[3] arXiv:0812.2476 [ps, pdf, other] Title: A Millimetre Survey of Starburst Dominated Ultraluminous Infrared Galaxies at z~2 Authors: J. D. Younger (CfA/Harvard), A. Omont (IAP), N. Fiolet (IAP), J.-S. Huang (CfA/Harvard), G. G. Fazio (CfA/Harvard), K. Lai (CfA/Harvard), M. Polletta (INAF-IASF Milano), D. Rigopoulou (Oxford), R. Zylka (IRAM) Comments: 11 pages, 10 figures, resubmitted to MNRAS with minor revisions Subjects: Astrophysics (astro-ph) We present millimetre observations of a sample of 12 high redshift ultraluminous infrared galaxies (ULIRGs) in the Extended Growth Strip (EGS). These objects were initially selected on the basis of their observed mid--IR colours (0.0 < [3.6]-[4.5] < 0.4 and -0.7 < [3.6]-[8.0] < 0.5) to lie at high redshift 1.5 < z < 3, and subsequent 20-38 micron mid-IR spectroscopy confirms that they lie in a narrow redshift window centered on z=2. We detect 9/12 of the objects in our sample at high significance (>3 sigma) with a mean 1200\micron flux of = 1.6+/-0.1 mJy. Our millimetre photometry, combined with existing far-IR photometry from the Far-IR Deep Extragalactic Legacy (FIDEL) Survey and accurate spectroscopic redshifts, places constraints both sides of the thermal dust peak. This allows us to estimate the dust properties, including the far--IR luminosity, dust temperature, and dust mass. We find that our sample is similar to other high-z and intermediate-z ULIRGs, and local systems, but has a different dust selection function than submillimeter-selected galaxies. Finally, we use existing 20cm radio continuum imaging to test the far-IR/radio correlation at high redshift. We find that our sample is consistent with the local relation, implying little evolution. Furthermore, this suggests that our sample selection method is efficient at identifying ultraluminous, starburst--dominated systems within a very narrow redshift range centered at z~2. [7] arXiv:0812.2481 [ps, pdf, other] Title: A Highly Complete Spectroscopic Survey of the GOODS-N Field Authors: A. J. Barger, L. L. Cowie, W.-H. Wang Comments: 24 pages, published in ApJ Journal-ref: The Astrophysical Journal, 689, 687 (2008) Subjects: Astrophysics (astro-ph) We present a table of redshifts for 2907 galaxies and stars in the 145 square arcmin HST ACS GOODS-North, making this the most spectroscopically complete redshift sample obtained to date in a field of this size. We also include the redshifts, where available, in a table containing just under 7000 galaxies from the ACS area with K_s(AB)<24.5 measured from a deep K_s image obtained with WIRCam on the CFHT, as well as in a table containing 1016 sources with NUV(AB)<25 and 478 sources with FUV(AB)<25.5 (there is considerable overlap) measured from the deep GALEX images in the ACS area. Finally, we include the redshifts, where available, in a table containing the 1199 24 micron sources to 80 uJy measured from the wider-area Spitzer GOODS-North. The redshift identifications are greater than 90% complete to magnitudes of F435W(AB)=24.5, F850LP(AB)=23.3, and K_s(AB)=21.5 and to 24 micron fluxes of 250 uJy. An extensive analysis of these data will appear in a parallel paper, but here we determine how efficient color-selection techniques are at identifying high-redshift galaxies and Active Galactic Nuclei. We also examine the feasibility of doing tomography of the intergalactic medium with a 30 m telescope. 49] arXiv:0812.2814 [ps, pdf, other] Title: Overdensities of galaxies at z ~ 3.7 in CDF-S Authors: Eugene Kang, Myungshin Im Comments: 5 pages, 3 figures, Accepted for publication in ApJ Letters Subjects: Astrophysics (astro-ph) We report the discovery of possible overdensities of galaxies at z~3.7 in the Chandra Deep Field South (CDF-S). These overdensities are identified from the photometric redshift selected sample, and the BVz-selected sample. One over-density is identified in the proximity of 2 AGNs and LBGs at z=3.66 and z=3.70 at 7-sigma significance level. The other over-density is less significant. It is identified around six z_{spec}~3.6 