Seyfert galaxy

Seyfert galaxies are one of the two largest groups of active galaxies, along with quasars. They have quasar-like nuclei (very luminous sources of electromagnetic radiation that are outside of our own galaxy) with very high surface brightnesses whose spectra reveal strong, high-ionisation emission lines, but unlike quasars, their host galaxies are clearly detectable. Seyfert galaxies account for about 10% of all galaxies and are some of the most intensely studied objects in astronomy, as they are thought to be powered by the same phenomena that occur in quasars, although they are closer and less luminous than quasars. These galaxies have supermassive black holes at their centers which are surrounded by accretion discs of in-falling material. The accretion discs are believed to be the source of the observed ultraviolet radiation. Ultraviolet emission and absorption lines provide the best diagnostics for the composition o

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PHYS-402: Astrophysics IV : observational cosmology

Cosmology is the study of the structure and evolution of the universe as a whole. This course describes the principal themes of cosmology, as seen from the point of view of observations.

PHYS-209: Astrophysics I: introduction to astrophysics

Ce cours décrit de façon simple les processus physiques qui expliquent l'univers dans lequel nous vivons. En couvrant une large gamme de sujets, le but du cours est aussi de donner un aperçu général des objets astrophysiques qui nous entourent.

LESSER: a catalogue of spectroscopically selected sample of Lyman-alpha emitters lensed by galaxies

Jean-Paul Richard Kneib

We introduce the LEnSed laeS in the Eboss suRvey (LESSER) project, which aims to search for lensed Lyman-alpha emitters (LAEs) in the Extended Baryon Oscillation Spectroscopic Survey (eBOSS). The final catalogue contains 361 candidate lensing systems. The lens galaxies are luminous red galaxies (LRGs) at redshift 0.4 < z < 0.8, and the source galaxies are LAEs at redshift 2 < z < 3. The spectral resolution of eBOSS (similar to 2000) allows us to further identify the fine structures of Lyman-alpha (Ly alpha) emissions. Among our lensed LAE candidates, 281 systems present single-peaked line profiles while 80 systems show double-peaked features. Future spectroscopic/imaging follow-up observations of the catalogue may shed light on the origin of diverse Ly alpha line morphology, and provide promising labs for studying low-mass dark matter haloes/subhaloes.

OXFORD UNIV PRESS2020

The completed SDSS-IV extended Baryon Oscillation Spectroscopic Survey: measurement of the BAO and growth rate of structure of the emission line galaxy sample from the anisotropic power spectrum between redshift 0.6 and 1.1

Johan Comparat, Claudio Gorgoni, Anand Stéphane Raichoor, Amélie Tamone, Yuting Wang, Cheng Zhao

We analyse the large-scale clustering in Fourier space of emission line galaxies (ELG) from the Data Release 16 of the Sloan Digital Sky Survey IV extended Baryon Oscillation Spectroscopic Survey. The ELG sample contains 173736 galaxies covering 1170deg(2) in the redshift range 0.6 < z < 1.1. We perform a BAO measurement from the post-reconstruction power spectrum monopole, and study redshift space distortions (RSD) in the first three even multipoles. Photometric variations yield fluctuations of both the angular and radial survey selection functions. Those are directly inferred from data, imposing integral constraints which we model consistently. The full data set has only a weak preference for a BAO feature (1.4 sigma). At the effective redshift z(eff) = 0.845 we measure , with D-V the volume-averaged distance and r(drag) the comoving sound horizon at the drag epoch. In combination with the RSD measurement, at z(eff) = 0.85 we find , with f the growth rate of structure and sigma(8) the normalization of the linear power spectrum, and D-M(z(eff))/r(drag) = 19.17 +/- 0.99 with D-H and D-M the Hubble and comoving angular distances, respectively. These results are in agreement with those obtained in configuration space, thus allowing a consensus measurement of f sigma(8)(z(eff)) = 0.315 +/- 0.095, and D-M(z(eff))/r(drag) = 19.5 +/- 1.0. This measurement is consistent with a flat Lambda CDM model with Planck parameters.

OXFORD UNIV PRESS2021

Validation of emission-line galaxies target selection algorithms for the Dark Energy Spectroscopic Instrument using the MMT Binospec

Anand Stéphane Raichoor

The forthcoming Dark Energy Spectroscopic Instrument (DESI) experiment plans to measure the effects of dark energy on the expansion of the Universe and create a 3D map of the Universe using galaxies up to z similar to 1.6 and QSOs up to z similar to 3.5. In order to create this map, DESI will obtain spectroscopic redshifts of over 30 million objects; among them, a majority are [OII] emitting star-forming galaxies known as emission-line galaxies (ELGs). These ELG targets will be pre-selected by drawing a selection region on the g - r versus r - z colour-colour plot, where high-redshift ELGs form a separate locus from the lower redshift ELGs and interlopers. In this paper, we study the efficiency of three ELG target selection algorithms - the Final Design Report (FDR) cut based on the DEEP2 photometry, Number Density Modelling (NDM) and Random Forest - to determine how the combination of these three algorithms can be best used to yield a simple selection boundary that will be best suited to meet DESI's science goals. To do this, we selected 17 small patches in the DESI footprint where we run the three target selection algorithms to pre-select ELGs based on their photometry. We observed the pre-selected ELGs using the MMT Binospec, which is similar in functionality to the DESI instrument, to obtain their spectroscopic redshifts and fluxes of 1054 ELGs. By analysing the redshift and fluxing distribution of these galaxies, we find that although NDM performed the best, simple changes in the FDR definition would also yield sufficient performance.

OXFORD UNIV PRESS2020

Galaxy

A galaxy is a system of stars, stellar remnants, interstellar gas, dust, and dark matter bound together by gravity. The word is derived from

Astronomy

Astronomy is a natural science that studies celestial objects and phenomena. It uses mathematics, physics, and chemistry in order to explain their origin and evolution. Objects of interest include p

Active galactic nucleus

An active galactic nucleus (AGN) is a compact region at the center of a galaxy that has a much-higher-than-normal luminosity over at least some portion of the electromagnetic spectrum with character