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

Did Galaxy Assembly and Supermassive Black-Hole Growth go hand-in-hand?

In this paper, we address whether the growth of supermassive black-holes has kept pace with the process of galaxy assembly. For this purpose, we first searched the Hubble Ultra Deep Field (HUDF) for "tadpole galaxies", which have a knot at one end and an extended tail. They appear dynamically unrelaxed -- presumably early-stage mergers -- and make up ~6% of the field galaxy population. Their redshift distribution follows that of field galaxies, indicating that -- if tadpole galaxies are indeed dynamically young -- the process of galaxy assembly generally kept up with the reservoir of field galaxies as a function of epoch. Next, we present a search for HUDF objects with point-source components that are optically variable (at the >~3.0 sigma level) on timescales of weeks--months. Among 4644 objects to i_AB=28.0 mag (10 sigma), 45 have variable point-like components, which are likely weak AGN. About 1% of all field objects show variability for 0.1 < z < 4.5, and their redshift distribution is similar to that of field galaxies. Hence supermassive black-hole growth in weak AGN likely also kept up with the process of galaxy assembly. However, the faint AGN sample has almost no overlap with the tadpole sample, which was predicted by recent hydrodynamical numerical simulations. This suggests that tadpole galaxies are early-stage mergers, which likely preceded the ``turn-on'' of the AGN component and the onset of visible point-source variability by >~1 Gyr.Comment: 9 pages, Latex2e requires 'elsart' and 'elsart3' (included), 10 postscript figures. To appear in the Proceedings of the Leiden Workshop on "QSO Host Galaxies: Evolution and Environment", eds. P.D. Barthel & D.B. Sanders (New Astron. Rev., 2006

The UDF05 follow-up of the Hubble Ultra Deep Field. I. The faint-end slope of the Lyman Break Galaxy Population at z ~ 5

We present the UDF05 HST program, which consists of three disjoint fields—NICP12, NICP34, plus the HUDF—with deep ACS (F606W, F775W, and F850LP) and NICMOS (F110W and F160W) imaging. Here we use the ACS data for the NICP12 and HUDF fields to implement a (V − i) − (i − z) selection criterion that allows us to identify a sample of 101 (133) z ~ 5 Lyman break galaxies (LBGs) down to z850 = 28.5 (29.25) mag in NICP12 (HUDF). We construct the rest-frame 1400 Å LBG luminosity function (LF) over the range M1400 = [ − 21.4, − 17.1] , i.e. down to ~0.04L* at z ~ 5, and use Subaru Deep Field results (Yoshida et al. 2006) to constrain our LF at the bright end (M1400 ≥ − 22.2). We show that (1) different assumptions regarding the LBG SED distribution, dust properties, and intergalactic absorption result in a 25% variation in the number density of LBGs at z ~ 5; (2) under consistent assumptions for dust properties and intergalactic absorption, the HUDF is ~30% underdense in z ~ 5 LBGs relative to the NICP12 field, a variation which is well explained by cosmic variance; and (3) the faint-end slope of the LF does not depend on the input parameters, and has a value of α ~ − 1.6, similar to the faint-end slope of the LF of z ~ 3 and z ~ 6 LBGs. Our study therefore supports no variation in the faint end of the LBG LF over the whole redshift range z ~ 3 to z ~ 6. Based on a comparison with semianalytical models, we speculate that the z ~ 5 LBGs might have a top-heavy IMF

The Hubble Space Telescope Wide Field Camera 3 Early Release Science data: Panchromatic Faint Object Counts for 0.2-2 microns wavelength