galaxies at 3-sigma significance level. The line of sight velocity dispersions of these overdensities are found to be sigma_{v}~ 500-800 km/sec, comparable to the velocity dispersions of clusters of galaxies today. Through the spectral energy distribution (SED) fitting, we find ~15 massive galaxies with M > 10^{11}M_sun around the z~3.7 overdensity. The mass of the z~3.7 overdensity is found to be a few times 10^{14}M_sun. Our result suggests that high redshift over-dense regions can be found in a supposedly blank field, and that the emergence of massive structures can be traced back to redshift as high as z~3.7. 34] arXiv:0812.3020 [ps, pdf, other] Title: Dwarf Galaxy Clustering and Missing Satellites Authors: R. G. Carlberg, M. Sullivan, D. Le Borgne Comments: revised version submitted to Astrophysical Journal Subjects: Astrophysics (astro-ph) At redshifts around 0.1 the CFHT Legacy Survey Deep fields contain some 6x10^4 galaxies spanning the mass range from 10^5 to 10^12 Msun. We measure the stellar mass dependence of the two point correlation using angular measurements to largely bypass the errors, approximately 0.02 in the median, of the photometric redshifts. Inverting the power-law fits with Limber's equation we find that the auto-correlation length increases from a very low 0.4hMpc at 10^5.5 Msun to the conventional 4.5hMpc at 10^10.5 Msun. The power law fit to the correlation function has a slope which increases from gamma approximately 1.6 at high mass to gamma approximately 2.3 at low mass. The spatial cross-correlation of dwarf galaxies with more massive galaxies shows fairly similar trends, with a steeper radial dependence at low mass than predicted in numerical simulations of sub-halos within galaxy halos. To examine the issue of missing satellites we combine the cross-correlation measurements with our estimates of the low mass galaxy number density. We find on the average there are 60+/-20 dwarfs in sub-halos with M(total) > 10^7 Msun for a typical Local Group M(total)/M(stars)=30, corresponding to M/L_V approximately 100 for a galaxy with no recent star formation. The number of dwarfs per galaxy is about a factor of two larger than currently found for the Milky Way. Nevertheless, the average dwarf counts are about a factor of 30 below LCDM simulation results. The divergence from LCDM predictions is one of slope of the relation, approximately dN/dlnM approximately -0.5 rather than the predicted -0.9, not sudden onset at some characteristic scale. The dwarf galaxy star formation rates span the range from passive to bursting, which suggests that there are few completely dark halos. arXiv:0812.3081 [ps, pdf, other] Title: The UKIRT Wide Field Camera ZYJHK Photometric System: Calibration from 2MASS Authors: S. T. Hodgkin, M. J. Irwin, P. C. Hewett, S. J. Warren Comments: Accepted on 2008 December 11 for publication in the MNRAS, 20 pages Subjects: Astrophysics (astro-ph) In this paper we describe the photometric calibration of data taken with the near-infrared Wide Field Camera (WFCAM) on the United Kingdom Infrared Telescope (UKIRT). The broadband ZYJHK data are directly calibrated from 2MASS point sources which are abundant in every WFCAM pointing. We perform an analysis of spatial systematics in the photometric calibration, both inter- and intra-detector and show that these are present at up to the 5 per cent level in WFCAM. Although the causes of these systematics are not yet fully understood, a method for their removal is developed and tested. Following application of the correction procedure the photometric calibration of WFCAM is found to be accurate to approximately 1.5 per cent for the JHK bands and 2 per cent for the ZY bands, meeting the survey requirements. We investigate the transformations between the 2MASS and WFCAM systems and find that the Z and Y calibration is sensitive to the effects of interstellar reddening for large values of E(B-V)', but that the JHK filters remain largely unaffected. We measure a small correction to the WFCAM Y-band photometry required to place WFCAM on a Vega system, and investigate WFCAM measurements of published standard stars from the list of UKIRT faint standards. Finally we present empirically determined throughput measurements for WFCAM. 