Intense and complex instrumental backgrounds, against which the much smaller signals from celestial sources have to be discerned, are a notorious problem for low- and intermediate-energy {gamma}-ray astronomy (~50keV-10MeV). Therefore, a detailed qualitative and quantitative understanding of instrumental line and continuum backgrounds is crucial for most stages of {gamma}-ray astronomy missions, ranging from the design and development of new instrumentation through performance prediction to data reduction. We have developed MGGPOD, a user-friendly suite of Monte Carlo codes built around the widely used GEANT (ver. 3.21) package, to simulate ab initio the physical processes relevant for the production of instrumental backgrounds. These include the build-up and delayed decay of radioactive isotopes as well as the prompt de-excitation of excited nuclei, both of which give rise to a plethora of instrumental {gamma}-ray background lines in addition to continuum backgrounds. The MGGPOD package and documentation are publicly available online (http://sigma-2.cesr.fr/spi/MGGPOD/). We demonstrate the capabilities of the MGGPOD suite by modeling high-resolution {gamma}-ray spectra recorded by the Transient Gamma-Ray Spectrometer (TGRS) on board Wind during 1995. The TGRS is a Ge spectrometer operating in the 40keV-8MeV range. Because of its fine energy resolution, these spectra reveal the complex instrumental background in formidable detail, particularly the many prompt and delayed {gamma}-ray lines. We evaluate the successes and failures of the MGGPOD package in reproducing TGRS data and provide identifications for the numerous instrumental lines.
Using laboratory hollow cathode spectra we have identified lines of the less common magnesium isotopologues of MgH, ^25^MgH and ^26^MgH, in the A^2^{Pi}-X^2^{Sigma}^+^ system. Based on the previous analysis of ^24^MgH, molecular lines have been measured and molecular constants derived for ^25^MgH and ^26^MgH. Term values and linelists, in both wavenumber and wavelength units, are presented. The A^2^{Pi}-X^2^{Sigma}^+^ system of MgH is important for measuring the magnesium isotope ratios in stars.
Using the near-infrared spectral stellar library of Cenarro et al. (J/MNRAS/326/959), the behaviour of the MgI line at 8807{AA} and nearby TiO bands is analyzed in terms of the effective temperature, surface gravity and metallicity of the library stars. New spectroscopic indices for both spectral features - namely MgI and sTiO - are defined, and their sensitivities to different signal-to-noise ratios, spectral resolutions, flux calibrations and sky emission-line residuals are characterized. The two new indices exhibit interesting properties. In particular, MgI is a good indicator of the Mg abundance, whereas sTiO is a powerful dwarf-to-giant discriminator for cold spectral types. Empirical fitting polynomials that reproduce the strength of the new indices as a function of the stellar atmospheric parameters are computed, and a fortran routine with the fitting function predictions is made available. A thorough study of several error sources, non-solar [Mg/Fe] ratios and their influence on the fitting function residuals is also presented. From this analysis, an [Mg/Fe] underabundance of ~-0.04 is derived for the Galactic open cluster M67.
From a sample of 97 very bright M-giant stars in the Solar neighbourhood, high-quality `intrinsic' spectra in the spectral range [380-900]nm for all M-spectral subclasses of the Case and MK classification systems are obtained. The results are fitted to photospheric synthetic spectra in the range [99-12500]nm in order to infer the corresponding continua. The synthetic spectra are also compared to the intrinsic spectra. The effective temperatures are derived and mathematical spectral classification criteria are found. The (UB)j(VRI)c(JHKLM)eso photometric data of the sample are also given.
We present reliable measurements of the metallicity distribution function (MDF) at different points along the tidal stream of the Sagittarius (Sgr) dwarf spheroidal (dSph) galaxy, based on high-resolution, echelle spectroscopy of candidate M giant members of the Sgr system.
We study the connections between ongoing star formation, galaxy mass, and extended halo gas, in order to distinguish between starburst-driven outflows and infalling clouds that produce the majority of observed MgII absorbers at large galactic radii (>~10h^-1^kpc) and to gain insights into halo gas contents around galaxies. We present new measurements of total stellar mass (M_star_), H{alpha} emission line strength (EW(H{alpha})), and specific star formation rate (sSFR) for the 94 galaxies described by Chen et al.'s 2010 paper (Cat. J/ApJ/714/1521).
