The VIMOS Ultra Deep Survey. Luminosity and stellar mass dependence of galaxy clustering at z~3

We present the study of the dependence of galaxy clustering on luminosity and stellar mass in the redshift range 2$<$z$<$3.5 using 3236 galaxies with robust spectroscopic redshifts from the VIMOS Ultra Deep Survey (VUDS). We measure the two-point real-space correlation function $w_p(r_p)$ for four volume-limited stellar mass and four luminosity, M$_{UV}$ absolute magnitude selected, sub-samples. We find that the scale dependent clustering amplitude $r_0$ significantly increases with increasing luminosity and stellar mass indicating a strong galaxy clustering dependence on these properties. This corresponds to a strong relative bias between these two sub-samples of $\Delta$b/b$^*$=0.43. Fitting a 5-parameter HOD model we find that the most luminous and massive galaxies occupy the most massive dark matter haloes with $\langle$M$_h$$\rangle$ = 10$^{12.30}$ h$^{-1}$ M$_{\odot}$. Similar to the trends observed at lower redshift, the minimum halo mass M$_{min}$ depends on the luminosity and stellar mass of galaxies and grows from M$_{min}$ =10$^{9.73}$ h$^{-1}$M$_{\odot}$ to M$_{min}$=10$^{11.58}$ h$^{-1}$M$_{\odot}$ from the faintest to the brightest among our galaxy sample, respectively. We find the difference between these halo masses to be much more pronounced than is observed for local galaxies of similar properties. Moreover, at z~3, we observe that the masses at which a halo hosts, on average, one satellite and one central galaxy is M$_1$$\approx$4M$_{min}$ over all luminosity ranges, significantly lower than observed at z~0 indicating that the halo satellite occupation increases with redshift. The luminosity and stellar mass dependence is also reflected in the measurements of the large scale galaxy bias, which we model as b$_{g,HOD}$($>$L)=1.92+25.36(L/L$^*$)$^{7.01}$. We conclude our study with measurements of the stellar-to-halo mass ratio (SHMR).Comment: 20 pages, 11 figures, A&A in press, v2. revised discussion in sec. 5.5, changed Fig. 4 and Fig. 11, added reference

The extended epoch of galaxy formation: age dating of ~3600 galaxies with 2<z<6.5 in the VIMOS Ultra-Deep Survey

We aim at improving constraints on the epoch of galaxy formation by measuring the ages of 3597 galaxies with spectroscopic redshifts 2<z<6.5 in the VIMOS Ultra Deep Survey (VUDS). We derive ages and other physical parameters from the simultaneous fitting with the GOSSIP+ software of observed UV rest-frame spectra and photometric data from the u-band up to 4.5 microns using composite stellar population models. We conclude from extensive simulations that at z>2 the joint analysis of spectroscopy and photometry combined with restricted age possibilities when taking into account the age of the Universe substantially reduces systematic uncertainties and degeneracies in the age derivation. We find galaxy ages ranging from very young with a few tens of million years to substantially evolved with ages up to ~1.5-2 Gyr. The formation redshifts z_f derived from the measured ages indicate that galaxies may have started forming stars as early as z_f~15. We produce the formation redshift function (FzF), the number of galaxies per unit volume formed at a redshift z_f, and compare the FzF in increasing redshift bins finding a remarkably constant 'universal' FzF. The FzF is parametrized with (1+z)^\zeta, with \zeta~0.58+/-0.06, indicating a smooth 2 dex increase from z~15 to z~2. Remarkably this observed increase is of the same order as the observed rise in the star formation rate density (SFRD). The ratio of the SFRD with the FzF gives an average SFR per galaxy of ~7-17Msun/yr at z~4-6, in agreement with the measured SFR for galaxies at these redshifts. From the smooth rise in the FzF we infer that the period of galaxy formation extends from the highest possible redshifts that we can probe at z~15 down to redshifts z~2. This indicates that galaxy formation is a continuous process over cosmic time, with a higher number of galaxies forming at the peak in SFRD at z~2 than at earlier epochs. (Abridged)Comment: Submitted to A&A, 24 page

Breaking the Curve with CANDELS: A Bayesian Approach to Reveal the Non-Universality of the Dust-Attenuation Law at High Redshift

