The numbers of z ∼ 2 star-forming and passive galaxies in 2.5 square degrees of deep CFHT imaging

Publisher's version/PDFWe use an adaptation of the BzK[subscript s] technique to select ∼40 000 z ∼ 2 galaxies (to K[subscript AB] = 24), including ∼5000 passively evolving (PE) objects (to K[subscript AB] = 23), from 2.5 deg[superscript 2] of deep Canada–France–Hawaii Telescope (CFHT) imaging. The passive galaxy luminosity function (LF) exhibits a clear peak at R = 22 and a declining faint-end slope ([alpha] = −0.12[superscript +0.16][subscript −0.14), while that of star-forming galaxies is characterized by a steep faint-end slope [[alpha] = −1.43 [plus or minus] 0.02(systematic)[superscript +0.05][subscript −0.04](random)]. The details of the LFs are somewhat sensitive (at the [less than]25 per cent level) to cosmic variance even in these large (∼0.5 deg[superscript 2]) fields, with the D2 field (located in the Cosmological Evolution Survey, COSMOS field) most discrepant from the mean. The shape of the z ∼ 2 stellar mass function of passive galaxies is remarkably similar to that at z ∼ 0.9, save for a factor of ∼4 lower number density. This similarity suggests that the same mechanism may be responsible for the formation of passive galaxies seen at both these epochs. This same formation mechanism may also operate down to z ∼ 0 if the local PE galaxy mass function, known to be two-component, contains two distinct galaxy populations. This scenario is qualitatively in agreement with recent phenomenological mass-quenching models and extends them to span more than three quarters of the history of the Universe

Angular clustering of z ∼ 2 star-forming and passive galaxies in 2.5 square degrees of deep CFHT imaging

Publisher's version/PDFWe study the angular clustering of z ∼ 2 galaxies using ∼40 000 star-forming (SF) and ∼5000 passively evolving (PE) galaxies selected from ∼2.5 deg[superscript 2] of deep (K[subscript lim] = 23–24 AB) Canada–France–Hawaii Telescope imaging. For both populations, the clustering is stronger for galaxies brighter in rest-frame optical and the trend is particularly strong for PE galaxies, indicating that passive galaxies with larger stellar masses reside in more massive haloes. In contrast, at rest-frame ultraviolet we find that while the clustering of SF galaxies increases with increasing luminosity, it decreases for PE galaxies; a possible explanation lies in quenching of star formation in the most massive haloes. Furthermore, we find two components in the correlation functions for both SF and PE galaxies, attributable to one- and two-halo terms. The presence of one-halo terms for both PE and SF galaxies suggests that environmental effects were producing passive galaxies in virtualized environments already by z ∼ 2. Finally, we find notable clustering differences between the four widely separated fields in our study; the popular COSMOS field is the most discrepant (as is also the case for number counts and luminosity functions), highlighting the need for very large areas and multiple sightlines in galaxy evolution statistical studies

Keck Deep Fields. IV. Luminosity-dependent clustering and galaxy downsizing in UV-selected galaxies at z = 4, 3, and 2

Publisher's version/PDFWe investigate the luminosity-dependent clustering of rest-frame UV-selected galaxies at z ∼ 4, 3, 2.2, and 1.7 in the Keck Deep Fields, which are complete to R = 27 and cover 169 arcmin[superscript 2]. We find that at z ∼ 4 and 3, UV-bright galaxies cluster more strongly than UV-faint ones, but at z ∼ 2.2 and 1.7, the UV-bright galaxies are no longer the most strongly clustered. We derive mass estimates for objects in our sample by comparing our measurements to the predicted clustering of dark matter halos in the Millennium Simulation. From these estimates, we infer relationships between halo mass and star formation rate (SFR), and find that the most massive dark matter halos in our sample host galaxies with high SFRs (M[subscript 1700] 50 M[subscript circled dot] yr[superscript −1]) at z ∼ 3 and 4, moderate SFRs (−20 < M[subscript 1700] < −19, or ∼20 M[subscript circled dot] yr[superscript −1]) at z ∼ 2.2, and lower SFRs (−19 < M[subscript 1700] < −18, or ∼2 M[subscript circled dot] yr[superscript −1]) at z ∼ 1.7. We believe our measurements may provide a new line of evidence for galaxy downsizing by extending that concept from stellar to halo mass. We also find that the objects with blue UV colors in our sample are much more strongly clustered than those with red UV colors, and we propose that this may be due to the presence of the 2175 [Angstrom] dust absorption bump in more massive halos, which contain the older stellar populations and dust needed to produce the feature. The relatively small area covered by the survey means that the absolute values of the correlation lengths and halo masses we derive are heavily dependent on the “integral constraint” correction, but the uniformly deep coverage across a large-redshift interval allows us to detect several important trends that are independent of this correction