We describe the Hubble Space Telescope (HST) Wide Field Camera 3 (WFC3) Early Release Science (ERS) observations in the Great Observatories Origins Deep Survey (GOODS) South field. The new WFC3 ERS data provide calibrated, drizzled mosaics in the UV filters F225W, F275W, and F336W, as well as in the near-IR filters F098M (Ys), F125W (J), and F160W (H) with 1-2 HST orbits per filter. Together with the existing HST Advanced Camera for Surveys (ACS) GOODS-South mosaics in the BViz filters, these panchromatic 10-band ERS data cover 40-50 square arcmin at 0.2-1.7 {\mu}m in wavelength at 0.07-0.15" FWHM resolution and 0.090" Multidrizzled pixels to depths of AB\simeq 26.0-27.0 mag (5-{\sigma}) for point sources, and AB\simeq 25.5-26.5 mag for compact galaxies. In this paper, we describe: a) the scientific rationale, and the data taking plus reduction procedures of the panchromatic 10-band ERS mosaics; b) the procedure of generating object catalogs across the 10 different ERS filters, and the specific star-galaxy separation techniques used; and c) the reliability and completeness of the object catalogs from the WFC3 ERS mosaics. The excellent 0.07-0.15" FWHM resolution of HST/WFC3 and ACS makes star- galaxy separation straightforward over a factor of 10 in wavelength to AB\simeq 25-26 mag from the UV to the near-IR, respectively.Comment: 51 pages, 71 figures Accepted to ApJS 2011.01.2

Black Hole Growth Is Mainly Linked to Host-galaxy Stellar Mass Rather Than Star Formation Rate

We investigate the dependence of black-hole accretion rate (BHAR) on host-galaxy star formation rate (SFR) and stellar mass (M∗) in the CANDELS/GOODS-South field in the redshift range of 0.5≤z<2.0. Our sample consists of ≈18000 galaxies, allowing us to probe galaxies with 0.1≲SFR≲100 M⊙ yr−1 and/or 108≲M∗≲1011 M⊙. We use sample-mean BHAR to approximate long-term average BHAR. Our sample-mean BHARs are derived from the Chandra Deep Field-South 7 Ms observations, while the SFRs and M∗ have been estimated by the CANDELS team through SED fitting. The average BHAR is correlated positively with both SFR and M∗, and the BHAR-SFR and BHAR-M∗ relations can both be described acceptably by linear models with a slope of unity. However, BHAR appears to be correlated more strongly with M∗ than SFR. This result indicates that M∗ is the primary host-galaxy property related to black-hole growth, and the apparent BHAR-SFR relation is largely a secondary effect due to the star-forming main sequence. Among our sources, massive galaxies (M∗≳1010M⊙) have significantly higher BHAR/SFR ratios than less-massive galaxies, indicating the former have higher black-hole fueling efficiency and/or higher SMBH occupation fraction than the latter. Our results can naturally explain the observed proportionality between MBH and M∗ for local giant ellipticals, and suggest their MBH/M∗ is higher than that of local star-forming galaxies. Among local star-forming galaxies, massive systems might have higher MBH/M∗ compared to dwarfs

Governing the anthropocene: agency, governance, knowledge

The growing body of literature on the idea of the Anthropocene has opened up serious questions that go to the heart of the social and human sciences. There has been as yet no satisfactory theoretical framework for the analysis of the Anthropocene debate in the social and human sciences. The notion of the Anthropocene is not only a condition in which humans have become geologic agents, thus signalling a temporal shift in Earth history: it can be seen as a new object of knowledge and an order of governance. A promising direction for theorizing in the social and human science is to approach the notion of the Anthropocene as exemplified in new knowledge practices that have implications for governance. It invokes new conceptions of time, agency, knowledge and governance. The Anthropocene has become a way in which the human world is re-imagined culturally and politically in terms of its relation with the Earth. It entails a cultural model, that is an interpretative category by which contemporary societies make sense of the world as embedded in the Earth, and articulate a new kind of historical self-understanding, by which an alternative order of governance is projected. This points in the direction of cosmopolitics – and thus of a ‘Cosmopolocene’ – rather than a geologization of the social or in the post-humanist philosophy, the end of the human condition as one marked by agency