3] arXiv:0812.3151 [ps, pdf, other] Title: Ultra faint dwarfs: probing early cosmic star formation Authors: Stefania Salvadori, Andrea Ferrara Comments: 5 pages, 4 figures, submitted to MNRAS this http URL Subjects: Astrophysics (astro-ph) We investigate the nature of the newly discovered Ultra Faint dwarf spheroidal galaxies (UF dSphs) in a general cosmological context simultaneously accounting for various ``classical`` dSphs and Milky Way properties including their Metallicity Distribution Function (MDF). To this aim we extend the merger tree approach previously developed to include the presence of star-forming minihaloes, and an heuristic prescription for radiative feedback. The model successfully reproduces both the observed [Fe/H]-Luminosity relation and the mean MDF of UFs. In this picture UFs are the oldest, most dark matter-dominated (M/L > 100) dSphs with a total mass M= 10^{7-8}Msun; they are leftovers of H_2-cooling minihaloes formed at z > 8.5, i.e. before reionization. Their MDF is broader (because of a more prolonged SF) and shifted towards lower [Fe/H] (as a result of a lower gas metallicity at the time of formation) than that of classical dSphs. These systems are very ineffectively star-forming, turning into stars by z=0 only <3% of the potentially available baryons. We provide a useful fit for the star formation efficiency of dSphs. [4] arXiv:0812.3152 [ps, pdf, other] Title: Evolution in the properties of Lyman-alpha emitters from redshifts z ~ 3 to z ~ 2 Authors: Kim K. Nilsson (1), Christian Tapken (1), Palle Moeller (2), Wolfram Freudling (2), Johan P.U. Fynbo (3), Klaus Meisenheimer (1), Peter Laursen (3), Goeran Oestlin (4) ((1) MPIA Heidelberg, (2) ESO Garching, (3) Dark Cosmology Centre, (4) Stockholm Observatory) Comments: 12 pages, 9 figures, 5 tables, re-submitted to A&A after answering referees comments. Table 2 available in full from the authors Subjects: Astrophysics (astro-ph) Context: Narrow-band surveys for Ly-alpha emitters (LAEs) is a powerful tool in detecting high, and very high, redshift galaxies. Even though samples are growing at redshifts z = 3 - 6, the nature of these galaxies is still poorly known. Aims: To study the properties of z = 2.25 LAEs and compare those with the properties of z > 3 LAEs. Methods: We present narrow-band imaging made with the MPG/ESO 2.2m telescope with the WFI detector. We have made a selection for emission-line objects and find 170 candidate typical LAEs and 17 candidates which we regard as high UV-transmission LAEs. We have derived the magnitudes of these objects in 8 bands from u* to Ks, and studied if they have X-ray and/or radio counterparts. Results: We show that there has been significant evolution in the properties of LAEs between redshift z ~ 3 and z = 2.25. The spread in spectral energy distributions (SEDs) at the lower redshift is larger and we detect a significant AGN contribution in the sample. The distribution of the equivalent widths is narrower than at z ~ 3, with only a few candidates with rest-frame equivalent width above the predicted limit of 240 A. The star formation rates derived from the Ly-alpha emission compared to that derived from the UV emission are lower by on average a factor of ~ 1.8, indicating a large absorption of dust. Conclusion: LAEs at redshift z = 2.25 may be more evolved than LAEs at higher redshift. The red SEDs imply more massive, older and/or more dusty galaxies at lower redshift than observed at higher redshifts. The decrease in equivalent widths and star formation rates indicate more quiescent galaxies, with in general less star formation than in higher redshift galaxies. At z = 2.25, AGN appear to be more abundant and also to contribute more to the LAE population. [Abridged] 6] arXiv:0812.3154 [ps, pdf, other] Title: The halo merger rate in the