David Herrera

Lyα Emission-Line Galaxies at z = 3.1 in the Extended Chandra Deep Field-South

We describe the results of an extremely deep, 0.28 deg^2 survey for z = 3.1 Ly-alpha emission-line galaxies in the Extended Chandra Deep Field South. By using a narrow-band 5000 Anstrom filter and complementary broadband photometry from the MUSYC survey, we identify a statistically complete sample of 162 galaxies with monochromatic fluxes brighter than 1.5 x 10^-17 ergs cm^-2 s^-1 and observers frame equivalent widths greater than 80 Angstroms. We show that the equivalent width distribution of these objects follows an exponential with a rest-frame scale length of w_0 = 76 +/- 10 Angstroms. In addition, we show that in the emission line, the luminosity function of Ly-alpha galaxies has a faint-end power-law slope of alpha = -1.49 +/- 0.4, a bright-end cutoff of log L^* = 42.64 +/- 0.2, and a space density above our detection thresholds of 1.46 +/- 0.12 x 10^-3 h70^3 galaxies Mpc^-3. Finally, by comparing the emission-line and continuum properties of the LAEs, we show that the star-formation rates derived from Ly-alpha are ~3 times lower than those inferred from the rest-frame UV continuum. We use this offset to deduce the existence of a small amount of internal extinction within the host galaxies. This extinction, coupled with the lack of extremely-high equivalent width emitters, argues that these galaxies are not primordial Pop III objects, though they are young and relatively chemically unevolved.

Spectroscopic Identification of Massive Galaxies at z ~ 2.3 with Strongly Suppressed Star Formation*

We present first results of a spectroscopic survey targeting K-selected galaxies at z = 2.0-2.7 using the Gemini near-infrared spectrograph (GNIRS). We obtained near-infrared spectra with a wavelength coverage of 1.0-2.5 μm for 26 K-bright galaxies (K < 19.7) selected from the Multi-wavelength Survey by Yale-Chile (MUSYC) using photometric redshifts. We successfully derived spectroscopic redshifts for all 26 galaxies using rest-frame optical emission lines or the redshifted Balmer/4000 A break. Twenty galaxies have spectroscopic redshifts in the range 2.0 < z < 2.7, for which bright emission lines like Hα and [O III] fall in atmospheric windows. Surprisingly, we detected no emission lines for nine of these 20 galaxies. The median 2 σ upper limit on the rest-frame equivalent width of Hα for these nine galaxies is ~10 A. The stellar continuum emission of these same nine galaxies is best fitted by evolved stellar population models. The best-fit star formation rate (SFR) is zero for five out of nine galaxies and is consistent with zero within 1 σ for the remaining four. Thus, both the Hα measurements and the independent stellar continuum modeling imply that 45% of our K-selected galaxies are not forming stars intensely. This high fraction of galaxies without detected line emission and low SFRs may imply that the suppression of star formation in massive galaxies occurs at higher redshift than is predicted by current cold dark matter (CDM) galaxy formation models. However, obscured star formation may have been missed, and deep mid-infrared imaging is needed to clarify this situation.

THE SOUTHERN PROPER MOTION PROGRAM. IV. THE SPM4 CATALOG

We present the fourth installment of the Yale/San Juan Southern Proper Motion Catalog, SPM4. The SPM4 contains absolute proper motions, celestial coordinates, and B, V photometry for over 103 million stars and galaxies between the south celestial pole and -20{sup 0} declination. The catalog is roughly complete to V = 17.5 and is based on photographic and CCD observations taken with the Yale Southern Observatorys double astrograph at Cesco Observatory in El Leoncito, Argentina. The proper-motion precision, for well-measured stars, is estimated to be 2-3 mas yr{sup -1}, depending on the type of second-epoch material. At the bright end, proper motions are on the International Celestial Reference System by way of Hipparcos Catalog stars, while the faint end is anchored to the inertial system using external galaxies. Systematic uncertainties in the absolute proper motions are on the order of 1 mas yr{sup -1}.