A spectroscopic measurement of galaxy formation time-scales with the Redshift One LDSS3 Emission line Survey

Publisher's version/PDFWe present measurements of the specific star formation rate (SSFR)–stellar mass relation for star-forming galaxies. Our deep spectroscopic samples are based on the Redshift One LDSS3 Emission line Survey (ROLES) and European Southern Observatory (ESO) public spectroscopy at z = 1, and on the Sloan Digital Sky Survey (SDSS) at z = 0.1. These data sets cover an equally deep mass range of 8.5 [less than or similar to] log(M[subscript ∗]/M[subscript circled dot]) [less than or similar to] 11 at both epochs. We find that the SSFR–mass relation evolves in a way which is remarkably independent of stellar mass, as we previously found for the SFR density (SFRD)–mass relation. However, we see a subtle upturn in SSFR–mass for the lowest mass galaxies (which may at least partly be driven by mass-incompleteness in the K-selected sample). This upturn is suggestive of greater evolution for lower mass galaxies, which may be explained by less massive galaxies forming their stars later and on longer time-scales than higher mass galaxies, as implied by the ‘cosmic downsizing’ scenario. Parametrizing the e-folding time-scale and formation redshift as simple functions of baryonic mass gives best-fitting parametrizations of [tau] (M[subscript b]) [alpha] M[superscript −1.01][subscript b] and 1 + z[subscript f](M[subscript b]) [alpha] M[superscript 0.30][subscript b]. This subtle upturn is also seen in the SFRD as a function of stellar mass. At higher masses, such as those probed by previous surveys, the evolution in SSFR–mass is almost independent of stellar mass. At higher masses [log(M[subscript ∗]/M[subscript circled dot]) [greater than] 10] the shapes of the cumulative cosmic SFRDs are very similar at both z = 0.1 and 1.0, both showing 70 per cent of the total SFRD above a mass of log(M[subscript *]/M[subscript circled dot]) [greater than] 10. Mass functions are constructed for star-forming galaxies and found to evolve by only [less than]35 per cent between z = 1 and 0.1 over the whole mass range. The evolution is such that the mass function decreases with increasing cosmic time, confirming that galaxies are leaving the star-forming sequence/blue cloud. The observational results are extended to z ∼ 2 by adding two recent Lyman break galaxy samples, and data at these three epochs (z = 0.1, 1, 2) are compared with the GALFORM semi-analytic model of galaxy formation. GALFORM predicts an overall SFRD as a function of stellar mass in reasonable agreement with the observations. The star formation time-scales inferred from 1/SSFR also give reasonable overall agreement, with the agreement becoming worse at the lowest and highest masses. The models do not reproduce the SSFR upturn seen in our data at low masses, where the effects of extinction and active galactic nuclei feedback should be minimal and the comparison should be most robust

A Magellan IMACS spectroscopic search for Ly[alpha]-emitting galaxies at redshift 5.7

