A Dependence of the Tidal Disruption Event Rate on Global Stellar Surface Mass Density and Stellar Velocity Dispersion

© 2018. The American Astronomical Society. All rights reserved. The rate of tidal disruption events (TDEs), R TDE , is predicted to depend on stellar conditions near the super-massive black hole (SMBH), which are on difficult-to-measure sub-parsec scales. We test whether R TDE depends on kpcscale global galaxy properties, which are observable. We concentrate on stellar surface mass density, ∑ M∗ , and velocity dispersion, σ v , which correlate with the stellar density and velocity dispersion of the stars around the SMBH. We consider 35 TDE candidates, with and without known X-ray emission. The hosts range from starforming to quiescent to quiescent with strong Balmer absorption lines. The last (often with post-starburst spectra) are overrepresented in our sample by a factor of 35 +21 -17 or 18 +8 -7 , depending on the strength of the Hδ absorption line. For a subsample of hosts with homogeneous measurements, ∑ M∗ = 10 9 -10 10 M ⊙ /kpc 2 , higher on average than for a volume-weighted control sample of Sloan Digital Sky Survey galaxies with similar redshifts and stellar masses. This is because (1) most of the TDE hosts here are quiescent galaxies, which tend to have higher ∑ M∗ than the star-forming galaxies that dominate the control, and (2) the star-forming hosts have higher average ∑ M∗ than the star-forming control. There is also a weak suggestion that TDE hosts have lower σ v than for the quiescent control. Assuming that R TDE ∝ ∑ M∗ α × σ v β , and applying a statistical model to the TDE hosts and control sample, we estimate α = 0.9 ; 0.2 and β = -1.0 0.6. This is broadly consistent with RTDE being tied to the dynamical relaxation of stars surrounding the SMBH

The luminosity function of field galaxies

Schmidt's method for construction of luminosity function of galaxies is generalized by taking into account the dependence of density of galaxies from the distance in the near Universe. The logarithmical luminosity function (LLF) of field galaxies depending on morphological type is constructed. We show that the LLF for all galaxies, and also separately for elliptical and lenticular galaxies can be presented by Schechter function in narrow area of absolute magnitudes. The LLF of spiral galaxies was presented by Schechter function for enough wide area of absolute magnitudes: . Spiral galaxies differ slightly by parameter . At transition from early spirals to the late spirals parameter in Schechter function is reduced. The reduction of mean luminosity of galaxies is observed at transition from elliptical galaxies to lenticular galaxies, to early spiral galaxies, and further, to late spiral galaxies, in a bright end, . The completeness and the average density of samples of galaxies of different morphological types are estimated. In the range the mean number density of all galaxies is equal 0.127 Mpc-3.Comment: 14 page, 8 figures, to appear in Astrophysic

Cosmological parameters from the clustering of AGN

We attempt to put constraints on different cosmological and biasing models by combining the recent clustering results of X-ray sources in the local ($z\le 0.1$) and distant universe ($z\sim 1$).Comment: 9 pages, 3 figures, to be published in the proceedings of the ''2nd Hellenic Cosmology Workshop'', Athens 2001, eds, Manolis Plionis & Spiros Kotsaki

Checkpoint kinase inhibitor AZD7762 strongly sensitises urothelial carcinoma cells to gemcitabine

Background: More effective chemotherapies are urgently needed for bladder cancer, a major cause of morbidity and mortality worldwide. We therefore explored the efficacy of the combination of gemcitabine and AZD7762, a checkpoint kinase 1/2 (CHK1/2) inhibitor, for bladder cancer. Methods: Viability, clonogenicity, cell cycle distribution and apoptosis were assessed in urothelial cancer cell lines and various non-malignant urothelial cells treated with gemcitabine and AZD7762. DNA damage was assessed by ?H2A.X and 53-BP1 staining and checkpoint activation was followed by Western blotting. Pharmacological inhibition of CHK1 and CHK2 was compared to downregulation of either CHK1 or CHK2 using siRNAs. Results: Combined use of gemcitabine and AZD7762 synergistically reduced urothelial carcinoma cell viability and colony formation relative to either single treatment. Non-malignant urothelial cells were substantially less sensitive to this drug combination. Gemcitabine plus AZD7762 inhibited cell cycle progression causing cell accumulation in S-phase. Moreover, the combination induced pronounced levels of apoptosis as indicated by an increase in the fraction of sub-G1 cells, in the levels of cleaved PARP, and in caspase 3/7 activity. Mechanistic investigations showed that AZD7762 treatment inhibited the repair of gemcitabine-induced double strand breaks by interference with CHK1, since siRNA-mediated depletion of CHK1 but not of CHK2 mimicked the effects of AZD7762. Conclusions: AZD7762 enhanced sensitivity of urothelial carcinoma cells to gemcitabine by inhibiting DNA repair and disturbing checkpoints. Combining gemcitabine with CHK1 inhibition holds promise for urothelial cancer therapy

A Dependence of the Tidal Disruption Event Rate on Global Stellar Surface Mass Density and Stellar Velocity Dispersion