MgII absorption systems for Flat-Spectrum Radio QSOs
Short Name:
J/ApJ/754/38
Date:
21 Oct 2021
Publisher:
CDS
Description:
The conventional wisdom that the rate of incidence of MgII absorption systems, dN/dz (excluding "associated systems" having a velocity {beta}c relative to the active galactic nucleus (AGN) of less than ~5000km/s), is totally independent of the background AGNs has been challenged by a recent finding that dN/dz for strong MgII absorption systems toward distant blazars is 2.2+/-^0.8^_0.6_ times the value known for normal optically selected quasars (QSOs). This has led to the suggestion that a significant fraction of even the absorption systems with {beta} as high as ~0.1 may have been ejected by the relativistic jets in the blazars, which are expected to be pointed close to our direction. Here, we investigate this scenario using a large sample of 115 flat-spectrum radio-loud quasars (FSRQs) that also possess powerful jets, but are only weakly polarized. We show, for the first time, that dN/dz toward FSRQs is, on the whole, quite similar to that known for QSOs and that the comparative excess of strong MgII absorption systems seen toward blazars is mainly confined to {beta}<0.15. The excess relative to FSRQs probably results from a likely closer alignment of blazar jets with our direction; hence, any gas clouds accelerated by them are more likely to be on the line of sight to the active quasar nucleus.
We probed the magnetic fields in high-redshift galaxies using excess extragalactic contribution to residual rotation measure (RRM) for quasar sightlines with intervening MgII absorbers. Based on a large sample of 1132 quasars, we have computed RRM distributions broadening using median absolute deviation from the mean ({sigma}_rrm_^md^), and found it to be 17.1+/-0.7rad/m^2^ for 352 sightlines having MgII intervening absorbers in comparison to its value of 15.1+/-0.6rad/m^2^ for 780 sightlines without such absorbers, resulting in an excess broadening ({sigma}_rrm_^ex^) of 8.0+/-1.9rad:m^2^ among these two subsamples. This value of {sigma}_rrm_^ex^, has allowed us to constrain the average strength of magnetic field (rest frame) in high-redshift galaxies responsible for these Mg II absorbers, to be ~1.3+/-0.3{mu}G at a median redshift of 0.92. This estimate of magnetic field is consistent with the reported estimate in earlier studies based on radio-infrared correlation and energy equipartition for galaxies in the local universe. A similar analysis on subsample split based on the radio spectral index, {alpha} (with F_{nu}_{propto}{nu}^{alpha}^), for flat ({alpha}>=-0.3; 315 sources) and steep ({alpha}<=-0.7; 476 sources) spectrum sources shows a significant {sigma}_rrm_^ex^ (at 3.5{sigma} level) for the former and absent in the latter. An anticorrelation found between the {sigma}_rrm_^md^ and percentage polarization (p) with a similar Pearson correlation of -0.62 and -0.87 for subsamples with and without MgII, respectively, suggests the main contribution for decrements in the p value to be intrinsic to the local environment of quasars.
We report the detection of a statistically significant flare-like event in the MgII {lambda}2800 emission line of 3C 454.3 during the outburst of autumn 2010. The highest levels of emission line flux recorded over the monitoring period (2008-2011) coincide with a superluminal jet component traversing through the radio core. This finding crucially links the broad emission line fluctuations to the non-thermal continuum emission produced by relativistically moving material in the jet and hence to the presence of broad-line region clouds surrounding the radio core. If the radio core were located at several parsecs from the central black hole, then our results would suggest the presence of broad-line region material outside the inner parsec where the canonical broad-line region is envisaged to be located. We briefly discuss the implications of broad emission line material ionized by non-thermal continuum in the context of virial black hole mass estimates and gamma-ray production mechanisms.
We analyze the cross-correlation of MgII({lambda}2796, 2803) quasar absorption systems with luminous red galaxies (LRGs) from the Fifth Data Release (DR5) of the Sloan Digital Sky Survey. The absorption line sample consists of 2705 unambiguously intervening MgII absorption systems, detected at a 4{sigma} level, covering a redshift range (0.36<=z_abs_<=0.8) and a rest equivalent-width range of 0.8{AA}<=W^{lambda}2796^_r_<=5.0{AA}. We cross-correlate these absorbers with 1495604 LRGs with accurate photometric redshifts in the same redshift range and examine the relationship of MgII equivalent width and clustering amplitude.
