The Statefinder hierarchy: An extended null diagnostic for concordance cosmology

We show how higher derivatives of the expansion factor can be developed into a null diagnostic for concordance cosmology (LCDM). It is well known that the Statefinder -- the third derivative of the expansion factor written in dimensionless form, a^{(3)}/aH^3, equals unity for LCDM. We generalize this result to higher derivatives of the expansion factor and demonstrate that the hierarchy, a^{(n)}/aH^n, can be converted to a form that stays pegged at unity in concordance cosmology. This remarkable property of the Statefinder hierarchy enables it to be used as an extended null diagnostic for the cosmological constant. The Statefinder hierarchy combined with the growth rate of matter perturbations defines a composite null diagnostic which can distinguish evolving dark energy from LCDM.Comment: 6 pages, 6 figures; to appear in Phys. Rev.

Reconstructing the Properties of Dark Energy using Standard Sirens

Future space-based gravity wave experiments such as the Big Bang Observatory (BBO), with their excellent projected, one sigma angular resolution, will measure the luminosity distance to a large number of gravity wave (GW) sources to high precision, and the redshift of the single galaxies in the narrow solid angles towards the sources will provide the redshifts of the gravity wave sources. One sigma BBO beams contain the actual source only in 68 per cent cases; the beams that do not contain the source may contain a spurious single galaxy, leading to misidentification. To increase the probability of the source falling within the beam, larger beams have to be considered, decreasing the chances of finding single galaxies in the beams. Saini, Sethi and Sahni (2010) argued, largely analytically, that identifying even a small number of GW source galaxies furnishes a rough distance-redshift relation, which could be used to further resolve sources that have multiple objects in the angular beam. In this work we further develop this idea by introducing a self-calibrating iterative scheme which works in conjunction with Monte-Carlo simulations to determine the luminosity distance to GW sources with progressively greater accuracy. This iterative scheme allows one to determine the equation of state of dark energy to within an accuracy of a few percent for a gravity wave experiment possessing a beam width an order of magnitude larger than BBO (and therefore having a far poorer angular resolution). This is achieved with no prior information about the nature of dark energy from other data sets such as SN Ia, BAO, CMB etc.Comment: 12 pages, 10 figures. Expanded discussion, additional references. Main results unchanged. Matches published versio

First measurement of HI 21cm emission from a GRB host galaxy indicates a post-merger system

We report the detection and mapping of atomic hydrogen in HI 21cm emission from ESO 184-G82, the host galaxy of the gamma ray burst 980425. This is the first instance where HI in emission has been detected from a galaxy hosting a gamma ray burst. ESO 184-G82 is an isolated galaxy and contains a Wolf-Rayet region close to the location of the gamma ray burst and the associated supernova, SN 1998bw. This is one of the most luminous HII regions identified in the local Universe, with a very high inferred density of star formation. The HI 21cm observations reveal a high HI mass for the galaxy, twice as large as the stellar mass. The spatial and velocity distribution of the HI 21cm emission reveals a disturbed rotating gas disk, which suggests that the galaxy has undergone a recent minor merger that disrupted its rotation. We find that the Wolf-Rayet region and the gamma ray burst are both located in the highest HI column density region of the galaxy. We speculate that the merger event has resulted in shock compression of the gas, triggering extreme star formation activity, and resulting in the formation of both the Wolf-Rayet region and the gamma ray burst. The high HI column density environment of the GRB is consistent with the high HI column densities seen in absorption in the host galaxies of high redshift gamma ray bursts.Comment: Accepted for publication in MNRAS Letters. 5 pages, 5 figures, 2 tables. For the definitive version visit http://mnrasl.oxfordjournals.org

On the mass-metallicity relation, velocity dispersion and gravitational well depth of GRB host galaxies