Dust attenuation affects nearly all observational aspects of galaxy evolution, yet very little is known about the form of the dust-attenuation law in the distant Universe. Here, we model the spectral energy distributions (SEDs) of galaxies at z = 1.5--3 from CANDELS with rest-frame UV to near-IR imaging under different assumptions about the dust law, and compare the amount of inferred attenuated light with the observed infrared (IR) luminosities. Some individual galaxies show strong Bayesian evidence in preference of one dust law over another, and this preference agrees with their observed location on the plane of infrared excess (IRX, $L_{\text{TIR}}/L_{\text{UV}}$) and UV slope ($\beta$). We generalize the shape of the dust law with an empirical model, $A_{\lambda,\delta}=E(B-V)\ k_\lambda\ (\lambda/\lambda_V)^\delta$ where $k_\lambda$ is the dust law of Calzetti et al. (2000), and show that there exists a correlation between the color excess ${E(B-V)}$ and tilt $\delta$ with ${\delta=(0.62\pm0.05)\log(E(B-V))}$+ ${(0.26~\pm~0.02)}$. Galaxies with high color excess have a shallower, starburst-like law, and those with low color excess have a steeper, SMC-like law. Surprisingly, the galaxies in our sample show no correlation between the shape of the dust law and stellar mass, star-formation rate, or $\beta$. The change in the dust law with color excess is consistent with a model where attenuation is caused by by scattering, a mixed star-dust geometry, and/or trends with stellar population age, metallicity, and dust grain size. This rest-frame UV-to-near-IR method shows potential to constrain the dust law at even higher ($z>3$) redshifts.Comment: 20 pages, 18 figures, resubmitted to Ap

Comprehensive comparison between azacytidine and decitabine treatment in an acute myeloid leukemia cell line

Azacytidine (AzaC) and decitabine (AzadC) are cytosine analogs that covalently trap DNA methyltransferases, which place the important epigenetic mark 5-methyl-2’-deoxycytidine by methylating 2’-deoxycytidine (dC) at the C5 position. AzaC and AzadC are used in the clinic as antimetabolites to treat myelodysplastic syndrome and acute myeloid leukemia and are explored against other types of cancer. Although their principal mechanism of action is known, the downstream effects of AzaC and AzadC treatment are not well understood and the cellular prerequisites that determine sensitivity toward AzaC and AzadC remain elusive. Here, we investigated the effects and phenotype of AzaC and AzadC exposure on the acute myeloid leukemia cell line MOLM-13. We found that while AzaC and AzadC share many effects on the cellular level, including decreased global DNA methylation, increased formation of DNA double-strand breaks, transcriptional downregulation of important oncogenes and similar changes on the proteome level, AzaC failed in contrast to AzadC to induce apoptosis efficiently in MOLM-13. The only cellular marker that correlated with this clear phenotypical outcome was the level of hydroxy-methyl-dC, an additional epigenetic mark that is placed by TET enzymes and repressed in cancer cells. Whereas AzadC increased hmdC substantially in MOLM-13, AzaC treatment did not result in any increase at all. This suggests that hmdC levels in cancer cells should be monitored as a response toward AzaC and AzadC and considered as a biomarker to judge whether AzaC or AzadC treatment leads to cell death in leukemic cells

CANDELS Sheds Light on the Environmental Quenching of Low-mass Galaxies

We investigate the environmental quenching of galaxies, especially those with stellar masses (M*)$<10^{9.5} M_\odot$, beyond the local universe. Essentially all local low-mass quenched galaxies (QGs) are believed to live close to massive central galaxies, which is a demonstration of environmental quenching. We use CANDELS data to test {\it whether or not} such a dwarf QG--massive central galaxy connection exists beyond the local universe. To this purpose, we only need a statistically representative, rather than a complete, sample of low-mass galaxies, which enables our study to $z\gtrsim1.5$. For each low-mass galaxy, we measure the projected distance ($d_{proj}$) to its nearest massive neighbor (M*$>10^{10.5} M_\odot$) within a redshift range. At a given redshift and M*, the environmental quenching effect is considered to be observed if the $d_{proj}$ distribution of QGs ($d_{proj}^Q$) is significantly skewed toward lower values than that of star-forming galaxies ($d_{proj}^{SF}$). For galaxies with $10^{8} M_\odot < M* < 10^{10} M_\odot$, such a difference between $d_{proj}^Q$ and $d_{proj}^{SF}$ is detected up to $z\sim1$. Also, about 10\% of the quenched galaxies in our sample are located between two and four virial radii ($R_{Vir}$) of the massive halos. The median projected distance from low-mass QGs to their massive neighbors, $d_{proj}^Q / R_{Vir}$, decreases with satellite M* at $M* \lesssim 10^{9.5} M_\odot$, but increases with satellite M* at $M* \gtrsim 10^{9.5} M_\odot$. This trend suggests a smooth, if any, transition of the quenching timescale around $M* \sim 10^{9.5} M_\odot$ at $0.5<z<1.0$.Comment: 8 pages, 5 figures. ApJL accepted. Typos correcte