© 2018. The American Astronomical Society. All rights reserved. The rate of tidal disruption events (TDEs), R TDE , is predicted to depend on stellar conditions near the super-massive black hole (SMBH), which are on difficult-to-measure sub-parsec scales. We test whether R TDE depends on kpcscale global galaxy properties, which are observable. We concentrate on stellar surface mass density, ∑ M∗ , and velocity dispersion, σ v , which correlate with the stellar density and velocity dispersion of the stars around the SMBH. We consider 35 TDE candidates, with and without known X-ray emission. The hosts range from starforming to quiescent to quiescent with strong Balmer absorption lines. The last (often with post-starburst spectra) are overrepresented in our sample by a factor of 35 +21 -17 or 18 +8 -7 , depending on the strength of the Hδ absorption line. For a subsample of hosts with homogeneous measurements, ∑ M∗ = 10 9 -10 10 M ⊙ /kpc 2 , higher on average than for a volume-weighted control sample of Sloan Digital Sky Survey galaxies with similar redshifts and stellar masses. This is because (1) most of the TDE hosts here are quiescent galaxies, which tend to have higher ∑ M∗ than the star-forming galaxies that dominate the control, and (2) the star-forming hosts have higher average ∑ M∗ than the star-forming control. There is also a weak suggestion that TDE hosts have lower σ v than for the quiescent control. Assuming that R TDE ∝ ∑ M∗ α × σ v β , and applying a statistical model to the TDE hosts and control sample, we estimate α = 0.9 ; 0.2 and β = -1.0 0.6. This is broadly consistent with RTDE being tied to the dynamical relaxation of stars surrounding the SMBH

Probing galaxy formation with He II cooling lines

Using high-resolution cosmological simulations, we study hydrogen and helium gravitational cooling radiation from gas accretion by young galaxies. We focus on the He II cooling lines, which arise from gas with a different temperature history (Tmax ~ 105 K) than H I line-emitting gas. We examine whether three major atomic cooling lines, H I λ1216, He II λ1640, and He II λ304, are observable, finding that Lyα and He II λ1640 cooling emission at z = 2-3 are potentially detectable with deep narrowband (R \u3e 100) imaging and/or spectroscopy from the ground. While the expected strength of H I λ1216 cooling emission depends strongly on the treatment of the self-shielded phase of the IGM in the simulations, our predictions for the He II λ1640 line are more robust, because the He II emissivity is negligible below T ~ 104.5 K and less sensitive to the UV background. Although He II λ1640 cooling emission is fainter than Lyα by at least a factor of 10 and, unlike Lyα, might not be resolved spatially with current observational facilities, it is more suitable to study gas accretion in the galaxy formation process because it is optically thin and less contaminated by the recombination lines from star-forming galaxies. The He II λ1640 line can be used to distinguish among mechanisms for powering the so-called Lyα blobs—including gravitational cooling radiation, photoionization by stellar populations, and starburst-driven superwinds—because (1) He II λ1640 emission is limited to very low metallicity [log(Z/Z) -5.3] and Population III stars and (2) the blob\u27s kinematics are probed unambiguously through the He II line width, which for cooling radiation is narrower (σ \u3c 400 km s-1) than typical wind speeds

The Las Campanas/Anglo-Australian Telescope Rich Cluster Survey - III. Spectroscopic studies of X-ray bright galaxy clusters at z similar to 0.1

We present the analysis of the spectroscopic and photometric catalogues of 11 X-ray luminous clusters at 0.07 < z < 0.16 from the Las Campanas/Anglo-Australian Telescope Rich Cluster Survey. Our spectroscopic data set consists of over 1600 galaxy cluster members, of which two-thirds are outside r(200). These spectra allow us to assign cluster membership using a detailed mass model and expand on our previous work on the cluster colour-magnitude relation ( CMR) where membership was inferred statistically. We confirm that the modal colours of galaxies on the CMR become progressively bluer with increasing radius d( B - R)/dr(p) = - 0.011 +/- 0.003 and with decreasing local galaxy density d( B - R)/dlog ( Sigma)= - 0.062 +/- 0.009. Interpreted as an age effect, we hypothesize that these trends in galaxy colour should be reflected in mean H delta equivalent width. We confirm that passive galaxies in the cluster increase in Hd line strength as dH delta/dr(p) = 0.35 +/- 0.06. Therefore, those galaxies in the cluster outskirts may have younger luminosity-weighted stellar populations; up to 3 Gyr younger than those in the cluster centre assuming d( B - R)/dt = 0.03 mag per Gyr. A variation of star formation rate, as measured by [ O II]lambda 3727 angstrom, with increasing local density of the environment is discernible and is shown to be in broad agreement with previous studies from the 2dF Galaxy Redshift Survey and the Sloan Digital Sky Survey. We divide our spectra into a variety of types based upon the MORPHs classification scheme. We find that clusters at z similar to 0.1 are less active than their higher-redshift analogues: about 60 per cent of the cluster galaxy population is non-star forming, with a further 20 per cent in the post-starburst class and 20 per cent in the currently active class, demonstrating that evolution is visible within the past 2 - 3 Gyr. We also investigate unusual populations of blue and very red non-star forming galaxies and we suggest that the former are likely to be the progenitors of galaxies which will lie on the CMR, while the colours of the latter possibly reflect dust reddening. We show that the cluster galaxies at large radii consist of both backsplash ones and those that are infalling to the cluster for the first time. We make a comparison to the field population at z similar to 0.1 and examine the broad differences between the two populations. Individually, the clusters show significant variation in their galaxy populations which we suggest reflects their recent infall histories

