \mu Jy, which corresponds to a rest-frame luminosity
density of L_1.4 GHz = 2.32 +/- 0.40 x 10^25 / u W / Hz, where u is the
magnification from a probable gravitational lens. The radio-derived total IR
luminosity and star-formation rate are L_8-1000 \mu m = 5.6^+4.1_-2.4 x 10^13 /
u L_sol and SFR = 9.4^+7.4_-4.9 x 10^3 / u M_sol / yr, respectively, which are
~9 times smaller than those previously reported. These differences are
attributed to the IR spectral energy distribution of MM 18423+5938 being poorly
constrained by the limited number of reliable photometric data that are
currently available, and from a previous misidentification of the object at 70
\mu m. Using the radio derived total IR luminosity as a constraint, the
temperature of the cold dust component is found to be T ~ 24^+7_-5 K for a dust
emissivity of \beta = 1.5 +/- 0.5. The radio-derived properties of this galaxy
are still large given the low excitation temperature implied by the CO emission
lines and the temperature of the cold dust. Therefore, we conclude that MM
18423+5938 is probably gravitationally lensed.Comment: 5 pages, 2 figures, 1 table, accepted for publication in MNRAS
Letter
VALES: IV. Exploring the transition of star formation efficiencies between normal and starburst galaxies using APEX/SEPIA Band-5 and ALMA at low redshift
In this work we present new APEX/SEPIA Band-5 observations targeting the CO
() emission line of 24 Herschel-detected galaxies at .
Combining this sample {with} our recent new Valpara\'iso ALMA Line Emission
Survey (VALES), we investigate the star formation efficiencies (SFEs =
SFR/) of galaxies at low redshift. We find the SFE of our sample
bridges the gap between normal star-forming galaxies and Ultra-Luminous
Infrared Galaxies (ULIRGs), which are thought to be triggered by different star
formation modes. Considering the as the SFR and the
ratio, our data show a continuous and smooth increment as a function of
infrared luminosity (or star formation rate) with a scatter about 0.5 dex,
instead of a steep jump with a bimodal behaviour. This result is due to the use
of a sample with a much larger range of sSFR/sSFR using LIRGs, with
luminosities covering the range between normal and ULIRGs. We conclude that the
main parameters controlling the scatter of the SFE in star-forming galaxies are
the systematic uncertainty of the conversion factor, the gas
fraction and physical size.Comment: 9pages, 7 figures, 1 table, accepted for publication in MNRA
Spectroscopy of superluminous supernova host galaxies. A preference of hydrogen-poor events for extreme emission line galaxies
Superluminous supernovae (SLSNe) are very bright explosions that were only
discovered recently and that show a preference for occurring in faint dwarf
galaxies. Understanding why stellar evolution yields different types of stellar
explosions in these environments is fundamental in order to both uncover the
elusive progenitors of SLSNe and to study star formation in dwarf galaxies. In
this paper, we present the first results of our project to study SUperluminous
Supernova Host galaxIES, focusing on the sample for which we have obtained
spectroscopy. We show that SLSNe-I and SLSNe-R (hydrogen-poor) often (~50% in
our sample) occur in a class of galaxies that is known as Extreme Emission Line
Galaxies (EELGs). The probability of this happening by chance is negligible and
we therefore conclude that the extreme environmental conditions and the SLSN
phenomenon are related. In contrast, SLSNe-II (hydrogen-rich) occur in more
massive, more metal-rich galaxies with softer radiation fields. Therefore, if
SLSNe-II constitute a uniform class, their progenitor systems are likely
different from those of H-poor SLSNe. Gamma-ray bursts (GRBs) are, on average,
not found in as extreme environments as H-poor SLSNe. We propose that H-poor
SLSNe result from the very first stars exploding in a starburst, even earlier
than GRBs. This might indicate a bottom-light initial mass function in these
systems. SLSNe present a novel method of selecting candidate EELGs independent
of their luminosity.Comment: Published version, matches proofs. Accepted 2015 February 13. 23
pages, 8 figures, 4 tables. Minor changes with respect to previous versio
Linking the X-ray and infrared properties of star-forming galaxies at z < 1.5
We present the most complete study to date of the X-ray emission from star formation in high-redshift (median z = 0.7; z −3 in both hard and soft X-ray bands. From the sources which are star formation dominated, only a small fraction are individually X-ray detected and for the bulk of the sample we calculate average X-ray luminosities through stacking. We find an average soft X-ray to infrared ratio of log ?L SX /L IR ? = −4.3 and an average hard X-ray to infrared ratio of log?L HX /L IR ?=−3.8.WereportthattheX-ray/IRcorrelationisapproximatelylinearthrough the entire range of L IR and z probed and, although broadly consistent with the local (z < 0.1) one, it does display some discrepancies. We suggest that these discrepancies are unlikely to be physical, i.e. due to an intrinsic change in the X-ray properties of star-forming galaxies with cosmic time, as there is no significant evidence for evolution of the L X /L IR ratio with redshift. Instead, they are possibly due to selection effects and remaining AGN contamination.