Millennium Simulation and implications for observed galaxy merger fractions Authors: S. Genel, R. Genzel, N. Bouché, T. Naab, A. Sternberg Comments: 15 pages, 13 figures. Submitted to the Astrophysical Journal Subjects: Astrophysics (astro-ph) We developed a new method to extract the halo merger rate from the Millennium Simulation. First, by removing superfluous mergers that are artifacts of the Friends-Of-Friends (FOF) halo identification algorithm, we find a lower merger rate compared to previous work. The reductions, up to factors of a few, are more significant at lower redshifts and halo masses, and especially for minor mergers. This correction results in a better agreement with predictions from the extended Press-Schechter model. Second, we find that the FOF halo finder overestimates the halo mass by up to 50% for halos that are about to merge, which leads to an additional ~20% overestimate of the merger rate. Therefore, we define halo masses by including only particles gravitationally bound to their FOF groups. In addition, we extract the merger rate per progenitor halo, rather than per descendant halo. The former is the quantity that should be related to observed galaxy merger fractions when they are measured via pair counting. At low mass/redshift the merger rate increases moderately with mass and steeply with redshift. At high enough mass/redshift (for the rarest halos with masses much above the "knee" of the mass function) these trends break down, and the merger rate decreases with mass and increases only moderately with redshift. Defining the merger rate per progenitor halo also allows us to quantify the rate at which halos are being accreted onto larger halos, in addition to the minor and major merger rates. We provide an analytic formula that converts any given merger rate per descendant halo into a merger rate per progenitor halo. Finally, we compare observed merger fractions with the halo major merger fraction in the Millennium Simulation, and find a fair agreement, within the large uncertainties of the observations. [14] arXiv:0812.3219 [ps, pdf, other] Title: A pilot survey of stellar tidal streams in nearby spiral galaxies Authors: David Martinez-Delgado (IAC, MPIA), R. Jay Gabany (Black Bird Obs.), Jorge Penarrubia (IoA), Hans-Walter Rix (MPIA), Steven R. Majewski (U. Virginia), Ignacio Trujillo (IAC), M. Pohlen (Cardiff) Comments: Invited talk in "Hightlights of Spanish Astrophysics V", Proceedings of the VIII Scientific Meeting of the Spanish Astronomical Society (SEA), Springer, 8 pages. A high resolution version can be download here: this http URL Subjects: Astrophysics (astro-ph) Within the hierarchical framework for galaxy formation, merging and tidal interactions are expected to shape large galaxies to this day. While major mergers are quite rare at present, minor mergers and satellite disruptions - which result in stellar streams - should be common, and are indeed seen in both the Milky Way and the Andromeda Galaxy. As a pilot study, we have carried out ultra-deep, wide-field imaging of some spiral galaxies in the Local Volume, which has revealed external views of such stellar tidal streams at unprecedented detail, with data taken at small robotic telescopes (0.1-0.5-meter) that provide exquisite surface brightness sensitivity. The goal of this project is to undertake the first systematic and comprehensive imaging survey of stellar tidal streams, from a sample of ~50 nearby Milky-Way-like spiral galaxies within 15 Mpc, that features a surface brightness sensitivity of ~ 30 mag/arcsec^2 The survey will result in estimates of the incidence, size/geometry and stellar luminosity/mass distribution of such streams. This will not only put our Milky Way and M31 in context but, for the first time, also provide an extensive statistical basis for comparison with state-of-the-art, self-consistent cosmological simulations of this phenomenon. 