arXiv subjects

H. U. Norgaard-Nielsen

Publications and source records attributed to H. U. Norgaard-Nielsen.

6 recordsLinked to original sources

arXiv2019

Investigating the physical properties of galaxies in the Epoch of Reionization with MIRI/JWST spectroscopy

The James Webb Space Telescope will provide deep imaging and spectroscopy for sources at redshifts above 6, covering the Epoch of Reionization (EoR, 6 < z < 10). The Mid-IR instrument (MIRI) integral field spectrograph (MRS) will be the only instrument on board JWST able to observe the brightest optical emission lines H$α$ and [OIII]0.5007$μ$m at redshifts above 7 and 9, respectively. This paper presents a study of the H$α$ fluxes predicted by FIRSTLIGHT cosmological simulations for galaxies at redshifts of 6.5 to 10.5, and its detectability with MIRI. Deep (40 ks) spectroscopic integrations with MRS will be able to detect (S/N > 5) EoR sources at redshifts above 7 with intrinsic star formation rates of more than 2 M$_{\odot}$ yr$^{-1}$, and stellar masses above 4-9 $\times$ 10$^7$ M$_{\odot}$. In addition, the paper presents realistic MRS simulated observations of the expected (rest-frame) optical and near-infrared spectra for some spectroscopically confirmed EoR sources detected by ALMA as [OIII]88$μ$m emitters. The MRS simulated spectra cover a wide range of low metallicities from about 0.2 to 0.02Z$_{\odot}$, and different [OIII]88$μ$m/[OIII]0.5007$μ$m line ratios. The simulated 10ks MRS spectra show S/N in the range of 5 to 90 for H$β$, [OIII]0.4959,0.5007$μ$m, H$α$ and HeI1.083$μ$m emission lines of MACS1149-JD1 at z = 9.11, independent of metallicity. In addition, deep 40 ks simulated spectra of the luminous merger candidate B14-65666 at z=7.15 shows the MRS capabilities of detecting, or putting strong upper limits, on the [NII]0.6584$μ$m, [SII]0.6717,0.6731$μ$m, and [SIII]0.9069,0.9532$μ$m emission lines. In summary, MRS will enable the detailed study of key physical properties like internal extinction, instantaneous star formation, hardness of the ionising continuum, and metallicity, in bright (intrinsic or lensed) EoR sources.

astro-ph.GA↗

arXiv2013

Interacting Supernovae and Supernova Impostors. SN 2009ip, is this the end?

We report the results of a 3 year-long dedicated monitoring campaign of a restless Luminous Blue Variable (LBV) in NGC 7259. The object, named SN 2009ip, was observed photometrically and spectroscopically in the optical and near-infrared domains. We monitored a number of erupting episodes in the past few years, and increased the density of our observations during eruptive episodes. In this paper we present the full historical data set from 2009-2012 with multi-wavelength dense coverage of the two high luminosity events between August - September 2012. We construct bolometric light curves and measure the total luminosities of these eruptive or explosive events. We label them the 2012a event (lasting ~50 days) with a peak of 3x10^41 erg/s, and the 2012b event (14 day rise time, still ongoing) with a peak of 8x10^42 erg/s. The latter event reached an absolute R-band magnitude of about -18, comparable to that of a core-collapse supernova (SN). Our historical monitoring has detected high-velocity spectral features (~13000 km/s) in September 2011, one year before the current SN-like event. This implies that the detection of such high velocity outflows cannot, conclusively, point to a core-collapse SN origin. We suggest that the initial peak in the 2012a event was unlikely to be due to a faint core-collapse SN. We propose that the high intrinsic luminosity of the latest peak, the variability history of SN 2009ip, and the detection of broad spectral lines indicative of high-velocity ejecta are consistent with a pulsational pair-instability event, and that the star may have survived the last outburst. The question of the survival of the LBV progenitor star and its future fate remain open issues, only to be answered with future monitoring of this historically unique explosion.

astro-ph.SR↗

arXiv2008

Foreground removal from CMB temperature maps using an MLP neural network

One of the main obstacles in extracting the Cosmic Microwave Background (CMB) signal from observations in the mm-submm range is the foreground contamination by emission from galactic components: mainly synchrotron, free-free and thermal dust emission. Due to the statistical nature of the intrinsic CMB signal it is essential to minimize the systematic errors in the CMB temperature determinations. Following the available knowledge of the spectral behavior of the galactic foregrounds simple, power law-like spectra have been assumed. The feasibility of using a simple neural network for extracting the CMB temperature signal from the combined CMB and foreground signals has been investigated. As a specific example, we have analysed simulated data, like that expected from the ESA Planck Surveyor mission. A simple multilayer perceptron neural network with 2 hidden layers can provide temperature estimates, over more than 80 percent of the sky, that are to a high degree uncorrelated with the foreground signals. A single network will be able to cover the dynamic range of the Planck noise level over the entire sky.

astro-ph↗

arXiv2003

The Spectrum of Integrated Millimeter Flux of the Magellanic Clouds and 30-Doradus from TopHat and DIRBE Data

We present measurements of the integrated flux relative to the local background of the Large and Small Magellanic Clouds and the region 30-Doradus (the Tarantula Nebula) in the LMC in four frequency bands centered at 245, 400, 460, and 630 GHz, based on observations made with the TopHat telescope. We combine these observations with the corresponding measurements for the DIRBE bands 8, 9, and 10 to cover the frequency range 245 - 3000 GHz (100 - 1220 micrometers) for these objects. We present spectra for all three objects and fit these spectra to a single-component greybody emission model and report best-fit dust temperatures, optical depths, and emissivity power-law indices, and we compare these results with other measurements in these regions and elsewhere. Using published dust grain opacities, we estimate the mass of the measured dust component in the three regions.

astro-ph↗

arXiv2000

Power filtration of CMB observational data

We propose a power filter Gp for linear reconstruction of the CMB signal from observational maps. This Gp filter preserves the power spectrum of the CMB signal in contrast to the Wiener filter which diminishes the power spectrum of the reconstructed CMB signal. We demonstrate how peak statistics and a cluster analysis can be used to estimate the probability of the presence of a CMB signal in observational records. The efficiency of the Gp filter is demonstrated on a toy model of an observational record consisting of a CMB signal and noise in the form of foreground point sources.

astro-ph↗

arXiv2000

ISO far-infrared observations of rich galaxy clusters II. Sersic 159-03

The far-infrared emission from rich galaxy clusters is investigated. Maps have been obtained by ISO at 60, 100, 135, and 200 microns using the PHT-C camera. Ground based imaging and spectroscopy were also acquired. Here we present the results for the cooling flow cluster Sersic 159-03. An infrared source coincident with the dominant cD galaxy is found. Some off-center sources are also present, but without any obvious counterparts.

astro-ph↗