Examinando por Autor "Geier, S."

Mostrando 1 - 3 de 3

Acceso Abierto
Exploring nine simultaneously occurring transients on April 12th 1950
(Nature Research Journals, 2021-06-17) Villarroel, B.; Marcy, G. W.; Geier, S.; Streblyanska, A.; Andruk, V. N.; Shultz, M. E.; Gupta, A. C.; Mattsson, L.; Solano, Enrique; Agencia Estatal de Investigación (AEI)
Nine point sources appeared within half an hour on a region within ∼ 10 arcmin of a red-sensitive photographic plate taken in April 1950 as part of the historic Palomar Sky Survey. All nine sources are absent on both previous and later photographic images, and absent in modern surveys with CCD detectors which go several magnitudes deeper. We present deep CCD images with the 10.4-m Gran Telescopio Canarias, reaching brightness r∼26 mag, that reveal possible optical counterparts, although these counterparts could equally well be just chance projections. The incidence of transients in the investigated photographic plate is far higher than expected from known detection rates of optical counterparts to e.g. flaring dwarf stars, Fast Radio Bursts, Gamma Ray Bursts or microlensing events. One possible explanation is that the plates have been subjected to an unknown type of contamination producing mainly point sources with of varying intensities along with some mechanism of concentration within a radius of ∼ 10 arcmin on the plate. If contamination as an explanation can be fully excluded, another possibility is fast (t <0.5 s) solar reflections from objects near geosynchronous orbits. An alternative route to confirm the latter scenario is by looking for images from the First Palomar Sky Survey where multiple transients follow a line.
Restringido
Probing the existence of a rich galaxy overdensity at z = 5.2
(Oxford Academics: Oxford University Press, 2021-04-05) Calvi, R.; Dannerbauer, H.; Arrabal Haro, P.; Rodríguez Espinosa, J. M.; Muñoz Tuñón, C.; Pérez González, P. G.; Geier, S.; Ministerio de Economía y Competitividad (MINECO); Agencia Estatal de Investigación (AEI); 0000-0003-4528-5639
We report the results of a pilot spectroscopic program of a region at z = 5.2 in the GOODS-N field containing an overdensity of galaxies around the well-known submillimetre galaxy (SMG) HDF850.1. We have selected candidate cluster members from the optical 25 medium-band photometric catalogue of the project SHARDS (Survey for High-z Absorption Red and Dead Sources). 17 rest-frame ultraviolet (UV)-selected galaxies (LAEs and LBGs) with 5.15 < zphot < 5.27, candidates to be physically associated with the overdensity, have been observed with the instrument OSIRIS at the GranTeCan telescope. 13 out of these 17 (76 per cent) sources have secure spectroscopic confirmations via the Ly α line at the redshift of the galaxy protocluster PCl−HDF850.1, demonstrating the high reliability of our photometric redshift method. 10 out of 13 sources are newly confirmed members. Thus, we increase the number of confirmed members in this overdensity from 13 to 23 objects. In order to fully characterize this structure we combined our data set with the sample from the literature. Beside the SMG HDF850.1, none of the 23 spectroscopically confirmed members are bright in the far-infrared/sub-mm wavelength regime (SFRIR < few hundred M⊙ yr−1). The clustering analysis of the whole sample of 23 confirmed members reveals four distinct components in physical space in different evolutionary states, within Δz < 0.04 from the central region hosting SMG HDF850.1. The halo mass of the whole structure at z = 5.2, estimated by a variety of methods, range between 2 and 8×1012M⊙⁠. The comparison with literature suggests a large-scale assembly comparable to the formation of a central Virgo-like cluster at z = 0 with several satellite components which will possibly be incorporated in a single halo if the protocluster is the progenitor of a more massive Coma-like cluster (⁠>1015M⊙⁠).
Acceso Abierto
Rest-frame UV properties of luminous strong gravitationally lensed Lyα emitters from the BELLS GALLERY Survey
(Oxford Academics: Oxford University Press, 2020-02-10) Marques Chaves, R.; Pérez Fournon, I.; Shu, Y.; Colina, L.; Bolton, A.; Álvarez Márquez, J.; Brownstein, J.; Cornachione, M.; Geier, S.; Jiménez Ángel, C.; Kojima, T.; Mao, S.; Montero Dorta, A.; Oguri, M.; Ouchi, M.; Poidevin, F.; Shirley, Y.; Zheng, Z.; Agencia Estatal de Investigación (AEI); National Science Foundation (NSF); Ministerio de Economía y Competitividad (MINECO); Poidevin, F. [0000-0002-5391-5568]; Marqués Chaves, R. [0000-0001-8442-1846]; Shu, Y. [0000-0002-9063-698X]; Shirley, R. [0000-0002-1114-0135]; Unidad de Excelencia Científica María de Maeztu Centro de Astrobiología del Instituto Nacional de Técnica Aeroespacial y CSIC, MDM-2017-0737
We present deep rest-frame UV spectroscopic observations using the Gran Telescopio Canarias of six gravitationally lensed Ly alpha emitters (LAEs) at 2.36 < z < 2.82 selected from the BELLS GALLERY survey. By taking the magnifications into account, we show that LAEs can be as luminous as L-Ly alpha similar or equal to 30 x 10(42) erg s(-1) and M-UV similar or equal to -23 (AB) without invoking an AGN component, in contrast with previous findings. We measure Ly alpha rest-frame equivalent widths, EW0 (Ly alpha), ranging from 16 to 50 angstrom and Ly alpha escape fractions, f(esc) (Ly alpha), from 10 per cent to 40 per cent. Large EW0 (Ly alpha) and f(esc) (Ly alpha) are found predominantly in LAEs showing weak low-ionization ISM absorption (EW0 less than or similar to 1A) and narrow Ly alpha profiles (less than or similar to 300 km s(-1) FWHM) with their peak close (less than or similar to 80 km s(-1)) to their systemic redshifts, suggestive of less scatter from low HI column densities that favours the escape of Ly alpha photons. We infer stellar metallicities of Z/Z(circle dot) similar or equal to 0.2 in almost all LAEs by comparing the P-Cygni profiles of the wind lines NV1240 angstrom and C IV1549 angstrom with those from stellar synthesis models. We also find a trend between M-UV and the velocity offset of ISM absorption lines, such as the most luminous LAEs experience stronger outflows. The most luminous LAEs show star formation rates up to similar or equal to 180 M-circle dot yr(-1), yet they appear relatively blue (beta(UV) similar or equal to -1.8 to -2.0) showing evidence of little dust attenuation [E(B - V) = 0.10-0.14]. These luminous LAEs may be particular cases of young starburst galaxies that have had no time to form large amounts of dust. If so, they are ideal laboratories to study the early phase of massive star formation, stellar and dust mass growth, and chemical enrichment histories of starburst galaxies at high-z.