The VIMOS Ultra-Deep Survey: A major merger origin for the high fraction of galaxies at 2 &lt; z &lt; 6 with two bright clumps

(Abridged) The properties of stellar clumps in star forming galaxies and their evolution over the redshift range $2\lesssim z \lesssim 6$ are presented and discussed in the context of the build-up of massive galaxies at early cosmic times. We use HST/ACS images of galaxies with spectroscopic redshifts from the VIMOS Ultra Deep Survey (VUDS) to identify clumps within a 20 kpc radius. We find that the population of galaxies with more than one clump is dominated by galaxies with two clumps, representing $\sim21-25$\% of the population, while the fraction of galaxies with 3, or 4 and more, clumps is 8-11 and 7-9\%, respectively. The fraction of clumpy galaxies is in the range $\sim35-55\%$ over $2<z<6$, increasing at higher redshifts, indicating that the fraction of irregular galaxies remains high up to the highest redshifts. The large and bright clumps (M$_{\star}\sim10^9$ up to $\sim10^{10}$M$_\odot$) are found to reside predominantly in galaxies with two clumps. Smaller and lower luminosity clumps ($\log_{10}\left(M_{\star}/\mathrm{M_\odot}\right)<9$) are found in galaxies with three clumps or more. We interpret these results as evidence for two different modes of clump formation working in parallel. The small low luminosity clumps are likely the result of disc fragmentation, with violent disc instabilities (VDI) forming several long-lived clumps in-situ, as suggested from simulations. A fraction of these clumps is also likely coming from minor mergers. The clumps in the dominating population of galaxies with two clumps are significantly more massive and have properties akin to those in merging pairs observed at similar redshifts; they appear as more massive than the most massive clumps observed in VDI numerical simulations

SDSS-III Baryon Oscillation Spectroscopic Survey data release 12 : galaxy target selection and large-scale structure catalogues

The Baryon Oscillation Spectroscopic Survey (BOSS), part of the Sloan Digital Sky Survey (SDSS) III project, has provided the largest survey of galaxy redshifts available to date, in terms of both the number of galaxy redshifts measured by a single survey, and the effective cosmological volume covered. Key to analysing the clustering of these data to provide cosmological measurements is understanding the detailed properties of this sample. Potential issues include variations in the target catalogue caused by changes either in the targeting algorithm or properties of the data used, the pattern of spectroscopic observations, the spatial distribution of targets for which redshifts were not obtained, and variations in the target sky density due to observational systematics. We document here the target selection algorithms used to create the galaxy samples that comprise BOSS. We also present the algorithms used to create large-scale structure catalogues for the final Data Release (DR12) samples and the associated random catalogues that quantify the survey mask. The algorithms are an evolution of those used by the BOSS team to construct catalogues from earlier data, and have been designed to accurately quantify the galaxy sample. The code used, designated mksample, is released with this paper.Publisher PDFPeer reviewe

The VIMOS Ultra Deep Survey: Lyα\alpha Emission and Stellar Populations of Star-Forming Galaxies at 2<z<2.5

The aim of this paper is to investigate spectral and photometric properties of 854 faint ($i_{AB}$<~25 mag) star-forming galaxies (SFGs) at 2<z<2.5 using the VIMOS Ultra-Deep Survey (VUDS) spectroscopic data and deep multi-wavelength photometric data in three extensively studied extragalactic fields (ECDFS, VVDS, COSMOS). These SFGs were targeted for spectroscopy based on their photometric redshifts. The VUDS spectra are used to measure the UV spectral slopes ($\beta$) as well as Ly$\alpha$ equivalent widths (EW). On average, the spectroscopically measured $\beta$ (-1.36$\pm$0.02), is comparable to the photometrically measured $\beta$ (-1.32$\pm$0.02), and has smaller measurement uncertainties. The positive correlation of $\beta$ with the Spectral Energy Distribution (SED)-based measurement of dust extinction, E$_{\rm s}$(B-V), emphasizes the importance of $\beta$ as an alternative dust indicator at high redshifts. To make a proper comparison, we divide these SFGs into three subgroups based on their rest-frame Ly$\alpha$ EW: SFGs with no Ly$\alpha$ emission (SFG$_{\rm N}$; EW$\le$0\AA), SFGs with Ly$\alpha$ emission (SFG$_{\rm L}$; EW$>$0\AA), and Ly$\alpha$ emitters (LAEs; EW$\ge$20\AA). The fraction of LAEs at these redshifts is $\sim$10%, which is consistent with previous observations. We compared best-fit SED-estimated stellar parameters of the SFG$_{\rm N}$, SFG$_{\rm L}$ and LAE samples. For the luminosities probed here ($\sim$L$^*$), we find that galaxies with and without Ly$\alpha$ in emission have small but significant differences in their SED-based properties. We find that LAEs have less dust, and lower star-formation rates (SFR) compared to non-LAEs. We also find that LAEs are less massive compared to non-LAEs, though the difference is smaller and less significant compared to the SFR and E$_{\rm s}$(B-V). [abridged]Comment: Accepted for publication in A&A, 19 pages, 10 figures, 1 tabl

