754 research outputs found
The star formation rate distribution function of the local Universe
We present total infrared (IR) and ultraviolet (UV) luminosity functions derived from large representative samples of galaxies at z ~ 0, selected at IR and UV wavelengths from the Imperial IRAS Faint Source Catalogue redshift data base (IIFSCz) catalogue, and the GALEX All-Sky Imaging Survey (AIS), respectively. We augment these with deep Spitzer and GALEX imaging of galaxies in the 11 Mpc Local Volume Legacy (LVL) Survey, allowing us to extend these luminosity functions to lower luminosities (~10^6 L_⊙), and providing good constraints on the slope of the luminosity function at the extreme faint end for the first time. Using conventional star formation prescriptions, we generate from our data the star formation rate (SFR) distribution function for the local Universe. We find that it has a Schechter form, the faint-end slope has a constant value (to the limits of our data) of α=−1.51 ± 0.08 and the 'characteristic' SFR ψ^* is 9.2 M_⊙ yr^(−1). We also show the distribution function of the SFR volume density; we then use this to calculate a value for the total SFR volume density at z ~ 0 of 0.025 ± 0.0016 M_⊙ yr^(−1) Mpc^(−3), of which ~20 per cent is occurring in starbursts. Decomposing the total star formation by infrared luminosity, it can be seen that 9 ± 1 per cent is due to LIRGs, and 0.7 ± 0.2 per cent is occurring in ULIRGs. By comparing UV and IR emission for galaxies in our sample, we also calculate the fraction of star formation occurring in dust-obscured environments, and examine the distribution of dusty star formation: we find a very shallow slope at the highly extincted end, which may be attributable to line-of-sight orientation effects as well as conventional internal extinction
Collective atomic scattering and motional effects in a dense coherent medium
We investigate collective emission from coherently driven ultracold 88Sr atoms. We perform two sets of experiments using a strong and weak transition that are insensitive and sensitive, respectively, to atomic motion at 1 μK. We observe highly directional forward emission with a peak intensity that is enhanced, for the strong transition, by >103 compared with that in the transverse direction. This is accompanied by substantial broadening of spectral lines. For the weak transition, the forward enhancement is substantially reduced due to motion. Meanwhile, a density-dependent frequency shift of the weak transition (∼10% of the natural linewidth) is observed. In contrast, this shift is suppressed to <1% of the natural linewidth for the strong transition. Along the transverse direction, we observe strong polarization dependences of the fluorescence intensity and line broadening for both transitions. The measurements are reproduced with a theoretical model treating the atoms as coherent, interacting radiating dipoles
SPT0346-52: Negligible AGN Activity in a Compact, Hyper-starburst Galaxy at z = 5.7
We present Chandra ACIS-S and ATCA radio continuum observations of the
strongly lensed dusty, star-forming galaxy SPT-S J034640-5204.9 (hereafter
SPT0346-52) at = 5.656. This galaxy has also been observed with ALMA, HST,
Spitzer, Herschel, APEX, and the VLT. Previous observations indicate that if
the infrared (IR) emission is driven by star formation, then the inferred
lensing-corrected star formation rate ( 4500 M_{\sun} yr) and
star formation rate surface density ( 2000 M_{\sun}
{yr^{-1}} {kpc^{-2}}) are both exceptionally high. It remained unclear from
the previous data, however, whether a central active galactic nucleus (AGN)
contributes appreciably to the IR luminosity. The {\it Chandra} upper limit
shows that SPT0346-52 is consistent with being star-formation dominated in the
X-ray, and any AGN contribution to the IR emission is negligible. The ATCA
radio continuum upper limits are also consistent with the FIR-to-radio
correlation for star-forming galaxies with no indication of an additional AGN
contribution. The observed prodigious intrinsic IR luminosity of (3.6
0.3) 10 L_{\sun} originates almost solely from vigorous star
formation activity. With an intrinsic source size of 0.61 0.03 kpc,
SPT0346-52 is confirmed to have one of the highest of any known
galaxy. This high , which approaches the Eddington limit for a
radiation pressure supported starburst, may be explained by a combination of
very high star formation efficiency and gas fraction.Comment: 8 pages, 6 figures, accepted for publication in Ap
The Rest-Frame Submillimeter Spectrum of High-Redshift, Dusty, Star-Forming Galaxies
We present the average rest-frame spectrum of high-redshift dusty,
star-forming galaxies from 250-770GHz. This spectrum was constructed by
stacking ALMA 3mm spectra of 22 such sources discovered by the South Pole
Telescope and spanning z=2.0-5.7. In addition to multiple bright spectral
features of 12CO, [CI], and H2O, we also detect several faint transitions of
13CO, HCN, HNC, HCO+, and CN, and use the observed line strengths to
characterize the typical properties of the interstellar medium of these
high-redshift starburst galaxies. We find that the 13CO brightness in these
objects is comparable to that of the only other z>2 star-forming galaxy in
which 13CO has been observed. We show that the emission from the high-critical
density molecules HCN, HNC, HCO+, and CN is consistent with a warm, dense
medium with T_kin ~ 55K and n_H2 >~ 10^5.5 cm^-3. High molecular hydrogen
densities are required to reproduce the observed line ratios, and we
demonstrate that alternatives to purely collisional excitation are unlikely to
be significant for the bulk of these systems. We quantify the average emission
from several species with no individually detected transitions, and find
emission from the hydride CH and the linear molecule CCH for the first time at
high redshift, indicating that these molecules may be powerful probes of
interstellar chemistry in high-redshift systems. These observations represent
the first constraints on many molecular species with rest-frame transitions
from 0.4-1.2mm in star-forming systems at high redshift, and will be invaluable
in making effective use of ALMA in full science operations.Comment: 19 pages, 10 figures (2 in appendices); accepted for publication in
Ap
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Mutation of A DNA Repair Enzyme Causes Lupus in Mice
A replication study of a previous genome-wide association study (GWAS) suggested that a SNP linked to the POLβ gene is associated with systemic lupus erythematosus (SLE). This SNP is correlated with decreased expression of Pol β, a key enzyme in the base excision repair (BER) pathway. To determine whether decreased Pol β activity results in SLE, we constructed a mouse model of POLβ that encodes an enzyme with slow DNA polymerase activity. We show that mice expressing this hypomorphic POLβ allele develop an autoimmune pathology that strongly resembles SLE. Of note, the mutant mice have shorter immunoglobulin heavy-chain junctions and somatic hypermutation is dramatically increased. These results demonstrate that decreased Pol β activity during the generation of immune diversity leads to lupus-like disease in mice, and suggest that decreased expression of Pol β in humans is an underlying cause of SLE
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