We analyze a sample of 16 absorption systems intrinsic to long duration GRB host galaxies at $z \gtrsim 2$ for which the metallicities are known. We compare the relation between the metallicity and cold gas velocity width for this sample to that of the QSO-DLAs, and find complete agreement. We then compare the redshift evolution of the mass-metallicity relation of our sample to that of QSO-DLAs and find that also GRB hosts favour a late onset of this evolution, around a redshift of $\approx 2.6$. We compute predicted stellar masses for the GRB host galaxies using the prescription determined from QSO-DLA samples and compare the measured stellar masses for the four hosts where stellar masses have been determined from SED fits. We find excellent agreement and conclude that, on basis of all available data and tests, long duration GRB-DLA hosts and intervening QSO-DLAs are consistent with being drawn from the same underlying population. GRB host galaxies and QSO-DLAs are found to have different impact parameter distributions and we briefly discuss how this may affect statistical samples. The impact parameter distribution has two effects. First any metallicity gradient will shift the measured metallicity away from the metallicity in the centre of the galaxy, second the path of the sightline through different parts of the potential well of the dark matter halo will cause different velocity fields to be sampled. We report evidence suggesting that this second effect may have been detected.Comment: 11 pages, 6 figures, 6 tables. Accepted for publication in MNRAS Main Journal. For the definitive version visit http://mnras.oxfordjournals.org

Antioxidant and chemopreventive effects of Asperugo procumbens in a rat model of hepatocellular carcinoma

Introduction: Hepatocellular carcinoma (HCC) cancer is the fifth most common malignancy, with 0.25–1 million new cases diagnosed annually worldwide. The objective of the present study was to evaluate the antioxidant and chemopreventive effects of aqueous extract of Asperugo procumbens L. (AAP) against diethylnitrosamine (DEN)-induced hepatocellular carcinoma (HCC) in rats. Methods and Results: The model of hepatocellular carcinoma was induced by a single intraperitoneal injection of DEN (200 mg/kg) as an initiator that after two weeks followed by daily oral administration of 2-acetylaminofluorene (30 mg/kg) as a promoter for two weeks. AAP-treated rats were pretreated with the extract intragastrically at three different doses two weeks prior to DEN injection. At the end of the experiment, the marked reduction of serum biomarkers of liver damage and cancer, including alfa-fetoprotein (AFP), gamma glutamyl transpeptidase (GGT), alanine transaminase (ALT), and aspartate transaminase (AST) were observed in AAP complemented rats as compared to DEN-treated animals. Besides, the extract exhibited in vivo antioxidant activity that evident by increasing GSH concentration along with lipid peroxidation prevention in the liver tissues of HCC animals. In addition, A. procumbens showed in vitro free radical scavenging activity that determined by 1, 1-Diphenyl-2-picryl hydroxyl (DPPH) antioxidant assay. The relative weight of liver was also reduced in AAP-treaded rats as a prognostic marker in HCC. Conclusions: Our results obviously confirmed that A. procumbens possesses a chemopreventive effect against primary liver cancer induced by DEN in rats as well as  in vitro and in vivo antioxidant activities

H i 21 cm mapping of the host galaxy of AT2018cow: a fast-evolving luminous transient within a ring of high column density gas

International audienceWe report Giant Metrewave Radio Telescope H i 21 cm imaging of CGCG 137–068, the host galaxy of the fast-evolving luminous transient (FELT) AT2018cow. This is the first study of the gas properties of a FELT host galaxy. We obtain a total H i mass of (6.6 ± 0.9) × 10^8 M_⊙ for the host galaxy, which implies an atomic gas depletion time of 3 Gyr and a gas-to-stellar mass ratio of 0.47, consistent with values in normal star-forming dwarf galaxies. At spatial resolutions of ≥6 kpc, the H i of CGCG 137–068 appears to be distributed in a disc, in mostly regular rotation. However, at spatial resolutions of 2 kpc, the highest column density H i is found to lie in an asymmetric ring around the central regions, with H i column densities ≥10^21 cm^−2; AT2018cow lies within this high column density ring. This H i ring could be suggestive of an interaction between CGCG 137–068 and a companion galaxy. Such a ring is ideal for the formation of compact regions of star formation hosting massive stars, favouring massive star progenitor models for AT2018cow. We measure a 1.4 GHz flux density of 1.13 ± 0.13 mJy for AT2018cow on 2018 August 27