The scientific potential of space-based gravitational wave detectors

The millihertz gravitational wave band can only be accessed with a space-based interferometer, but it is one of the richest in potential sources. Observations in this band have amazing scientific potential. The mergers between massive black holes with mass in the range 10 thousand to 10 million solar masses, which are expected to occur following the mergers of their host galaxies, produce strong millihertz gravitational radiation. Observations of these systems will trace the hierarchical assembly of structure in the Universe in a mass range that is very difficult to probe electromagnetically. Stellar mass compact objects falling into such black holes in the centres of galaxies generate detectable gravitational radiation for several years prior to the final plunge and merger with the central black hole. Measurements of these systems offer an unprecedented opportunity to probe the predictions of general relativity in the strong-field and dynamical regime. Millihertz gravitational waves are also generated by millions of ultra-compact binaries in the Milky Way, providing a new way to probe galactic stellar populations. ESA has recognised this great scientific potential by selecting The Gravitational Universe as its theme for the L3 large satellite mission, scheduled for launch in ~2034. In this article we will review the likely sources for millihertz gravitational wave detectors and describe the wide applications that observations of these sources could have for astrophysics, cosmology and fundamental physics.Comment: 18 pages, 2 figures, contribution to Gravitational Wave Astrophysics, the proceedings of the 2014 Sant Cugat Forum on Astrophysics; v2 includes one additional referenc

New constraints on the evolution of the stellar-to-dark matter connection : a combined analysis of galaxy-galaxy lensing, clustering, and stellar mass functions from z = 0.2 to z = 1

Using data from the COSMOS survey, we perform the first joint analysis of galaxy-galaxy weak lensing, galaxy spatial clustering, and galaxy number densities. Carefully accounting for sample variance and for scatter between stellar and halo mass, we model all three observables simultaneously using a novel and self-consistent theoretical framework. Our results provide strong constraints on the shape and redshift evolution of the stellar-to-halo mass relation (SHMR) from z = 0.2 to z = 1. At low stellar mass, we find that halo mass scales as Mh vpropM 0.46 * and that this scaling does not evolve significantly with redshift from z = 0.2 to z = 1. The slope of the SHMR rises sharply at M * > 5 × 1010 M ☉ and as a consequence, the stellar mass of a central galaxy becomes a poor tracer of its parent halo mass. We show that the dark-to-stellar ratio, Mh /M *, varies from low to high masses, reaching a minimum of Mh /M * ~ 27 at M * = 4.5 × 1010 M ☉ and Mh = 1.2 × 1012 M ☉. This minimum is important for models of galaxy formation because it marks the mass at which the accumulated stellar growth of the central galaxy has been the most efficient. We describe the SHMR at this minimum in terms of the "pivot stellar mass," M piv *, the "pivot halo mass," M piv h , and the "pivot ratio," (Mh /M *)piv. Thanks to a homogeneous analysis of a single data set spanning a large redshift range, we report the first detection of mass downsizing trends for both M piv h and M piv *. The pivot stellar mass decreases from M piv * = 5.75 ± 0.13 × 1010 M ☉ at z = 0.88 to M piv * = 3.55 ± 0.17 × 1010 M ☉ at z = 0.37. Intriguingly, however, the corresponding evolution of M piv h leaves the pivot ratio constant with redshift at (Mh /M *)piv ~ 27. We use simple arguments to show how this result raises the possibility that star formation quenching may ultimately depend on Mh /M * and not simply on Mh , as is commonly assumed. We show that simple models with such a dependence naturally lead to downsizing in the sites of star formation. Finally, we discuss the implications of our results in the context of popular quenching models, including disk instabilities and active galactic nucleus feedback

The LABOCA survey of the extended Chandra Deep Field South : two modes of star formation in active galactic nucleus hosts?