Publisher's version/PDFWe present results from a blind, spectroscopic survey for z ~ 5.7 Ly[alpha]-emitting galaxies (LAEs) using the Inamori Magellan Areal Camera and Spectrograph. A total of ~200 arcmin[superscript 2] were observed in the COSMOS and LCIRS fields using a narrowband filter, which transmits between atmospheric emission lines at 8190 [Angstrom], and a mask with 100 long slits. This observing technique provides higher emission-line sensitivity than narrowband imaging and probes larger volumes than strong lensing. We find 170 emission-line galaxies and identify their redshifts spectroscopically. We confirm three LAEs, the first discovered using multislit narrowband spectroscopy. Their line profiles are narrow, but fitted models suggest intrinsic, unattenuated widths ~400 km s[superscript -1] FWHM. The red wing of the line profiles presents features consistent with galactic winds. The star formation rates of these galaxies are at least 5–7 M[subscript circled dot] yr[superscript -1] and likely a factor of 2 higher. We estimate that the number density of L [greater or less than] 5 x 10[superscript 42] erg s[superscript -1] LAEs is 9.0[superscript +12][subscript -4] x 10[superscript -5] h[superscript 3][subscript 70] Mpc[superscript -3] at redshift 5.7 and constrain the Schechter function parameters describing this population. Galaxies fainter than our detection limit may well be the primary source of ionizing photons at z ~ 6. We argue, however, that the break luminosity L[subscript *], [subscript Ly[alpha]] is not yet well constrained. If this break luminosity is near our detection limit, and somewhat lower than previous estimates, then the detected LAE population could be responsible for ionizing the intergalactic gas at redshift z ~ 6. We discuss the potential of multislit narrowband spectroscopy for deeper emission-line surveys

Confirmation of a steep luminosity function for Ly[alpha] emitters at z = 5.7: a major component of reionization

Publisher's version/PDFWe report the first direct and robust measurement of the faint-end slope of the Ly[alpha] emitter (LAE) luminosity function (LF) at z = 5.7. Candidate LAEs from a low-spectral-resolution blind search with IMACS on Magellan-Baade were targeted at higher resolution to distinguish high-redshift LAEs from foreground galaxies. All but 2 of our 42 single-emission-line systems have flux F [less than] 2.0 × 10[superscript −17] ergs s[superscript −1] cm[superscript −2], making these the faintest emission-lines observed for a z = 5.7 sample with known completeness, an essential property for determining the faint end slope of the LAE LF. We find 13 LAEs as compared to 29 foreground galaxies, in very good agreement with the modeled foreground counts predicted in Dressler et al. that had been used to estimate a faint-end slope of [alpha] = −2.0 for the LAE LF. A 32% LAE fraction, LAE/(LAE+foreground) within the flux interval F = 2−20 × 10[superscript −18] ergs s[superscript −1] cm[superscript −2] constrains the faint end slope of the LF to −2.35 [less than] [alpha] [less than] −1.95 (1[sigma]). We show how this steep LF should provide, to the limit of our observations, M[subscript UV] ∼ −16, more than 20% of the flux necessary to maintain ionization at z = 5.7, with a factor of 10 extrapolation in flux reaching more than 50%. This is in addition to the comparable contribution by brighter Lyman Break Galaxies M[subscript UV] [less than or similar to] −18. We suggest that this bodes well for a sufficient supply of Lyman continuum photons by similar, low-mass star-forming galaxies within the reionization epoch at z [approximate to] 7, only 250 Myr earlier

The Next Generation Virgo Cluster Survey. XV. The photometric estimation for background sources