Clustering of K-selected Galaxies at 2 < z < 3.5: Evidence for a Color-Density Relation

We study the clustering properties of K-selected galaxies at 2 2.3 distant red galaxies (DRGs) have r0 ~ 11 h-1 Mpc. Furthermore, contrary to findings for optically selected galaxies, K-selected galaxies that are faint in the R band cluster more strongly than brighter galaxies. These results suggest that a color-density relation was in place at z > 2; it will be interesting to see whether this relation is driven by galaxies with old stellar populations or by dusty star-forming galaxies. Irrespective of the cause, our results indicate that K-bright blue galaxies and K-bright red galaxies are fundamentally different, having different clustering properties. Using a simple model of one galaxy per halo, we infer halo masses ~5 × 1012 M☉ for K < 21 galaxies and ~2 × 1013 M☉ for DRGs. A comparison of the observed space density of DRGs to that of their host halos suggests large halo occupation numbers; however, this result conflicts with the lack of a strong small-scale excess in the angular correlation function. Using the predicted evolution of halo mass to investigate relationships between galaxy populations at different redshifts, we find that the z = 0 descendants of the galaxies considered here reside primarily in groups and clusters.

THE EVOLUTION OF Lyα-EMITTING GALAXIES BETWEEN z = 2.1 AND z = 3.1

We describe the results of a new, wide-field survey for z=3.1 Ly-alpha emission-line galaxies (LAEs) in the Extended Chandra Deep Field South (ECDF-S). By using a nearly top-hat 5010 Angstrom filter and complementary broadband photometry from the MUSYC survey, we identify a complete sample of 141 objects with monochromatic fluxes brighter than 2.4E-17 ergs/cm^2/s and observers-frame equivalent widths greater than ~ 80 Angstroms (i.e., 20 Angstroms in the rest-frame of Ly-alpha). The bright-end of this dataset is dominated by x-ray sources and foreground objects with GALEX detections, but when these interlopers are removed, we are still left with a sample of 130 LAE candidates, 39 of which have spectroscopic confirmations. This sample overlaps the set of objects found in an earlier ECDF-S survey, but due to our filters redder bandpass, it also includes 68 previously uncataloged sources. We confirm earlier measurements of the z=3.1 LAE emission-line luminosity function, and show that an apparent anti-correlation between equivalent width and continuum brightness is likely due to the effect of correlated errors in our heteroskedastic dataset. Finally, we compare the properties of z=3.1 LAEs to LAEs found at z=2.1. We show that in the ~1 Gyr after z~3, the LAE luminosity function evolved significantly, with L* fading by ~0.4 mag, the number density of sources with L > 1.5E42 ergs/s declining by ~50%, and the equivalent width scale-length contracting from 70^{+7}_{-5} Angstroms to 50^{+9}_{-6} Angstroms. When combined with literature results, our observations demonstrate that over the redshift range z~0 to z~4, LAEs contain less than ~10% of the star-formation rate density of the universe.

SPACE VELOCITIES OF SOUTHERN GLOBULAR CLUSTERS. V. A LOW GALACTIC LATITUDE SAMPLE

We have measured the absolute proper motions of globular clusters NGC 2808, 3201, 4372, 4833, 5927, and 5986. The proper motions are on the Hipparcos system, and they are the first determinations ever made for these low Galactic latitude clusters. The proper-motion uncertainties range from 0.3 to 0.5 mas yr-1. The inferred orbits indicate that (1) the single metal-rich cluster in our sample, NGC 5927, dynamically belongs to the thick disk; (2) the remaining metal-poor clusters have rather low-energy orbits of high eccentricity, and among these there appear to be two pairs of dynamically associated clusters; (3) the most energetic cluster in our sample, NGC 3201, is on a highly retrograde orbit?which had already been surmised from radial velocity alone?with an apocentric distance of 22 kpc; and (4) none of the metal-poor clusters appear to be associated with the recently detected SDSS streams or with the Monoceros structure. These are the first results of the Southern Proper Motion program where the second-epoch observations are taken with the recent CCD camera system installed on the double astrograph at El Leoncito, Argentina.