The Las Campanas/AAT rich cluster survey - I. Precision and reliabilityof the photometric catalogue

The Las Campanas Observatory and Anglo--Australian Telescope Rich Cluster Survey (LARCS) is a panoramic imaging and spectroscopic survey of an X-ray luminosity-selected sample of 21 clusters of galaxies at 0.07<z<0.16. CCD imaging was obtained in B and R of typically 2-degree wide regions centred on the 21 clusters, and the galaxy sample selected from the imaging is being used for an on-going spectroscopic survey of the clusters with the 2dF spectrograph on the Anglo-Australian Telescope. This paper presents the reduction of the imaging data and the photometric analysis used in the survey. Based on an overlapping area of 12.3 square degrees, we compare the CCD-based LARCS catalogue with the photographic-based galaxy catalogue used for the input to the 2dF Galaxy Redshift Survey (2dFGRS) from the APM, to the completeness of the GRS/APM catalogue, b_J=19.45. This comparison confirms the reliability of the photometry across our mosaics and between the clusters in our survey. This comparison also provides useful information about the properties of the GRS/APM. The stellar contamination in the GRS/APM galaxy catalogue is confirmed to be around 5-10 percent, as originally estimated. However, using the superior sensitivity and spatial resolution in the LARCS survey, we find evidence for four distinct populations of galaxies that are systematically omitted from the GRS/APM catalogue. The characteristics of the `missing' galaxy populations are described, reasons for their absence examined and the impact they will have on the conclusions drawn from the 2dF Galaxy Redshift Survey are discussed.Comment: 14 pages, 12 figures. Accepted for publication in MNRAS. Typographical errors correcte

Probing galaxy formation with He II cooling lines

This is the pre-published version harvested from ArXiv. The published version is located at http://iopscience.iop.org/0004-637X/640/2/539/Using high-resolution cosmological simulations, we study hydrogen and helium gravitational cooling radiation from gas accretion by young galaxies. We focus on the He II cooling lines, which arise from gas with a different temperature history (Tmax ~ 105 K) than H I line-emitting gas. We examine whether three major atomic cooling lines, H I λ1216, He II λ1640, and He II λ304, are observable, finding that Lyα and He II λ1640 cooling emission at z = 2-3 are potentially detectable with deep narrowband (R > 100) imaging and/or spectroscopy from the ground. While the expected strength of H I λ1216 cooling emission depends strongly on the treatment of the self-shielded phase of the IGM in the simulations, our predictions for the He II λ1640 line are more robust, because the He II emissivity is negligible below T ~ 104.5 K and less sensitive to the UV background. Although He II λ1640 cooling emission is fainter than Lyα by at least a factor of 10 and, unlike Lyα, might not be resolved spatially with current observational facilities, it is more suitable to study gas accretion in the galaxy formation process because it is optically thin and less contaminated by the recombination lines from star-forming galaxies. The He II λ1640 line can be used to distinguish among mechanisms for powering the so-called Lyα blobs—including gravitational cooling radiation, photoionization by stellar populations, and starburst-driven superwinds—because (1) He II λ1640 emission is limited to very low metallicity [log(Z/Z) -5.3] and Population III stars and (2) the blob's kinematics are probed unambiguously through the He II line width, which for cooling radiation is narrower (σ < 400 km s-1) than typical wind speeds.539-55

The Velocity Dispersions Distribution of Galaxy Clusters

We compute the distribution of internal velocity dispersions, a, for a sample of 153 nearby Abell-ACO galaxy clusters (z less than or equal to 0.15), each of which has at least 30 available galaxy redshifts. Throughout our work we applied homogeneous procedures to the analysis of the redshifts of the clusters selected. Previous sigma-distributions, based on smaller cluster samples, are complete for the Abell richness class R greater than or equal to 1. In order to improve sigma completeness, we enlarge our sample by including also poorer clusters. By resampling our 153 clusters, according to the richness class frequencies of the Edinburgh-Durham Cluster Catalog (EDCC), we obtain a cluster sample which can be taken as representative of the nearby Universe. Our cumulative sigma-distribution agrees with previous distributions within their sigma completeness limit (sigma greater than or equal to 800 km s(-1)). We estimate that our distribution is complete for at least sigma greater than or equal to 650 km s(-1). In this completeness range, a fit of the form dN alpha sigma(alpha)d sigma gives alpha = -(7.4(-0.8)(+0.7)), in fair agreement with results coming from the X-ray temperature distributions of nearby clusters