We study the co-existence of star formation and active galactic nucleus (AGN) activity in Chandra X-ray-selected AGN by analyzing stacked 870 μm submillimeter emission from a deep and wide map of the Extended Chandra Deep Field South (ECDFS), obtained with the LABOCA instrument at the APEX telescope. The total X-ray sample of 895 sources with median redshift z ~ 1 drawn from the combined (E)CDFS X-ray catalogs is detected at >11σ significance at a mean submillimeter flux of 0.49 ± 0.04 mJy, corresponding to a typical star formation rate (SFR) around 30 M sun yr-1 for a T = 35 K, β = 1.5 graybody far-infrared spectral energy distribution. The good signal-to-noise ratio permits stacking analyses for major subgroups, splitting the sample by redshift, intrinsic luminosity, and AGN obscuration properties. We observe a trend of SFR increasing with redshift. An increase of SFR with AGN luminosity is indicated at the highest L 2-10 keV >~ 1044 erg s-1 luminosities only. Increasing trends with X-ray obscuration as expected in some AGN evolutionary scenarios are not observed for the bulk of the X-ray AGN sample but may be present for the highest intrinsic luminosity objects with L 2-10 keV >~ 1044 erg s-1. This behavior suggests a transition between two modes in the co-existence of AGN activity and star formation. For the bulk of the sample, the X-ray luminosity and obscuration of the AGN are not intimately linked to the global SFR of their hosts. The hosts are likely massive and forming stars secularly, at rates similar to the pervasive star formation seen in massive galaxies without an AGN at similar redshifts. In these systems, star formation is not linked to a specific state of the AGN and the period of moderately luminous AGN activity may not highlight a major evolutionary transition of the galaxy. The change indicated toward more intense star formation, and a more pronounced increase in SFRs between unobscured and obscured AGN reported in the literature at highest (L 2-10 keV >~ 1044 erg s-1) luminosities suggests that these luminous AGNs follow an evolutionary path on which obscured AGN activity and intense star formation are linked, possibly via merging. Comparison to local hard X-ray-selected AGN supports this interpretation. SFRs in the hosts of moderate luminosity AGN at z ~ 1 are an order of magnitude higher than at z ~ 0, following the increase in the non-AGN massive galaxy population. At high AGN luminosities, hosts on the evolutionary link/merger path emerge from this secular level of star formation

Physical Characterization of an Unlensed, Dusty Star-forming Galaxy at z = 5.85

We present a physical characterization of MM J100026.36+021527.9 (a.k.a. "Mambo-9"), a dusty star-forming galaxy (DSFG) at z = 5.850 \ub1 0.001. This is the highest-redshift unlensed DSFG (and fourth most distant overall) found to date and is the first source identified in a new 2 mm blank-field map in the COSMOS field. Though identified in prior samples of DSFGs at 850 \u3bcm to 1.2 mm with unknown redshift, the detection at 2 mm prompted further follow-up as it indicated a much higher probability that the source was likely to sit at z &gt; 4. Deep observations from the Atacama Large Millimeter and submillimeter Array (ALMA) presented here confirm the redshift through the secure detection of 12CO(J = 6\u21925) and p-H2O (21,1 \u2192 20,2). Mambo-9 is composed of a pair of galaxies separated by 6 kpc with corresponding star formation rates of 590 M o\u2d9 yr-1 and 220 M o\u2d9 yr-1, total molecular hydrogen gas mass of (1.7 \ub1 0.4) 7 1011 M o\u2d9, dust mass of (1.3 \ub1 0.3) 7 109 M o\u2d9, and stellar mass of (3.2-1.5+1.0) 7 109 M o\u2d9. The total halo mass, (3.3 \ub1 0.8) 7 1012 M o\u2d9, is predicted to exceed 1015 M o\u2d9 by z = 0. The system is undergoing a merger-driven starburst that will increase the stellar mass of the system tenfold in \u3c4 depl = 40-80 Myr, converting its large molecular gas reservoir (gas fraction of 96-2+1) into stars. Mambo-9 evaded firm spectroscopic identification for a decade, following a pattern that has emerged for some of the highest-redshift DSFGs found. And yet, the systematic identification of unlensed DSFGs like Mambo-9 is key to measuring the global contribution of obscured star formation to the star formation rate density at z \u2a86 4, the formation of the first massive galaxies, and the formation of interstellar dust at early times ( 721 Gyr)