Erik Zackrisson

The Spectral Evolution of the First Galaxies. I. James Webb Space Telescope Detection Limits and Color Criteria for Population III Galaxies

The James Webb Space Telescope (JWST) is expected to revolutionize our understanding of the high-redshift universe, and may be able to test the prediction that the first, chemically pristine (Popul ...

Stellar clusters in M83: formation, evolution, disruption and the influence of the environment

We study the stellar cluster population in two adjacent fields in the nearby, face-on spiral galaxy M83 using multiwavelength Wide Field Camera 3/Hubble Space Telescope imaging. After automatic det ...

Escape of Lyman continuum radiation from local galaxies - Detection of leakage from the young starburst Tol 1247-232

Context. It has been suggested that the escape fraction of hydrogen ionizing photons (f(esc)) from galaxies is evolving with time, but the picture is far from clear. While evidence for significant ...

First detection of Lyman continuum escape from a local starburst galaxy. I. Observations of the luminous blue compact galaxy Haro 11 with the Far Ultraviolet Spectroscopic Explorer (FUSE)

The dominating reionization source in the young universe has yet to be identified. Possible candidates include metal poor starburst dwarf galaxies of which the Blue Compact Galaxy Haro 11 may represent a local counterpart. Using the Far Ultraviolet Spectroscopic Explorer (FUSE) we obtained spectra of Haro 11 to search for leaking ionizing radiation. A weak signal shortwards of the Lyman break is identified as Lyman continuum (LyC) emission escaping from the ongoing starburst. From profile fitting to weak metal lines we derive column densities of the low ionization species. Adopting a metallicity typical of the H II regions of Haro 11, the corresponding H I column density is optically thick in the LyC. Therefore most of the LyC photons must escape through transparent holes in the interstellar medium. Using spectral evolutionary models we constrain the escape fraction of the produced LyC photons to between 4 and 10%, assuming a normal Salpeter IMF. We argue that in a hierarchical galaxy formation scenario, this allows for a substantial contribution to cosmic reionization by starburst dwarf galaxies at high redshifts.

Super star clusters in Haro 11: properties of a very young starburst and evidence for a near-infrared flux excess

We have used multiband imaging to investigate the nature of an extreme starburst environment in the nearby Lyman break galaxy analogue Haro 11 (ESO350-IG038) by means of its stellar cluster population. The central starburst region has been observed in eight different high-resolution Hubble Space Telescope (HST) wavebands, sampling the stellar and gas components from UV to near-infrared. Photometric imaging of the galaxy was also carried out at 2.16μm by NaCo AO instrument at the ESO Very Large Telescope. We constructed integrated spectral energy distributions (SEDs) for about 200 star clusters located in the active star-forming regions and compared them with single stellar population models (suitable for physical properties of very young cluster population) in order to derive ages, masses and extinctions of the star clusters. The cluster age distribution we recover confirms that the present starburst has lasted for 40Myr, and shows a peak of cluster formation only 3.5 Myr old. With such an extremely young cluster population, Haro 11 represents a unique opportunity to investigate the youngest phase of the cluster formation process and evolution in starburst systems. We looked for possible relations between cluster ages, extinctions and masses. Extinction tends to diminish as a function of the cluster age, but the spread is large and reaches the highest dispersion for clusters in partial embedded phases ( 8000A which cannot be explained by simple stellar evolutionary models. Fitting SED models over all wavebands leads to systematic overestimates of cluster ages and incorrect masses for the stellar population supplying the light in these clusters. We show that the red excess affects also the HST F814W filter, which is typically used to constrain cluster physical properties. The clusters which show the red excess are younger than 40Myr we discuss possible physical explanations for the phenomenon. Finally, we estimate that Haro 11 has produced bound clusters at a rate almost a factor of 10 higher than the massive and regular spirals, like the Milky Way. The present cluster formation efficiency is ~38 per cent of the galactic star formation rate.

Probing cluster formation under extreme conditions: massive star clusters in blue compact galaxies

The numerous and massive young star clusters in blue compact galaxies (BCG) are used to investigate the properties of their hosts. We test whether BCGs follow claimed relations between the cluster ...

A model of spectral galaxy evolution including the effects of nebular emission

This paper presents a new spectral evolutionary model of galaxies, properly taking the effects of nebular emission and pre-main sequence evolution into account. The impact of these features in different photometric filters is evaluated, along with the influence that variations in the physical conditions of the gas may have on broadband colours, line ratios and equivalent widths. Inclusion of nebular emission is demonstrated to radically change the predicted ultraviolet, optical and near-infrared colours during active star formation. Pre-main sequence evolution is also seen to give a non-negligible contribution to the luminosity in the near-infrared during the first few million years of evolution and should not be omitted when very young systems are being modelled. Finally, we present a comparison of our predictions to observations and two other recent codes of evolutionary synthesis.

The Spectral Evolution of the First Galaxies. II. Spectral Signatures of Lyman Continuum Leakage from Galaxies in the Reionization Epoch

The fraction of ionizing photons that escape (f esc) from z 6 galaxies is an important parameter for assessing the role of these objects in the reionization of the universe, but the opacity of the intergalactic medium precludes a direct measurement of f esc for individual galaxies at these epochs. We argue that since f esc regulates the impact of nebular emission on the spectra of galaxies, it should nonetheless be possible to indirectly probe f esc well into the reionization epoch. As a first step, we demonstrate that by combining measurements of the rest-frame UV slope β with the equivalent width of the Hβ emission line, galaxies with very high Lyman continuum escape fractions (f esc ≥ 0.5) should be identifiable up to z 9 through spectroscopy with the upcoming James Webb Space Telescope (JWST). By targeting strongly lensed galaxies behind low-redshift galaxy clusters, JWST spectra of sufficiently good quality can be obtained for M 1500 –16.0 galaxies at z 7 and for M 1500 –17.5 galaxies at z 9. Dust-obscured star formation may complicate the analysis, but supporting observations with ALMA or the planned SPICA mission may provide useful constraints on this effect.

The impact of nebular emission on the broadband fluxes of high-redshift galaxies

A substantial fraction of the light emitted from young or star-forming galaxies at ultraviolet to near-infrared wavelengths comes from the ionized interstellar medium in the form of emission lines and a nebular continuum. At high redshifts, star formation rates are on average higher and stellar populations younger than in the local universe. Both of these effects act to boost the impact of nebular emission on the overall spectrum of galaxies. Even so, the broadband fluxes and colors of high-redshift galaxies are routinely analyzed under the assumption that the light observed originates directly from stars. Here we assess the impact of nebular emission on broadband fluxes in Johnson/Cousins BVR1JHK, Sloan Digital Sky Survey griz and Spitzer IRAC/MIPS filters as a function of observed redshift (up to z = 15) for galaxies with different star formation histories. We find that nebular z p 15 emission may account for a nonnegligible fraction of the light received from high-redshift galaxies. The ages and masses inferred for such objects through the use of spectral evolutionary models that omit the nebular contribution are therefore likely to contain systematic errors. We argue that a careful treatment of the nebular component will be essential for the interpretation of the rest-frame ultraviolet-to-infrared properties of the first galaxies formed, like the ones expected to be detected with the James Webb Space Telescope.

Detecting direct collapse black holes : making the case for CR7

We propose that one of the sources in the recently detected system CR7 by Sobral et al. through spectrophotometric measurements at z=6.6 harbours a direct collapse black hole (DCBH). We argue that ...