arXiv subjects

Palle Møller

Publications and source records attributed to Palle Møller.

22 records · Page 2Linked to original sources

arXiv2011

The nature of z ~ 2.3 Lyman-alpha emitters

We study the multi-wavelength properties of a set of 171 Ly-alpha emitting candidates at redshift z = 2.25 found in the COSMOS field, with the aim of understanding the underlying stellar populations in the galaxies. We especially seek to understand what the dust contents, ages and stellar masses of the galaxies are, and how they relate to similar properties of Ly-alpha emitters at other redshifts. The candidates here are shown to have different properties from those of Ly-alpha emitters found at higher redshift, by fitting the spectral energy distributions (SEDs) using a Monte-Carlo Markov-Chain technique and including nebular emission in the spectra. The stellar masses, and possibly the dust contents, are higher, with stellar masses in the range log M_* = 8.5 - 11.0 M_sun and A_V = 0.0 - 2.5 mag. Young population ages are well constrained, but the ages of older populations are typically unconstrained. In 15% of the galaxies only a single, young population of stars is observed. We show that the Ly-alpha fluxes of the best fit galaxies are correlated with their dust properties, with higher dust extinction in Ly-alpha faint galaxies. Testing for whether results derived from a light-weighted stack of objects correlate to those found when fitting individual objects we see that stellar masses are robust to stacking, but ages and especially dust extinctions are derived incorrectly from stacks. We conclude that the stellar properties of Ly-alpha emitters at z = 2.25 are different from those at higher redshift and that they are diverse. Ly-alpha selection appears to be tracing systematically different galaxies at different redshifts.

astro-ph.CO↗

arXiv2011

Lyman-alpha emitters as tracers of the transitioning Universe

Of the many ways of detecting high redshift galaxies, the selection of objects due to their redshifted Ly-alpha emission has become one of the most successful. But what types of galaxies are selected in this way? Until recently, Ly-alpha emitters were understood to be small star-forming galaxies, possible building-blocks of larger galaxies. But with increased number of observations of Ly-alpha emitters at lower redshifts, a new picture emerges. Ly-alpha emitters display strong evolution in their properties from higher to lower redshift. It has previously been shown that the fraction of ultra-luminous infrared galaxies (ULIRGs) among the Ly-alpha emitters increases dramatically between redshift three and two. Here, the fraction of AGN among the LAEs is shown to follow a similar evolutionary path. We argue that Ly-alpha emitters are not a homogeneous class of objects, and that the objects selected with this method reflect the general star forming and active galaxy populations at that redshift. Ly-alpha emitters should hence be excellent tracers of galaxy evolution in future simulations and modeling.

astro-ph.CO↗

arXiv2003

A very energetic supernova associated with the gamma-ray burst of 29 March 2003

Over the past five years evidence has mounted that long-duration (> 2 s) gamma-ray bursts (GRBs)--the most brilliant of all astronomical explosions--signal the collapse of massive stars in our Universe. This evidence was originally based on the probable association of one unusual GRB with a supernova, but now includes the association of GRBs with regions of massive star formation in distant galaxies, the appearance of supernova-like 'bumps' in the optical afterglow light curves of several bursts and lines of freshly synthesized elements in the spectra of a few X-ray afterglows. These observations support, but do not yet conclusively demonstrate, the idea that long-duration GRBs are associated with the deaths of massive stars, presumably arising from core collapse. Here we report evidence that a very energetic supernova (a hypernova) was temporally and spatially coincident with a GRB at redshift z = 0.1685. The timing of the supernova indicates that it exploded within a few days of the GRB, strongly suggesting that core-collapse events can give rise to GRBs, thereby favouring the 'collapsar' model.

astro-ph↗

arXiv1993

The metal systems in Q0000--2619 at high resolution

We have obtained high, 11 and 14 \kms, and medium, 40 and 53 \kms, resolution spectra of the $z_{em} = 4.11$ quasar Q0000--2619 covering the range 4400 Å to 9265 Å. We identify nine metal absorption systems, of which four were previously known. A fifth previously suggested system at $z_{abs} \approx 3.409$ (Turnshek et al~ 1991) is ruled out by our data. Two of the eight systems for which the \lya~ line is in the observable range have a damped \lya~ line. Six of the nine systems show evidence for complex sub--component structure. At our resolution and S/N we identify a total of 21 sub--components in the nine systems. Five of the nine systems (11 of the 21 components) fall within the $\pm 5000$ \kms~ range of the emission redshift, and are hence classified as \zae~ absorbers. For the two damped systems we find metal abundances of $\leq 1$% and $\leq 8$% of solar values at redshifts of 3.0541 and 3.3901 respectively. These upper limits are consistent with what would be expected from previous determinations at lower redshifts, and our data are hence compatible with earlier conclusions that no evidence is yet found for chemical evolution of intervening damped and Lyman limit absorbers. For the \zae~ systems we found indications of metallicities comparable to, and even in excess of solar values. These much higher values compared to the damped systems, are in favour of the intrinsic hypothesis for these systems.

astro-ph↗