The evolution of clustering length, large-scale bias and host halo mass at 2<z<5 in the VIMOS Ultra Deep Survey (VUDS)

We investigate the evolution of galaxy clustering for galaxies in the redshift range 2.0<$z$<5.0 using the VIMOS Ultra Deep Survey (VUDS). We present the projected (real-space) two-point correlation function $w_p(r_p)$ measured by using 3022 galaxies with robust spectroscopic redshifts in two independent fields (COSMOS and VVDS-02h) covering in total 0.8 deg$^2$. We quantify how the scale dependent clustering amplitude $r_0$ changes with redshift making use of mock samples to evaluate and correct the survey selection function. Using a power-law model $\xi(r) = (r/r_0)^{-\gamma}$ we find that the correlation function for the general population is best fit by a model with a clustering length $r_0$=3.95$^{+0.48}_{-0.54}$ h$^{-1}$Mpc and slope $\gamma$=1.8$^{+0.02}_{-0.06}$ at $z$~2.5, $r_0$=4.35$\pm$0.60 h$^{-1}$Mpc and $\gamma$=1.6$^{+0.12}_{-0.13}$ at $z$~3.5. We use these clustering parameters to derive the large-scale linear galaxy bias $b_L^{PL}$, between galaxies and dark matter. We find $b_L^{PL}$ = 2.68$\pm$0.22 at redshift $z$~3 (assuming $\sigma_8$ = 0.8), significantly higher than found at intermediate and low redshifts. We fit an HOD model to the data and we obtain that the average halo mass at redshift $z$~3 is $M_h$=10$^{11.75\pm0.23}$ h$^{-1}$M$_{\odot}$. From this fit we confirm that the large-scale linear galaxy bias is relatively high at $b_L^{HOD}$ = 2.82$\pm$0.27. Comparing these measurements with similar measurements at lower redshifts we infer that the star-forming population of galaxies at $z$~3 should evolve into the massive and bright ($M_r$<-21.5) galaxy population which typically occupy haloes of mass $\langle M_h\rangle$ = 10$^{13.9}$ h$^{-1}$ $M_{\odot}$ at redshift $z$=0.Comment: 19 pages, 10 figures, submitted to A&

Combined analysis of Hubble and VLT photometry of the intermediate mass black hole ESO 243-49 HLX-1

In this paper, we present a combined analysis of data obtained with the Hubble Space Telescope (HST), Very Large Telescope (VLT) and Swift X-ray telescope of the intermediate-mass black hole ESO 243-49 HLX-1 that were taken two months apart between 2010 September and November. Previous separate analyses of these data found that they were consistent with an irradiated accretion disc with contribution from either a very young or very old stellar population, and also indicated that the optical flux of the HLX-1 counterpart could be variable. Such variability could only be attributed to a varying accretion disc, so simultaneous analysis of all data sets should break the degeneracies in the model fits. We thus simultaneously fit the broad-band spectral energy distribution (SED) from near-infrared through to X-ray wavelengths of the two epochs of data with a model consisting of an irradiated accretion disc and a stellar population. We show that this combined analysis rules out an old stellar population, finding that the SED is dominated by emission from an accretion disc with moderate reprocessing in the outer disc around an intermediate-mass black hole imbedded in a young (&tilde;20 Myr) stellar cluster with a mass of &tilde;105 M&amp;sun;. We also place an upper limit on the mass of an additional hidden old stellar population of &tilde;106 M&amp;sun;. However, optical r&#39;-band observations of HLX-1 obtained with the Gemini-South telescope covering part of the decay from a later X-ray outburst are consistent with constant optical flux, indicating that the observed variability between the HST and VLT observations could be spurious caused by differences in the background subtraction applied to the two optical data sets. In this scenario, the contribution of the stellar population, and thus the stellar mass of the cluster, may be higher. Nonetheless, variability of &lt;50 per cent cannot be ruled out by the Gemini data and thus they are still consistent within the errors with an exponential decay similar to that observed in X-rays.</p