17] arXiv:0812.3237 [ps, pdf, other] Title: The Structures of Distant Galaxies - III: The Merger History of over 20,000 Massive Galaxies at z < 1.2 Authors: Christopher J. Conselice, Cui Yang, Asa F. L. Bluck Comments: MNRAS, in press, 20 pages Subjects: Astrophysics (astro-ph) Utilizing deep Hubble Space Telescope imaging from the two largest field galaxy surveys, the Extended Groth Strip (EGS) and the COSMOS survey, we examine the structural properties, and derive the merger history for 21,902 galaxies with M_*>10^{10} M_0 at z<1.2. We examine the structural CAS parameters of these galaxies, deriving merger fractions, at 0.210^{10} M_0, the merger fraction can be parameterised by f_m = f_0*(1+z)^m with the power-law slope m=2.3+/-0.4. By using the best available z = 0 prior the slope increases to m=3.8+/-0.2, showing how critical the measurement of local merger properties are for deriving the evolution of the merger fraction. We furthermore show that the merger fraction derived through structure is roughly a factor of 3-6 higher than pair fractions. Based on the latest cosmological simulations of mergers we show that this ratio is predicted, and that both methods are likely tracing the merger fraction and rate properly. We calculate, utilising merger time scales from simulations, and previously published merger fractions that the merger rate of galaxies with M_*>10^{10} M_0 increases linearly between z = 0.7 and z = 3, and that a typical M_*>10^{10} M_0 galaxy undergoes between 1-2 major mergers at z<1.2. [3] arXiv:0812.3402 [ps, pdf, other] Title: The Environments of Active Galactic Nuclei within the zCOSMOS Density Field Authors: J.D. Silverman, K. Kovac, C. Knobel, S. Lilly, M. Bolzonella, F. Lamareille, V. Mainieri, M. Brusa, N. Cappelluti, Y. Peng, G. Hasinger, G. Zamorani, M. Scodeggio, T. Contini, C. M.Carollo, K. Jahnke, J. -P. Kneib, O. Le Fevre, S. Bardelli, A. Bongiorno, H. Brunner, K. Caputi, F. Civano, A. Comastri, G. Coppa, O. Cucciati, S. de la Torre, L. de Ravel, M. Elvis, A. Finoguenov, F. Fiore, P. Franzetti, B. Garilli, R. Gilli, R. Griffiths, A. Iovino, P. Kampczyk, J. -F. Le Borgne, V. Le Brun, C. Maier, M. Mignoli, R. Pello, E. Perez Montero, E. Ricciardelli, M. Tanaka, L. Tasca, L. Tresse, D. Vergani, C. Vignali, E. Zucca, D. Bottini, A. Cappi, P. Cassata, M. Fumana, C. Marinoni, H. J. McCracken, P. Memeo, B. Meneux, P. Oesch, C. Porciani, M. Salvato Comments: 13 pages; 11 figures; To appear in The Astrophysical Journal Subjects: Astrophysics (astro-ph) The impact of environment on AGN activity up to z~1 is assessed by utilizing a mass-selected sample of galaxies from the 10k catalog of the zCOSMOS spectroscopic redshift survey. We identify 147 AGN by their X-ray emission as detected by XMM-Newton from a parent sample of 7234 galaxies. We measure the fraction of galaxies with stellar mass M_*>2.5x10^10 Msun that host an AGN as a function of local overdensity using the 5th, 10th and 20th nearest neighbors that cover a range of physical scales (~1-4 Mpc). Overall, we find that AGNs prefer to reside in environments equivalent to massive galaxies with substantial levels of star formation. Specifically, AGNs with host masses between 0.25-1x10^11 Msun span the full range of environments (i.e., field-to-group) exhibited by galaxies of the same mass and rest-frame color or specific star formation rate. Host galaxies having M_*>10^11 Msun clearly illustrate the association with star formation since they are predominantly bluer than the underlying galaxy population and exhibit a preference for lower density regions analogous to SDSS studies of narrow-line AGN. To probe the environment on smaller physical scales, we determine the fraction of galaxies (M_*>2.5x10^10 Msun) hosting AGNs inside optically-selected groups, and find no significant difference with field galaxies. We interpret our results as evidence that AGN activity requires a sufficient fuel supply; the probability of a massive galaxy to have retained some sufficient amount of gas, as evidence by its ongoing star formation, is higher in underdense regions where disruptive processes (i.e., galaxy harrassment, tidal stripping) are lessened.