We also examine whether dust obscuration in the galaxy plays a role in attenuating X-rays from star formation, by investigating changes in the L X /L IR ratio as a function of the average dust temperature. We conclude that X-rays do not suffer any measurable attenuation in the host galaxy
The ALMA Frontier Fields Survey - IV. Lensing-corrected 1.1 mm number counts in Abell 2744, MACSJ0416.1-2403 and MACSJ1149.5+2223
[abridged] Characterizing the number counts of faint, dusty star-forming
galaxies is currently a challenge even for deep, high-resolution observations
in the FIR-to-mm regime. They are predicted to account for approximately half
of the total extragalactic background light at those wavelengths. Searching for
dusty star-forming galaxies behind massive galaxy clusters benefits from strong
lensing, enhancing their measured emission while increasing spatial resolution.
Derived number counts depend, however, on mass reconstruction models that
properly constrain these clusters. We estimate the 1.1 mm number counts along
the line of sight of three galaxy clusters, i.e. Abell 2744, MACSJ0416.1-2403
and MACSJ1149.5+2223, which are part of the ALMA Frontier Fields Survey. We
perform detailed simulations to correct these counts for lensing effects. We
use several publicly available lensing models for the galaxy clusters to derive
the intrinsic flux densities of our sources. We perform Monte Carlo simulations
of the number counts for a detailed treatment of the uncertainties in the
magnifications and adopted source redshifts. We find an overall agreement among
the number counts derived for the different lens models, despite their
systematic variations regarding source magnifications and effective areas. Our
number counts span ~2.5 dex in demagnified flux density, from several mJy down
to tens of uJy. Our number counts are consistent with recent estimates from
deep ALMA observations at a 3 level. Below 0.1 mJy, however,
our cumulative counts are lower by 1 dex, suggesting a flattening in
the number counts. In our deepest ALMA mosaic, we estimate number counts for
intrinsic flux densities 4 times fainter than the rms level. This
highlights the potential of probing the sub-10 uJy population in larger samples
of galaxy cluster fields with deeper ALMA observations.Comment: 19 pages, 14 figures, 3 tables. Accepted for publication in A&
The RCK Domain of the KtrAB K+ Transporter: Multiple Conformations of an Octameric Ring
SummaryThe KtrAB ion transporter is a complex of the KtrB membrane protein and KtrA, an RCK domain. RCK domains regulate eukaryotic and prokaryotic membrane proteins involved in K+ transport. Conflicting functional models have proposed two different oligomeric arrangements for RCK domains, tetramer versus octamer. Our results for the KtrAB RCK domain clearly show an octamer in solution and in the crystal. We determined the structure of this protein in three different octameric ring conformations that resemble the RCK-domain octamer observed in the MthK potassium channel but show striking differences in size and symmetry. We present experimental evidence for the association between one RCK octameric ring and two KtrB membrane proteins. These results provide insights into the quaternary organization of the KtrAB transporter and its mechanism of activation and show that the RCK-domain octameric ring model is generally applicable to other ion-transport systems
Wild-type minimal inhibitory concentration distributions in bacteria of animal origin in Argentina
AbstractThe aim of this study was to determine the antimicrobial resistance profiles of indicator bacteria isolated from domestic animal feces. Minimal inhibitory concentration (MIC) was determined by agar dilution. Interpretative criteria on the basis of wild-type MIC distributions and epidemiological cutoff values (ECOFF or ECV) were used according to the ‘European Committee on Antimicrobial Susceptibility Testing’ (EUCAST) data. Results from 237 isolates of Escherichia coli showed reduced susceptibility for ampicillin, streptomycin and tetracycline, the antimicrobials commonly used in intensive breeding of pigs and hens. Regarding all the species of the genus Enterococcus spp., there are only ECOFF or ECV for vancomycin. Of the 173 Enterococcus spp. isolated, only one showed reduced susceptibility to vancomycin and was classified as ‘non-wild-type’ (NWT) population. This is the first report in Argentina showing data of epidemiological cutoff values in animal bacteria
Witnessing the birth of the red sequence: the physical scale and morphology of dust emission in hyper-luminous starbursts in the early Universe
We present high-spatial-resolution ( or at ) ALMA m dust continuum observations of a sample of
44 ultrared dusty star-forming galaxies (DSFGs) selected from the H-ATLAS and
HerMES far-infrared surveys because of their red colors from 250 to 500 m:
and . With photometric
redshifts in the range -6, our sample includes the most luminous
starbursting systems in the early Universe known so far, with total obscured
star-formation rates (SFRs) of up to ,
as well as a population of lensed, less intrinsically luminous sources. The
lower limit on the number of ultrared DSFGs at 870 m (with flux densities
measured from the ALMA maps and thus not affected by source confusion) derived
in this work is in reasonable agreement with models of galaxy evolution,
whereas there have been reports of conflicts at 500 m (where flux
densities are derived from SPIRE). Ultrared DSFGs have a variety of
morphologies (from relatively extended disks with smooth radial profiles, to
compact sources, both isolated and interacting) and an average size,
, of , considerably smaller than
the values reported in previous work for less-luminous DSFGs at lower
redshifts. The size and the estimated gas-depletion times of our sources are
compatible with their being the progenitors of the most massive, compact,
red-and-dead galaxies at -3, and ultimately of local ultra-massive
elliptical galaxies or massive galaxy clusters. We are witnessing the birth of
the high-mass tail of the red sequence of galaxies.Comment: Submitted to ApJ. Comments welcom
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