The Multiwavelength Survey by Yale-Chile (MUSYC): Wide K-Band Imaging, Photometric Catalogs, Clustering, and Physical Properties of Galaxies at z ~ 2

We present K-band imaging of two � 30 0 ; 30 0 fields covered by the Multiwavelength Survey by Yale-Chile (MUSYC) Wide NIR Survey. The SDSS 1030+05 and Cast 1255 fields were imaged with the Infrared Side Port Imager(ISPI)onthe4mBlancotelescopeattheCerroTololoInter-American Observatory(CTIO)toa5 � point-source limitingdepthofK � 20(Vega).Combiningthese datawiththeMUSYCopticalUBVRIzimaging, wecreatedmultiband K-selected source catalogs for both fields. These catalogs, together with the MUSYC K-band catalog of the ExtendedChandraDeepFieldSouth(ECDF-S)field,wereusedtoselectK < 20BzKgalaxiesoveranareaof 0.71deg 2 . This is the largest area ever surveyed for BzK galaxies. We present number counts, redshift distributions, and stellar masses for our sample of 3261 BzK galaxies (2502 star-forming [sBzK] and 759 passively evolving [pBzK]), as well as reddening and star formation rate estimates for the star-forming BzK systems. We also present two-point angular correlation functions and spatial correlation lengths for both sBzK and pBzK galaxies and show that previous estimates of the correlation function of these galaxies were affected by cosmic variance due to the small areas surveyed. We have measured correlation lengths r0 of 8:89 � 2:03 and 10:82 � 1:72 Mpc for sBzK and pBzK galaxies, respec

PROPER-MOTION STUDY OF THE MAGELLANIC CLOUDS USING SPM MATERIAL

Resumen en: Absolute proper motions are determined for stars and galaxies to V = 17.5 over a 450 square degree area that encloses both Magellanic Clouds. The proper ...

The Calán-Yale Deep Extragalactic Research (CYDER) Survey: Optical Properties and Deep Spectroscopy of Serendipitous X-Ray Sources*

We present the first results from the Cal?n-Yale Deep Extragalactic Research (CYDER) survey. The main goal of this survey is to study serendipitous X-ray sources detected by Chandra in an intermediate flux range (10-15 to 10-12 ergs s-1) that comprises most of the X-ray background. A total of 267 X-ray sources spread over five archived fields were detected. The log N- log S distribution obtained for this sample is consistent with the results of other surveys. Deep V and I images were taken of these fields in order to calculate X-ray-to-optical flux ratios. Identifications and redshifts were obtained for 106 sources using optical spectroscopy from 8 m class telescopes to reach the optically faintest sources, to the same level as deeper X-ray fields like the Chandra Deep Fields, showing that the nature of sources detected depends mostly on the optical limit for spectroscopy. In general, sources optically classified as obscured active galactic nuclei (AGNs) have redder optical colors than unobscured AGNs. A rough correlation between fX/fopt and hard X-ray luminosity was found for obscured AGNs, confirming the prediction by existing models that in obscured AGNs the optical light is completely dominated by the host galaxy. The previously claimed decrease of the obscured-to-unobscured AGN ratio with increasing X-ray luminosity is observed. However, this correlation can be explained as a selection effect caused by the lower optical flux of obscured AGNs. Comparison between the observed NH distribution and predictions by existing models shows that the sample appears complete up to NH < 3 ? 1022 cm-2, while for more obscured sources incompleteness plays an important role in the observed obscured-to-unobscured AGN ratio.

An X-Ray-selected Active Galactic Nucleus at z=4.6 Discovered by the CYDER Survey

We present the discovery of a high-redshift, X-ray-selected active galactic nucleus (AGN) by the Calan-Yale Deep Extragalactic Research (CYDER) survey: CXOCY J033716.7-050153, located at z = 4.61, the second high-redshift AGN discovered by this survey. Here we present its optical, near-IR, and X-ray properties and compare it with other optical and X-ray-selected high-redshift AGNs. The optical luminosity of this object is significantly lower than most optically selected high-redshift quasars. It also has a lower rest-frame UV to X-ray emission ratio than most known quasars at this redshift. This mild deviation can be explained either by dust obscuring the UV radiation of a normal radio-quiet AGN emitting at 10% of its Eddington luminosity or because this is intrinsically a low-luminosity radio-loud AGN with a supermassive black hole of ~108 M☉ emitting at 1% of its Eddington luminosity. Deep radio observations can discriminate between these two hypotheses.