Publisher's version/PDFThe Next Generation Virgo Cluster Survey (NGVS) is an optical imaging survey covering 104 deg[superscript 2] centered on the Virgo cluster. Currently, the complete survey area has been observed in the u[superscript ∗] giz bands and one third in the r band. We present the photometric redshift estimation for the NGVS background sources. After a dedicated data reduction, we perform accurate photometry, with special attention to precise color measurements through pointspread function homogenization. We then estimate the photometric redshifts with the Le Phare and BPZ codes. We add a new prior that extends to i[subscript AB] = 12.5 mag. When using the u[superscript ∗]griz bands, our photometric redshifts for 15.5 mag [less than or equal to] i [less than or similar to] 23 mag or z[subscript phot] [less than or similar to] 1 galaxies have a bias |[Delta]z| [less than] 0.02, less than 5% outliers, a scatter [sigma][subscript outl.rej.], and an individual error on z[subscript phot] that increases with magnitude (from 0.02 to 0.05 and from 0.03 to 0.10, respectively). When using the u[superscript ∗] giz bands over the same magnitude and redshift range, the lack of the r band increases the uncertainties in the 0.3 [less than or similar to] z[subscript phot] [less than or similar to] 0.8 range (−0.05 [less than] [Delta]z [less than] −0.02, [sigma][subscript outl.rej ∼ 0.06, 10%–15% outliers, and z[subscript phot.err.] ∼ 0.15). We also present a joint analysis of the photometric redshift accuracy as a function of redshift and magnitude. We assess the quality of our photometric redshifts by comparison to spectroscopic samples and by verifying that the angular auto- and cross-correlation function w([theta]) of the entire NGVS photometric redshift sample across redshift bins is in agreement with the expectations

The Next Generation Virgo Cluster Survey (NGVS). I. Introduction to the survey

Publisher's version/PDFThe Next Generation Virgo Cluster Survey (NGVS) is a program that uses the 1 deg[superscript 2] MegaCam instrument on the Canada–France–Hawaii Telescope to carry out a comprehensive optical imaging survey of the Virgo cluster, from its core to its virial radius—covering a total area of 104 deg[superscript 2]—in the u[superscript ∗] griz bandpasses. Thanks to a dedicated data acquisition strategy and processing pipeline, the NGVS reaches a point-source depth of g [approximate to] 25.9 mag (10[sigma]) and a surface brightness limit of [micron][subscript g] ∼ 29 mag arcsec[superscript −2] (2[sigma] above the mean sky level), thus superseding all previous optical studies of this benchmark galaxy cluster. In this paper, we give an overview of the technical aspects of the survey, such as areal coverage, field placement, choice of filters, limiting magnitudes, observing strategies, data processing and calibration pipelines, survey timeline, and data products. We also describe the primary scientific topics of the NGVS, which include: the galaxy luminosity and mass functions; the color–magnitude relation; galaxy scaling relations; compact stellar systems; galactic nuclei; the extragalactic distance scale; the large-scale environment of the cluster and its relationship to the Local Supercluster; diffuse light and the intracluster medium; galaxy interactions and evolutionary processes; and extragalactic star clusters. In addition, we describe a number of ancillary programs dealing with “foreground” and “background” science topics, including the study of high-inclination trans-Neptunian objects; the structure of the Galactic halo in the direction of the Virgo Overdensity and Sagittarius Stream; the measurement of cosmic shear, galaxy–galaxy, and cluster lensing; and the identification of distant galaxy clusters, and strong-lensing events

The DEEP2 redshift survey: Ly[alpha] emitters in the spectroscopic database

Publisher's version/PDFWe present the first results of a search for Ly[alpha] emitters (LAEs) in the DEEP2 spectroscopic database that uses a search technique that is different from but complementary to traditional narrowband imaging surveys.We have visually inspected ~20% of the available DEEP2 spectroscopic data and have found nine high-quality LAEs with clearly asymmetric line profiles and an additional 10 objects of lower quality, some of which may also be LAEs. Our survey is most sensitive to LAEs at z = 4.4-4.9 and that is indeed where all but one of our high-quality objects are found. We find the number density of our spectroscopically discovered LAEs to be consistent with those found in narrowband imaging searches. The combined, averaged spectrum of our nine high-quality objects is well fit by a two-component model, with a second, lower amplitude component redshifted by ~420 km s[superscript -1] with respect to the primary Ly[alpha] line, consistent with large-scale outflows from these objects. We conclude by discussing the advantages and future prospects of blank-sky spectroscopic surveys for high-z LAEs